Effects of annealing prior to stretching on strain induced crystallization of polyethylene terephthalate

Abstract : Polyethylene terephthalate (PET) is widely used in packaging and fiber industries. However, despite of its straininduced crystallization (SIC) behavior, stretching procedures sometimes lead to dimensional instabilities upon time or at intermediate temperatures (hot filling for example). One of the solutions involves heating the sample during a specific time at a given temperature, generally after stretching, to promote more stable microstructure without endangering the texture. In this study, the effect of a light thermal treatment before stretching was explored. Herein, a study on strain-induced PET microstructure is carried out using this thermal treatment method, prior to stretching, to validate the improvement on the dimensional stability after uniaxial and biaxial stretching. While annealing leads to relaxation of any pre-organization, higher apparent crystallinity and better dimensional stability has been indeed observed after stretching using dynamic mechanical analysis and X-Ray scattering technique.