Thermal properties and crystallization behaviors of polylactide and its enantiomeric blends

Thermal properties and crystallization behaviors of polylactide and its enantiomeric blends are investigated. DSC results demonstrate that only homopolymer crystallite is observed in PDLA and PLLA single polymers. A relatively stronger crystal structure, stereocomplex, can be achieved by mixing the two PLAs in a 1:1 ratio. For non-equimolar blends, both types of crystallites are formed at lower temperature than that of the single polymer counterparts. The degree of reduction in crystallization temperature is dependent on the degree of deviation of blend content from the equimolar value and the mobility of the polymer chain. The composition of the two crystallite domains is also dependent on the blend content, where the stereocomplex content is maximized in a 1:1 blend, and decreases upon varying the mixing ratio from equimolar value. infrared spectroscopy is employed to follow the crystallization mechanisms of the non-equimolar blend. Results indicate a domination of stereocomplex formation band characteristics, despite evidences suggesting an existent of homopolymer crystallite formation, probably due to the involvement of C-H center dot center dot O=C hydrogen bonding, which leads to larger change in dipole moment responsible for infrared transitions.