Contributions of intramolecular and intermolecular energy changes to strain-induced enthalpy relaxation in uniaxially drawn poly(lactic acid) films

摘要

Blends of poly(lactic acid)s (PLAs) containing three different concentrations of D-isomer (i.e., 1, 4, and 10 mol%; referred to as PLA1, PIA4, and PLA10, respectively) with poly(DL-lactic acid) (PDLLA) were prepared via solution blending. The three PLAs were miscible with PDLLA, as determined by dynamic mechanical analysis. Drawn films of PLA1/PDLLA, PLA4/PDLLA, and PLA10/PDLLA blends exhibited endothermic peaks just above the glass transition temperature, which is evidence of strain-induced enthalpy relaxation. A thermodynamic model for the miscible blend system was applied to determine contributions of intramolecular and intermolecular energy changes to strain-induced enthalpy relaxation for PLA1, PLA4, and PLA10; the resultant values suggested that intramolecular energy changes are mainly responsible for strain-induced enthalpy relaxation. (C) 2015 Elsevier Ltd. All rights reserved.