Stress-induced textures in polymers

The effect of an applied stress on the annealing texture of polyethylene is demonstrated by means of stress annealing experiments. Cold-drawn polyethylene specimens were annealed for various times at 126°C with and without a compression stress of 0.4 kg/mm² normal to the drawing direction. The observed change in the annealing texture resulting from the compression stress indicates that stress-induced alignment of the crystalline regions in the polyethylene occurs (stress-induced texture). The alignment may be understood in terms of the elastic energy stored in the material during annealing. The stored elastic energy is minimized by aligning the crystallites such that the crystallographic direction of lowest modulus is parallel to the direction of the applied stress. The importance of this observation for the interpretation of the high-temperature deformation textures of polymers is discussed.