**2.4 Effect of finishing**

There are many researches in the literature related with the effects of finishing process on sensational properties of the fabrics. The diversity of fabric types with finishes available for any end-use continues to increase, making the selection of the most appropriate fabric an increasingly difficult task (Shanmugasundaram, 2008).

Different kind of end products can be produced from the same unfinished woven or knitted fabric by using various finishing treatments. High-speed scouring and milling create a fibrous surface as well as modifying other properties of the fabric, notably shear rigidity and specific volume. Heat treatments may cause fibres to crimp, increasing the bulkiness of the fabric. Soft handle and in some cases the 'peach skin' effect can be obtained by enzymatic treatment. By using cellulose enzyme, which acts on the fibril ends and causes their shortening, a slight pick-out surface can be obtained. Light brushing is another mechanical treatment that gives peach-skin effect to the fabrics. Raising and teaseling are the mechanical processes which draw fibres to the surface of a fabric to create a pile. Calendaring and also many chemical treatments (softening compounds, resins) give flatter surface that affect the fabric hand. Pressing and decatising are designed to flatten the fabric and create a smooth surface. Cropping and singeing are the processes which are designed to remove fibrous protrusions from the body of the fabric and thereby create a smooth surface. After the process of flame-retardant finishing, the stiffness parameters, especially bending and shear properties, increase significantly (Le et al., n.d., as cited in Stewart & Postle, 1974; as cited in Boos, 1988; Shanmugasundaram, 2008; Mamalis et al., 2001; Frydrych et al., 2002).

Sensorial Comfort of Textile Materials 241

The last part of the load extension curve, is due to the yarn extension. As the crimp is decreased, the magnitude of the loading force rises very steeply, and as a result, the fibers themselves begin to be extended. This is clearly a region of higher modulus (Figure 2a).

If the fabric undergoes in a cycling loading process, the fabric is first stretched from zero stress to a maximum and the stress is fully released, then an unloading process follows the loading process. As a result, a residual strain ε0 is observed, since textile materials are viscoelastic in nature. Due to the existence of residual strain, the recovery curve never return to the origin, as shown in Figure 2b. This is the hysteresis effect which denotes the energy lost during the loading and unloading cycle. Due to the existence of hysteresis, a deformed

 (a) (b) Fig. 2. (a) Schematic of a typical load- extension curve for a woven fabric (Schwartz, 2008),

Bending properties of fabrics govern much of their performance, such as hang and drape, and are an essential parts of complex fabric deformation analysis. The bending properties of a fabrics are determined by yarn bending behavior, the weave of the fabric and the finishing treatment of the fabric, the relationship among them are highly complex (Schwartz, 2008). Two parameters that characterize the fabric bending behavior are its bending rigidity and bending hysteresis. Bending rigidity can be defined as the resistance of textile against flexion by its specific weight and external force. Bending hysteresis can be considered as a

Figure 3 illustrates the typical bending curve for a woven fabric. For this curve, there are two stages with a hysteresis loop under low stress deformation. Firstly, there is an initial, higher stiffness non linear region (OA); within this region the curve shows that effective stiffness of the fabric decreases with increasing curvature from the zero motion position, as more and more of the constituent fibers are set in motion at the contact points. Secondly, a close to linear region (AB), since all the contact points are set in motion, the stiffness of the

In applications, where the fabrics are subjected to low curvature bending, such as in drapes, the hysteresis is attributed to the energy loss in overcoming the frictional forces. Under high curvature bending, the viscoelastic properties of the fibers must be considered (Schwartz, 2008).

fabric cannot resume its original geometrical state (Hu, 2004; Schwartz, 2008).

(b) Loading and unloading cycle in the tensile stress-strain curve (Hu, 2004)

measure of fabric's ability to recover (Pavlinić & Gerśak, 2003).

fabric seems to be close–to-constant (Schwartz, 2008).

**3.2 Bending properties of woven fabrics** 

Pigment printing is the most effective finishing process on the stiffness of the fabrics and mercerization before dyeing and printing results in improvements in various fabric properties; however cause negative effect in the fabric softness values (Özgüney et al., 2009).

The effects of the stiffness and softening agents on the friction and stiffness properties of the fabrics are apparent. When compared to the untreated fabric, all the softening and stiffening treatments result in decrease in the both static and dynamic friction coefficient values. Especially for softeners, this decrease is obvious. Shirley stiffness values of the fabrics treated with stiffeners are quite higher compared to untreated one whereas all the fabrics treated with softeners have lower values. The most stiffening effect is obtained with starch (Namligöz et al, 2008).
