| Carbon fibers with many premium properties are becoming indispensable material used for military and civilian fields. Among the three commercialized carbon fibers, polyacrylonitrile (PAN) based carbon fiber has been predominantly developed for its combination properties. Several major factors such as the fiber's orientation, crystallinity and diameter determine the strength of carbon fibers. Therefore if the modification of precursor or carbon fibers can increase their degree of orientation and crystallinity while decrease the defects and diameter, then it is beneficial to prepare carbon fibers with better properties.The material named graphene which has a special two dimensional layered structure can play a important role in carbon fibers modification. Firstly, the graphene with layered structure can enhance the degree of orientation and crystallinity of fibers by inducing the polymer chains to align along the graphene during the gelation and stretching process. Secondly, during the heat treatment the graphene can constrain the disorientation for the fibers shrinkage and then increase the fibers'degree of orientation. At last the During the carbonization process the graphene can act as a template to induce the fiber's structure transformation and then help to form better graphitic structure while the graphene merge into the graphitic structure without introducing defects for the similar structure.Although the graphene has very apparent advantages in modifying carbon fibers, it is very hard for graphene to disperse in solvents for its steady chemical structure, which limit the application of graphene greatly. Therefore we choose the graphene oxides(GOs) to substitute the graphene. Graphene oxides can disperse well in many solvents for its surface containing a lot of functional groups. Then the GOs can disperse in PAN matrixes by solvents, which will change to graphene by heat treatment.In order to make sure the graphene can disperse well in the PAN matrixes, the PAN/GOs compounds were prepared by in situ polymerization. Therefore we mainly need to study the dispersion ability of GOs in the solvent of dimethyl sulfoxide(DMSO) and in the matrixes. Besides, we need to research on the influence of GOs on the polymerization process, the matrixes' structure and thermal properties. These works are helpful to evaluate the effect of GOs on the PAN and then guide us to prepare high quality spinning solution and high performances precursors.In this paper the GOs were prepared by Hummers method and treated by ultrasonic to disperse well in the solvent of DMSO. The PAN/GOs compounds were prepared by in situ polymerization. During the polymerization the GOs inhibited the reaction for the samples' conversion rate decreased by 5%. Besides, with the increasing of the addition of GOs the samples' viscosity-average molecular weight decreased from 69000 g/mol to 53000 g/mol. The 1R and XRD research indicated that the GOs with a content of less than 2.5wt% were dispersed well in the PAN matrixes. Besides, it also showed hydrogen bonds and chemical bonds were formed between PAN chains and GOs. The GOs also played an important role in improving the PAN matrixes'crystallization process, and with 0.5wt% GOs addition in the matrixes the degree of crystallization increased to 41%,8% higher than pure samples. The results by the DSC tests showed that with a suitable content of GOs like 0.5wt% in the samples were helpful to mitigate the cyclization reaction and decrease the breakage to the samples'structure, which was beneficial to obtain more steady structure. The weight lost results also showed the GOs are helpful to improve the samples thermal stability, the sample with a content of 0.5wt% GOs had more steady structure for its carbon yield was 5% higher than the pure samples. |
