Contribution of the Initially Entangled State and Particle Size to the Sintering Kinetics of UHMWPE

Nascent particles of ultrahigh-molecular-weight polyethylene (UHMWPE) with different entangled states and particle sizes have been processed by means of sintering. The chain entanglement formation of the sintered UHMWPE was investigated using a small-amplitude oscillatory shear measurement, where the contribution of the initially entangled state and particle size to the entanglement formation of long chains was addressed. The chain dynamics of the bulk phase and interfacial phase in the particles was calculated based on the McLeish theory to quantitatively address the contribution of the particle size and entangled state to the entanglement formation. The mechanical properties were then well explained based on the entanglement formation across interfaces. The motion of long chains was restrained by a large number of physically entangled points in the highly entangled domains, which limited the interfacial chain fusion and entanglement formation. In this case, small particles promoted chain diffusion and particle fusion owing to the large specific area for welding. The heterogeneously distributed entanglement in the less entangled UHMWPE enhanced the motion of chain segments, leading to rapid entanglement formation throughout the interfaces, especially in small particles. Therefore, a very short sintering time (5 min) was enough to make the fine particles reach the thermally stable state, exhibiting excellent mechanical properties.