Material and sample preparation procedure
PLLA (Mw= 1.1 × 105g/mol, Mn= 4.5 × 104g/mol) used in thepresent study was supplied from Mitsubishi Plastic Inc. AmorphousPLLA film were prepared by compression molding at 190◦C for5 min at molten state. Two different thickness PLLA films were pre-pared. The films about 40 m were used for the FTIR measurementand the thick films about 1 mm were used for the DSC and WAXDmeasurement.
For preparing a set of PLLA specimens with ˛ form, the speci-mens were firstly heated at 100◦C/min up to 190◦C from the roomtemperature and annealed 2 min in order to erase the thermal his-tory, and then cooled to 125◦C at 150◦C/min for annealing differenttime. After such thermal treatments, the specimens with differentcrystallinity were cooled to 25◦C for IR measurement. For prepar-ing the PLLA specimens with ˛form, the isothermal crystallizationtemperature at 90◦C was chose, and the other procedures were thesame as those for PLLA specimens with ˛ form. The schematic dia-grams of thermal treatment for sample preparation were shownin Fig. 1. The isothermal crystallization curves derived from thein situ IR data were also included for indicating how to choose thecrystallization time for obtaining a set of specimens with differentcrystallinity.
For the DSC and WAXD measurement, a small piece of PLLA filmabout 1 mm thick was annealed at 90◦C for 2 h and 125◦C for 1 hin the Linkam heating stage following the previous procedures toget the crystallized ˛ and ˛crystal form specimens.