International audienceUltrahigh-molecular-weight polyethylene (UHMWPE) has been processed by means of sintering of a nascent powder. Particular attention was paid to the precompaction of the powder just below the melting point (Tm) under vacuum. The particle welding was subsequently carried out under pressure at various temperatures above Tm for various durations. Tensile drawing experiments performed on sintered samples either at room temperature or above Tm were specifically aimed at discriminating the role of chain interdiffusion through the particle interfaces from that of cocrystallization in the mechanism of particle welding. It turned out that efficient welding occurred within a very short time. One of the novel results of the work is the much weaker influence of sintering time as compared with temperature, giving evidence that chain interdiffusion is not governed by a reptation process. The entropy-driven melting explosion over distances much larger than the chain length between entanglements is suggested to be the main mechanism of the fast chain re-entanglement and particle welding in the present case of a nascent powder consisting of nonequilibrium chain-disentangled crystals. Another major aspect of this study is the demonstration of the huge cocrystallization efficiency in the interface consolidation in the solid state that significantly hides the kinetics of chain intertwining occurring in the melt

The phenomenon of cavitation generally appears close to yielding in the high-density polyethylene. It can affect the yield stress and the properties at large strains. The influence of the microstructural and molecular parameters on cavitation is not well established; it is not even clear whether the cavitation is a cause or a consequence of plasticity. In this work, we focus on the initiation of cavitation and on the nucleation rate. Various polyethylenes with a wide range of microstructural and molecular parameters have been obtained. The cavitation is followed up by SAXS in-situ tensile tests. It is found that, depending on the polyethylene, cavitation can be avoided or, on the contrary, appears before or after yielding. The stresses necessary to initiate cavitation and crystallite shearing have been relied respectively on stress transmitters (tie molecules, interphase, etc.) and crystallite thickness. Then the comparison between the materials has allowed predicting the various polyethylene behaviors. All of the latter have been explained by a simple model based on very few microstructural parameters. Surprisingly, our results have shown that all the scenarios of plasticity and cavitation are possible. One is the cause or the consequence of the other in accordance with the molecular topology and the microstructure.