Fibres, which are polymeric materials, are the main elements of all types of fabrics.
To resist destruction, fabric must be capable of absorbing the energy imparted to it by the application of stress and releasing this energy upon removal of the stress, without any failure occurring. In other words, the fundamental physical properties of materials govern their ability to absorb and return energy. To eliminate the effects of form factor on samples investigated during experimental studies, fila- ment yarns with a minimum of twist were used (Hamburger, 1945). Similarly, much complexity is eliminated if the fabric specimen is constructed from mono- filament yarns (Backer and Tanenhaus, 1951).
Dimensional stability, tensile properties, friction, and fatigue phenomena are among the important durability properties of polymeric materials. Saville (2000) believes that there are a number of different causes of dimensional change. In that study, the following types of dimensional change connected with fibre behaviour are mentioned: hygral expansion, relaxation shrinkage, swelling shrinkage, and felting shrinkage. Additional information on this subject is given by Abbott et al.
(1964) and Cookson (1992).
Load–elongation diagrams of mechanically conditioned specimens were used
10 Understanding and improving the durability of textiles
by Hamburger (1945) for predicting the inherent abrasion resistance of textile materials. In that study, the desirable stress–strain properties of a fibre for maximum abrasion resistance were listed as follows: low modulus of elasticity;
large immediate elastic deflection; high ratio of primary to secondary creep; and high rate of primary creep. Gagliardi and Nuessle (1950) also have stressed the importance of fibre elongation as a requisite for higher abrasion resistance in fabrics. McNally and McCord (1960) believe that for good abrasion resistance, the values of fibre elongation and elasticity are more important than strength.
Elastic and visco-elastic properties, in particular, together with fibre-to-fibre frictional properties, are the main cause of fabric bagging (Hunter, 2009a).
Resistance to bagging deformation increases with an increasing fibre initial modulus. Recovery from deformation depends mainly upon the elastic and visco- elastic properties of the fibres. Friction, surface cutting, and fibre plucking are mentioned by Backer (1951) in a study of the mechanics of fabric abrasion.
Friction and surface cutting cause direct damage to the fibre at its points of contact with abrasive particles. Plucking may cause an immediate or dynamic fatigue rupture of the fibre at the point in the fibre length where the maximum stress concentration occurs. Frictional adhesion at the textile material surface may result in secondary damage to the fabric that far exceeds the direct effects of frictional wear. This indirect damage is caused by the transmitting of frictional forces along the length of the surface fibres and is evidenced in the tensile or bending fatigue of the fibre or in its removal from the yarn.
Pills are formed by a rubbing action on loose fibres present on the fabric surface (Saville, 2000). The greater the breaking strength and the lower the bending stiffness of the fibres, the more likely they are to be pulled out of the fabric structure. Hunter (2009b) believes that stronger and higher-elongation fibres generally lead to a greater degree of pilling. Other studies deal with the interaction between types of polymer and the durability of textile fibres or yarns. Thomson and Traill (1947) studied the flexural endurance of several fibres. The results of the study are not strictly comparable since the stresses developed in the fibres vary with their diameter, but the superiority of wool and polyamide and the poor performance of cellulose acetate, casein and glass fibre are notable. A study made by Hicks and Scroggie (1948) found that the abrasion resistance of yarns increased in the following order: acetate rayon, normal viscose rayon, medium-high-tenacity viscose rayon, acrylic, and polyamide. High abrasion resistance in polyester was reported by Amirbayat and Cooke (1989). Ozdil et al. (2009) also noted that synthetic fibres such as polyester, polyamide fibres or elastane filaments, increase the abrasion resistance of a textile material. The resistance of wool, which was also studied in this paper, was found to be higher than that of acrylic. Elastane, which has good recovery properties, will also favourably affect the bagging performance of textiles (Hunter, 2009a).
The durability of blended structures with two components, as well as those with novel fibres, has also been studied (Candan and Onal, 2002). In this study, knits
Influence of fabric construction and fibre type on textile durability 11 from a blend of 50% cotton/50% polyester spun yarns tended to show a greater tendency to pill than did knits using cotton spun yarns. Kalaoglu et al. (2003) investigated the abrasion properties of two variants of 50% wool/50% polyester blended fabrics, the spun yarns of which were made from a novel polyester fibre with a special channelled contour, and conventional polyester fibre. The results suggested that the novel polyester fibre caused a slight decrease in the resistance of the fabric to abrasion.
One more group of factors affecting fabric durability is that of fibre geometry.
The influence of fibre diameter, length and crimp has been widely studied. Finch (1951), in a study of inter-fibre stress and its transmission, showed that the geometrical area of individual fibres depends upon the normal load at the point of contact, the principal curvatures of the fibre, the contour of the fibre cross-section and the fibre bulk modulus. The bulk modulus is a major factor in fabric structures, influencing the contact area under a given load. The local load at a fibre point will be smaller where the bulk modulus is low. As local load is reduced, the actual area of contact at each point is also reduced and the abrasive protuberance will descend into the yarn structure to a lesser degree. Increasing the fibre diameter up to a limit improves the abrasion resistance (Saville, 2000). Similarly, in spunbonded nonwoven fabric (Kothari and Das, 1993), a fine fibre may bend under a lower load than a coarser fibre and, as a result, fabric made of finer fibres should have a higher degree of compressibility. The propensity to pilling decreases when the fibre diameter is increased (Beltran et al., 2006b) because stiffer fibres are more resistant to entanglement (Hunter, 2009b). Fabrics made from bulked continuous filament yarns are particularly susceptible to the formation of snags (Saville, 2000). These are loops of fibres which are pulled from a fabric when it comes into contact with a rough object. Longer fibres incorporated into a fabric confer better abrasion resistance than shorter fibres because they are more difficult to remove from the yarn. For the same reason, filament yarns are more resistant to abrasion than staple yarns made from the same fibre. Thus, for example, longer polyester and combed cotton improve abrasion resistance (Bhortakke et al., 1997). Hunter (2009b) claims that longer fibres are generally preferable in terms of pilling. An increase in fibre crimp is also generally associated with a reduction in fabric pilling.
1.3.1 The effect of yarn structure on fabric durability
The values of yarn geometry and yarn properties have been widely studied, with the intention of showing their effect on durability characteristics, especially those of abrasion resistance, compressibility, bagging and pilling performance. Current studies include durability tests on yarn sheets and on the durability of fabrics made from different types of yarns. Yarn twist, yarn diameter, yarn ply, and other parameters of yarn geometry have been studied as factors impacting upon fabric durability.
12 Understanding and improving the durability of textiles
Morton (1948) believed that for good wear resistance, any tearing-out action is reduced by firm binding of the fibres. This increased cohesion may be achieved in both filament and spun yarns through increasing their solidity by means of a greater number of twists. The effect of twists on a sheet of yarns was examined by Hicks and Scroggie (1948). In this research, the abrasion resistance reached a maximum with an increased number of twists. A decrease in durability at a lower number of twists is thought to be due to the ease with which snagging or picking may occur in filaments that are only loosely intertwined with each other. Where there is a higher number of twists, the durability decreases, which may be due to an increasing movement of components in the direction of the wheel path.
Evaluations of wear resistance in fabrics differing only in yarn twist have been carried out by Backer and Tanenhaus (1951). These tests showed a very slight, though consistent, improvement in fabric wear as the value of the twist factor of either the warp or weft yarn was increased. It is important to note that the use of a lower number of twists is an alternative method of increasing the contact between individual yarn crowns in a woven structure and the abradant. So the compressive properties of a yarn and its cohesion play a dual role in determining abrasion resistance as the number of twists is altered. These results accord with the finding (Saville, 2000) that there is an optimum amount of twist in a yarn which will give the best resistance.
Beltran et al. (2006b) examined pilling in fabrics made from wool yarns.
According to that study, the propensity towards pilling decreases with an increase in the twist factor of a spun yarn. However, at the highest twist level, there is little further effect on pilling (Hunter, 2009b). Stankovic and de Araujo (2010) exam- ined the effect of twists in cotton yarn on compression in knitted fabrics, finding it to be the result of complex interactions of yarn bulk and residual torque.
Yarns with increased twist may be used to improve the bagging performance of fabrics (Hunter, 2009a). Smooth yarns with low hairiness exhibit better bagging performance.
The association of greater wear life with increased thickness of a given material has been reported many times. For instance, important data on the abrasion of vinylidene monofilaments have been reported by Backer and Tanenhaus (1951).
Two series of experiments on multi-filament yarns were discussed by Hicks and Scroggie (1948). One series was concerned with the abrasion testing of yarns of different linear densities but with the same linear density per filament. The increase in abrasion life with increased linear density was thought to be due to the large number of filaments that must be abraded before a single yarn failure would occur in a given yarn sheet. The indications were that these results are in accordance with the generic experience which shows the abrasion resistance of fabrics made from coarser yarn to be considerably greater than that of fabrics made from finer yarn.
Another series of results is given to show the effect of filament linear density in a yarn. Fine-filament yarns have poorer wearing properties than coarser-filament yarns. Kretzschmar et al. (2007) and Ozdil et al. (2009) also noted that the use of
Influence of fabric construction and fibre type on textile durability 13 coarse yarns improves abrasion resistance. However, an increase in linear density increases the tendency to pilling (Beltran et al., 2006b). Hunter (2009b) affirms that although there is conflicting evidence concerning the relationship between yarn linear density and pilling propensity, the balance of evidence indicates that finer yarns produce less pilling if all other factors are constant. Abrasion resistance in plied yarns depends upon the number of plies, as well as on the yarn size.
Abrams and Whitten (1954) have shown the resistance of a two-ply yarn to be approximately five times that of a single yarn of equal linear density. Plying also tends to decrease the propensity to pilling (Hunter, 2009b).
In recent years, the wear behaviour of textiles made of a variety of spun yarn structures, e.g. sirospun yarns, ring yarns, compact yarns and open-end yarns, has been intensively investigated. Kalaoglu et al. (2003) studied the abrasion charac- teristics of wool/polyester blended fabrics and compared two-strand sirospun yarns and two-fold ring yarns. The samples made from sirospun yarns were found to wear faster than the samples from ring yarns, but the differences in their mass losses and structural degradation (SEM views were taken) were not significant.
Alpay et al. (2005) examined the colour differences and percentage reflectivity changes that occur in dyed cotton woven fabric after abrasion. In this study, ring and open-end spun yarns were used in the weft direction and, in many cases, only slight differences were observed. However, fabric with thicker open-end spun weft yarn was more affected than that with thinner open-end spun weft yarn. In three samples with different yarn twists, it was observed that the smallest colour differences occurred in weft yarn with the highest twist, and the greatest colour differences occurred in weft yarn with a medium twist value when compared with the wefts of the other two. Fabric with two-ply weft yarn was more affected than fabric made from a single yarn. The percentage reflectivity and colour difference are less obvious in samples with regular spun yarns, e.g. ring spun yarns.
In studies by Ozdil et al. (2005) of fabrics made from compact spun yarns and ring spun yarns, compact spun yarns were found to exhibit a better pilling performance. Similarly, Omeroglu and Ulku (2007) found that fabrics manufac- tured from compact spun yarns had better pilling and abrasion resistance than those produced from ring spun yarns. Fabrics made from compact spun yarns also experienced a lower loss of mass when compared to those produced from ring spun yarns. This is explained by the different degree of hairiness of the yarns. Akaydin and Can (2010) pointed out that the fibres of compact spun yarns hold together more tightly within the yarn structure as they have a more dense and close structure than ring spun yarns. As a result, the fibre movements that cause abrasion and pilling are limited. Therefore, the abrasion resistance and pilling performance of fabrics produced from compact yarns are higher than those made from ring spun yarns. Candan et al. (2000) concluded that because the hairiness of cotton ring spun yarns is higher than that of open-end spun yarns, the fabrics from ring spun yarns tend to pill more. This trend is in line with the observations of Candan and Onal (2002).
14 Understanding and improving the durability of textiles
The wear properties of fabrics manufactured from ring carded, ring combed and open-end rotor spun yarns have been studied by Can (2008). In this study, the abrasion resistance and pilling performance of fabrics made from open-end rotor spun yarns had a maximum value, while the same performance factors of fabrics produced from ring carded spun yarns had a minimum value. Can (2008) believes that hairiness is the characteristic quality of yarn that affects abrasion resistance and pilling, i.e. an increase in yarn hairiness reduces fabric abrasion resistance and pilling performance. Hunter (2009b) indicates that air-jet and rotor spun yarns perform better than ring spun yarns in terms of pilling. Kretzschmar et al. (2007) noted that the type of manufacturing (compact or conventional ring) and the twist coefficient of spun yarn did not have a significant effect on the abrasion resistance values of knitted fabrics. However, the pilling values of fabrics knitted with compact spun yarns were better than those produced with ring spun yarns. Pilling values also improve when the twist of the yarn is increased. Trends in pilling have been explained by the low hairiness values of compact spun yarns and of highly twisted yarns.
In several studies, the wear properties of textile materials made from fancy yarns were examined to determine the effect of yarn factors. Nergis and Candan (2003) tested the abrasion resistance and pilling performance of plain knitted fabric made from fancy (chenille) yarns. The study showed that yarn properties, i.e. the linear density of component yarns and pile length, do not influence the pilling perform- ance of the samples. In dry relaxed fabrics, the loss of mass tended to increase as the pile length increased and the component yarn became finer. Ulku et al. (2003) noted that in chenille fabrics, the average mass loss has a tendency to decrease with an increase in twist level and pile length. Ozdemir and Ceven (2004) studied the influence of the manufacturing parameters of chenille yarns on the resistance of yarn and upholstery fabric to abrasion. The yarn twist and pile length were found to have a significant effect. Chenille yarns with high twist levels will undergo less abrasion than yarns with low twist levels. Yarns with longer pile lengths are more resistant to rubbing than those with short pile lengths.