High temperature resistant polysulfone/silica double-wall microcapsules and their application in self-lubricating polypropylene

Polysulfone (PSF)/silica hybrid double-wall microcapsules containing lubricant are synthesized. The lubricant-loaded PSF microcapsules are prepared by a simple solvent evaporation method, and the surface of the PSF microcapsules are modified and activated by dopamine. The activated PSF microcapsules are then microencapsulated again by a silica wall using a sol-gel method. The mean diameter and wall thickness of the synthesized double-wall microcapsules are approximately 90 and 6 mm, respectively. High thermal stability of the microcapsules with a thermal degradation onset temperature of 300 degrees C is obtained. The microcapsules are able to withstand the high-temperature shaping conditions necessary for the polypropylene (PP) composites system used (260 degrees C for 60 min). The silica walls effectively protect the PSF microcapsules from softening transformation. Tribology testing of PP self-lubricating composites incorporating 10 wt% lubricant-loaded microcapsules yields 54.9% and 54.3% reductions in the coefficient friction and wear rate under middle load and middle sliding speed conditions, respectively, compared to the pure PP. The tribological behavior of the self-lubricating PP is further assessed under different applied loads and sliding speed combinations. The formation of a boundary lubricating film from releasing lubricant and the entrapment of wear debris in the cavities left by the ruptured microcapsules are the major self-lubricating mechanisms. These PSF/silica hybrids double-wall microcapsules can be applied to many other polymers to produce unique selflubricating materials.