Easy-care finishing of silk

Abstract

Keywords: silk, easy-care, polycarboxylic acid, zero-formaldehyde, finishing, cross- linking, machine-washable, silicone, softener, swelling agent. A zero-formaldehyde, easy-care finish for silk fabric has been developed using a polycarboxylic acid (PCA) finishing system. This thesis confirms that treatment of silk fabric with selected PCA finishing systems improves the stability of silk fabric. The treated fabric had improved stability to heat, reduced swelling in solvents, and improved elastic recovery in the dry and wet states. A number of interesting mechanistic possibilities are proposed for improving the easy- care performance of silk fabrics with a PCA finishing system. It is postulated that the improvement in elastic and stability properties of the treated silk fabrics could be as a consequence of new fibre inter-chain cross-links and/or a new intra-fibre PCA polymer network being formed within the silk fibres. Three different types of possible bonds between the PCA and silk fibroin were proposed : • Ester links formed via acid and/or base catalysis with hydroxyl containing amino acids, serine, threonine and tyrosine, in silk fibroin. • Amide links may also be formed between the basic amino acids, arginine, lysine and histidine, in silk fibroin and acid anhydrides formed during curing. • Hydrogen bonds formed with acid, basic and hydroxy side groups and with the silk fibroin backbone. This thesis extends previous research with respect to PCA finishing. It proposes the use of a new analytical method to pre-determine the effectiveness of an acid/catalyst system as an easy-care finish. It recommends the use of combination acids to compete with 1,2,3,4-butanetetracarboxylic acid and proposes the use of monosodium citrate as an alternative catalyst to sodium hypophosphite when cured at 165°C. Good easy-care performance was achieved with silk fabrics treated with selective PCA/catalyst finish in the presence of a swelling agent, such as formic acid or acrylic acid, followed by after-treatment with a silicone softener. The finish produced a super soft, minimum iron fabric with enhanced resistance to fabric abrasion. The treated fabric was machine-washable.