Research On The Properties Of Surface Modified Carbon Fiber Reinforced Thermoplastic Resin Composites

Carbon fibers(CF)present exceptional properties,such as high stiffness,high specific strength,and outstanding wear resistance,which have attracted considerable research interest in exploiting them as excellent reinforcements for thermoplastic resin composites.Properties of composites mainly depend on the interfacial bonding strength between fiber and the matrix.In the present work,electrochemical oxidation treatment,MDI(Methylene Diphenyl Diisocyanate)grafting and coating treatment and nitric acid oxidation treatment have been applied to modify carbon fibers and three kinds of modified fibers(e CF,MDI-CF and m CF)are obtained.After compositing with thermoplastic polyurethane(TPU)and polyoxymethylene(POM),a series of TPU/CF,TPU/e CF,TPU/MDI-CF,POM/CF and POM/m CF composites with the fiber weight content from 5 wt.%-30 wt.%are obtained.In this study,surface properties before and after the modification treatments of carbon fiber have been characterized from multidimensional aspects.The mechanism of modification methods,the mechanism and the overall properties(including the mechanical property and friction property)effect of the modified carbon fiber on TPU and POM composites have been proposed,separately.The concluding remarks of this study are summarized as follows.(1)The fiber surface properties have obviously changed after electrochemical oxidation treatment,MDI grafting and coating treatment and nitric acid oxidation treatment,respectively.The roughness of the surface and disorder of carbon atoms increase significantly.Reactive functional groups,for instance,hydroxyl,carboxy,have been introduced to the fiber surface,while contents of oxygen,nitrogen and oxygen containing functional groups are increased.The aforementioned contents are advantageous to promote the reactivity of fibers.(2)Impregnation property and interfacial adhesion between modified fibers and the matrix are greatly improved.Contact angle measurement indicates that MDI grafting and coating treatment is the most effective way to improve the impregnation properties.SEM micrographs of the fracture surface of composites verify a better mechanical bonding between fibers and matrix generated.(3)Electrochemical oxidation treatment and MDI grafting and coating treatment have a significant effect on the mechanical properties of TPU composites.The tensile strength,tensile modulus,elongation at break,roughness and storage modulus of TPU/e CF and TPU/MDI-CF are superior to those of TPU/CF composites.MDI grafting and coating treatment can effectively increase the friction properties of TPU/CF due to the lower abrasion of TPU/MDI-CF composites to TPU/CF composites.When the MDI-CF fiber content is larger than 5 wt.%,the decrement of abrasion for TPU/MDI-CF composites reaches to the maximum valed,namely 18.20%.(4)The nitric acid treatment enhances the overall performance of the POM composites.Compared with POM/CF composites,the impact strength and modulus of POM/m CF composites increase.Simultaneously,the tan?peak heights of POM/m CF composites are lower than that of POM/CF composites,which indicates a good adhesion between the fiber and the matrix.The incorporation of m CF in POM improves the wear resistance and reduces the wear ratio.T_onsetincreases by 0.6°C-5.7°C,T_maxincreases by 3.3°C-9.0°C and the thermal stability of the composites increases.