Degradation of chitosan and sodium alginate by gamma radiation, sonochemical and ultraviolet methods

Three degradation methods: ultrasonic, ultraviolet and gamma irradiation were applied to sodium alginate and chitosan in aqueous solutions. The changes in molecular weight were monitored by GPC measurements. It has been found that from the energetic point of view the most effective method for both polymers is gamma radiation method with a yield of scission Gs=0.55×10 -7mol/J for 1% alginate and Gs=3.53×10 -7mol/J for 1% chitosan. However, considering the reaction time, the ultraviolet method is the most effective, with reaction rate constant k=0.52h-1 for alginate and 1.6 h-1 for chitosan. Based on FTIR spectra, taken before and after degradation it was revealed, that degradation undergoes by the breakage of the glycosidic bonds of polymers. UV spectroscopy showed absorption peak at 265 nm for alginate, and two peaks at the range of 250-280 nm for chitosan. UV spectroscopy for ultrasonic is not revealed and any peak suggesting ultrasonic degradation undergoes different mechanism than ultraviolet and gamma degradations, probably mechanical one. © 2004 Elsevier Ltd. All rights reserved.