Induced crystallinity during stretch-blow moulding process and its influence on mechanical strength of poly(ethylene terephthalate) bottles

Microstructural evolution in poly(ethylene terephthalate) during a stretch blow process has an important influence on the final mechanical properties. To obtain information other than thickness distributions from numerical simulations of the blow moulding process, it is necessary to take into account the evolution of these characteristics (molecular orientation, crystallinity, etc). Numerical simulations of top loading tests at ambient temperature have been carried out on bottles and compared with experimental results. Good agreement was obtained if appropriate anisotropic moduli were used. In the present paper, results of tensile measurements made on stretch-blow moulded samples and experimental tensile tests on poly(ethylene terephthalate) specimens are presented. The influence of draw ratio, temperature, and clongational strain rate on the final strength of the bottle are analysed. A correlation between the mechanical characteristics and the induced crystallinity is demonstrated and used to predict mechanical characteristics at different locations on the bottle.