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The five knitted fabrics were analysed and their properties are presented in Table 5.1. The mass per unit area (g/m2_{) ranged from lightweight (70−100 g/m}2_{) to heavy weight}

(300−375 g/m2_{), as classified by Collier and Epps [44]. These weight ranges were selected}

to evaluate which fabric could best hide body contour while retaining the benefits of a knitted structure. Among all the fabrics, fabric N100 was the heaviest at 349 g/m2 _and

thickest (1.15 mm) with the lowest thread density in both the course and wale directions. This is because fabric N100 was made from coarse yarn (20 tex) and had an interlock knit structure. This resulted in the tightest structure and the lowest optical porosity among the fabrics [63]. Fabric P96E4 was slightly heavier (184 g/m2_{) than the other medium weight}

fabrics. It is likely that this was brought about by contraction of the 4% elastane component when the fabric came off the knitting needles. Fabrics W50N50, P65C35 and W100 were made of staple fibres. Fabrics P65C35 and W100 had similar medium weight, stitch density, optical porosity and cover factor, but different thickness and structure. Fabric P65C35 was thicker than fabric W100 because it had a double jersey knit structure. In addition, hairiness due to the cotton component (Figure 5.1) could also be a contributing factor. Comparing similar data for woven fabrics (Table 4.1), it can be observed that most of the knitted fabrics were thicker and heavier.

SEM images at 100× magnification were used to observe the fabric structure. Figure 5.1 confirms that there were notable differences between the fabrics under the same magnification and imaging conditions. Some key variations are the knit structures and the thread density.

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Figure 5.1 Knitted fabric images from a Scanning Electron Microscope.

Table 5.1 Physical properties of knitted fabrics.

Fabric code N100 W50N50 P96E4 P65C35 W100

Knit structure Interlock Single jersey Single jersey Double jersey Single jersey

Fibre composition 100% _{nylon wool/nylon} 50/50 polyester/ 96/4 elastane

65/35 polyester/

cotton 100% wool

Yarn structure Filament _{Nylon: filament} Wool: spun, Filament Spun yarn Spun yarn

Yarn count [tex] 20 18 17 18 20

Fabric mass [g/m2_{] 349 127 184 176 174} Thickness [mm] 1.15 0.64 0.50 0.80 0.54 Courses/cm 18 16 22 20 20 Wales/cm 12 15 20 15 17 Optical porosity [%] 1.45 8.51 6.45 8.66 5.64 Cover factor 0.95 1.37 1.78 1.40 1.77

5.3.2 Stretch and recovery

The stretch and recovery properties of the fabrics are shown in Figure 5.2 and Figure 5.3. The results indicate that P96E4 had the highest stretchability and lowest residual extension in the course-wise direction as compared to the other fabrics. This is most likely due to the presence of elastane filaments [181, 182]. A higher percentage of recovery after stretching indicates better dimensional stability on loading of knitted fabrics [183]. According to Senthilkumar et al. [184], even a low percentage (2–3%) of elastane is sufficient to provide desirable stretch properties of woven or knitted fabrics. It should be

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noted that here the elastane serves to promote dimensional stability rather than increase adherence to body contour. This is significant considering that the abaya is worn over other garments. Fabric W100 showed the lowest residual extension possibly due to its single jersey structure, which could be a suitable characteristic for abayas. It is advantageous if an abaya has excellent recovery properties in the wale-wise direction so as to maintain its original shape.

Figure 5.2 Stretchability of abaya knitted fabrics.

Figure 5.3 Residual extension after recovery under load of 30 (N) of the abaya knitted fabrics.

5.3.3 Fabric drape

The average values of the fabric drape coefficient (DC) (Figure 5.4) indicate a range from 20% to 50%. Thus the fabrics fall between the limp and medium categories [59]. Fabric N100 with nearly 50% DC is classified as a medium fabric. Fabrics W100, W50N50,

0 40 80 120 160 200 N WN PE PC W St ret ch (%) Fabric

Wales-wise stretch Course-wise stretch

0 4 8 12 16 N100 W50N50 P96E4 P65C35 W100 Resid u al ex tent io n (%) Fabric

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P65C35 and P96E4 exhibit drapeability in the range between 20−40% because they were thin and flexible. The results are in agreement with those of Wang [181], who stated that drape behaviour is affected by knit fabric structure. Fabrics W100, W50N50 and P96E4 would be more suitable for abayas, because drapeable fabrics display more nodes or folds in a circular draped configuration [185]. In addition, knitted fabrics with a lower drape coefficient (<20%) can be formed more easily and they fit easily to the shape of the body [186], hence, the DC property between the limp and medium categories is desirable for knitted abaya because the fabric will not reveal too much body contours. Although the abaya is a loose-fitting outer garment, it may occasionally reveal body contour if made from fabrics that drape well. Chen et al. [187] evaluated the relationship between fabric thickness and drape coefficient; they found that DC increases proportionately to thickness when fabric thickness is between 0.4 and 0.8 mm, which means drapeability is good. The thickness of fabrics W100, W50N50 and P96E4 was determined to be 0.54mm, 0.64mm and 0.5mm respectively. These are in the range studied by Chen and may be considered as possessing good drapeability. However, fabrics N100 and P65C35 with thickness ≥0.8mm show higher DC values than the other fabrics. These fabrics may be expected to show medium drapeability compared with fabrics W100, W50N50 and P96E4.

Figure 5.4 Comparison of drape coefficients of abaya knitted fabrics

0 10 20 30 40 50 60 N100 W50N50 P96E4 P65C35 W100 Dr ap e coff ic ie nt s (DC ) % Fabrics

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5.3.4 Air permeability

The air permeability is mainly dependent on a fabric’s weight and construction (thickness and porosity) [58, 175, 188]. Air permeability was measured with 50 Pa pressure difference across the fabrics because for some fabrics the instrument could not generate the 100 Pa pressure difference required by EN ISO 9237-1995. Figure 5.5 shows that all tested fabrics were highly air permeable, except fabric N100. This may be due to the fact that fabric N100 was thicker and heavier, with lower optical porosity, than the other fabrics. Thus the fabric is less porous, and this restricted the flow of air through the fabric. The air permeability of fabrics W50N50 and P65C35 was higher than that of the other fabrics because of their more open structures, as seen in Figure 5.1. Higher air permeability reduces perspiration discomfort [23]. These two fabrics had high optical porosity, low cover factor and fewer courses/cm (Table 5.1), which facilitated the passage of air through them. The experimental results agree with those of Ogulata and Mavruz [69], who found that fabrics with the lowest course count per cm and yarn number in tex had the highest air permeability values. Therefore, increasing loop length resulted in a looser surface on the fabric, thereby increasing the air permeability.

Linear regression line (Figure 5.6) shows that there was a significant relation r ≤= 0.9762, (p<0.001) between air permeability and optical porosity: as air permeability increased, optical porosity increased. These results agree with those of Ogulata and Mavruz [69], who found that air permeability and optical porosity are strongly related to each other. If a fabric has very high porosity, it can be assumed that it is permeable. Fabrics P96E4 and W100 also showed moderate air permeability. These fabrics had almost the same stitch densities and lower porosities (Table 5.1) and the structures of the fabrics were a little tighter than those of W50N50 and P65C35. This observation agrees with various studies reported on the factors affecting the air permeability of knitted fabrics [62, 63, 67, 69, 189] depending on geometrical parameters such as courses per cm, wales per cm, stitch length, fabric thickness, yarn count and fibre density.

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Figure 5.5 Comparison of air permeability values.

Figure 5.6 Correlation between air permeability and optical porosity.