thermal behaviour and structural features of chemically...

Indian Journal of Fibre & Textile Research Vol. 32, September 2007, pp. 355-365

Thermal behaviour and structural features of chemically and bio-chemically modified jute substrate

Ashis Kumar Samantaa, Deepali Singheeb, Gautam Basuc

& Santosh Kumar Biswas

Institute of Jute Technology, 35 Ballygunge Circular Road, Kolkata 700 019, India

Received 23 January 2006; accepted 9 August 2006

Effects of NaOH treatment, conventional hot H2O2 bleaching, H2O2 and K2S2O8 combined room-temperature bleaching, mixed enzyme treatment and N-methylol resin finishing on thermal behaviour and structural features of jute substrate have been studied. Differential scanning calorimetric study under nitrogen cover reveals distinct peaks for thermal degradation of cellulose, hemicellulose and lignin components of chemically and bio-chemically modified jute, showing some positive or negative shifts of thermal degradation temperatures for each of the three major constituents of jute owing to alkaline / oxidative or enzymolytic degradation or resinification of the jute components. Thiourea formaldehyde (TUF)-resin treatment renders the jute substrate with maximum thermal stability. There is a measurable increase in the crystallinilty percentage for 1-5% NaOH treatment, and the same is decreased on oxidative or enzyme treatment and remains almost unaffected for AMF-resin or TUF-resin treatment. Observed chemical changes / interactions have been explained by the analysis of FTIR spectra and copper number of differently treated jute substrate. Higher copper number is observed for room-temperature bleaching than that for conventional H2O2 bleaching. Changes in the overall surface morphology of the treated fabrics have also been characterized by scanning electron microscopic study. Room-temperature bleaching followed by mixed enzyme treatment shows maximum surface cleanliness with a smooth and less hairy surface appearance. Both AMF-resin and TUF-resin treatments show a surface coverage with a resin film.

Keywords: Alkali treatment, Differential scanning calorimetry, FTIR spectroscopy, Jute, Mixed enzyme treatment, Resin finishing, Room-temperature bleaching, X-ray crystallinity

IPC Code: Int. Cl.8 D06C29/00, D06L 1 Introduction

Effects of dilute alkali (NaOH) treatment, mixed enzyme (mixture of cellulase, xylanase and pectinase) treatment, conventional hot (850C) 3% H2O2 blea-ching, room-temperature bleaching using a combi-nation of H2O2 and K2S2O8 at 300C and finishing treatments using N-methylol resins (dimethylol-dihydroxyethyleneurea, acrylamide-formaldehyde or N-methylolacrylamide and thiourea formaldehyde) on textile related properties of jute and jute-cotton union fabrics have been reported earlier.1-3 Reports of some preliminary studies4-8 on mixed enzyme treatment, ambient temperature bleaching and methylol-resin finishing of jute fibre/fabric are also available in literature. Most of these studies are related to the

corresponding changes in relevant property para-meters only. Investigations on structural features and thermal behaviour of chemically modified jute substrate are rare and sporadic. It is known from earlier reports1,5 that dil. NaOH pretreated or desized, scoured and conventional 3% H2O2 bleached jute based fabrics are more responsive to mixed enzyme action than the corresponding raw jute fabric. The recipe and treatment conditions for room-temperature (30°C) bleaching of jute and jute-cotton union fabrics have been optimized in our earlier study.2 It has also been observed3 that the application of both acrlyl-amide formaldehyde (AMF) resin using a specific dual catalyst system (K2S2O8 and MgCl2) and thiourea formaldehyde resin using MgCl2 as a catalyst are somewhat advantageous rendering reduced photo-yellowing of bleached jute on exposure to sunlight besides improvement in the crease recovery property. Thus, the above-mentioned three distinct treatments cause either limited extent of oxidative degradation or alkali/enzyme initiated hydrolytic degradation or

________________ a To whom all the correspondence should be addressed. E-mail: [email protected]

b Present address: J. D. Birla Institute, 11 Lower Rawdon Street, Kolkata 700 020, India c Present address: National Institute of Research on Jute & Allied Fibre Technology, 12 Regent Park, Kolkata 700 040, India.

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resinification of major jute constituents, which alter the overall nature and chemical composition as well as structural integrity of the major jute constituents along with some expected changes in their thermal degradation pattern. In the present work, a detailed investigation on the changes in thermal behaviour and structural features (morphology, fine structure, chemical structure and functional group pattern) of chemically and bio-chemically modified jute substrate has been carried out.

2 Materials and Methods 2.1 Materials 2.1.1 Jute Fabric

Raw jute fabric (plain weave) of decorative variety, obtained from M/s Champdany Industries, Rishra, Hooghly, having the specifications: warp thread density, 63 ends/dm; weft thread density, 59 picks/ dm; fabric area density, 260 g/m2; warp count, 195 tex; weft count, 214 tex; and fabric thickness, 0.9 mm was used for the study. After conventional desizing and scouring the area density of the fabric became 252 g/m2. After conventional (hot) H2O2 bleaching, the area density of the jute fabric became 244 g/m2.

2.1.2 Chemicals

Commercial grade sodium hydroxide pellets (assay 98%), sodium metasilicate (Na2SiO3.5H2O), potassium per-oxo-disulphate (K2S2O8), magnesium chloride (MgCl2, 5H2O), hydrogen peroxide (50% strength), ethylene diamine tetraacetic acid (EDTA), non-ionic wetting agent (Ultravon-JU) and non-ionic detergent (Nonidet P-40), sodium acetate and acetic acid, all obtained from a local supplier, were used. Stabilizer-AWNI (a non-silicate organo-phosphate stabilizer), supplied by M/s Clariant, India, and a specific mixed enzyme solution (mixture of 35 units/ml of cellulase, 96 units/ml of xylanase and 136 units/ml of pectinase), obtained from M/s Biocon India Ltd, Bangalore, were used. Acrylamide formaldehyde (AMF) resin and thiourea formaldehyde (TUF) resin

were prepared at IJT laboratory by following the standard methods as reported earlier.3 2.2 Methods 2.2.1 Selective Chemical Pretreatments and Mixed Enzyme Treatment

Dilute alkali pretreatment, desizing, scouring, conventional hot H2O2 bleaching, H2O2 and K2S2O8 combined room-temperature bleaching and mixed enzyme treatment were carried out separately using the recipes as given below:

Alkali pretreatment8 Material : Raw jute NaOH (aq.) : 1% Temperature : 30°C Time : 30 min MLR : 1:20 (w/v) Desizing9, 10 Material : Raw jute Water : Boiling Temperature : 100°C Time : 30 min MLR : 1:5 (w/v) (In laboratory jigger) Scouring9, 10 Material : Desized jute Na2CO3 : 4 gpl (2% owf) Nonidet P-40 : 1 gpl (0.5% owf) Temperature : 80°C pH : 8-9 Time : 30 min MLR : 1:5 (w/v) (In laboratory jigger) Conventional H2O2 bleaching10, 11 Material : Desized and scoured jute H2O2 : 3% (owf) Sodium metasilicate : 8% (owf) NaOH : 0.7% (owf) EDTA : 0.05% (owf) Ultravon-JU : 0.5% (owf) Temperature : 85°C pH : 10.5-11.0 Time : 2h MLR : 1:5 (w/v) (In laboratory jigger) Room-temperature bleaching2 Material : Desized and scoured jute H2O2 : 3% (owf) K2S2O8 : 0.75% (owf) Sodium metasilicate : 8% (owf) NaOH : 2.5% (owf) EDTA : 0.05% (owf) Ultravon-JU : 0.5% (owf) Temperature : 30°C pH : 9.8-10.0 Time : 6h MLR : 1:20 (In standing exhaust bath and pad-roll technique) Mixed enzyme treatment1, 4 Materials : Desized, scoured and conventional

H2O2 bleached jute / NaOH treated jute/H2O2 + K2S2O8 combined room-temperature bleached jute.

Mixed enzyme : 4% (35 units/ml cellulose + 96units/ml xylanase + 136 units/mlpectinase)

Buffer solution : Sodium acetate + acetic acid

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(1/20th part of total volume ofliquor)

Temperature : 55°C (raised to 90°C for 15 min after treatment to deactivateenzyme)

pH : 4.8-5.0 Time : 2h MLR : 1:20 (In launderometer with rotating beakers at 40 rpm using 5 nossmall steel balls for agitation)

In each case, the treated fabrics were neutralized and washed under running water and dried in air. 2.2.2 Resin Finishing of Jute Fabric

Raw and bleached jute fabric samples were impregnated3 with 8% (owf) aqueous solution of AMF and TUF resins containing 2% (owf) MgCl2 as catalyst using a 2-bowl padding mangle (by two-dip and two-nip sequence), adjusted to 100% wet pick-up in each case. The resin impregnated jute fabrics were further subjected to drying at 100oC for 10 min, followed by curing at 140oC for 5 min in a laboratory hot-air curing unit for each sample. However, in case of AMF-resin application, the fabric was initially pre-soaked with 0.5% (owf) K2S2O8 solution3,12 prior to resin application. K2S2O8 initiate vinyl radical poly-merization utilizing the vinylic double bond present in acrylamide moieties of AMF-resin. MgCl2 facilitates alkylol-ether crosslink formation through acidic poly-condensation reaction between AMF-resin and -OH group of jute cellulose/hemicellulose. The proposed reaction mechanism for AMF-resin finishing of jute using K2S2O8 and MgCl2 as a dual catalyst system has been reported in an earlier publication.12

2.2.3 Determination of X-Ray Crystallinity

The wide-angle X-ray diffraction patterns for jute fibre samples taken out from untreated and treated jute fabric were obtained using a Philips X-ray dif-fractometer (Model 1710) by rotation powder method.13 The radial scanning of finely cut fibre samples was taken with nickel filtered CuKα radiation (1.54 Å) at an operating voltage of 40 kV and a filament current of 30 mA. The crystallinity percentage was calculated from the plot of integral intensity (in arbitrary unit) vs. diffraction angle (2θ) varying from 10° to 33°. Observed X-ray crystallinity data were finally corrected taking into account the associated weight loss or gain in the jute substrate in order to eliminate the consequent apparent change in X-ray crystallinity percentage owing to associated

weight loss or gain only. This was done to understand the true increase/decrease in crystallinity percentage under the influence of these treatments.

2.2.4 Determination of Weight Loss or Gain and Moisture Regain

Weight loss of the modified jute fabric after the selective treatments was determined by the usual oven dry weight method14, taking bone dry weight of the samples before and after the treatments and expres-sing the results as a percentage of initial bone dry weight of the material taken.

The moisture regain of selected oven dry jute fibre samples taken out from the jute fabric was determined according to the ASTM-D2654-76 method15 under standard atmospheric conditions of 65±2% RH and 27±2°C, after allowing equilibrium moisture absorp-tion for 48 h in a desiccator set with saturated aqueous solution of NaNO3.

2.2.5 Determination of Copper Number

Copper number of selective jute fibres taken out from untreated and treated jute fabric was determined following standard Schwalby-Braidy method.16 2.2.6 Scanning Electron Microscopic Study

Surface morphology of untreated and treated jute fabrics and bleached jute fibres post-treated with AMF-resin and TUF-resin was examined using a scanning electron microscope (Model Jeol-JSM-5200). The relevant jute fabric / fibre samples were mounted on a specimen stub with double sided adhesive tape and then subjected to coating with gold-palladium alloy using a sputter coater to avoid charging of the specimen.17 The observations were made at an operating voltage of 20 kV and magnification of ×35 for fabric samples and ×1000 for fibre samples.

2.2.7 Differential Scanning Colorimetric and Fourier Transform Infrared Spectroscopic Study Differential Scanning Colorimetry (DSC)

The DSC thermograms of jute not only give an indication of its thermal behaviour, but also give a clear reflection regarding the degree of chemical changes/interaction of the major constituents of jute, altering their relative thermal resistance. DSC study of untreated and treated jute fibre samples (finely crushed) after being taken out from the corresponding untreated and treated jute fabrics was carried out following usual procedure18 on a Shimadzu Differen-tial Scanning Calorimeter (Model DSC-50) under


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flowing nitrogen (flow rate 50 cm3/min) at a heating rate of 10°C/min, using a pre-fixed sample weight of exactly 2 mg over a temperature range from 30°C (ambient) to 500°C.

Fourier Transform Infrared Spectroscopy (FTIR)

Selected jute fibre (finely crushed) samples (3 mg) taken out from untreated and treated fabrics were examined in a double beam FTIR spectrophotometer (BOMEM, MB 104) using KBr disc technique.12,19

The fibre samples taken for both DSC and FTIR studies were initially washed throughly in running water followed by washing in a mixture of 1:1 alcohol-benzene and then in 100% acetone for the removal of all impurities. These samples were further washed in distilled water and dried in air. The washed and dried fibre samples were finally crushed to fine powder before being taken for both the DSC and FTIR studies.

3 Results and Discussion 3.1 Study of Surface Morphology

A comparison of fabric surface appearance of raw and differently treated jute fabrics, as revealed from relevant scanning electron micrographs (Figs 1a-e), indicate that both conventional bleaching and room-temperature bleaching with H2O2 + K2S2O8 make the fibre assembly on the fabric surface more entangled and hairy [Figs 1a, 1b and 1d as compared to Fig. 1a], while 4% mixed enzyme treatment subsequent to both conventional H2O2 bleaching and room-temperature bleaching with H2O2+K2S2O8 makes the fabric surface much smoother, clearly showing some removal/ reduction in surface fuzz/entanglement, thereby appreciating a relatively clean and smooth surface appearance [Figs 1c and 1e].

It is revealed from Figs 1b and 1d that room-temperature H2O2+K2S2O8 bleaching causes less surface entanglement showing relatively smoother but same level of hairy surface with less brighter appearance as compared to that obtained by conven-tional H2O2 bleaching of the same fabric. Less surface entanglement obtained in the case of room-tempera-ture bleaching may be due to the effect of slow (much controlled) and milder oxidative action of H2O2 and

K2S2O8 at 30°C. However, the longer period of treatment under dual oxidizers causes relatively higher oxidative degradation and chain scission of cellulose and hemicellulose in jute, as revealed by higher copper number (Table 1) in comparison to that observed by conventional hot H2O2 bleaching,

showing less oxidative degradation of cellulosic / hemicellulosic chains but higher surface roughening and entanglement of the surface fibres. Comparison of Figs 1c and 1e reveals that the cleanliness and surface smoothness are relatively more predominant in case of room-temperature bleached jute fabric as compared to that obtained by conventional H2O2 bleached jute fabric, when both the samples are subjected to mixed enzyme treatment under specific treatment conditions.

A comparison of Figs 1a, 1f and 1g respectively for control scoured jute fabric, NaOH treated raw jute fabric and NaOH treated jute fabric subsequently treated with mixed enzyme reveals that the initial NaOH treatment makes the jute yarn more fluffy (bulked) and the apparent cover factor of the fabric is much improved. The fabric structure thus appears more compact, which is subsequently loosened to some extent after mixed enzyme treatment on the same.

Comparison of Figs 1b, 1h and 1j reveals that both the AMF-resin and TUF-resin treatments make the surface fibres of the resin treated jute fabric apparently covered to a certain degree with the bound resin; the resultant film and the same is more prominent in case of AMF-resin treatment than that of TUF-resin treatment. This effect is more clearly understood from magnified (×1000) relevant micro-graphs (Figs 1i and 1k) for AMF-resin and TUF-resin treated bleached jute fibres taken out from the correspondingly treated fabrics.

3.2 X-Ray Crystallinity, Moisture Regain and Copper Number

The changes in the copper number, moisture regain and X-ray crystallinity percentages along with the associated weight loss/gain owing to the selective treatments of jute fabrics are shown in Table 1. Due to some loss of intercellular encrusting materials from jute particularly from non-crystalline zone by alkali / enzyme/oxidative treatments, there is an improvement in the degree of moisture absorbency due to expected increase in pore volume. Among all these treatments, H2O2 + K2S2O8 combined room-temperature bleaching process followed by mixed enzyme treatment shows highest moisture regain value. While for both AMF-resin and TUF-resin treatments, there is measurable weight gain due to anchoring of the resins by crosslink formation between −OH groups of cellulose and methylol groups of the resins. For AMF-resin, there is a marginal increase or retention of moisture regain level owing to the hydrophilic nature of the


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polyacrylamide or poly-AMF film formed by K2S2O8 initiation, though the moisture regain is reduced marginally due to alkylol-ether crosslink formation. That is why, for the application of TUF-resin, there is a small decrease in the moisture regain value.

The observed and corrected X-ray crystallinity data (Table 1) also reveal that the degree of crystallinity gets substantially increased in few cases and it also gets somewhat reduced in other cases when compared against the corresponding X-ray crystallinity data for

desized and scoured control jute sample. It is observed that the crystallinity increases in case of treatment with NaOH solution and sequential treat-ment with NaOH followed by mixed enzyme treatment. This is mainly due to some loss of jute hemicellulose and other minor constituents from the non-crystalline part as well as the additional effect of structural re-orientation and stress redistribution of the molecular chains by the plasticizing and swelling action of the alkali during the treatment. On the other

Fig. 1 — SEM photographs showing surface morphology of (a) control scoured jute fabric, (b) conventional hot H2O2 bleached jute fabric, (c) jute fabric subjected to hot H2O2 bleaching followed by mixed enzyme treatment, (d) room-temperature H2O + K2S2O8 bleached jute fabric, (e) room-temperature H2O + K2S2O8 bleached jute fabric further subjected to mixed enzyme treatment, (f) jute fabric subjected to NaOH treatment, (g) jute fabric treated with NaOH followed by mixed enzyme treatment, (h) conventional H2O2 bleached jute fibre post-treated with AMF-resin, (i) conventional H2O2 bleached jute fibre post-treated with AMF-resin (enlarged view) and (j) conventional H2O2 bleached jute fabric post-treated with TUF-resin and (k) conventional H2O2 bleached jute fibre post-treated with TUF-resin (enlarged view)


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hand, the crystallinity is reduced marginally in case of conventional H2O2 bleaching, conventional H2O2 bleaching treatment followed by mixed enzyme treatment, room-temperature H2O2+K2S2O8 combined bleaching as well as sequential room-temperature H2O2 + K2S2O8 combined bleaching followed by mixed enzyme treatment. This reduction in crystal-lanity is relatively higher in the last two cases, involving room-temperature bleaching possibly due to longer treatment time (6 h) and use of K2S2O8 as peroxide booster and second oxidizer.

Longer duration (6 h) for room-temperature H2O2 + K2S2O8 combined bleaching produces relatively higher amounts of aldehyde groups as indicated by the observed higher value of copper number (Table 1) as compared to that for conventional H2O2 bleaching. The same observation was also made in our earlier work.2

Both the AMF-resin and TUF-resin treatments of jute fabric/fibre samples exhibit an apparent reduction in overall per cent crystallinity data as compared to those for desized and scoured control jute and conventionally H2O2 bleached jute. But, after re-calculation of crystallinity percentage on the basis of weight of equivalent amount of total jute content (i.e. weight of jute + resin for eliminating the effect of the resin present in the treated jute), there is hardly any difference in per cent crystallinity between resin-treated sample and conventional H2O2 bleached sample. This observation implies that the fine or crystalline structure of bleached jute virtually remains unaffected after both AMF-resin and TUF resin post-treatment and the bound resin overwhelmingly finds location in the non-crystalline zone of bleached jute substrate.

Table 1—Weight loss, copper number, moisture regain and X-ray crystallinity data for untreated and differently treated jute substrate

Expt. Treatment Weight Degree of X-ray crystallinity, % Copper Moisture No. loss (-) or gain (+) Observed a Corrected b number regain, % 1 Nil (raw jute fabric) ---- 58.7 58.7 2.06 13.00 2 Desized and scoured jute (control) (-) 3.20 61.2 59.2 2.40 13.50 3 1% NaOH treatment (-) 3.50 63.7 61.5 1.80 13.70 4 Conventional H2O2 bleaching (-) 6.00 59.5 55.9 2.72 14.20 5 Room-temperature H2O2 + K2S2O8

combined bleaching (-) 4.20 57.0 54.6 3.10 14.60

6 Sequential treatment with 1% NaOH soln. followed by treatment with mixed enzyme

(-) 6.90 64.8 60.3 2.40 15.60

7 Conventional H2O2 bleaching followed

by mixed enzyme treatment (-) 8.60 59.5 54.3 3.20 15.90

8 Room-temperature H2O2 + K2S2O8 combined bleaching followed by mixed enzyme treatment

(-) 7.00 56.5 52.5 3.60 16.50

9 Conventional bleached jute pre-soaked with 0.5% K2S2O8 and treated with 8% AMF-resin and 2% MgCl2 by pad-dry-cure (1400C for 5 min)

(-) 6.00 (+) 6.42

[(+) 0.42]d

52.6 52.4 (56.0) c

2.96 15.10

10 Conventional bleached jute treated with 8% TUF-resin and 2% MgCl2 by pad-dry-cure (1400C for 5 min)

(-) 6.00 (+) 6.12

[(+) 0.12] d

52.7 52.6 (55.9) c

2.88 12.80

a Based on initial bone dry weight of jute sample in each case. b Corrected after accounting for the weight loss or gain of jute due to corresponding treatments. c Apparent crystallinity (%) on the basis of total jute content as equivalent to the total weight of resin-treated jute for both AMF-resin and TUF-resin. d Combined effect of weight loss and gain indicating net weight gain.


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3.3 Thermal Stability

Differential scanning calorimetric (DSC) thermo-grams for untreated and differentially treated jute fibres taken out from corresponding untreated and treated jute fabrics have been investigated (Fig. 2). Figure 2a shows two endothermic peaks at 78°C and 364°C and two exothermic peaks at 293°C and 425°C. The relatively low-temperature endothermic peak at 78°C is attributed to the usual evaporation of absorbed moisture from hygroscopic jute fibre.12,18,20,21 A weak broad exotherm over the range of 250° - 320°C, showing a broader hump or small peak at 293°C, is attributed to thermal degradation of the hemicellulose fraction12,18,20,21 of jute. The relatively sharp endotherm showing a sharp endothermic peak at 364°C is attributed to thermal degradation of the major cellulose component12,18,20,21 of untreated jute. The prominent exotherm at a relatively higher tempe-rature showing a broader peak at 425°C is attributed to the exothermic decomposition of the lignin component12,18,20,21 of untreated jute fibre. Thus, among the three major constituents of jute, hemi-cellulose is least thermal resistant and lignin is most thermal resistant, while cellulose is placed in between the two.

DSC thermograms (Figs 2b, 2c and 2d) for selective pretreatments of jute with dilute alkali (NaOH) and oxidising agents (H2O2 and mixture of H2O2+K2S2O8), by and large, retain the similar thermal characteristics of the untreated raw jute fibres, but show some minor to major shifts in the position of the exothermic and endothermic peaks even showing a duplet nature sometimes instead of the corresponding singlet peaks. These shifts/change in the nature of peaks are believed to be due to the consequent effects of different degree of alkaline hydrolysis/oxidative cleavage of cellulose, hemi-cellulose and lignin chains and their interunit linkages even with possible segregation of low and high molecular weight component and structural re-arrangement associated with partial removal of major and minor jute constituents under different conditions of treatments.

The appearance of duplet nature of peaks, showing two different temperatures for thermal degradation of any one jute constituent instead of showing usual singlet peak after selective treatments, is believed to be due to a relatively better separation or segregation of relevant jute constituent into two types, viz. (i) easily accessible part or low molecular weight

fragment showing early thermal degradation and (ii) hardly accessible part or relatively higher molecular weight fragment showing higher temperature of thermal degradation.

Fig. 2 — DSC thermograms of (a) control scoured jute, (b) conventional H2O2 bleached jute, (c) room-temperature H2O2 + K2S2O8 bleached jute, (d) jute subjected to NaOH treatment, (e) conventional H2O2 bleached jute further subjected to mixed enzyme treatment, (f) room-temperature H2O2 + K2S2O8 bleached jute further subjected to mixed enzyme treatment, (g) NaOH treatment followed by mixed enzyme treatment, (h) conventional H2O2 bleached jute post-treated jute with AMF-resin and (i) conventional H2O2 bleached jute post-treated jute with TUF-resin

Comparison of thermograms for control scoured jute (Fig. 2a), conventional H2O2 bleached jute (Fig. 2b), AMF-resin post-treated jute after conventional H2O2 bleaching (Fig. 2h) and TUF-resin post-treated jute after conventional H2O2 bleaching (Fig. 2i) reveals that the thermal stability of all the three main constituents of jute (hemicellulose, cellulose and lignin) is increased after both AMF-resin and TUF- resin post-treatments as compared to those for both control scoured jute and jute subjected to conventional H2O2 bleaching; the degree of improvement in


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thermal stability being maximum for the hemi-cellulose component, low to moderate for lignin and cellulose component, thus indicating the preferred location of more resin binding to the hemicellulose component of jute, which is mostly available in the non-crystalline zone of jute fibre. The increase in the thermal stability for both AMF-resin and TUF-resin treatments on conventional H2O2 bleached jute is due to the increased molecular weight of the corres-ponding jute components by additional anchorage of resin moities on all the three major constituents of jute along with formation of some crosslinks. However, among the two resin systems (AMF and TUF), the thermal stability of the lignin component is relatively higher for TUF-resin treated jute, possibly due to

additional fire retardancy character22 of thiourea and possible formation of lignin-thiourea linkage, utilizing the unsaturation of lignin and higher co-ordinating power of sulphur present in TUF-resin. Moreover, AMF-resin and TUF-resin post-treated jute samples (Figs 2h and 2i) show further unification of duplets (formed during initial oxidative treatment) to a singlet peak of higher thermal stability for each of the main constituent of jute, where the chains of both low molecular weight and high fractions are re-linked through crosslinks formed or resinification by both AMF-resin and TUF-resin.

The summary of the changes in the nature and position of DSC peaks (Figs 2a-i) with minor and major shifts of thermal degradation temperatures for

Table 2—Observed shifts of endothermic and exothermic peaks showing extent of ± shifts in DSC peaks in the treated jute samples

Expt. DSC- Nature and position of DSC peak for major jute constituents No. thermogram Moisture Hemicellulose Cellulose fraction Lignin fraction

identity (Fig. 2) evaporation fraction

2 (a) Single endotherm at 78°C

Single exotherm at 293°C

Single endotherm at 364°C

Single exotherm at 425°C

3 (b) Single endotherm at

78°C (±0°C) Doublet exotherm at

284°C and 312°C (−9°C and +19°C)

Doublet endotherm at 346°C and 364°C (−18°C and ±0°C)

Doublet exotherm at 396°C and 475°C

(−29°C and +50°C)

4 (c ) Single endotherm at 78°C (±0°C)

Doublet exotherm at 289°C and 312°C (−4°C and +19°C)

Doublet endotherm at 340°C and 364°C (−24°C and ±0°C)


(−29°C and +25°C)

5 (d) Single endotherm at 79°C (+1°C)

Single exotherm at 312°C (+19°C)

Single endotherm at 346°C (−18°C)


(−29°C and +25°C)

6 (e) Single endotherm at 63°C (−15°C)

Single exotherm at 290°C (−3°C)

Doublet endotherm at 332°C and 378°C

(−32°C and +14°C)

Doublet exotherm at 388°C and 425°C (−37°C and ±0°C)

7 (f) Single endotherm at

77°C (−1°C) Single exotherm at

289°C (−4°C) Doublet endotherm at

327°C and 373°C (−37°C and +9°C)

Doublet exotherm at 396°C and 425°C (−29°C and ±0°C)

8 (g) Single endotherm at

64°C (−14°C) Single exotherm at 302°C and 348°C (+9°C and +55°C)

Doublet endotherm at 367°C and 384°C (+3°C and +2°C)


(−29°C and +50°C)

9 (h) Single endotherm at 75°C (−3°C)

Single endotherm at 347°C (+54°C)

Single endotherm at 373°C (+9°C)

Single exotherm at 465°C (+40°C)

10 (i) Single endotherm at

68°C (−10°C) Single exotherm at

347°C (+54°C) Single endotherm at

374°C (+10°C) Single exotherm at

475°C (+50°C)

Values in parentheses indicate the minor/major shift (I) of position of peak values in DSC thermograms as compared to control scoured jute.


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each constituents of differently treated jute substrate is shown in Table 2.

3.4 FTIR Spectroscopic Study FTIR spectra of raw (untreated), desized & scoured

(control), and differently treated jute are shown in Fig. 3. Absorption peaks corresponding to 668 cm-1 (−OH out of plane bending), 897 cm-1 (β-glycosidic linkage), 1210 cm-1 (−C−O−C stretching of side substituent of xylan), 1245-1250 cm-1 (−C−O−C and −C=O stretching in xylan side substituent and lignin aromatic C=O stretching), 1335 cm-1 (−OH in plane bending), a number of milder peaks at 1376-1460 cm-1 (−CH, −CH2 and −CH3 bending), 1508 cm-1 (lignin aromatic ring vibration and stretching), 1540-1550 cm-1 (C=C stretching in lignin olefinic units), 1630 cm-1 ( C=O stretching of aldehyde group), 1650-1655 cm-1 (H−O−H bending of absorbed water and for lignin C−H deformation), 1735 cm-1 (C=O stretching of ester group), 2143 cm-1 (O−H stretching of absorbed moisture), 2340-2365 cm-1 (C−H stretching in polysaccharide chains), and 2905-2920 cm-1 (C−H stretching vibrations of aliphatic methylene groups) are common to raw (untreated) jute12,23-25 and differently treated jute fibres. Conventional H2O2 bleached oxy-jute (Fig. 3b), room-temperature H2O2 + K2S2O8 combined bleached oxy-jute (Fig. 3c) and conventional hot H2O2 bleached jute further subjected to mixed enzyme treatment (Fig. 3d), by and large, retain similar characteristics in their FTIR spectra as that obtained for the raw (untreated) jute12, 23, thereby showing only minor changes in chemical functional group pattern by the said oxidative (H2O2) and enzyme treatment, leading to minor decrease / increase or weakening/strengthening of some FTIR peaks/bands. The changes / weakening / strengthening of band intensity or appearance of new peaks / bonds in FTIR spectra of differently treated jute are summarized in Table 3.

Fig. 3 — FTIR- spectra of (a) control scoured jute, (b) conven-tional H2O2 bleached jute, (c) low-temperature H2O2 + K2S2O8 bleached jute, (d) conventional H2O2 bleached jute further subjected to mixed enzyme treatment, (e) conventional H2O2 bleached jute post-treated with AMF-resin and (f) conventional H2O2 bleached jute post-treated with TUF-resin.

Table 3 —Changes in band intensity or appearance of additional peaks in FTIR spectra of scoured, differently bleached and

mixed enzyme and resin treated jute (Fig. 3) Change in functional group pattern23-26 and its reason Expt

No. Position of bands, cm-1

Nature of bands and corresponding changes

2 & 3 1210 Small additional band −COO stretch vibration of carboxylate for saponification of ester groups 1735, 1247 Minor reduction in

intensity and size Loss of some hemicellulose with carboxylate substituents

865 Shoulder appeared Some loss of lignin fraction 4 591, 630,

661, 697 Doublet arising out from 608 and 668 cm-1 peaks

Influence of additional oxidative action of persulphate, altering −OH out-of-plane bending of hydroxyl groups present in jute

Contd


364

Table 3 —Changes in band intensity or appearance of additional peaks in FTIR spectra of scoured, differently bleached and mixed enzyme and resin treated jute (Fig. 3)—Contd

Expt No.

Position of bands, cm-1

Nature of bands and corresponding changes

Change in functional group pattern23-26 and its reason

1560 New small peak Increased carboxylate anion stretching vibration due to inter-unit linkage 1715 Very small sharp peak Indicating quinone formation in jute lignin27 1735, 1830,

1867 Reduced band intensity. Additional duplet peak

Higher saponification of the ester groups, partial larger shift of 1630 and 1735 cm−1 bands due to formation of some aldehyde moieties

865 Shoulder Appeared Marginal loss of lignin fraction 897 Weakening of band size Cleavage of β-glycosidic linkage of cellulose and hemicellulose by enzymes 1210, 1247 Reduction in band size Partial removal of some hemicellulose or xylan with aldehyde / acid /

carboxylate side substituents26 1376 Weakening of band size Minor removal of hemi-lignin fraction 1460 Reduced peak intensity Part removal of some hemicellulose rupturing, some interunit linkages 1560 Small new peak Increased carboxylate anion stretching for breakage of some inter-unit linkages 1596, 1655 Reduction in band size

and sharpening of peak Removal of small part of gluco-lignin

1685-1690 Appearance of medium strong peak and shoulder

Generation of more −CHO groups through cleavage of β-glycosidic linkage of cellulose or hemicellulose by enzyme action

1735 Reduced band intensity Decrease in carboxylate anion due to partial removal of hemicellulose

6

1840-1870 Additional doublet due to additional

Larger shift of 1630 and 1735 cm-1 bands due to formation of more and more aldehyde moieties generated by oxidative/ enzymatic degradative action on jute.

591, 630 Additional small peaks -OH out-of-plane bending interaction due to reaction of AMF-resin moieties with some –OH group of jute-cellulose and hemicellulose

970–955 A pair of small bands −C−H bending of residual vinyl group 24, 25 of AMF-resin in modified jute 1520-1560, 1650, 1690

Small and sharp bands N−H deformation and C−N stretch-vibration of primary amide from AMF

1715 Small sharp peak Quinone structure formation on jute lignin by oxidation 1840, 1870 Very weak doublet peaks Larger shift in the band intensity at 1735 and 1650 cm−1 for ester and aldehyde

groups of hemicellulose, after AMF-resin finish with K2S2O8 2400 A broader sharp band Overlapping of bands at 2355 and 2365 cm−1 due to −C−H− stretching of

polysaccharides and −C=C− stretch-vibration of residual vinyl units of AMF

9

2855 Additional small band Additional C−H stretching of AMF-resin moieties (coupled with the −C−H stretching of jute constituents appearing at 2905– 2920 cm−1) 12

1110 Weakened band intensity C=S stretching vibrations of thiourea formaldehyde 10 1130, 1300 Broader small peaks Associated C-N vibration from associated AMF resin moieties

4 Conclusions

4.1 Room-temperature bleaching with H2O2+ K2S2O8 followed by mixed enzyme treatment renders maximum cleanliness, least hairiness and smooth surface appearance to the fibre/fabric surface.

4.2 Although weight loss is relatively lower for room-temperature H2O2+K2S2O8 combined bleaching than that for conventional H2O2 bleaching, the former treatment results in a higher copper number, thereby showing a relatively more hydrolytic/oxidative damage due to additional oxidative action of K2S2O8 and also for higher duration of treatment time. This also shows relatively higher increase in moisture

regain. FTIR-spectroscopic analysis confirms some of the postulated chemical changes, attributing the observed changes in the functional group patterns.

4.3 There is a measurable increase in the crystal-linity percentage for NaOH (1-5%) treatment although a decrease is observed in the crystallinity for both room-temperature H2O2+K2S2O8 combined bleaching and conventional H2O2 bleaching followed by mixed enzyme treatment. Both AMF-resin and TUF-resin treated jute apparently show a reduction in crystallinity percentage, but on further in-depth analysis, it is understood that the resin crosslinks are mostly located in the non-crystalline zone and does


365

not affect the crystallinity percentage, when the same is re-calculated on the basis of weight of equivalent jute content only

4.4 In most of the cases of alkali/oxidative/ enzymolytic treatments, each of the major three jute constituents (cellulose, hemicellulose and lignin) is segreggated into two fractions of low and high molecular weight components and show duplet nature of thermal degradation peaks with some minor / major shifts, reducing their thermal stability in case of lower molecular weight fragment and exhibiting a relatively higher thermal stability for higher molecular weight fragment.

4.5 Both AMF-resin and TUF-resin post-treat-ments on conventional H2O2 bleached jute show an increase in thermal stability of each major consti-tuents of jute (which is maximum for hemicellulose), thereby evidencing the unification of the low and high molecular weight fragments of jute constituents through crosslinking to give again singlet nature of thermal degradation peak at relatively higher tempera-tures for each major constituents of resin treated jute. However, TUF-resin treatment shows a relatively higher thermal stability for the lignin fraction as compared to AMF-resin treatment.

Acknowledgement

The authors express their sincere thanks to Prof. Prabir Ray, Principal, Institute of Jute Technology (IJT), Kolkata for providing all facility to carry out the work at IJT. They are also thankful to Dr. S K Kundu of NIRJAFT, Kolkata and Dr. R Bhar of Department of Instrumentation Science, Jadavpur University, Kolkata for necessary help in carrying out X-ray crystallinity study and scanning electron micro-graphic studies respectively. One of the authors (DS) is thankful to the then Principal, J D Birla Institute, Kolkata for her support to carry out this work. One of the authors (GB) is thankful to the Director, NIRJAFT, Kolkata for granting study leave. Both AKS and SKB of IJT are also thankful to All India Council for Technical Education (AICTE), Govt. of India, for the grant-in-aid received for this RPS Project (F No. 8022/RID/NPROJ/RPS-33/2003-04).

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