Plastic deformation of crystalline polymers

Draw ratios have been measured for samples of polyethylene and trons‐polyisoprene, crystallized at various temperatures and at various degrees of orientation. The values obtained range from unity, i. e., no drawing is observed, up to values of about 15X for materials crystallized in the oriented state and then drawn in a perpendicular direction. The results are in rough accord with a simple molecular network model in which network strands are incorporated into crystallites with a number of reversals of direction (folds), and the remainder of a strand between network junctions is randomly arranged. The reduction in draw ratio with increasing temperature of crystallization and with increasing orientation at the time of crystallization is then accounted for in terms of a reduction in the number of reversals (folds) per molecular strand. Differences in natural draw ratio for different polymers are attributed to variations in characteristic sequence length within a crystallite and in the number of folds per network strand.