Dependence of Molecular Orientation, Crystallinity, and Thermal Dimensional Stability of Poly(ethylene Terephthalate) on Elongation Temperature

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Abstract
Orientation of amorphous chain segments and oriented crystallization of amorphous poly(ethylene terephthalate) (PET) were affected by the elongation temperature. That is, the crystallinity and birefringence of the specimen stretched in 65°C water below the glass transition temperature Tg increased, when the elongation ratio was beyond λ = 2.25, while crystallinity and birefringence in 80°C were constant values equivalent to those in the film prior to stretching. The Young's modulus and thermal dimensional stability were also dependent on the crystallinity of the drawn PET film. The experimental result for the thermal dimensional stability was estimated using the statistical theory of rubber elasticity. The observed result was somewhat in agreement with the calculated result.