Tuning chain entanglement density in UHMWPE via sintering: crystallization suppression and cryogenic toughening mechanism
Wenbo Wang, Huazhao Wang, Jingbo Chen
Abstract
A continuous, solvent-free sintering strategy was devised to systematically adjust the molecular chain entanglement density (ν e ) of UHMWPE by controlling chain diffusion through adjustments in heating rate and sintering temperature. Entanglement density was quantified by melt‐state rheology and above‐melting tensile tests, yielding values from 40 % to 100 % of the equilibrium state. DMA and DSC revealed that increasing ν e delays crystallization onset, reduces overall crystallinity from 56.3 % to 41.2 %, decreases lamellar thickness from 26.9 to 25.98 nm, and lowers the melting temperature from 140.2 °C to 135.4 °C. At room temperature, higher ν e correlates with reductions in tensile modulus, strength, and elongation at break, whereas at −196 °C (liquid-nitrogen conditions) impact toughness increases sharply from 18.8 to 27.1 kJ/m 2 , a 44 % improvement. Comparative tests on UHMWPE grades with molecular weights of 1.9, 2.8, and 8.2 × 10 3 kg/mol confirm that higher molecular weight enhances cryogenic toughness via elevated ν e . Microstructure and fracture-surface analyses attribute improved low-temperature energy dissipation to reinforced interparticle welding and an internal “chain-spring” network formed by dense entanglements. This work clarifies the interplay among entanglement, crystallinity, and mechanical performance in UHMWPE and provides a scalable route to engineer polyethylene for both room and extreme-temperature applications.