Relationship between phase morphologies and mechanical properties of thermoplastic starch/poly(butylene adipate-co-terephthalate) composite films prepared by extrusion blowing.

Biodegradable films with various weight proportions of thermoplastic starch (TPS) and poly(butylene adipate-co-terephthalate) (PBAT) were prepared by extrusion blowing. Relationship between phase morphologies and mechanical properties of TPS/PBAT composite films was investigated and discussed. Iodine dyeing technique was used to clearly identify TPS and PBAT phases in the composite films. Such blending systems proved to be immiscible and the phase morphology evolution with changes in TPS/PBAT proportions was elucidated. Two phase transition points were found near PBAT content of 30 and 70 wt%, respectively, where mechanical properties of the composite films leaped. Significant correlations were established between mechanical properties and continuity indices of the two phases, namely a positive correlation with continuity index of PBAT and a negative correlation with that of TPS. Inducing the formation and enhancement of continuous structure of PBAT phase is proposed as a practical approach to improve mechanical properties of TPS/PBAT composite films.