Sintering evolution monitoring of ultra-high-molecular-weight polyethylene

UHMWPE nascent powders have been commercially processed by sintering for decades although key aspects of the mechanisms and kinetics of this process are not fully understood. Herein, the volume change during each stage of the sintering is monitored by in-situ measurements with other characterization methods. Results indicate that the & alpha;-transition plays a crucial role in the early stages of the sintering process. Without pressure during sintering, a large expansion is observed during heating through the & alpha;-transition well before melting and this apparent volume change is also related to the residual stress resulting from the compaction. However, the application of a moderate pressure during heating leads to a significant densification. Specifically, five distinct processes are identified from the in-situ measurements via customized pressure sintering apparatus. These include room temperature densification, subsequent densification while heating through the & alpha;-transition, process of melt explosion that involves the enthalpic process of crystal melting and the entropic process density changes during the isothermal sintering of non-equilibrium melt, and the subsequent recrystallization under pressure. The density evolution offers a comprehensive understanding of the intricate processing of UHMWPE nascent powder and this can be effectively employed to investigate the impact of various processing parameters on the sintering process.