Different levels of textile materials structure, i.e. fibre level, yarn level, and fabric construction level, can be applied to fabrics that are not homogeneous isotropic materials. Figure 1.1 shows that there are three main types of fabrics: woven, knitted and nonwovens. As indicated in Fig. 1.1, these may be further subdivided into several classes. Fabrics represent a two-phase system of air and fibre. Fibres and/or yarns, and sometimes other materials, are components of a fabric construc- tion. In a typical yarn, each fibre is helically twisted, or compacted by other means, into a cylinder of varying hardness with other rod-like fibres that differ somewhat in diameter, length, cross-section and morphology. Conventional woven fabrics of two-dimensional (2D) structure are made by interlacing two sets of yarns at right angles to each other. The yarns running along the cloth length are called the warp;
the yarns in the perpendicular direction, the weft. The weave, together with yarn linear density and thread spacing, determines the construction of woven fabric.
There is a very large variety of weaves in woven fabrics, but plain, twill and satin weaves are the basic (elementary) weaves that are widely applied in a great number of single woven fabrics. In the plain weave structure, as shown in Fig. 1.2(a), each warp yarn interlaces with each weft yarn alternately, on the one-up/one-down
Influence of fabric construction and fibre type on textile durability 5
1.1 Main types of fabric construction.
principle. Thus the plain weave represents the closest possible interlacing of warp and weft. In twill weaves, the warp or weft floats on the surface of the fabric producing a diagonal pattern (Z or S twill lines). Figure 1.2(b) shows a 1/3 twill weave with a Z twill line. The twill lines are produced by allowing all the warp ends to interlace in the same way, but displacing the interlacing points of each end by one pick relative to that of the previous end. Satin weaves have long yarn floats (over four yarns minimum), with a progression of interlacing by a defined number (over two yarns minimum). If the warp covers the surface, as shown in Fig. 1.2(c), the fabric is called warp satin cloth. When weft yarns predominate on the face of the fabric (see Fig. 1.2(d)), sateen is produced, a weft-faced fabric. Other classes of weaves are derivative, combined and complex weaves. Besides the above- mentioned single fabrics, there are compound woven fabrics, e.g. double, treble cloths, tubular fabrics, pile fabrics, three-dimensional (3D) fabrics and tri-axial fabrics.
Knitted fabric can be made by inter-looping from a single yarn or an assembly of yarns. In a knitted structure, the basic element is a needle loop. The knitted stitch is the basic unit of inter-meshing and there will usually be three or more intermeshed needle loops in a knitted stitch. Knitted structures may be composed of stitches containing both open and closed loops.
Woven fabrics Single woven fabrics Compound woven fabrics
Fabrics
Knitted fabrics Weft knitted fabrics Warp knitted fabrics
Stitchbonded fabrics Adhesive-bonded fabrics
Spunbonded fabrics Spunlaced fabrics Needlebonded fabrics
Nonwovens
6 Understanding and improving the durability of textiles
1.2 Weaves of woven fabrics: (a) plain; (b) 1/3 twill; (c) 8-end warp satin; (d) 8-end sateen.
Figure 1.1 shows the two classes of knitted structures: weft knitted fabrics and warp knitted fabrics. As shown in Fig. 1.3, a weft knitted fabric is constructed from a single yarn, with the loops made horizontally across the fabric. There are three basic structures of weft knitted fabrics: plain pattern, rib pattern, and purl knit pattern. There is also a wide range of weft knitted derivatives, but the knit-miss pattern and the interlock pattern are the most widely used. Warp knitted fabric, as shown in Fig. 1.4, is a vertical loop construction made from one or more sets of warp by forming loops. There is a large variety of warp knitted fabrics. Pillar stitch, single (bar) tricot stitch, and atlas are the simplest one bar warp knitted structures.
A wide range of knitted fabrics can be made on several bar warp knitting machines.
Directionally oriented warp knitted fabrics (see Section 1.4.2), 3D knitted fabrics (see Section 1.6), and a great number of other knits are textile materials of complex structure. In addition to the above-mentioned woven and knitted fabrics, some textile structures have a combined woven–knitted construction consisting of alternating woven and knitted stripes.
Nonwovens are another type of textile structure. In the current study, this term is applied generically to textile materials made from a web of fibres only, or from fibres and sets of yarns (such as Maliwatt or Malimo), or from fibres and a bonding agent and by other unconventional methods. Both web formation and bonding may take several forms. Homogeneous and heterogeneous nonwovens, and materials with isotropic (random) and anisotropic structures are widely used.
Figure 1.1 shows the main classes of nonwovens: stitchbonded fabrics, adhe- sive-bonded fabrics, spunbonded fabrics, spunlaced fabrics and needlebonded (needlepunched) fabrics. Additional new production technologies have also intro- duced new nonwoven structures. One example of such a structure (Maliwatt) consists of using warp knitting technology units to stitch a fibre web with yarn.
Another stitchbonded structure (Malimo) uses three sets of yarns in which the warp and weft sets are stitched together using a third system consisting of sewing threads. In adhesive-bonded fabric structures, webs of fibres are strengthened by
(a) (b) (c) (d)
Influence of fabric construction and fibre type on textile durability 7
1.3 Schematic construction of weft knitted fabric (example of plain pattern).
1.4 Schematic construction of warp knitted fabric (example of tricot pattern).
fibre-to-fibre adhesion. The fibre distribution of the web may be random or oriented. Adhesion is achieved by means of a bonding agent, which may be a thermoplastic additive or an aqueous emulsion. The thermoplastic materials used for bonding web fibres are yarns, films, powders, nets and fibres (including hollow and bi-component fibres). Spunbonded fabrics consist of a web in which extruded manufactured fibres are bonded together on a moving surface by means of
8 Understanding and improving the durability of textiles
adhesive, thermobonding, or needlepunching. Spunlaced fabrics are made by the entanglement of fibres in the web by means of high-pressure water streams.
Needlebonded fabrics may be produced by using a web of fibres of various types and blends, which are interlocked by using needles to transfer the fibres.
In addition to woven, knitted and nonwoven fabrics, various other combined forms should be noted. These include coated textile materials, multilayer textile packets and laminated structures, some of which are likely to be of future importance.
1.2.1 Characterising different fabric structures
Because woven fabrics, knitted fabrics, and nonwovens may be composed of various types of fibres and systems of yarns, or other components used for covering, laminating or special finishing (e.g. antistatic, flame-retardant, breath- able), a large number of indices are applicable to fibres, yarns and fabrics. The properties of fibres are determined by the nature of their chemical composition, by the fine molecular structure of the constituent polymer and by the external structure of the fibres. One of the main factors that can affect the properties of yarn is the fibre and yarn geometry. The geometrical factors of fibre linear density, fibre length, yarn linear density and yarn twist are particularly important. Additional information on a variety of characteristics that define the geometry of various fibres and yarns is given by Hearle et al. (1969), Hongu and Phillips (1997), Lawrence (2003), Hongu et al. (2005), Petrulis (2009), Chen and Hearle (2010), Grishanov (2010) and Ognjanovic (2010).
Fibres are used in the form of spun yarns, filament yarns or webs in the manufacture of various types of fabrics. The main construction indices of woven, knitted and nonwoven fabrics are given below. The parameters used in the manufacture of woven fabrics are the linear densities (count) of the constituent yarns (warp and weft), the warp and weft sets and the weave. These factors and the fabric manufacturing conditions (tension control parameters, etc.), taken together with other properties of the yarns, affect the parameters of grey fabric (i.e. fabric in the loom state) construction. These fabric construction parameters include cloth densities in the warp and weft directions, the crimp of the warp and weft, various indices of cover factor, the fabric area density (mass per unit area) and the thickness of the cloth. The sources for woven fabric construction are studies by Hearle et al. (1969), Zurek and Kopias (1983), Hu (2004), Chen and Hearle (2010) and Vidal-Salle and Boisse (2010).
The construction of knitted structures is characterised by the shape and size of loops, the linear density of the constituent yarns and the type of tricot structure. The values of the loop width and height, the loop shape factor and other parameters, are used to analyse the loop geometry. Other important indices of knitted fabric construction are the cover factor (tightness), stitch density (i.e. wale density, course density and the total number of loops in a measured area of knitted fabric),
Influence of fabric construction and fibre type on textile durability 9 area density, and thickness. Additional data on the construction indices of knitted structures are given by Hearle et al. (1969), Spencer (2001), Chen and Hearle (2010) and Kyosev and Renkens (2010).
Indices of area density and thickness, data on the uniformity of nonwovens and various indices of their integral parts or layers and connecting (bonding) param- eters may be applied when characterising the construction of nonwovens. Fibre orientation in the web and the fineness, cross-sectional shape, length and crimp parameters of fibres are important factors in a great number of nonwovens. The structural parameters of bond points include the bonding area, bond point distribu- tion, bonding shape and bonding density. More data about nonwoven structures and their characteristics are given by Hearle et al. (1969), Jirsak and Wadsworth (1999), Magel and Bieber (2003), Magel et al. (2003) and Mao and Russell (2010).
In more complex or specific textile structures, for example compound fabrics and combined forms of nonwovens, additional construction parameters may be sug- gested.
The indices of textile material construction, including area density and thick- ness, are different after finishing when compared with those of grey products.
Therefore, knowledge of the construction characteristics of finished materials is essential for understanding the durability properties of the final products. This may be applied not only for newly finished materials, but also after a period of wear.
These changes of fabric construction can be characterised by parameters of dimensional stability.