Effect of chemical texturization on physical and relaxation properties of jutepolypropylene

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1 ndian Journal of Fibre & Textile Research Vol. 26, September 2001, pp Effect of chemical texturization on physical and relaxation properties of jutepolypropylene ply yams S Sengupta" & P K Ganguly National nstitute of Research on Jute and Allied Fibre Technology, 12 Regent Park, Calcutta , ndia and Samar Kanti Ghosh National Jute Manufacturers Corporation, Khardah , ndia Received 20 September 1999; revised received 2 February 2000; accepted 11 May 2000 Two-. three- and four-ply jute-polypropylene (70:30) yarns have been prepared and chemically texturized using 18% (w/w) NaOH solution. t is observed that as the number of ply increases, the tenacity, breaking elongation, work of rupture, packing factor and flexural rigidity of untextured yarns improve. Chemical texturization of ply yarn brings about moderate increase in tenacity along with considerable improvement in bulk. However, after texturization, the tenacity, breaking elongation, work of rupture and packing improve while the initial modulus and flexural rigidity are adversely affected with the increase in number of ply. As revealed by the stress relaxation and cyclic loading of ply yarns, the stress decay and permanent set increase with the increase in number of ply at low deformation level, while at high extension level, the stress decay decreases. n the textured yarn, the stress decay and permanent set are always higher as compared to that of their untextured counterparts. Wetting of ply yarn results in lowering of tenaci ty, modulus and flexural rigidity and enhancement of elongation-at-break, work of rupture, stress decay and permanent set values. Keywords: Extension cycling, Jute, Packing factor, Ply yarn, Polypropylene, Specific flexural rigidity, Stress relaxation, Texturi zation 1 ntroduction Jute is an important cash crop of eastern ndia and the backbone of economy for the poor and marginal farmers. However, jute is facing difficulty due to the low profitability of conventional products and stiff competition from synthetic packaging products in the overseas and domestic markets. To overcome this situation, an idea of product diversification has been generalized for the last few years and some commendable work has already been done in this area 1.2. Blending of other fibres including synthetic fibres with jute 3 and chemical texturization 4-6 have proved their applicability to manufacture various diversified jute products. With respect to the chemical texturization of jute-polypropylene blended yarn, some research work has been carried out on physical properties of single yarn 5 but no work has yet been reported on physical and relaxation properties of chemically-texturized ply yarn. Jute-polypropylene blended ply yarn after texturiz3tion can be used in a To whom all the correspondence should be addressed. Phone: ; Fax: ; nirjaft@wb.nic.in upholstery, floor-covering and furnishing fabrics. Therefore, an attempt has been made to investigate the physical and relaxation properties of chemically texturized jute-polypropylene (70:30) blended ply yarns. 2 Materials and Methods 2.1 Materials Tossa jute (grade TD-5)7 and polypropylene fibre (Denekalon) of 120 mm staple length and 1.7 tex linear density were used for spinning of yarns. The physical properties of these fibres are given in Table Methods Preparation of Blended Yarn The raw jute fibre was passed through a softener machine, sprayed with oil emulsion and binned for 72 h. Slivers of jute and polypropylene staple fibres were prepared in a JF-2 breaker card and a flax finisher card respectively. These slivers were then fed into JF- 4 finisher card in a weight proportion of 70:30. The jute-polypropylene blended sliver thus obtained from finisher card was passed through three passages of Mackie's gill drawing frames, and the yarn was spun

2 262 NDAN J. FBRE TEXT. RES., SEPTEMBER 2001 Table - Physical properties of fibres Fibre Density Linear Tenacity Extension g/cc density cn/tex at-break tex % Jute Polypropylene Chemically texturized jute Table 2 - Constructional details of 70:30 jute-polypropylene ply yarns Sample Number Single yarn Ply yarn Ply twist code of ply Count count tpcm tex tex X Y Z Xc on a Mackie's slip draft spinning frame using two linear densities of 212 tex and 325 tex and a twist multiplier of The constructional details of the ply yarns are given in Table 2. Doubling was done with TM in the ring doubler. Two-, three- and four-ply (S on Z) yams, referred to as X,Y and Z respectively, were made from fine yam (212 tex) and only two-ply yarn (Xc) was made from coarse yam (325 tex) at the same yarn tension Chemical Texturization of Ply Yarn Jute-polypropylene blended yams were texturized by treating the yams with 18%(w/w) NaOH solution at room temperature for 30 min, maintaining the material-to-liquor ratio at 1 :20. The yam was then washed thoroughly in running water, soured with 2% acetic acid solution for 20 min, washed with water till free from acid and finally dried in air. No tension was applied during texturizing Determination of Tensile Properties The tensile properties of fibres and yarns were determined at 65 % RH and C on an nstron tensile tester. The load elongation curves for raw jute, texturized jute and polypropylene fibres were drawn for 25 samples using 5 cm gauge length and 0.5 cm/min strain rate. The test length and crosshead speed used were 30 cm and 25 cm/min respectively. Wet tests were carried out after wetting the yarn in water containing 0.1 % anionic wetting agent for 30 min. For each sample, 20 tests were performed. The master stress-strain curves (Figs 1-3) were drawn from the load-elongation curves by adopting the technique suggested by Meredith 8 )( \ ~ 7 z o.; 6.. l" CiS ' /! j / i i Extension, % Fig. - Stress-extension diagram of 70:30 jute-polypropylene ply yarns [2P - two-ply yarn, 3P - three-ply yarn, and 4P - fourply yarn] Q) ~ Z U P x J 10 f,'''/ ui '. ) 8 2P,, ~. U5 6 3P,',,./, 4,,,./,,, / 2,/,-,' /.,,;' 0.-, Extension, % Fig. 2 - Stress-extension diagram of 70:30 jute-polypropylene textured ply yarns [2P - two-ply yarn, 3P - three-ply yarn, and 4P - four-ply yarn] The initial modulus was evaluated as the ratio of stress and strain at 1 % extension for untextured yarns while for textured yams it was calculated at the point of strain hardening. Stress relaxation of the yarn samples was determined by stretching the yarns to 30% (0.3BE) or 70% (0.7BE) of their average breaking extensions and allowing them to relax for 5 min at the extended condition. The stress decay, characterizing the stress relaxation, was calculated as follows: T. -T Stress decay = _1 2 X 100 7;

3 SENGUPTA et al. : JUTE- POLYPROPYLENE PLY YARNS ," ~ 10 ""... " y1',, YW YTW,",/ Extension, % Fig. 3 - Stress-extension diagram of 70:30 jute-polypropylene three-ply yarn [Y - normal yarn, YW - wet yam, YT - textured yarn, and YTW - wet textured yarn] where T and T2 are the loads on the yarn at the onset of the stress decay and after stress decay for 5 min respectively. The yarn samples were further extended to break after stress relaxation and the respective breaking load and extension values were evaluated. Yarn samples from each specimen were also subjected to extension cycling at 30% of average breaking extension for 10 cycles before straining them to break. Permanent set (%) on extension cycling was taken to be equivalent to the per cent strain at zero load condition after extension cycling. n each case, the average of 10 test results has been reported after testing the statistical significance of the difference between the mean values at 5% level. The work of rupture was calculated by the area under the stress-strain curve taking up to the maximum load value and then dividing it by the tex value to make the parameter independent of linear density Determination of Linear Density Yarns of 100 m length were weighed and the average of ten such readings was taken as a measure of linear density using standard method Determination of Flexural Rigidity Specific flexural rigidity of the yarn samples was determined by the standard ring-loop method Packing Factor and A vailable Air Space The diameter of yarn samples was measured with a projection microscope (magnification, lox). Average of 30 readings taken at random was taken. Packing factor was calculated from the yarn diameter and considering the density of jute fibre 1.48 and polypropylene fibre Per cent avai lable air space in the yarn was calculated by (-Packing factor). 3 Results and Discussion Yarn properties basically depend on the constituent fibre properties and the structure of the yarn. Jute is a coarse and brittle fibre with very low extensibility and polypropylene is a flexible, highly extensible, strong and tough fibre with a very low density. However, jute, when chemically texturized, has a considerably higher extensibility, mainly due to its crimped nature and change in fine structure l2. Therefore, texturization 13 of yarns brings about some inherent changes in the jute fibre while polypropylene remains unaffected. The properties of jute, polypropylene and chemically texturized jute are shown in Table 1. n addition, the plying of yarns improves the structural integrity and evenness Properties of Jute-Polypropylene Blended Ply Yarns The physical properties of jute-polypropylene blended ply yarns are shown in Table 3. t is observed that the higher the number of ply, the higher is the tenacity, elongation-at-break, initial modulus, work of rupture and packing, whereas lower is the rigidity of yarn. As the number of ply increases, the change in structure improves the regularity and inter-yarn radial forces, which, in turn, improve the effective contribution of fibre length towards the tenacity and is reflected as better packing or decrease in available air space in higher ply. A pressure is applied to the outside of each single component during tensile deformation. Ply yarn thus utilizes the strength contribution of the ineffective layer of fibres. On the contrary, the bending deformation is a very low-load phenomenon where the role of radial forces is insignificant and, therefore, relative fibre mobility within and between the component yarns is higher as the number of ply increases which is reflected in lower specific flexural rigidity. Fig. 1 shows the stress-strain curves of 2-ply, 3-ply and 4-ply jute polypropylene blended yarns which clearly demonstrate the tensile behaviour of these yarns at different extension levels. Table 4 shows that the wetting of 3-ply yarn reduces tenacity, modulus and rigidity significantly. On the contrary, elongation-at-break and hence work of rupture improves on wetting. n the blended yarn, the polypropylene component is highly hydrophobic and the water film between polypropylene fibres may have acted as a slipping agent and consequently the inter-fibre friction reduced within the yarn. Stressstrain behaviour of wet 3-ply yarn (Fig. 3) shows a plastically deformable region or creep due to the continuous slipping and breaking of fibres and then a

4 264 NDAN J. FBRE TEXT. RES., SEPTEMBER 2001 Table 3 - Physical properties of untextured and textured 70:30 jute-polypropylene ply yarns Sample Linear ncrease Tenacity Extension-at nitial Work of Packing Available Specific flexural code density in tex cnltex -break modulus rupture factor air space rigidityxlo- 6 tex % % cnltex cncrnltex % cncm 2 /tex 2 X XT Y YT Z ZT Xc XcT T - Texturized yarn Table 4 - Effect of wetting on properties of untextured and textured 70:30 jute-polypropylene ply yarns Sample Sample Tenacity Elongation-alcode condition en/lex break % Y Dry Wet YT Dry T - Texturized yarn Wet nitial Work of Specific fl ex ural modulus rupture rigidityx 0. 6 cn/tex cncmltex cncm 2 /tex catastrophic break instead of stick-slip rupture of the dry yarn. 3.2 Effect of Chemical Texturization Table 3 shows that the linear density as well as bulk of the ply yarn increase after chemical texturization which was also observed by Gupta et al. 5 for single yarn. As the number of ply increases, the bulkiness also increases significantly. This is evident from the per cent increase in tex values, packing factor and available air space values. Chemical texturization of jute-polypropylene blended yarn results in shrinkage and crimping of the jute fibre, and during texturization the relaxation process brings about torque decay. The simultaneous torque decay and shrinkage-cum-crimping of jute fibres result in partial destruction of the helical structure of the yarn. Redistribution of twist and further entanglement of the fibre elements take place within the yarn matrix. During chemical texturization, jute fibre shrinks, while the non-shrinking PP fibres form loops and kinks. The result of these preferential rearrangement of fibre improves the feel or generates soft tactile hand. Similar observations of low-shrinkage acrylic fibres on the surface of bulked acrylic yarns were reported by Pillar ' 5. Texturization of ply yarn results in moderate increase in its tenacity and substantial increase in its extension-at-break and work of rupture. This follows an increasing trend with the increase in number of ply in the yam. The marked improvement in tensile properties may be attributed to the entanglement generated by shrinkage, twisting and crimping of jute fibres simultaneously during the chemical texturization. This causes the generation of hi gher degree of inter-fibre and inter-yarn radial forces after crimp removal in high load condition. The increase in tenacity of yarn after texturization in spite of decrease in tenacity of jute fibre is basically due to the effect of plying, bulking and the higher inter-yarn radial forces. The initial part of stress-strain curve of untextured yarn is governed by the inextensible jute fibre, but at higher extension, polypropylene also starts contributing. Such a yarn shows a step break (Fig. ) because while the weaker jute breaks, polypropylene bears the load. After texturization, the entanglement between jute and polypropylene increases. Fig. 2 shows that there is a significant crimp removal zone in the stress-strain curve of the textured yarn, where neither jute nor polypropylene bears the load but they rearrange and interlock themselves in such a way that both polypropylene and jute contribute to load from the beginning of the post-decrimping zone and in high strain condition both the fibres simultaneausly bear the load till break. t never shows step break at rupture (Fig. 2). These are probably the reasons behind the

5 SENGUPT A et al. : JUTE- POLYPROPYLENE PLY YARNS 265 improvement in jute-polypropylene blended ply yam strength after texturization. On the contrary, the initial modulus and flexural rigi<}ity values follow a decreasing trend with the increase in number of ply because these attributes, which are measured at low load condition, are mai nl y governed by the bulk of the yam, which follows an increasing trend with the increase in number of ply, as evidenced by the higher ai r space values of such yarns (Table 3). Ply yam with coarser component yam shows an inferior effect on texturization, apparently due to the higher rigidity of the component yarns. The effect of wetting on the physical properties of 3-ply un textured and textured yarns is shown in Table 4 and Fig. 3. t is apparent that the wetting results in lowering of tenacity, initial modulus and flexural ri gidity of all the three types of yarn studied. This is possibly due to the lowering of strength and stiffness of jute fibre on wetting and also to the presence of water particles between hydrophobic polypropylene fibres including slipping and reduction in inter-fibre friction. The hi gher elongation-at-break of the untextured ply yarn may also be accounted for by the phenomenon of water-induced slippage of fibres. However, in case of textured yarns, wetting tends to reduce the elongation-at-break, apparently due to some loss in crimp of chemically texturized jute fibres as observed by Chakravorty 16. Another factor responsible for the decrease in elongation-at-break might be an increase in rad ial pressure between the components of the ply yarn due to the swelling of jute on wetting. nterestingly, the lowering of strength and elongation-at-break on wetting of chemically texturized ply yarns is not accompanied by the lowering of work of rupture. On the contrary, the work of rupture of un textured and texturized ply yarns increases significantly on wetting (Table 4). This is also indicated in the stress-strain diagrams of the wet yarns (Fig. 3). The shape of the stress-strain curves of wet yarn is such that the area under the curve, i.e. work of rupture, is significantly higher than that of its dry counterpart. Moreover, the wet yarn shows a significant creep or plastically deformable region before rupture which also increases the work of rupture. 3.3 Stress Relaxation There are two parts of stress relaxation : one is due to time-dependant viscoelastic nature of fibres and yam, and the other is shearing or flow between component fibres. t appears that in low deformation level the former one is predominant, while in high deformation level the latter is mainly responsible. Table 5 shows that with the increase in number of ply, the stress decay of jute-polypropylene blended yarns increases at 30% breaking extension both for untextured and textured yarns. Apparently, this is due to the variation in yarn structure which leads to difference in modulus values of ply yarns (Figs and 2). Though the stress values of all the untextured and textured yarns are almost similar, the stress decay increases with the increase in ply due to the decrease in elasticity. On the contrary, at 70% breaking extension the stress decay shows a decreasing trend as the number of ply increases (Table 5). n case of high tensile deformation, the stress relaxation leads to partial disruption of the compact and interlocked yarn structure due to some irrecoverable flow among fibre elements. Quite expectedly, this flow is higher for lesser number of ply due to its higher modulus both fo r untextured and textured yarns (Figs 1 and 2). Moreover, this effect is pronounced in case of bulky textured yarns. Table 5 - Stress relaxation behaviour of untextured and textured 70:30 jute-polypropylene ply yarns Sample Stress relaxation Tenacity after Breaking extension code relaxation, cn/tex after relaxation, % 0.30E Stress decay 0.7BE Stress decay 0.3BE 0.7BE 0.3BE 0.7BE % at 0.3BE.% % ato.7be,% X Y Z Xc XT YT ZT XcT BE - Breaking extension

6 266 NDAN J. FBRE TEXT. RES., SEPTEMBER 2001 Table 6 - Sample Sample Stress relaxation code condition Stress decay Tenacity % cn/tex Stress relaxation and cyclic deformation behaviour of wet yarn 0.3BE 0.7BE 0.3BE 0.7BE Y Dry Wet YT Dry Wet t is apparent that the textured yarn shows higher stress decay at 0.3BE level and lower stress decay at 0.7BE level compared to its untextured counterpart. On chemical texturization of jute-polypropylene blended yarns, the bulk increases due to the shrinkage and crimp formation in the jute component, resulting in the lower elasticity at low extension as it is basically governed by decrimping process. When the textured yarn is subjected to stress relaxation at large deformation, well beyond their decrimping regions, the shearing of fibre elements is restricted compared to untextured yarn due to the higher entanglement within the yarn matrix. Plying with coarser component yarns (Xc and XcT) improves the elasticity in untextured yarn and deteriorates elasticity in textured yarn compared to its finer component ply yarn, at low extension level, whereas at 0.7BE level, no significant change is observed. However, when the yarns are ruptured after being subjected to stress relaxation, the tenacity and elongation-at-break show higher values in all the cases, except for textured yarns subjected to stress relaxation at 0.7BE level. When a yarn is held at extension, controlled shearing (flow) between fibre and yarn elements is expected to take place to minimize the localized stress concentration as far as possible and this is manifested as stress decay. Due to the redistribution of stress concentration, the yarn is expected to rupture at higher load. But when bulky textured yarn is deformed to a large extension and allowed to relax stress, the irrecoverable flow between fibre elements occurs and this might be responsible for the reduction in breaking stress and extension of ply textured yarns on stress relaxation. The wetting of ply yarn exhibits the increase in stress decay at both the levels of extension studied for both untextured and textured yarns (Table 6). This is apparently due to the presence of water particles which act as a lubricant in the jute-polypropylene blended yarn matrix. However, the tenacity of wet Extension cycling Elongation-at- Permanent Tenacity Elongationbreak,% set, % cn/tex at-break, % 0.3BE 0.7BE Table 7 - Extension cycling behaviour of 70:30 untextured and textured jute-polypropylene ply yarns Sample Permanent Tenacity after Elongation-at -break code set extension after extension % cycling, cn/tex cycling, % X Y Z Xc XT i9.44 YT ZT XcT stress-relaxed yarns decreases apparently due to the slippage between component fibres. Table 6 also indicates that the elongation-at-break of wet stressrelaxed textured yarn deteriorates while quite expectedly, the same of the textured yarn improves. 3.4 Cyclic Loading The effects of extension cycling (10 cycles) at 0.3BE on elasticity of the yarns as indicated by the permanent set achieved after extension cycling are shown in Table 7. t is observed that the elasticity decreases as the ply of yarn increases which is evident from the higher permanent set values. These findings are similar to that shown in the case of stress relaxation at 0.3BE level (section 3.3). The response of untextured ply yarn made out of coarser (Xc) and finer(x) component yarns is almost identical to cyclic loading. However, it is expected that the textured yarns are having lower elasticity, i.e. higher permanent set values, than untextured yarns as also shown for stress relaxation at low extension level. Moreover, it appears from Fig. 2 that the stress developed in textured yarn after tensile deformation up to 0.3BE is very near to zero stress, and the cyclic loading between zero BE and 0.3BE leads to permanent set value which is lower than zero stress extension of textured yarn, resulting in reduction in zero stress extension. Therefore, such a cyclic

7 SENGUfYf A et al. : JUTE- POL YPROPYLENE PLY YARNS 267 deformation of textured yarn, fibre redistribution and straightening take place, making the yarn structure more compact which is reflected in higher tenacity and elongation-at-break at rupture after cyclic loading. Otherwise, the tenacity and elongation-atbreak values follow a trend similar to the one observed for parent yarns (Table 3) with respect to number of pl y. Cyclic loading of wet ply yarn shows higher permanent set or lower elasticity and higher extension-at-break with lower tenacity (Table 6). t indicates the sli ppi ng action as well as deterioration in yarn structure during tensile loading due to the presence of water particles and hydrophobic polypropylene fibres which reduces the inter-fibre friction within the blended yarn. On the contrary, the lowering of permanent set, i.e. improvement in elasticity, is observed in wet textured yarn with very little change in tenacity and elongation-at-break. Due to wetting of textured yarn, the swelling and shrinkage of texturized jute enhances the entanglement and inter-fibre friction, resulting in the improvement in elasticity which was also observed by Chakravorty et al. i6 4 Conclusions 4.1 Texturization of ply yarn results in moderate increase in tenacity and sustantial increase in elongation along with the improvement in bulk. 4.2 Ply yarn made from coarser components shows less improvement in properties than the yarn made fro m fi ner counterpart. 4.3 n ply yarn, as the number of ply increases, the tenacity, elongation-at-break, work of rupture, packing and rigidity of untextured yarn improve. After texturization, the tenacity, breaking extension, work of rupture and bulk increase and the initial modulus and flexural rigidity decrease with the increase in number of ply. 4.4 n general, the stress decay or the permanent set of textured yarns is always and signi ficantly higher than that of untextured yarns. 4.5 Jute-polypropylene textured and untextured yarns show an increasing trend in stress decay and permanent set values at O.3BE level, indicating lower resilience or elasticity with the increase in number of ply. The high level of deformation (O.7BE) leads to decrease in stress decay as the number of ply increases. 4.6 The rupture after stress relaxation and cyclic loading of ply yarn improve the tenacity and elongation-at-break in all the cases except for textured yarns. For texturized yarns, the tenacity increases in spite of the decrease in elongation-at-break. 4.7 Wetting of ply untextured and textured yarns shows deterioration in tenacity, modulus and rigidity, and improvement in elongation-at-break and work of rupture. Stress-strain behaviour of wet jutepolypropylene yarn shows a creep region just before the rupture. Stress decay and permanent set increase on wetting for both untextured and textured yarns. On the contrary, tenacity and elongation-at-break decrease after rupture, showing lower values for textured yarn. Acknowledgement The authors are grateful to Dr S K Bhattacharya, Director, and Dr B P Sarkar, Head, Mechanical Processing Division, both of NRJAFT, for encouragement and valuable support during the study. References Samanta A K, Chakraborty P, Choudhury A & Chandra D B. ndian Text J, OO( 0)( 1990)60. 2 Ranganathan S R & Quayyum Z, New Horizonsjor Jute (National nformation Centre for Textile and Allied Subjecis. Ahmedabad), 1993,31. 3 Ghosh S K, Text Trends. 30(8)(1987) 1. 4 Gangul y P K, Mukherjee A & Sur D, ndian J Fibre Text Res. 20( 1995)86. 5 Gupta N P, Majumdar A, Bhattacharya G K, Sur D & Roy D, Text Res J, 52 (1982) Sinha A K & Gupta N P, ndian J Text Res, (1986)35. 7 lldian Standards Specifications S:271 (B ureau of ndian Standards, New Delhi), Meredith R. J Textlnst. 36( 1945)Tl07. 9 dian Standards Specificalions S: 1315(Bureau of ndi an Standards, New Delhi), Morton W E & Hearle J W S, Physical Properties oj Textile Fibres (The Textile nstitute, Heinemam, London), Goswami B C, Martindale J G & Scardino F L, Textile Ya m s-technology, Structure and Applications (John-Wiley and Sons, New York), 1977, Maj umdar A, Samajpati S, Ganguly P K, Sardar D & Dasgupta P C, Texl Res J, 50( 1980) Macmillan W G, Sengupta A B & Majumdar S K, J Texl lnsl, 45( 1954 )T Oxtoby E, Spun Yam Technology (Butterworths, London). 1987, Pillar B, Bulked Yams: Produclion, Processing and Applicario.'ls (Textile Trade Press, Manchester), 1973, Chakravorty A C, Jute Bull, 33( 1970)83.