Effects Of Surface Treatment On The Mechanical Properties Of Injection Molded Short Carbon Fiber Reinforced Polyetherimide Composites

Short fiber reinforced polymer composites have the advantages of easy processing,low density,excellent mechanical properties and corrosion resistance and have been widely used in the automotive,marine and sporting goods fields.Polyetherimide(PEI),as a special engineering plastic,has the characteristics of excellent heat resistance,good insulation property,flame retardantance and easy molding but its mechanical,friction and wear properties are relatively low compared to metals.Therefore,in order to meet the requirements of high-end applications such as aerospace and military equipment,short carbon fibers are usually added to improve the mechanical,thermal,electrical,friction and wear characteristics of PEI.Because the properties of composites critically depend on the interfacial properties of fibers and polymers,the modification of fiber surfaces is the key for the preparation of high-performance composites.In order to improve the interface bonding between short carbon fibers and PEI,this paper uses heat treatment,chemical treatment and nano coating to modify the surfaces of short carbon fibers.A series of short carbon fiber(SCF)reinforced PEI composites were prepared by extrusion and injection molding,and their tensile and bending properties were tested.The effects of different modification methods on the SCF surface structure,the interface characteristics and mechanical properties of SCF/PEI composite were discussed.Specific works are given as follows:(1)Modification of SCFs by heat treatment and chemical treatment and mechanical properties of SCF/PEI composites.The surface modification of SCFs was carried out by four processes: high temperature heat treatment,micritic acid oxidation,polydopamine impregnation and polyimide impregnation.And the effects of modification method on the mechanical properties of SCF/PEI composites were studied.The results show that the mechanical properties of SCF/PEI composites prepared by high temperature heat treatment method are the best.Infrared spectroscopy result showed that high temperature heat treatment,microric acid oxidation and polydopamine impregnation all left a series of polar groups on the surface of short carbon fibers,which increased the surface activity of short carbon fibers and improved the mechanical properties of PEI composites.The SEM results show that the surface roughness of SCFs is increased after these modifications compared to the untreated SCFs and the wetting property of SCFs with PEI is significantly improved.(2)Coating of SCFs by carbon nanotubes(CNT)and the mechanical properties of SCF/PEI composites.CNT@SCFs were prepared by direct impregnation of CNT on SCF surfaces,PDA-CNT@SCFs were prepared by mixing CNT with polydopamine(PDA)and then impregnating with SCFs,PDA-CNT@MDA-SCFs were prepared by mixing of CNT with polydopamine(PDA)and then impregnating with SCFs modified by micritic acid,PDA-CNT@HT-SCFs were prepared by mixing of CNT with polydopamine(PAD)and then impregnating with SCFs at high temperature.And the mechanical properties of CNT@SCF/PEI,PDA-CNT@SCF/PEI,PDA-CNT@MDA-SCF/PEI and PDA-CNT@HT-SCF/PEI composites were studied and compared.The results showed that the PDA-CNT@HT-SCF/PEI composite had the best mechanical properties and its tensile strength and bending strength were increased by16.41% and 18.5%,respectively.The mechanical properties of PDA-CNT@SCF/PEI composites were the second with the tensile strength increased by 12.4% and the bending strength almost unchanged.The mechanical properties of CNT@SCF/PEI composites were the worst,which are nearly the same as those of SCF/PEI composites.The results of this thesis showed that the interface failure mechanism of SCF/PEI composites changed from weak interface peeling to strong resin cohesive failure after the surface modification of short carbon fibers,thus improving the mechanical properties of the PEI composites.The high temperature heat treatment,polydopamine treatment and polyimide coating on short carbon fibers could not only improve the mechanical properties of the composites but also shorten the processing time and simplify the process.In the composites prepared by SCFs modified by CNTs,the addition of polydopamine can solve the agglomeration problem of CNTs,while the SCFs modified by the high-temperature heat treatment can form polar groups to bind to polydopamine and graft CNTs onto the surfaces of SCFs.Therefore,the obtained composite material showed the best mechanical properties...