Environmental Influence on Degradation of Chitosan Bioplastics

Mineralization rates of chitosan flakes and films representing various molecular weights, solubilizing acids, and postdrying treatments were measured over time using a commercial respirometer. While molecular weight and solubilizing acid did not result in significant differences in mineralization in compost, neutralization of chitosan with hydroxide base led to slower initial mineralization rates for home (25 °C) compost (first-order rate constant, k = 0.55 ± 0.11 vs 1.97 ± 0.27 months^–1) and industrial (58 °C) compost (k = 0.77 ± 0.11 vs 3.32 ± 0.11 months^–1) conditions. Adding glycerin to the water-soluble films also slowed the mineralization rate for the first 10 days (k = 1.19 ± 0.12 vs 1.97 ± 0.27 months^–1). Increasing degradation temperature from 25 to 58 °C led to faster initial rates for the water-soluble films (k = 1.97 ± 0.27 vs 3.32 ± 0.11 months^–1), but not for the neutralized films; increasing temperature only increased the maximum mineralization (28 ± 3 vs 45 ± 3%) for the neutralized films. Treating films with base or adding additives like glycerin can influence film properties and increase the utility of chitosan films as sustainable alternatives for petroleum-derived plastics in agriculture, industry, and medicine.