THERMAL COMFORT PROPERTIES OF A BI-LAYER KNITTED FABRIC STRUCTURE FOR FOOTBALL SPORTSWEAR

Alemu Aduna^* and Sakthivel Santhanem
^*Correspondence: Alemu Aduna, Department of Textile Technology Faculty of Textile and Apparel Fashion Technology, Ethiopia, Email:

Keywords

Thermal comfort • Bi-layer • Sportswear • SAS.

Introduction

The producers of sportswear have been focusing their efforts on modifying their strategic position, productivity, added value product variety and niche positions in order to expand their markets [1].

Football players are much more aware of sportswear and demand more specific functions to be performed by it. As a result, a few fibers and fabrics are used to satisfy the needs and developments arising mainly in the areas of comfort and aesthetic acceptability [2]. Sports wears are worn next to the skin and are key to the physiological comfort of players and their attributes in this aspect are critical to their performance [3]. In traditional sportswear, players face problems like sweating and feeling hot while run. The requirements of football are sweat absorption, fast drying and cooling [4]. The comfort of sportswear can be achieved by thermo-physiological, skin sensorial, and psychological comfort. Moisture movement and the drying ability of fabrics are vital factors affecting the functional comfort of sportswear [5,6]. The capacity of layered fabric in thermo-regulation is better comparing to single layer structure [7-9]. For doubled layer fabric, it is recommended that the inner layer, which touches the skin, is made from synthetic fibers having good moisture transfer properties, such as polyester, acrylic and nylon. The outer layer should be made from fibers that have good moisture absorption properties such as cotton, wool, viscose or their blends [10]. Advancements in synthetic fibers have opened up huge avenues for their use in sportswear to meet specific requirements [11]. The growth in improvement and use of high-tech materials used in sportswear and outdoor leisure clothing is amazingly increased. The requirements of these products are properties of thermal insulation, blocking to liquids, stretch, thermal comfort etc. [12]. Sport tech and sports equipment that improve comfort and performance are grouped into three classes i.e. sportswear, sports good and games equipment. Synthetic fibers play a great role in current high technology sports uniform: warmth, wind resistance, moisture absorbency, and lightness; comfort and feel like natural fibers and style and variety of colors [13,14]. The objective of this study was to produce a bi-layer knitted fabric that will be comfortable for football sports. Characteristics of this structure concern the existence of two different fabric layers: the outer layer has hydrophilic properties, in which cotton yarn was used due to its high moisture absorption property; the inner part is hydrophobic fiber; polyester was selected due to its high-water transfer capillarity, lightweight and easy-care properties.

Materials and Methods

Two different types of yarns, cotton and polyester were used for sample preparation. The yarn linear density for cotton and polyester is 150 Decitex.

The bi-layer fabrics were knitted on an interlock jacquard knitting machine (Mayer & Cie – OVJA 36) machine gauge of 20, with a machine diameter of 32-inch, and number of feeders 36. Six samples were manufactured, two samples were plain single jersey structures, two samples were rib knitted structures and two samples were bi-layer knitted constructions as shown in (Table 1).

The yarn used for the inner surface is fed in the dial needle and the outer surface in the cylinder needle. The cam setting and needle order is shown in Figure 1. Due to heat generation around the back, under arm, and waist line, sweat is accumulated in sportswear, which is uncomfortable for players and disturbing their performance. Sweat generated should be evaporated to the atmosphere to keep the fabric dry. This can be performed by a bi-layer structure fabric in which the inner surface is made up of hydrophobic yarn and the outer surface of hydrophilic yarn.

Property Tests

Course and wale density were evaluated as per the ASTEM D3887 Standard [15]. Fabric thickness was evaluated as per ASTEM D1777 [16] and Fabric weight per unit area was according to ASTM D3776 [17]. The tightness factor of the samples was calculated by the formula below.

The air permeability of sample was measured using KES–F8 AP1, with the Air Permeability Tester following the BS 5636 1990 standard [18]. Thermal conductivity was measured using Lee’s disk instrument as per to Standard ASTM D7340 [19]. Water vapor permeability test is conducted using the evaporative dish method based on BS 7209:1990 [20].

Result and Discussion

Fabric structural parameters

As it is shown in table 2 below the areal density of all six samples varies according to the fabric structure (Tables 2 and 3).

Therma conductivity

It is related to the sample thickness, material type, and structure.

From table 3. It was observed that the value of thermal conductivity for S4 is higher whereas the lowest was for S6. Because S4 had lower thickness and higher volume of air with in it. It is significant to note that the higher number of tuck points increase in thickness shows a comparatively lower thickness than for one tuck point bi-layer fabrics. As it is seen from the figure 2, sample T4 has lower thickness value (0.70 mm) and higher thermal conductivity (0.051 Wm-1k-1) related to other bi-layer knitted fabrics. T5 and T6 have higher thickness of 0.98 and 0.81mm respectively with lower thermal conductivity of 0.039 and 0.024Wm-1k-1) respectively. This is because of the thermal conductivity of bi-layer knitted fabrics is highly dependent on the weight and thickness of the sample. As it is seen from the figure 2, sample T4 has lower thickness value (0.70 mm) and higher thermal conductivity (0.051 Wm-1k-1) related to other bi-layer knitted fabrics. T5 and T6 have higher thickness of 0.98 and 0.81mm respectively with lower thermal conductivity of 0.039 and 0.024Wm-1k-1) respectively. This is because of the thermal conductivity of bi-layer knitted fabrics is highly dependent on the weight and thickness of the sample (Figure 2).

Air permeability

This property is affected by the pores & thickness of the samples. Air permeability value of one tuck point in S4 was higher due to decrease in stitch density, as indicated in table 2 and 3. Lower of air permeability was mentioned in plain/single jersey, because loops are closely filled than bi-layer Knitted samples. Air permeability was lower for S5 and S6 because of more tuck points and higher thickness. The movement of air will be less in thicker samples and vice versa. Generally, air permeability of bi-layer samples decrease with the increase in thickness and stitch density. During sport activity sweat is formed and the fabric is wet, so the fabric should have enough air permeability results in higher vapor transfer. From figure 3, sample S4 has higher drying and wet ability 850 cc/sec/cm2 and 650 cc/ sec/cm2 respectively. Sample S5 has lower drying and wet ability 264 and 225 cc/sec/cm2 respectively. This is because of the thickness, weight and structural variations. The air permeability value was lower for S5 and S6 due to the presence of more tuck points, higher thickness and increased number of loops present per area. The movement of air will be less in thicker samples. Bi-layer fabric on S5 has thicker value so; it takes many times to dry and wet. The air flow theory states that the movement of air will be less in thicker fabric and more in thinner fabric. Even though the thickness is less for plain structure S1, and S2 the presence of more tuck stitches in S5 and S6 increases the flow of air from one-layer surface to the other. Finally, the air permeability of bi-layer sample fabrics can decrease with increased stitch density and thickness of the samples (Figure 3).

Water Vapor Permeability

Figure 4, indicates that Sample with lower thickness shows higher water vapor permeability. So, sample T4 and T6 had higher water vapor values of 2300 and 1855 gm-2.day-1 respectively because their thickness values (0.7 mm and 0.81 mm respectively) were lower than T5. As shown in table 4, sample S4 and S6 had higher water vapor values because their weight and thickness value were lower than S5. WVP of a sample is influenced by thickness, porosity and structure. S5 had lower air permeability because it had more thickness value. Sample with low moisture value can deposit sweat in the fabric which is uncomfortable. Fiber related factors, such as the cross-sectional shape and moisture absorbing properties, do not play a significant role.

Absorbency

As shown in table 3, bi-layer fabrics have greater value of water absorbency as related to other. S5 and S6 had higher absorbency of 92.4% and 82.1% respectively. Because as stitch density increase the moisture stored in the cloth increases. Bi-layer fabric with one tuck point (S4) had lower absorbency (79.6%) than bi-layer with five and seven tuck points (S5 and S6) fabrics because its thickness and weight were lower and vice versa.

Dry Behavior

The fabrics should have a quick drying capacity for the regulation of body heat. S5 has higher rate of drying. The drying capacity of a sample is dependable on thickness and weight. The sample with lower thickness value has the ability to transfer perspiration from inner surface to outer then easily dried. It is clearly seen on figure 5, that as the thickness of bi-layer fabrics increases, moisture absorbency also increases with the decrease drying behavior/ability. So, sample S4 and S5 has small thickness and easily drying ability (10.6 and 8.9 minutes). The drying ability of bi-layer and rib fabrics was greatly influenced by the thickness and weight of the fabrics, as a result of which there was lower thickness and the presence of a layer structure which has the ability to transfer perspiration from the inner layer (Polyester) of the fabric to the outer layer (cotton), which it easily gets evaporated and dried (Figure 5).

Statistical Analysis Using Sas Software

SAS software is used to analyze the effect of thermal comfort characteristics on plain, rib and bi-layer fabrics. The value of significance for the tests is 0.05 and the DF (Degree of freedom) is 3, 18 for plain, rib and Fcritical is 2.75. DF for bi-layer sample is 4,22 and Fcritical is 2.59. The summary of SAS is shown in table 4, which investigates the significant difference between the thermal comfort properties of plain, rib and bi-layer knitted structures. The value of Fcritical< Factual indicate that changes in the layer structures and types of fiber between Plain and rib fabrics show a significant difference with respect to thermal comfort properties (Table 4).

Conclusion

This research stresses on the thermal comfort properties of plain, rib and bi-layer knitted structures. The analysis results indicate that air permeability and thermal conductivity of bi-layer fabric with one tuck point are greatly influenced by the thickness and structure of the fabric. The WVP of the bi-layer fabric increases with a decrease in the thickness and presence of porous in the fabric. The structure also plays important role on the water permeability. During experimental work it is clearly seen that the moisture absorbency of the bi-layer knitted structure increases with an increase in the stitch density. The thickness and weight have influence on the drying ability of bi-layer fabric with one tuck point. Bi-layer fabric with one tuck point has the ability to transfers perspiration from the inner layer of the fabric to the outer layer, and it can easily evaporate and dried. The principal necessity of football sportswear is the rapid passage of perspiration away from the body and to keep the fabric dry as much as possible. This can be achieved by a bi-layer knitted fabric structure made up of polyester as the inner layer and cotton as the outer layer, recommended as sportswear for football players.

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