Improved performance balance of polyethylene by simultaneously forming oriented crystals and blending ultrahigh-molecular-weight polyethylene

Abstract

Polyethylene as a versatile polymer is being increasingly used for parts whose surfaces are in contact with moving metallic components or solid particles. This needs polyethylene to be greatly improved in mechanical properties as well as wear resistance. To this end, in the current work, various contents of ultrahigh-molecular-weight polyethylene (UHMWPE) were added into high-density polyethylene (HDPE) for enhancement of wear resistance, while the oriented crystals, i.e., shish-kebabs, were induced by shear flow for mechanical reinforcement. With 30 wt% UHMWPE was added, highly improved performance balance was achieved. The tensile strength rose from 26.4 MPa for normal HDPE samples to 68.5 MPa for the modified HDPE blends. The same trend was observed for impact toughness, where the impact strength increased from 6.3 to 34.1 kJ m⁻². Moreover, addition of UHMWPE could reduce the wear rate from 22.1 to 7.6 mg MC⁻¹. A very interesting phenomenon was observed, in which the overall properties of the modified HDPE blends were constantly enhanced with the increase of UHMWPE content though UHMWPE itself does not have much better mechanical properties than the oriented HDPE. This was ascribed to the amplified shear effect as a result of UHMWPE addition. The exceptionally high melt viscosity of UHMWPE assumes a gel state even at high temperature, making it just deform and hardly flow under the shear field, which amplifies the flow velocity difference between UHMWPE phase and HDPE melt. The amplified shear effect resulted in more pronounced molecular orientation and thus formation of a higher content of shish-kebab microstructure. Our work indicated that the melt processing-structure control strategy can desirably manipulate polyethylene products with desired properties.