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Nonwovens & Technical Textiles
  Hand related characteristics of polyurethane-oated fabrics

Fabric thickness, bending rigidity, drape coefficient and water repellancy increase, whereas crease recovery angle and air permeability reduce in cotton, polyester and polyester/viscose fabrics on coating with polyurethane polymer and the maximum effect is obtained with 22% polyurethane content, infer G K Tyagi, V P Singh, A Chauhan, A Sharma, A Goyal and B B Malik.

Water proof breathable fabrics are designed for use in garment that provide protection from weather, that is, from rain, wind and loss of body heat. Water proof breathable fabrics completely prevent the penetration and absorption of liquid water from outside to inside the clothing, and permit the penetration of water vapour from inside the clothing to the outside atmosphere. Traditionally fabric is made water proof by coating it with synthetics polymers such as polyvinyl chloride (PVC) and polyurethane. However, coated fabrics are considered to be less comfortable to wear, as they are relatively stiff and do not allow the passage of perspiration vapour.

Research conducted so far on water proof breathable fabrics mainly deals with the comparison of performance characteristics of different types of water proof breathable fabrics1,2,3,4. There are occasional references to the characteristic features of breathable rain wear materials with respect to protection, physiology and durability5. References on handle characteristics of polyurethane coated fabrics, however, are very rare. This study focuses on hand related characteristics of micro polyester fibre, cotton and polyester-viscose fabrics. The effect of coating solution concentration on fabric hand has also been studied.

Materials and methods

Preparation of fabric samples

Polyester filament, combed cotton and 60:40 polyester/viscose fabrics were used for the study. A plain woven micro denier polyester filament fabric (118 g/m2) with 40 ends per inch and 40 picks per inch was prepared on the CIMCO sample loom. The polyester/viscose and cotton fabrics were procured from Ajanta Textiles.

Fabrics samples measuring 20 x 20 cm were impregnated in the chemical bath containing polyurethane coating solution (concentration; 18%, 20% and 22%; solvent, DMF) for 30 minutes and padded through squeeze rollers. The details of fabric constructional parameters and typical treatment formulations are given in Table 1. The padded samples were oven dried for 30 minutes and stored under standard atmospheric conditions before evaluating handle and other characteristics.

Table 1: Fabric constructional parameters
Sample ref no Fabric Weave Yarn linear density, tex Polyurethane concentration %
      Warp Weft  
F1 Cotton Plain     Nil
F2 Cotton Plain 26.8 16.4 18
F3 Cotton Plain     20
F4 Cotton Plain     22
F5 Polyester Plain     Nil
F6 Polyester Plain 9.0 8.4 18
F7 Polyester Plain     20
F8 Polyester Plain     22
F9 60:40 Polyester/Viscose Plain     Nil
F10 60:40 Polyester/Viscose Plain 9.0 8.4 18
F11 60:40 Polyester/Viscose Plain     20
F12 60:40 Polyester/Viscose Plain     22

Tests

Selected handle properties-bending length, crease recovery, air permeability, water absorbency and drape of both types of fabrics were evaluated. Air permeability was determined using the Shirley air permeability tester. The drop penetration method was used to measure the water absorbency of the coated fabrics. Specimens for all tests were randomised according to ASTM test methods.

Results and discussion

The influence of process variables on the handle and other characteristics of polyurethane coated cotton, polyester and polyester/viscose fabrics were assessed for significance using analysis of variance (Table 2). Only first order interactions were considered.

Table 2: ANOVA test resultsss
Process parameters Fabric characteristics
  Thickness Bending rigidity Crease recovery Drape coefficient Air permeability Water repellancy
Fibre type s s s s s s
Coating treatment s s s s s s
Polyurethane concentration s s s s s s
s-Significant at 99% confidence level.

Fabric thickness

The thickness values of various untreated and coated fabrics are given in Table 3. Under all experimental conditions, the polyurethane coated fabrics display higher thickness than the corresponding the grey fabrics, mainly due to the addition of an added layer of polyurethane bond on their surface. The data show that the fabric thickness is highly dependent on the fibrous material, and the cotton fabric yields much higher thickness as compared to polyester and polyester/viscose fabrics, presumably on account of the greater bulk of the yarn structure arising from high bending rigidity of the cotton fibre. Furthermore, the coated polyester fabric sustains an unusually high increased thickness, which further increases with the increase in polyurethane polymer concentration from 18% to 22%. The hydrophobic polymer probably contributes to the extra coating retention.

Bending rigidity

The bending rigidity of the dry fabrics, both in weft & warp directions, is substantially reduced from the loom state after coating with polyurethane polymer (Table 3), which is due to addition of polyurethane layer. Such layering may restrict the movement of substance during bending. The data also indicate that the fabric bending rigidity increases with the increase in polyurethane content. The increase in bending rigidity with the increase in polyurethane concentration occurs due to reduction in micro pores in the yarn, which makes the structure rigid and hence difficult to bend during the exertion of load. Moreover, bending rigidities of fabrics made from cotton and polyester/viscose yarns are observed quite close to each other.

Crease recovery

Crease recovery is the property of the fabric to recover back to its original position after removal of certain load from the folded fabric. A larger value means that it is easy to alter the shape. Table 3 clearly shows a significant decrease in recovery angle on coating with polyurethane polymers. The effect could be conceivably due to the increased toughness during coating as a result of additional layer of polyurethane polymer.

Moreover, the crease recovery angle of fabrics made from polyester yarn is significantly higher as compared to the fabrics made either from cotton or polyester-viscose yarn, and for all experimental combinations, the fabrics coated with higher polyurethane concentration display smaller crease recovery angle both in warp and weft directions on account of the higher bending stiffness of the fabric matrix. However, the decrease in crease recovery angle is less marked in cotton than in polyester fabric. This is quite understandable because cotton absorbs more polymer and hence less amount of coat is present on the surface.

Drape

Fabric drape is the hanging property of the fabric and is inversely proportional to drape coefficient of the fabric. A high value means that the fabric is less limply and more stiff. Table 3 shows that the drape coefficient of all fabrics increases significantly after polyurethane polymer coating. However, in general, the drape coefficient of cotton fabric is relatively higher than the values for fabrics from polyester and polyester-viscose yarns, and it significantly increase as polymer content is increased from 18% to 22%. Analysis of variance results verifies that the effect of the yarn composition and polymer concentration on the drape coefficient is significant.

Air permeability

Air Permeability values in Table 3 indicate that cotton fabric is more air permeable than its polyester and polyester-viscose couples on account of less dense packing of fibres in the former. The air permeability of both cotton and polyester-viscose fabrics reduces on coating with polyurethane polymer. As polyurethane polymer is confined to the surface of the yarn and fabric, the air permeability reduces through the surface effect of enhancing the resistance to the flow of air through the fabric. The micro denier polyester filament fabric, on the other hand, shows consistence increase in air permeability after being coated with polyurethane polymer. Very remarkably, the air permeability reduces noticeably with the increase in concentration of coating polymer regardless of the fibrous material used.

Water repellancy

The water repellancy of all fabrics is substantially enhanced from the loom state after coating with polyurethane polymer possibly due to the hydrophobic nature of the polymer (Table 3), indicating that these fabrics can be used as water proof fabrics. The impact of fibre type on water repellancy is along the expected lines. In general, the water repellancy is highest for the micro denier polyester fabric and it further increases with the increase in polymer concentration on account of the decrease in micro pores, leading to the reduction in the diffusion rate.

Conclusion

The polyurethane coating increases fabric thickness, bending rigidity, drape coefficient and water repellancy, but reduces crease recovery angle and air permeability. Moreover, use of higher polyurethane contents contributes to the production of poor quality fabrics with high bending rigidity and thus stiff handle and poor drape characteristics. However, water repellancy results support the expectation of obtaining enhanced water proofing characteristics with the high polyurethane content. The fibrous assembly itself is another important factor in determining fabric water proofing response. The fabric woven from micro denier polyester filament is more water repellent, less rigid, has smaller crease recovery angle and has good drape properties; but is less air permeable when compared with a cotton fabric.

References

1. Holmes D A, Grundy G, Rowe H D: J Cloth Technol Manag, 12 (3) (1995) 142.

2. Ruckmam J E: Int J Cloth Sci Technol, 9 (1) (1997) 10, 23,141.

3. Oszevski R J: Text Res J, 66 (1) (1996) 24.

4. Gretton J C: J Coated Fabrics, 26 (January) (1997) 212.

5. Weder M: J Coated Fabrics, 27 (October) (1997) 146.

Note: For detailed version of this article please refer the print version of The Indian Textile Journal June 2011 issue.

G K Tyagi
M L V Textile & Engineering College,
Bhilwara, Rajasthan.

V P Singh
M L V Textile & Engineering College,
Bhilwara, Rajasthan.

A Chauhan,
Technological Institute of Textile & Sciences,
Bhiwani, Haryana.

A Sharma,
Technological Institute of Textile & Sciences,
Bhiwani, Haryana.

A Goyal
Technological Institute of Textile & Sciences,
Bhiwani, Haryana.

B B Malik
Technological Institute of Textile & Sciences,
Bhiwani, Haryana.

published June , 2011
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