Polymer Engineering Faculty Research


The Effect of Deformation and Composition on the Structure Evolution in the Pre-Oriented PET/PEI Blend Films during the Heat Setting Process

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The objective of this research is to affect the deformation and thermal behavior PET through synergistic blending strategies. For this purpose, a series of crystallizable compositions of PET (Tg=70°C) and PEI (Tg=215°C) were prepared. The structure evolution during uniaxial deformation was investigated. The very fast structural rearrangement processes that take place during the heat setting process were investigated using the newly developed Spectral Birefringence Technique. In 100/0 PET/PEI samples, above the onset of strain hardening the birefringence rapidly increases with time. The total increase in birefringence decreases with the increased levels of orientation and crystallinity imparted during the stretching stage. The introduction of PEI and the increase of its concentration tend to dilute the crystallizable PET chains. This, in turn, introduces a relaxation step at the early stages of heat setting at 180°C even in samples that were stretched to high stretch ratios. We also demonstrated that our Spectral Birefringence Technique is fast enough to keep up with the very rapid changes that take place at 180°C where the fastest crystallization is experienced.

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