PROPERTIES AND MORPHOLOGIES OF POLY(L-LACTIDE) .1. ANNEALING CONDITION EFFECTS ON PROPERTIES AND MORPHOLOGIES OF POLY(L-LACTIDE)

摘要

The effects of annealing on the thermal properties, morphologies and mechanical properties of poly(L-lactide) (PLLA) films were investigated by differential scanning calorimetry, polarizing microscopy and tensile testing. PLLA films prepared by solution casting were annealed by three different processes: process A, direct annealing of the as-cast film; process B, melting and annealing; and process C, melting, quenching and annealing. In the case of process B, the morphology depended strongly on the annealing temperature, while it depended only slightly on the annealing temperature in the case of processes A and C. In process C, nucleation occurred upon quenching or in the process of temperature rise after quenching, and its nucleation density was higher than that obtained by process B. Therefore, in process C, overall crystallization lasted for a shorter time than in process B, and the radius of the spherulites formed was much smaller compared with that of the spherulites formed by process B. The crystallinity and melting temperature increased with increasing annealing temperature and time of processes B and C, whereas in process A the annealing conditions only slightly affected those values. Young's modulus increased with increasing crystallinity for all the films annealed by the three processes. Tensile strength showed similar behaviour to Young's modulus, but decreased when large crystallites or spherulites were formed. In the case of processes A and B, elongation at break decreased with increasing crystallinity. [References: 35]