Incorporating shape memory properties in poly(ethylene terephthalate) film by isothermal crystallization

In this paper the peculiar shape memory property of semicrystalline PET films is studied. The shape memory samples were prepared through isothermal crystallization of glassy PET films at different temperatures between 120 and 230 A degrees C for 15 and 4 minutes. It was assumed that the incorporated shape memory constitution is due to crystalline and amorphous parts and also third phase i.e. a rigid amorphous fraction (RAF) which rose by increasing the degree of crystallinity. The microstructure of samples was probed by DSC and WAXD analysis, and concluded that isothermal crystallization at temperature which spinodal decomposition mechanism is dominant, brings the formation of secondary crystal lamellas in amorphous regions between pre-existing lamellar stacks, incorporating shape recovery in the samples. As the crystallization proceeds with time or at higher temperatures, the fraction of RAF increases leading to suppression of shape memory effect.