Resin or wrinkle free finishing is widely used in the textile industry to impart wrinkle-resistance to cotton fabrics and garments. Considerable loss in strength and abrasion resistance of the finished fabrics has been a major concern for the industry. Enhancing dimensional stability and wrinkle resistance with resin finishing of cotton has constantly been correlated with lower abrasion resistance and tear strength. The strength of the fibre depends on how much the cross-linked chains can still be mutually displaced under tension in order to sufficiently resist the applied load. The rigid cross-links that are formed with the DMDHEU obviously prevent the redistribution of stress by preventing movement within the fibre microstructure. The cross-linking of cellulose molecules with these relatively rigid cross-links causes stiffening of the cellulosic macromolecular network and fibre embitterment, thus dropping the mechanical strength of the treated cotton fabrics. These same mechanisms are responsible for reduced mechanical properties of the fibre surface, thus leading to strength loss. Fibre surface property alteration, such as through the use of softeners, has been shown to play an important task in minimising strength loss.
The mixture of inadequate scratch resistance and relatively severe tensile and tear strength loss has been a major disadvantage for resin finished 100% cotton fabrics. The objectives of this work are to investigate the cause and mechanism of loss in abrasion resistance of cross linked cotton fabrics; relationships between the molecular structure of cross-linking agents and their effect on the mechanical properties of cross-linked textile structures; and develop a technology for improving the tear strength of resin finished cotton fabrics by adding special silicones.
Tear and Tensile Resistance
An overwhelming majority of durable press finishing agents used today are formaldehyde based reagents, such as dimethyloldihydroxyethyleneurea (DMDHEU) and modified DMDHEU, with magnesium chloride as a catalyst.
The following summarises some of the important aspects so far:
1. The catalysts used for DMDHEU systems, such as magnesium chloride, cause degradation of cellulose, thus reducing the tensile and tear strength of cotton fabric. The magnitude of fabric strength loss is affected by temperature, time, and concentration of the catalyst. Fabric strength loss also depends on both the cation and anion of the catalyst. An activated catalyst system, which includes an organic acid, causes more severe fabric tensile strength loss.
2. Tensile strength loss of cotton fabric treated with DMDHEU is due to both the cross-linking of cellulose and the degradation of cellulose caused by the catalyst. Because a catalyst system plays such an important role in influencing the strength loss of cotton fabrics cross-linked by DMDHEU, the selection of the catalyst system and its concentration is crucial for optimising the tensile strength retention of the finished fabrics.
3. DMDHEU can be removed from the finished fabric by using an alkali treatment, as evidenced by the decrease in wrinkle recovery angle with removal. The fabric strength gradually increases as the hydrolysis of the cross-linked fabric progresses, indicating that the fabric strength loss due to cross-linking the cellulose molecules is reversible and that it can be restored by removing the cross-links. The remainder of the strength loss, which has been described as being due to acid-induced de-polymerisation, is permanent and is not reversible upon hydrolysis of the cross-links.