Synthesis and characterization of biodegradable hydrogels based on starch and succinic anhydride

Synthesis of novel hydrogels has been investigated with the reaction of starch and succinic anhydride (SA), using 4-dimethylaminopyridine as esterification catalyst and dimethylsulfoxide (DMSO) or water as solvent, followed by NaOH neutralization. The reaction products in DMSO were soluble in organic solvents such as methanol, so they could not be isolated by precipitation. Instead, dialysis was carried out for purification of the reaction products. During the dialysis, the products gradually separated as gel, so they could be separated by precipitation. Their degree of substitution (DS) was in the range of 0.4–1.4. The maximum water absorbency of the products was about 120 g-water/g-dry gel. On the contrary, the reaction products in water were insoluble in methanol, so precipitation in methanol was conducted for isolation of the products. They possessed lower DS (0.1–0.3) and exhibited lower absorbency; its maximum absorbency in water was ca. 70 g/g. The products in the present study biologically degraded up to 60–80% after 20 days, which shows their good biodegradability.