DIFFERENTIAL SCANNING CALORIMETRY INVESTIGATION OF PHASE-TRANSITIONS IN WATER CHITOSAN SYSTEMS

Transition temperatures of water/chitosan systems with water contents ranging from 8 to 300% (weight per cent of water per dry polymer weight) are measured by differential scanning calorimetry (d.s.c.). Upon heating, three kinds of phases, which vary with the water content, are observed for the system: cold crystallization, melting of freezable water, and a birefringent to isotropic phase which occurs for samples containing 44-190% water with a transition temperature that does not vary significantly with the water content. The glass transition temperature (Tg) of chitosan is observed at approximately 303 K for water contents ranging from 8 to 30%. From the d.s.c, data, a transition map for the water/chitosan system is compiled.