Preparation And Tribological Properties Of Self-lubricating Microcapsule/Polymer Composites

In this paper, self-lubricating microcapsules containing methyl silicone oil as core material were prepared with poly(melamine-formaldehyde) (PMF) as shell material by in-situ polymerization method. The MCLMs/polystyrene (PS) composites were synthesized through bulk polymerization method using MCLMs as self lubricating addtives; The MCLMs/PU binary and SCFs/MCLMs/PU ternary composites were prepared through in situ synthesis by adding MCLMs and surface-modified short carbon fibers(SCFs) as lubricating reinforcement addtives to the polyurethane(PU); The MCLMs/EP binary and PTWs/MCLMs/EP ternary composites were fabricated by mold casting method through dispersing surface-treated titanium hexatitanate whiskers(PTWs) and microcapsules into the epoxy resin. Furthermore, the mechanical properties and tribological behaviors of as-synthesized composites have been investigated,the wear mechanism of composites was discussed and the details are described as follows:The morphology of MCLMs was evaluated using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The particle size distribution, micromechanical properties and thermal stability of MCLMs was evaluated by particle size analyzer,nano-hardness tester thermgravimetric analyzer(TGA),respectively.The tribological properties,thermal stability and mechanical properties of the composites were investigated by using block-on-ring high speed wear tester,thermgravimetric analyzer (TGA) and universal testing machine and the wear mechanism of the composites was discussed according to the wear morphology of the composites.The results show that the self-lubricating microcapsules (MCLMs),which were successfully prepared by in-situ polymerization, had uniform particle size and clear spherical structure. The particle size and shell hardness of microcapsules was about 5 ?m and 17.02 MPa. Meanwhile, the MCLMs can disperse uniformly in the all the three matrix adopted in this thesis, and form good compatibility with the matrix. The results of the mechanical and tribological properties of MCLMs/PS binary composites showed that the composites with 15% MCLMs can achieve good toughening and anti-friction effect, and the average friction coefficient and wear rate of composites were decreased by 68.66% and 92% respectively, compared with neat PS resin. For the MCLMs/PU binary or SCFs/MCLMs/PU ternary composites, the results showed that the average friction coefficient and wear rate of the MCLMs/PU binary composites with 10% MCLMs were decreased by 42.2% and 94.14% respectively, but the mechanical properties of the binary composites were decreased as well. After adding 15% SCFs and 10% MCLMs simultaneously to the polyurethane matrix, the tensile and flexural strength of the SCFs/MCLMs/PU ternary composites were increased and maximally increased by 16.89% and 43.2% compared to its corresponding binary composite when the content of the SCFs reaches 15%,meanwhile, the friction coefficient and wear rate of the SCFs/MCLMs/PU ternary composites with 15% SCFs decreased by 44.26% and 98.72%compared to neat PU. The results of the mechanical properties, thermal stability and tribological properties of MCLMs/EP binary composites and PTWs/MCLMs/EP ternary composites demonstrated that the tribological properties of the binary composites were significantly improved with the incorporation of MCLMs. However, the mechanical and thermal stability of the binary composites was reduced due to the plasticization effect and lower thermal stability of the MCLMs. For the PTWs/MCLMs/EP ternary composites, not only the mechanical properties and thermal stability of were improved by the reinforcing effect of PTWs, but also the friction reduction and anti-wear effect of ternary composite are further enhanced which demonstrated that the synergistic effect of the MCLMs and PTWs on the matrix was remarkable. The wear mechanism of composites of the PU and EP composites showed that the methyl silicone oil which was released during the friction was transferred to the counterpart ring to form lubricating transfer film, consequently, the transfer film can prevent the direct contact between the composites and the counterpart ring which lead to an excellent anti-friction and anti-wear properties, meanwhile, the wear mechanism for the binary composites was adhesive wear. For the tenary composite, on the one hand, the shear resistance of composites was improved, on the other hand, the SCFs/PTWs were peeled off from PU or EP due to the thermal deformation of the matrix arised from the friction heat,part of which were dispersed in the friction surface and the other part was transferred to counterpart surface along with the lubricating transfer film.As a result, it will greatly reduce the friction coefficient and wear rate, and the abrasive wear should be the main mechanism. The synergistic effect of the MCLMs, SCFs and PTWs on the matrix was remarkable in the whole friction process.