The Research And Evaluation Of Performance On The Carbon Fiber Surface And Interface

The carbon fibers (CF) as a new kind of inorganic materials have been used broadly in reinforcement of advanced composites. The property of CF composites depends mainly on the quality of the interface between the matrix and the reinforcement, which determined the way that the loads can be transferred from the matrix to the carbon fiber.The improvement of the interfacial adhesion strength between the carbon fiber and polymer matrix is a key factor to improve mechanics performance of composite materials. Therefore,the analyzing of many influence factors for the interfacial adhesion strength of CF composites is direct measure to improve the composite’s general performance.Firstly, the carbon fibers were sized with self-developed epoxy-polyurethane coating agent, and it was discussed that the coating agent’s role in the carbon fibers surface and composites interface. Secondly, the problem of the interfacial adhesion strength between the carbon fiber and coating was resolved with the plasma-grating treatment. The properties changing of the carbon fibers surface was studied during plasma-grafted-coating processing, and the reaction mechanism of composites interface between the carbon fiber, coating and resin was also discussed in this comprehensive approach.The chemical and physical changes on carbon fibers and composites were examined using scanning electron microscopy (SEM), dynamic contact angle tester, X-ray photoelectron spectroscopy (XPS), thermo gravimetric analyzer (TG), Fourier transform infrared spectroscopy (FTIR), etc. The treatment of sizing slightly improved the strength of single carbon fiber, this result showed that made up the defects of carbon fiber surface by sizing treatment, and also improved the wear resistance, the amount of hairiness, but the wet ability increased. The percentage sizing and wear resistance obviously increased by the prebake treatment before sizing. In addition, the experiment results showed that the soaking time and drying temperature were two important factors in the sizing process.The results of FT-IR and XPS analysis indicated that the concentration of the C-O, C-C, C=O and O-C=O groups increased on the carbon fiber surface, the infiltrating performance between the carbon fiber and resin was improved. The IFSS (interfacial shear strength) of carbon fiber/epoxy composite was tested by the single fiber composites (SFC) experiment. The IFSS of sized carbon fibers composites were clearly enhanced compared with control samples, and were influenced by different plasticizer. The plasticizer of the coating agent had a major effect on wear resistance and the amount of hairiness, but had little effect on water absorption, surface roughness and the dispersive component of the surface energy.The experiment results by the electrical methods of the atmospheric pressure dielectric barrier discharge (DBD) plasma showed that the power discharge and gas composition were two important factors in the discharge process. The power discharge was not linearly related to energy distribution and density in plasma zone, but they were closely related with each other. Especially, the discharge energy declined after it was emitted by nitrogen oxygen, this could also happen with the increasing of oxygen content. Therefore, the power discharge and gas composition could be regarded as two major control parameters during the parameter optimization discharge process.Scanning electron microscopy (SEM) photographs showed that the carbon fiber surface grooves were deeper with plasma treatment. Surface energy (SE) implied that the plasma treatment with lower power and longer treated time produced identical efficacy as higher power and shorter treated time, and that the oxygen added to the treating ambience had a big influence on carbon fiber SE. The plasma treatment with lower power and shorter treated time reduced the discreteness of the carbon fiber strengths. Finally, the optimum plasma processing condition was as follows:the power60w,the treated time90s.The treatment of plasma-sizing slightly improved the carbon fiber percentage sizing, wear resistance and surface energy when compared to sizing treatment. In contrast, the strength of the carbon fibers had remained about the same. Meanwhile the plasma treatment causes the increase of surface roughness, this increased mechanical engagement made the percentage sizing easier to maintain and enhance. The results of XPS analysis indicated that the polar group content for plasma-sizing treated carbon fiber increased1.65%respectively than the sizing treatment. The IFSS of plasma-sized carbon fiber composites increased19.29%than sized carbon fiber.The experiment result indicated that the carbon fiber percentage sizing was decreased under the plasma-grafted treatment with higher power and longer treated time. It was obviously shown that the surface roughness increased for grafting maleic anhydride polymer on the carbon fiber surface. The surface energy increased with the increasing of the carbon fiber percentage sizing. The results of FT-IR, TG (thermo gravimetric analysis) and XPS analyses revealed that the polar oxygen group of the C-O, C=O and O-C=O showed a large increase under the plasma-grated treatment. The IFSS (interfacial shear strength) of carbon fiber/epoxy composite with plasma-grafted treatment were enhanced by30.03%respectively compared with plasma treatment.The treatment of plasma-grafted-sizing obviously improved the carbon fiber percentage sizing,wear resistance, the amount of hairiness and single fiber strength when compared to sizing treatment. Furthermore the water absorption was also effectively reduced to about0.1%. The results of SE analysis indicated that the polar groups generated by reaction between the surface and coating increased than sizing carbon fiber. The results of FT-IR and XPS analysis indicated that the concentration of the C-O, C=O, O-C=O and anhydride groups clearly increased on the carbon fiber surface, it was the reaction products of surface polar groups with epoxy group of the coating agent, and improved the wet ability. The IFSS of plasma-grafted-sized carbon fiber composites were enhanced by about100%compared with untreated carbon fiber composites. The effect of plasma-grafted-coating treatment on IFSS was researched that had two main factors. The activated groups of carbon fiber surface were increased by the surface treatment, which result in the surface free energy of carbon fibers significantly increased. The increase of the carbon fiber surface energy induced a part increase of the adhesion strength between carbon fiber and matrix. On the other hand, the carbon fibers surface were covered by the grafting polymer particles, this inlaid structure increased the surface roughness, which led to increase the interfacial adhesion between the fibers and the matrix.