Abstract
High temperature pad-steam bleaching of cotton was experimented under the following conditions and the Hunter's whiteness W and DP of the bleached cotton were measured. The conditions: NaClO2 1_??_1.5%, pH 7_??_3.5, liquor ratio 1:1, temperature 110°_??_160°C, time 15 sec_??_20min. The results obtained are:
(1) The rate of bleaching decreases remarkably as the pH of the NaClO2 solution increases, while the rate of depolymerization is influenced by the pH value not so severely as in the case of the rate of bleaching, Hence longer time is necessary for bleaching at higher pH, during which the depolymerization of the cotton proceeds remarkably. Consequently the bleaching must be made speedily by lowering the pH of the NaClO2 solution to 3.5_??_5, then the depolymerization is tolerable.
(2) When a bleaching is made at 120°_??_110°C for 30_??_60 sec, using a 1.5% NaClO2 solution at pH 3.6, W and DP were 92 and 1100 respectively, DP of the unbleached cotton being 1270.
It is conclude that a high temperature continuous pad-steam bleaching of cotton is possible under suitable conditons
