Wear Resistance Mechanisms Of Ultrahigh Molecular Weight Polyethylene (UHMWPE) And Bulk UHMWPE Composites

Ultrahigh molecular weight polyethylene(UHMWPE),a relatively recent engineering material of the polyethylene family,has good application prospects:UHMWPE is referred as an "advanced material" with excellent properties.Unfortunately,the poor wear/abrasion resistance of UHMWPE narrows its commercial applications,although UHMWPE appears to be the most wear-resistance plastomer.It is imperative to answer this question-how to enhance the wear performance of UHMWPE efficiently.To start with,we investigated the effects of molecular weight(M?:67-685 ×104 g mol-1)on the wear behavior of UHMWPE—the wear resistance improved upon increasing the molecular weight.We determined the multi-level structures—the crystalline structures(crystallinity Xc;lamellar thickness lc;crystallite size D);the amorphous structures(average molecular weight between entanglements Me);the interphase fractions and the surface characteristics(surface roughness Ra;surface free energy Es)-of the various polyethylene samples.We unveiled that the wear resistance of UHMWPE enhanced upon decreasing the value of Me and increasing the value of ?i.Subsequently,we studied the effects of filler loading(0,0.5-5.0 wt%)of silicon carbide(SiC)on the wear behavior of UHMWPE—the wear resistance improved initially,reached a maximum,and thereafter decreased upon increasing the filler loadings.We characterized the multi-level structures—the structures(crystalline/amorphous/interphase)of the UHMWPE matrix and the external effects(bearing loads/transferring friction heat)of the SiC fillers—of the bulk UHMWPE composites.We disclosed that the incorporation of SiC fillers improved the wear resistance of UHMWPE due to their high rigidity and thermal conductivity;unfortunately,the addition of large amounts of fillers would undermine the wear resistance because of the severe agglomeration and the triggered three-body abrasion.Lastly,we examined the effects of filler size(0,40-600 nm)on the wear behavior of UHMWPE—a SiC filler of medium size(150 nm)had the greatest enhancement.We evaluated the multi-level structures—the UHMWPE matrix structures;matrix-filler interactions;and the external effects of the SiC fillers—of the various UHMWPE composites.Besides the key factors described above,we demystified the paramount role of another parameter—D—the wear resistance of UHMWPE improved upon increasing the value of D.