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Some studies on structure and properties of wrapped jute (parafil) yarns

ndian Journal of Fibre & Textile Research Vol. 16, June 1991, pp Some studies on structure and properties of wrapped jute (parafil) yarns A K Sengupta, R S Chattopadhyay & S Sengupta Department
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ndian Journal of Fibre & Textile Research Vol. 16, June 1991, pp Some studies on structure and properties of wrapped jute (parafil) yarns A K Sengupta, R S Chattopadhyay & S Sengupta Department of Textile Technology, ndian nstitute of Technology, New Delhi , ndia and D P Khatua ndian Jute ndustries' Research Association, 17 Taratola Road, Calcutta , ndia Received 6 November 1990; accepted 19 November 1990 Parafil Yarns usingjute as core and polyester, nylon and HDPE as wrapper filaments have been prepared using a six-spindle Suessen Parafil parallel yarn spinning machine and the influence of wrapping material and wrapsm on yarn properties has been studied. t is observed that the mechanical properties of parafil yarns are greatly influenced by the packing density of the yarn, which, in turn, is influenced by both wrapsm and type of wrapping filament used. There is a good correlation between packing coefficient and breaking energy of the wrapped yarn. Heat-setting of wrapped yarn under constant length condition improves the breaking energy of yarns by more than 20%. Keywords: High-density polyethylene, Jute yarn, Parafil yarn, Polyester, Nylon, Wrapped yarn 1 ntroduction The technological and economic limitations of conventional ring spinning have resulted in the exploration of many new methods of yarn manufacture. One of the latest development in this area is the hollow-spindle technique. n this technology, a yarn is produced by wrapping a continuous filament aronnd a core consisting of straight and parallel fibres. The continuous filament provides radial tens'lon and, consequently, friction between the individual fibres. As the structure of this yarn is quite different from the conventional yarns, and the fibres in the yarn are held together by the frictional pressure induced by the wraps, it is expected that the properties of the wrapper filament as well as the wrap density will have a strong influence on the mechanical properties of the yarn. Using the parafil yarn technology, it is expected that a better quality yarn can be manufactured from jute which would satisfy more stringent requirements for applications other than packaging, such as decorative fabrics and carpets. n view of the above considerations, an attempt has been made to investigate the structure-property relationship of parafil yarns prepared using jute as core and high-density polyethylene (HOPE), nylon and polyester as wrapper filaments 2 Materials and methods 2.1 Materials Tossa-daiscejute (TO,) fibre was used to prepare jute yarns. HOPE, nylon and polyester were used as wrapper filaments. The physical properties of the raw materials used are given in Table. 2.2 Methods 2.2,1 Preparation of Yarn Samples The wrapped yarn samples with 200, 220, 240, 260 and 280 wrapsm were prepared using a six-spindle Suessen Parafil-2000 parallel yarn spinning machine. The total draft, break draft and front roller speed (mmin) used were 53, 1.82 and 100respectively. Table -Physical properties of core fibre and wrapper filaments Material Jute fibre (Tossa-daisee) HDPE monofilament Nylon (20 filaments) Polyester (36 filaments) Linear density tex Tenacity gtex Extension at break % SEN GUPTA et at.: WRAPPED JUTE (PARAFL) YARNS The linear densities of the JuteHDPE, jutenylon and jutepolyester yarns were 260, 236 and 237 tex respectively. The leas of jute yarns wrapped by HDPE, nylon and polyester were kept inside drying oven under constant length condition and heat-set for 6 min passing dry hot air. The temperatures used were 82, 165 and 180 C for HDPE-, nylon- and polyester-wrapped yarns respectit'ely Linear Density Yarns of 100 m length were weighed and the average of ten such readings was taken as a measure of linear density. filaments (Fig.2), it may be observed that polyester records the highest stress at low strains which is followed by nylon and then HDPE. Moreover, HDPE has higher bending rigidity due to its being a -.. .~. .' 0 3,5 c n.. '1. c-2eo 25r-. b-240 2'Or Jut.HDPE! ~ .41Q-i\ \ Q \. \ t i JU. \,. 0 5' Ju~Nylon '~~ Y t i'. j. 1' \ Jut.,Polynl«Q } 2'01- :: 4 \ 200 'VlWfQPstm 1 b c A \ i Y \ '';''~, 'A : V' 0,;:1 i i't 2'5r A', :::, ~ i : 1.M l,j:1. ' 051--' ; \ 0 O 30, ;1! Tensile Properties nstron tensile tester with 50 cm gauge length,s cmmin crosshead speed and 20 cmmin chart speed was used for tensile tests of yarns. An average of 50 tests was taken for each sample Flexural Rigidity Shirley weighted ring yarn stiffness tester using 21.8 cm former was used. An average of 15 tests was taken for each sample. Specific flexural rigidity was computed using the following relationship Flexural rigidity Specific flexural rigidity = o tex~ Packing Coefficient Diameter of yarns under constant tension was measured in Projectina using a magnification of 30. From an average of 30 readings for each sample, packing coefficient was calculated using a density of 1.48 for jute fibre. 3 Results and Discussion 3.1 nfluence of Wrapper Characteristics on Mechanical Properties of Parafil Yarn Rupture The rupture process of jute yarns varies considerably with the change in property of wrapper filament (Fig. 1). The yarns show the elastically deformation region in the initial stages due to resistance to slippage which increases due to the increase in lateral pressure, but after that HDPE-wrapped yarn shows stick-slip effect and polyester-wrapped yam shows catastrophic break whereas the nylon-wrapped yarn shows an intermediate between these two {ailure behaviours. From the stress-strain curves of the wrapper '0 25 3,0 ELONGATON, em Fig. L()ad-~()ngati()n curves lar diff~r~nt para ii yarns 129 NDAN J.FBRE TEXT. RES.. JUNE 1991 monofilament. So, the radial pressure exerted by HOPE is lower than that exerted by other filaments at low extensions. At the rupture point of fibres in the wrapped yarn, some core fibres, which have already reached their breaking extension, rupture and instantaneously the load value falls as the fibres start slipping. Ouring this, the filament extends and exerts more radial pressure and arrests further slippage. The load value thus increases again. This occurs several times and gives step-wise breaks which continue to much higher extension (Fig., Jute HOPE). Nylon has lower extensibility (Table ), higher tenacity (Fig.2) and lower bending rigidity (multifilament) compared to HOPE. This gives rise to ~ 1' ~ 250' GO, oil 0: ::: ~~o :;; Jor. ',, o o 10 Q ~~, b STRAN,' r. &0 ~ 90 ;00 Fig. 2 Stress-strain curves of filaments used as wrappers [(a) Polyester. (b) Nylon. and (e) HDPE] higher radial pressure on the core fibres. n the rupture process, the proneness of stick -slip effect is reduced from HOPE-wrapped yarn due to this higher radial pressure which does not allow the core fibres to slip easily (Fig., JuteNylon). n case of polyester-wrapped yarn, the rupture process does not show any stick-slip effect and the failure is catastrophic in all wrapping situations (Fig., JutePolyester). This is mainly due to higher initial modulus and lower extensibility of polyester (Table and Fig.2) compared to HOPE and nylon. Moreover, the polyester wrapper being a multifilament has lower bending rigidity compared to HOPE. These properties raise the stress value of polyester filament, and higher radial pressure gives higher intcrflbre friction but does not allow the core flbre to slip at a]1.~s there is no slippage, the yarn load does not fall, other core flbres bearing the load successfully. But. as soon as the majority fibres break, the remaining flbrcs cannot sustain the load and catastrophic break occurs. 3. \.2 Tenacity Table 2 shows that for equivalent wrap densities, the polyester wrapper gives higher tenacity yarn than nylon followed by HOPE. The reasons are given below: Polyester exerts higher radial compressive force to the core fibres and the frictional force between core fibres increases due to high radial pressure and resists the slippage of core fibres. That is why it gives highest tenacity. Moreover, HOPE is monofilament and nylon and polyester are multifilaments. So, with the same wrapping tension, HOPE winds like a stiffwire Wraps m Yarn sample at HUO S Extension W J rigidity cofficient X.57 U X.1\4 4.X9 Tenacty Packing break Sp g.cm2rupture Work flexural. ( x 10- of 5) g.cm2 Jute HDPE Jute Nylon Jute Polyester 130 SEN GUPTA et al..: WRAPPED JUTE (PARAFL) YARNS whereas nylon and polyester take the shape of a ribbon wound around the fibrous structure. Therefore, the fibre-to-filament contact area is lower in the case of HDPE compared to nylon and polyester. Low contact area increases the proneness to slippage of core fibres. Nylon wrap gives better tenacity compared to HDPE because of higher radial pressure during yarn extension, higher stresses developed during wrapping and higher contact area with the core fibres Flexural Rigidity Table 2 shows that jutehdpe gives lower flexural rigidity compared to jutenylon and jutepolyester. The higher radial pressure of nylon and polyester gives higher fibre-to-fibre friction and lower allowance for the movement of core fibres during bending. Therefore, more force is required to bend the polyester- and nylon-wrapped yarns compared to HDPE-wrapped yarn where the movement of core fibre is easier Packing Coefficient Table 2 shows that jutehdpe gives lower packing compared to jutenylon and jutepolyester. The reason is same as for flexural rigidity. The jutenylon and jutepolyester yarns pack more closely compared to jutehdpe yarn. the wrapping filament are not strong enough to closely pack the fibrous core which results in low interfibre friction between the individual fibres. With the increase in wrapsm, the fibrous core becomes more compact and more coherent. This may be due to action of higher radial compressive forces exerted by the wrapped continuous filament Flexural Rigidity, Packing Coefficient and Work of Rupture All the above mentioned properties increase with the increase in wrapsm (Table 2). Flexural rigidity increases due to increase in fibre-to-fibre friction which resists the fibre from sliding. Packing coefficient increases due to higher radial pressure. n the case of work of rupture, higher wrapsm gives higher tenacity a-nd extension-at-break which are responsible for higher work of rupture. 3.3 nfluence of Packing Coefficient on Structural ntegrity. of Parafil Yam From the above results it is observed that the conditions of producing wrapped structure which induce higher lateral pressure on the fibrous core result in higher appreciation of mechanical properties. As the failure behaviour in the wrapped yarn structure studied is essentially associated with the failure of the fibre matrix, it is to be expected that an increase in packing density should relate well to the 3.2 nfluence of Wrap Density (Wrapsm) on Mechanical breaking energy or the energy needed to disintegrate Properties of Parafil Yam the structure. For all the jute core yarns wrapped with Rupture different wrapper materials as well as with various JuteHDPE shows a progressive change in the wrapsm, a relationship between packing coefficient rupture process (Fig. 1) with the increase in wrapsm. and work of rupture is presented in Fig.3. t is At 200 wrapsm, the rupture shows.. 2 2r a: C frequent UJ [] a.. E a:. ; '~ ~... 01'2 ~1'8 ;:)1'4 ll. ::0:: ~2' '0, 0 [] [] stick-slip effect. The frequency of stick-slip decreases with the increase in wrapsm. n the case of jutenylon (Fig. ), the frequency of stick-slip also decreases with the increase in wrapsm and at high wrapsm (280), there is no stick-slip and only catastrophic break occurs. With the increase in wrapsm the filament-to-fibre contact area increases which gives higher radial pressure to the core. This increases the interfibre friction and the core fibres are restrained from slippage. n the case of jutepolyester (Fig; 1), there is no effect ofwrapsm on the mode offailure, because even the minimum wrapsm (200) is enough to arrest the slippage of core fibres Tenacity Table 2 shows that the tenacity increases with increase in wrapsm for all the wrapped jute yarns studied. At very low wrapsm, the forces exerted by 0'38 0'42 0'46 0'50 0'54 PACKNG COEFFCENT Fig. 3---Correlation between packing coefficient and work of rupture (Correlation coefficient ) 131 NDAN J.FBRE TEXT. RES., JUNE S. Jutt'HOPE b4 ~ 1 r: L. \ '-. a Bt'fort'hEO-St'lling observed that there is a linear relationship between packing coefficient and work of rupture with a correlation coefficient of The correlation would, probably, have improved further if only one type of wrapper filament had been used in the study as the radial compressive forces exerted by the filament at failure would be governed by the stresses developed on the filament, which in turn, would depend on the stress-strain characteristics of the wrapper material..x Jult'Nylon 0' ~ 0 --' Jult'Polyt'sler 2 1-5'- 0'- 230S 3 S 10'- -a O-S J '- S'-, '...- Oy- ' b ~ Alt'r ht'ot -tt' tli ng bi 1 f 3.4 nfluence of Heat-Setting on Mechanical Properties Fig.4 shows that the load-elongation curves before and after heat-setting for HDPE-, nylon- and polyester-wrapped jute yarns with uniform wrapping density of 240m. t is observed that heat-setting increases the extensibility of polyesterand HDPE-wrapped yarns and tenacity of nylon-wrapped yarns considerably. n all the cases, there is a significant increase in breaking energy, showing the usefulness of heat-setting in enhancing the structural integrity of the parafil yarns~ Heat-setting results- in a contractile force in the wrapper filament which ~xpresses itselfin both lateral and longitudinal compressive forces on the core yarn. The magnitudes of these compressive forces would depend, amongst other things, on the wrapping density. The average increase in breaking energy in terms of work of rupture values for yarns with different wrapsm taken together is 22.3, 17'.6 and 23.7% respectively for jutehdpe, jutenylon and jutepolyester yarns. Acknowledgement The authors wish to thank Dr S R Ranganathan, Director, JRA, for providing all the facilities in carrying out this work. {) S 2-0 : S ELONGATON,em 30 3 S Fig. 4---Load-elongation curves of different parafil yarns at 240 wrapsjm 132
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