Abstract
Our previous study showed that an anion exchangeable cotton yarn was capable of adsorbing hydrolyzed reactive dyes in waste water, This yarn was prepared by Hofmann-degradative treatment of poly (acrylamide) -cotton graft copolymers by using hypochlorite. In this paper we report on the improvement of the preparation of anion-exchangeable cotton yarns. For enhancing grafting ratio and conversion ratio of the graft copolymerization of acrylamide onto cotton yarns, a Fe+2-H2O2 redox system was used as an initiator. The ferrous salt was adsorbed on cotton yarns and then added to a monomer solution containing H2O2. This redox system as an initiator gave three times higher grafting ratio than the cerium salt system. The conversion ratio of graft copolymerization was dependent on the monomer concentration and the bath ratio. The maximum conversion ratio (78%) was obtained with 10% acrylamide at bath ratio, 1:8 by using this redox system. The capacity of yarns for adsorbing hydrolyzed reactive dyes was dependent on the conditions of Hofmann-degradative treatment. The maximum capacity of dye adsorption (230mg/g) was attained when the grafted yarn was treated at room temperature for 6h in the solution containing a large excess of NaOH and hypochlorite, where the active chlorite was 1.4 times as much as the molar quantities of the grafted acrylamide. The adsorbed dye on the cotton yarn was easily eluted with dilute NaOH solution and the maximum desorption of dyes (96.3%) was attained with 0.05% NaOH solution. This yarn adsorbed the dye more effectively even at a high flow rate (SV 215) than the activated carbon in the column method.
