Tribological Property Of Expanded Graphite/polyethersulfone Composite Reinforced With Chemical Modification

Polyethersulfone?PES?is a special engineering thermoplastic polymer with excellent comprehensive performances,so it has been applied extensively in industries fields such as aerospace,engineering machinery and transportation,due to its outstanding mechanical property and self-lubricating characteristics.Unfortunately,the friction coefficient of PES resin is relatively large,and the wear rate of this polymer is also high.These drawbacks constrain the generalization and application of PES in the engineering field of tribology.In order to improve the tribological properties of PES composites,nanoscale reinforcing fillersincludingexpandedgraphite?EG?,graphiteoxide?GO?and3-aminopropyltriethoxysilane modified graphite oxide?APTES-GO?were employed to modify this polymer in the dissertation.Meanwhile,sulfonated polyethersulfone?PES-SO₃H?and ammoniated polyethersulfone?PES-NH₂?were synthesized,then they were successfully compounded with these aforementioned nanofillers.The effects of chemical modification for expanded graphite and polyethersulfone resin on the tribological properties of PES-based composites were investigated.Simultaneously,the antifriction and wear resistance mechanisms of PES-based self-lubricating composites were analyzed.The main research contents and conclusions can be drawn as follows:Firstly,vermicular-like EG particles were prepared from natural graphite flakes by the microwave radiation method.GO and APTES-GO nano-sized sheets could be fabricated from the oxidation treatment and silane coupling agent modification of these EG particles,respectively.The effects of these above-mentioned nanofillers on the mechanical properties,thermal stability and tribological performances of PES composites were comparatively investigated.The influence rules of nanofiller content,applied load and sliding velocity on the friction coefficient and wear rate for PES self-lubricating composites were analyzed.Meanwhile,the appropriate load range and critical sliding velocity of various nanofiller reinforced PES composites under drying sliding condition were also discussed.The strengthening and toughening mechanisms of nano-sized fillers on the PES composites were investigated.Also,the wear failure mechanisms of PES self-lubricating composites were clarified.The enhancement in friction reducing and wear resistance performances of APTES-GO/PES composites can be attributed to the uniform dispersion of APTES-GO sheets in the PES matrix as well as the strong interfacial interaction between them.In addition,the formation of uniform continuous PES self-lubricating transfer film also plays an important role in improving the tribological properties of these composites.Secondly,chlorosulfonic acid,concentrated sulfuric acid,diethylenetriamine and some chemical reagents were used to modify PES resin by sulfonation and ammoniation reaction.The effects of chemical modification methods on the crystalline structures,chemical functional groups,surface morphology,thermal stability and mechanical strengths of PES resins were analysed in detailed.The results show that the crystalline structures of PES resin aren't affected by sulfonated modification.But the ammoniation reaction has changed the the crystalline structures of PES resin in a certain extent.Both sulfonation modification and ammoniation reaction result in the decrease of thermal decomposition temperatures and mechanical strengths for PES resin.Nevertheless,the kind and the number of active chemical functional groups contained in PES-SO₃H and PES-NH₂ materials are greatly enhanced.This increases the chemical reaction sites in which interfacial bonding between nanofillers and polymer matrix occur,which is conducive to enhance their interfacial bonding strength.Accordingly,the friction and wear properties of PES self-lubricating composites are promoted.Finally,three kinds of nanofillers were succeesfully compounded with PES-SO₃H and PES-NH₂ materials through the solution blending method.And then they were blended into PES matrix to prepare PES-based self-lubricating composites via the processes of vacuum-assisted compression molding.Various physical and chemical characterization technologies such as infrared spectrum analysis,X-ray diffraction analysis and X-photoelectron spectroscopy analysis were adopted to reveal the chemical bonding principles between nanofillers and modified PES resin.Also,the friction-reducing and antiwear mechanisms of PES-based self-lubricating composites were clarified.The tested results confirm that amino and carboxyl groups existed on the surfaces of APTES-GO nanofillers can react with sulfonic acid groups of PES-SO₃H and amino groups of PES-NH₂,respectively,to from strong chemical covalent bonds.This would strengthen the interfacial bonding properties between nanofillers and modified PES.Compared with the other four PES-based composites,mechanical performances,thermal stability and tribological properties of APTES-GO/PES-SO₃H and APTES-GO/PES-NH₂composites are improved significantly.Under the dual influences of the enhancement of nanofillers and the chemical medification of PES resin,both the friction coefficients and wear rates of PES-matrix composites reduce sharply.Furthermore,the wear failures of PES composites reinforced with APTES-GO nanofillers have changed from adhesive wear to abrasive wear.