BULETINUL INSTITUTULUI POLITEHNIC DIN IAŞI Publicat de Universitatea Tehnică Gheorghe Asachi din Iaşi Tomul LVI (LX), Fasc. 2, 2010 SecŃia TEXTILE. PIELĂIE BIODEGADABLE YANS FO WEAVES USED FO COMPOSITE MATEIALS BY DOIN AVAM and LILIANA BUHU Abstract. In this paper we have created the characteristics of yarns from biodegradable fibres, which will be used for weaving. Weaves for composite materials improves the physical-mechanical characteristics of composite materials with reinforced from textile and wood. Key words: biodegradability, biodegradable yarns, weaves and composite materials. 1. Introduction Composite material consists of two or more structures physically and/or chemically distinct, suitable arranged or distributed phases, with an interface separating them. The concept of composite materials is classic: to combine different materials to produce a new material with performance inaccessible by the individual constituents. The constituents of composites can be in the form of fibres, yarns, fabrics, etc. [1]. Biocomposites are the combination of natural fibres such as wood fibres (hardwood and softwood) or non-wood fibres (flax, hemp, jute, kenaf, coir, sisal, and corn) with polymer matrices from both of the renewable and nonrenewable resources. Natural fibres offer many advantages such as renewability, recyclability, biodegradability, low specific gravity and high specific strength. Biocomposites have been used widely for making building products such as window, door, siding, fencing, roofing, decking, etc. [1]. Composite materials with reinforced from textile fibres (glass fibre, carbon or aramid fibres) and matrix from epoxy and unsaturated polyester had an important role in recent times due to multiple fields of use where mechanical strength and high module are very important.
18 Dorin Avram and Liliana Buhu Natural fibres like jute, flax, ramie and sisal can be used in green composites as reinforced; as matrix are used biodegradable resins obtained from cellulose, starch, lactic acid etc. The fact that both constituents are biodegradable composite is the great advantage of these composites. Using natural fibres to the glass is advantageous because they have the less cost, low density, acceptable strength and biodegradability. Another advantage of using natural fibres is the low temperature required to obtain the composite because it the possible occurrence of thermal degradation of the fibres, which will influence the composite properties. The main disadvantage of natural fibres is their hydrophilic, because it reduces the compatibility with hydrophobic polymer matrix during to obtaining the composite. Therefore the weak adhesion between fibres and matrix lead to reduced mechanical properties [2]. In addition now the expensive cost of biodegradable resins may limit their application to green composites, but is expected to reduce these costs in the near future. 2. Experimental Part 2.1. Characteristics of the Fibres Yarn characteristics are obtained by transferring the fibre characteristics through their structure. Fibre characteristics, such as: fineness (count), strength, elongation, density are transferred in the yarn characteristics of the same type, while the fibre length influence the mode of and the statistical parameters (dispersion, coefficient of variation) of these characteristics. To obtain yarns biodegradable were chosen flax fibres that respond to the requirements imposed by biodegradability. Characteristics of fibres have chosen depending on the processing technology. The main characteristics of fibres are experimentally determined and are presented in Table 1. Table 1 The Main Characteristics of Flax Fibres Characteristics of fibres UM Average count [m/g] 360 Length: average [mm] 98 CV [%] 75 Average strength [cn] 55.7 Tenacity [cn/tex] 20 Elongation [%] 4 Density [kg/m 3 ] 1,500 Legal moisture [%] 12 Fibre length influences the processing and appearance of the yarn, as well as the transfer of the fibre strength to yarn. The length of fibres used in
Bul. Inst. Polit. Iaşi, t. LVI (LX), f. 2, 2010 19 carding and combing processing were included in the following categories: short fibre with lengths below 40 mm, average fibre length between 40 to 100 mm, long fibre length from 100 to 150 mm and very long fibres with length over 150 mm [3],,[5]. Modelling of variation for flax fibres length used in processing technology by carding and combing draws to the Weibull distribution by means of which it can determine the statistical parameters of fibre length (average, dispersion variance and variation).values obtained from statistical Weibull function are presented by frequency and cumulative curves (Fig. 1). Fig. 1 Frequency and cumulative curves for the length of flax fibres. where: f i frequency according to Weibull function for shape parameter α = 1.3 and the scale parameter β = 100; F i cumulative frequency according to Weibull function; l med = 90.16 mm - average length of fibres; D 2 = 4,562 - dispersion variance of fibre length; σ = 67.54 - standard deviation of fibre length; CV = 74.9% coefficient of variation of fibre length. The yarn destination is for composite materials made of biodegradable woven fabric and a wooden structure. Fabric characteristics are adopted in accordance to required properties of composite: longitudinal and transversal composite strength; reduced burst strength; low fabric mass; formability; lower costs, etc. The fabric selected based on these requirements has: weight 400 450 g/m² and density of the warp yarns in woven fabric of 72 yarns/10 cm and density of the weft yarns in woven fabric 62 yarns/10cm. The fabric used yarns count Nm 5/2 for warp and Nm 5/1 for weft. Warp and weft yarns are obtained from same carded and combed blend of flax. The following aspects were considered in yarn processing: the general yarn characteristics in order to ensure its processability and the mass per unit area. The yarn aspect characteristics were not considered important.
20 Dorin Avram and Liliana Buhu 2.2. Characteristics of the Single Yarn a) Count. Yarn count is created in terms of influence on mass of fabric and is appreciated by the nominal value, the effective value and count variation. The selected nominal yarn count was Nm 5, in accordance to the fabric characteristics and the industrial nominal values [5]. The effective value is obtained based on equation: (1) Nm = Nm a eff nom ± where: a count deviation and it is determined by equation: (2) t σ a= n where: t Student s t test parameter that takes the value 2.04 for the number of measurements (n = 30) and level of significance 5%; σ standard deviation of yarn count, determined by equation: (3) σ = CV Nm Nm 100 where: CV Nm is the variation of yarn count CV Nm ; Nm average yarn count. In view of the fact that CV Nm = 7.5% for Nm = 5 it results that σ = 0.38 m/g and a = 0.14 m/g representing 2.8% from the nominal value. Effective yarn count is Nm ef = 5± 0. 14 m/g. b) Twist. The yarns manufactured through carding and combing technology are characterised by a yarn torsion factor αm = 100, and the yarn torsion is 100 5 = 224 t/m, while the adopted torsion was 220 t/m. Because of the variable distribution of fibre length, the diameter yarn varies between 0.77... 0.35 mm characterised of: coefficient of variation 13%; standard deviation 18.074 t/m; coefficient of variation 13.64%; variation interval for torsion 220 ± 10.5 t/m. It can be observed that torsion variation is high for such yarns, because the sectional variation is high, which leads to a different distribution of torsion according to thickness variation, i.e. on the thin portions the number of torsions is bigger than on the thick portions. c) Strength. Yarn strength is a transfer characteristic obtained by equation [5]: (4) F = n rf k u where: n number of fibres in the yarn cross section; r f average fibre strength; ku transfer coefficient of strength fibres in strength yarn.
Bul. Inst. Polit. Iaşi, t. LVI (LX), f. 2, 2010 21 The yarn strength was determined to be 19.76 N for 72 fibres crosssection, the average strength of fibres being 55.7 cn (see Table 1) and transfer coefficient 0.5. The yarn strength can be considered a random variable with normal distribution behaviour with parameters: average value of 19.76 N and standard deviation 5 N and variation interval 9.96 to 29.56 N, for a level of significance α=0.05. Strength coefficient of variation is 25%. d) Tenacity. The average tenacity is 0.0988 N/tex for the yarn average strength and average fineness (tex). e) Elongation. Elongation is a transfer characteristic of yarn obtained by the equation [5]: (5) A = a ka F where: a f average fibre elongation; ka elongation transfer coefficient from fibres to yarn. Yarn elongation is determined by fibre elongation as well as the yarn structure, because the fibres are loose in the yarn, i.e. at the beginning of the tensile test the fibres slip until they become fixed and then the fibre elongation is transferred to yarn level. For 4% elongation of flax fibres (see Table 1) and 1.08 transfer coefficient results 4.32% yarn elongation. f) Force elongation curve. Average force elongation curve of the single yarn can be approximated by a straight line (Fig. 2), with equation: (6) F= 4.057 A 0. 619 where: F yarn strength, [N]; A yarn elongation, [mm]. f Fig. 2 Force - elongation curve of the single yarn. The coefficient of determination 2 = 0.9854 shows a good approximation of the experimental data with a straight line, which is specific for the yarns with very small elongations.
22 Dorin Avram and Liliana Buhu From force-elongation curve of the yarn were calculated: index of the work to break: 190 N mm; index of specific work to break: 9.5 N mm/tex; secant longitudinal elastic modulus of yarn: 9.5 N/tex [6]. 2.3. Characteristics of the Twisted Yarn a) Count. The woven fabric was produced using twisted yarns count Nm 5/2 as warp yarns. The designed twisted yarn is based on the characteristics of the single yarn. The nominal yarn count is Nm 2.5, and the effective count is between the limits given by the equation: (7) Nm e = Nm ± a where: a count deviation for the twisted yarn, given by (8) a t σ = n where: t = 2.04 for n = 30 and level of significance α = 0.05, while standard deviation for the twisted yarn count is: σ (9) σ = = 0. 35 σ 2 2 For σ = 0.38 m/g, it results σ = 0.133 m/g and a = 0.27 m/g. b) Diameter. Diameter of the twisted yarn depends on its packing factor and the average fibres density. The packing factor is 0.3 0.4 for thick carded and combed flax yarns (0.35 was adopted). The density of twisted yarn is: ρ = ν ρ f = 0.35 1.5= 0.525 g/cm 3. Yarn diameter is determined with equation: (10) D 2 =, [mm] π Nm ρ The diameter of the twisted yarn is D = 0.98 mm. c) Twist. Twist of yarn is calculated with equation: (11) T = αm Nm, [t/m] where: α m twist factor. Yarns for woven fabrics have twist factor of 100, resulting a nominal twist value of 160 t/m. For the average twist the confidence interval is
Bul. Inst. Polit. Iaşi, t. LVI (LX), f. 2, 2010 23 determined. The deviation of twist is 7.68 t/m for n = 30, level of significance α = 0.05, Student s test parameter t = 2.04 and twist standard deviation σ T = 0.35 18 = 6.3 t/m. d) Strength. Strength of the twisted yarn is determined from the transfer condition of the single yarn strength in the twisted yarn strength depending on the twisted yarn structure and is calculated with the equation [5]: (12) = N F Ku where: N number of yarns in the structure of the twisted yarn (N = 2); F single yarn strength ( F = 19.76 N); Ku strength transfer coefficient from single yarn to twisted yarn. The transfer coefficient from single yarn to twisted yarn depends on structure of the twisted yarn, particularly on twist, twisting direction and single yarn roughness. Strength transfer coefficient is 2 2.5 for the weaves made from thick flax yarns with S twist. If Ku = 2 the minimum strength of twisted yarns is = 79 N. The coefficient of variation of twisted yarn strength is lower than in the case of single yarn strength due to the plying effect, its maximum value being 25 / 2 = 18%. e) Force elongation curve. Force elongation curve for the twisted yarn can be approximate with a straight line that has the equation: (13) F = 5.32 a 5. 29 where: F strength of twisted yarn [N]; a elongation of twisted yarn [mm]. Fig. 3 presents the average force-elongation curve of the twisted yarn. Fig. 3 Force elongation curve of the twisted yarn. The following parameters can be determined based on the forceelongation curve:
24 Dorin Avram and Liliana Buhu - index of the work to break: 518 N mm; - index of specific work to break: 1.3 N mm/tex; - secant modulus of yarn: 6.6 N/tex [6]. 3. Conclusions Production of a biodegradable composite from flax woven fabrics and wood contributes to improving of composite s characteristics especially by: decreasing the mass per unit area; reducing the composite thickness; improving transversal and longitudinal tensile behaviour of the composite material; improving impact behaviour of composite material; It also offers the possibility of modelling the composite behaviour depending on destination. The yarns designed for the fabric used for the composite material satisfy the processability conditions. The experimental values presented in the paper constitute calculus elements for the fabrics design and for determining the characteristics of these fabrics. eceived: September 15, 2009 Gheorghe Asachi Technical University of Iaşi, Department of Technology and Design of Textile Products e-mail: davram@tex.tuiasi.ro E F E E N C E S 1. Golbabaie M., Applications of Biocomposites in Building Industry. Department of Plant Agriculture. University of Guelph, 2006. 2. Koichi G., Yong C., J. of Solid Mech. and Mat. Eng., 1, 9, 1073 (2007). 3. Avram D., Structura firelor. Edit. Performantica, Iaşi (2005). 4. Avram D., Structura şi designul firelor. Edit. PIM, Iaşi (2008). 5. Avram M., Avram D., Structura şi proprietăńile. Edit. Cermi, Iaşi (1998). 6. Hearle J.W.S., Grosberg P., Backer S., Willey Interscience, London (1969). FIE BIODEGADABILE PENTU łesătui UTILIZATE PENTU OBłINEEA MATEIALELO COMPOZITE (ezumat) În această lucrare au fost create caracteristicile firelor obńinute din fibre biodegradabile, care se vor utiliza la obńinerea Ńesăturilor. łesăturile pentru materialele compozite îmbunătăńesc caracteristicile fizico-mecanice ale compozitelor din lemn şi inserńii textile.