Mechanisms of chain re-entanglement during sintering of UHMWPE nascent powder: effect of molecular weight
Résumé
Nascent powders of ultrahigh molecular weight polyethylene (UHMWPE) with different molecular weights in the range 0.6 < M-v < 10.5 million g/mol have been processed by means of sintering. The interface consolidation or particle welding was carried out under pressure at various temperatures above the melting point and for various durations. Tensile drawing experiments performed above the melting point enabled to study the role of chain interdiffusion through the particle interface. The melting explosion phenomenon was demonstrated to occur for each molecular weight. The higher is M-v, the greater is the efficiency of the phenomenon. But this does not allow a homogenization of the entanglement network of the sintered sample. Indeed, heterogeneity of deformation between the grain and the interface clearly appears during tensile tests above the melting temperature. The differences in mechanical behavior in the molten state between the molecular weights seem exacerbated by crystallization under tension. After melting explosion, end-chain diffusion as well as sideways motions are probably involved in the healing of very long chains polymer interfaces to reach a sufficiently high entanglement density. This latter phenomenon seems thermally activated.