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The unique effect of chain entanglements and particle morphology on the sintering of ultrahigh molecular weight polyethylene

Nascent ultrahigh molecular weight polyethylene (UHMWPE) is a thermoplastic material, consisting of nodular-fibrillar structure making it too much porous. At the present work, the effect of both particle morphology and chain entanglements on the sintering of UHMWPE was investigated. Neck growth for particles of three different commercial grades was determined as a function of time at isothermal sintering temperatures. A comparison between the experimental data and predictions from a theoretical model based on Maxwell constitutive equations revealed a complicated effect of particle size and morphology. It was observed that at early stages of sintering, Bellehumeur’s model was in an excellent agreement with the experimental data, while it was deviated at late stages when the neck growth ratio (y/a) exceeds 0.8. Unlike commercially entangled samples, melted disentangled powder particles did not flow toward each other even after a long time had elapsed. Disentangled UHMWPE pellets, sintered for 10 min near the melting temperature, showed great transparency indicating low air voids and developing the sintering process, while grain boundaries remained undeveloped for entangled pellets.