Preparation And Properties Of Graphene/Poly(Ether Ether Ketone) Conductive Composites

A unique combination of excellent electrical, thermal and mechanical propertieshas made graphene a multi-functional modifier for polymers. The research work isfocused on three aspects: exfoliation of graphite for higher surface area, developmentof effective strategies for processing and characterization of graphene/polymercomposites and understanding their processing, structure and property relationships.This thesis mainly studied the preparation of graphene/poly (ether ether ketone)conductive electrical composites.We adopted modified Hummers method to prepare graphene of stripping layersfrom graphene oxide (GO). Graphene oxide modified by silane coupling agent(KH550) was processed by two-step reduction: hydrazine hydrate reduction and lowtemperature thermal reduction. The dispersion of modified graphene (CRG-KH550)in poly (ether ether ketone)(PEEK) matrix was improved and the interface bindingforce of CRG-KH550with PEEK matrix was enhanced. Though thermal stability andintrinsic conductivity of modified graphene decreased a little bit, but the modificationwas beneficial to get high strength and low percolation threshold of the conductivecomposites. First of all, CRG-KH550/PEEK composites were fabricated by meltblending, then the test samples were molded by hot pressing technique. The electricalconductivity of CRG-KH550/PEEK composites was greatly improved byincorporating CRG-KH550, resulting in a sharp transition from electrical insulator tosemiconductor with a low percolation threshold of0.2vol.%. The research onCRG-KH550/PEEK composites crystallization behavior showed that the nucleationeffect was promoted when the CRG-KH550content was low, and led to thecrystallization temperature and the crystallinity of CRG-KH550/PEEK compositesincreasing slightly. As the CRG-KH550content is higher, the increase of filler limitsthe regular arrangement of PEEK segments so as to hinder the crystallization process of PEEK. The thermal stability of the composites was not decreased by CRG-KH550,which suggested that CRG-KH550could be suitable for the melt processing of PEEK.In order to further improve the electrical conductivity of the graphene/PEEKcomposites, thermally reduced graphene (TRG) was formed by high-temperaturerapid pyrolysis of GO. Despite size reduction and distortion in the flat graphenestructure by thermal treatments, TRG still possessed high conductivity and thermalstability, thereby the conductivity of the composites could be improved. TheGraphene was modified by poly (ether sulfone)(PES)(m-TRG) and the dispersion inPEEK matrix could be greatly improved. The electrical conductivity of m-TRG/PEEKcomposites was greatly improved by incorporating m-TRG with a low percolationthreshold of0.76vol.%. A high electrical conductivity of0.18S m-1was achievedwith3.84vol.%of m-TRG. The m-TRG/PEEK composites exhibited goodmechanical properties and the tensile strength and modulus of the composites couldmatch those of other PEEK composites filled with commercial reinforcements, e.g.carbon nanotubes and natural graphite. The thermal stability of the m-TRG/PEEKcomposites was greatly improved, i.e.5%weight loss temperature and10%weightloss temperature of the composites were improved24℃and28℃, respectively.The morphological investigation of the composites showed the well dispersion ofm-TRG in PEEK matrix.The main achievement of this research was lied in to reveal the relationship amongthe preparation method, morphology of graphene and the resulting performance ofgraphene/PEEK composites based on high melting temperature and high meltingviscosity of PEEK resin, and then to choice suitable method of modification andprocessing to fabricate graphene/polymer composites, so as to reasonably tailor theproperties of the composites for application requirement of different fields.