Abstract
In order to clarify the mechanism underlying the deformation of crystalline polymers, the change in their morphology with uniaxial elongation has been studied by electronmicroscopy for the polyethylene films having the so-called“a-axis orientation”and the b-axis orientation, both of which can be assumed to have more simplified textures than those of isotropic spherulitic films.
A commercial blown film was used as the sample of the so-called“a-axis orientation”and films giving the b-axis orientation were prepared by moving them through the gap between the two metal plates having a thermal gradient. In the former case, the stress-strain curve depends considerably on the drawn direction as against the machine direction of the blowing, whereas such an anisotropy has not been observed in the latter case. This anisotropy may be attributable to the firm interconnection between lamellae, which probably resulted from the screw dislocation during the crystallization, in the case of the blown films.
The yield stress was not various among the samples studied, suggesting that the intra-lamellar (inter-ribbon) slip governs the large deformation. The electronmicroscopy revealed that only small unfolding occurred, and that locally, in all the cases studied.
