| With the fact that the domestically produced CCF300 has poor comprehensive performance compared with the imported T300, this paper is focused on carbonized modification of CCF300 using phenolic resin. First-principle calculation has been carried out firstly in the calculation of PF/CF interface layer behavior to analyze isosurface of charge density difference maps, charge density difference maps of various slices and Mulliken population of chemical bonds. Competition of surface physical chemical properties and mechanical properties among carbonization modified carbon fiber, T300 and CCF300 before desizing and after follows the calculation. Method of coating with a layer of PF on the surface of domestic carbon fiber and carbonizing under high temperature in the protection of the inert gas are adopted. Finally, the influence of concentration of PF and carbonizing temperature on surface state for carbon fiber are.The result of First-principle calculation of PF/CF interface layer shows that functional groups have large affection to interface layer isosurface of charge density difference maps, especially carboxyl. Serious distortion of isosurface of charge density difference maps exists with overlapping electron clouds. This indicates strong covalent bond between PF carbonized layer and carbon fiber interface. Charge density difference analysis of slices in different cross section has taken, and the result shows obviously differences of charge density difference maps in these interface layers with functional group on. This means apparently electron exchange. The influence of functional group is not only limited to charge density difference, but also to arrangement of C atom,which makes C atoms deviating in a certain degree and damaging hexagonal structure.The result of the Mulliken population of interface layer bond, impacted by carboxyl,indicates the combination of a strong covalent bond between the PF carbonized layer and carbon fiber surface layer. This proves theoretically there is a strong covalent bond in PF/CF interface layer. Therefore, with the method of carbonizing phenolic resin,carbonized layer can be attached to the surface layer of carbon fiber by the covalent bond, which forming a stable interface layer.Coating PF on the surface of carbon fiber for carbonized modification, it is found that with the decrease of the concentration of PF, the coated quantity of PF decreases,and the most suitable concentration of the PF is 1:70. At this time, the amount of coating content of PF is similar with the sizing agent of original wire. The coating layer is complete and the thickness is appropriate. When carbonizing temperature of PF increases, the noumenal tensile strength of carbon fiber monofilament ontology reduces,and the suitable carbonizing temperature is 700 ℃. When concentration of carbon fibermodified by PF is 1:70, carbonizing under the high temperature of 700 ℃, there is a layer of porous carbon structure which is uniform and complete adhering on the surface of the carbon fiber. Because of the presence of these porous carbon structure, roughness and specific surface area of carbon fibers are greatly increased. The roughness is as high as 107.4%, which are increased by 218.7% and 234.6% compared with CCF300 and T300 respectively. The surface roughness is 43.67 m J·m-2, which is increased by 13.7%and 8.3% compared with CCF300 and T300 respectively. Through XPS analysis, it is found that the O/C and content of functional groups are increased by 7.6% and 1.2%respectively compared with CCF300. By means of interfacial evaluating device for composite materials to characterize interfacial shear strength, it is found that under the optimum processing condition, IFSS for PF carbonized modification of carbon fiber is105.8 MPa, which are increased by 26.4% and 12.7% compared with CCF300 with and without desizing respectively. |
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