Concurrent dyeing and finishing of cotton with natural colour and citric acid in the presence of NaH2PO4 as catalyst under thermal treatment

Cotton fabric was simultaneously modified and dyed with citric acid and Camellia sinensis, and citric acid and Punica granatum in the presence of sodium di-hydrogen phosphate (NaH2PO4) as the catalyst using a pad-dry-cure technique. Treatment with 10% citric acid, 15% NaH2PO4 and any of the above-mentioned dyes at 100% wet pick-up, followed by drying at 95 degrees C for 5 min and curing of the dried fabric at 140 degrees C for 5 min produced most balanced improvements in respect of the depth of shade, wrinkle recovery and colour fastness to light, wash and rubbing with retention of more than 70% of the original strength. Infrared analysis of the dyed cotton fabric indicated that the treatment of cotton with citric acid and either Camellia sinensis or Punica granatum under the influence of an esterification catalyst led to the esterification of carboxyl groups of citric acid and of hydroxyl groups of cotton cellulose and with that of both the dyes. The said process also led to some degree of cross-linking of polymeric chains of cotton.