Abstract
Starch based superabsorbents are generally prepared by a 2-step process: The first step is the graft copolymerization of acrylonitrile (AN) onto starch, washing and drying of the graft copolymer, and the second step is the hydrolysis of the starch-g-polyacrylonitrile (SPAN) powder in aqueous NaOH solution. During hydrolysis, the graft copolymer becomes a thick gummy mass which can not be stirred to ensure uniform reactionand it also becomes very difficult to isolate the superabsorbent. To simplify the process and to avoid the formation of the thick gummy mass, hydrolysis was carried out by addition of NaOH to the graft copolymerization mixture directly without washing and drying. This method allows more uniform reaction since stirring is possible and easier isolation of the superabsorbents. The starch based superabsorbents containing up to 25% PAN prepared by direct hydrolysis have similar absorbency, water retention, and absorption rates compared with those prepared by the general hydrolysis method.
