Preparation And Self-lubrication Properties Of Oil Containing Microcapsule/Polymer Composites

The liquid lubricant encapsulated to obtain the microcapsules with organic or inorganic shell is released during the rubbing process,which not only provides the advantages of fluid lubrication but also eliminates the disadvantages of external lubrication.Moreover,a small proportion of lubricating microcapsules can significantly improve the tribological properties of the matrix.In this thesis,self-lubricating microcapsules(SLMs)with liquid paraffin as core material and melamine-formaldehyde resin as wall material were prepared by in situ polymerization.By evaluating the influence of stirring speed,core-wall ratio and p H on the morphology and properties of the microcapsules,the optimum synthesis conditions were proposed.The morphology,thermal stability and chemical structure of microcapsules were analyzed by scanning electron microscopy(SEM),thermogravimetric analysis(TGA)and Fourier transform infrared spectroscopy(FT-IR).The results illustrated that the optimum conditions for the preparation of microcapsules were described as follows: the ratio of the core to the wall was 1.4:1,the p H was set as 4-5,and the stirring speed was 400 rpm.Adopting the as-fabricated microcapsules as lubricating additives,potassium hexatitanate whiskers(PTWs)or short carbon fibers(SCFs)as a reinforcing agent,polybutylene terephthalate(PBT)and monomer casting nylon(MC nylon)as matrix,SLMs/PTWs/PBT binary and ternary composite,SLMs/SCFs/MC nylon binary and ternary composites were prepared by melt blending and bulk casting methods,respectively.With the addition of SLMs,the friction and wear properties of SLMs/PBT binary composites can be effectively improved.When the content of microcapsules is 15wt%,the friction coefficient of the composites is reduced by 56.5% compared with the pure PBT,and the volume wear rate is reduced by 97.7%.However,due to the addition of microcapsules,the composite material tends to generate stress concentration and the mechanical properties decrease.When PTWs were added into the composites,the mechanical properties of the composites were significantly improved and their tribological properties were further improved as well.The wear mechanism for pure PBT is severe adhesive wear and for the SLMs/PBT binary composites,it is slight adhesive wear.For the SLMs/PTWs/PBT,the wear mechanism turns out to be abrasive wear.The results of MC nylon binary and ternary composite materialsdemonstrate that the addition of microcapsules can effectively reduce the friction coefficient and wear of composite materials,when the content of microcapsules is 5%,the friction coefficient and wear rate of microcapsules/MC nylon composites decrease by 50.38% and 97.3%,respectively.However,due to the low mechanical strength of the microcapsule shell material and the plasticizing effect of the core material,mechanical properties of SLMs/MC nylon binary composites are significantly reduced.The addition of SCFs to the binary composites can significantly improve the mechanical properties and wear resistance of the composites and play a synergistic role in anti-friction and anti-wear performance.The comprehensive result exhibited that synergistic anti-wear effect of microcapsules and PTWs/SCFs is mainly due to the fact that on the one hand the broken microcapsules during the rubbing process released liquid paraffin which can form a continuous transfer film at the friction interface and effectively prevents the direct contact between the two friction interfaces and consequently reduces the friction and wear.On the other hand,due to the addition of PTWs/SCFs,the hardness of the material increases which reduce the real contact area between the composite and the steel ring,and reduce the material adhesion.Meanwhile,it can effectively prevent the thermal deformation caused by friction temperature increases,hence improve the friction and wear properties.