Improvement in brightness and fineness of jute fibre by treatment with EDT A and polysaccharide-degrading enzymes

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1 Indian Journal of Fibre & Textile Research Vol. 16, June 1991, pp Improvement in brightness and fineness of jute fibre by treatment with EDT A and polysaccharide-degrading enzymes S K Chakrabarti, B S Ghosh, A B Kundu & B L Gho&h Biology Division, Indian Jute Industries' Research Association, 17 Taratola Road, Calcutta , India Received 15 June 1990;accepted 24 September 1990 The brightness and fineness of the lignocellulosic jute fibre have been improved by 5-8% and 6-7% respectively by treatment with I mm EDT A at 30 C for 1h. The improvement in brightness has been found to be due to the loss of tannin which is present in fibre as insoluble coloured complexes with transition metal ions whereas the improvement in fineness has been attributed to the loss of pectic substances and calcium and magnesium ions. Further increase in fineness has been achieved by applying a mixed enzyme preparation containing cellulase, xylanase and pectinase on EDT A-treated fibre. Step-wise treatment with EDT A followed by enzyme has been found to be more effective than their combined application on fibre as pretreatment of fibre with EDT A removes a portion of tannin which inhibits the action of enzymes. Keywords: Brightness, EDT A, Enzyme, Fibre fineness,. Jute fibre, Metal ion, Pectin, Tannin 1 Introduction Jute is a lignocellulosic fibre extracted from the stem of the plant Corchorus capsularis and C. olitorius. The brightness and fineness are the two important parametersl which govern its quality. The fibres of commerce are never uniform and vary widely in physical properties. For instance, the brightness of jute is dependent on its colour which ranges from golden through creamy white to grey and dark grey shades. While the golden and creamy white fibres are widely consumed in industry the grey fibres have found only restricted use because of their dull appearance. Similarly, the jute fibres differ widely in fineness since the spinnable unit injute is a filament2 composed of superimposablc cells of varying length, width and maturity. These cells are cemented together by intracellular pectic substances which form a layer of middle lamella between the cells. The fineness of each filament depends largely on the number of cells and also on its maturity. Fine fibres are easy to spin and are required for making value added products. Attempts have been made to improve such physical properties of jute fibre by using various kinds of treatments. Washing with mineral acid or oxalic acid3.4 was suggested to improve brightness by removing dark colour of jute, while extracellular fungal enzymes5-7 containing cellulase, xylanase and pectinase are now used for improving the fineness. and softness of fibre. It is obvious that any treatment which can improve the brightness and fineness of fibre is of interest provided the procedure is inexpensive and easy to operate in industry. This paper shows how the raw jute fibre could be improved with reference to fineness and brightness by treatment with the chelating agent like EDT A. The results have also shown that the fineness of EDT A-treated fibre can be improved further by treatment with polysaccharide-degrading enzymes. The reasons related to such improvement have been examined and discussed. 2 Materials and Methods 2.1 Materials Two types of jute fibre (golden and grey) of C. olitorius and one type (white) of C. capsularis were used. Samples were taken from the same lot of fibre for various experiments. 2.2 EDTA Treatment 100 g of fibre was immersed in 300 ml of I mm EDT A at 30 C for 1 h and then washed with distilled water. Control samples were treated similarly and air-dried. 2.3 Brightness Index It is a measure of reflected light from fibre by a photovolt reflection meter (Photovolt Corporation, model No. 670, New York). The fibre samples were 154

2 CHAKRABARTI et al.: BRIGHTNESS AND FINENESS OF JUTE FIBRE homogenized in a power driven mixer. Fibre pellets of 5 cm diameter (weighing 2 g each) were prepared with the help of a hydraulic press at a fixed pressure. The tristimulus green reflectance was measured on both the sides of 5 such pellets for each sample and compared against the reflectance of freshly prepared magnesium oxide deposition. 2.4 Fineness. Fibre fineness was measured following the method of Bandyopadhyay et af.8. A split portion (l cm in length) of fibres was taken and the filaments were separated under microscope and weighed after conditioning (65% RH; 25 C) in a chamber for seven days. The fibre fineness was measured in terms of tex. 2.5 Tenacity Fibre tenacity was determined as per the method laid down in the Indian standard specifications9 and expressed in g/tex. 2.6 Metal Ions 20 g of dried fibre was kept at 600 Cfor 8 h in a muffle furnace. The ash obtained was weighed and a portion (0.1 g) of it was digested in a water bath (90 C)with 2 N HCI by repeated addition of water and finally evaporated to dryness. The residue was dissolved in water (100 ml) and metal ions were measured by an atomic absorption spectrophotometer (Varian AA-575, USA) against appropriate standards. 2.7 Pectin and Tanni~ The pectin content of fibre was estimated gravimetrically after isolation by ammonium oxalate following the method ofsaha et a/.10 Tannin content was determined aft~r extraction with acidified acetone by the method of Ghosh et a/.' J. 2.8 Enzyme Preparation An ei)zyme preparation was obtained through solid state fermentations of wheat bran by Aspergillus terreus. The aqueous extract (20% w/v) of enzyme was dialyzed against 0.01 M acetate buffer ph 4.8, concentrated and then precipitated \\': It cold ethanol (200% v/v). The protein obtained after centrifugation was dissolved in 100 ml of the above buffer. This preparation has the following activities per ml-i:ellulase12, 0.5 units; xylanasej3, 0.28 units; and pectinase1t, 30 units. 2.9 Treatment with Enzyme Jute fibre (5 g, Wcm in length) was treated with 25 ml of above enzyme solution containing I mm EDT A at 30 C for I h and then washed and dried. In some experiments, fibre samples were treated separately by EDT A or enzymes, keeping all other conditions identical. Appropriate control samples were also prepared and dried Enzyme Acti,ity 011 Fibre The action of enzymes on fibre was assayed by measuring1 Sreducing sugars, after incubating,50mg of dry jute fibre (I cm long) in I ml of 0.05' M citrate buffer ph 4.8 and 0.5 ml of enzyme solution at 50 C for I h. In some experiments, tannin (isolated from jute) or EDTA was added to the reaction system. Results were obtained after comparing with various appropriate control samples. 3 Results and Discussion 3.1 Impro'ement in Brightness The main constituent of jute are cellulose (58-63%), hemicellul~se (21-24%), lignin (12-14%) and pectin ( %). Besides, it contains ioris16 of metals like Fe, Cr, Cu, Mn, Ca, Mg and varying amounts of tannin ( %). Noddar et a/.3 showed evidences that dark grey colour of jute originates by the interaction of the tannin component of fibre with iron, while Sengupta et au suggested that a fraction of lignin, possessing tannin like properties, produced the dark colour derivatives with iron which could be removed~ by simple washing with dilute mineral acid or oxalic acid. Washing with acids, however, is not preferred since it causes loss' in strength of fibre and corrosion of textile machineries. Treatment with chelating agent like EDT A eliminates the aboye difficulties and has been found to improve the brightness of all the three types of jute fibres tested without any loss in strength (Table I). Fig. I presents a visual appearance of treated grey fibre along with untreated control. The improved brightness of treated fibre can be attributed to the loss of 40-67% of tannin (Table 2), which, in all probability, is present as insoluble metal complexes in fibre; treatment with EDT A chelated out the metal ions from tannin complex rendering thereby a portion of tannin to be dissolved and removed: That the removal of tannin is accomplished by loss of metal ions is evident from Table 2. which shows a decrease in transition metal ion contents in all the treatments. Table 2 also shows that the % loss of iron is lowest among the transition metal ions tested. While the previous workersj.4 singled out iron-tannin complex for the grey colour, the present results indicate that Cr, Cu and Mn ions have also contributed to the colour shade development of fibre 155

3 INDIAN J.FIBRE TEXT. RES., JUNE 1991 Table I-Effect of EDTAtreatmenton the propertiesof jute fibre Property Grey Treated Control Golden White Type of jute fibre Brightness index, % Fineness, tex Tenacity,g/tex Fig. I--EDT A-treated grey jute fibres: (I) treated, and (2) untreated control since these are also capable of forming insoluble coloured complexes! 7 with tannin. 3.2 Improvement in Fineness Table I shows that the fineness of all the three types of fibres increased by 5-7% after EDT A treatment. Such improvement can be attributed to the simultaneous loss of about 25% of pectin (Table 2) and of calcium and magnesium ions (Table 2) from fibre, the latter being known to confer rigidity to cell walls by forming ionic bonds between polygalacturonic acid chains of pectic substances 18. EDT A is often used for the isolation IlJ of pectic substances from plant tissue and in the present experiment, its action caused partial loss of pectin from fibre by chelating calcium and magnesi um ions. The net effect is the loss of a cementing material between the cells and hence the formation of finer filament. This behaviour of chelating agent has been used by Sharma20 for extracting fine fibre from desiccated flax stem by removing non-cellulosic cementing materials, Table 3 shows that improvement in fineness was also achieved by treatment with a mixed enzyme preparation containing cellulase, xylanase and pectinase. Similar results were reported earlier for bothjute5-7 and flax21 fibre. Whether ~uch a!nixed enzyme preparation can improve further the fineness of EDT A-treated fibre was examined. The results in Table 3 show that 6-7% increase in flnehess could be achieved by individual treatment with EDT A or enzyme, while their combined action resulted in 10% improvement, well short of their additive functions. The step-wise application of EDT A followed by enzyme was found much more effective than their combined application. The excess 7% increase in fineness may only be attributed to the enhanced enzyme action on EDT A-treated fibre. In order to explain the above phenomena, activities of enzymes were measured (in terms of reducing sugars released) using untreated and treated fibres as substrates. Table 4 shows that the enzymes were more active on EDT A-treated fibre as it showed 41 % higher activity compared to untreated control. The relatively high activity exhibited by treated fibre seems probable since the treated fibre contained lesser amount of tannin (Table 2) which is capable of interfering with enzyme activity. The possible interference of tannin was examined by measuring reducing sugars in reactions containing varying amounts of externally added tannin and 156

4 CHAKRABARTI et at.: BRIGHTNESS AND FINENESS OF JUTE FIBRE PLCT Table Loss of Golden White pectin and tannin contents and metal ions from jute fibre by treatment with EDTA aexpressed Fe+2 in Ilg per 100 g of fibre except Ca+2 and Mg+2 which are expressed in mg per 100 g of fibre. Type of jute fibre Table 3-Effect of EDT A and enzyme treatments on the fineness of jute fibre Treatment Fineness tex Increase in fineness 0/0 a:: -:.:; - l:i?: u 0'ii > 50 Water(control) EDTA Enzyme EDTA'and enzyme (combined) EDTA followed by enzyme 2.01 ± ± ± ± ± Table 4--Relative enzyme activities using grey jute fibre as substrate with various additives and treatments Treatment Substrate and additives No. 1 Untreated fibre(control) (I) 2 EDT A-treated fibre(i1) 3 (II) Ilg of isolated tannin" 4 (II) Ilg of isolated tannin 5 (II), Ilg of isolated tannin 6 (I) + EDTA (I mm) 7 (I) + EDTA (3 mm) 8 (I) + EDTA (5 mm) atannin isolated from jute. Relative enzyme activity EDT A-treated fibre as substrate. Table 4 shows that the release of reducing sugar was reduced proportionately with increased concentration of tannin. Besides, it is observed from Table 4 that EDT A itself did not alter the enzyme activities, as release of reducing sugars from untreated fibre was found to remain unchanged in the presence of varying concentrations of chelating agent. In such reactions Fig. 2-Effect Tannic acid,}jg I ml of tannic acid on cellulose activity the tannin released from fibre by the action of EDT A was retained in the reaction system and thereby offered equal inhibition in all the treatments. Further, it is evident from Fig. 2 that the inhibitory action of tannin was not dependent on the nature of substrate since cellulase activitylz was found to be decreased by tannic acid in reaction containing pure cellulose (filter paper) as substrate. Similar experiments with soluble xylan and pectin could not be carried out since these substrates got precipitated from solution by tannic acid. It may be concluded from the results in Tables 3 and 4 that (i) tannin present in jute fibre inhibits the action of enzymes, and (ii) pretreatment with EDT A helps to remove the inhibitory substance to get an enhanced action of enzymes and hence an improved fineness. References 1 Ghosh T, Handbook on jute (FAO plant production and protection 51, Rome), 1983,

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