Structure and Tribological Performance of Monomer Casting Nylon-6/Colloidal Graphite Composites Synthesized through in Situ Polymerization

Abstract

ABSTRACTA series of monomer casting nylon-6/colloidal graphite composites were synthesized through in situ anionic ring-opening polymerization. It was found that colloidal graphite layers modified with titanate coupling agent had a uniform distribution in the matrix, and the molecular weight of monomer casting nylon-6 decreased slightly below 5 wt% titanate coupling agent-colloidal graphite content. The crystallizing ability was much improved at lower titanate coupling agent-colloidal graphite content, indicating the nucleation effect of titanate coupling agent-colloidal graphite on monomer casting nylon-6. The notched charpy impact strength of the composites increased by addition of 0.5–1 wt% titanate coupling agent-colloidal graphite, and the obvious ductile fracture characteristics was presented. Meanwhile the storage modulus and the glass transition temperature (Tg) increased, and the loss factor (tan δ) decreased by addition of titanate coupling agent-colloidal graphite, indicating the toughening effect of titanate coupling agent-colloidal graphite on monomer casting nylon-6 matrix and improvement of the stiffness of the composites. Compared with neat monomer casting nylon-6 specimen, the composites presented a remarkable lower friction coefficient at the initial friction stage, and the wear resistance of monomer casting nylon-6/4 wt% titanate coupling agent-colloidal graphite specimen was enhanced by more than 10-fold. For neat monomer casting nylon-6, the melting and crystallization temperature, and crystallinity of the worn surface were obviously higher than that of the bulk part, indicating that the surface was fully annealed and the crystallizing ability was improved under produced friction heat, resulting in a poor anti-wear performance with abrasive wear form. For monomer casting nylon-6/titanate coupling agent-colloidal graphite composite, the annealing degree of the surfaces exhibited much lower than that of neat monomer casting nylon-6, due to the protective effect and suppression effect of titanate coupling agent-colloidal graphite layers and reduction of friction heat, resulting in the formation of uniform transfer film and a significant improvement of the wear resistance of the composites with the adhesive wear form.