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Conformational changes of amorphous poly(ethylene terephthalate) films during uniaxial stretching

1991; Wiley; Volume: 192; Issue: 2 Linguagem: Inglês

10.1002/macp.1991.021920212

0025-116X

Deyan Shen, Fujin Long, Zaiqing Wen, Renyuan Qian,

Material Properties and Processing

Abstract Rapid scanning Fourier transform infra‐red spectroscopy was used to follow the changes in the population of trans conformers and in the infra‐red dichroic functions of the bands characterizing the trans (T) and gauche (G) conformers and the chains in the amorphous regions during stretching of a solution‐cast amorphous poly(ethylene terephthalate) (PET) film A in the glassy state (67°C) and in the rubbery state (88°C). Stretching at 67°C showed a yield stress peak followed by strain softening in the stress‐strain curve. The population of trans conformers in the amorphous and crystalline regions, T a + T c , decreased in the pre‐yielding region and then increased continuously after yielding. The T conformers formed during post‐yield stretching showed high orientation, while the G conformers remained in low degree of orientation. Stretching at 88°C showed no pronounced yield stress peak in the stress‐strain curve, and the population of T conformers did not change until the beginning strain‐induced crystallization. A solvent‐cast PET film annealed at 67°C for 24 h, the film N, showed a sharp and high yield stress peak in the stress‐strain curve, and strain‐induced crystallization occurred at lower draw ratio as compared to the film A. The film A showed a non‐equilibrium high population of T a conformers, part of which reverted to G conformers during sub‐ T g annealing.