Behaviour of chemically modified cottons towards flame-retardancy finishing

Abstract

The effect of structural changes in cotton cellulose, brought about by introducing N-containing groups, on the flame-retardancy finish has been studied. Introduction of these groups was effected by modifying cotton fabric via carbamoylethylation, acrylamidomethylation and carbamation. The nitrogen-containing modified cottons, thus obtained were used as starting substrates for flame retardancy finishing. This was carried out using formulations of Pyrovatex CP, etherified methylolated melamine (EMM) and ammonium sulphate catalyst and using the pad-dry-cure technique. Other catalysts used included metal salts, Lewis acid and other latent catalysts. The finished samples were monitored for nitrogen content, phosphorus content, flammability, crease recovery and strength properties. The results obtained indicated that the nitrogen content, phosphorus content and flame-retardancy properties of the finished fabric are increased by increasing the Pyrovatex CP concentration as well as the EMM concentration. Similarly, these properties are improved by increasing the ammonium sulphate concentration up to 15 g/litre. While ammonium sulphate proved to be the best catalyst for the flame-retardancy finishing treatment, magnesium chloride hexahydrate is the least. On the other hand, tensile strength and elongation at break decreases while the crease recovery exhibits significant improvement. These findings are encountered regardless of the substrate used. However, the flame-retardancy properties of the substrates used follow the order: CED>cellulose carbamate>AMC>unmodified cotton. The order reflects the extra nitrogen of the modified cottons which is increased by the nitrogen which originates from the EMM and Pyrovatex CP interaction products. Most probably, the nitrogen from these different sources bonds with the phosphorus via initial NP bond formation. Once this occurs, formation of levoglucosan is minimized and products containing NP bonds consolidate the char thereby enhancing the flame-retardancy properties.