Changes in light scattering from poly(ethylene terephthalate) and nylon 6 films upon stretching in relation to the deformation mechanism

Unoriented T‐die flat films of nylon 6 and PET films annealed at 90°C were stretched in water at 80°C. Amorphous PET films were stretched in water at 65–75°C. Changes in the light scattering patterns from these samples upon stretching were investigated. One of the observed LS patterns from the stretched samples is the H v eight‐leaf pattern consisting of four lobes and streaks. In the nylon 6 and heat‐treated PET showing this pattern, spherulitic patterns can be seen in polarization microscopy. The microscopic spherulitic superstructure may possibly be the factor responsible for producing the lobe‐and‐streak pattern. On the other hand, many microscopic eight‐leaf patterns can be observed in amorphous unannealed PET showing the lobe‐and‐streak pattern. These microscopic patterns are due to retardation at stress concentrations around impurities and nuclei. The superstructure giving these microscopic patterns must be the origin of the lobe‐and‐streak pattern from unannealed PET. Another scattering pattern, the V v cruciform pattern, was observed in both stretched nylon 6 and unannealed PET. This pattern is due to an orientation change across the slip lines observed under a polarizing microscope. It is noted ( 1 ) that the appearance of the slip lines in PET coincides with the occurrence of oriented crystallization on stretching, ( 2 ) that the lobe‐and‐streak pattern from PET in which orientation crystallization has taken place is fairly stable to heat treatment and does not disappear until just before melting, and ( 3 ) that the superstructures produced at low stretching seem to be deformed on further stretching, in accordance with affine deformation theory.