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MASTER’S THESIS2006:023 CIV

PATRICIA NORDELL

Wet-Strength Development of Paper

Modifi cation of cellulose fi bres by adsorptionof a natural biopolymer

MASTER OF SCIENCE PROGRAMMEMechanical Engineering • EEIGM

Luleå University of TechnologyDepartment of Applied Physics and Mechanical Engineering

Division of Engineering Materials

2006:023 CIV • ISSN: 1402 - 1617 • ISRN: LTU - EX - - 06/23 - - SE

Wet-strength development of paper:

Modification of cellulose fibres by adsorption of a natural biopolymer

Patricia Nordell, Luleå University of Technology SCA Graphic Research AB, Sundsvall, Supervisor: Bo Andreasson,

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ACKNOWLEDGEMENTS I would like to express my gratitude towards my supervisor Bo Andreasson and my co- supervisor Kent Malmgren for their guiding and engagement in this work. Other persons who have helped me through the laboratory work are Inger Nygren, Bengt Wiberg and Thomas Nordqvist.

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ABSTRACT

Wet-strength development of paper: Modification of cellulose fibres by adsorption of a natural biopolymer KEYWORDS: Natural biopolymer, cationic reactive functions, wet-strength polymer, cellulose fibre, pulp, polymer adsorption, fibre charge, surface charge, tensile strength, modified starch, PAE, CMC. A natural biopolymer that contains cationic reactive functions was tested for pre-treatment of bleached and unbeaten cellulose fibres. This work proved that the biopolymer is quite efficient as wet-strength agent but pre-treatments of fibres should be done under controlled conditions. Wet-strength polymers are used to develop or conserve the mechanical strength of paper when wetted. Wet-strength agents are added in various paper products such as; hand towels, hygiene paper and packaging grades. According to the chemical composition of these agents they can act either as protective agents by preventing fibre swelling and protecting already existing bonds, or they form new and water resistant bonds through reinforcement mechanisms. The natural biopolymer has a structure that is very similar to the cellulose structure. This fact together with the reactive functions of the biopolymer probably makes it possible to adsorb it to cellulose fibres. In earlier studies, wet strength was developed when the natural biopolymer was added directly to a suspension of beaten and untreated fibres. However, for this study, only unbeaten fibres were used in order to study nothing but the effect of adding the natural biopolymer. Beating increases the adsorption of wet-strength polymers since it enhances the total specific fibre area. Initially, a precipitation study of the biopolymer in acidic solution was done to find the best conditions for polymer adsorption. Pre-treatments of fibres were done by adding 0.5 and 2% biopolymer to the paper pulp. The adsorption was evaluated by measuring the surface charge of pre-treated fibres. To examine the paper strength, hand sheets of the pre-treated fibres were prepared, but also from other fibre mixtures. The sheets were then stripped and put in a tensile tester to evaluate wet- and dry strength. It was shown that sheets made of fibres that had been pre-treated with biopolymer had a relative wet strength of 13%. In contrast, sheets of untreated cellulose fibre are in total lack of wet strength.

Diagram 1

Tensile strengths for treated fibres (non-cured)

0

5

10

15

20

25

30

35

1 2 3 4Tens

ile st

reng

th in

dex

(kN

m/k

g)

dry strength wet strength relative wet strength (%)

Pre- treated fibres (2%

biopolymer)

1% PAE to untreated

fibres

Pre- treated fibres (0.5% biopolymer)+2% mod.starch

Pre- treated fibres (2% biopolymer) + 2% mod.starch

Diagram 1 shows the tensile-strength test results for manufactured sheets. Fibres that had been pre-treated with biopolymer had about the same relative wet strength as uncured fibres treated with PAE (poly(aminoamide)-epichlorohydrin)). It was also seen that curing the fibres at 140°C had no effect on the relative wet strength of pre-treated fibres. The relative wet strength was increased to 21% when modified starch was added to the pre-treated fibres. This result is just as good as for fibres treated with PAE.

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TABLE OF CONTENTS:

ACKNOWLEDGMENTS…..……………………………………………………...2 ABSTRACT…………………………………………………………………………………..3 1. INTRODUCTION………………………………………………………………………...4

2. THEORETICAL BACKGROUND

2.1 Wood fibre structure…………………………………………………………………...7 2.2 Wet strength mechanisms……………………………………………………………...8 2.3 Background to test plan:……………………………………………………………….9 2.3.1 Fibre charge………………………………………………………………………….9 2.3.2 Polymer adsorption…...……………………………………………………………...9 2.3.3 The natural biopolymer….……………………………………………………….…..9 2.3.4 Irreversible adsorption of CMC (Carboxy methylcellulose)………………….……10 2.3.5 Modified starch………………………..……………………………………………11 2.3.6 Kraft pulp…………………………………………………………………………...11

3. EXPERIMENTAL

3.1 Material……………………………………………………………………………….12 3.2 Precipitation of the natural biopolymer………...…..………………………………...12 3.3 Adsorption of natural biopolymer to bleached Kraft fibres:…………………...……..13 3.3.1 Treatment in plastic bag…………………………………………………………….13 3.3.2 Treatment in stirred reactor…………………………………………………………13 3.3.3 Washing…………………………………………………………………………….14 3.4 Measuring methods:………………………………………………………………….14 3.4.1 Turbidity……………………………………………………………………………14 3.4.2 PET...……………………………………………………………………………….14 3.4.3 PET by Mütek PCD………………………………………………………………...15 3.4.4 Nitrogen Analysis…………………………………………………………………..15 3.5 Sheet preparation…………………..…………………………………………….…...15 3.6 Tensile testing of laboratory sheets…………………………………………………..16 3.6.1 Parameter definition for paper testing…………………….………………………..16

3.6.2 Grammage and thickness…………………………………………………………...16

4. RESULTS AND DISCUSSION 4.1 Precipitation of the natural biopolymer….………..……………………….………….17 4.2 Charge measurements the biopolymer……………….………..…….………………..18 4.3 Adsorption of natural biopolymer to bleached Kraft fibres……………...…………....19 4.3.1 Retention values by surface charge measurements (PET by Mütek PCD) .…….…..19 4.3.2 Nitrogen Analysis………………………………………………………….….…….22

4.4 Tensile strength…………………………………………………………….………….24 4.4.1 Dry strength…………………………………………………………………………24

4.4.2 Wet strength……………………………………………………………….………...25 5. CONCLUSIONS………………………………………………………………………….28 6. RECOMMENDATIONS…………………………………………………………………29 7. REFERENCES……………………………………………………………………………30

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APPENDICES: A. Turbidity diagrams during the precipitation of highly viscous (HV) and practical grade (PG) biopolymer in 0.2M or 0.4M acetic acid at 25°C or 70°C B. Charge determinations of highly viscous and practical grade biopolymer in 0.2M or 0.4M acetic acid. C. Adsorption isotherms for pre-treated fibres (after different washing steps) D. Nitrogen analysis results E. Tensile test results

1. INTRODUCTION Wet strength is one of paper’s most important properties. It can be developed by addition of wet strength additives during the fabrication process. Hereby paper products that require high wet strength, such as kitchen towels and bank note paper, are achieved. Through the years, the ability of different polymers to increase wet strength of paper has been investigated. The first wet-strength polymer used in papermaking was discovered in 1930 (polyethyleneimine) but its wet strength mechanisms were not well understood. Some years later, cheaper and better resins based on formaldehyde were developed. Nonetheless, formaldehyde resins are toxic and the search for new wet-strength polymers went on. In 1960, wet-strength resins based on PAE (poly (aminoamide)-epichlorohydrin)) replaced the formaldehyde resins. This polymer is still the most popular wet-strength chemical but presents some drawbacks. PAE makes paper stiffer and decreases the absorption capacity which is useful in packaging products but not in tissue paper. Other drawbacks of PAE are its bad repulpability, degradability and toxic monomers. (2,1) This study aims to examine new wet-strength polymers for future use. One of them, a natural biopolymer, has in earlier studies proved to work as wet strength additive. The objective of this work was to evaluate in what extent this biopolymer could improve wet strength. The final evaluation was based on mechanical testing of sheets made from bleached Kraft fibres modified by the biopolymer. 2. THEORETICAL BACKGROUND 2.1 Wood fibre structure Wood consists of cellulose, hemicelluloses and lignin. Cellulose forms the skeleton and hemicelluloses and lignin are in the surrounding matrix. Around 40 to 45% of the dry substance in most wood species consists of cellulose, located predominantly in the secondary cell wall. Cellulose is a linear homo polysaccharide built up from glucose units. Cellulose molecules form intra- and intermolecular hydrogen bonds. These interactions lead to formation of microfibrils that build up fibrils, which in turn build up cellulose fibres.

OH

O

OO

O

H

CH2OH

OH

H H

H

OH

H

CH2OH

H H

HOHOH

OH

H

H

H

H

CH2OHH

OHH

H

C-2

C-2

C-2 Figure 1. Molecular structure of cellulose Hemicellulose is a group of amorphous polysaccharides, mainly glucomannan and xylan (in softwood). It binds cellulose and lignin together and hereby gives flexibility and strength to the fibres. Lignin is a binder between the cellulose fibres and is an amorphous polymeric compound consisting of phenylpropan units linked together in different ways. The lignin concentration is highest in the middle lamella, but most lignin is located in the inner fibre wall (S2) due to its dominant size. Wood also contains a small part of extractives (organic compounds) with low molecular weight. The most common ones are terpenoids, phenols, fats and waxes.

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The fibre wall is built up from different layers: the middle lamella, 0.1-1.0µm, is located between the fibres. It consists of 60-80% lignin. The primary wall, 0.1-0.3 µm, contains cellulose and hemicelluloses in a matrix of lignin. The secondary wall is built up from three layers, S1, S2 and S3. S2 contributes to 80% of the cell wall thickness and hence most of the fibre strength. It consists of cellulose, hemicelluloses and lignin. In the central part of each cell there is an empty space called lumen. (3).

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Secondary wall

Lumen

Primary wall

S1

S2

S3

Middle lamella

Figure 2. The wood structure showing the middle lamella (ML), the primary wall (P), the outer (S1), the middle (S2) and the inner (S3) layers of the secondary wall and Lumen (L). 2.2 Wet strength mechanisms Wet strength of paper is often referred to as relative wet-strength, the ratio between wet strength and dry strength. Normally, 10 to15% is considered as a wet-strengthened paper. In contrast to dry strength, that origins in the hydrogen bonds present in natural cellulose, wet strength requires water stable (covalent) bonds. Naturally, cellulose contains few covalent bonds, and therefore wet-strength chemicals are necessary. Polymer resins are often used to increase wet strength. Two different wet-strength mechanisms exist, the protection mechanism and the reinforcement mechanism, see Figure 3 and 4. The protection mechanism involves diffusion of the wet-strength polymer to the fibre surface where it cross-links through and around the fibres. Such cross-linked networks prevent fibre swelling and helps to preserve covalent bonds when the paper is exposed to water. In contrast, the reinforcement mechanism means that new bonds between the wet-strength polymer and the fibres are formed. (1)

Figure 3. Protection mechanism Figure 4. Reinforcement mechanism

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2.3 Background to test plan 2.3.1 Fibre charge

Fibre charge is an important factor that influences the papermaking process as well as the paper properties. Cellulose fibres contain various ionisable groups: carboxyl-, sulfonic acid-, phenolic- and hydroxyl groups and are therefore negatively charged at all pH values. Under normal papermaking conditions, the negative fibre charge is due to carboxyl and sulfonic acid groups. These charged groups are located either on the fibre surface or inside the cell wall; hence they are referred to as surface- and bulk charges, respectively. Surface charges are important for fibre- and paper strength. (4) 2.3.2 Polymer adsorption Adsorption of polymers is used in many applications. The driving force is a strong polymer-surface interaction. If the solvent is poor, then adsorption is more favourable than the polymer-solvent interaction. A condition for most cationic additives is the ability to adsorb to the fibre surface. That is why polymer additives used in papermaking often are cationic. The density and distribution of charges are also very important. Other factors that affect the adsorption are the molecular weight of the polymer and the presence of fibre segments called “fines”. Fines have large specific area and their capacity to adsorb polymers is therefore higher than for whole fibres. Polymer adsorption is often reversible and there is a probability that they will detach from the surface. This probability is generally low since all segments have to detach at the same time. However, changes in pH, ionic strength etc might cause desorption of polymers from the fibre surface. (2) 2.3.3 The natural biopolymer A natural biopolymer is generally characterized in terms of its: quality (heavy metal/protein content, pyrogenicity, cytotoxy, clarity etc), intrinsic properties (molecular weight, viscosity, degree of deacetylation, stability) and physical form (size etc). The commercial prospect of the actual biopolymer is good since its natural resources are abundant. The natural biopolymer has the following properties: -Availability and ability to be used in varying form; powder, solution and gels. -Non-toxicity -Biocompatibility -Good absorption capacity -Non-water solubility Its largest use is as flocculent and chelator of toxic and radioactive metals but some other important applications can be cited: as a component in wound dressings and drug delivery systems thanks to its biocompatibility, non-toxicity and wound-healing effect. Through selective binding of acidic lipids it can also diminish blood cholesterol levels. The natural biopolymer is also an excellent moisturizer and is therefore used in hair- and skin care products. The actual biopolymer has, like cellulose, a linear structure but instead of the hydroxyl group there is another reactive group. At acidic pH these groups become positively charged groups with high reactivity. Thus, they are very efficient in neutralizing the negatively charged fibres.

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The possibility of the natural biopolymer to be used as wet-strength additive lies within its structure, which is very similar to that of cellulose or CMC (Carboxy methylcellulose); the glucose units are linked together by ß (1-4) glycoside bonds. The close similarity to cellulose probably makes it possible for the natural biopolymer to form strong hydrogen bonds to cellulose. By studying the irreversible adsorption of CMC to cellulose some general wet- strength mechanisms can be understood. 2.3.4 Irreversible adsorption of CMC (Carboxy methylcellulose) CMC is the most widely used water-soluble derivate of cellulose. It is produced by reacting cellulose with monochloracetate. CMC is used as stabilizer and protective colloid in detergents, ice cream, paper coatings, pharmaceuticals, cosmetics and food. The world consumption of CMC is estimated to 280 000 tons. (2) Irreversible adsorption of CMC is an alternative to improve paper strength. CMC can be irreversibly attached to cellulose at high temperature and in presence of an electrolyte. A salt is used to shield the repulsion between negatively charged fibres and CMC, making it possible for CMC to approach the fibre surface and attach. The irreversible adsorption is believed to be a matter of co-crystallisation mechanisms. An irreversible adsorption is thermodynamically stable and cannot be washed away. (6,7) A common technique for wet-strength development of paper is to add CMC together with PAE to the pulp. Cationic PAE helps to retain the anionic CMC to the fibre surface. Both dry- and wet strength are improved. The surface conformation and properties of such fibres will be different compared to when only CMC is added. Temperature has strong effect on CMC adsorption. The adsorption increases rapidly with temperature up to 120ºC. High electrolyte concentration also promotes the adsorption. At low electrolyte concentration no CMC is attached between pH 6 and 11 whereas high electrolyte concentration makes the adsorption less pH dependent. Acidic conditions are more favourable and the adsorption increases when a divalent- instead of a monovalent ion is used. (2,5). Another factor is pulp consistency; high consistency promotes the attachment when divalent ions are used. The attachment also depends on the DS (degree of substitution); namely, it decreases for higher DS, due to the charge repulsion between CMC and fibres. Co-crystallisation mechanisms are also more efficient with purer cellulose fibres than if lignin and hemicelluloses are present. (2,5,6,7). The great advantage of CMC is that it can improve wet strength without beating of the fibres. This is very useful for the production of tissue paper that requires softness and good adsorption since beating gives stiffer paper with less porosity.

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2.3.5 Modified starch In this work, sheets of paper were made from fibres that had been pre-treated with the natural biopolymer. A few other wet- strength additives were also tested. One of them was modified starch. Starch can be extracted from potato shell for example, which is oxidized and then chemically treated to a compound with reactive functions. The wet-strength mechanisms of modified starch come from the combination of anionic charges and another type of reactive function. These functions are cross-linkable and form (hemi-) acetal bonds with cellulose fibres. The anionic functions charges need, like CMC, a cationic polymer for adsorption to fibres. To optimise wet strength, it is believed that modified starch with a low degree of substitution should be used that is; anionic but with many reactive groups present. A careful evaluation of cost, performance, degradability and repulpability is necessary to decide if modified starch has a future in paper fabrication. 2.3.6 Kraft pulp A bleached Kraft pulp, produced at Östrand Mill in Timrå, Sweden and with quality code K42, was used within this study. This pulp type mainly consists of cellulose, but some hemicelluloses and a small amount of lignin is also present. This pulp is chemical; the fibres have been extracted from their matrix of hemicelluloses and lignin by chemical way and pressure. In contrast, in a mechanical pulp the fibres have been solved out mechanically with high pressure. In this study, an unbeaten pulp was used to study nothing but the effect of the biopolymer on fibre strength. Unbeaten pulp gives weaker paper than beaten fibres and therefore the influence of the polymer should be easier to detect. Beating of the fibres increases dry- and wet strength as the fibre interaction gets stronger, but at the same time it decreases the porosity, adsorption capacity and softness. (8, 9).

3. EXPERIMENTAL 3.1 Material A bleached and unbeaten Kraft pulp (K42) from Östrand mill was used to prepare the fibres for pre-treatments with biopolymer. Two quality grades of natural biopolymer, one practical grade (PG) and the other a highly viscous grade (HV), were studied before the pre-treatments were initiated. CMC, a common wet-strength polymer was used in combination with the pre-treated fibres. It had the following specifications: CMC Cekol 4000 H3801, from Noviant, with degree of substitution equal to 0.77. The anionic charge was 3.7mekv/g (milliekvivalents). Modified starch, prepared by SCA, was also used in combination with the pre-treated fibres. It had a degree of substitution of 0.23 and anionic charge of 1.42mekv/g. The PAE polymer came from Eka Chemicals with specification WS XO. Acetic acid (>99.999%) by Merck was used to dissolve the natural biopolymer before it could be used for the fibre treatment.

Figure 7. Practical grade of the biopolymer (left) and Figure 8. Crystals of MACS highly viscous grade of the same biopolymer (right). 3.2 Precipitation of the natural biopolymer A precipitation study was made before adsorption of the natural biopolymer to bleached Kraft pulp was done. The natural biopolymer was precipitated in acetic acid solution by a slow increase of pH. The aim was to find out for what pH or acid concentration the precipitation starts. Precipitation occurs when repelling charge on the biopolymer molecules become deprotonated. Precipitation of natural biopolymer on the fibre surface should take place at lower pH than in solution for electrostatic reasons. This assumption is based on the fact that the fibre surface is slightly negatively charged, which should favour the adsorption of cationic biopolymer. Two grades of natural biopolymer were tested, highly viscous and practical grade. Solutions of 2g/L were prepared from these grades with respectively 0.2M and 0.4M acetic acid. Magnetic stirring dissolved the biopolymer particles in the acid and the solutions were then vacuum-filtered on a büchner funnel. 16 ml of each solution was put in a test tube and precipitation was initiated by addition of NaOH. The precipitation was studied by measuring the turbidity value, pH, and addition of NaOH. All precipitations were also done at 70°C.

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3.3 Adsorption of natural biopolymer to bleached Kraft fibres Sheets of Kraft fibre (K42) were left in deionised water for 3 hours. The sheets were then torn into pieces and disintegrated with 2L of water in a laboratory standard device. The pulp was dewatered and filtered on a büchner funnel to a consistency of 15-20%. High consistency of the filtered cake is needed to make a good estimation of fibre content, which is necessary when preparing sheets and taking samples for charge determinations, but such cakes gave more flocculation problems. The dewatered pulp was prepared to 3 and 5% consistency and the dosage of biopolymer was set to 0.6, 2.0 or 5% in each case (see table 1). Treatments No 1-3 were carried out in a plastic bag. The pH value was adjusted to 6.8 in the first experiment and to 6.2 in the second experiment (pulp at pH 7.0). In the third experiment pH was set to 6.6. To optimise the adsorption, treatments No 4-6 were done in a stirred isothermal glass reactor with careful mixing and pH control. Table 1. Treatments of bleached and unbeaten Kraft fibres

treatment No:

consist-ency (fibre-%)

biopolymer (% relative to fibres)

pH, start

pH, end

T,°C type of reactor:

1 5 0.6 6.8 6.8 25 plastic bag

- ׀׀- 25 6.5 6.2 2.0 5 2

- ׀׀ - 70 6.6 6.6 2.0 5 3

4 3 2.0 3.6 9.9 70 glass reactor

- ׀׀ - 70 7.2 3.6 2.0 3 5

6a 3 2.0 3.5 7.0 70 - ׀׀ -

6b 3 2.0 3.7 7.0 70 - ׀׀ -

- ׀׀ - 70 7.2 3.9 0.5 3 7

3.3.1 Treatment in plastic bag This method was used for CMC adsorption and was therefore thought to be appropriate for this biopolymer as well. The biopolymer and pulp were pH-adjusted separately and then mixed by hand kneading in a plastic bag. The mixture was left to cure for 3 hours at room temperature and also at 70°C. The pulp was then dewatered and washed in different ways. 3.3.2 Treatment in stirred reactor An isothermal double-walled glass reactor with a volume of 2 litres and equipped with heating system, pH-electrode, thermometer, condenser and mechanical stirring was used to optimise the adsorption. The biopolymer was added to the pulp and pH was adjusted close to precipitation and then slowly increased by adding NaOH. The time between the first and the last addition of NaOH was 2 hours. The treated pulp was then dewatered and washed in the same manner as the pulp from the wet-bag reaction.

Figure 9. Experimental equipment The temperature was kept at 70°C since it is believed that higher temperature improves the adsorption to the fibre surfaces, as in the case of CMC. The precipitation was controlled carefully by a slow increase of pH. 3.3.4 Washing The fibres treated with biopolymer were washed in different ways to investigate if the adsorption was irreversible. In that case, the surface charge should remain constant with washing. Dewatered, water-washed and samples washed in acetic acid were filtered and dewatered on a büchner funnel. In addition, three- and four steps washes were made with acid or water respectively. All washing steps were made by diluation of the pulp to 1% consistency followed by filtering. 3.4. Measuring methods:

3.4.1 Turbidity

Turbidity is an optical property of a liquid defined as the number of particles in the liquid that absorb and scatter light. Turbidity is influenced by the size, shape and concentration of the particles as well as by the liquids scattering index and temperature. Turbidity measurements were done to predict for what pH value (or acid concentration) precipitation starts. (10). 3.4.2 PET Polyelectrolyte titration was used to determine the polymer charge and adsorption to fibres. A highly charged polymer is then added to a known amount of sample and OTB (ortotoluidinblue) indicates the charge neutralisation during titration. Each solution was diluted to a concentration of 0.1g/L and a number of test points (dosages of polymer) were taken. Each sample was put in a glass device and completed with deionised water to a volume of 50 ml. (11).

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3.4.3 PET by Mütek PCD This method was used to determinate the amount of natural biopolymer that had been adsorbed to the fibres. In contrast to ordinary PET, this method is based on measuring the streaming potential produced between a Teflon wall and a mobile piston put in motion. (12) An excess of anionic KPVS (Potassium poly vinyl sulfate) was added to the (now hopefully) cationic fibres and then titrated by polyDADMAC. For each sample, the adsorbed amount of polymer (KPVS), in mg/g is plotted as function of the equilibrium concentration of KPVS (mg/g). The surface charge is then calculated from the plateau value of the adsorption isotherm: Fibre charge [µekv/g] =Ap*qp Ap is the plateau value and qp the polymer charge [µekv/g] A certain amount of KPVS was added to 0.5 g of dry fibre. The sample was completed with 100ml of deionised water. A pH adjustment to a value of 4 or less assures maximal charge of the biopolymer. After reaction for 30 min on a shaking table, the sample was vacuum-filtered. The filter paper and fibre was dried at 105°C and put in a desiccator. The filtrate was saved for titration. (13). 3.4.4 Nitrogen Analysis

To compare the values from the surface charge determination, some samples were sent for Nitrogen Analysis (MikroKemi AB, Sweden). As the name indicates, such analysis gives the nitrogen content in mass-%. The amount of biopolymer adsorbed to the fibres was calculated knowing that the reference, highly viscous grade biopolymer, contains 7.6% of nitrogen. 3.5 Sheet preparation

Circular laboratory sheets of fibres treated with the biopolymer were made to study the physical effects. The sheets should have a grammage of 40g/m2. Consequently, 400ml of fibre suspension (2g/L) for each sheet was put in the sheet making mould. The sheets were manually pressed with a six-pound weight and blotting paper for 20 seconds. Then, a new blotting paper was put against each sheet and the whole assemble of sheets were pressed in a laboratory press for 5 min. The blotting papers were switched before the last pressing for 2 min was done. The sheets, still attached to carbon plates were left to dry under restrain in a conditioned room at 23°C and with a relative humidity of 50%. Table 2 below shows the different fibre mixtures that were used for the sheet preparation. At first, sheets were prepared exclusively from fibres pre-treated with biopolymer, 1. These fibres were then mixed with untreated fibres in proportions: 75/25, 50/50 and 25/75, 2. Natural biopolymer was also added to suspensions of untreated fibre in dosages of 0.5, 1 and 2% (3a-c). CMC was added together with 0.5 and 2% of biopolymer to untreated fibres (3d-f). The dosage of CMC was chosen such to attain charge neutrality, thus estimated from surface charge measurements of natural biopolymer and CMC. CMC was also added to the pre-treated fibres, 4. The dosage for charge neutrality was calculated in this case as well. PAE was added to untreated fibres, 5, as a reference. The standard dosage of 1% PAE was chosen.

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Then, an interesting experiment was made by adding 2% of modified starch to pre-treated fibres, 6, disregarding the fact that 5% of modified starch would have been needed to achieve charge neutrality). pH was adjusted to 4.3 to optimise the effect of modified starch. Table 2: Fibres used in the sheet preparation.

Sheet description: 0 Untreated fibres 3c 2 1 Pre-treated fibres 3d1 3a + CMC to charge zero 2 Pre-treated fibres+ untreated fibres: 3d2 3a + half dose of CMC 2a 25/75 3e 3c + CMC to charge 0 2b 50/50 3f 3c + half dose of CMC 2c 75/25 4a P-treated fibres + CMC to charge 0 3 Biopolymer (in %) to untreated fibres: 4b Biopolymer-treated fibres + half dose of CMC 3a 0.5 5 1%PAE to untreated fibres 3b 1 6 Pre-treated fibres + 2% mod. starch 3.6 Tensile testing of laboratory sheets Tensile tests were performed to evaluate the strength of the hand sheets. Strips of paper are pulled to rupture at constant speed in a tensile tester. The force is registered as function of strain. Laboratory sheets have no particular direction and therefore the values in machine- and cross direction are the same. 3.6.1 Parameter definition for paper testing: Tensile strength [N/m]: maximal load before the sample is brought to rupture Grammage [g/m2]: surface weight for a sample Bulk [cm3/g]: thickness/basis weight 3.6.2 Grammage and thickness The parameters tensile strength and tensile stiffness are divided by the grammage to compensate for variations when sheets with different grammage are tested. These values, in (kNm/kg) are then referred to as indices, which make the comparison of different samples more exact. The grammage was determined by weighting each sheet and then a mean value was calculated. The thickness was measured by putting a stack of four sheets into a precision micrometer. The bulk is then calculated from values of thickness and grammage. The sheets were detached from the carbon plates and measurements of grammage and thickness were done before tensile testing. The sheets were then stripped in a cutting machine to a width of 15mm and put in the tensile tester. To measure wet strength, the strips were put in a bowl to soak up water for a few seconds. The excess of water was adsorbed by a moistened blotting paper and the strips were then carefully placed in the machine. (14).

4. RESULTS/DISCUSSION 4.1 Precipitation of natural biopolymer Large precipitates of the biopolymer appeared as pH was increased. But this ´local´ precipitation disappeared when stirred magnetically. The liquid suddenly became very turbid with a large amount of precipitates. In diagram 1, turbidity is shown as function of pH during the precipitation (highly viscous grade). It is seen that precipitation starts at about same pH for both concentrations of acid. Therefore it was stated that turbidity and thereby precipitation is governed by pH rather than acid concentration.

Biopolymer HV in 0.2M acid

0

50

100

150

200

250

6,4 6,5 6,6 6,7 6,8 6,9 7 7,1 7,2 7,3 7,4 7,5

pH

Turb

idity


0

50

100

150

200

6 6,3 6,6 6,9 7,2 7,5 7,8 8,1 8,4 8,7 9

pH

Turb

idity

Diagram 1a and 1b: Changes in turbidity indicate when precipitation starts. At 70°C, precipitation started at lower pH, see diagram 2a and 2b. This was contrary to that precipitation often is delayed at higher temperature. The results were similar for precipitation of practical grade biopolymer. Precipitation starts when OH- groups have exceeded the number of acid groups and then begin to de-protonate the reactive groups of the biopolymer.

Biopolymer HV in 0.2M acid, 70°C

050

100150200

5 5,6 6,2 6,8 7,4 8 8,6 9,2 9,8 10,4

11

pH

Turb

idity

Biopolymer HV in 0.4M acid, 70°C

0

10

20

30

40

5,5 5,6 5,7 5,8 5,9 6 6,1 6,2 6,3

pH

Turb

idity

Diagram 2a and 2b. Precipitation curves (as in Diagram 1a and 1b) but now at 70°C.

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4.2 Charge measurements of the natural biopolymer KPVS (Potassium Polyvinyl Sulphate) with a charge of 5.8 ekv*/L (*ekvivalent is a measure of charge) was used as titrant during charge determination of the biopolymer. Graphically, the consumption of KPVS*10-7 (ekv) is plotted against the mass of polymer (biopolymer) *10-4 (g). The charge is given from the slope, in mekv/g. Charge determinations for both grades of natural biopolymer in 0.2M and 0.4M of acetic acid can be seen in diagram 3a-d and are summarised in Table 3.

Charge of biopolymer HV in 0.2M acid

y = 4,3852x + 0,7538R2 = 0,9941

02468

1012

0 0,5 1 1,5 2 2,5

amount of biopolymer (g)*10^-4

ekvK

PVS*

10^-

7

Charge of biopolymer HV in 0.4M acid

y = 4,8216x + 0,4402R2 = 0,9682

0

2

4

6

8

10

12

0 0,5 1 1,5 2 2,5amount of biopolymer (g)

*10^-4

ekvK

PVS*

10^-

7

Charge of biopolymer PG in 0.2M acid

y = 4,2896x + 0,8965R2 = 0,9942

02468

1012

0 0,5 1 1,5 2 2,5

amount of biopolymer (g)*10^-4

ekvK

PVS*

10^-

7

Charge of biopolymer PG 0.4M

y = 4,3872x + 0,9506R2 = 0,982

02468

1012

0 0,5 1 1,5 2 2,5amount of biopolymer (g)

*10^-4

ekvK

PVS*

10^-

7

Diagrams 3a, 3b, 3c and 3d. Charge measurements of two different grades of natural biopolymer (practical grade and highly viscous grade) in 0.2 and 0.4M of acetic acid. As seen from the diagrams above, the charge increases with higher acid concentration for both biopolymer types. The highest charge was measured for highly viscous biopolymer in 0.4M of acid. Table 3: Charge measurements of the natural biopolymer: Charge in mekv / g: 0.2M (pH=3.8) 0.4M (pH=3.54) Biopolymer HV 4.39 4.82 Biopolymer PG 4.29 4.39

18

4.3 Adsorption of natural biopolymer to bleached Kraft fibres Flocculation was observed for the pulp treated with natural biopolymer at 70°C. Many and hard splices were present in dewatered pulp or pulp washed in water. However, disintegration in a laboratory standard device dissolved the splices before charge determination was done. There are different mechanisms that could explain the flocculation and these mechanisms should be well understood and eliminated to make the adsorption successful. 4.3.1 Retention values by surface charge measurements (PET by Mütek PCD) The retention of biopolymer is strongly pH dependent. A comparison between treatment No 1 and 2, in diagram 4 shows that 2% of the biopolymer did not increase the surface charge of the fibres (see Table 1) more than 0.6% did. This is due to that pH during treatment No 2 was not high enough to promote precipitation.

Pre-treated fibres (0.6% biopolymer) washed in 4 x water

(Treatment No 1)

0,000,501,001,502,002,503,003,504,004,505,005,506,006,507,00

0,00 5,00 10,00 15,00 20,00

Equilibrium polymer concentration (mg/l)

Ads

pol

ymer

(mg/

g)

Pre-treated fibres (2% biopolymer) washed in 3 x water (Treatment No

2)

0,000,501,001,502,002,503,003,504,004,505,005,506,006,507,00

0,00 10,00 20,00 30,00


Ads

pol

ymer

(mg/

g)

Diagram 4. Adsorption isotherms indicate the amount of biopolymer that is adsorbed to the fibre surface. The amount is larger for higher plateau values on the y-axis (where curves level out).

19

According to diagram 5, the surface charge decreases only little when repeated washes in water are done. The surface charge decreases with the first wash but then it remains constant. This indicates that the adsorption is irreversible.

Pre-treated (2% biopolymer) and dewatered fibres (Treatment No 2)

0,000,501,001,502,002,503,003,504,004,505,005,506,006,507,00

0,00 10,00 20,00 30,00


Ads

pol

ymer

(mg/

g)

Pre-treated fibres (2% biopolymer) washed in 3 x water (Treatment No 2)

0,000,501,001,502,002,503,003,504,004,505,005,506,006,507,00

0,00 10,00 20,00 30,00

Equilibrium polymer concentration (mg/l)A

ds p

olym

er (m

g/g)

Diagram 5. The surface charge (or amount of biopolymer adsorbed to the fibres) of pre-treated fibres remains nearly constant when repeated washes in water are done. In treatment No 3, the temperature was raised to 70°C and the surface charge increased. However, it is hard to tell if this is a result of higher temperature or better pH control. This diagram is not shown here but can be found in appendix C. The surface charge decreases when wash in acid was done, see diagram 6. However, this is not very important since the principal aim is water stable adsorption.

Fibres treated with 2% of biopolymer, washed in acid x 1

(Treatment No 3).

0,000,501,001,502,002,503,003,504,004,505,005,506,006,507,00

0,00 5,00 10,00 15,00 20,00


Ads

pol

ymer

(mg/

g)

Fibres treated with 2% of biopolymer, washed in acid x 3

(Treatment No 3).

0,000,501,001,502,002,503,003,504,004,505,005,506,006,507,00

0,00 10,00 20,00 30,00


Ads

pol

ymer

(mg/

g)

Diagram 6. The surface charge of treated fibres diminishes for every acid wash. 20

The adsorption was then optimised with better mixing and pH control. Consequently, the surface charge (adsorption) increased drastically (diagram 7).

Fibres treated with 2% of biopolymer, washed in water x 1

(Treatment No 5).

10,0010,5011,0011,5012,0012,5013,0013,5014,0014,5015,00

0,00 10,00 20,00 30,00


Ads

pol

ymer

(mg/

g)Fibres treated with 0.5% of

biopolymer, washed in water x 1 (Treatment No 7).

0,000,501,001,502,002,503,003,504,004,505,005,506,00

0,00 10,00 20,00 30,00 40,00


Ads

pol

ymer

(mg/

g)

Diagram 7. Diagram 8. Diagrams 7 and 8 show the surface charges of treated fibres for two different dosages of biopolymer, 2% and 0.5%. The amount of adsorbed biopolymer in proportion to the dosage is in fact, higher for 0.5% than for 2% of biopolymer. An addition of 2% biopolymer corresponds to 20 mg biopolymer per gram fibre. The surface charge of the natural biopolymer is 4,82 mekv/g (highly viscous in 0.4M acid). Thus, a 100% retention corresponds to 0,020*4,82mekv/g =96,4 µekv/g. In the same way, if 0.5% of the biopolymer is added then 100% retention corresponds to a maximal surface charge of 24,1 µekv/g. The surface charge of untreated anionic fibre is 5 µekv/g. The charge adsorption is therefore equal to the surface charge value plus this value. Table 4. Results from surface charge measurements by PET. Treatment 2 (2% biopolymer, 25°C, plastic bag)

Surface charge, µekv/g

Charge adsorption µekv/g

Retention, mg/g

Retention in %

1. Dewatered 22.6 27,6 5,73 28.7 2. 1 x water 19.72 24,72 5,13 25.7 3. 3 x water 19.72 24,72 5,13 25.7 4. 1 x HAc 14.5 19,5 4,05 20.3 5. 3 x HAc 9,86 14,86 3,08 15.4 Treatment 5 (2% biopolymer, 70°C, stirred reactor)



Retention, mg/g

Retention in %

1 x water 73.37 78.37 16.3 81.3 Treatment 7 (0.5% biopolymer, 70°C, stirred reactor)



Retention mg/g

Retention in %

1 x water 25.81>24.1!

30.81(>29.1!)

5,12 (>0.5%)

>100%!

21

The retention increases from 5mg/g, in Treatment No 2, to 16mg/g for Treatment No 5 for samples washed in water x 1. The PET-value in Treatment No 7 corresponds to over 100% retention! However, the total amount of biopolymer adsorbed to the fibre surface cannot exceed the dosage that was used for the treatment.

4.3.2 Nitrogen Analysis The retention value can be calculated from the nitrogen content in each sample. For example, if the sample contains 0,06 mass-% of nitrogen (0.6 mg N per g fibre) the retention is given by:

gfibrergbiopolymergbiopolymemgN

gfibremgN /0079.0/

/76

6.0=

The retention (in %) is this value divided by 20 mg/g (2% biopolymer) or 5mg/g (0.5% biopolymer), values that would correspond to retention of 100%. Table 5. Results from nitrogen analysis.

Treatment 2 (2% biopolymer, 25°C, plastic bag)

N-content, mass-%

Retention, mg/g

Retention in %

1. Biopolymer HV (reference)

7,6 7.6 - -

2. Dewatered 0,060 0,065 8.22 41.1 3. 1 x water 0,060 0,062 8.02 40.1 4. 3 x water 0,044 0,035 5.20 26.0 5. 1 x HAc 0,047 0,048 6.25 31.3 6. 3 x HAc 0,026 0,017

0,010 2.32 11.6

Treatment 4 (2% biopolymer, 70°C, stirred reactor

N-content, mass-%

Retention, mg/g

Retention in %

1. Dewatered 0,12 0,12 15.8 79 2. 1 x water 0,13 0,13 17.1 85.5 3. 3 x HAc 0,031 0,030 4.01 20.1 Treatment 5 (2% biopolymer, 70°C, stirred reactor

N-content, mass-%

Retention, mg/g

Retention in %

1.Dewaterd 0,14 0,13 17.8 89.0 2. 1 x water 0,12 0,13 15.8 79.0 3. 1 x HAc 0,053 0,043 6.32 31.6 4. 3 x HAc 0,043 0,043 5.66 28.3

22

23

Treatment 6 (2% biopolymer, 70°C, stirred reactor)

N-content, mass-%

Retention, mg/g

Retention in %

1. 1 x water 0,12 0,12 15.8 79.0 2. 2% biopolymer to suspension)

0,020 0,020 2.6 13.0

Treatment 7 (0.5% biopolymer, 70°C, stirred batch

N-content, mass-%

Retention, mg/g

Retention in %

1 x water 0,032 0,035 4.4 88.0 In treatment No 2, the retention values of the nitrogen analysis disagree with the PET values. This indicates that the biopolymer is unevenly distributed on the fibre surface. The retention in treatment No 7 has more than doubled compared to treatment No 2, which shows the good effects of mixing and raised temperature provided that the adsorption is carefully controlled by pH. There is a close similarity between the retention values in treatment No 4,5 and 6, which all lay around 16mg/g, corresponding to a retention of almost 90%. This tells us that the treatments were of equal success. The PET- and nitrogen analysis values also agree. Retention values from nitrogen analysis are in general higher than the PET-values, except for treatment No 7.

4.4 Tensile strength 4.4.1 Dry strength Dry strength was decreased for sheets made of pre-treated fibre, but after curing at 140°C the effect was the opposite. In diagram 9 it is seen that curing increases dry strength for all sheet types. Point 4 corresponds to untreated fibres (see Table 6). Curing had most effect on sheets at points 3,6,9,13. These points correspond to sheets made from pre-treated fibre (2% of biopolymer), pre-treated fibre (2% biopolymer) with 2% of CMC, 2% of biopolymer to untreated fibres and fibres treated with PAE. Thus, curing had the largest effect on sheets with a high content of biopolymer. PAE and modified starch increased dry strength of untreated fibres and pre-treated fibres, respectively.

The influence of curing on dry strength

0

5

10

15

20

25

30

35

1 2 3 4 5 6 7 8 9 10 11 12 13 14 Sheet type

Dry

tens

ile st

reng

th i

ndex

(kN

m/k

g)

non-curedcured

Diagram 9. Dry strength of different sheet types. For sheet descriptions, see Table 6. Table 6. Sheet descriptions for diagram 9: 1. Pre-treated fibres (2% biopolymer) + half dose of CMC 2. Pre-treated fibres (2% biopolymer) + untreated fibres: 50/50 3. Pre-treated fibres (2% biopolymer) 4. Untreated fibres 5. 2% of biopolymer to untreated fibres + half dose CMC 6. Pre-treated fibres (2% biopolymer) + CMC to zero charge 7. 0.5% of biopolymer to untreated fibres + CMC to zero charge 8. 1% of biopolymer to untreated fibres 9. 2% of biopolymer to untreated fibres 10. 0.5% of biopolymer to untreated fibres + half dose CMC 11. 2% of biopolymer to untreated fibres + CMC to zero charge 12. 0.5% of biopolymer to untreated fibres 13. 1% of PAE to untreated fibres 14. Pre-treated fibres (2% biopolymer) + modified starch

24

The influence of curing on dry strength pre-treated fibres (2% biopolymer)

0

5

10

15

20

25

30

35

1 2 3 4 5 6 7

Sheet typeDry

tens

ile st

reng

th in

dex

(kN

m/k

g)

non-curedcured

Diagram 10. Tensile test results for dry strength of the different fibres. For sheet descriptions, see Table 7. Table 7. Sheet descriptions for diagram 10.

1. Pre-treated fibres + CMC to zero charge 2. Pre-treated fibres + untreated fibres: 25/75 3. Pre-treated fibres + untreated fibres: 50/50 4. Pre-treated fibres + untreated fibres: 75/25 5. Pre-treated fibres + half dose CMC 6. Pre-treated fibres 7. Pre-treated fibres + modified starch

Curing increased dry strength for sheets at points 1,4,5,6, in diagram 10, in other words sheets with a large content of biopolymer and/or CMC. Modified starch increased the dry tensile strength here as well. 4.4.2 Wet strength Sheets made of pre-treated fibres presented many white spots and repelled water. This repellence towards water increased further with curing. This behaviour might have been caused by excessive dosage of biopolymer and therefore flocculation, but was not permanent since sheets that were left in water for 30 min absorbed an optimum of liquid. Such hydrophobic behaviour is good for packing grades but not in tissue paper. Wet strength was developed for sheets made of fibres that had been pre-treated with biopolymer. Curing had the effect that it increased the wet tensile strength indices. However, since dry tensile strength indices also increased, no effect on the relative wet strength of these fibres was detected. Wet strength was not detectable when pre-treated fibres were mixed with untreated fibres, but these sheets felt stronger than sheets made of untreated fibre. The biopolymer did not develop wet strength when it was added directly to suspensions of untreated fibre. Surface charge measurements showed that the adsorption of biopolymer to fibres was poor in this case. In fact, not more than 13% of a total dosage of 2% (2 mg

25

biopolymer per gram fibre) had adsorbed to the fibres (see Table 5, Treatment No 6, point 2). However, an addition of CMC promoted the adsorption of biopolymer and wet strength was detectable for the maximal dosage of biopolymer together with CMC (diagram 12, column 2). It was shown that curing is necessary for reaction between the amino groups of PAE and the carboxyl groups of the fibres (see diagram 11 and 12). Curing is also needed for reactions between CMCs carboxyl groups and the biopolymers reactive groups to take place. When modified starch is used, wet strength is developed in two steps. The anionic functions in modified starch attract the biopolymers cationic functions. The reactive functions of modified starch react with the hydroxyl groups on the fibre surface or they can cross-link under special conditions. To optimise the effect of modified starch, pH should be low (4.5 or less). In this study, higher relative wet strength would probably have been measured if pH had been correct when modified starch was added to fibre that was pre-treated with 2% of biopolymer.

Tensile strength for fibres treated with: biopolymer, 1% PAE or 2% modified starch (all sheets are non-cured)

0

5

10

15

20

25

30

35

1 2 3 4

Tens

ile st

reng

th in

dex

(kN

m/k

g)

dry strength wet strength relative wet strength (%)

Pre- treated fibres (2% biopolymer)

1% PAE to untreated fibres

2% mod.starch to pre- treated fibre (0.5% biopolymer)

2% mod.starch to pre- treated fibres (2% bi l )

Diagram 11. Tensile strength (indices) for uncured sheets.

26

Tensile strengths for fibres treated with: biopolymer, CMC, 1% PAE or 2% modified starch (all cured)

0

5

10

15

20

25

30

35

1 2 3 4 5 6 7 8

Tens

ile st

reng

th in

dex

(kN

m/k

g)

dry strength wet strength relative wet strength(%)

Pre-treated fibres (2% biopolymer)

2% CMC + 2% biopoly mer to untreated fibres

2% CMC to pre-treated fibres (2% biopolymer)

1% CMC to pre- treated fibres (2% biopolymer)

Pre-treated fibres (0.5% biopolymer)

2% mod.starch to pre- treated fibres (2% biopolymer)

1% PAE to untreated fibres

2% mod.starch to pre- treated fibres (0.5% biopolymer)

Diagram 12. Tensile strength indices for sheets made of fibres with different wet-strength agents The effects of curing fibres that are treated with biopolymer or other wet strength additives are shown in diagram 12. For fibres treated with 2% biopolymer wet strength is quite good, almost 14% of relative wet strength is achieved, see column 1. Wet strength measurements are possible only if wet strength exceed a certain detection limit. Sheets that showed detectable wet strength were:

- Non-cured (and cured) pre-treated fibres (2% biopolymer) - Cured pre-treated fibres (0.5% biopolymer) - Pre-treated fibres (0.5 and 2% biopolymer) with CMC - Non-cured and cured fibres with an addition of PAE - Non cured and cured pre-treated fibres (0.5 and 2% biopolymer) with addition of

modified starch. Wet strength was not measurable in the following cases:

- Pre-treated fibres mixed with untreated fibres - 0.5, 1 and 2% biopolymer added to untreated fibres - 0.5 and 1% biopolymer added to untreated fibres and in combination with

CMC. Wet strength was however detectable for cured sheets with 2% natural biopolymer and maximal dosage of CMC.

An interesting, and perhaps the most important observation, are points 6 and 7 in diagram 12. Here, wet strength is good. It is seen in point 7 that an addition of 2% modified starch to pre-treated fibres (0.5% biopolymer) gives the same relative wet strength as cured sheets made of PAE-treated fibres. Curing does not increase wet strength of the pre-treated fibres with modified starch. This is seen by comparing points 3 and 4 in diagram 11 to points 6 and 7 in diagram 12. 27

28

5. CONCLUSIONS Dry strength was decreased for sheets made of fibres pre-treated with biopolymer, but increased after curing.

Dry strength of pre-treated fibres was increased when CMC or modified starch was added.

Wet strength was developed for fibres that had been pre-treated with biopolymer.

Curing did not increase the relative wet strength of the pre-treated fibres.

Wet strength was not detectable for fibres where biopolymer was added to untreated fibres in suspension.

An addition of CMC to the pre-treated fibres increased the relative wet strength from 13

to 17%. Modified starch increased the relative wet strength of pre-treated fibres from 13 to 21%.

Curing had no effect on wet strength of pre-treated fibres with addition of modified starch.

When modified starch was added to pre-treated fibres (0.5% biopolymer) the relative wet strength was the same as for fibres treated with 1% PAE. The use of PAE requires curing whereas wet strength of the pre-treated fibres was achieved before curing.

29

6. RECOMMENDATIONS This work showed that the natural biopolymer, thanks to its reactive groups and structural similarity to cellulose, can be used in fibre treatments and as binder for further surface modifications of fibres. Its biodegradability is an important property and the fact that it gives temporary wet strength makes the paper products repulpable (important in recycling process). Modified starch also provides temporary wet strength through cross-linking between its reactive groups or through reactions between its anionic surface charges and cationic sites of the biopolymer. PAE, on the other hand, gives permanent wet strength, which can be advantageous in some products, for example packaging grades. An idea is to test cationic cellulose derivates instead of or in combination with natural biopolymer. Such derivates would, in the long run, lower the costs of wet strength development.

30

7. REFERENCES: 1. Andreasson B, The Chemistry of wet-strength development, SCA Research (1997) 2. Bengtsson M, CMC modification of recycled fibres, Master Thesis, Chalmers University of Technology (2005) 3. Theliander H, Paulsson M and Brelid H, Introduktion till Massa- och pappersframställning, Chalmers University of technology, Gothenburg, Sweden (2002) 4. Fors C and Norman B, The effect of fibre charge on web consolidation in papermaking, Licenciate thesis, STFI, Stockholm (2000) 5. Ekevåg P, Lundström T, Gellerstedt G and Lindström M, Addition of carboxymethylcellulose to the kraft cook, Nordic Pulp and Paper Research Journal Vol 19 no.2/2004 6. Laine J, Lindström T, Glad Nordmark G, Risinger G, Studies on topochemical modification of cellulosic fibres, Part 1. Chemical conditions for the attachment of carboxymethyl cellulose onto fibres, Nordic Pulp and Paper Research Journal Vol 15 no.5/2000 7. Laine J, Lindström T, Glad Nordmark G, Risinger G, Studies on topochemical modification of cellulosic fibres, Part 2, The effect of carboxymethyl cellulose attachment on fibre swelling and paper strength, Nordic Pulp and Paper Research Journal Vol 17 no.1/2002 8. Hartler N, Cellulosateknik, orienterande kurs, Royal university of Technology, KTH, Stockholm (1985) 9. Sjöström E, Wood Chemistry: Fundamentals and Applications (1981) 10. Turbiditet, Yt- och kolloidkemi, SCA Research (Internal method description) 11. Polyelektrolytitrering, Yt- och kolloidkemi, SCA Research (Internal method description) 12. Bley L, Measuring the concentration of anionic trash – the PCD, Paper Technology April (1992) 13. Laddningsbestämning med Mütek PCD, Yt- och kolloidkemi, SCA Research (Internal method description) 14. SCAN-P-67 Tensile strength (Internal method description)

Appendix A. Turbidity diagrams during the precipitation of highly viscous (HV) and practical grade (PG) biopolymer in 0.2M or 0.4M acetic acid at 25°C or 70°C


0

50

100

150

200

250

6,4 6,6 6,8 7 7,2 7,4

pH

Turb

idity

Biopolymer HV in 0.2M acid at 70°C

050

100150200

5 5,6 6,2 6,8 7,4 8 8,6 9,2 9,8 10,4

11

pH

Turb

idity


0

50

100

150

200

6 6,3 6,6 6,9 7,2 7,5 7,8 8,1 8,4 8,7 9

pH

Turb

idity

Biopolymer HV in 0.4M acid at 70°C

05

10152025303540

5,5 5,6 5,7 5,8 5,9 6 6,1 6,2 6,3

pH

Turb

idity

Biopolymer PG in 0.2M acid

0

50

100

150

200

250

6,6 6,7 6,8 6,9 7 7,1 7,2 7,3

pH

Turb

idity

Biopolymer PG in 0.2M acid, 70°C

05

10152025303540

5 5,2 5,4 5,6 5,8 6 6,2 6,4

pH

Turb

idity

31

Biopolymer PG in 0.4M acid

0

50

100

150

200

5,5 5,8 6,1 6,4 6,7 7 7,3 7,6 7,9 8,2 8,5 8,8

pH

Turb

idity

Biopolymer PG in 0.4M acid, 70°C

0

50

100

150

200

250

300

5,7 5,9 6,1 6,3 6,5 6,7 6,9 7,1 7,3 7,5 7,7

pH

Turb

idity

32

Appendix B. Charge determinations of highly viscous and practical grade biopolymer in 0.2M or 0.4M acetic acid.

Highly viscous biopolymer in 0.2M acetic acid

y = 4,3852x + 0,7538R2 = 0,9941

0

2

4

6

8

10

12

0 0,5 1 1,5 2 2,5

biopolymer mass*10^-4

ekvK

PVS*

10^-

7

Highly viscous biopolymer in 0.4M acetic acid

y = 4,8216x + 0,4402R2 = 0,9682

0

2

4

6

8

10

12

0 0,5 1 1,5 2 2,5


ekvK

PVS*

10^-

7

Practical grade biopolymer in 0.2M acetic acid

y = 4,2896x + 0,8965R2 = 0,9942

0

2

4

6

8

10

12

0 0,5 1 1,5 2 2,5


ekvK

PVS*

10^-

7

Practical grade biopolymer in 0.4M acetic acid

y = 4,3872x + 0,9506R2 = 0,982

0

2

4

6

8

10

12

0 0,5 1 1,5 2 2,5


ekvK

PVS*

10^-

7

33

Appendix C. Adsorption isotherms for pre-treated fibres (after different washing steps) Treatment No 1: (5% consistency, 0.6% biopolymer, pH=6.8 at 25°C in plastic bag).

4 x water

0,000,501,001,502,002,503,003,504,004,505,005,506,006,507,00

0,00 5,00 10,00 15,00 20,00


Ads

pol

ymer

(mg/

g)

4 x HAc

0,000,501,001,502,002,503,003,504,004,505,005,506,006,507,00

0,00 10,00 20,00 30,00


Ads

pol

ymer

(mg/

g)

34

Treatment No 2: (5% consistency, 2% biopolymer, pH=6.2(start) and 6.5(end) at 25°C in plastic bag).

1 x water

0,00

1,00

2,00

3,00

4,00

5,00

6,00

7,00

0,00 10,00 20,00 30,00


Ads

pol

ymer

(mg/

g)

3 x water

0,000,501,001,502,002,503,003,504,004,505,005,506,006,507,00

0,00 10,00 20,00 30,00


Ads

pol

ymer

(mg/

g)

1 x HAc

0,000,501,001,502,002,503,003,504,004,505,005,506,006,507,00

0,00 20,00 40,00 60,00


Ads

pol

ymer

(mg/

g)

3 x HAc

0,000,501,001,502,002,503,003,504,004,505,005,506,006,507,00

0,00 10,00 20,00 30,00


Ads

pol

ymer

(mg/

g)

35

Treatment No 3: (5% consistency, 2% biopolymer, pH=6.6 at 70°C, plastic bag).

1xHAc

0,000,501,001,502,002,503,003,504,004,505,005,506,006,507,00

0,00 5,00 10,00 15,00 20,00


Ads

pol

ymer

(mg/

g)3xHAc

0,000,501,001,502,002,503,003,504,004,505,005,506,006,507,00

0,00 10,00 20,00 30,00


Ads

pol

ymer

(mg/

g)

Treatment No 4: (3% consistency, 2% biopolymer, pH=3.6(start) to 9.9(end) at 70°C in glass reactor).

3 x HAc

0,000,501,001,502,002,503,003,504,004,505,005,506,006,507,00

0,00 5,00 10,00 15,00 20,00


Ads

pol

ymer

(mg/

g)

36

Treatment No 5: (3% consistency, 2% biopolymer, pH=3.6(start) to 7.2(end) at 70°C in glass reactor).

1 x water

10,0010,5011,0011,5012,0012,5013,0013,5014,0014,5015,00

0,00 5,00 10,00 15,00 20,00 25,00


Ads

pol

ymer

(mg/

g)

Treatment No 7: (3% consistency, 0.5% biopolymer, pH=3.9(start) to 7.2(end) at 70°C in glass reactor).

1 x water

0,000,501,001,502,002,503,003,504,004,505,005,506,00

0,00 10,00 20,00 30,00 40,00


Ads

pol

ymer

(mg/

g)

37

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