Comparison of High Thread Count Cotton Fabrics for Comfort and Mechanical Properties

Comparison of High Thread Count Cotton Fabrics for Comfort and Mechanical Properties
Anshul Raheja
M.Tech in Textile Engineering, Indian Institute of Technology,
Delhi, New Delhi-110016, India
Email: anshulraheja1241990@gmail.com



Abstract
The present paper is concerned with a brief review of comparison among high threads count percale, oxford and satin weave fabrics made of hygro and normal cotton yarn. For comparing properties of hygro and normal cotton yarn fabric, we have measured different fabric parameters like g/m², thickness, and yarn count. Various comfort related properties like air permeability, thermal resistance, water absorbency, water vapour transmission rate and durability properties like tensile strength, bursting strength, tearing strength and abrasion resistance have also been evaluated.All these observations help to find out which coporomfort and durability properties are better in either of high thread count hygro and normal cotton yarn fabrics. We have also examined the influence of repeated washing on the comfort related and mechanical properties of high thread count hygro yarn fabrics.

Key words: Air Permeability; Thermal Resistance; Comfort; Durability.

1. Introduction
Cotton is the most used and favoured fibre for bed sheets. There are many different types of cotton fibres used for bed sheets along with many blends. To determine the quality of a cotton sheet, most manufactures give a thread count. The thread count can range anywhere from 200 to 1200 with the majority accepting between 200 and 800 is enough for a good quality bed sheets. A higher thread count means a sheet retains its properties for longer and won’t need replacing.

The clothing comfort is dependent upon the low-stress mechanical, thermal and moisture transfer properties of the fabrics. There is a general agreement that moisture transmission through textiles has a great influence on the thermo-physiological comfort of the human body, which is maintained by perspiring both in vapour and in liquid form. Yoon and Buckey (1984) suggested that many of the transport and related properties of a fabric, such as air permeability, water transmission rate, thermal resistance and liquid water transmission properties, are highly dependent on constituent yarn geometry.

Recently, hollow/microporous yarn production and its application in fabrics have increased. Hollow/microporous yarn spinning is a technique used to increase the bulk of yarn without increasing its weight. Merati & Okamura (2000) found that friction-spun hollow cotton yarn possesses a higher degree of softness and bulkiness than conventional cotton yarns. The diameter and ellipticity ratio of the hollow yarn are higher than those of the cotton yarn (Merati & Okamura, 2001). In addition to higher compressibility, the hollow yarn shows better compressional recovery. The volume of the hollow yarn after compression is also greater than that of the conventional cotton yarn. Based on the study of cotton–PVA (polyvinyl alcohol)-blended ring spun yarn, Ishtiaque et al. (2008) found that the yarn-specific volume of a hollow yarn increases with increase in the PVA percentage. Consequently, the yarn packing factor decreases with the increase in the PVA content. Changes in yarn structure result in higher yarn compressibility.

Radiant heat resistance testing instrument
Fig. 1 Radiant heat resistance testing instrument
The air permeability of a fabric is affected by the fabric material such as fibre fineness, structural proper-ties such as shape and value of the pores of the fabric and the yarn, and fabric thickness. Thermal properties of textiles may be affected mainly by type of the fibre substance, thickness of the fabric, enclosed still air and bulk density of the fabrics.

The thermal conductivity and specific heat of the fibre substance may affect the thermal properties of the fabric, but is of little consequence. Water vapour canpass through textile fabrics by different processes namely (1) diffusion of the water vapour through the fabric; (2) absorption, transmission and desorption of the water vapour by the fibres; (3) adsorption and migration of the water vapour along the fibre surface; and (4) transmission of water vapour by forced convection.Liquid moisture transmission is determined mainly by type of fibre, yarn structure such as arrangement of the fibres, pore size, effective capillary pore distribution in the yarn packing density, and fabric structure such as size and number of the capillary paths through the fabric.

2. Material and Methods

2.1 Material
Eleven different fabrics were prepared of different weave like percale,oxford and satin. Two types of yarn were used for making fabric are hygro cotton yarn and normal cotton yarn. In hygro yarn composed of PVA fibres (10%-20%) that dissolved in water during processing. The hygro used as weft in the fabric and number of weft yarn can be inserted per pick 2 to 4. The specification like sample number, fabric type, weight/area, thickness, warp count, weft count, EPM (ends per metre), PPM (picks per metre) and porosity are given below in Table 1. & 2.

Satin weave in 500 TC
Satin weave in 500 TC
Satin weave in 400 TC
 Satin weave in 400 TC
Oxford weave in 400 TC
Oxford weave in 400 TC
Percale weave in 300 TC
 Percale weave in 300 TC
Percale weave in 400 TC
 Percale weave in 400 TC
Fig.2 Different types of weave structure used in fabrics

Table 1. Parameters of various hygro and normal yarn fabrics
Parameters of various hygro and normal yarn fabrics

Table 2. Parameters of various hygro 500 TC satin yarn fabrics
Parameters of various hygro 500 TC satin yarn fabrics

Table 2 shows the details of fabric parameters before washed and after repeated washing cycles (3, 5, 10, 15 and 20) of hygro 500 TC satin fabrics. Shrinkage of 2 % in warp direction and 1 % in weft directions was observed after first washing. There was no significant change in shrinkage after repeated washing cycles like 3, 5, 10, 15 and 20.

2.2 Testing methods
The end and pick densities were measured with the assistance of microscope instrument with ten randomly positions of each sample. To determine the fabric weight per unit area, fabric samples of 10 cm× 10 cm were cut and weighed on a highly sensitive electronic balance and from which, the weight of the fabric in grams per square meter (gms/m2) was calculated. An average of five readings was measured to calculate weight/area of each fabric sample. For determining the warp and weft count, forty threads corresponding to warp and weft side were unravelled and weighed on an electronic balance, warp and weft yarn crimp were measured with assistance of steel rule.For thickness measurement, Digital Thickness Tester was used and total 10 readings of each sample were measured to reduce the error percentage below 4% at 95% level of confidence.

The air permeability tester of model Textest FX3300was used to measure the air permeability at 98 Pa air pressure as per ASTM D737. An average of 10 readings for each sample was reported to get an error percentage much below 4% at the 95% level of confidence.The water absorbency testing was done in M/K GATS (Gravimetric Absorbency Testing System) tester and two readings were measured for each fabric. The testing of every sample was done in 300 seconds.

Alambeta device was used to measure the thermal resistance. An average of five readings was measured for each fabric sample.The moisture vapour transmission rate was measured in Lab think Testing Instrument at 88 RH and 38 degree Celsius temperature, which measures precise value up to 0.0001 gm. The high sensitive load cells are installed inside the instrument used for measuring weight. The specimen were cut in circular shape of 33 cm 2 area. The fabric must be inspected before marking or cutting to assure that the specimen must be clean, crease or wrinkle free and without fabric defects like holes etc.Sample of 4.25 inches diameter was cut for testing and an average of two readings was measured for each fabric sample.

The abrasion resistance was measured by using a flat abrasion tester with 4.5 lbs. per sq. inch diaphragm pressure with abrading paper of 1000number as per ASTM D3886 standard test method. The forward and backward oscillation of head was 4 cm. Total five readings were measured for each fabric sample to minimize the error percentage up to 4%. The bursting strength of different hygro and normal cotton yarn fabric were measured in Digital Hydraulic Bursting Tester as per ASTM D 3786 standard test method. Total five readings were conducted of each fabric. Zwick testing machine of model Z050 was used to measure peak strength in warp and weft direction with a gauge length of 75 mm as per ASTM D5035standard test method. The specimen width was 50 mm and the rate of specimen extension was set at 200 mm/min.The tearing strength was measured by using a falling-pendulum (Elmendorf-Type) apparatus as per ASTM D1424 standard test method. A slit was centrally pre-cut in a test specimen held between two clamps and the specimen was torn through a fixed distance.

2.3 Radiant heat resistance
This test method rates the non-steady state thermal resistance or insulating characteristics of clothing materials subjected to a continuous, standardized radiant heat exposure. A lamp of 1000 watts was used as a radiant heat source. A circular copper calorimeter, diameter 2cm and coated with black colour,was used as temperature sensor as shown in above Fig.1. The weight and specific heat of copper calorimeter was 16.44 g/m2 and 0.385kJ/kg.K. The thermocouple and data coding system was employed for reading temperature of fabric surface along with time. [9]
Radiant heat resistance testing instrument is given in introduction section Fig. 1.

2.4 Thermal protective performance on hot contact plate
This test method is used to measure the thermal insulation of materials used in protective clothing when contact for a short period of time. The details of instrument are similar to radiant heat resistance testing instrument, except that in this case, a hot contact plate is used as heat source instead of a 1000 watt bulb. [10]

Hot contact plate used to measure thermal protective performance
Fig. 3 Hot contact plate used to measure thermal protective performance
3. Results and Discussion
It is based upon the comfort and durability related properties of normal and hygro yarn fabric of three weaves, viz., percale, oxford and satin. The normal and hygro yarn fabrics were analysed with respect to their comfort characteristics such as air permeability, thermal resistance, water vapour transmission rate, water absorbency, radiant heat resistance (with and without water) and thermal protective resistance. The normal and hygro yarn fabrics were also analysed with respect to their durability characteristics such as abrasion resistance, tensile strength, tearing strength and bursting strength. The effect of repeated washing cycles hygro 500 TC satin were also analysed with respect to their comfort and durability characteristics.

Table.3 Observations of all measured properties of hygro and fabric normal yarn fabrics

Observations of all measured properties of hygro and fabric normal yarn fabrics

Table 4. Observations of comfort properties of various repeated washed hygro 500 TC fabrics
Observations of comfort properties of various repeated washed hygro 500 TC fabrics

3.1 Air permeability
The results shows that air permeability of normal yarn fabric is higher than hygro yarn fabric due to high bulk and compressibility of hygro yarns. The air permeability of normal 300 TC satin (N6) fabric is highest among all 11 fabrics because of the two main fabric parameters viz.,finer yarn count and satin weave, leading to drastic increase in air permeability. Air permeability of 300 TC fabric is higher than 400 TC and 500 TC fabrics due to lower fabric cover and high porosity. Air permeability of satin weave fabric is higher than oxford and percale weave due to larger pore size.The air permeability of before washed hygro 500 TC satin fabrics is high as compare to different hygro 500 TC satin washed fabrics, because of shrinkage of fabric, leading to increased cover and fabric sett.

3.2 Water absorbency
Water absorbency of hygro yarn fabric is substantially higher than normal yarn fabric due to high porous yarn structure produced, owing to dissolved PVA fibers. The water absorbency of 300 TC fabric is higher than 400 TC and 500 TC fabrics due to comparatively high float length and porosity. In above Table 3, water absorbency of hygro 400 TC satin is highest among all fabrics due to high weight/area and porosity. The water absorbency of satin weave fabric is comparatively higher than percale and oxford weave fabrics due to high float length and less number of interlacements between warp and weft.

The water absorbency of before washed hygro500 TC satin fabric is less as compared to different hygro 500 TC satin washed fabrics, because yarn packing density of before washed fabrics is higher than washed fabrics.

3.3 Thermal resistance
The thermal resistance value indicates the resistance of fabric under the influence of heat. The thermal resistance of normal cotton fabric is less than hygro cotton yarn fabric due more contact between fibre to fibre and less porosity compared to hygro yarn fabric. The percale fabric has lower thermal resistance than oxford and satin weave due to higher interlacement in its structure. The thermal resistance of 300 TC fabrics is higher than 400 TC and 500 TC fabrics due to less number of interlacements between warp and weft yarn and high float length.

The thermal resistance of unwashed hygro 500 TC satin is lower than different repeated washes fabrics due to the comparatively high thickness, fabric cover and porosity.

3.4 Water vapour transmission rate
The water vapour transmission rate of the hygro yarn fabric is higher than normal fabric, because high porous structure in hygro yarn allows large amount of accumulation and transition of water vapour from inside to the outside due to diffusion process.Water vapour transmission rate of resistance of 300 TC fabrics is higher than that of 400 TC and 500 TC fabrics due to comparatively low fabric cover and high float length.Water vapour transmission rate of normal 400 TC satin (N9)is highest among the other fabrics due to lower weight/area, thickness and fabric cover.

After repeating washing cycles, porosity of hygro yarn fabric increases, which increases the space for air, thus, rapidly increasing the diffusion process as the air has much a higher water vapour diffusion coefficient than the fibrous material.

3.5 Crease Recovery
The crease recovery of normal cotton yarn fabric is higher than hygro yarn fabric because the spring back ability of normal yarn is higher than hygro yarn. The higher interlacement in fabric structure causes more rigidity of fabric leading to high crease recovery. In the above Table 3, hygro 400 TC satin (H8) has highest crease recovery due to high thickness, and weight/area. The percale weave fabric has higher crease recovery than oxford and satin weave due to the higher number of warp and weft yarn interlacement.


The crease recovery angle of unwashed hygro 500 TC fabric is higher than that of washed hygro 500 TC fabric because of its high packing density and low compressibility.

3.6 Radiant heat resistance
The below observation shows that the radiant heat resistance of hygro cotton yarn fabric is higher than normal cotton yarn fabric, But the difference is not so much significant as shown in Table 5. The radiant heat resistance of repeated washed fabrics is higher than before washed hygro fabrics due to its porous structure and low packing density. It is seen in Table5 below that the rise in temperature in before washed fabric is 0.3 oC to 2.5 oC higher than washed fabrics.

Table 5. Radiant heat resistance of various normal and hygro yarn fabrics

Radiant heat resistance of various normal and hygro yarn fabrics

Table 6. Radiant heat resistance of hygro 500 TC yarn fabrics
Radiant heat resistance of hygro 500 TC yarn fabrics

3.7 Thermal protective resistance
As shown in Table 7, thermal protective performance on the hot surface contact of hygro yarn fabric is better than normal yarn fabric, because of comparatively less rise of surface temperature due to porous yarn structure. The thermal protective resistance of repeated washed fabrics is 0.9 to 3.0oC higher than unwashed fabrics due to porous yarn structure.

Table 7. Thermal protective resistance of normal and hygro yarn fabrics on hot surface contact

Thermal protective resistance of normal and hygro yarn fabrics on hot surface contact
Hot Plate Temp: 42 oC
Table 8. Thermal protective resistance of hygro 500 TC satin fabrics
Thermal protective resistance of hygro 500 TC satin fabrics
Hot Plate Temp: 42 oC
Table 9. Observations of mechanical properties of hygro and normal fabrics in warp and weft direction
Observations of mechanical properties of hygro and normal fabrics in warp and weft direction

3.8 Abrasion resistance
The abrasion resistance of hygro yarn fabric is higher than normal cotton yarn fabric, because of low twist in the hygro yarns get flexed during abrasion action.The abrasion resistance of 300 TC fabrics is higher than 400 TC and 500 TC fabrics due to comparatively high porosity.The abrasion resistance of normal 300 TC percale is highest among the others fabrics due to high thickness, weight/area and percale weave (higher interlacement). The abrasion resistance of percale weave fabric is comparatively higher than oxford and satin weave, because of high friction resistance due to high interlacement between warp and weft yarns.The abrasion resistance of unwashed 500 TC satin fabrics is higher than that of washed fabrics, because of abrasion with washing machine parts and loose structure (due to tumbling action) produced after washing.

Table 10. Observations of mechanical properties of hygro 500 TC satin fabrics in warp and weft direction

Observations of mechanical properties of hygro 500 TC satin fabrics in warp and weft direction

3.9 Tensile strength
Tensile strength of 300 TC fabrics is lower than 400 TC and 500 TC fabrics due to the comparatively lesser number of interlacement and fabric sett. Tensile strength of normal yarn fabrics is higher than hygro yarn fabrics due to comparatively low porosity leading to the high strength. Tensile strength corresponding to warp and weft direction of hygro 400 TC satin (H7) is highest than other eleven fabrics due to high weight/area, EPI and PPI. The tensile strength of percale weave is higher than oxford and satin weave due to comparatively more interlacement between warp and weft yarns.The tensile strength of hygro yarn fabric improved after washing in weft direction due to shrinkage but did not change significantly in warp direction.

3.10 Tearing strength
Tearing strength of 300 TC fabrics is higher than 400 TC and 500 TC fabrics due to the comparatively lesser number of warp and weft interlacement. Tearing strength of normal yarn fabrics is higher than hygro yarn fabrics due to the comparatively high strength of normal yarn.Warp way tearing force of hygro 300 TC satin (H5) is highest than among eleven fabrics due to coarser weft yarn and satin weave structure. The weft way tearing force of normal 300 TC satin (H6) is highest than among fabric because of normal yarn and satin weave structure. The tearing strength improved after washing both in warp and weft directions, because of shrinkage took place after washing.

3.11 Bursting strength
The bursting strength of hygro yarn fabric is comparatively lower than normal yarn fabric, because of low strength of hygro yarn attributed to low bursting strength. The bursting strength of 300 TC fabrics is lower than 400 TC and 500 TC fabrics due to comparatively low fabric crimp percentage and less number of threads. The bursting strength of normal 400 TC oxford (N4) is highest among the others fabrics due to high EPI, EPI and normal yarn. The bursting strength of fabric increases with increased number of repeated washing cycles, because of shrinkage of fabric leading to increase in EPI and PPI.

4. Conclusions
The comfort properties like water absorbency, thermal resistance, water vapour transmission rate, radiant heat resistance and thermal protective resistance is higher in higher thread count hygro yarn fabrics than normal yarn fabrics due to high porosity but trend of air permeability is reversed due to high bulkiness and compressibility of hygro yarns. The durable properties like tensile strength, tearing strength, bursting strength higher in normal yarn fabrics than hygro yarn fabrics due to high cohesiveness or packing density, but abrasion resistance is higher in hygro yarn fabrics than normal yarn fabrics. The crease recovery of hygro yarn fabrics is lower than that of normal yarn fabrics because of high spring back ability of normal cotton than hygro yarn.

From the comparisons of thread count (TC) of fabrics increased 300 TC from 500 TC leads to decrease comfort properties likeair permeability, water absorbency, thermal resistance, water vapour transmission rate radiant heat resistance and thermal protective resistance, but durability properties like tensile strength, tearing strength, bursting strength and abrasion resistance increases in both hygro and normal yarn fabric. The crease recovery improves when we move from 300 to 500 TC fabric because of more number of interlacement in warp and weft yarn.

The properties like air permeability, water absorbency, thermal resistance, water vapour transmission rate, tearing strength of satin weave fabrics is higher than oxford and percale weave fabrics, however properties like tensile strength,bursting strength and abrasion resistance shows the reverse trend.

The properties like water absorbency, thermal resistance, water vapour transmission rate, peak load and tearing force in warp and weft direction of hygro 500 TC satin fabrics are improved after washing, however properties like air permeability, abrasion resistance and crease recovery show reverse trend.

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