Effect of molecular weight on radiation chemical degradation yield of chain scission of γ-irradiated chitosan in solid state and in aqueous solution

Abstract

Chitosan A1, A2 and A3 with molecular weight of 471, 207 and 100kDa respectively, produced from squid pen chitin was degraded by gamma rays in the solid state and in aqueous solution with various doses in air at ambient temperature. Effect of molecular weight on radiation chemical degradation yield of chain scission and degradation rate constants of γ-irradiated chitosan in solid state and in aqueous solution was investigated. The radiation chemical degradation yield G(s) and degradation rate values were calculated. The molecular weight changes were monitored by capillary viscometry method and the chemical structure changes were followed by UV analysis. The results showed that, the degradation of chitosan was faster in solution, than in solid state. The values of G(s) in solid state and in aqueous solution were respectively 1.1×10−8mol/J and 0.074×10−7mol/J for A1, 4.42×10−8mol/J and 0.28×10−7mol/J for A2 and 6.08×10−8mol/J and 0.38×10−7mol/J for A3. Degradation rate constants values ranged from 0.41×10−5 to 2.1×10−5kGy−1 in solid state, whereas in solution they ranged from 13×10−5 to 68×10−5kGy−1. The chitosan A3 was more sensitive to radiolysis than A1 and A2. The chain scission yield, G(s) and degradation rate constants seems to be greatly influenced by the initial molecular weight of the chitosan. Structural changes in irradiated chitosan are revealed by the apparition of absorption peaks at 261 and 295nm, which could be attributed to the formation of carbonyl groups. In both conditions the peak intensity was higher in chitosan A3 than in A1 and A2, the oxidative products decreased with increasing molecular weight of chitosan.