Plastic deformation of polypropylene: Effect of molecular weight on drawing behavior and structural characteristics of ultra‐high‐modulus products

Abstract

Abstract The influence of molecular weight and temperature on the tensile drawing behavior of polypropylene has been studied, with particular reference to the production of ultra‐high‐modulus oriented materials. It has been shown that the optimum draw temperature is molecular weight independent to a good approximation, and that high‐modulus products can be obtained for M̄ w in the range 180,000–400,000, the highest modulus being achieved for polymer with M̄ w = 181,000. As in the case of linear polyethylene, under optimum drawing conditions the Young's modulus relates only to the draw ratio. Low‐temperature moduli as high as 25–27 GPa were recorded, which compare favorably with a previously reported value of 42 GPa for the crystal‐lattice modulus. Although the drawing behaviour of the samples studied appeared comparatively insensitive to molecular weight, some of the properties of the draw materials, notably melting point and shrinkage at high temperature, showed a wide range of behavior.