Preparation And Tribological Properties Of MWCNTs/GP/PEEK Composites

Poly(ether ether ketone),a high performance thermoplastics,has many excellent properties such as outstanding thermal,chemical,mechanical properties and biocompatibility and has been extensively used in the fields of aerospace,electronics,automobile,nuke industry,medical apparatus and instruments,and others.Selflubrication as one of its merits makes PEEK a well-performed anti-friction and wearresistant materials used in rotation and transmission device.With the growing requirements and demand in working environment and using life of the equipment and in order to expand the application fields of PEEK composites,incorporating appropriate fillers was an effective solution to improve the wear resistance of PEEK resin to meet more demanding applications.Graphite(GP)and Carbon nanotube(CNT)are two important filler particles to improve the tribological properties due to their high temperature resistance,excellent electrical and thermal conductivity,chemical stability,and self-lubrication.And because of its ultrahigh L/D ratio,CNT is considered to be ideal one-dimensional(1-D)fillers for the fabrication of high-performance and multifunctional polymer/CNT nanocomposite.Therefore,we choose graphite and multi-walled carbon nanotube(MWCNTs)as filler to prepare a series of GP/PEEK,nano-GP/PEEK composites and MWCNTs/PEEK to investigated the effect of particle size of graphite and L/D ratio of MWCNTs on tribological properties of PEEK composites,and on closely related to mechanical properties and thermal properties and provide theoretical data for preparing PEEK composites with lower friction coefficient and low wear rate.And from the aspect of interface enhancements between filler and resin,and to further improve the tribological properties,MWCNTs was modified using non-covalent(physical)and the covalent-bond(chemical)reaction,and different series of functionalized MWCNTs/PEEK and functionalized MWCNTs/GP/PEEK composites were prepared.These PEEK composites had excellent mechanical properties,lower frictional coefficient and excellent wear resistant,and was used to fabricate self-lubricating parts in high wear areas?The results showed that attributing to the unique layer structure,the incorporation of GP can effectively improve the frictional coefficient of PEEK composites,but resulted in the negative effects in wear rate and mechanical properties.Nanoparticles have many excellent properties,such as small dimension effect,quanta dimension effect,surface effect and macroscopical quanta tunnel effect,showing a series of specific physical and chemical characters.The most important characteristics among them,is the tremendously high surface area.By introducing the high surface area with nano-filler,a lot of interphase could be created in composites which would help in creating a very large amount of interphase in composites.Even in low nano-filler loading,the big interphase between the polymer matrix and the nano-filler could provide a strong interfaced interaction.Comparing to the improvement of micro-GP,the incorporating nano-GP can effectively improve the wear resistant at the same content.However,the bonding forces between the tubes due to van der Waals forces,capillary effect,and electrostatic effect makes them extremely difficult to be dispersed.This,in turn,leads to disappointing improvement in properties.The properties of composites depend on a good dispersion of the fillers in the polymer matrix and the interface interaction between fillers and polymer matrix,therefore,achieving a good dispersion of the CNTs in the polymer matrix and enhancing the interface interaction between fillers and polymer matrix is the key to fabricate composites with greatly enhanced properties.In order to improve the dispersion of CNTs in PEEK matrix,two methods were used to modify CNTs.Non-covalent modification could prevent damage to the CNTs via strong electrostatic adsorption and ?-stacking between polymers containing conjugated structure and CNTs.In this study,a series of copolymers(DPAFD0-100)containing conjugated fluorene groups as compatibilizers to improve the dispersion of multi-walled carbon nanotubes(MWCNTs)and interface interaction between MWCNTs and PEEK resin were prepared.The prepared PEEK composites prepared by adopting non-covalent functionalization of MWCNTs possessed lower wear rate and excellent mechanical properites,but the compsistes had higher coefficient of friction.To further improve the tribological properties,the non-covalent functionalization of MWCNTs and graphite were used as fillers to improve the tribological properties of composites by utilizing the synergistic effect between MWCNTs and graphite.The PEEK composites prepared by incorporating the non-covalent functionalized MWCNTs and graphite had good mechanical and tribological properties.Besides non-covalent functionalized MWCNTs,the MWCNTs were modified by covalent.The method of covalent modification could provide reactive sites for chemical functionalization.MWCNTs were treated with a solution of sulfolane containing NaOH and 4,4?-Difluoro diphenylmethanone.During this process,4,4?-Difluoro diphenylmethanone generated graft on surfaces of MWNCTs.The strong interface interaction was achieved by polycondensation of the functionalized MWCNTs and poly(ether ether ketone)chain.A good dispersion of MWCNTs in PEEK resin and strong interface interaction was achieved by incorporating the covalent functionalized MWCNTs.The PEEK composites with excellent tribological properties and excellent mechanical properites were prepared.