In order to evaluate the effect of uniaxial orientation on environmental stress cracking (ESC) in crystalline polymers, drawn samples were prepared from low-density polyethylene. The features of ESC in these samples were investigated under methanol environment. From the experiment, the following results were obtained: (1) The fracture angle increased with increasing the draw ratio and the change was distinct at low draw ratio. (2) In the experiment under a constant load, the crack length markedly increased to a critical value with increasing time. (3) The fracture surface was markedly changed with increasing the draw ratio. (4) The resistance to fracture increased with increasing the draw ratio and then decreased.
These experimental data were analyzed by considering the change of the stress distribution around a crack tip with drawing. Then, the following conclusions were reached: (1) The fracture angle is determined by the direction of largest negative hydrostatic pressure. (2) The resistance to cracking in uniaxially oriented samples can be qualitatively predicted from the calculation of the stress distribution around a crack tip.
