Filler processing and mixing effects of polyoxymethylene/graphene nanocomposite on tribo-mechanical performances

Binary nanocomposites based on polyoxymethylene (POM) and graphene nanoplatelet (GNP) were fabricated to improve the tribo-mechanical performances of high-precision sliding parts in linear drive system applications. Liquid-phase exfoliation technique and surface modification by 3-aminopropyltriethoxysilane (APTES) were used to process GNP filler for improved endowment of POM/e-GNP matrix-filler interfacial adhesion. Results show that processed e-GNP at optimal 0.5 wt% loading is distributed uniformly in the matrix and enables excellent stress-transfer during the mechanical loading, increasing flexural modulus, impact strength and elongation at break by 51.3 %, 41.9 % and 24.5 %, respectively, in contrast to neat POM. Simultaneously, coefficient of friction (COF) and specific wear rate ($W_s$) of POM in ambient temperature were also reduced substantially by e-GNP incorporation under both dry (COF by 19.5 %, $W_s$ by 40.6 %) and grease lubricated (COF by 38.2 %, $W_s$ by 76.4 %) sliding conditions. Smoothened wear surface and formation of homogeneous transfer film on the steel counterface were accounted for large specific surface coverage and low-shear strength of e-GNP at the contact interface, especially during the dry sliding. In addition, the accumulated energy dissipation by frictional work was calculated in the sliding interfaces based on friction force-displacement (F-D) hysteresis loop. However, pristine POM/GNP exhibited poor matrix-filler adhesion and deteriorated composite properties due to the aggregated structure which can cause subsurface defects and serve as a failure site. The proposed new material would extend the applications of precision parts by overcoming the tribo-mechanical related issues for quieter and accurate linear motion systems.