Effects of Polymerization Medium on Nascent UHMWPE Properties and Sintered Material Performance

Abstract

High-performance and easy-processing UHMWPE products with less entanglement and small particle size are difficult to synthesize efficiently in the polymerization process. In this study, a mixture of heptane and light paraffin is proposed as the polymerization medium to control the concentration of ethylene in the slurry during polymerization. Influences of the mixture composition on the polymerization behavior of ethylene, the particle size and its distribution of nascent UHMWPE, and the initial entangled state of UHMWPE were explored. Experimental results showed that as the volume fraction of heptane decreased, the viscosity of the solvent mixture increased exponentially, and ethylene solubility as well as mass transfer coefficient of ethylene in solvent decreased, which greatly affected the ethylene polymerization rate. By adjusting the volume fraction of heptane in the polymerization medium, the particle size, initial entanglement state density, and molecular weight of nascent UHMWPE will be coordinately controlled. UHMWPE with smaller particle size, lower entanglement density, and higher molecular weight can be prepared using the conventional Ziegler–Natta catalyst and polymerization medium with a lower heptane content, and its sintered UHMWPE material shows good mechanical properties.