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PHYSICAL, CHEMICAL, SODA PULPING AND

PAPERMAKING PROPERTIES OF KENAF AS A FUNCTION OF GROWTH

BY

S a e t Karakus

A thesis submitted in conformity with the requuements for the degree of Master of Science Graduate Department of Forestry

University of Toronto

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FACULlY OF FORESTRY University of Toronto

DEPARTMENTAL ORAL EXAMINATION FOR THE DEGREE OF MASTER OF SCIENCE IN FORESTRY

Examination of Mr. Safet KARAKUS

Examination Chair's Signature:

' 4

We approve this thesis and affirm that it meets the departmental oral examination requirements set down for the degree of Master of Science in Forestry.

Examination Committee:

Date: -&ba . '

ABSTRACT

Kenaf (Hibiscus canabims) is a promising non-wood plant fibre that can serve as a source fibre for

pulping and papemaking. Because the chernical and physical composition of the plant changes as

the plant develops, research is needed to determine its pulping properties at various stages of

growth in order to establish the optimum harvesting time. In the present work, the chernical

composition and pulping properties of kenaf as a function of growth have been studied. Kenaf

plants were harvested ai the end of 90, 120, 150, and 200 days (matunty). Extractive-free ground

samples of the stem were cooked at three different temperatures of 140 O C , 155 O C , and 170 O C ,

using soda cooking liquor of 32 g/L NaOH, with an active alkaii charge of 15% as Na20, and Liquor

to wood ratio of 6: 1.

The chernical anaiysis shows that the differences in holoceUulose and iignin content for 90, 120, and 1 50-

day old kenaf are not significant, while 200-day-old kenaf is significantly difFierent fiom others. Micro-

pulping properties of kenaf at various stages of growth are also not sigruficant. However, statistically

significant differences were observed in tems of physical properties of kenaf pulps. In c o m p ~ g the

yields of kenafpulps, it is observed that the average yield for 150-day-old kenaf, over the whole range of

cooking times and temperatures studied, is highest (60.4 %) amongst the group. Kenafcan be harvested

at the end of 150-day growth period, based on the results of chernical analyses to achieve higher yield,

with reasonably lower iignin content. Since 90-day-old kenaf showed highest breaking length and stretch

values, kenafmay also be harvested at the end of 90-day growth period, based on the physical properties

of kenaf pulps. This may also allow to obtain 2-3 crops per year depending on the location.

ACKNOWLEDGEMENTS

The author wishes to express his deep appreciations to many people who gave their encouragement and assistance to this project, in particular;

Dr. D.N. Roy, my supervisor, for his excellent guidance and constant enthusiasm and support throughout this work;

My supervisory comrnittee members, Dr. D.A.I. Goring, Dr.J.J. Balatinecz, and Dr. K. Goel for lending their considerable expertise in the area of wood science, pulping chemistry, critical comrnents, and helpful suggestions at various stages of this research;

My fellow students Warren Mabee, Fuhua Liu, Harshad Pande, and Ali Quoreshi for their assistance and valuable suggestions throughout the expenments and data analysis,

Domtar Innovation Centre for soi1 analyses and testing of kenaf handsheets,

Mr. J.A. Mccarron and Mr. D. Charles for their assistance in the greenhouse and equipment set- UP7

Finally, our little angel, Derya Nur Karakus (1 1 months old) who brought love and caring into our farnily and also kept me awake most of the nights so that I could study long hours and harder. 1 would like to thank my wife, Mrs. Turkan Karakus, whose constant support, encouragement, and patience has kept me going, still keeping a job, a family and the school for over 4 years. 1 will always remember her being there for me.

TABLE OF CONTENTS

Abstract

Acknowledgement

Table of Contents

Chapter 1 Introduction

Chapter U Literature Review

2.1 Kenaf

2.2 Pulping of kenaf

2.3 Kenaf'as a paperrnaking material

2.4 Juvenile wood in pulp and paper

2.5 Changes in fiber properties

Chapter UI Materials and Methods

3.1 Raw material preparation

3.2 Chemical characterization

3 -2.1 Extractives determination

3.2.2 Holocellulose, alpha-cellulose and hernicellulose determination

3.2.3 Determination of Klason lignin

3.2.4 Detemiination of acid-soluble lignin

3.3 Soda micro-pulping procedure

3.4 Statistical analysis

Chapter IV Results and Discussion

4.1 Chemical characteristics of kenaf as a tùnction of growth

4.2 Organic components

4.2.1 Extractive content

4.2.2 Lignin content

4.2.3 Wolocellulose content

4.2.4 Alpha-cellulose content

4 . 2 . 5 Hernicellulose content

4 . 3 Inorganic components

4 . 3 . 1 Ash content

Chapter V Soda Micro-pulping Characteristics of Kenaf as a Function of Growth

5.1 Pulp yield of kenaf as a function of growth

5 . 2 Delignification selectivity of pulping

5 .3 Delignification of kenaf as a function of growth

5 -3 .1 Soda Pulping of kenaf as a function of growth

5.4 Degradation of polysaccharides

Chapter VI Papermaking Potential of Keaaf as a Funetion of Growth

6.1 Pilot-scale pulping of kenaf

6.2 Pulp fiber properties

6 .3 Physical properties of kenaf as a function of growth

Chapter M Conclusions, Recommendations, and Implications

References

Appendix

Yield per acre

Soi1 analysis

CHAPTER 1

INTRODUCTION

The increased demand for pulpwood and rising production costs are directing attention towards

agricultural crops as a source of papermaking fibre (Watson et al. 1976). Such crops, under

favourable conditions, can produce large amounts of fibre in a matter of months, as compared

with the years or even decades required for pulpwood. However, agricultural crops are usually

seasonal and the harvested matenal has to be stored for long periods; this results in fibre losses

and increased costs.

Wood is a relative newcomer as a papermaking raw material; throughout most of its history paper

has been made almost exclusively from non-wood plant fibres. However, as a result of advances

in puiping and papermaking processes and equiprnent in the late 1800's. the economics of pulp

production changed to favour wood in most of the developed countries of the world (Watson et

al. 1976). The use of non-wood pulp fibres as fbmish for paper and paperboard production has

been found in populous developing countnes like China and India, where forest resources are

limited (Reeve and Weishar 1996). China, for example, produces approximately 73% of the world

total of non-wood pulp for papermaking while about 87% of its own papermaking pulp capacity

is non-wood fibre. With the recent dernands for altemate fibre sources, there has been renewed

interest in the West in the use of non-wood fibre as both a primary and as a supplementary fibre

source (Reeve and Weishar 1996).

A wide variety of non-wood plant fibers are used for papermaking. Kenaf is an example of non-

wood pulp source that is already used in parts of the world. Kenaf (Hibiscus cannabims) is a

herbaceous plant of the family Malvacae, which is grown in many parts of the tropics and in some

subtropical and warm temperate areas (Sabharwal et al. 1994). The plant grows to a height of

3.7-5.5 meters with a diameter of 25-5 1 mm. Kenaf has been grown successfuily in North

Arnenca and could become a pulp alternative to tree species in the Southem U.S. The use of non-

wood plants for pulp and paper in the US is almost negligible; although nearly 330 million tons

are available (Sabharwal et al. 1994). Kenaf bast yields long fibre pulps (2.5-5 .O mm), similar to

softwood fibres (2.7-4.6 mm); kenaf core gives short fibres (0.5-0.7 mm), much like temperate

zone hardwoods (0.7- 1.6 mm).

A search for new fibre crops by the U.S. Department of Agriculture in the 1960's and 70's

identified kenaf as a promising alternative fibrous raw material for paper making (Sabharwal et al.

1994). as a source of chemical pulp and later, mechanical pulp (Touzinsky 1987). Work by the

Amencan Newspaper Publishers Association (ANPA) and International Paper Co. has

demonstrated its suitability for newsprint. It has been studied by a number of other organizations,

particularly the Commonwealth Scientific and Industrial Research Organization (CSIRO) in

Australia (Touzinsky 1987). More recently, it was chosen as the raw material for a 70 000

MTIyear bleached kraft market pulp mil1 in Thailand.

It is well known that different parts of a plant have different chemical and physical properties.

That is, the chemical composition and fiber properties of plant tissue taken fiom the roots, stem,

trunk, and leaves are different. What is not so well known is that the chernical composition and

fiber properties of plant tissue are also different at different stages of the growing season (Rowell

el al. 1997).

The objective of this study is to investigate the kenaf fibres as a function of the growhg season

using TAPPI Standards under the foilowing headings; a) to characterize chemical properties of

fibres in terms of their cellulose, hemicellulose, 1igni.n and extractives contents, b) to illustrate

morphological features of fibres, c) to study the pulping and papemaking properties of kenaf as a

function of growth. The literature on juvenile wood will also be reviewed.

CHAPTER II

LITERATURE REWEW

2.1 KENAF

Kenafis an annual, nonwood fibrous plant native to east central Afnca. Kenaf was introduced into

the United States in the 1940's as a substitute for jute to produce cordage (Fisher 1994).

Beginning in 1956, the United States Department of Agriculture's Agricultural Research Service

(ARS) identified new plant species that could compete with pulpwood in fùmishing satisfactory

fibers for pulp (Fisher 1994). Of over 500 species screened, kenaf was considered the most

promising nonwood fibre source for pulp and paper manufacturing. Beginning in 1960 ARS and

CO-operating university and industry scientists conducted studies of kenaf as a raw material for

pulp and paper manufacture. Several kenaf pulping techniques were tested. The pulps were used

for a variety of paper machine mns to make several grades of paper including bond and newsprint.

In 1986 a joint Kenaf Task Force was formed to cooperatively plan and direct a program aimed at

achieving cornmercialization of kenaf for the manufactunng of newspnnt.

Kenaf (Hibiscus cannahinus) is an annual dicotyledon which probably originated in East Central

Africa (Touzinsky 1987). It is widely cultivated as a source of cordage fibre and grows

extensively in India and other parts of Southeast Asia. It is also grown to certain extent in

Argentina, China, Cuba, Egypt, Guatemala, M y , Mexico, Morocco and South Afnca. Kenaf is a

tropical plant and is now being comrnercially grown in the United States on, approximately 4,300

acres according to 1993 United States Department of Agriculture statistics (Schroeter 1994).

Kenaf can be cultivated under a wide range of conditions and requires relatively littie care (Fisher

1994). The planting and cultivation techniques used are similar to those of other f m crops. The

major varieties of interest are susceptible to the root-hot nematode found in the southeastem

U.S., but the nematodes can be controlled by current f m practices, and nematode resistant

3

varieties of ken& are being developed (Touzinsky 1987).

2.1.1 Fibre and Pulp Y ield

It is reported that the plant attains rnaturity in 120 to 130 days (Casey 1980). The crop is ready

for harvesting in 4 to 5 months, fiom the time of seeding, depending on the growing conditions.

The yield per hectare varies considerably; when properly cultivated and grown, it is reported that

the yield per acre have ranged Born 4 to 8 mett-ic tons of dry fibre per acre (Fisher 1994), 14 -22

m tonha or more (Touzinsky 1987), and 15 to 20 tonha (Casey 1980) depending on location and

growing conditions.

Kenaf yields in the southem United States are about 6 tons/acre/year, which is double the yield of

southem pine. Also, the delivered cost of kenaf per ton of pulp is less than that of southem pine

(Sabhanval et al. 1994). Kenaf is grown as a source of bast fibre for twine and rope. The bast

fibre is about 20% of the dry weight of the stalk. M e r retting (historically, harvested material was

soaked in ponds or lakes where "anaerobic bacteria degraded the glues and pectins that held the

fibers together), washing, and processing the yield of fibre is around 10%. The average annual

kenaf fibre and pulp yield per hectare are reported by Paavilainen et al. (1994) to be 15 t/ha/a and

6.5 t/ha/a respectively .

Kenaf can be adequately harvested with current fann equipment, but modified, strengthened gear

would be better (Touzinsky 1987). Of major concem is the elimination of din and Stone

contamination. This is especially important for chemithermomechanical pulping (CTMP) and

other mechanical pulping to avoid excessive plate damage.

2.1.2 Kenaf Plant Form and Anatomy

The long commercidy used fibres occur in the phloem or bast, which forms part of the bark. The

stems may be retted as in flax, so that the long fibrous strands in the bast may be easily peeled ofT

Watson et al. (1976) reported that the anatornical characteristics of the kenaf stem, except for

some increase in diameter, are the sarne over the length of the stem. The percentage of fibres and

the fibre lengths of sarnples taken at different heights show littie or no change. It was also found

by Watson et al. (1976) that fibre properties and the relative percentages of fibre to other

components showed little variation with time of cropping. These findings show the same generd

trends as those reported by the USDA investigations.

Tluee cropping times (90, 120 and 150 days) were also exarnined by Watson et al. (1976) for

each planting and for the first and second plantings, material was also collected at maturity. They

found that no systematic trends are evident either for times of harvesting or for the different

planting periods. It would appear within the limits of the experiment that the planting procedures,

time of planting and cropping times can be based solely on agronomie considerations and those

conditions selected which give the most economic retum (Watson et al. 1976).

2.1.3 Fibers of Kenaf

The individual fibres of kenaf are cylindrical with some surface irregulanties and cross-markings.

The ce11 wall is thick and surrounded by a thick median layer of lignin (Strelis et al. 1967). The

lumen is irregular in width has noticeable contractions, and at some points becomes

discontinuous. Fibre ends are irregularly thickened and blunt. Fibre cross-sections are polygonal.

Fibre length 2 to 6 mm, average 5 mm, and fibre width is 14 to 33 microns, average 21 microns

(Strelis et al. 1967).

Being a dicotyledon, kenaf has two distinctive stem regions (Figure l)(Nelson et al. 1966). The

outer portion or bast, which is the portion used for cordage fibre, is about 40% of the stem by

weight, and the inner, woody core is about 60%. Fibers fiom the bast portion of the stem are

about 2.5 mm in length and resemble softwood fibers, while those from the core are shorter, 0.6

mm, and resemble hardwood fibers (Touzinsky 1987. Fisher 1994).

Figure 1. Sectional views o f a typical monocotyIedon and dicotyledon, showving distribution of fibro-vascular bundles in the monoco~ledon

and of bast fibers in the bark of the dicotyledon. Source: Nelson et al. (1966)

Pnor to 1989 the focus on kenaf as a fibre source for U.S. industry was to utilize the entire stalk

of the plant consisting of the two fibre fractions together as one, and not the utilization of the

fibers in a separated form (Fisher 1994). In 1990 several kenaf cornpanies in the United States

began working on systems to mechanically separate the two fibre fractions (Fisher 1994). The

impetus to achieve a separation of the fiben was that each of the two fibre fiactions had quite

dEerent characteristics and as a result could be used in manufactunng different products. The

kenaf industry has felt strongly that separated fibers of kenafin total had more value and market

potential than one unseparated fraction.

The long bast fibers could be used to manufacture a number of products such as high grade pulps

for the pulp and paper industry, nonwowen needle punched mats (substituting for jute, coconut

and excelsior fibers), protective packaging for h i t s and vegetables, filters, composite boards and

textiles (Fisher 1994). The short core fibers could be used to manufacture products such as animal

bedding, and horticultural mixes.

2.1.4 The Fibers of Kenaf Bast

The fibers of kenaf bast are comparatively long, slightly shorter but much thinner than softwood

fibers. This is favourable for the ability of bonding and strength development. Bast fibers with

thicker ceIl wall and smaller lumen diameter, are favourable for porosity and opacity

developments as they are not readily collapsibie even under beating and/or refining (Juhua et al.

1996). The outer layer of the bast is a dense, thin epidermis film, which can readily be removed.

The bast is composed of fibre bundles, separated by parenchyma cells; some of them contain

starch and pectin (Juhua et al. 1996). The average bast fibre length is 2.5 mm; account for about

30-40 % of the OD weight of kenaf stems (Watson et al. 1976).

2.1.5 The Structure of Kenaf Core

The structure of the xylem is similar to that of hardwood and is consists of fibers, parenchyma

cells, vesse1 elements and ray cells. The ray structure starting fiom pith goes al1 the way through

the xylem and the bast to the epidermis film. Ray cells and pith are plentifil in kenaf. It is not

surprising, then, that there are much more fines in kenafxylem than found in wood species (Juhua

et al. 1996).

The fibres in the wood are shorter (0.5-0.7 mm), and have thin ce11 wail. They represent only

about 30-40 per cent of the woody tissue (Casey 1980, Watson et al. 1976, Schroeter 1994). The

remainder consists mainly of vessels, vertical parenchyma and ray cells. These vertical parenchyma

cells are unusual in that they are about the same length as the fibres. However, they are thinner-

walled and their ends are flat. They are lignified to at least some degree (Watson et al- 1976). The

parenchyma cells of the bast may be elongated or cuboid in shape.

2.1.6 Chemical Composition

The proximate chernical analysis data clearly indicate that kenaf has low ash and lignin. The

chemical requirement for pulping and pulp yield are comparable with other woody raw matenal

(Mittal et al. 1 994). It is also reported by Mittal et al. ( 1 994) that the chernical analysis of kenaf

grown in Thailand as follows: hot water solubility 5.5%, 1 .O% NaOH solubility 16.6%. alcohol-

benzene solubility 2.2%, lignin 14.7% and holocellulose 77.7%. Since the plant composition

(chemical and physiological) changes with the development stage of the plant, pulping properties

will change with the harvesting time (Paavilainen et al. 1994). The pulp yield increases as the

plant matures. The highest yields are achieved if the delayed harvesting system is used and the

lowest yields if the plant is harvested early in the surnmer.

2.2 PULPING OF KENAF

Attempts have been made to pulp the whole stalk. Bast and core pulped separately give different

pulps with unusual properties (Touzinsky 1987). The pulp tends to be slow in drainage

characteristics, and limit the paper machine speed. Kenaf bast fibers, however, yield pulp with

excellent strength characteristics (Casey 1980). Use of kenafbast alone as a source of long fibre

has been proposed for countnes, which lack domestic long fibre sources (Touzinslq 1987). In

fact, in S n Lanka kenaf bast fibre has to some extent replaced imported long fibre wood pulp for

blending with short fibers produced fiom agricultural residues (Casey 1980). However, any use of

bast or core separately must be able to bear the cost of separation. The most likely use is of the

whole kenaf stem, as at the Phoenix pulp mill, Khon Kaen, Thailand (Touzinsky 1987). When

considered for pulping, the interior woody portion of the stalk also needs to be used as a source

of fibre for economic reasons.

2.2.1 Chernical Pulps

Kenaf is readily pulped by the kraft and soda processes. Whole kenaf pulps bleach readily and

have good papermaking properties. This was demonstrated in the production of quality bond

paper fkom kenafmade at the U.S.D.A. Center, Peona, IL (Touzinsky 1987). It has been affirmed

by research and production that kenaf chernical pulp can be used to produce writing papers and

board. However, there are still problems in using kenaf chernimechanical pulp (CMP) to produce

quality newsprint (Juhua et al. 1996).

In contrast to the long-recognized superiority of sulphate wood pulps over wood soda pulps,

strength characteristics of kenaf soda pulps were equal to those of their respective sulfate pulps

(Bagby ef a[. 1975). Comparable yields of kenaf pulp are obtained by the two processes.

However, drainage of the kenaf soda pulps is slightly better than that of the kenaf sulfate pulps.

These favourable results reinforce the concept of employing the sulfùr-fiee soda technique for

pulping kenaf as a means for pollution abatement (Bagby d al. 1975). Conventional soda and

kraft pulping of whole kenaf yields pulps with strength properties somewhere between those of

softwood and hardwood pulps (Sabharwal et al. 1994). The chemical pulps fiom the bast

compare favorably with those of softwood pulps, whereas chemical pulps fiom the core have

relatively low tear strength but high tensile and burst strength when compared to hardwood pulps.

Another unique charactenstic of the production of kenaf bast chemical pulp is that only a fraction

of the refining energy required for a sofbvood pulp is necessary to develop strength properties

2.2.2 Pulping Conditions for Kenaf

The soda, sulfate, and neutral sulfite processes are suitable for pulping kenaf (Casey 1980).

Chipped and screened whole stalk kenaf is cooked in a rotary digester with 10Y0 caustic soda on

the dry weight of the matenal to produce bleachable grade pulp. The cooking tirne is 3.5 hr at a

temperature of 170 OC. The permanganate number ranges from 14 to 17. In the pulp washing

stage, severe foarning occurs due to the presence of saponin in kenaf stems, particularly when the

soda process is used for pulping (Casey 1980). Foilowing washing and cleaning, the pulp is

bleached to 70 brightness using two-stage hypochlonte in a bleaching hollander. Total chlorine

demand is 8 % and the bleached yield varies fiom 45 to 48 %.

2.2.3 Mechanicd Pulps and Newsprint

Straight rnechanical pulps fiom kenaf are usually weaker than corresponding wood pulps, but

satisfactory NSSC pulps have been produced (Touzinsky 1987). TMP, and especially CTMP,

provide pulps of good quality. Work at the Northem Regional Research Center, U.S.D.A.,

Peoria, IL, produced a good-quality expenmental newspnnt from bleached kenaf TMP

(Touzinsky 1987). Kenaf bast containing longer fibres is suitable for preparing good strength

chemical pulp, whereas woody core accounting for the major part of the whole stalk is suitable for

producing hi& yield CMP (Ou and Shi 1996).

2.3 KENAF AS A PAPERMAKING MATERIAL

Initial interest in Kenaf in North America was as a fibre source for rope, buriap and carpet

backing (Webber 1992). Today commercial pulping of kenaf for paper is taking place in countries

such as India and Thailand. There have been extensive laboratory trials of kenaf pulping in North

America, Australia and Japan (Kaldor et al. 1992). There is a considerable amount of published

data on the potential of kenaf as a source of papermaking fibre but this is confined mainly to

laboratory and pilot trials. The USDA research station at Perona has published a number of

papers on the pulping and papermaking properties of ken& and the bulk of this work has been on

whole stem material but the properties of the bast and core fiactions in the stem have also been

studied separately (Watson et al. 1976). The whole stem gave pulps (chemical and semichernical)

intemediate between softwood and hardwood pulps in strength properties, but pulps made fiorn

the bast had very good tearing strength.

In years past there have been numerous attempts to utihe kenaf cornmerciaily as a substitute for

wood fibre in the production of paper and paperboard. According to one trade magazine report,

in 1986 the US Department of Agriculture together with CTP Ltd. of Canada conducted a large

scale kenaf fibre evaluation study, using both freshly cut, as weU as stored kenaf fibre, for the

production of newsprint (Schroeter 1994).

The kenaf bast and the core fractions produce pulps with completely different papermaking

properties. Maddem et al. (1 989) studied the main papemaking properties of bleached soda-AQ

kenaf bast and core pulp. They found that the bast fibres are long, thin and stiff giving good tear

and light scattering and moderate bonding. They produce a bulky sheet with good bending

stifiess. Kenaf bast pulp compares quite favourably with bleached long fibre wood pulp and

could be used in similar applications. It is also suited to some speciaity grades such as tea and

cigarette tissue.

Madem et al. (1989) also reponed that the core fibres are short and wide with thin walls so that

they collapse readily, with little beating, producing a dense, very smooth, stiE well bonded sheet

with good optical properties. The woody core is difficult to pulp and the pulps, particularly in

regard to tear, are of lower quality. The pulps have slower drainage characteristics than wood

pulps made by the same processes and beating, although producing some irnprovement in bonding

properties, soon leads to unacceptably low drainage rates (Watson et al. 1976). The papermaking

properties of kenafcore are in general iderior to those of bleached eucalypt pulp. It could be used

in special circumstances where low beating requirement and good smoothness are important

(Madem et al. 1989).

2.4 S(IVENILE WOOD IN PULP AND PAPER

The relationship between juvenile wood and mature wood is sunilar to the relationship between

juvenile kenaf and mature kend Although a direct cornparison between the two may not be made,

insight into the relationship between juvenile wood and mature wood might shed light upon the

development of kenaf plants.

Wood is extremely heterogeneous material of great anatomical, physical, and chemicai

complexity, a fact that was not always fully appreciated in the past. In later years, attention has

been directed toward this lack of chemical uniformity, and studies have been reported on the

chemistry of separate wood regions, the different types of wood cells, and the location of the

various wood components within the ce11 wall (Timell 1986). Variations, however, can cause

difficulties for rnanufacturers, resulting in less effective production and processing (Zobel et al.

1983). In the manufacture of pulp and paper, when woods with variable properties, as in juvenile

and mature wood, are used together, low-density juvenile wood is certain to be cooked

sufficiently. This results in lower yields from the wood fumish and lower strength properties of

the fibres and paper (Zobel et al. 1983).

An undefined mass of tissue known as the pith marks the stem centre, and this region is

surrounded by a thin layer of primary xylern (Haygreen et al. 1989) Both the pith and primary

xylem are wholly formed in the first year of the Me of a stem, and both types of tissue dfler fiom

secondary xylern produced later by the cambium. An important point is that secondary xylem

produced for the first 5-25 years is different nom secondary xylem produced after this juvenile

period (Haygreen et al. 1989). Juvenile wood has been defined as secondary xylem produced by

cambial regions that are influenced by activity in the apical meristem. This definition serves to

explain why there is typically a gradua1 transition in wood properties between juvenile and mature

wood (Haygreen et al. 1989). Juvenile wood is less likely to form in the outer portions of stem

cross sections because as the cambium in a given location continues to cause diameter expansion,

it also becomes progressively farther fiom and therefore less subject to the infiuence of the apical

meristem (Haygreen et al. 1989).

There is a strong and irreversible trend toward growing and utilizing smaller, lower-quality timber

(Zobel et al. 1984). However, smailness is expected fiom the fast-growing plantations. The

causes for the increasing use of smaller timber, the first is that the large and old trees are being

harvested faster than they can be grown; the timber imbalance evident in some parts of the world

is the second primary reason (Zobel et al. 1984). Since the pulp and paper industry is using

roundwood of small diameter and some sawmills are cutting relatively smail-diameter matenai, the

properties of this juvenile wood are important (Moore el al. 1974). Juvenile wood differs

considerably from adult wood in both rnorphological and chemical properties. Generally the core

material has been show to have shorter fibre length and lower specific gravity and might,

therefore, be expected to yield pulps with charactenstic properties (Packman et al. 1967).

The future of the Canadian forest industry will depend on the successfùl conversion of the second-

growth resource into forest products. A managed second-growth resource will be characterized

by faster growth rates, smaller log diameter, and shorter rotation times (Hatton et al. 1992). The

result will be a marked increase in the proportion of juvenile or core wood in Canada's forests.

The physical properties of juvenile wood differ in several respects fiom those of mature wood,

and these differences rnust be quantified if the industry is to maximize the end-use potential of

these second-growth stands (Hatton et al. 1992). The wood of such trees, especially fkom the

conifers, is so different that it will have a major effect on utilkation and products standards.

Acceptability of wood fiom fast-grown plantations will change, as solid wood and paper quality

standards change (Zobel 198 1).

The changes in wood characteristics in a given tree fiom pith to bark (Le., with increasing tree

age) are fundarnentally related to the age or matunty of the cambium itsell; as well as to the

effects on activity caused by natural and induced changes in the environment. Both softwoods and

hardwoods are affected, but juvenility is especially well marked in the xylem of softwoods. In a

given year, the cambium produces juvenile wood near the tree top (near the crown and the centre

of the tree) and mature wood farther toward the base of the tree, which is farthest from the tree

crown and pith.

Contrasting juvenile wood in hardwoods with juvenile wood in conifers, hardwoods suffer less of

a reduction in fibre length and very little reduction in specific gravity. Also, reaction wood in

hardwoods has higher specific gravity, higher cellulose content, and often comparable or nearly

comparable pulp strength properties, whereas exactly the opposite is true for conifers (Einspahr

1976b). At the present time, most of this material is supplied to the mills as thinning or as small

roundwood from clear felling operations, and this furnish will contain a very high percentage of

juvenile wood. However, as more saw logs become available, the number of small-diameter tops

and slabbings (either in solid form or as chipped waste) offered to the rnills will increase. It

becomes necessary, therefore, to evaluate the pulping performance of juvenile wood from this

tirnber, and to consider the possible variation in pulp quality that may occur due to the use of a

"mixed" wood supply of this kind (Orsler et al. 1972).

It is important to understand that hardwoods differ from softwoods in physical, chernical, and

morphological traits and so must be considered separate entities yielding different paper qualities

after any comrnon processing. If hardwood pulps are to be substituted for sofhood pulps without

a change in end-product specification, innovative processing methods will be necessary (Amidon

1981). Although not as much is known about the pulp and paper quality of young hardwoods,

several recent investigations suggest that the use of this major source of fibre has considerable

promise. If short rotations are to be used, the quality and yields of wood from young hardwood

trees must be known to deterrnine if the juvenile wood wiii have as great an effect on pulp yield

and paper quality as has been found for the softwoods.

There will be a much wider usage of previously unused wood considered to be waste. This

resource includes thinning, top wood, and small, crooked and diseased trees formerly considered

to be unusable because of their high proportion of reaction wood, knotwood, included bark, and

resinous deposits. To use these smaü and young trees effectively and efficiently, major

adjustments must be made in manufacturing technology and equipment. Other adjustments are

required in acceptance of different product quality and utiüty (Zobel et ai. 1984).

The prime reasons for the wood differences are age and tree fonn and quality. Perhaps the

greatest overail cause of wood variation among conifers is the presence of juvenile wood and its

relative proportions to mature wood (Zobel et ai. 1989). Plantation trees are usually fast-grown

so they attain a merchantable size at a young age; thus the trees have a high proportion of juvenile

wood. This large proportion of juvenile wood can have a major effect on wood quaiities and

utilization standards.

The wood produced in young trees, the wood formed during the early or juvenile years of older

trees (including tree top and entire tree core), and rnost branches differ in several respects from

the wood formed in the outer tmnk of the same tree when the tree is more mature (Rowell 1984).

Juvenile wood, sometimes referred to as core wood, formed by a young vascular cambium and is

deposited within the first 5-20 growth rings from the pith (Timell 1986, Bendtsen 1978, Tsoumis

1968, Zobel 1984).

However, when juvenile wood constitutes more than 20% of the fùmish, a marked effect on yield

and quality is exerted. The high proportion of juvenile wood from thinning plantations will alter

the manufaauring systems and quality of products produced. Whole-tree chipping incorporates

the mature wood and juvenile wood of basal logs, the juvenile wood of the topwood and

limbwood, bark and leaves, al1 of which produce wood qualities different fiom those now used

(Zobel 1984).

2.4.1 Properties of Juvenile Wood

There is a diEerence between juvenile wood produced during the first 5 to 20 years of a tree's life

time and the mature wood produced thereafter (Kocurek et al. 1993, Thomas 1984, and Bendtsen

1978). Cornpared to mature wood, juvenile wood of conifers has these characteristics; Lower

specific gravity, thinner ce11 walls, high earlywoodliatewood ratio, shorter and narrower fibres,

lower cellulose content, higher hernicellulose content, higher iignin content, wider growth rings,

higher fraction reaction wood (compression wood), and also lower strength, lower stifhess,

higher longitudinal shrinkage, lower transverse shrinkage, higher moisture content (MC), larger

lumen diameters, larger fibril angle.

In successive rings from the tree centre, the SG increases, fibres become longer, and so on. The

demarcation between juvenile and mature wood is not clear because of the gradual change in

properties. In faa, the actual number of rings in the juvenile core depends upon how juvenile

wood is defined anatomically; ceIl length may reach maturity (relatively stable length) before ce11

wall thickness. However, the juvenile core includes anywhere from 5 to 20 rings depending

mostly upon species, but to some extent upon locality. Thus, the size of the juvenile core in any

one species depends upon growth rate.

Though a gradual transition in properties is typical, this characteristic is apparently more typical of

some species than others such as spruce, fir, and cypress (Zobel 1984). The substantial amounts

of reaction wood often occurring within the juvenile region contribute to the lack of a well-

defined juvenile wood zone. One study of southem yellow pine showed the juvenile wood region

to contain 42% reaction wood in cornparison to only 7% in the surrounding mature wood (Zobel

1984).

2.4.2 Juvenile Wood in Pulp and Paper

By most measures, juvenile wood is lower in quality than mature wood, this is particularly tnie of

the softwoods. In both hardwoods and sofboods, for example, juvenile wood cells are shorter

than those of mature wood. Mature cells of softwoods may be three to four times the length of

juvenile wood cells, while the mature fibres of hardwoods are comrnonly double the length of

those found near the pith. In addition to differences in ce11 length, ce11 structure differs as well.

There are relatively few latewood cells in the juvenile zone, and a high proportion of cells have

thin wall layers. The result is low density and a corresponding low strength in cornparison to adult

wood (Haygreen et al. 1989).

Wood property-paper property conceptual relationships, developed originally for conifers, have

been found to apply to hardwoods. Increases in wood cellulose content correlate positively with

pulp yield and fibre strength. Increases in wood lignin content correlate negatively with pulp yield

and fibre strength. Increases in the main hemicellulose component, xylan, may increase or

decrease pulp yields, depending on the chernical constituent for which it is being substituted.

Increases in other hemicelluloses correlate negatively with pulp yield.

As a raw material for high-grade and high-strength paper, juvenile wood has long been regarded

as inferior. However, it has been viewed with less disfavour by pulp and paper specialists as more

has become known about it. The bad reputation ofjuvenile wood is based partially on the fact that

its lignin and hemicellulose content is higher than in mature wood and the cellulose content lower.

The high proportion of lignin results in lower pulp yields, since chernical pulping processes

separate wood fibres by dissolving away lignin (Haygreeen et ai. 1989). The result, in addition to

lower yields, is higher chernical consurnption in the pulping process and up to a 10% increase in

manufacturing costs (Zobel and Kellison 1972). Yields of turpentine and possibly tail oil by-

products of kraft pulping are also reported lower when processing juvenile wood.

Pulp from juvenile wood has also been reported to be of low strength. However, juvenile wood

looks better when results of recent investigations are reviewed. Several investigators have found,

for example, that paper from juvenile wood has low tear strength (as much as 30% lower than

paper made fiom adult wood) but unusuaily high burst and folding strength (Semke 1984). The

thinner ce11 walls of juvenile wood result in tighter packing of fibre in a paper sheet, with more

contact between adjacent fibres. The result is higher sheet density and higher tensile and burst

strength. Tear strength, on the other hand, is directly and negatively infîuenced by a short fibre

length (Jackson et al. 1986).

When mechanical pulps are considered, the situation is much different. Because lignin is retained

along with cellulose and hemicellulose after mechanical pulping (meaning that high lignin content

does not adversely affect yield), and because low-density woods produce a more satisfactory

mechanical pulp than woods of high density, juvenile wood is quite suitable for use in production

of mechanical pulps (Haygreen et al. 1989).

Many problems associated with use of juvenile wood in pulp and paper manufacture develop

because the juvenile matenal is processed under conditions designed for mature wood. When

juvenile wood is cooked under the severe conditions necessary for mature wood, pulp yield and

strength must suffer. Yet when cooked alone under conditions tailored for it, the pulp yield and

strength fi-orn juvenile wood should improve. Hunt and Keays (1973) reported that there is little

difference in properties of juvenile and mature wood pulps when each are produced under ideal

conditions. Ideal treatments for juvenile wood are, incidentally, generally less energy intensive

than traditional ones, since cooking times required for juvenile wood are shorter and energy

requirernents for beating are lower (Einspahr 1976). Beating involves the forced movement of

sofiened wood fibres through a narrow gap between an apparatus like a paddle wheel and a

bedplate. As they pass through the gap, the fibres are subjected to a beating or pounding action

that flattens and unravels them, increasing potentiai for fibre-to-fibre bonding in a paper sheet.

2.5 CE€ANGES IN FIBER PROPERTIES AS A FUNCTION OF THE GROWING

SEASON

It is known that diffèrent parts of a plant have different chetnical and physid properties. That is, the

chernid composition and fiber properties of plant tissue taken fiom the mots, stem, ümk, and 1e8ves

are diffkent. Wbat is not so weii kmwo is that the chernical composition and nber pmperties of p k

tissue are also different at different stages of the growing season (Rowell et al. 1997).

The earliest reports on changes in chernid composition as a fbnction of the growing season were done

with wheat in the 1930s (Philips et aL 193 1). They found that cehiose content was highest in the eariy

part of the growing season and that lignin and ash content varied with the amount of f e used. In

a shdy using severai varieties of fla>s Overbeke and Mazingue (1949) found that both celllose and

lignin content increased with plant age but pectins, hemidulose, and ash content folowed no

systernatic progression with age.

On0 and Sato (1957) studied the relationship between ceildose, nitrogen, phosphorus, ash, end

pecîin as they related to rnaturïty. niey reported that immature lint contained a large amount of non-

cellulosic substances and hence lost b l e d and dye as wmpared to mature fiber. The reducing sugar

content was higher in immature lint and decreased as the plant aged (Ono and Sato 1957). In addition

to celidose, herniceliulose and iignin, agro f i b also contain protein and lipids. The stage of mehinty

determines the chernical composition. As the plant matures, the ceUuiose, hemicelulose and lignin

content increases, whereas the protein content decrases dramatically. However, agro fibres contain

less lignin dian w d (Paavileinen et ai. 1994).

Watson et al. (1976) reported that the anaîomicai characteristics of the kenaf stem, except for some

increase in diameter, are the same for material taken fiom the bottom to the top of the stem The

percentage o f fibres and the fibre lengths of samples taken at diffkrent heights showed linle or no

change. It was also found by Watson et aL (1976) that fibre properties and the relative percentages of

fibre to other components showed Little variation with tirne of cropping. These hdings show the sarne

general trends as those reported by the USDA investigations.

Three cropping tirnes (90, 120 and 150 days) were also examineci by Watson et al. (1976) for each

planting and for the first and second plantings, materiai was also collected at mahinty. They found that

no systematic trends were evident either for times of harvesting or for the &îerent planting penods.

CHAPTER III

MATERIALS AND METHODS

3.1 RAW MAïXIUAL PREPARATION

Kenaf plants were grown in the greenhouse of the Faculty of Forestry, University of Toronto. To

grow kenaf plants in the greenhouse of the faculty of forestry, pro-mix greenhouse select growing

medium was used. Pro-mix "GSX" is a peat-bark based professional growing medium designed

for the cultivation of horticultural plants with automated dnp and subimgation watering systems.

A combination of Canadian Sphagnum peat moss (50-60% by volume), composted softwood bark

(30-35% by volume) and coarse perlite, form a porous growing medium which allows water

drainage and air exchange for developing root systems. Dolomitic and calcitic limestone (pH

adjuster) and wetting agents are also components of pro-mix. Pro-mix was moistened pnor to

filling containers. Wetting was facilitated by constantly tuming the mix while applying a fine spray

of water until the desired moisture level was obtained. Pots of 4 L size were completely filled with

pro-mix, taking care not to compact and making sure that al1 containers have adequate drainage.

Seeds of kenaf were sown % inch deep, 4 to 6 inch apart in a row and 15 inches between the rows

in pots. Then these pots were placed on benches in the greenhouse. The soi1 was kept wet for

about 2-3 weeks d e r the seeding.

Initial plant development would occur without immediate fertilization. To ensure plants receive

adequate nutrients, it was essential to initiate a fertilization program d u h g the course of

production. For this reason, Plant-Prod, al1 purpose fertilizer (20-20-20) supplied by Plant

Products Co, Ltd. was used. The plants were fertilized every two weeks, foliowing the

instmctions given by the producer.

Two plants fiom each pot were hawested at the end of 90, 120, 150, and 200-day growing

period. The plants flowered at about 200 days, 4 days after fertilization. This was considered as

the maturity. The soil before sowing the seeds and after harvesting the plants were sent to the

Domtar Innovation Centre for analysis to measure the plant nutrient uptake from the soil. As can

be seen fkom the results of soil analysis (Table 1 and 2 in Appendix), potassium and phosphorous

content of soil after harvesting plants are higher than before sowing the seeds. This must be due

to the fact that the plants were harvested 4 days after fertilization. First, the plants could not

consume al1 the nutrients in 4 days; second, there were not enough plants in the pots (two plants

per pot were le&) at the end of growing season to use al1 the nutrients available.

The soil, which is used for growing kenaf plants, was analyzed before planting and after

harvesting the plants. The soil analysis results are presented in Table I and 2, in Appendix. The

kenaf plants were cut fiom the base of each plant and the leaves were discarded. The kenaf plant

stems were chipped into specified sizes for grinding and air dned for sorne time (about 3-4 weeks

depending on the conditions). The samples for chemical analysis and pulping were prepared

following Tappi standard (T 257 cm - 85). Mer grinding the chips in a Wiley Laboratory Mill

(Model 4), the finer material was separated by sifting on a 40-mesh (0.40 mm) power-driven

screen. Then, these sarnples were stored for further studies.

3.2 CHEMICAL CEIARACTERIZATION

3.2.1 Extractive Determination

Al1 species of wood and other plant tissues contain small quantities of chemical substances in

addition to the macromolecules of cellulose, hemicelluloses, and lignin (Browning 1969). To

distinguish them fiom the major ce1 wall components, these additional compounds are known as

the extraneous components. Many of these substances are extractable with neutral solvents, and

are referred to as extractives (Buchanan 1 963). With the exception of a srnail part of the lignin, aIl

wood ce11 wall components, in silu, are insoluble in organic solvents and in water (Wise 1952).

The extractives often play an important role in the utilization of wood, the importance of which is

out of al1 proportion to their amount- and influence the physical properties of wood (Buchanan

1963, Wise 1952).

The following types of organic compounds may be present among the extraneous components of

a wood: aliphatic and aromatic hydrocarbons, terpenes, aliphatic and aromatic acids and their

salts, alcohols, phenols, aldehydes, ketones and quinones, esters and ethers. Certain woods

contain appreciable amounts of essential oils, fixed oils, resin acids and sterols. Others contain

tannins and colouring matter (or their precursors). Some woods contain appreciable amounts of

water-soluble polysaccharides; others contain cyclitols. Al1 woods contain very small amounts of

proteins. Certain woods contain other physiologically active nitrogenous products-the alkaloids

(Wise 1952).

A favorite rnixed solvent for soxhlet extraction is ethanol-benzene (in the ratio of 1 :2). This serves

to remove tannins, certain oils, colonng matters and even some water-soluble extractives.

Pinosylvin, which is quite soluble in ether, is an example (Wise 1952). The screened samples of

kenaf tissues were quantitatively extracted first with a mixture of one volume ethanol (95%) and

two volumes of benzene, followed by an ethanol extraction, and finally a hot, distilled water

extraction, according to Tappi Standard Methods T 204 os-76 and T 207 om-8 1.

SmalI tea bags were made using Kimwipe tissue paper and about 2 gram of ground fibre sample

and MC of fibre was determined. The tea-bags were placed in a Soxhlet apparatus. Extraction

was done using a solvent mixture (250 ml) of ethanol (1 volume) and benzene (2 volume) for a

total period of 6 hours, allowing reflux and siphoning f?om the Soxhlet at least four times per

hour. Once this step was completed, the excess solvent was removed fiom the tea-bags by suction

and washing with ethanol and then air-drying in order to remove the remaining trace of ethanol-

benzene. Following the first stage of extraction, the tea bags were retumed to the Soxhlet. These

were then extracted with 95% ethanol for 4 hours. At the end of this stage, the excess solvent was

removed by suction followed by washing of the tea-bags with distilled water.

The hlly extracted samples were air-dried first for 10 days and then oven-dned (for 24 hours at

103k2 OC) and the extractive content was determined by measunng the weight Ioss after

extraction, on an oven dry (O.D.) weight basis. Ten replications were carried out for each group

of kenaf studied. Since extractive must be removed from the wood specimen pnor to the analysis

of other chernical components of fiber tissue, another set of extractions were run to prepare

extractive-fiee fibre samples to be used in holocellulose, alpha-cellulose, hemiceilulose, lignin

content determinations and for pulping.

3.2.2 Boloce1lulose, Alpha-cellulose and Bernicellulose Determinations

Holocellulose was measured following the procedure originally pioneered by Zobel et al. (1966).

The carbohydrate (holoceliulose) fiaction of fibre was isolated by removing the lignin 60m extractive-

free fibre using the acid chlorite method.. Air-dned, extractive-fiee fibre (0.70 g.) was placed into a

tared Erlenrneyer flask, and 10 ml of stock solution A (60 ml glacial acetic acid + 20 g NaOH per

litre of distilled water) and 1 ml of stock solution B (200 g NaCL02 per litre of distilled water)

were added. The flask was placed in a hot-water bath (701 2 OC). M e r 3/4 h, 1.5 h, and 2.5 h

additional 1 ml portions of solution B were added, swirling thoroughiy.

After cooking for 4 hours, the contents of the flask were transferred to a tared coarse crucible and

the liquid removed by suction on a filter flask. Once the sarnple was washed with 100 ml of 1%

acetic acid solution and then with two 5 ml portions of acetone, the holocellulose was equilibrated

in a conditioning chamber for a minimum of 4 days. Finally, the holocellulose-containhg crucible

was weighed and the holocellulose content was calculated based on O.D. weight of extractive-

fiee fibre.

For detemination of alpha-cellulose in kenaf fibre, NaOH (17.5%) was used to dissolve

hemicelluloses. The holocellulose-containhg crucible was placed in a Syracuse watch glas, which

contained water to a depth of 1 cm. Then, 3 mi of 17.5% NaOH was added to each crucible.

After 5 minutes, an additional 3 ml of 17.5% NaOH was added. The contents were allowed to

stand for 35 minutes, total of 42 minutes. M e r washing with 60 ml distiiled water, 5 ml of 10%

acetic acid was added. Five minutes later, the alpha-cellulose was washed with an additional 60 ml

of distilled water, and then with two 10-ml portions of acetone.

Finally, the sample was oven-dried to a constant weight (after 24 h at 103+2 OC), weighed, and

alpha-cellulose content was calculated based on OD weight of extractive-fiee wood. Subtracting

the amount of alpha-cellulose fkom the holocellulose content of kenaf tissue gave the total amount

of non-alpha-cellulose materials, Le. hemicellulose and beta- and gamma-celluloses. Replications

for each group or kenaf fiber tissue produced 40 holocellulose determinations, exarnining 10

samples for each group.

3.2.3 Determination of Klason Lignin

Lignin in plant tissue is not extractable by organic solvents. In determining the acid-insoluble

lignin in kenaf as a fùnction of growth, the Tappi Standard T 222 om-83 was followed. First, one

gram of extractive-fi-ee fibre was put in a 30 ml beaker. Then, 15 ml of 72% sulphunc acid was

carefully added. The acid was added in small increments while macerating the material with a

glass rod. The beaker was kept in a water bath at 20+1 for two hours. The mixture was stirred

fiequently during this tirne to ensure complete solution.

After 2 hours, (first stage of acid-hydrolysis), the sulphuric acid strength was brought down to

3% by adding 560 ml of distilled water. The solution was then boiied for 4 hours, maintai~ng

constant volume (at 575 ml for wood and 1540 ml for pulp) by fiequent addition of hot distilied

water. It is necessary that during the second stage of hydrolysis, the solution be not boiled under a

reflux condenser.

The insoluble matenal was allowed to settle, then the solution was quantitatively filtered. The

klason ügnin was washed with distilled water through a medium mesh filtering crucible to remove

acid and acid-soluble lignin. The lignin-containhg crucibles were then oven-dried at 103k2 OC for

two hours or to a constant mass. The Klason lignin content was determined in OD weight of

extractive-free kenaf fibre sample.

The Tappi method T 250 um-85 was used for the determination of acid-soluble lignin both in fibre

and pulp. The LJV absorbency was measured on the filtrate specimen in a cuvette with 10 mm

light path at 205 nrn, at which Iignin has its most characteristic absorption maximum and a high

sensitivity for variations in lignin concentration. Whenever the absorbency was higher than 0.7,

the filtrate was diluted in a volumetric flask to obtain absorbency in a range of 0.2 - 0.7. It is

essential in this measurement that 3% sulphunc acid be used both as the reference (blank) solution

and diluent. The acid-soluble lignin content in the filtrate in grams per 1000 ml, was calculated

from:

w here;

A : Absorbency

D : dilution factor of the filtrate, expressed as VoNo,

where;

VD is the volume of the diluted filtrate and,

Vo is the volume ofthe original filtrate taken.

An absorptivity of 1 10 Vgxm is used in this calculation as being an average value of that found on

dEerent raw materials and pulps (T 250 um-85).

The acid-soluble lignin content in the fibre or pulp sample was calculated fiorn:

Lignin ./O = B. V. 100/1000.W

which with eq.(l) gives:

where;

V : total volume of the filtrate, i.e. 575 ml for woods and 1540 ml for pulps,

W : oven-dry weight of fibre or pulp specimen in grarns.

The sum of the acid-soluble lignin and acid-insoluble lignin represents the total lignin content (%)

in a fibre or pulp sample.

3.3 Soda Micro-Pulping Procedure

Soda cooking liquor of 32 g/l NaOH with active aikali charge of 15% as Na20 was used. The

extractive-fiee ground fibre samples were placed in a stainless steel reactor (25 ml) with screw

caps, and soda cooking liquor was added to maintain the liquor to raw material ratio of 6: 1. For

each batch of the micro pulp digester (25 ml reactor) 15 ml pulping liquor and 2.5 g extractive-

free ground wood (40-mesh) were used. A pre-soaking period of 30 min. at temperature was

provided before irnmersing the reactors in a silicone oil bath, thermostatically controlled at the

desired temperature. The range of temperatures studied was 140 O C , 155 O C and 170 OC. The

time to reach the reaction temperature is the tirne required to regain the temperature after the

reactors are immersed in the oil bath and it varied with temperature, (12 min. at 170 OC, 10 min.

at 155 OC, and 8 min. at 140 OC). The reaction time reported is the time at temperature, and it

does not take into account the time to reach the temperature. The reaction was stopped by

quenching the reactor in a bath of ninning cold water. Before dipphg the reactors in cold water,

they were cleaned in a cooled kerosene bath which removed the silicone oil fiom the surface of

the reactors, thereby eliminating the possibility of contamination by silicon oil. The resulting pulp

with liquor was transferred to a Buchner tiinnel and washed with enough distilled water to

transfer the pulp with liquor from the reactors. The pulp was washed with water and the yield and

residual lignin content of the pulp was determined. The reported total residud lignin content is the

sum of the Klason lignin and the acid soluble lignin determined as per Tappi standard T222 om - 83 and Tappi UM 250.

The three pulping temperatures were chosen because; 170 OC is the most widely used cooking

temperature, while 140 OC and 155 O C are the temperature ranges that rnay possibly contribute

more to the initiai reactions between wood and pulping chernicals during heating-up period. In

addition, lower ternperatures were studied to find out the effects of low temperatures on kenaf

pulping at various stages of growth. Higher temperatures, such as 180 OC, were not used in order

to prevent extreme degradation of holocellulose and because of the added costs associated.

Three pulping experiments were performed for each kenaf age group, cooking time, temperature.

The residud lignin content in pulps was determined following Tappi Standard Method, as

mentioned in section 3.2.4. From the lignin residue in pulp, holocellulose content, delignification

and holocellulose degradation rates were calculated from:

Holocellulose ( b m i .. = 100 - Lignin [t,... ,,,,lp)

To caiculate delignification rate, Lignin (b., ,,pl had to be converted to Lignin *.O" W W ~ , by means

of:

Lignin &on W- = Yield . Lignin (b., ,IN I 100

Delignification = ( Ligninn. W O ~ , - Lignincaon nood)l . 100 / Ligninnn W O ~ ) (7)

The holocellulose removal rate was obtained by replacing the corresponding holocellulose figures

in equation (7) "delignification" .

3.4 Statistical Analysis

A randomized design was used for the analysis of the data from kenaf fibre tissues to determine if

there were differences among chernical and pulping characteristics of kenaf as a function of

growth.

The basic analysis of variance (ANOVA), i.e. mean, sum of square, mean of square, F and P

values, R-square, coefficient of variation, Root MS error, was performed on these variables at p,

0.05, a 95% confidence level. Duncan's Multiple Range Test was also used for each variable. Al1

statistical procedures were camed out using the Statistical Analysis Software (SAS).

CHAPTER IV

RESULTS AND DISCUSSION

CHEMICAL CHARACTERISTICS OF KENAF AS A FUNCTION OF GROWTH

4.1 Chernical Characterization of Kenaf as a Function of Growth

The chemical properties of kenaf as a function of growth were examined in terms of extractives,

lignin, holocellulose, alpha-cellulose7 and hernicellulose contents. These made it possible to study

the chernistry of soda pulping of kenaf as a function of growth. Al1 presented values are based on

extractive-fiee fibre, except those for extractive content. When one way anaiysis of variance was

performed to test the diferences in means among organic chernical components of 90, 120, 150

and 200-day-old kenaf, the following results were observed.

4.2 Organic Components of Kenaf as a Function of Growth

The chernical analysis of kenaf at various stages of growth studied is given in Table 3, and shown

in Figure 2 and Figure 3 in cornparison with the results of chemical analysis of kenaf grown in

Mississippi reported by Pande and Roy (1996), also with trembling aspen and black spnice

chernical analysis reported by Fengel and Wegener (1 983).

4.2.1 Exf ractive Content

Duncan's Multiple Range Test for the means of extractive contents of kenaf as a function of the

growing season is presented in Table 4, and show in Figure 3. The differences in the mean values

for extractive content are not significant among 120, 150, and 200-day old (mature) kenaf.

However, the extractive content of 90-day old kenaf is signincantly higher than the others. Not

only do extractives cause pitch problem, but they may also be responsible for pulp discoloration

(Levitin 1970).

Table 3. Cornparison and chernical composition of 90, 120, 150 and 200-day old (mature) kenaf grown

under greenhouse conditions, mature kenaf grown in Mississippi (Pande and Roy 1996), also with

trembling aspen and black spruce (Fengel and Wegener 1983)

Characteristics

90-day old kenaf

120-day old kenaf

---

15Oday old kenaf

200day old kenaf

Kenaf (Mississippi)

Trembling aspen (Populus tremzrloides

Black spruce (Pzcea mariana (Mill.) B.S.P.)

sarnples of ken 1 I

' fibre extracted first with ethanol-benzene ( 1 : washing with ethanol they were extracted with ethanol(95 %) for another 4 hours.

Ash (%)

2.9

2.6

Ethanol- benzene extract*

(%)

20.2

15 .O

Holocellulose (%)

81.4

81.3

Hemicellulose (%)

30.4

29.7

Alpha- cellulose

(%)

51.0

51.6

Lignin (%)

18.6

18.7

81.1

80.5

14.9

14.2

29.7

29.9

51.4

50.6

2.5

2.1

18.9

19.5

Holocellulose

O 120day-old kcnaf

ti 150-day-old kenaf

W 200-day-old k e d

IB Kcnaf (Mississipi)

A( 1 pha-cellulose Hcmiceilulose

Chemicai Components

Figure 2. Cornpanson and chernical composition of 90. 120. 150. and 200-day old (mature) kenaf grown under greenhouse conditions, mature kenaf grown in Mississippi, also with trembling aspen and black spruce.

E.vtractives

Chernical Components

Ash

Figure 3. Cornparison and chernical composition of 90, 120, 150, and 200-day old (mature) kenaf grown

under greenhouse condttions, mature kenaf grown in Mississippi (Pande and Roy 1996), also with

trembling aspen and black spruce (Fengel and Wegener 1983)

Ono and Sato (1957) studied the relationship between ceIldose, nitrogen, phosphorus, ash, wax, and

pectin as they related to maturity. They reported that immature lint containeci a large amount of non-

ceilulosic substances and hence lost a large amount of weight during pnification. Immature fier was

harder to bleach and dye as compared to mature fiber. The reducing sugar content was higher in

immature lint and decreased as the plant aged (Ono and Sato 1957).

Fujii et al. (1993) have done the most complete chernical analysis of bamboo as a function of its

growth. They found that cold water, alcohoVbenzene, and 1% NaOH extractives, as well as protein.,

content decreased as the plant aged. The extractives can be very different in juvede wood as

compared to mature wood. Extractives £?om juvenile wood are often more toxic and in higher

concentration. This may account for the decreased digestibility of new growth in birch trees (Palo et ai.

1985). The concentration of phenolic acids in the extractives is higher in juvenile wood just d e r l e h g

has started compared to mature wood.

Clark and Wolff( 1969) canied out the first studies on the changes in chernical composition of kenaf as

a tiinction of the growing season. They also shidied the chernical dserences dong the stem and

behween laves and stem. They found that the protein and hot water extractives content decreases with

age for the values taken fiom the bottom (all but the top 0.66 meter of the plant). Data taken ffom the

top part of the plant shows sirnilar trends but the top part has higher hot water extractives and protein

than the bottom part of the plant Clark and WolfF (1969). Han et al. (1995) reported that solvent

extractive content varied as a fùnaion of growth. In general, they were high at the beginning,

decreased during the first part of the growing time, and then increased again.

The chemical analysis of green house grown kenaf as a function of growth showed that the green

house grown kenaf has considerably higher extractive content than field-grown ken& The reason

for this may be that kenaf grown in green house conditions contains high percentages of protein

and chlorophyll and also some of the water soluble sugars may also be extracteci during

ethanobenzene extraction @.N.Roy, personal communications). The reducing sugar content was

higher in immature lint and decreased as the plant aged (RoweU et ai. (1997). The decrease in

extractive content of kenafwith plant age is in good agreement with the results reported in literature.

There is no literature that reports high extractive contents for field-grown kenaf. Most likely

because the green kenaf is being dejuiced before pulping and therefore has not been considered.

Clark et al. (1971) reported that behaviour of the green and field-dned kenaf in the screw feeder

of a Pandia Chemipulper differed significantly. The green material with its high-moisture content,

about 80%, caused no problem other than slowness of introduction rate into the reaction unit

(Clark et al. 1971). This behaviour results fiom the slimy, mucilaginous character of the plant

juice. Even though a substantial amount of this juice was expelled through weepholes in the screw

feeder, the residual juice acted as a lubricant on the feed screw. In tum, slippage occurred

whenever the speed of the feed screw was increased. A steady rate could be achieved if this

cntical rate was not exceeded. On the basis of other experiments the efficiency of the digester

would have been improved had dejuicing and washing of the green material been performed

before its introduction into the screw feeder. When washing follows dejuicing, the slimy character

is lost. In batch operations juice removal also reduces chernical requirements and improved

pulping (Clark et al. 197 1).

Problems most ofien mentioned concerning kenaf as a pulp fiber crop are nematode damage,

transportation, handling, and storage (Moore et al. 1976). The last three are associated with its

seasonal production and bulky nature. Compressing harvested kenaf into pellets, cubes, or high-

density bales near its source could potentially reduce the transportation, handling, and storage

difficulties (Moore et al. 1976).

One of the reasons why extractive content values are higher than field-grown kenaf, may be due

to the fact that top part of the plant stems had not been removed prior to testing. This part of the

plant is reported to have a large amount of protein and extractives (Clark and WoW 1969). Data

34

taken from the top part of the plant shows similar trends in chemical composition af'ter extraction, but

the top part has higher hot water extractives and protein than the bottom part of the plant (Clark and

Wolff 1969). The literature indicates that in most cases for a green chop, removal of the le* top

portion is desirable (White et al. 1969). but ody the leaves were removed pior to this study. It

has also been reported that the upper part of the plant had to be removed. The upper 3 feet were

removed to reduce the amount of foliage before chopping the stalks to 1-in. lengths. Foliage does

not contribute to a pulp of good quality (Clark et al. 1971). The upper 3 feet were not removed

pnor to this study.

The other reason for high extractive content of green house grown kenaf may be that the green

house grown kenaf was still alive, very green from bottom to the top part of the plant stem when

harvested. This may indicate that green house grown kenaf is significantly higher in protein and

chlorophyll content than field-grown kenaf. Therefore, it can be suggested that kenaf plants

should be dried in the field before they are harvested. There are also other advantages of drying

the stems before harvesting. Kaldor (1989) suggested that drying the stem prior to harvesting

reduced transportation costs, because most of the moisture was removed. Because storage has to

be considered for an annual crop, chances of biological breakdown are greatly reduced by dry

crop harvesting. Kaldor (1990) emphasizes again that it is preferable to harvest the kenaf crop

when the fiber is air-dry (approximately 10 % moisture content). This is achieved by leaving the

crop standing in the field (Kaldor 1990). M e r growing periods of 5-7 months, the plants were

killed by spraying with an acceptable defoliant and were allowed to dry. (Altematively, in mild-

temperature areas, frost will kill the crop). The dead, dry stems could be lefi standing in the field

for considerable periods without showing any obvious signs of decay (Kaldor 1989).

The other reason for field-grown kenaf to have lower extractives content than greenhouse-grown

kenaf may be due to the fact that field-grown kenaf rnay be retted before processing. Non-wood

plants like jute, kenaf and flax are retted for textile industry. Retting is the first aep in turning flax

into linen. Histoncally, harvested flax was soaked in ponds or lakes where anaerobic bacteria

degraded the glues and pectins that held the fibers together (Brennanl998). Environmental laws

put an end to that approach because of the stench and pollution produced by the fermentation.

Now flax is "dew-retted. Fust, the plant is pulled fiom the ground and laid out on the field.

Then, when moisture conditions and temperature are nght, indigenous fungi colonize the plant

and begin to degrade it (Brennan 1998). Waiting for that to happen can take fiom four to eight

weeks. Akin et al. (1995) studied the structure and chernical composition of retted and unretted

ken& to identify structural characteristics of fibers and surrounding tissues and by NMR

spectroscopy to charactenze the carbohydrate and aromatic constituents. They found that

histochemical staining for lignin types indicated both coniferaldehyde and syringyl groups. NMR

indicated that lignin was mostly the syringyl type. Chernical retting removed most of the lignin as

show by histochemical and NMR analyses (Akin et al. 1998). Funher, cellulose crystallinity (by

NMR methods) was increased by chemical retting. In contrast, bacterial retting resulted in little

change from unretted fiber and was considerably inferior to chemical retting (Akin et ai. 1998).

4.2.2 Lignin Content

The total lignin consists of Kiason lignin and acid-soluble lignin fractions.

4.2.2.1 Klason Lignin (Acid-insoluble Lignin)

Wood contains from about 20 to 30 % lignin, softwood (26.32%) and hardwood (20-28%)

(Sjostrorn, 1993), removal of which is a main objective of pulping and bleaching processes.

Detemination of lignin content in wood and pulps provides information for evaluation and

application of the processes. Hardness, bleachability, and other pulp properties, such as colour,

are also associated with the lignin content (Anon. 1983). Table 5 summarizes the results of

Duncan's Multiple Range Test for Klason lignin content variations due to age differences of ken&

The differences in lignin content of kenaf at various stages of growth are sigruficant only for

mature ken& Higher lignin content in 200-day old (mature) kenaf compared with 90, 120, 150-

day old kenaf indicates the need for high consumption of chernicals during pulping and bleaching.

Chatte jee (1959) working at the Technological Jute Research Laboratories in Calcuta, India first

reported the changes in chemical composition at different stages of jute plant growth. His results

show that there is little dinerence in lignin content as the plant matures. Migita (1947) studied the

changes in chemical composition in bamboo during its growing season and reported that lignin

content increased steadily from 8.4 % to 24.0 % fiom a week to three years. Fujii el al. (1993)

has done complete chemical analysis of bamboo as a function of its growth. They found that

protein content decreased as the plant aged while lignin increased with plant age.

Klason lignin analysis was done after the extraction by Han et al. (1995). The Klason ügnin values

increased fiom 4% at the beginning to 10% at the end of growing season. Theander (1991) completed

a study of the changes in chemical composition of several grasses as a fùnction of growing tirne. He

found that lignin increased as the plant matured while protein decreased in reed c a n q gras (Phaimis

at-wdir~ucea). Pectin remained constant during the entire plant Me.

Han et ai. (1995) found that plant height increased with plant age at an even rate. This is a

function of the growing conditions and would change with different moisture and Sun conditions.

The diameter of the stalk also increased gradually with age until reaching 160 days after planting

(DAP). At the end of 160 DAP, the rate of growth became more significant. However, this

drarnatic increase in volume is indicative of an increase in core and not bast fiber. A maximum

weekly growth of 30 cm was achieved during high temperature and a good rainfall. Clark and

Wolff (1969) carrîed out the first studies on the changes in chemical composition of kenaf as a

function of the growing season. They also studied the chemical difEerences dong the stem and

between leaves and stem. They found that ügnh content is increasing with age for the values

taken from the bottom (all but the top 0.66 meter of the plant). Data taken f?om the top part of

the piant shows similar trends but the top part has less lignin but higher protein than the bottom

part of the plant.

Lignin content of 16.0 % was repotted for whole kenaf grown in Mississipi (Pande and Roy 1996).

Han et ai. (1995) deteTmined the weight ratios of core to bast as a fùnction of growth. They found that

weight ratios between kenaf bast and core (corehast) increased as the growing days advanced. The

maximum of 1.8 was reached at 175 days after planting (Han et al. 1995). Weight ratios between bast

and core (corehast) was higher in Our kenaf plants grown in the green house that may be the

explanation why Our lignin content was higher than the reporteci values for whole kenaf in Meranire.

Another explanation why lignin contents were higher for green house grown kenaf as a hction of the

growing season, may be related to protein content of kenaffibers.

Han et ai. (1995) determined protein content of bast and core before and after the extraction. Protein

content decreased as the plant reached rnaturity. The actual value of Klason iignin could be lower than

it appears to be due to the presence of protein in the ken&. Kjeldahl determination of protein was

performed (Han et al. 1995) on several batches of combined Klason lignin samples and the amount of

protein in the EUason tignin was measured. The protein content of kenaf is between 4 to 14 % of the

klason lignin depending upon the age of the plant. Only 38 % of the protein were found in the Klason

lignin and the rest was found in the hydrolysate.

Table 5 . Duncan's Multiple Range Test for the means of Klason lignin contents of kenaf fibres at different

Means with the same letter are not significantly different.

stqes of growth, alpha=0.05 and df=36, MSE=O. 13660 1

Duncan Grouping

B

B

B

A

Mean (%)

14.8

15.0

14.9

15.5

N

15

7

8

10

Harvest tirne (days)

9Oday

1 20-day

15 O-day

200-day (mature)

4.2.2.2 Acid-soluble Lignin

Part of the lignin in hardwoods is not recoverable as an insoluble residue after the sulphunc acid

hydrolysis of the Klason lignin determination (Swan 1965). Some of the lignin dissolves in acid

solution during the test and is not included in the test results. In softwoods (coniferous woods)

and in sulfate pulps, the amount of soluble lignin is small, about 0.2 to 0.5%. In hardwoods

(deciduous woods), non-wood fibres, and in sulphite pulps, the content of soluble lignin is about 3

ro 5%. In semi-bleached pulps, soluble lignin could amount to about one-half or more of the total

lignin content (Anon. 1983).

Table 6. Duncan's Multiple Range Test for the means of acid-soluble ligm contents of kenaf fibres at dif rent s es of rowth, al~ha=0.05 and d+36. MSE=0.03069

---r Duncan Grouping

1 1

Means with the sarne letter are not significantly different.

Harvest time (days)

90+

1 2Oday

1 5 O-day

200-day (mature)

It can be concluded that, in comparing softwoods and hardwoods with kenaf as a function of the

growing season, kenaf grown in the green house has lower Klason lignin content and high

amounts of acid-soluble lignin. There was no data about the soluble lignin content of kenaf as a

funaion of growth in literature to compare with the results obtained in this study.

The Duncan's Test shows that the differences in the mean values of acid-soluble lignin content of

kenaf as a fùnction of the growing season, are significant for 90 and 120-day old, 150 and 200-

39

day old (mature kenaf) as can be seen from Table 6. Acid-soluble lignin content decreased for 90,

120, 150-day old kenaf then increased for 200-day old (mature) kenaf with plant age.

4.2.3 HoIocellulose Content

An ideal delignification should result in a total removal of lignin without chernical attack on the

polysaccharides, but there is no delignification procedure, which can satisQ this requirement.

Three important criteria cm be defined for holocelluloses (Fengel and Wegener 1989): a) low

residual lignin content, b) minimal loss of polysaccharides, c) minimal oxidative and hydrolytic

degradation of cellulose. As mentioned, a small percentage of residual lignin generally remains

within the holocellulose (Fengel and Wegener 1989). Portions of this residual lignin are altered

during the delignification, thus becoming soluble during the determination of acid-insoluble

residual lignin by acid hydrolysis of the holocellulose. This acid soluble lignin causes errors of up

to 9 % in the summative analysis of wood.

Table 7. Duncan's Multiple Range Test for the means of holocellulose contents of kenaf fibres at different sta :s of growth, alpha=O. (

Duncan Grouping

i and df=36, MSE=O. 17

Mean (%) Harvest tirne (days)

90-day

120-day

1 5 O-day

200-day (mature)

Means with the same letter are not sigruficantly different.

The Duncan's Multiple Range Test for the means of holocellulose content (Table 7) showed that

the variations among 90, 120, 150-day old kenaf are not significant, except for 200-day old

(mature) kenaf at 95 % confidence level. The percentage decrease in holocellulose content up to

mature ken& indicates that it would give lower pulp yield and strength as the plant reaches

maturity .

Han et al. (1 995) found that the juvenile ken& samples had low holocellulose values, which

gradually increased as the plant aged. L-Arabinose, L-rhamnose, L-galactose, and D-mannose

content decreased as a function of growth while D-glucose and D-xylose content increased over

this same period of time. Chattejee (1959) working at the Technological Jute Research

Laboratories in Calcuta, India first reported the changes in chemical composition at different

stages ofjute plant growth. His results show that there is little difference in holoceIlulose, but that

xylan content decreases as the plant matures. Fujii et al. (1993) has done the most complete

chemical analysis of bamboo as a Function of its growth. They found that holocellulose, pentosan,

and crystallinity increased with plant age.

4.2.4 Alpha-cellulose Content

In any isolation method cellulose can not be obtained in a pure state, but only as a more or less

crude preparation which is generally called alpha-cellulose (Fengel and Wegener 1989). This term

is used for wood cellulose, which is insoluble in a strong sodium hydroxide solution. The portion

which is soluble in the alkaline medium but precipitable from the neutralized solution was called

p-cellulose. Gamma-cellulose is the name for the portion which remains soluble even in the

neutraiized solution. Cellulose is the main constituent of wood. Approximately 40-45 % of the dry

substance in most wood species is cellulose, located predominantly in the secondary ce11 wall

(Sjostrom 1993).

There is not much variation in the alpha-cellulose content (Table 8) of kenaf at various stages of

Table 8. Duncan's Multiple Range Test for the r different stages of growth, alpha=0.05 and &32, M

Duncan Grouping Mean (%)

ieans of alpha-cellulose SE= 2.117514

contents of kenaf fibres at

W e s t tirne (days)

90day

120day

1 5 O-day

200day (mature)

Means with the sarne letter are not significantly different.

growth and the differences are not statistically significant. Otoguro et ai. (1991) reported that

cellulose content decreased with plant age. Migita (1947) studied the changes in chemical composition

in bamboo during its growing season and reported that the alpha-cellulose content was aimost constant

from a week to three years. Theander (1991) completed a study of the changes in chernical

composition of several grasses as a fùnction of growing tirne. He found that cellulose content increased

as the plant matured in reed canary gras (PhaIrms m~ndinacea).

Clark and WoW(1969) canied out the fkst studies on the changes in chernical composition of kenafas

a funaion of the growir~g season. They also studied the chemical dxerences dong the stem and

between leaves and stem. They found that alpha-celiulose content is increasing with age for the values

taken fiorn the bottom (ail but the top 0.66 meter of the plant). Data taken from the top part of the

plant shows similar trends but the top part has less ceiiulose than the bottom part of the plant.

4.2.5 Hemicellulose Content

Hemicelluloses belong to a group of heterogeneous polysaccharides, which are formed through

biosynthetic routes different from that of cellulose (Sjostrom 1993). In contrast to cellulose,

which is a homopolysaccharide, hernicelluloses are heteropolysaccharides, and iike ceilulose most

42

hemicelluloses function as supporting matenal in the ce11 walls.

The Duncan's Multiple Range Test for the means of hernicellulose content showed that the

difference among 90, 120, 150, and 200-day old kenaf are not significant at 95 % confidence

level. Theander (199 1) completed a shidy of the changes in chernical composition of severai grasses as

a fùnction of growing tirne. He found that hemiceliulose content and pectin remained constant d u ~ g

the entire plant life. ûtoguro et al. (1 99 1) reported that cellulose and hemice~ulose content decreased

with plant age. Chand and Hashmi (1993) found that hemicellulose content was found to be the highest

when the plant was 5 years old.

Table 9. Duncan's Multiple Range Test for the means of hemicellulose contents of kenaf fibres at ifferent stages of growl

Duncan Grouping

A

A

A

A

, alpha=0.05 and &32

Mean (%) Harvest time (days)

90-day old

120-day old

150day old

200day oId (mature)

Means with the sanie letter are not significantly different.

4.3 iNORGANiC COMPONENTS

4.3.1 Ash Content

The differences in the mean values of ash content of kenaf at various stages of growth are

significant as can be seen in Table 3 and Figure. 3. Ash content of 90-day old kenaf is the highest

at 2.9 % and there is a decrease to 2.6 % then to 2.5 % for 120-day and 150-day old kenaf. A

decrease in ash content of kenaf as a function of growth is in good agreement with the reported

trend in literature. Mature kenaf ash content at 2.1 % is also in good agreement with the ash

content of kenaf grown in Mississippi.

Chatterjee (1959) reported the changes in chernical composition at different stages of jute plant

growth. His results show that ash and iron content decrease as the plant matures. Fujü et al. (1993)

also reported that ash content and protein decreased as the plant aged. Han et al. (1994) studied

changes in chemical composition during the growing season for four varieties of ken& Ash content of

ken& bast and core was determined before and d e r extraction. Ash content decreased as the plant

reached matunty.

The non-wood plants have increasing percentage of silica in their plant structure which in pulping

and chemical recovery causes many problems like a) scale formation in evaporator tubes. b) hard

smelt deposits on fumace walls of recovery boiler, c) slow settling rate of recausticized white

liquor, and d) make lime sludge unsuitable for lime mud rebuming. As a result the chemical

recovery operation and its economy are adversely affected (Judt 1987).

Table 10. Duncan's Multiple Range Test for the means of ash contents of kenaf fibres at different stages of

90-day old

1 20-day old

150-day old

200day old (mature)

growth. alpha=0.05 and &20. MSE= 0.07973 1

Means with the same letter are not significantly dflerent.

A hi& ash content, consisting maidy of siicates, is typical of grasses. The amount of silica h the gras

depends on the harvesting tirne; the total ash and silica contents increase slightly when harvesting is

Harvest t h e (days) N Duncan Grouping Mean (%)

delayed (Seisto 1997). At the sarne tirne, however, the homogeneity of the raw matenal improves, and

the pulp yield increases. Most of the silica present in gras is located in the leaves. In reed canary grass,

the siica content of the stem is haK that of the leaves. The amount of siica in the pulp is therefore

highly dependent on the proportion of leaves in the raw material and may Vary h m cook to cook.

The purpose of this part of the study was to provide basic information with respect to the

chemical components of kenaf as a function of growth as a raw material for further studies,

pulping. It is clear fiom these results that, disregarding the differences which were al1 within the

limits of the methods used, and also considering the fact that there may be some lignin lefi in

holocellulose and alpha-cellulose, the differences in extractive, holocellulose, and lignin contents

between the age groups of kenaf were significant.

As wood with iow lignin and extractive and a high alpha-cellulose content is desired in the

pulping and papemaking industry, it is interesting to consider how differently kenaf at various

stages of growth behave dunng the soda pulping process with various cooking times and

temperatures.

CHAPTER V

SODA MICRO-PULPING CHARACTERISTICS OF KENAF AS A FUNCTION OF GROWTH

5.1 PULP YIELD

Yield is generally the most important economic factor effecting chernical pulping processes.

Knowledge of how process variables and changes in the raw materials influence the yield is

vay important (Kleppe, 1970b). It is obvious that variations in the chernical composition of

wood will influence the pulp yield considerably (Kleppe 1970a).

The Duncan's Range Test indicate that the differences in mean values of percentage yields of

kenaf at various stages of growth are not significant. In comparing the yields of pulps from

kenaf at various stages of growth, it is observed that 150dayold kenaf gives about 2 % higher

yield (60.4 %) than 90-day-old (58.8 %), 120day-old (58.7 %) and 200-day-old (mature)

kenaf (58.8 %), for al1 cooking times and temperatures studied. For example, cooks at 170 OC

for 1 80 minutes gave pulp yields of 52.0, 5 1.2, 54.7, and 49.0 % respectively for 9û, 120, 150

and 200-day-dd (maîure) kenaf (Table 11). Mature (200dayold) kenaf pulp yield is lower

compared to the others in the group. At industrial pulping conditions, i.e., cooking at 170 OC

for 120 minutes, pulp yields of 54.5, 5 1.7, 55.6, and 52.7 % were found for 90, 120, 150 and

200-daysld (mature) kenaf respective1 y.

As seen in Table 11, and Figures 4, 5, and 6, a marked loss in yield occurred when pulp was

cooked 30 minutes at al1 temperatures studied. Cooking at 140 OC for 150 minutes gave pulp

yields of 62.1, 6 1.5,64.3, and 62.6 % respectively for 90, 120, 150 and 20ûdaysld (mature)

kenaf that contained 10.0, 10.3, 10.9, and 9.9 % residual lignin respedively. Pulping at 155 OC

for the same tirne 150 minutes decreased the yield to 56.8 (5 % decrease), 59.6 (2 %), 5 7.4 (7

%), and 55.3 % (7 % decrease), corresponding to the residual lignin contents of 6.3, 8.0, 7.8,

and 7.0 % (based on raw maîerial) respectively.

Table 1 1. Pulp yield ( ? ? (of exiractive-fk raw mataial) of soda plping of kenaf fibre as a

90-day-old kenaf 12O-day-old kenaf 5day-old kenaf 200-day-~ld

min.

Holocelluiose (% of fibre) + 90-day1old kenaf + 12ûday-old kenaf + 150-dayi)ld kenaf -X-200-day~ld kenaf

O 30 60 90 120 150 180

Time, min.

Figure 4. The relationship between yield holocellulose (% of fibre), a d ooohg time for kenaf

at various stages of growth at 140 O C

\ Yield

O 30 60 90 120 150 180

Time, min.

Figure 5. The relationship between yield (%), holocelluiose (% of fibre), and cooking t h e at 155 O C

Holocelluiose (% of fibre) + 120-day-old kenaf + 150daydd kenaf -X=2ûûdaydd kenaf

O 30 60 90 1 20 150 180

Time, min.

Figure 6. The rehtionship W e e n yield (%), holocelluiose (% of fibre), and cooking time at 170 O C

The yield losses were high in the initial phase of pulping (30 minutes), at each temperature

shidied. The losses of carbohydrates are high in the beginning of the cook which means that

they are attacked even at a relatively low temperature when delignification d l proaeds

slowly (Sjostrom, 1993). The yield losses of 40.5.4 1.2,42.0, and 43.7 % for 90, 120, 1 50 and

200-day-old (mature) kenaf were due to; 10.7 % lignin removai, and 29.8 % holocellulose

degrdation for 90-day-old kenaf, 9.8 % lignin rem@ and 3 1.4 % holocellulose degradation

for 1 20-day-old kenaf, 10.4 % lignin removal, and 3 1.6 % holoceUulose degradation for 1 50-

dayold kenaf, 1 1.9 % lignin removal, and 3 1.7 % holocellulose degradation for 200-day-old

(mature) kenaf. Cwking at 170 OC produceci bleachable-grade pulps with low @in content

(about 5 % lignin content, Table 12) from al1 age groups compared but the yields obtained

were around 50 %. For example, cuoking at 1 70 O C for 1 20 minutes is presented in Figure 7.

I 0 90day-old kenaf O 120-day-old kenaf 1

Kappa #

Figure 7. Soda pulping of kenafat 170 O C for 120 minutes

5.2 DELIGNIF'ICATION SELEC'IWITY

The properties of chernical pulps are to a high degree determined by their fibre morphology

and lignin content, other factors of prscticai importance king the effective active alkali

charge and sulfidity (Paavilainen 1989). Earlier studies show that at least 80./0 and in some

cases 90 % of the quality variations in paper-grade pulps can te interpreted as originating

fiom the morphological properties of the wood fibres. The conneaion between

papermaking potential and yield (kappa number) is well known in the case of both board

and paper-grade pulps; attention in ment years, however, has focusseci on studying the

selectivity of prolonged cooking.

The selectivity of the pulping chemicals towards delignification determines the yield of the

pulping process and to some extend the pulp properties. Duncan's Multiple Range Test

indicate that the differences in the mean values of percentage yields of kenaf at various stages

of growth are not significant. In comparing the yields of pulps fiom kenafat various stages of

growth, it is observed that 150-day-old kenaf gives about 2 % higher yield (60.4 Yo) than 90-

&y-old (58.8 %), 12Maysld (58.7 %) and 200-day-old (mature) kenaf (58.8 %), for al1

cooking times and temperatures studied.

Simultaneously with the dissolution of Iignin, more or less carbohydrates are removed fiom

the wood dunng pulping. The selectivity of delignification cm be expressed as the weight

ratio of the lignin and cerbohydrates removed fiom the wood &a a certain cooking time or at

a given degree of delignification. A high selectivity thus means low carbohydrate losses

(Sjostrom, 1993).

Carbohydrate losses in cooking are due to peeling reactions and to alkaline hyrolysis of

glycosidic bonds. An increase in hydrosulphide concentration accelerates the dissolution of

lignin but has no significant effect on the rate of carbohydrate degradation, whereas a high

hydroxyl ion concentration increases both lignin dissolution and carbohydrate degradation.

Therefore, both a decrease in sulphidity and an increase in the effective alkali charge will

reduce the yield at a given kappa level (Paavilainen 1989).

An increase in the effective alkali charge not only reduces the carbohydrate yield but also

alters the proportions of the different carbohydrate compounds in the pulp. The percentage

of gluwmannan increases ody slightly, but there is a sigaificant decrease in the

percentage of xylan. This is due to the fact that a high hydroxyl ion concentration has a

greater effect on the rate of the xylan degredation than on that of glucomannan. While the

increase in alkali charge reduces the selectivity of delignification, the total hemicellulose

content of the pulp will also be higher with a low effective alkali charge (Paavilainen

1989).

The most important lignin degradation reactions taking place during pulping and

bleaching follow mechanisms which apply also to the carbohydrate reactions during these

processes (Gierer 1985). Exarnples for the analogies between the mechanisms of lignin

and carbohydrate reactions are given to provide an explanation for the limited selectivity

of current pulping and bleaching processes with respect to lignin degradation and

dissolution.

Examples of fiagmentation and condensation reactions of lignins and of corresponding

reactions of carbohydrates, taking place during pulping (Gierer 1985):

Acidic cleavage of aryl ether bonds and glycosidic bonds

Alkaline cleavage of aryl ether bonds and glycosidic bonds

Alkali-induced cleavage of alpha-aryl ether bonds and beta-elimination during peeling

Alkali-promoted cleovage of carbon-carbon bonds in lignin and carbohydrates

Condensation reactions between lignin fiagments, and between lignin-and

carbohydrate fiagments.

Tabie 12. Residual lignin content, (%) (of extractivefkee raw material) of kenaf as a fiinction

90-dayold kenaf 120-day-old kenaf 150-dayold k e d 200-day-old kenaf Temperature OC

Tirne, min. 140 155 170 1 4 0 155 170 140 155 170 140 155 170

kenaf

O 120-day-old kenaf

A ISOday-old ken&

O 4 8 12 16

Residuai Lignin, % (on fibre)

Figure 8. Delignification selectivity curves for 90, 120, 1 JO anci 200dayold (mature) kenaf.

Delignification selectivity curves, residual lignin, (% of extractive-fiee raw material, Table

12) versus pulp yield (% of extractive-free raw materiai, Table 1 1) for 90, 120, 150, and 200-

day-old (mature) kenaf are show in Figure 8. The average yield for 150day-old kaiaf over

the whole range of cooking times and temperatures studied is the highest (60.4 %), amongst

the group compared.

Degree of delignification versus holocellulose dissolution is show in Figure 9. It shows

that the buk phase of delignification statted at approximately 20 % delignification, and up to

this point, in the initial phase of delignification, most of the carbohydrates dissolved (25 to 30

%). In the bulk delignification phase of pulping, holocellulose dissolution is slow (0.06 % p a

minute) and stays almost contant at percentage increases of (28 to 33 %), (30 to 33 %), (25 to

32 %), and (25 to 35 %) for 90,120,150, and 2Oeday-old (mature) kenaf respectively for ail

the cooking times and temperatures shidied, as seen in Figure 9. The degree of delignification

inaeases fiom about 21 % to 83 % d u ~ g the whole cooking times and temperatures. As

stated before Figure 9, also does not show any trend that any of the age groups of kenaf

studied is more selective than the other.

O Qû-day-old kenaf

o 12Way-old kenaf

A 1 5 W a y-old kenaf

x 20Way-oiâ kenaf

O 20 40 60 80 1 O0 Degree of delignification (%)

Figure 9. Selectivity of soda pulping (holocellulose dissolution vs. degree of delignification)

of kenaf at various stages of growth

5.3 DELIGNIETCATION OF KENAF AS A FUNCTION OF GROWTH

5.3.1 Soda Pulping of Kaaf a3 a hiaction of Growth

Besides morphological fibre properties, the polysaccharide reactions in alkaline medium

and the degree of delignification detemine the character of a pulp (Fengel and Wegener,

1983). The arnount of residual lignin (usually expressed by the kappa number) is the

criterion for whether the pulp is to be used as an unbleached grade or bleached for printing

paper qualities.

Numerous studies on the reactions of lignin in alkaline pulping have reveded the

fundamental importance of the presence of fiee phenolic hydrowl groups. In lignin units

containing such groups, the alkaline conditions prevailing in kraft and soda cooking

liquors lead to the formation of methylene quinones (Gellerstedt and Lindfors, 1984).

These structures are unstable and are readily attacked by nucleophiles such as

hydrogensulfide ions or various organic carbonions present in the readon medium.

Ahematively, methylene quinones are stabilited via elimination reactions leading to the

formation of stilbene and styrene structures.

The extent and distribution of these reactions determine the stnictural modification of

lignin, including lignin fragmentation and condensation, taking place during pulping. In

addition to these reactions, the dissolution of lignin in the delignification of wood must be

dependent upon the presence of hydrophilic groups. In kraft and soda cooking these

consist mainly of phenolic hydroxyl groups, minor amounts of carboxylic acid groups also

being present (Gellerst edt and Lind fors, 1 984).

Lignin begins to dissolve at 140 O C and continues to do so rapidly during the bulk

delignification stage until a kappa level of about 35 reached, at which point delignification

reactions start to slow dom (Paavilainen 1989). The transition point between bulk and

residual delignification shifis to higher lignin contents if the sulphidity or effective alkali

charge is reduced.

The initial hydrosulphide and hydroxyl ion concentrations greatly affect the reaction rates

in bulk and residual delignification. However, increasing its hydroxyl ion concentration

c m also accelerate delignification in the residual phase, aithough an increase in

hydrosulp hide ion concentration has only minimal effect (Paavilainen 1 989).

Prolonged delignification of bleached-grade kraft pulps has been proposed as a method of

decreasing the subsequent consumption of expensive bleaching chemicals and of reducing

the effkct of bleaching effluents on the environment (Axegard et al. 1983). In that case it

is, however, essential to improve the selectivity Le. to minimize the attack of alkali on

carbohydrates in order to avoid a decrease in pulp strength and a loss in pulp yield. One

way of detemining how the selectivity in the cook may be improved is to investigate

systematically the kinetics of delignification in the various phases of the cook (Axegard et

al. 1983).

Sundquist (1985) presents a differentiated model for residual lignin in unbleached

chemical pulp. In this model residual lignin has been divided into six hypothetical

fragments. Because the amount and chemical properties of various fragments depend on

the cooking method, the residual lignin patterns of different types of pulps are different,

which means different bleachability, too. These fragments are; high molecular weight

crosslinked lignin, iignin chemically bonded to polysaccharides LC-complexes, and

probably also lignin resorbed ont0 fibers during cooking belong to the category which can

be removed only by using bleaching chemicals (Sundquist 1985).

However, there are also lignin fragments that could, in theory, be removed fiom the pulp

without the use of chlorine. These include the lignin molecules entangled in the

microstructure of fiber wali. The entangled lignin (Favis et al. 1981) of kraft pulp diffises

extremely slowly from the pulp. Soluble lignin, which diffises faster, is found in

macropores and capillaries inside the fibers and also h e e n the fibers in the outer liquid

of pulp (Sundquist 1985). This partly hypothetical model can genedly be u s d to shidy

Table 13. Average residual klason lipin, acidioluble lignin, and togl lignin content of 9ûday- old kenafsoda pulp at different cwking times and temperatures

I 1

T h e (minutes) KLip ASL TLign

O 30 60 80 120 160 110 C d n g fhr (min.)

Figure 10. Average residual klason lignin content of 9Oy-old kenaf soda pulp at different cooking times and temperatures

Table 14. Average residual klason lignin, acid-soluble Li* and total lignin content of 120day- old kenafsoda pulp at different cooking times and temperatures

r m

Time (min.) Klignin ASL T.Lignjn Klignin ASL T.Lignin Klignin ASL T.Lignin I I

e m

O 1 1 1 I I

O 30 60 90 120 150 180 cooking time

Figure 1 1 . Klason iignin content of 120&y-old kenaf soda pulp at dinerent cooking times and temperatures

Table 15. Average midual ldason lignin, acid-soluble lignin, ad total lignin coatent of 15Oday- old kenaf soda pulp at differed cooking times and temperatures.

Temperature O C

The (min.) Kii- ASL T.L-

O 30 60 90 120 160 180 Cooking Time (min.)

Figure 12. Average residual klason lignin content of 150-day~ld kenaf soda pulp at different cooking times and temperatures

Table 16. Average residual ldason lignin, acid-soluble tignin, and total lignin content of 2004ay- old keaaf soda pulp at di&rent caaking times and temperatures

I

Time (min) Klignin ASL T.Lignh Klignin ASL T.Lignin

ways of producing chernical pulps that cause less harrn to the envuonment, for example by

trying to render soluble as many of the fragments as possible during the cook.

nie average residud klason lignin, acid-soluble and total lignin contents @ a d on pulp) of

kenaf pulps for 90, 120, 150 and 200day-old kenaf are given in Tables 13, 14, 15, 16 and

shown in Figures IO, 11, 12, and 13. It can be seen h m these tables and figures thai

delignification at 140 O C is very slow for each age group of kenaf. Delignification increases

with increesing tempaature. Delignification phases of soda pulping of kenaf at various stages

of growth are not obvious. The logarithm of residual lignin content @ a d on raw material)

of kenaf pulps as a function of growth are given in Tables 17, 18, 19, and 20, and shown in

Figures 14, 15, 16, and 17. The stages of delignification are evident here with temperatures

above 140 O C , with kenaf at various stages of growth.

The dissolution of lignin can be divided into three phases (Sjostrom, 1993). Initially, there

is a rapid removal of approximately 20-25 per cent of the lignin, followed by a slower

bulk delignification stage and even slower residual delignification stage. The initial phase

of delignification takes place at temperatures below 140 O C and is controlled by diffision.

The initial phase comprises the pulping treatment and results in dissolution of 20-25 % of

the total amount of lignin present in the wood (Gierer, 1980). The alkaline cleavage of a-

aryl ether linkages, and the sulfidolytic cleavage of P-aryl ether linkages, in phenolic units

generate new phenolic units which may undergo the same types of cleavage provided

they, in their tum, contain a-and /or P-aryl ether bonds to the adjacent lignin unit. Thus,

the degradation of lignin during the initial phase, involving only phenolic units may

continue until it reaches units which are not of the a- or P-aryl ether type ("peeling" of

lignin) (Gierer 1980).

These figures show that the percentage loss of carbohydrates is higher during initial phase of

delignification than other phases. As can be seen fiom these Figures that percentage lignin

removal is higher during initial phase of delignification than any osha phases. Lignin

removal is especially higher at higher temperatures which indicates that delignincation is

tempaature dependent, as can be seen cooking at 170 OC. The initiai phase of mks at 140

OC is obvious for each age of kenaf but the shift fkom initiai to bulle and buk to final phase is

not clear (Figures 14, 15, 16, and 17). The transition points ôetwe!en delignification phases

are more obvious for cooks made at 155 OC and 170 OC.

During initial phase of the cook at 140 OC, lignin removal rate was 6.0, 6.5, 3.9, and 6.2 %

for 3,4, 5 month old and mature kenaf respectively (Tables 21.2, 23, and 24, Figures 14, 15,

16, and 17). But during bulk and final phase ofcooking at 140 OC, only 2.6, 2.3,4.3, and 4.4

% lignin removal was achieved. Degree of delignifications achieved at the end of the codt at

140 OC were 46.3, 43.7, 40.6, and 55.0 % respectively for 90, 120, 150, and 2OOaay-old

kenaf (Tables 25,26,27,28).

Above 140 OC, the rate of delignification becornes controlled by chernical reactions and

accelerates steadily with increasing temperature. The rate of lignin dissolution rernains high

during this "bulk delignification" phase, until about 90 % of the lignin have been removed.

The final slow phase is t e n d "residual delignification" and can be regulated to some degree

by varying the alkali charge and the cooking temperature (Sjostrom, 1993). The buk phase

includes the heating period from 150 to 170 O C and the cooking treatment at 170 OC, and

results in the dissolution of the main portion (about 60 %) of the lignin present in the wood.

Buik delignification is first-order with respect to lignin concentration, almost linearly

dependent on the hydroxide, but only slightly dependent on the hydosulfide concentration

(Gierer, 1980).

The rate of bulk delignification appears to be chemidly controlled. Cleavage of P-aryl ether

linkages in non-phenolic units also liberates new phenolic structures, which may consthte

the starting point for the two types of cleavage reactions operating during the initiai phase,

Le. cleavage of a-aryl and Paryl ether bonds in phenolic units. As a result of these reactions,

lignin degradation during the bulk phase, initiated by the ratadeterminhg cleavage of B-aryl

ether bonds in non-phenolic units, is extended to the point where dissolution takes place.

Thus, the subsequent fast reactions have no infiuence on the rate, but a great influence on the

extent, of lignin degradation (Gierer, 1980). In this way, they contribute extensively to the

rate of lignin dissolution during the buk phase.

Comparing cooking at 155 OC with 140 OC, the percentage lignin removal was higher during

initial phase, 8.0, 8.5, 6.9, and 9.0 % rrespectively and peroenSege delignification achieved

was 43.4, 45.5, 37.0, and 46.0 % respectively for 90, 120, 150 and 200-day-old (mature)

kenaf at 155 OC. During bulk delignification of pulping at 155 OC, the lignin removal was 2.4,

2.0,4.0, and 3.5 % respdvely 90, 120, 150 and 2ûûday-old (mahue) kenaf assuming that

bulk delignification ended at the end of 150 minutes cooking (Figures 14, 15, 16, and 17). As

can be seen fiom the figures that hnal slow phase of delignification starts at 150 minutes of

cooking for 155 OC, and at 120 minutes cooking for 170 O C . In some cases there is aiso

indication of lignin condensation reactions taking place at this final phase of delignification.

The three stages of delignification were more apparent during cooking at 170 OC. The

initial phase lasted about 30 minutes, dunng which 10.7, 9.8, 10.4, and 11.9 % lignin

removal was achieved respectively for 90, 120, 150 and 2004ay-old (mature) kenaf

(Tables 1 7, 1 8, 1 9,20 and also 2 1, 22, 23, 24, Figures 14, 1 5, 16, and 1 7). The bulk phase

of cooking at 170 OC ended after cooking 120 minutes dunng which the degree of lignin

removal was 14.0, 14.2, 12.9, and 14.8 % respectively for 90, 120, 150 and 200-day-old

(mature) kenaf (Tables 21, 22, 23, Figures 20). Residual lignin contents of pups were 4.6,

4.6, 5 -9, and 4.7 % (based on o.d wt of raw material), the yields obtained 54.5, 5 1.7, 55.2,

and 52.7 % (Table 11) and kappa number were 51.3, 54.5, 64.7, and 54.2 respectively for

90, 120, 1 50 and 200-day-old (mature) kenaf.

A turning point exists between the bulk and residual delignification stages, which is

referred to as the phare transition point of delignification (Kleinert 1974). The point for

residual delignification tends toward higher lignin contents at lower cooking temperatures

such as 140 O C as seen fkom the Figures 10 to 13. It is suggested that the "residual lignin"

is fonned during the cook, and that this stage represents the alkaline degradation of a

cellulosic portion (Kleinert, 1966). The existence of a condensed lignin at the end of a

cook is also possible.

The residual phase of delignification includes the final treatment at 170 O C and leads to a

dissolution of roughly 10-15 % of the lignin originally present in wood. This process is

very slow, the rate being dependent on the temperature and hydroxide ion concentration,

but aimost independent of the hydrosulfide ion concentration (Gierer, 1980). This phase of

delignification could be due, at lecist in part, to fiagmentation via alkaliprornoted cleavage

of carbon-carbon linkages onginally present or generated by condensation reactions.

Solvolytic ether cleavage reactions not assisted by neighboring groups might also, to a

smail extent, contribute to this phase. The low rate of lignin dissolution couid then be

ascnbed to the fact that while reactions of these types require high alkalinity, the

concentration of alkali at this stage of pulping is wnsiderably lower than during the

preceding phases due to neutralization reactions with various degradation products,

particularly those arising from carbohydrates (Gierer, 1980).

Remarkably, decrease of the cooking temperature was found to shifl the residual

delignification point not only to a longer cooking time, but also to a higher pulp lignin

content (Kleinert, 1965). During "residual delignification" a considerable loss of pulp

yield calculated 6ee of lignin t w k place. Per unit weight of lignin solubilized, this yield

loss was about 10 times greater than that observed in the range of bulk delignification.

Strong evidence was found that, dunng bulk delignification, lignin solubilization results

fiom rapid fiagmentation of the lignin macromolecules with immeûiate formation of

alkali-stable productq and that in cornparison, d u ~ g residual delignification, it consists in

a slow removal of lignin-carbohydrate complexes probably formed by secondary grafiing

reactions (Kleinert, 1965).

In general, the lignin remaining undissolved in the wood at the transition point fiom bulk

to residual delignification was found to increase when cooking time was extended by

lowering temperature (Kleinert, 1966).

Table 17. Residual lignin content on raw niaterial versus reaction tirne for 90daydd kenaf sada pulp at dinerent cooking times and 4

I

T i e (minutes) Residud lignin , (% on raw material)

Fùsidual lignin , (Oh on raw material)

Residual lignin , (% on raw material)

O 30 80 90 120 1SO la0 Cooking Thne (min.)

Figure 14. Residual lignin content on raw material vems reaction time for 90&y-dd kenaf soda pulp at different cookulg times and temperatures

Table 18. Residual lignin content on raw material versus reaction time for 12Odaydd kenaf soda pulp at different cooking tirne I 1

I Residuai lignin (% on raw material)

and tem~eratures

Residual Lignin (0/0 on raw material)

ReSidual1ign.b WO on raw material)

O 30 60 90 120 160 la0

cooking Thle (min.)

Figure 15. Residual lignin content on raw material versus reaction time for 120-day-old kenaf soda pulp at Merent cooking times and temperatures

Table 19. Resiciuai lignin content on raw material versus d o n tirne for 150-dayd kenaf soda pulp at Merent cooking times and temperatures

I I I

Time (minutes)

1 Temperature OC

Residual lignin (% on raw material)

Residual lignin (O? on raw material)

1 -

140 OC

Residuai ligniu (O! on raw material)

O 30 40 90 120 1so lu0

C U n g Tkm (min.)

155 OC

Figure 16. Residual lignin cantent on raw material versus reaction tune for lSO&y-old keaaf soda pulp at difFerent cooking times and temperatures

170 OC

Table 20. Residual lignin content on raw material versus reaction t h e for 200daydd

Residual lignin (% on raw material)

(mature) kenaf soda pulp at different cooking times and tempe

O 30 60 90 120 150 180

Cooking T i e (min.)

Temperature OC

Time (minutes)

Figure 17. Residual lignin content on raw material versus reaction time for 200-day=old (mature) k d & puip at difEereat coolring times and temperatures

140 OC

Residuai lignin ! % on w e )

155 OC

Residual iignin (O/o on raw material)

The content of phenoüc groups starts to decrease and the amount of carbohydrates

attached to kraft lignin to increase when the transition point between the bulk and residual

phase is passed. The lignin portions redeposited dunng the last stage of alkaline woking

contribute especially strongly to low brightness value (Fengel and Wegener, 1983). The

residual lignin contents of kraft pulps to be bleached are usually about 2% (based on pulp)

in the case of hardwoodq or 3-4 % in the case of softwwds. Unbleached grades have

higher lignin contents, which may exceed 10% in high-yield kraft pulping.

Axegard et al. (1983) studied how the amount of residual lignin is afSected by

temperature in the different phases and concentration of OIT and HS in the bulk phase.

They reported that the concentration of OH in the initial and bulk phases was varied, no

significant effect on the amount of the residual lignin could be observed, nor was the rate

in the final phase affected. They also found that there is no significant effect of

concentration of OK in the bulk phase on the amount of residual lignin. While variations

of O H concentration (above a certain minimum level) in the initial and bulk phases seem

to have a very small or negligible effect on the amount of residual lignin a direct shortage

of alkali during some period of the previous phase gives rise to a significant formation of

"residual lignin" (Axegard et al. 1983).

The negative effect of alkali shortage may be explaineci by condensation reactions. This is,

however, not the only possible explanation. It is possible that the degree of swelling

decreases as a results of alkali shortage. A fiber wall in an unswelled state may resist

diffusion. It has also been show that dissolved lignin is precipitated inside the fibers

when the alkaiinity is lowered (Axegard et aï. 1983). It is therefore possible that a

partially i~eversible precipitation of degradeci but not dissolved lignins occurs when the

alkalinity is lowered.

During the course of a kraft cook there is an inaease in the content of phenolic hydroxyl

groups per unit weight ofresidual lignin. Throughout the c d the content of these groups is,

however, much lower than the content of phenolic hydroxyl groups present in the dissolved

kraft lignins (Gellerstedt and Lindfors, 1984). It was further fouad that the residual lignin in a

soda pulp wntains a significantly smaller arnounts of phenolic hydroxyl p u p s than the

lignin in a kraft pulp at the same degree of delignification (Gellerstedt and Lindfors, 1984).

Kleinert (1966) showed that the amount of residual lignin to be removed by the

comparatively slow final phase decrases with increasing cooking temperature. A study of

the effect of reaction temperature in the range 130-185 O C revealeâ that the change from

bulk to residual delignification took place at a lower lignin value in kraft cooking

compared to caustic soda cooking (Kleinert, 1966). The lignin remaining undissolved at

the transition increased as the reaction temperature was lowered. The influence of the

effective alkali charge on bulk delignification was investigated using 20 min at 182.5 OC.

The logarithm of pulp lignin remaining at the end of the cook decreased linearly as the

effective alkali content increased. The relationship between the solubilization of lignin and

hemicelIuloses was studied by deterrnining and plotting the total pulp yield venus lignin

content on wood at 175-180 OC and 130-140 OC. Very little increase in total yield was

obtained at the lower temperature. It is ~ggested that commercial kraft pulping should be

limited to the period of bulk delignification when the ratio of lignin to carbohydrate is

approximately 1 : 0.6 rather than continue tu the penod of residual delignification when the

ratio is approximately 1: 6.7 (Kleinert, 1966).

5.4 DEGRADATION OF POLYSACCHARIDES

The alkaline degradation of cellulose and polyoses is an essentid factor in kraft and soda

pulping (Fengel and Wegener, 1983). Initial reactions are solvation of hydroxyl groups by

hydroxyl ions causing a swollen state. At elevated temperatures the polysaccharides are

attacked by strong alkali solutions, with a large number of reactions taking place. The

most important ones:

a) dissolution of undegraded polysaccharides,

b) peeling of end-groups with formation of alkali stable end-groups,

c) alkaline hydrolysis of glycosidic bonds,

d) degradation and decomposition of dissolved polysaccharides, hydrolyzed fragments,

and peeled monosaccharides

The most important reactions responsible for the loss of polysaccharides and reduction of

the chain length of cellulose in alkaline pulping are peeling and hydrolytic reactions.

In conventional alkaline pulping, chip impregnation takes place over an extended period

during a relatively slow rise to maximum temperature. As a result, some hemicelluloses

are solu bilized prior to reaching maximum temperature, and this causes physicc-chemical

changes of the lignin-carbohydrate association in the wood, which in tum adversely affect

delignification during the cooking stage (Kleinert, 1965).

At temperatures of about 100 OC, occurring during the heating period in pulping, the

degradation of polysaccharide chain starts f?om the existing reducing end-groups by the

so-called peeling reactions (primary peeling). At temperatures above 150 OC chains are

split by alkaline hydrolysis. Thus new reducing end-groups are formed, which are also

subjected to endwise degradation (secondary peeling). The peeling reaction of

polysaccharides involves the elimination of reducing end-groups by a beta-alkoxy

elimination to various carboxylic acids, thus reducing the chains by one monomeric unit at

a tirne.

Table 2 1 . Li* removal and holocellulose dissolution fiom 9edaydd k e d with soda pulping at different &king times and temperatures

Ti, min Holoceli %

Lignin %

Table 22. Ligoin removal and holocellulose dissolution fiorn 120dayold kenaf with soda pulpiag at different cooking times and temperatures

Holoceli %

Temperature O C

Lignin %

Tie , min

HoIoce11 %

140 O C

Lignin %

Holocell %

155 OC

Lignin %

170 O C

Holoceli %

Lignin %

Table 23. Lignin removal and holocellulose dissolution fiom t50dayold kenaf with soda pulping at different cooking times and tempenituns

Temperature O C

Ti, min

Table 24. Lignin removal and holocellulose dissolution fiom 200-day-old (mature) kenaf with soda pulping at different cooking times and temperatures

Lignin %

3.9 5.6 7.0 7.4 7.9 7.6

Holocell %

25.4 26.2 28.7 29.0 27.8 27.0

The, min

30 60 90 120 150 180

Holocell %

31.7 30.9 32.3 32.5 35 .O 35.1

Lignin %

6.9 9.6 10.0 11.0 11.0 12.9

Holocell %

27.2 28.0 28.7 32.1 32.2 32.3

Holocell %

28.8 30.5 30.5 30.0 31.7 30.8

Lignin %

10.4 11.8 14.0 12.9 13.3 13.7

Lignin %

11.9 13.7 14.3 14.8 15.0 15.8

Holocell %

31.6 31.2 29.7 31.5 32.2 31.6

Li@ %

9.0 9.3 10.1 10.6 12.5 12.7

Lignin %

6.2 6.7 7.5 7.5 9.7 10.8

1

Hoioceli %

25.2 26.0 27.3 28.8 27.7 30.2

The holocellulose dissolution is faster and higher than lignin removal at any cooking

temperature studied for 90, 120, 150 and 200-daysld (mature) k e d . As can be e n fiom

Tables 21, 22, 23, and 24 that during the initiai phase after 30 minutes of cooking at 140

OC, 27.7, 30.3, 25.4, and 25.2 % of total carbohydrates present in kenaf fibre calculateci

fkom the lignin content of pulp were dissolved. At this stage the holocellulose dissolution

was higher for 90 and 120-daysld h a f but lower for 150-dayold and 200-daysld

(mature) kenaf at 25.4, and 25.2 %.

The holocellulose dissolution then increased to about 29 to 30 % then stayed almost

constant during the entire cook at 140 OC (Figure 18). At the end of cooking at 140 OC, the

pulp yields obtained were 6 1.8, 62.3, 65.3, and 59.0 % respectively for 90, 120, 150 and

200-day-old (mature) kenaf. The holocellulose dissolution rate for 150-day-old kenaf was

lower compared to 90, 120-day-old and 200-day-old (mature) kenaf for ail cooking times

and temperatures studied (Tables 2 1,22, 23,24, and Figures 18, 19, 20).

As can be seen tiom these figures that the losses of carbohydrates are especially high at

the beginning of the cooks which is expected as reported in literature. During the initial

phase, when oniy 6.0, 6.5, 3.9, and 6.2 % of lignin removed, 27.7, 30.3, 25.4, and 25.2 %

of carbohydrates were lost, probably mainly hemicelluloses (Kleinert, 1965).

The loss of carbohydrates continued to the end of the cook but at a slower rate than lignin

removal for each time and temperature studied. Cooking at 140 OC and 155 OC showed

sirnilar trends of carbohydrate dissolution for 90 and 120-day-old kenaf but for 150-day-

old kenaf and 200-day-old (mature) kenaf, the holocellulose dissolution rate was about 2

% higher for higher temperatures such as 170 OC (Figures 21,22, 23 and 24).

O 30 60 90 120 150 180 210

Time, min.

Figure 18. Lignin and holocellulose removal for soda pulping of kenaf (at 140 OC) as a function of growth

O 30 60 90 120 150 180 2 10

Time, min.

+ 90-day-old kenaf

O 120dayold kenaf

A 150day-oId k d

X 2ûû-day-01d kenaf

Figure 19. Lignin and holocellulose removal for soda pulping of kenaf (at 155 O C ) as a M o n of wwth

o 90-dayi)ld kenaf

ci 12O-day-old kenaf

A ISO-day-old kenaf

X 200-day-old kenaf

O 30 60 90 120 1 50 1 80 210

Time, min.

Figure 20. Lignin and holocellulose removai for soda pulping of kenaf (at 170 OC) as a fùnction of g r o d

Without the stopping reaction even a whole molecule may be destroyed by peeling

(Fengel and Wegener, 1983).

Acetic acid and small amounts of dicarboxylic acids are also arnong the alkaline

degradation products of cellulose, hexosans and pentosans. While formic acid is liberated

during the peeling reaction, acetic acid results fiom the cleavage of acetyl groups of

hardwood xylans and softwood mannans, ocaimng at very early stages of alkaline

pulping procedures. The dissolved, deacetylated xylan chains are known to be redeposited

on the fibres. Glucuronic acid groups of xylans are mostly lost at maximum cooking

temperature of alkaline pulping, whether by dissolution of xylan portions bearing acid

side-groups or alkaline hydrolysis of these groups (Fengel and Wegener, 1983).

In addition to the peeling of end-groups, alkaline hydrolysis (depolymerization) of

polysaccharides becomes important at high temperatures of about 170 O C , which give rise

to furthet- peeling reactions. The probable mechanism of alkaline hydrolysis occurs much

much more slowly than acidic hydrolysis (Fengel and Wegener, 1983).

Table 25 . Delignification and holocellulose degradation degrees for 9 W a y l d kenafwith soda pulping at different cooking times and temperatures

Ti, min

Table 26. Delignification and holocellulose degradation degrees for 120-day-old kenaf with soda pulping at different cooking times and temperatures

Delign %

Tie , min

30 60 90 120 150 180

Delign %

35 .O 38.7 38.0 41.0 44.8 43 -7

Table 27. Detipification and hoIocellulose degradation degrees for 1 5 k h y ~ i d kenaf witb soda pulping at different cooking times and temperahins

Holocell desrada

%

Deiign %

Table 28. Delignification and holocellulose degradation degrees for 200-day-old kenaf with soda pulping at different cdcing times and temperatures

Time, min Holocell degtada.

%

3 1.3 32.3 33.9 35.8 34.4 37.5

Holocell degrada

%

39.4 38.3 40.2 40.4 43.5 43.6

Degree of holocellulose degradation

O !mlay*ld kenaf

0 120lday~ld knaf

A 1SCFday-old k n a f

x 2ûûday*ld kenaf

O 30 60 90 120 150 180 210

The, min.

Figm 2 1. De- of &ügnifi,cation ancl hoIoalluIose degradation va d o n îime for soda pdping of kenaf (a!

o 9Oldaydd kenaf

üi 120day-old kenaf

A 15ûday-old keaaf

% 200day4d kenaf

O 30 60 90 120 150 180 2 10

Time, min.

Figure 22. Degrex of Qlignincation and ho1ocelluiose degradation vs d o n tim for soda puiping of kenaf (aî 155 O C ) as a fiinction of growth

O 9Oday4ld kenaf

0 12O-day-old kenaf

A 150day-old kenaf

x 200+4d kenaf

O 30 60 90 120 150 180 210 Tirne, min.

Figure 23. Delipification and degree of holocellulose degradation for soda pulping of kenaf (at 170 O C ) as a fiction of growth

In the case of cellulose about 50-60 glucose units are expected to be cleaved on an average

by endwise peeling until a competing reaction takes place which terminates the

degradation (Fengel and Wegener, 1983). The highly important, so-called stopping

reaction is initiated by a beta-hydroxy elirnination at the C4-position to a tautomeric

intemediate, which is converted to an alkali-stable metasaccharinic acid end-group (3-

deoxyaldonic acid). Other possible end-group formations are C2-methylglyceric acid and

to some extend aldonic acid, indicating the participation of some oxidative reactions.

Green et al. (1977) has studied the alkaline degradation of cellobiose in aqueous NaOH up

to 170 OC. Glucose is found, as well as isosaccharinic acid, as a product of peeling. The

rate of the reaction bears a linear relationship to temperature. It is concluded that the

peeling react ion, previousl y observeci at tower temperatures, aiso exists at higher

temperatures under pulping conditions. The rate of reaction is constant with respect to

allcali concentration above 0.5 N NaOH and is not affécted by sulfidity (Green et al.

1977). Therefore, competing condensation reactions become more important and fiuther

retard lignin dissolution (Gierer, 1980).

H - Factor

Figure 24. Lignin removal in soda pulping of 90, 120, 150 and 200-daysld (mature) kenaf

as a fiinction of H - Factor

A plot of percentage residual lignin content based on raw material as a hction of H - factor

for 90, 120, 150 and 200dayold (mature) kenaf is shown in Figure 24. As can be seen in

Figure 24, the initial phase of delignification is short and yield is high, over 60 (%) for kenaf

pulp at various stages of growth. In the final phase the selectivity due to slow delignification

is poor and yield falls below 50 % (Table 11). Deligoificetion studies of kenaf at various

stages of growth indicated that al1 of the age groups studied showed similar trends in lignin

dissolution and holocellulose degradation and these trends are not significantly diEerent fiom

each other. It is also shown that cooking of kenaf can be stopped at the end of 120 minutes

cooking to prevent further degradaiion of polysaccharides, to obtain optimum pulp yields

with low lignin content.

To avoid or at least to diminish peeling reactions, the reducing aldehyde end-groups can

be wnverted by reduction or oxidation to alcohol or carboxyl groups, respectively, or

subst ituteâ to yield other alkaii-stable end-groups. A polysaccharide stabilization, meaning

increased pulp yields, can be reached e.g. by the presence of polysulfides, m s i n g

oxidation to aldonic and metasaccharinic acids. Reâuction to alditol and thioalditol groups

is pedomed by treatments with sodium borohydride and hydrogen sulfide, respectively

(Kleppe, 1970).

Another type of additive, which stabilizes polysaccharides against alkaline peeling, is

anthraquinone (AQ) or related compounds such as anthraquinone-2-sulfonic acid. AQ

causes an oxidation of aldehyde end-groups to alkali-stable aldonic acids of different types

and amounts, itself being reduced to anthrahydroquinone (AHQ). This product was proved

to reaa with lignin, resulting in improved delignification, itself being oxidized to AQ.

This reduction-oxidation conversion is a prerequisite for an effective polysaccharide

stabilization in alkaline pulping, as large portions of the involveci catalytic AQ amounts

(about 0.1 % based on wood) are consumed by solubilized degradation compounds in the

liquor.

CHAPTER VI

PAPERMAKING POTENTIA. OF KENAF AS A FUNCTION OF GROWTH

6.1 Pilot-sde Pulping of Kenaf

Results of studies on delignification kinetics showed that the residud lignin content of

kenaf soda pulp was between 6 % and 9 % (baseci on pulp). The results also indicated that

lignin precipitation has occurred, which indicates the shortage of aikali in the final phase

of delignification. To obtain bleachable-grade kenaf soda pulps, alkalinity and ratio of

cooking liquor to raw material had to be increased. The chipped whole kenaf was woked

using 24.29 gR. AA (active alkali) as Na20, with active alkali charge of 17 % (2 %

increase fiom original 15 %) as Na20 bas4 on o.d weight of the raw matenal. The results

showed about 8% of uncooked rejects. Based on the calculations fiom micro-pulping

experiments, active alkali charge was fùrther increased to 20 % as Na20. The chipped

whole kenaf was pulped in a computenzed laboratory digester (h4X Systems, Inc.) using

soda cooking liquor of 36.88 g/L NaOH with an active alkali charge of 20 (%) as Na20,

and liquor to fibre ratio of 7: 1. Pulping conditions are given in Table 29.

It is reported by Calsbro (1992) that an increase in the caustic soda quantity above 15%

generally led to limited improvements of the yield and the mechanical properties. A soda

concentration of 20 % (with respect to the dry weight of the material) was suficient to

ensure an almost complete elimination of noncellulosic matter. Therefore, any m e t

increase in the chernicals concentration above this value did not produce any substantial

yield changes, but quantities in excess of 20 % did cause a downtum in the papennaking

properties, suggesting the beginnings of a pulp degradation at this level (Calabro 1992).

By using the same cooking conditions for al1 samples of kenaf at different stages of

growth, any differences in yield, ease of pulping or papemaking properties of the pulps

could be attributed to variations in the plant material. Mer cooking, the pulps were

washed on a fine filter placed on the wire mesh, then transferred to a Buchner fùmel and

washed thoroughly with fresh water. Washing was continued until the filtrates fiom pulp

were cdourless. Severe foaming occurred during pulp washing stage, which indicates the

presence of saponins in kenaf (Casey 1980). The pulps were screened over a vibratory

screen with 0.008-mm slotq and screeneâ yield (%), and screen rejects (%) were

detemineci. Kappa numbers for 90, 120, 150 and 2Oeday-old kenaf wae determincd

according to Tappi Procedure T 236 cm-85. The pilot-scale pulping results of kenaf as a

fùnction of growth are surnmarized in Table 30 and shown in Figure 26. The conditions

selected for pulping kenaf at different stages of growth gave rather high kappa numbers

for al1 amples.

Table 29. Pulping process conditions for soda cooking of kenaf as a function of growth using Mn< pilot scale digester

Aikali charge, % NaOH (as Na20 based on o.d fibre) Liquor to fibre ratio Time to maximum temperature, min., Cwking temperature, OC Time at maximum temperature, min, H factor

Table 30. Pilot-scale soda pulping results of kenaf as a fùnction of growth

C haracteristics

Pulp yield, unscreened, (%) Screened yield, (%) Screened rejects, (%) Kappa number,

l l 1 90-day- 1 20-day- 1 5 O-day-

old kenaf old kenaf old kenaf 200-day- old kenaf

47.2 42.6 4.0 34.7

6.2 Pulp Fiber Properties

Fiber properties were analyzed using the Op Test Fiber Quality Analyzer (FQA). The

reporied values are an average of four tests on each group of (whole stem) kenaf pulp. The

calculations of the weight-weighted average length are based on the assumption that

warseness increases linearly with fiber length, which may not be the case. Therefore, the

average length-weighted length was measured instead, since this parameter does not

depend on any sirnpliQing assumption (Carvalho et al. 1997).

Table 3 1. The results of Fiber Quality Analysis (FQA) of kenaf pulps as a fùnction of growth

Characteristics 200-day-old kenaf

- -

90-day-01d kenaf

-. . . - . . .. . . . . . - . - . .

Mean length, (Length weighted), (mm) Percent fines (<O2 mm), (length weighted), (Yo) Coarseness, mglm

Test results of FQA analysis of kenaf pulp as a fûnction of growth are given in Figure 25

and Table 3 1. As can be seen in Table 3 1, the fibre length of kenaf pulp (length weighted)

is highest at 90-day-old kenaf and decreases with increase in plant age. There is a negative

correlation with kenaf fibre length and plant age. Fibre length of kenaf. pulp is smallest in

150-day-old and 200-day-old kenaf at 1.5 mm. Ray et al. (1988) studied the physical

characteristics of pulps obtained ftom mesta (Hibiscus s a h y u ) plants of difFerent ages,

and found that the lengths of both short and long fibres decreased as the plant aged fkom

120 days to 150 days, whereas the ce11 wall thickness of fibres of 150-daysld plant was

greater than found in 120-daysld plants. Greater ce11 wall thickness appears to play an

important role toward increasing the strength of paper £tom pulp of 150-daysld plants

(Ray et al. 1988).

120-daysld kenaf

1 50-day-old kenaf

15.28 90-day-old kenaf 15 1

s ize in MM

9.77 150day-old kcnaf

slze in MM

200-day-oId kenaf x

Figure 25. Length histograms for kenaf pulp at various stages of growth

The decrease in the length of fibres, after reaching a maximum length at 90 days of

growth, is in agreement with the results obtained with jute as reported by Ray et ou.

(1 988). Mukherjee et al. (1986) studied characteristics of jute fiber at different stages of

growth. They found that at the early stages of growth, there was an incomplete formation of

the middle lamella in the ce11 wall and the parallel bundles of fibrils were oriented at an angle

with respect to the fiber axis that gradually decreased with growth It was shown that 35 days

of growth, the fibrils run parallel to the fibre axis. In the mature plant, a few heiically oriented

fibrils in the Z-direction were obswed just below the primary ce11 wall layer.

Clark et al. (1967) also studied the changes in fiber properties durhg the growing season.

They found that the bast fibers are longer than core fibers and both decrease in length with

age. Core fibers are twice as wide and have twice the ce11 wall thickness as bast fibers and

both dimensions decrease with age. Finally the lumen width is wider in pith fibers as

compared to bast fibers and both decrease with age.

The findings by Clark et al. (1967) are disputai in the literature. Han et al. (1995) found that

the average fiber length of a bast and core fiber increased as the plant aged, in contrast to

Clark et al. (1967). Chatterjee (1959) reported the changes in chemical composition at

different stages of jute plant growth. His results show that the fiber length increases as the

growing season progresses.

Han et al. (1994) have done scaming electron microscopy (SEM) shidies on kenaf plants

harvested at 63 days, 7 1 days, 84 and 1 12 days. SEM observations indicate that the bast fiber

bundles are thin walled at 63 days and are in the process of thickening. The middle lamella is

not well formed as suggested by the weak bonding. At 71 days, the plants became

comparatively stronger as the bast fiber bundles occupied more area, the fiber wall thickened,

and lignification of middle lamella led to the development of tiber bundles, which allows

more area to be occupied by fiber bundles.

At 84 and 108 days, the bast fiber bundles comprised of primary and secondary phloem

fibers tend to show more thickening and separation of primary and secondaiy phloem fibers

become obvious. The secondary phloem fibers start thickening but with a somewhat weak

middle lamella. At this stage of development, in addition to wall thickening, deposition of

silica on wall surface is seen. The fibers are long and broad mainly comprised of an S2 layer

which is encrusted with amorphous silica (Han et al. 1994).

At 1 12 days, bast fiber bundles comprised of primary phloem fibers and secondary phloem

fibers are thickened with prominent middle larnella formation. The cells are compact with

thickened ce11 walls and decreased lumen width. The middle lamella is not well lignified at

this stage of maturity, and the fibers are long and broad with a well fonned S2 layer (Han et

al. (1994).

R 1 50-day-old kenaf

O 200-day-old kmaf

Screened rejects, % Screened yield, % Unscreened yield, % Kappa number

Figure 2ti. Pilot scale-pulping results of kenaf as a function of growth

h 3 wî 2 t:

4

n

Fiber Length, (mm)

Figure 27. Fines content vs. average length-weighted fiber Iength as a funaion of growth.

6.2.1 Fibre Length and Coaneness

A very important fact about the fiber properties should not be overlooked when disaissing

fiber length (Marton et al. 1963). The characteristics of a given fiber fiaction onginating

from the same pulp are different, depending on whether short fibers were b'manufactured"

by cuning the long fibers, or if they originated as such from wood (Marton et al. 1963). It

is found that chernical and physical differences between the fine fiactions onginally

present in an unbeaten pulp and those produced by beating. The differences between the

various dimensional fiactions of pulp suggests that some of these fiactions may

preferentially control a given property of the "whole pulp" and such, at least, is the role of

"fines" (Marton et al. 1963).

The importance of coarseness when comparing pulps at a given lignin content level is that

together with fibre length, it determines the number of load-bearing fibres in the paper

sheet. It is also important for the light scattering ability of the sheet. The coarseness

differences resulting âom changes in effective alkali charge or sulphidity are quite small

in practical t ems however, so that a yield improvement of 1% means a loss of only 2% in

the number of fibres. At the same lignin content, a higher yield will give a higher

coarseness value, which means a minor but measurable increase in weight per unit length

when the sulphidity level is increased or the effective alkali charge reduced (Paavilainen

1989). Very strong correlations were found between handsheet properties and wood/chip

density, fiber length, and fiber coarseness (Hatton and Cook 1992).

It is reporteci that the average fiber contents of bast and wre fibers are about 21 and 28 %,

ovendry basis, respectively, and are unaffected by plant population density or maturity

(Clark et al. 1971).

- -

1.9 1.6 1.5 1.5

Fiber Length, (mm)

Figure 28. Coarseness vs. average length-weighted fiber length as a function of growth

6.3 PHYSICAL PROPERTIES OF KENAF PULPS AS A FUNCTION OF

GROWTH

Kenaf pulps of 90, 120, 150, and 200-daysld kenaf were produced under sarne conditions

as given in Table 29. Hand sheets of 60 g/m2 were made according to Tappi Standard

Procedure T 205 sp-95 and tested for tensile strength (stretch and tensile energy

absorption), bursting strength, tearing resistance, breaking length as per Tappi Procedure

T 220 sp-96. Papemaking properties of unbleached kenaf pulps are summarized in Table

30 and some of the properties are shown in Figure 29. The physical testing of kenaf pulp

as a fùnction of growth indicate that the average tear index of 90, 120, 150 and 200-day-

old kenaf is 10.3, 10.7, 10.0 and 10.7 r n ~ * r n ~ / ~ respectively and the differences between

these values are not significant. Average burst inda values for 90, 120, 150 and 200-day-

old kenaf are also given as 5.17,4.98,4.3 2, and 4.94 (lcpa*m2lg) respectively.

Table 32. The physical properties of unbleached kenaf pulps as a fùnction of growth

b i s weigbt (g/m2)

Dryness (%)

Bulk (cm3@

Caliper ( m)

Tear Index (rnbJ*m2/g)

Burst Index (kPa*m2/g)

Zero-Span Tensile Breaking Length

(km)

Breaking Length (km)

Stretch (%)

TEA (Um2)

9ûdaydd 120-day-old 150-day-old 200-day-old

kenaf kenaf kenaf kenaf

6.3.1 Bulk or Density

It is reported that density is a ftndamental property and that anything that affects density

will also have a great effect on the other properties of the sheet (Marton et al 1963). The

constant density of the various chemical pulp fractions can be explained by assuming

equal flexibility of the different length fibers, i.e., equal ''wnformability to packing". It is

also reported that fiber length has no effect on sheet bulk of chemical pulps. The

somewhat higher densities of the fine fiactions are due to the ability of the very fine

particles to fil1 out voids in the paper structure. This 'Hlling" e f f i is also shown in the

whole pulps, which have a density pa t e r than any fkaction except fines (Marton et al.

1963). The bulk is telated duectly to fiber ngidity, as measured by w or &Id, and to l or

Ud (w = wall thickness, I = fiber length, d = fiber diameter )(Dïmwoodie 1966).

In assessing the regression of both unbeaten and beaten pulp, fiber rigidity is more

important than 1 or Ud. It would appear that the diameter term should be consideml with

either w or Vd The rigidity of the fiber determines the bulk of the shed by influencing the

wet plasticity and degree of collapse of the fiber. This in tum determines the arnount of

confomability within the sheet, a higher degree of conformability giviag rise to a sheet of

lower bulk (higher paper density) (Dinwoodie 1966). An increase in length et a constant

diameter will increase the number of fiber crossings and hence raise the bulk, while an

increase in diameter at constant length will increase the amount of fiber collapse, thereby

increasing conformability within the sheet and reducing the bulk (Dinwoodie 1966). The

Duncan's Multiple Range Test indicates that the diflerences in the mean values of bulk for

90, 120, 150 and 200-day-old kenaf are not significant as can be seen fkom Table 32.

6.3.2 Fibre strength

The zero-span fibre strength index (FSI) includes the effect of both the intrinsic fibre

strength and the number of fibres able to take part in bearing the load (Paavilainen 1989).

The intrinsic fibre strength can be derived âom the zero-span breaking load by employing

the coarseness value to obtain the number of fibres in the breaking zone. Factors other

than raw material that affect the intrinsic fibre strength of pulp are crystalinity, cellulose

DP, the distribution of long chained material in the fibre and the number of dislocations.

Duncan's Multiple Range Test indicates that the differences in the mean values of zero-

span tensile breaking length for 90, 129 150 and 200-daysld kenaf are not significant, as

can be seen fiom Table 32.

6.3.3 Burst factor

The principal factor detennining the burst strength is again fber density, as measured by

either w or 2w/d The density of the fiber determines its flexibility, which in tuni

influences the extent of bonding within a sheet (Diiwoodie 1966). Fiber length has been

shown to Hêct the bursting strength below some critical level, which has been found to

be about 4 mm. In some cases, the critical level of fiber length is lower in burst than it is

in breaking length (Dinwoodie 1966). Duncan's Multiple Range Test indicates that the

differences in the mean values of burst index are not significanty different for 90, 120, and

200-day-old ken& but are significantly differred for 1 5eday-old kenaf. 1 50-day-old

kenaf has lowest burst index, 4.32 kpa*m21g (0.62 kI?a*m2lg lower than 200aayold at

4.94 kpa*m21g and 0.85 k ~ a * r n ~ l ~ lower than 90-daysld ken& at 5.17 kPa*mzlg)

amongst the group compared.

6.3.4 Tensile strength (Breaking Length)

Fibre strength, bonding degree (bonding strength and bonded area), fibre curliness and

"weak points" determine the tensile strength of the paper sheet. Therefore, the tensile

strength differences between the pulps must arise fiom fibre strength andlor bonding.

When paper is subjected to tensile forces, strong fibres tend to pull out f'rom the network

intact, while weak fibres break (Paavilainen 1989).

Chernical pulps exhibit increased tensile strength with increased fiber length (lower

fiaction number), while high yield mechanical pulps increase in tensile strength with

decreasing fiber length (higher fiaction number). The short fibers and fines have a great

influence on the breaking length (Marton et al. 1963). The fines of full chemical pulps are

considerably weaker than any of the longer fractions.

The Duncan's Multiple Range Test indicates that the differences in the mean values of

tensile strength (breaking length) for 90, 120, 150 and 200-day-old kenaf are significant

for 90-daysld kenaf As can be seen from Table 32, 90-day-old kenaf has significantly

higher tensile strength than the other age groups of kenaf studied. Since the chemical

pulps exhibit increased tensile strength with increased fiber length, it is not unusual for 90-

daysld kenaf to have higher tensile strength with incread fiber length as show in Table

3 1. 90-day-old kenaf indicated 1.16 km higher tensile strength (breakhg length) (6.96 km)

than the lowest one, 150-day-old kenaf(5.80 km).

6.3.5 Tear strength

According to Van den Akker's strength theory, tearing work is composed of two different

phenomena: the work of breaking the fibres and the fictional work pulling them out of the

network undamaged. It is suggested that there are also other energy-consuming

mechanisms in tearing, e.g. interaction between the tom edges of the sample, bending and

splining the tearing sample. B a d on the tear strength theories it seems that the tear

strength differences between the pulps can be explained by reference to the following pulp

fibre and network properties: fibre length, fibre strength, bonding degree and fibre

stiflhess (Paavilainen 1989).

Chemical pulps show a very marked reduction in tear strength as fiber length decreased

(Marton et al. 1963). That iq chemical pulp tear strength is strongly influenced by fiber

length, probably because the long fibers are very pliable and entangled at many points,

and thus are able to distribute stresses over a wide area (Marton et al. 1963). Thus, it

appears that where fiber length and intrinsic fiber strength are critical, the strongest pulps

are obtained where the fiber is itself least damaged (e.g., chemical pulp) and the weakest

pulps are those with considerable fiber damage ftom refining (e.g., groundwood) (Marton

et al. 1 963).

The tear resistance is apparently influenced by two principal factors in both the unbeaten

and beaten pulps @inwoodie 1966). The rigidity of the fibers, as detennined by the

positive relationship with the ratio 2w/d or w is slightly more important than the length of

the fibers, I (positive correlation). It is now apparent that in the assessrnent of the factors

affecting paper properties in general, and tear in particular, sharp distinction must be

drawn between softwoods and hardwoods. In softwood pulps in which there is generally

adequate bonding in the unbeaten pulp, an increase in bonding owing to beating or to the

selection of more flexible fibers will give rise to a decrease in tear (Dinwoodie 1966).

The Duncan's Multiple Range Test indicates that the differences in the mean values of

tear for 90, 120, 150 and 200-day-old kenaf are not significant as can be seen from Table

6.3.6 Stretch

The most important variables determining the amount of elongation at rapture are f or I/d

for beaten pulps (Dinwoodie 1966). An increase in I at a fixed d will give a more open

network of fibers, which can be distorted more readily in one direction. For a given value

of 1, an increase in d will increase the area of bonding, thereby reducing the amount of

bond shearing or fiber rotation dunng extension and giving rise to a lower stretch value

(Dinwoodie 1966). The Duncan's Multiple Range Test indicates that the differences in the

mean values of stretch for 90, 120, 150 and 200-day-old kenaf are significant, as can be

seen from Table 32. 120 and 150-day-old kenaf showed significantly lower values than 90

and 200-day-old kenaf It can be concluded that for a given value of f an increase in d

would result in a lower stretch. When cornparhg 150 and 200-daysld kenaf at a given

fiber length of 1.5 mm, 200-day-old kenaf has significantly higher stretch value than 150-

daysld kenaf. It can also be seen fiom Table 32 that 90-day-old kenaf showed highest

stretch amongst the group compared. This could be due to the fact that ai the early stages

of growth, fibril angle is greater in S2 layer of the plant ce11 wall (Mukhejee et al. 1986).

Therefore, fibers with a higher fibril angle would stretch further than fibers with a lower

fibril angle.

6.3.7 Y ield

When the yield was expressed as a percentage of the o.d weight of wood there was little

difference in the yield fiom different rings of the same species or fiom different species

even after correcthg for varying percentages of extractives (Dinwoodie 1966).This

confirms previous results indicating that the yield of pulp is detemineci primarily by the

density of the wood. Since juvenile wood density known to be lower than mature wood

density (Kocurek et al. 1993), we can assume that the 90-day-old kenaf has lower density

than the other age groups of kenaf studied. Thus the low yield for the 90-day-old kenaf is

expected (Figure 26).

Bunt Index, Breaking Length, km kPa*m2/g

Tear Index, Zero-spp Tensile mN*m2/g Breakhg Iength, km

Figure 29. The physical properties of unbleached kenaf pulps as a function of growth.

CHAPTER VII

CONCLUSIONS, RECOMMENIDATIONS AND

IMPLICATIONS

The chemical analyses indicate that the differences in holocellulose, and lignin content fbr

90, 120, 150-daysld kenaf are not significant, except for 200dayold kenaf. SStatistical

analysis indicates that these differences are significant, but they are t w small(0.6 % only) to

consider significant. 200-dayold kenaf had higher lignin and lower holocellulose content.

Higher lignin content indicates the need for high consumption of chernicals for pulping and

bleaching. Lower holocellulose content on the other hand gives lower pulp yield and strength

properties. The differences in the mean values of extractives oontent are not significant

amongst 120, 150, and 200-day-old kenaf, but are significantly differred for 90dayold

kenaf. The extractive content of 9Maysld kenaf is significantly higher than the other age

groups compared. Ash content of kenaf at different stages of growth are significant at 95%

confidence level. 9û-day-old kenaf has highest ash content amongst the group compared. Ash

content decreases with plant age and this is in agreement with the reported trend in literature.

B a d on the results of chemical analyses of this study, kenaf may be harvested at the end of

150-&y growth period. In this case, the yield per acre per year would be higher but with a

lower holocellulose and higher lignin content, cornpared to 90dayold kenaf. The yield per

hectare per year inaeases at 200-&y of growth but again with slightiy lower holocellulose

and higher lignin content, compared to 150day-old kenaf.

nie Duncan's test indicates that the differences in the mean values of soda pulping properties

of kenaf at various stages of growth are not signifiant. The average yield for 15Mayold

kenaf over the whole range of ~ o k i n g times and temperatures studied is highest (60.4 %)

amongst the group studied. Physical properties of unbleached whole kenaf pulps indicate thaî

W-day-old kenaf has highest breaking length and stretch values, amongst the group

comparai. It shows that kenaf produces a strong paper at this stage of growth with longer

fibers. B a d on physical propdes of kenaf pulpq kenaf plants can be harvested at the end

of 90day growth period which allows 2-3 crops per year depending on the location. The

yield will be lower compared to mature ke@ but fibre with higher holocellulose and lowa

lignin content and also with better paper properties can be obtained.

Further work is still needed to investigate the following areas:

An examination of the relative amounts of variations for ce11 wall thickness (w) and the ratio

of wall thickness to diameter (2w/d) is suggested to see if ceIl wall thickness is increasing or

deaeasing with plant age. It can also be suggested that the protein rich top portion of kenaf

plants which does not produce quality pulps can be used as animal feed as suggested in

literature. The feasibility of producing and marketing of this type of product should be

studied. The extractives content of field-grown green kenaf should be determined so that the

factors leading to high extractives content can be identifieci.

By knowing the nght time to harvest the industry can save money and time. Based on

physical properties of kenaf pulps at different stages of growth, 90-day-old kenaf showed

highest breaking length and stretch values. Therefore, this study suggests that kenaf plants

may be harvested at the end of 90-day growing period to obtain strong paper fiom ken&

The yield would be lower compared to mature kenaf but harvesting earlier than a mature

plant would also allow 2-3 crops per year depending on location. This study also suggests

that kenaf plants can be harvested at the end of 150-day growing period based on their

chernical composition. The results of this study indicate that iignin content increases and

the holocellulose content decreases with plant age. As stated before fiber with higher

lignin content would consume higher amounts of pulping and bleaching chemicals. On the

other hand, decrease in holocellulose content is an indication of lower pulp yield and

paper strength. Growing the plants for a longer period than 150-day, of course, would

increase the dry mass of fiber but with a higher lignin content. In some cases, with

increasing extractives content that may also cause problems in pulping.

Akin, D.E., Ramaswamy, G.N., Rigsby, L.L., Gamble, GR. and Momson III, W.H. 1995.

Structure and chemical composition of retted and unretted kenaf. Kenaf conference

proceedings, pp. 85. International Kenaf Association, Ladonia, Texas, USA.

Axegard, P. and Wiken, J-E. 1983. Delignification studies - factors afT'ecting the amount

of "residual lignin". Svensk papperstidning, pp. R 178 - 184.

Browning, B. L. 1963. The chemistry of wood. Interscience Publishers, New York, NY,

USA.

Brolin,A. B., Noren, A., and Stahl, E.G. 1995. Wood and pulp characteristics of juvenile

Norway spruce: A comparison between a forest and an agricultural stand. Tappi Journal,

Vol. 78 No. 4, pp. 203-214.

Buchanan, M. A. 1963. Extraneous components of wood. In: The Chemistry of Wood.

Interscience Publishers, New York, NY, USA.

Calabro, G. 1992. Kenaf properties as a function of their composition, yield, and fieeness.

Tappi pulping conference proceedings, pp. 609 - 6 17.

Carvalho, M. G., Ferreira, P.J., Martins, A. A. and Figueiredo, M.M. 1997. A comparative

study of two automated techniques for measuring fiber length. Tappi Journal, Vol. 80, No.

2, pp. 137 - 142.

Casey, J. P. 1980. Pulping of kenaf In: Puly and Paper. Chernistry and Chemical

Technology. Third edition, Volume I, John Wiley & Sons, Ne;v York, NY, USA

Chand, N. and Hashmi, S.A.R 1993. Effect of plant age on structure and strength of sisal

fibre. Metals, Materials and Processes, Vol. 5, No. 1, pp.51.

Cheng, Z., Leminen, J., Kari, A.K., and Paulapuro, H. 1994. The basic drainage properties

of chinese wheat straw pulp. In: Tappi pulping conference proceedings book 2, November

6-1 0, Sheraton harbor island, San Diego, California. Tappi press, Atlanta, GA, USA.

Clark, T.F., Nelson, G.H., Nieschlag, H.J. and Wolff, 1,A. 1962. Tappi Journal, Vol. 45, pp.

780.

Clark, T.F., Cunningham, R.L., and Wolff, I.A. 1971. Aserach for new fiber crops. Tappi

Journal, Vol. 54, No. 1, pp. 63-65.

Deka, G. C. 1987. Physical, chemical, and pulping characteristics of hybrid salix clones. Ph.

D. Thesis. Faculty of Forestry, University of Toronto. Toronto.

Deka, G. C., Wong, B. M., and Roy, D. N. 1992. Suitability of hybnd willow as a source of

pulp. J. Wood Chem. and Tech., Vol. 12, No. 2, pp. 197-2 1 1.

Dinwoodie, J.M. 1965. The relationship between fiber rnorphology and paper properties.

Tappi Jomal, Vol. 48, No. 8, pp. 440- 447.

Dinwoodie, J.M. 1966. The influence of anatomical and chemical characteristics of

softwood fibers on the properties of sulfate pulp. Tappi Joumal, Vol. 49, No. 2, pp. 57 -

67.

Favis, B.D., Choi, P.M.K., Adler, P.M., and Goring, D. AI. 198 1. The leaching of lignin from

unbleached kraft fibres suspended in water. Trans. Tech. Sea. CPPA, Vol. 7, pp. TR 35-

TR40.

Fengel, D. and Wegener, W. 1983. Wood chemistry, ultra structure, readions, Walter de Gniyter, Berlin.

Fisher, G. 1994. Availability of kenaf fibers for the U.S. paper industry. Inr Tappi pulping

conference proceedings book 2, November 6-10, Sheroton harbor island, San Diego,

California. Tappi press, Atlanta, GA, USA.

Fujii, Y., Anima, J., Marchessault, RH., Morin, F.G., Aibara, S. and Okamura, K. 1993.

Chemical composition change of bamboo accompanying its growth. Holzforschung Vol. 47,

No. 2, pp. 109 -1 15.

Gierer, J. 1980. Chemical aspects of kraft pulping. Wood Sci. Technol., Vol. 14, pp. 24 1 - 266.

Gierer, J. Kjellman, M. and Noren, 1. 1983. Alkaline Delignification in the presence of

anthraquinondanthrahydroquinone. Holzforschung, Vol. 37, pp. 17 - 22.

Ch-een, J. W., Pearl, I.A., Hardacker, K.W., Andrews, B.D. and Haigh, F.C. 1977. The

peeling reactions in alkaline pulping. Tappi Journal, Vol. 60, No. 10, pp. 120- 125.

Han, J. S., Kim, W. and Rowell, R.M. 1994. Chernical and physical properties of kenaf as a

function of growth. In: Kenaf conference proceedings, the International Kenaf Association,

Ining, Texas, USA.

Han, J.S., Kim, W. and Rowell, RM. 1995. Chernical and physical properties of kenaf as a

funaion of growth. In: Kenaf conference proceedings, pp. 63. The International Kenaf

Association, Ladonia, Texas, USA.

Hatton, J. V. and Johal, S. S. 1994. Chernithennomechanical pulping of second-growth

lodgepole pine fkom Western Canada 1n:Tappi pulping conference proceedings, Book 2,

November 6-10, Sheraton harbor island, San Diego, California. Tappi press, Atlanta, GA USA.

Hatton, J. V., and Hejjas, J. 1972. Effea of time, temperature and effective alkali in kraft

pulping of trembling aspen. Pulp and Paper Magazine of Canada, Vol. 73, No. 9, pp. 74 -78.

Hatton, J.V. and Cook, J. 1992. Kraft pulps from second-growth Douglas-fir: relationships

between wood, fibre, pulps, and handsheet properties. Tappi Journal, pp. 13 7- 144.

Hanon, J.V. and Johal, S. S. 1994. Mechanical and chemithermomechanical pulps from

second-growth softwoods. Pulp and Paper Canada, Vol. 95, No. 12, pp. 67-73.

Haygreen, J.G. and Bowyer, J.L. 1989. Forest Products and Wood Science. Iowa State

University Press, Arnes, Iowa 500 10, USA.

Hunt, K., and Keays, 5. L. 1973. Short-rotation trembling aspen trees (Populus tremuloides

Michx.) for kraft pulp. Can. J. For. Res., Vol. 3, pp. 180-184.

Hom, R., Wegner, T., and Kugler, D. 1992. Newspnnt from blends of kenaf CTMP and

deinked recycled newsprint. Tappi Journal, Vol. 75, No. 12, pp. 69-72.

Isebrands, J. G., and Parham, R A. 1974. Tension wood anatomy of short rotation Populus

spp. before and after kraft pulping. Wood Science, Vol. 6, No. 3, pp. 256-265.

Judt, M.F. 1987. Chernistry problems with non-woody materials for pulp and paper

making in developing countnes as seen by UMDO.Fourth international symposium on

wood and pulping chemistry. Vol. 1, IIA- IIE.

Juhua, W., Yanzao, H., Rui, W., Zhibin, H., Chongyun, X., and Yufeng, L. 1996.

Morp hological characteristics and ultrastructure of kenaf xy lem CMP fi bers. In: Third

international non-wood fibre pulping and papemaking conference proceedings, Volume I,

October 15- 18, 1996, Beijing, P. R China.

Kaldor, A. 1989. Preparation of kenaf bast and core fibers for pulping by the Ankal

method. Tappi Joumal, No. 9, pp. 137 -140.

Kaldor, A.F., Karlgren, C., and Venvest, H. 1990. Kenaf - a fast growing fiber source for

papermaking. Tappi Joumal, No. 1 1, pp. 205 -209.

Kaldor, A., Brasher, B., and Fuller, M. 1992. A strategy for the development of a kenaf-

based pulp and paper industry. Tappi Joumal, Vol. 75, No. 1, pp. 87-9 1.

Kleinert, T.N. 1965. Discussion of results and of the principles of rapid delignification. Tappi

Joumal, Vol. 48, No. 8, pp. 447-451.

Kleinert, T.N. 1966. Mechanisms of alkaline delignification. 1. The overall reaction pattern.

Tappi Joumal, Vol. 49, N0.2, pp.53-56.

Kleppe, P.J. 1 97Oa. Kr& Pulping. Tappi Joumal, Vol. 53, No. 1, pp. 35-47.

Kleppe, P.J. 1970b. The Process of and Products fiom Kraft Pulping of Southem Pine. For. Prod. J., Vol. 20, No. 5, pp. 50-53.

Labosky, Jr.P., Bowersox, T.W., and Blankenhorn, P.R 1983. Kraft pulp yields and paper

properties obtained fiom fust and second rotations of three hybrid poplar clones. Wood and

Fibre Science, Vol. 15, No. 1, pp. 8 1-89.

Lan shi, S., ren Hu, H., and zhi Liang, W. 1996. Mildew detenoration and moth attack on

stored kenaf and their effects on the chemical composition and pulpability of the kenaf In:

Third international non-wood fibre pulping and papemaking conference proceedings,

Volume I, October 15-1 8, 1996, Beijing, P. R China.

Lonnberg, B. 1976a. Short-rotation hardwood species as whole-tree raw rnatenal for pulp

and paper. 5. Bleached pulps; fine papers. Papen ja Puu, Vol. 58, No. 8, pp. 455-472.

Lomberg, B. 1976b. Short-rotation hardwood species as whole-tree raw material for pulp

and paper. 6. Chernimechanical pulps. Paperi ja Puu, Vol. 58, No. 9, pp. 630-648.

Maddem, K.N. 1989. Pulping of eucalyptus and pinus radiata. In: Wood processing and

utilization. Edited by Kennedy, J.F., Philips, (3.0. and Williams, P.A. Ellis Harwood

Limited, West Sussex, England.

Maddem, K. N., and French, J. 1989. Papemaking properties of some Australian non-wood

fibres. Appita, Vol. 42, No. 6, pp. 433 - 437.

Manji, A. H. 1996. Kraft pulping of coastal softwood from British Columbia using AQ

and a digester additive. Tappi Journal, Vol. 79, No. 10, pp. 147 - 152.

Marton, R. and Alexander, S.D. 1963. Prope~ies of fiber fiactions from chemical and

mechanical pulps. 1. Softwood pulps. Tappi Journal, Vol. 46, No. 2, pp. 65-70.

Marton, R, Stairs, G.R. and Schreiner, E.J. 1968. Influence of growth rate and clona1 effects

on wood anatomy and pulping properties of hybrid poplars. Tappi Journal, Vol. 51, No. 5 ,

pp. 230-235.

Moore, C.A., Trotter, W.K., Corkern, R.S., and Bagby, M.O. 1976. Economic potential of

kenaf production. Tappi Joumal, Vol. 59, No. 1, pp. 1 17 -120.

Mortha, G., Sarkanen, K., and Gustafson, R 1992. Alkaline pulping kinetics of short

rotation, intensively cultured hybnd poplar. Tappi Journal, Vol. 75, No. 11, pp. 99- 104.

Mukhe jee, A.C., Mukhopadhyay, A.K., and Mukhopadhyay, U. 1986. Surface

characteristics of jute fibers at different stages of growth. Textile Res. J., Vol. 56, No. 9, pp.

562.

Nelson, G.H., Clark, T.F., Wolff, I.A., and Jones, Q. 1966. A search for new fibre crops:

Analytical evaluations. Tappi Journal, Vol. 49, No. 1, pp. 40-43.

Pande, H., and Roy, D.N. 1996. Delignification khetics of soda pulping of kenaf. J. of Wood Chem. and Tech., Vol. 16, No. 3, pp. 31 1-325.

Panshin, A.J., and Zeeuw, C. de. 1980. Textbook of Wood Technology. McGraw-Hill

Publishing Company, New York, NY, USA

Paavilainen, L. 1 989. Effect of sulphate cooking parameters on the papemaking potential

of pulp fibers. Papen ja Puu - Paper and Timber, Vol. 4, pp. 356 - 363.

Paavilainen, L., and Torgilsson, R. 1994. Reed canary grass - A new nordic papermaking

fibre. In: Tappi pulping conference proceedings, book 2, November 6- 10, 1994. Tappi

Press, Atlanta, GA USA.

Ray, P.K., Das, B.K., Day, A., and Banarjee, S.K. 1988. Physical characteristics of pulps

obtained fiom meaa (ffzbiscus sabckzrtffa) plants of different ages. Tappi Journal, No. 2, pp.

67-69.

Reeve, D., and Weishar, K.M. 1996. Optimal bleaching of non-wood chemical pulps with

chlorine dioxide. In: Third international non-wood fibre pulping and papemaking

conference proceedings, Volume I, October 15-18, 1996, Beijing, P. R China.

Rowell, RM., Young, RA, and Rowell, J.K. 1997. Paper and Composites From Agro-Based

Resources. Lewis Publishers, New York, NY, USA

Sabharwal, RS., Akhtar, M., Blanchette, RA., and Young, RA. 1994. Bio-refiner

mechanical pulping of basî type fibers. In: Tappi Pulping conference proceedings, book 2,

November 6-1 0, 1994. Tappi Press, Atlanta, GA, USA

Sano, A., Sano, Y. 1996. Novel pulping of kenaf for conversion of biomass - Aikaline

oxygen pulping of bast with epidermis. In: Third international non-wood fibre pulping and

papemaking conference proceedings, Volume I, October 15-1 8, 1996, Beijing, P. R China.

Seisto, A, and Poppius-Levlin, K. 1997. Peroxyformic acid pulping of nonwood plants by

the MILOX method - Part 1: Pulping and bleaching. Tappi Journal, Vol. 80, No.9, pp. 215 - 221.

Semke, L.K. 1984. Effect of juvenile pine fibres on kraft paper properties. In: Utilization of

the Changing Wood Resource in the Southem United States. North Carolina State University.

NC, U.S.A.

Sjostrom, E. 1993. Wood Chemistry, Fundamentals and Application. Second edition, Academic press, Inc. San Diego, USA.

Sundquist, J. 1985. The multiform nature of residual lignin in chernical pulps. international

Symposium on Wood and Pulping Chemistry. Vancouver, B.C., Canada.

Swan, B. 1965. Isolation of acid-soluble lignin from the Klason lignin detemination. Svensk

Papperstidning, Vol. 68, No. 22, pp. 791-79.

Steinbeck, K. and Gleaton, E.N. 1974. Young sycamore cuttings give promise in fine paper

tests. Pulp and Paper, No. 12, pp. 96-97.

Strelis, I., and Kennedy, R W. 1967. Identification of North Amencan Commercial

Pulpwoods and Pulp Fibres. Pulp and Paper Research Institute of Canada. Printed by

University of Toronto. Toronto.

Theander, 0. 199 1. In: Production and utilization of lignocellulosics. G.C. Galletti, ed.

Elsever Applied Science, London, WC, pp. 49.

Thomas, RI. 1984. The characteristics of juvenile wood. In: Symposium on Utilization of

the Changing Wood Resource in the Southem United States. North Camlina State University,

Raleigh, North Carolina, June 1 2- 1 3, 1 984.

Touzinsky, G.F. 1987. Kenaf. In: Pulp and Paper Manufacture. Volume 3, Sewndary fibers

and non-wood pulping. Tappi Press, Atlanta, GA.

Ou, Y., and Shi, S. 1996. Optimization of the sulfonation stage in kenaf core SCMP. In:

Third international non-wood fibre pulping and papennaking conference proceedings,

Volume I, October 15-1 8, 1996, Beijing, P. R China.

Otoguro, C., Hikawa, Y. and Matsuno, 0. 1991. Changes in physical and chemical

composition of edible burdock (Arctium l q p a L.) in relation to varieties and growth.

Yamanashi-Ken Kogyo Gijutsu Senta Kenkyu Hokoku, Vol. 5 , No. 74.

Overbeke, M. van and Maringue, G. 1949. Chernical study of several varieties of flax. Bull.

Inst. Textile France, Vol. 13, No. 23.

Yang, S., Li, Y., and Yan, D. 1996. The mechanism of chemical pretreatment with alkaline

peroxide and alkaline sodium sulfite in kenaf CMP. In: Third international non-wood fibre

pulping and papermaking conference proceedings, Volume I, October 1 5- 18, 1996, Beijing,

P. R. China.

Watson, A. J., Davies, G. W., and Gartside, G. 1976. Pulping and papermaking properties of

kend Appita, Vol. 30, No. 2, pp. 129434.

Webber, C.L. 1992. Varietal differences in kenaf yield components. Tappi Journal, Vol. 75,

NO. 8, pp. 153-1 55.

White, G.A., Adamson, W.C., and Higgins, J.J. Kenaf-An annual pulp crop for the United

States.

Wong, A 1996. Ken& farming for market pulp production in the northem temtory,

Australia. In: Third international non-wood fibre pulping and papermaking conference

proceedings, Volume I, October 15-1 8, 1996, Beijing, P. R China.

Zarges, R V., Neuman, R D., and Cnst J. B. 1980. Kraft pulp and paper properties of

Populus clones grown under short rotation intensive culture. Tappi Joumal, Vol. 63, No. 7,

pp. 9 1-94,

Zobel, B. J., and McElwee, R L. 1966. Variation of cellulose in loblolly pine. Tappi

Journal, Vol. 49, No. 9, pp. 383-387.

APPENDIX

Kenaf Fibre Yield per Acre

The weight of 90-day-old kenaf was (average of 4 air dry plant stems) 17.1 gram per plant at

the end of growing period. Using the 15 inch between the row and 4 to 6 inches apart within

a row, (which is 60 to 90 square inches per plant) the yield is 1.2 to 1.8 tondacrdyear. The

extractive content was 20.2 % and holocellulose content 81.4 %. Using 61.2 % for the

overall, the yield for 90-day-old kenaf is 0.7 to 1.0 tondacre gear. The weight of 120-day-

old kenaf (average) 22.4 gram per plant at the end of growing period. Using the sarne

growing conditions, the yield is 1.6 to 2.3 tons/acre/year. The extractive was 15% and

holocellulose content was 81.3 %. Using 66.3 % for the overall, the yield for 120-day-old

kenaf is 1.1 to 1.5 tonslacrelyear. The weight of 150-day-old kenaf (average) 43.9 gram per

plant at the end of growing period. Using the sarne growing conditions, the yield is 3.0 to

4.6 tondacdyear. The extractive content was 14.9% and holocellulose content was 8 1.1%.

Using 66.2% for the overall, the yield for 1 50-day-old kenaf is 2.0 to 3.0 tons/acre/year. The

weight of 200-day-old kenaf (average) 75.8 gram per plant at the end of growing period.

Using the same growing conditions above, the yield is 5.3 to 7.9 tondacdyear. The

extractive content was 14.2% and holocellulose content was 80.5%. Using 66.3% for the

overall, the yield for 200-day-old kenaf is 3.5 to 5.2 tondacdyear.

S O L ANALYSIS - NPK (NITROGEN, PEOSPHOROUS, POTASSIUM)

The soi1 samples were analyzed by the Domtar Innovation Centre. The soi1 samples were

dried at 45 O C and sieved through a Tyler 12 and Tyler 20 mesh screen due to the presence

of large particulate matter, i.e. twigs, particles of perlite, and small pebbles. The fiaction

passing 20 mesh was analysed by x-ray fluorescence method SMX-15 for potassium and

phosphorous. A portion of each sarnple also was sent to Maxxarn's analytical laboratories

for a total Ntrogen determination by Kjeldahl digestion. The particle size distribution and

analytical results of each sarnple is presented below.

Table 1. The particle size distribution of each soil sample

Tyler Mesh S ieve Size

Cumulative % Total w 1 OOg)

% Total w 1 OOg)

BEFORE PLANTING 1

12 mesh

AFTER HARVESTlNG Cumulative

12 to 20 mesh

Less than 20 mesh

Both fractions passing the 20 mesh screen were selected for analysis. The sarnples were ashed at a temperature of 525 O C as per the standard Tappi method and at 900 O C to determine the loss on ignition. The BEFORE samples had a 525 O C ash of 67.46 % and a 900 O C ash of 58.32 %.

Table 2. NPK results on soil fiactions ~assinp; 20 mesh

Note: Al1 results are based on the dried sarnple hction passing a 20 mesh Tyler sieve.

Sarnple

BEFORE PLANTING

AFTER HARVESrnG

Conclusion

The nitrogen results are representative of what might be expected due to the depletion of

nitrogen between the two samples. The x-ray results however are inconclusive since the

analysis is based on the elements also present in the rninerals, which are not readily

available to the growing flora Furthemore, the two fractions, although similar in

% Nitrogen w 1 OOg)

0.32

0.25

% Potassium (d 100 g)

0.87

0 -95

% Phosphorous w 1 OOg)

0.057

0.074

distribution, are not necessady equivalent due to dflerences in organic material, which

would most likely affect the nitrogen results.

As stated before, (in "Raw Matenal Preparation"), the results of soi1 analysis (Table 1 and

2), indicated that potassium and phosphorous content of soi1 after harvesting plants are

higher than before sowing the seeds. This must be due to the fact that the plants were

harvested 4 days after fertilization. First, the plants could not consume dl the nutrients in 4

days, second, there were not enough plants in the pots at the end of growing season to use al1

the nutrients available.