Changes of crystallization and mechanical properties with annealing and boiling of strip-biaxially stretched poly (ethylene terephthalate) films

Non-stretched poly (ethylene terephthalate) (PET) films and strip-biaxially stretched PET films were annealed and treated with boiling water, and we h ave used tensile testing to investigate the behavior of stress-strain curve with variation of crystallinity. As PET sheets were stretched at 80 degree s C, the stress-strain curve of non-stretched PET films was explored at roo m temperature and 80 degrees C. The off-axis angle stretching of strip-biax ially stretched PET films was done at room temperature, and the stress-stra in curve was explored at room temperature. The results were analyzed on the basis of the series model of crystalline and amorphous phases of non-stret ched and strip-biaxially stretched PET films to give the ratios of Young's modulus and yield stress of crystalline and amorphous phases.