Evaluation of Impact of Yarn Count and Stitch Length on Pilling, Abrasion, Shrinkage and Tightness Factor of 1 × 1 Rib Cotton Knitted Fabrics

This study investigates the impact of yarn count and stitch length of 100% cotton knitted fabrics. 1 × 1 ribs structured fabrics were used in this research work. The stitch length 2.50 mm, 2.52 mm, 2.60 mm, 2.70 mm, 2.80 mm and 2.96 mm were used of the yarn count of 26Ne, 28Ne and 36Ne. The areal densities of the grey fabrics were in various amounts. The impacts of yarn count and stitch length were measured concerning pilling resistance, abrasion resistance, and shrinkage and tightness factor. The result showed that the fabric pilling grade decreased while number of cycle increased. Abrasion resistance decreased but length wise shrinkage increased despite the fact that the stitch length increased. The results also exposed that the tightness factor of the fabric increased with the increase of the stitch length in both dyeing and washing state and finished state compared to grey state for the yarn count 26Ne and homogeneous result not found for yarn count 28Ne and 36 Ne. Evaluation of Impact of Yarn Count and Stitch Length on Pilling, Abrasion, Shrinkage and Tightness Factor of 1 × 1 Rib Cotton Knitted Fabrics


Introduction
The most widely used fabric forming method is knitting and its principles is divided into two major sections namely warp and weft knitting [1]. In general, the knitted fabrics have more stretchable property compared to the woven fabrics [2,3]. Rib is a more costly and heavier structured fabric to produce than plain fabric [4]. The main utilization of knitted rib structures are in providing welts, cuffs, and collars for garments with plain-knitted bodies and sleeves [5]. Moreover, the knitted rib structures are also widely used in body lengths for outerwear.
The impact of different factors such as yarn count, twist, stitch length, various processing stage such as dyeing, finishing and washing process on the dimensional and physical properties such as pilling resistance, abrasion resistance, shrinkage and tightness factor of knitted fabric have been examined by many researchers.
Pilling is a surface defect and it's a noteworthy problem for textile manufacturers. The fabric quality considerably decreases and a negative influence on the user's comfort observed due to pilling [6]. The pilling is noticed as small fiber balls or group consisting of intervened fibers during wear and washing [7]. The fabric of compact construction shows less pills and opposite phenomenon for loosely knitted or woven fabric. Many scientists have investigated the factors affecting the pilling performance [8][9][10][11][12]. Pilling attitude is prejudiced by fiber properties, e.g. tensile strength, percent elongation, bending rigidity, shape of fiber cross-section and friction and structure of the yarn and fabric [13,14].
Physical damage of textile materials like fibres, yarns, and fabrics has made due to abrasion and abrasion occurs during wearing and washing. Abrasion ultimately results in the loss of performance characteristics, such as strength, but it also affects the appearance of the fabric [15]. The service life of the garment seriously depends on its end use. Abrasion is a serious problem for home textiles like as carpets and upholstery fabrics, socks and technical textiles as well [16,17]. The abrasion property of textile materials is effected by many factors (e.g. fibre fineness, yarn count, yarn type, weave etc.) in a very complex manner [18].
Fabric shrinkage is a serious problem for knitwear, which originates from dimensional changes in the fabric and it is a combined effect of number of factors such as relaxation, finishing, dyeing, and effects of machinery [22,23]. Shrinkage is very important to maintain the aesthetics of knitted products in the user ends. Different factors such as fiber characteristics, yarn parameters, Stitch length, yarn count, structure of fabric, machine parameters influence the dimensional characteristics of knitted fabrics [24,25]. The significance of shrinkage was investigated by many researchers [8,13,14,[26][27][28][29][30][31].
Fabric tightness implies the looseness and tightness and it varies with the stitch length of knitted fabrics. When the stitch length is big, the fabrics become slack and when the loops are small, the fabric is tighter [32,33]. Fabric area shrinkage is lower with a lower tightness factor and increases with the twist factor of the yarn. Tightness factor significantly influences the dimensional changes of knitted fabrics. Fabric tightness factor has examined by several researchers [34][35][36].
The objectives of this study were to disclose the effect of yarn count and stitch length on various fabric properties such as pilling resistance, abrasion resistance, and shrinkage and tightness factor (Figures 1-4).

Experimental Materials
The fabrics were collected from "DIVINE GROUP LIMITED", kaliakoir, Gazipur, Bangladesh [5]. The areal density, average course per inch (CPI) and wales per inch (WPI) of the grey samples are mentioned in the Figures 5-7 respectively.        Determination of abrasion resistance: By using the Martindale abrasion tester ISO 12947-1:1998 test method the abrasion resistance property was tested [41]. The samples are assumed for 500 cycles (Table  3 and Figures 5-8).

Fabric pilling
The Figures 9-11 illustrates the results of fabric pilling resistance. It is clearly evident from the figures that the pilling grade remarkably affected by number of cycles. For constant yarn count, the stitch length has no significant effect on the pill formations. The result showed that the fabric pilling grade deteriorated whilst the number of cycle increased. The lowest grade of pilling 2-3 is reported in the all samples except A and E for 2000 cycles. No pill formation or excellent pilling resistance is observed in the sample A for 125 cycles.

Abrasion resistance
The Figures 12-14       Determination of shrinkage: ISO 6330 test method was used to measure the shrinkage. Distance of points (which was marked in 35 × 35 cm 2 before wash) was measured in both lengthwise and width wise direction. The following formulas (1) and (2) were used to calculate the shrinkage percentage.

Series of experiment
Length Wise Shrinkage = (Before wash Length-After wash Length)/ (Before wash Length)×100% (1) Width Wise Shrinkage = (Before wash Width-After wash Width)/ (Before wash Width)×100% (2) Determination of tightness factor: The tightness factor is the measurement of level of fabric density [35,36]. The tightness factor was calculated by using equation 3 (Tables 4-6    weight loss percentage increased with the increase of stitch length when yarn count was kept in constant. But opposite scenario was observed for the sample H. During increasing stitch length from 2.52 mm to 2.60 mm for 36 Ne yarn, the weight loss percentage was decreased. It is clearly evident from the Figures 12-14 that the abrasion resistance is higher for lower stitch length.

Shrinkage
Fabric shrinkage is the most common problem of knitted fabrics. The good serviceable fabric should have least shrinkage. Figures 15-17 exhibits the outcome of fabric shrinkage. The length wise and width wise shrinkage were measured and plotted in the Figures 15-17. It is clearly evident from the figures that the width wise shrinkage is lower           than the length wise shrinkage except for the sample B. All samples showed positive shrinkage in both length wise and width wise direction while only sample F showed negative shrinkage in width wise direction. The highest shrinkage 10.29% is found in length direction for the sample of F and lowest shrinkage -2% is found for same sample in width wise direction.  represents the impact of parameters which are taken in the consideration in this work on fabric tightness factor. Tightness factors were measured in various processing stages. From the Figure  18, it is observed that the tightness factor of the fabric increased with the increase of the stitch length in both dyeing and washing state and finished state compared to grey state. The tightness factor were increased as 2.26%, 4.12% and 9.92% at dyeing and washing state and 7.91%, 10% and 14.91% at finished state accordingly for the samples A, B and C as compared to grey state ( Figure 18).

Tightness factor
From the Figure 19, it is identified that the tightness factor of the fabric increased with the increase of the stitch length in dyeing and washing state and decreased in finished state compared to grey state. The tightness factor were increased as 0.58%, 0.61% and 3.14% at dyeing and washing state for the samples D, E and F as compared to grey state. In finished state, the tightness factors were increased as 2.33% and 5.45% for the sample D and E and 1.89% decreased for the sample F as compared to grey state ( Figure 19).
It is clearly evident from the Figure 20 that with the increasing of the stitch length, the tightness factor of the fabric has increased in dyeing and washing state and finished state compared to grey state except for the sample F in the finished state. The tightness factor were increased as 5.59%, 1.92% and 2.68% accordingly for the samples G, B, H and I at dyeing and washing state compared to grey state. On the other hand, the tightness factor were decreased 3.73% for the sample G and increased 1.28 % and 10.07% for the samples H and I at finished state compared to grey state.

Conclusion
In this work, an attempt has been carried out to determine the physical characteristics such as pilling resistance, abrasion resistance and shrinkage of 1 × 1 rib structured 100% cotton knitted fabrics. The tightness factor was also investigated in different processing stages. Here, impacts of some controlling parameters like yarn count and stitch length were disclosed. From the above mentioned data it has been identified that the pilling resistance decreased when the number of cycle increased. Alternatively, abrasion resistance decreased while stitch length increased. The unveiled data has also indicated that the length wise shrinkage is higher than width wise shrinkage. The highest tightness factor was observed 1.91 for the sample of 2.70 mm stitch length of 26 Ne yarn at finished state.

Author Contributions
The objectives and methodology of this works were proposed by N.A.S. and R.U.R. The specimen fabrication, characterization and data treatment carried out by R.U.R. and N.A.S. with the help of N. A. The article was written by R.U.R. and. M.S.I. and revised by N.A.S., D.P., R.A.M., N. A. and S.S.