The hard elasticity of polypropylene and its blends with polyethylene

Hard elastic monofilaments from polypropylene (PP) and its blends with polyethylene (PE) have been studied. Filaments with sharply different degrees of hard elasticity have been obtained by the same melt‐spinning process from three types of PP resin with almost the same isotacticity, molecular weight, and melt index and from blends of one of the PP resin with PE or high‐molecular weight PP (HMPP). With addition of a small amount of HDPE or HMPP to the parent PP resin, the hard elasticity of the filaments is increased significantly. Filaments with high hard elasticity can be prepared from PP resins of blends which show a relatively slow spherulitic growth rate. It is argued that the increased hard elasticity is due to row lamellae in PP fibers containing more adjacent folded chains and fewer tie molecules between lamellae and chain entanglements in the amorphous phase.