chapter 4 characterization and analysis of milkweed...
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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
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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.
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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%
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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
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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
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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.
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(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.
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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
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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
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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)
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(b)
(c)
Figure 4.5 FT-IR spectra of milkweed fibre sample (a) Raw (b) NaOH Treated and (c) Dyed
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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).
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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.
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(a)
( b)
(c)
Figure 4.6 XRD patterns of milkweed fibre sample (a) Raw fibre (b) NaOH treated fibre (c) Dyed fibre
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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
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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).
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(a)
(b)
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(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
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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.
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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
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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)
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(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
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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)
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(b)
(c)
Figure 4.9 Analysis of moisture desorption characteristics of milkweed fibre sample by DSC (a) Raw (b) Alkali treated (c) dyed fibre
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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
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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.