Research on Chain Diffusion and Entanglement via Controlling the Sintering Process of Nascent UHMWPE

The diffusion and entanglement of molecular chains have a significant impact on ultrahigh-molecular-weight polyethylene (UHMWPE) processing and product qualities. During sintering, the relationship between the melting behavior and chain diffusion in nascent UHMWPE remains unclear. In this work, nascent UHMWPE with different degrees of entanglement was used for sintering under different temperature conditions. Tensile drawing experiments performed above the melting point were used to study the degree of chain diffusion. The results reveal that the chain diffusion degree is proportional to the heating rate (S) at the same sintering temperature when S is above 1 °C/min. The chain diffusion is more sensitive to the sintering temperature at higher heating rates. The melting process suggests that rapid heating is necessary for melting explosion, which leads to a rapid chain diffusion. When heated slowly, crystals are melted more gently, and the chains may melt successively from the surface to the center, resulting in a lesser degree of chain diffusion or entanglement. Finally, the high melting point of nascent crystals and the variation of the melting point with heating rate may be related to the increasing entropy during melting.