81

CHAPTER 4

CHARACTERIZATION AND ANALYSIS OF

MILKWEED FIBRES

4.1 INTRODUCTION

The characterization of textile fibres is important to many fields

such as industrial production and textile conservation where information

about the source and condition of the fibre is required. In this chapter, the

basic characteristics of milkweed fibres like physical, chemical,

morphological and thermal properties were tested to understand its nature.

Also the changes in the structure of milkweed fibre and properties due to

chemical modification are discussed.

4.2 MATERIALS AND METHODS

The particulars of chemicals used, methods of estimation of

chemical composition of fibres, method of testing of physical, morphological

and thermal properties of fibres are given in various sections of Chapter 3.

4.3 RESULTS AND DISCUSSION

4.3.1 Effect of Chemical Treatments on the Composition of

Milkweed Fibres

The milkweed fibres were analyzed and the estimated average

chemical composition of the raw, alkali treated and dyed fibre samples

82

without considering the moisture are given in Table 4.1. The composition of

cotton fibre is also reported for comparison.

Table 4.1 Chemical composition of milkweed fibres

Material Cotton Milkweed

Raw Alkali Treated Dyed

Cellulose (%) 94.0 59 ± 2.0 74 ± 2.0 62 ± 2.0 Hemi cellulose (%) 2.5 23 ± 1.0 14 ± 1.4 21 ± 1.0 Lignin (%) 0.0 13 ± 0.8 8 ± 1.2 12 ± 0.8 Wax & Fatty matters (%) 0.9 4 ± 0.5 1.0 ± 0.5 2.5 ± 0.5 Ash content (%) 1.2 1.5 2.0 1.6

Most of the ligno-cellulosic agricultural by-products have cellulosic

content of about 40 45% (Gassan & Bledzki 1999) but the cellulosic content

of the milkweed fibres is relatively on the higher side. The milkweed fibres

are stiff and brittle due to high lignin content. The alkali treatment of fibre

resulted in a change of colour from off-white to brownish yellow. The change

in colour is attributed to the light absorption in the near UV and visible

regions due to structural change from benzenoid to quinonoid in the lignin

moiety and generation of other chromophores during partial delignification

(He et al 2005). The hemi-cellulose, lignin and wax content were reduced by

approximately 39%, 38% and 75% respectively after alkali treatment. In dyed

sample, the wax content approximately reduced by 37.5% but changes in

other compositions were not noticed.

83

4.3.2 Physical Properties of Milkweed Fibres

4.3.2.1 Bundle fibre properties

The single and bundle fibre properties of cotton and raw milkweed

fibres measured in Baer sorter, HVI and AFIS are given in Table 4.2. From

the table, it is evident that the 2.5% span length of milkweed fibre measured

in HVI and effective length measured from Baer sorter diagram are

comparable with cotton.

Table 4.2 Characteristics of Cotton and Milkweed fibres

Sl. No Sample Cotton (S4) Raw milkweed 1 2.5% Span Length (mm) 28.3 (5.34) 29.09 (9.56) 2 50% Span Length (mm) 13.67 (8.49) 12.68 (9.6) 3 Effective Length (mm) 29 (2.2) 31 (1.8) 4 Mean Length (mm) 27.12 (1.3) 26.14 (2.3) 5 Uniformity Ratio (%) 45.2 (7.41) 41.6 (6.26) 6 Strength (g/tex) 21.3 (4.7) 20.5 (7.99) 7 Elongation (%) 6.3 (1.51) 3.9 (2.7) 8 Micronaire (µg/inch) 3.5 (1.42) < 2.4 9 SFI (w) % 7.50 (8.2) 12.90 (9.78)

10 Short fibre (%) 8.3 (2.1) 10.52 (4.8) 11 SFC (n) 25.2 (8.5) 33.3 (7.3) 12 SFC (w) 10.1 (11.2) 19.0 (6.2) 13 Nep Count/g 231 (10.9) 45 (6.7) 14 Nep size (µm) 856 (4.9) 648 (4.2) 15 Seed Coat Neps/g 13 (27.4) 5 (15.6) 16 Seed Coat Nep size (µm) 1286 (13.7) 900 (15.5) 17 Immature Fibre Content 7.6(8.8) 12.0 (12.3) 18 Maturity Ratio 0.82 (1.1) 0.79 (1.3) 19 Moisture regain (%) 8.2 (2.3) 10.5 (1.5) 20 Reflectance (Rd) 73.4 (1.1) 67.8 (1.4) 21 Yellowness (+b) 9.8 (2.4) 12.6 (2.9) 22 Colour grade 32-1 34-1

Values in parentheses represent CV%

84

The arrangement of milkweed fibres in velvet pad in descending

order of its length for Baer sorter diagram is shown in Appendix A1.1. The

uniformity ratio is slightly lower than cotton due to more number of fibres in

the short length range indicated by short fibre % and short fibre index (SFI).

The bundle fibre strength and elongation of milkweed fibres is

lower than that of cotton fibres due to the absence of convolutions or crimp

like structure. Highly stretched arrangement of fibres in the milkweed pod and

the elongated milkweed pods as compared to circular cotton bolls might have

resulted in crimpless structure as shown in Figure 4.1.

Figure 4.1 Stretched arrangement of milkweed fibres in the matured pod

Since the milkweed fibres are manually separated from their seeds,

the neps/g, seed coat and corresponding nep sizes were found less compared

to cotton fibres. The maturity ratio of milkweed fibres is slightly lower than

cotton fibres as reflected in higher IFC values as shown in

Table 4.2. This could be due to the hollow nature of milkweed fibres.

The moisture regain of milkweed fibres are found to be higher than

cotton due to more amorphous region as revealed in XRD patterns later in this

Chapter. The colour appearance of the fibres was analyzed in HVI. From the

85

table, it is evident that Rd (reflectance) value of milkweed fibres is lesser than

cotton and +b (yellowness) values are higher than cotton. The colour grade of

cotton fibres obtained from Nickerson-Hunter colour chart (Figure A1.2) lie

between middling to light spotted but in case of milkweed fibres it is between

middling to tinged one indicating that the milkweed fibres are dull in white

colour and rich in yellowish tone compared to cotton fibres. This could be due

to high amount of lignin in the fibres (Subramanian et al 2005).

4.3.2.2 Tensile properties of single fibres

The linear density of cotton and milkweed fibres calculated using

Vibrodyn and gravimetric method was found to be around 1.25 and 1.05

denier respectively. The tensile properties of single fibres measured in Instron

tester is given in Table 4.3.

Table 4.3 Tensile properties of cotton and milkweed fibres

Fibre Property Cotton Milkweed fibre

Raw Alkali treated Dyed

Fibre Denier 1.25 (12.7) 1.05 (18.6) 1.04 (16.2) 1.04 (17.5) Breaking strength (gf) 5.1 (35.72) 3.92 (44.63) 4.02 (57.13) 3.96 (39.22)

Tenacity (g/den) 4.1 (34.1) 3.73 (37.6) 3.87 (53.5) 3.81 (42.1) Breaking Elongation (%) 8.1% (23.2) 3.05% (33.7) 4.83% (39.6) 3.1% (35.4)

Initial Modulus (gf/den) 101.8 (42.33) 210.89 (33.7) 140.8 (45.38) 197.36 (52.23)

Values in parentheses represent CV%

From the Table 4.3, it is noticed that the cotton fibres have higher

tenacity and elongation values compared to raw and chemically treated

milkweed fibres and are coarser than milkweed. The initial modulus of raw

86

milkweed fibres is significantly higher than the cotton fibres, which could be

due to the low elongation-at-break of milkweed compared to cotton. The

tenacity and elongation of alkali treated milkweed fibre slightly increases as

compared to the raw fibre. This may be due to re-arrangement of molecular

chains and formation of convolutions after alkali treatment. Though the fibre

elongation has improved after alkali treatment, it is relatively lower than

cotton. Such lower elongation values could result in fibre breakage during

opening in blow room and carding processes. The dyed milkweed fibre

sample does not show a significant difference in tensile properties than raw

fibres.

4.3.2.3 Fibre density and diameter

The fibre densities of raw milkweed fibres is found to be in the

range of 0.92-0.95 g/cm3 when the fibre is put it over the gradient column

without cutting and squeezing the fibres and it is around 1.48 g/cm3 when the

fibres are cut and squeezed to remove the air pockets inside it to get the

density of the wall without considering the hollowness. The fibre density by

considering the air inside the hollowness of fibres is lesser compared to the

density of cotton fibre 1.54 g/cm3 (Klemm et al 2001).

The fibre diameter observed on projection microscope and SEM is

shown in Figure 4.2. The variation in the dimensions was found to be in the

range of 15 35 µm with a mean value of 22 µm. The alkali treated fibres

showed a slight decrease in diameter due to the collapse of hollow structure

and partial removal of lignin.

87

(a) (b)

Figure 4.2 Fibre diameter measurements of milkweed fibre (a) projection microscope and (b) SEM

The slenderness ratio (l/D ratio), which defines a textile fibre

generally starts from 1:100 for most of the useful fibres. The natural fibres,

namely, cotton, flax and ramie has l/D ratios around 1:1400, 1:1209 and

1:3000 respectively. The l/D ratio of milkweed fibres was found to be around

1:1180, which is well within the definition of a textile fibre.

4.3.2.4 Effect of chemical treatments on frictional property of

milkweed fibres

The fibre-to-fibre friction co-efficient is measured on the fibre

friction tester. It shows a value of 0.33 for cotton fibre and 0.16, 0.28, 0.22 for

raw, alkali treated and dyed milkweed fibres respectively. The values are

relatively lower than cotton indicating a smooth surface without convolutions

or crimps. The chemical treatments significantly improved the frictional co-

efficient. The alkali treated fibre showed higher friction co-efficient followed

by dyed fibre. This is due to the irregular collapse of hollow structure and

formation of convolutions in the milkweed fibres.

88

4.3.3 Influence of Chemical Treatments on Surface Morphology of

Milkweed Fibres

In order to examine the effect of chemical treatments on the

morphology of milkweed fibres, the raw and treated fibres were observed by

SEM and optical microscope and the results are shown in Figures 4.3 and 4.4

respectively.

(a) (b)

(c) (d)

Figure 4.3 SEM micrographs of raw and chemically treated milkweed fibre (a) Longitudinal view of raw fibre (b) Cross-sectional view of raw fibre (c) NaOH treated fibre (d) Dyed fibre

89

Like cotton, milkweed fibre is a single cell fibre but without

convolutions. Although milkweed fibre does not collapse upon drying due to

low cell wall thickness, it does collapse during chemical treatments. The

Figure 4.3a and 4.3b shows the longitudinal and cross-sectional SEM images

of the raw milkweed fibres. It could be seen that the raw fibres possess a

smooth, uniform and lustrous surface due to higher wax content and are

hollow in nature. After alkali treatment, the hollow nature of the fibre

collapses due to partial removal of hemi-cellulose and lignin and forms

convolutions like cotton as shown in Figure 4.3c. The partial or uneven

removal of wax from the surface of dyed milkweed fibre produces

considerable roughness on the fibre surface. The deposition of dyes on the

fibre surface may also be contributed to the increase in surface roughness of

dyed fibres as shown in Figure 4.3d.

The longitudinal and cross-sectional images of raw milkweed fibres

obtained from polarized light microscope are shown in Figures 4.4a and 4.4b.

The grooves noticed along the longitudinal direction could induce the fibres

to have excellent capillary effect, hygroscopicity and air permeability. The

hollow nature of fibres is also confirmed in Figure 4.4b.

(a) (b)

Figure 4.4 Polarized Light Micrographs of raw milkweed fibre (a) Longitudinal view (b) Cross-sectional view

90

4.3.4 Influence of Chemical Treatments on FTIR Spectrogram of

Milkweed Fibres

The raw, alkali treated and dyed fibre samples showed common

absorptions (Figure 4.5) around 3400, 2925, 1470, 1356, 1169 and 1038 cm-1

and they were identified as reported in other ligno-cellulosic fibres (Nelson &

O'Connor 1964; Marchessault & Liang 1960). The assignment of the

characteristic IR peaks and their common relative sources are given in

Table 4.4 (Subramanian et al 2005) and Table A1.1.

It can be noted that the absorption band at ~1730 cm-1 and

1240cm-1 seen in the raw and dyed fibres is less pronounced for alkali treated

fibres. These bands which are attributed to the stretching vibrations of C=O

and C O groups are reduced after alkali treatment. These groups are prevalent

in lignin and hemi-cellulosic structures (Favaro et al 2010).

(a)

Figure 4.5 (Continued)

91

(b)

(c)

Figure 4.5 FT-IR spectra of milkweed fibre sample (a) Raw (b) NaOH Treated and (c) Dyed

92

Table 4.4 Assignment of FT-IR peaks and their relative sources

Wave number (cm-1) Vibration Source

3300 O-H linked shearing Polysaccharides 2885 C-H symmetrical stretching Polysaccharides 2850 CH2 symmetrical stretching Wax 1732 C=O unconjucated Hemicellulose 1650-1630 OH (Water) Water 1505 C=C aromatic symmetrical

stretching Lignin

1425 CH2 symmetrical bending C=C stretching in aromatic groups

Pectins, Lignins, Hemicelluloses, calcium pectates

1370 In-the-plane CH bending Polysaccharides 1335 C-O aromatic ring Cellulose 1240 C-O aryl group Lignin 1162 C-O-C asymmetrical stretching Cellulose,

hemicellulose 895 Glycosidic bonds Polysaccharides 670 C-OH out-of-plane bending Cellulose

The hemi-celluloses have groups that attract in the carbonyl section

and ester group on the surface of fibre and they are soluble in alkaline

medium. This was more likely attributed to the presence of >C=O group in

the lignin moiety as well as in other soluble polysaccharides, which could

have been removed during the chemical treatment. During alkali treatment, a

substantial portion of uronic acid and fatty substances might be removed

resulting in reduction of this peak at ~1730 cm-1 and reduction in peak

intensity at 1240 cm-1 (Liu & Dai 2007). Further, the reduction in the peak

intensity at 1370 cm-1 indicated the partial removal of lignin (Wang et al

2009).

93

The peak intensity at 1650-1630 cm-1, which corresponds to water

absorbed in cellulose molecule, increases slightly after delignification

treatment. Indeed, NaOH reacts with OH ions present in cellulose to form

water molecules. During the alkali treatment the water molecules in the

structure of the fibre were evaporated and this tends to increase the

transmittance of fibre (Segal et al 1959).

In alkali treated and dyed milkweed fibre samples, the peak at 2850

cm-1 representing waxes and oils present in the substrate decreases, indicating

the partial removal of waxes. Whereas the intensity of the peak characteristic

of polysaccharides hydroxyl bonds located near 3300 cm-1 increases. It could

be seen from Figure 4.5 that the raw milkweed O-H stretching absorption was

around 3487 cm-1 and NaOH treated and dyed fibres showed a transition to

the absorption peaks at 3392.12 and 3355.12 cm1, which indicated that

hydrogen bond of the treated fibres was stronger than that of the raw fibres,

these result was in accord with Subramanian et al (2005).

4.3.5 Influence of Chemical Treatments on Crystallinity of Milkweed

Fibres

XRD studies were done to determine the crystallinity index which

measures the orientation of cellulose crystals in a fibre to the fibre axis and

the patterns are shown in Figure 4.6.

The crystallinity index of the raw, alkali treated and dyed fibres are

summarized in Table 4.5. The results in Figure 4.6 shows two main peaks,

respectively, which are assigned to Cellulose I.

94

(a)

( b)

(c)

Figure 4.6 XRD patterns of milkweed fibre sample (a) Raw fibre (b) NaOH treated fibre (c) Dyed fibre

95

The peak intensity at 22.46º is said to represent the total intensity

(crystalline + amorphous) of material and peak intensity at 16o correspond to

the amorphous material in the cellulose. Compared to raw fibres, there was no

crystalline transformation of the structure in treated samples due to invisible

changes in the diffraction angle (2 ).

Table 4.5 Crystallinity of milkweed fibres

Samples Raw fibre Alkali treated Dyed Crystallinity (%) 56 62 57

The dyed fibre does not show a significant difference in the

crystallinity index indicating no change in amorphous and crystalline regions

of the fibre after treatment; however, the alkali treated fibre exhibited slightly

higher crystallinity index than untreated fibre. The delignification treatment

hydrolyzes the amorphous region of cellulose present in the fibres leaving

behind the crystalline cellulose. The reaction between cellulose and caustic

soda is shown below:

Cellulose-OH + NaOH Cellulose O-Na+ + H2O + impurities (4.1)

Na+ ions come to fit in the unit cell of cellulose, increasing the cell

parameter (Goda et al 2006). This phenomenon can be explained as follows.

At lower concentrations of alkali, the hydroxide ions could be fully hydrated

and may not be able to penetrate and disrupt the cellulose lattice due to size

restriction. Only the amorphous regions and crystal surfaces in the cellulose

structure can react with alkali and get removed. Thus, the inter-fibrillar

regions are expected to be less dense and less inflexible and thereby make the

fibrils more capable of rearranging by themselves (Liu & Hu et al 2008). The

break downs of the crystal structure of the cellulose fibres and the

96

reorientation of the degraded chains that are devoid of hemicellulose are quite

apparent in alkali treated fibres. Consequently, the crystallinity index of fibres

increases at lower NaOH concentration, which is confirmed by the results in

Table 4.5. The raw and treated milkweed fibres have a lower crystalline

fraction due to the lower amount of cellulose compared with the other ligno-

cellulosic fibres: 75% for sisal, 83% for cotton, 63.5% for jute, 72.4% for

ramie, 71% for flax, and 63.5-82.2% for hemp (Bledzki & Gassan 1999; Goda

et al 2006; Gassan & Bledzki 1999)

4.3.6 Influence of Chemical Treatments on Thermal Stability of

Milkweed Fibres

Thermal stability studies were carried out for milkweed fibres as

most of the natural fibres are low in thermal stability. The degradation

temperature of cellulosic fibres depends on their molecular weight, polymer

morphology and crystallinity (Rosen 1993). TGA curves of milkweed fibres

before and after chemical treatments are shown in Figure 4.7.

From the TGA curves of raw and chemical treated milkweed fibres,

three different regions were observed during thermal degradation of material.

The first phase of weight loss started from 30-110 ºC, which is related to

evaporation of water. The second major degradation occurred in the

temperature range of 180-420 ºC, which could be related to the degradation of

lignin and hemicellulose in the fibre. The last phase of weight loss occurred in

the range of 360-580 ºC w -cellulose and

other non-cellulosic components of the fibre. The findings are in agreement

with Dollimore & Holt (1973). The thermal degradation of cotton fibres

generally occurs in three phases at temperature ranges of 37-150 ºC,

225-425 ºC and 425-600 ºC respectively (Schwenker & Zuccarello 1964).

97

(a)

(b)

98

(c)

Figure 4.7 TGA and DTG Curves of milkweed fibre sample (a) Raw (b) Alkali treated (c) Dyed milkweed fibres

In all the curves, the initial weight loss due to evaporation of water

in sample were around 10%, 10.5% and 9% respectively for raw, alkali

treated and dyed fibres. The volatilization of structural water takes place at

temperatures above 100 ºC, because these molecules are strongly attached to

the cellulosic fibres due to its hydrophilic character. The first phase of

cellulose decomposition usually involves an intra-molecular reaction with the

elimination of water, which forms levoglucosan and depolymerization

reactions that lead to shorter chains (Klemm et al 2001). The amount of

moisture absorbed increased moderately with alkali treatment. This could be

explained on the basis of changes occurring in the fine structure and

morphology of milkweed fibres due to alkali treatment. The increased amount

of absorbed water might be the result of removal of hydrophobic lignin

content from the milkweed. Further, increase in hydrophilic nature of

99

cellulose content after alkali treatment and removal of waxes and other

impurities during alkali treatment improves the moisture content in the

sample.

For raw milkweed fibre, considerable weight losses were observed

from 180°C to 400°C. The raw fibre did not undergo any degradation until the

temperature reached 180°C. This temperature corresponds to the beginning

of thermal degradation (Td) which occurs due to thermal de-polymerization of

non-cellulosic materials and the main weight loss phase corresponded to the

decomposition of cellulose with a maximum decomposition temperature (Tdm)

of 400°C. The Td and Tdm values were 230°C and 435°C for alkali treated

fibres and 210°C and 420°C for dyed milkweed fibres respectively. The

weight losses were rapid in this temperature range and the raw, alkali treated

and dyed samples lost around 72.5%, 76.24% and 82.76% for raw, alkali

treated and dyed samples respectively. The thermal degradation temperature

(Td) of milkweed fibres is found to be lower compared to other cellulosic

fibres such as cotton and viscose.

By observing the Td and Tdm values, the thermal stability of alkali

treated milkweed fibres are found to be higher followed by dyed and raw

fibres. This could be due to the increase in crystalline percentage of alkali

treated fibres when compared to raw milkweed fibres. The inter-molecular

hydrogen bonds are tougher in the crystalline zones than the non-crystalline

zones and therefore require more energy to break before the decomposition

can proceed. Further, the removal of hemicellulose by the alkali treatment

makes the fibre thermally stable. The thermal stability of milkweed fibres is

also improved after dyeing. Normally, the dyes are concentrated in the non-

crystalline region of milkweed fibres. The slight improvement in thermal

stability of dyed milkweed fibre could be due to the adsorption of dyes in

non-crystalline region.

100

Further, small decreases in the weight of all samples were noticed

in the temperature range between 400°C - 700°C after which no noticeable

change in weight occurred. The small tail peak were observed in alkali treated

samples at 510 °C, which can be attributed to the release of volatile by-

products which could have formed during decomposition at earlier stage or

due to oxidative degradation of the charred residue. A certain percentage of

residues above 800°C were noticed in all samples due to charring. The DTG

of raw and treated fibres as a function of rate of weight loss (%/°C) are given

in Table 4.6.

Table 4.6 DTG analysis of milkweed fibres

Sample Temperature (°C) Rate of weight loss (%/°C)

Raw 40 0.45

300 0.8 340 1.2

Alkali Treated 60 0.05

340 0.35 400 0.95

Dyed 70 0.05

350 0.75 390 1.05

From the table it is clear that, the initial weight loss due to

evaporation of water is very rapid in case of raw milkweed fibres compared to

alkali treated and dyed fibres. The second peak is for degradation of

hemicellulose and third peak for cellulose and lignin. From the table, it is

clear that the second and third peaks which corresponds to degradation of

hemicellulose and cellulose respectively is more prominent in raw fibres

compared to alkali treated and dyed samples. Hence, it could be concluded

101

from the DTG studies that the rate thermal decomposition of alkali treated

fibres is less followed by dyed and raw milkweed fibres.

Figure 4.8 shows the DSC of raw and chemical treated fibres. In the

calorimetric study by DSC, numerous processes related to water desorption

and polymer decomposition was observed. The DSC of milkweed fibre

showed exothermic peak in the temperature range between 90-110° C in raw,

alkali treated and dyed samples, which corresponds with the evaporation of

water restrained in the fibre. From Figures 4.8 a, b and c, it is observed that

the region between 110-200°C does not reveal any exothermic or endothermic

changes indicating that the fibres were thermally stable.

(a)

102

(b)

(c)

Figure 4.8 DSC of milkweed fibre sample (a) Raw (b) Alkali treated and (c) dyed fibre

In natural cellulose fibres, lignin degrades at temperatures around

200°C while the other polysaccharide such as cellulose degrades at a higher

temperature. Therefore, the peaks which are at higher temperature above

200°C indicate the decomposition of cellulose in the fibres. Thermal

degradation in milkweed fibres starts above 200ºC with breakage of bonds

103

and formation of volatile components. Volatilization of components due to

lignin and hemicellulose decomposition represents the first endothermic peak

between 200-250°C. The first endothermic peak were observed at 206.41°C,

258.75°C and 232.96°C for raw, alkali treated and dyed milkweed fibres

respectively. Due to partial removal of lignin and hemicellulose in alkali

treated fibre as shown in Figure 4.8b the energy required in J/g to decompose

the non-cellulosic components was less compared to raw milkweed fibres.

Further, the endothermic peak was observed around 258.75 °C which is

higher compared to raw fibres indicating better thermal stability of alkali

treated fibres. With further supply of energy, thermal degradation of sample

continues to occur resulting in breakage of cellulosic chains and formation of

volatile by-products. The very strong second endothermic peak corresponding

to degradation of cellulose were noticed around 357.21°C, 373°C and

366.1°C for raw, alkali treated and dyed milkweed fibres respectively.

The water desorption regions were analyzed for raw, alkali treated

and dyes samples and are shown in Figure 4.9 a, b and c.

(a)

Figure 4.9 (Continued)

104

(b)

(c)

Figure 4.9 Analysis of moisture desorption characteristics of milkweed fibre sample by DSC (a) Raw (b) Alkali treated (c) dyed fibre

105

From the Figure, it is observed that, the raw milkweed fibres

showed the exothermic peak at 85.65°C and corresponding values for the

alkali treated and dyed fibres are 102.04°C and 90.33°C respectively.

From DSC curves it is evident that the temperature at which

moisture started to be liberated was higher for alkali-treated samples. From

the analysis of XRD of fibres, it is clear that the crystallinity of alkali treated

samples is higher than raw fibres. Therefore, the tendency to liberate absorbed

moisture upon heating will decrease, as moisture is strongly held within a

tightly packed structure, leading to a higher finished temperature. This is in

abeyance with Pejic et al (2008). In dyed fibres, the adsorption of dyes in

fibres reduced the moisture content.

4.4 CONCLUSIONS

The pergularia daemia fibre which belongs to the milkweed family

is not much studied in terms of their structure and properties. This study aims

to reveal the physical, chemical, morphological and thermal properties of this

fibre. The results showed that the physical properties of milkweed fibre

resemble that of cotton except for elongation at break and short fibre

percentage. The milkweed fibre elongation is lower and short fibre percentage

is higher compared to cotton. The milkweed fibres are finer, less dense and

yellowish in colour when compared to cotton.

Literatures reveal that 100% milkweed fibres are not directly

spinnable due to its intrinsic nature. This nature of milkweed fibres, however,

could be modified by chemical treatments. This issue had not been dealt by

research works earlier and therefore forms a main part of this work. The study

focusses on analyzing the effect of delignification and dyeing of milkweed

fibres on its structure and properties. Compared to cotton, the raw milkweed

fibres are circular and hollow in nature an attribute vital for thermal

106

insulation. The surface of raw milkweed fibre is smooth and develops

convolutions after alkali treatment. The milkweed fibre friction increases after

alkali treatment and dyeing. The crystalline percentage of milkweed fibre is

around 56% which is lesser compared to cotton fibres.

The raw milkweed fibres start degrading at around 180°C

compared to 230°C - 250°C in case of cotton. The thermal stability of raw

milkweed fibres is lower than cotton but increased significantly with alkali

treatment of milkweed fibres.