Aging and cold crystallization of melt-extruded poly(trim ethylene terephthalate) films

We analyzed the thermal crystallization, glass-transition behavior, and mechanical properties of melt-extruded poly(trimethylene terephthalate) (PTT) films to investigate their physical aging and annealing effects. The physical aging and annealing of PTT films had an influence on the glass-transition temperature, recrystallization behavior, and mechanical properties. When samples were aged at an ambient temperature, the crystallization temperature decreased largely within 5 h, the heat of crystallization increased, and the breaking stress and breaking elongation increased. The glass-transition temperature of annealed samples, which was obtained from differential scanning calorimetry and dynamic mechanical measurements, increased with increasing annealing temperature below 80 degreesC but decreased above that temperature. In addition, the glass-transition temperature and modulus of annealed samples were largely affected by the annealing time; in particular, they increased sharply within I h on annealing at 50 degreesC. Consequently, the change in the glass-transition temperature on annealing was ascribed to the fact that the molecular constraint due to recrystallization and the mobility of rigid amorphous PTT chains competed with each other, being dependent on the annealing temperature. The mechanical properties of aged samples were closely related to their cold-crystallization behavior. (C) 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 1920-1927, 2001.