BEHAVIOR OF CHEMICALLY-MODIFIED COTTONS TOWARDS FLAME-RETARDANCY FINISHING

The effect of structural changes in cotton cellulose, brought about by introducing N-containing groups, on the flame-retardancy finish has b een studied. Introduction of these groups was effected by modifying co tton fabric vi a carbamoylethylation, acrylamidomethylation and carbam ation. The nitrogen-containing modified cottons, thus obtained were us ed as starting substrates for flame retardancy finishing. This was car ried out using formulations of Pyrovatex CP, etherified methylolated m elamine (EMM) and ammonium sulphate catalyst and using the pad-dry-cur e technique. Other catalysts used included metal salts, Lewis acid and other latent catalysts. The finished samples were monitored for nitro gen content, phosphorus content, flammability, crease recovery and str ength properties. The results obtained indicated that the nitrogen con tent, phosphorus content and flame-retardancy properties of the finish ed fabric are increased by increasing the Pyrovatex CP concentration a s well as the EMM concentration. Similarly, these properties are impro ved 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 de creases while the crease recovery exhibits significant improvement. Th ese findings are encountered regardless of the substrate used. However , the flame-retardancy properties of the substrates used follow the or der: CEC > cellulose carbamate > AMC > unmodified cotton. The order re flects the extra nitrogen of the modified cottons which is increased b y the nitrogen which originates from the EMM and Pyrovatex CP interact ion products. Most probably, the nitrogen from these different sources bonds with the phosphorus via initial N-P bond formation. Once this o ccurs, formation of levoglucosan is minimized and products containing N-P bonds consolidate the char thereby enhancing the flame-retardancy properties.