PREPARATION CONDITIONS AND SWELLING EQUILIBRIA OF HYDROGEL PREPARED BY GAMMA-IRRADIATION FROM MICROBIAL POLY(GAMMA-GLUTAMIC ACID)

Crosslinked microbial poly(gamma-glutamic acid) (PGA) hydrogels were prepared by gamma-irradiation, and their preparation conditions such as irradiation dose and PGA concentration were studied. When PGA solution was exposed to gamma-radiation, PGA was crosslinked to yield high water sorption materials with specific water content of 100-1400 times their dry volume depending on the preparation conditions [e.g. irradiation dose ( > 20 kGy), PGA concentration (2-10 wt%)]. With an increase of gamma-irradiation dosage, the gel content of PGA gels was inclined to increase but the specific water content decreased markedly. The equilibrium swelling behaviour in various aqueous solutions was investigated as a function of pH and concentration of electrolyte (NaCl, Na2SO4, CaCl2). These PGA hydrogels exhibited reduced swelling when exposed to low pH or electrolyte solutions. The ionic contribution to swelling thus seems to be the main factor governing the swelling of these gels. In addition, the thermal hydrolytic degradability was measured in excess deionized water. PGA gels were almost completely degraded after about 1 h at 100 degrees C.