The bleached cotton yarn type of 10/1 (8400 yds/lb) obtained from a local market in Chiang Mai, Thailand was used. The cotton fibres (100 g) were first washed in a bath containing 10 g of a long chain fatty acid sodium soap (C18H37COONa), 16 g of sodium carbonate, and 1000 ml of water at 80e90 C for 1 h. Repeated rinsing under distilled water was followed, the cotton fibres were then air-dried