Structural variation of melt-crystallized PTT during the heating process revealed by FTIR and SAXS

Time-resolved FTIR, WAXD/SAXS and DSC have been used to investigate the structural variation of non-isothermally crystallized poly(trimethylene terephthalate) (PTT) during the heating process. The three-phase model: the lamellar phase, the mobile amorphous phase (MAP) and the rigid amorphous phase (RAP) between lamellae is suggested to describe the structure of melt-crystallized PTT. According to FTIR results, the conformation of RAP in the constrained state is different from that of MAP. The increased content of amorphous phase in the temperature range from 120 to 192°C is ascribed to the relaxation of RAP, rather than the melting of defective crystals. When the PTT is heated to a temperature above 192°C, the recrystallization/crystal perfection of original defective lamellae occurs without a pre-melting process, which leads to an increase in lamellar thickness and probably connects two adjacent lamellar stacks. This is responsible for an increase in crystallinity as well as a higher major melting temperature.