Thermal Crystallinity and Mechanical Behavior of Polyethylene Terephthalate

Polyethylene Terephthalate's (PET) properties are particularly sensitive to its processing history. Processing impacts the extent of crystallinity. Mechanical stretching and melt flow history influence the extent and structure of crystalline domains in the semi-crystalline polymer. Typical processing parameters include the rate of cooling and the amount of stretch. Both influence crystallization differently. Isolating the contribution from stretch or thermal crystallization is valuable for identifying the relationship to mechanical properties. In this work, the influence of thermal crystallinity on the mechanical behavior of PET was observed. Annealed injection molded samples with thermal crystallinity were tested Young's modulus. Using the two-phase composite approach, mechanical behavior of injection molded semi-crystalline PET samples was modeled based on crystallinity from density. Crystallinity measured from different techniques did not always agree.