Effects of distortional components in biaxial stretching of poly (ethylene terephthalate) sheets on dimensional stability and structure |
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Authors: | L. Mascia Z. Fekkai G. Guerra L. Parravicini F. Auriemma |
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Affiliation: | (1) Institute of Polymer Technology and Materials Engineering, Loughborough University of Technology, LE11 3TU Loughborough, Leics, UK;(2) Dipartimento di Chimica, Universita' di Napoli - Federico II, Via Mezzocannone 4, I-80134 Naples, Italy |
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Abstract: | Thin sheets of poly (ethylene terephthalate) were stretched biaxially over a wide range to temperatures below the melting point of the polymer. The linear shrinkage occurring at temperatures between 85 and 100 °C decreased with increasing draw temperature and draw ratio. Specimens taken near the edges of the drawn sheets, which had been subjected to in-plane shear deformations, were found to exhibit linear shrinkage 5–8 times lower than those taken from the middle of the sheet. Subsequent experiments, using purpose-built clamps to achieve a more uniform state of shear in both directions of the biaxially drawn samples, confirmed the universality of the principle of shrinkage suppression by the superposition of shear deformations. X-ray diffraction studies revealed that the phenomenon was not related to differences in type of orientation of the crystals. The information from the X-ray diffraction studies and data from thermal analysis have led to the conclusion that the enhanced dimensional stability of biaxially drawn sheets subjected to superimposed shear deformations results from a combination of a higher rate of stress-induced crystallization and a reduction in the level of orientation within the amorphous phase. |
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