Effect of physical-chemical nature of UHMWPE and PPS thermoplastic matrices on mechanical and tribological properties formation in their carbon fiber filled composites

The effect of carbon fiber size on mechanical and tribological properties of the composites based on two thermoplastic matrices of different physical-chemical nature (polyphenylene sulfide (PPS) and ultrahigh molecular weight polyethylene (UHMWPE)) has been compared. It is shown that permolecular structure formed during compressing sintering of PPS and UHMWPE controls distribution pattern of various dimension carbon fibers in the matrix. This in turn, affects the level of tribological properties. Structural and tribotechnical purpose composites based on high-strength PPS matrix filled with short carbon fibers (70 μm) can be fabricated at their high loading degree (40 wt. %). In doing so, the wear resistance increases by 5 times, while the friction coefficient decreases 1.7 times. Increasing wear resistance is realized through the formation of a third body consisting of wear debris that substantially reduces the coefficient of friction. Loading of the PPS with carbon nanofibers modifies the polymer matrix structure through the dispersion hardening mechanism and is not accompanied by the increasing tribological properties. Adding of chopped carbon fibers (with a length of units of millimeter) into the PPS matrix gives rise to substantial hardening but significantly reduces tribological properties. The fabrication of structural and tribotechnical purposes composites based on UHMWPE matrix can be achieved through loading of chopped carbon fibers at their content of 10 wt. %. The latter should by evenly distributed in the polymer matrix. In so doing, carbon nanofibers (CNF) should also be added into the polymer matrix. Carbon nanofibers are discussed to be the most efficient fillers for the UHMWPE matrix with a spherulitic permolecular structure from the standpoint of increasing wear resistance. The latter play the role of a solid lubricant media (wear resistance increases 2.7 times, the friction coefficient is decreased twice). Chopped carbon fibers of millimeter range in contrast to ones of tens and hundreds micrometer long (70 μm, 200 μm) play a reinforcing role. However they do not increase friction coefficient but ensures abrasive wear of steel counterpart. The role of interphase adhesion, hardness and chemical activity of the polymer matrices, as well as permolecular structure in providing tribomechanical properties of carbon composites based on thermoplastic matrices of various physical-chemical nature and their reasons are discussed.

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