Carbon nanofiber defects come in many different forms and types. The defects can be roughly divided into surface defects and internal defects. For defects of the same size, surface defects have a greater impact on their tensile strength than internal defects. The editor will give you an introduction to the surface defects of carbon nanofibers and their causes.

Observation under a microscope, if you find that there are round spot-shaped deposits on the surface of the nano-carbon fiber. This may be produced in the fiber-forming process of wet spinning, that is, the micro-suspended matter in the coagulation bath is deposited on the surface of the nascent fiber and then pre-oxidized and carbonized. Therefore, the circulating coagulation liquid needs to be filtered to filter out the suspended matter to prevent contamination of the nascent fibers. In addition, the surface is a round spot deposit, which is probably caused by the deposition of tiny spinning droplets.

Some also have internal cracks or obvious skin-core structures. The occurrence of such internal cracks is likely to be the result of thermal degradation of the core without sufficient pre-oxidation and without forming a trapezoidal structure during the carbonization process. In other words, the dense skin is the result of pyrolysis and condensation of the trapezoidal structure, and the core is composed of resin carbon that is thermally degraded by linear molecular chains. There is more thermal degradation and less residue, resulting in the formation of loose structures and cracks.

There may be large holes inside the carbon nanofibers. Undoubtedly, the existence of these large holes reduces the effective cross-sectional area of the load bearing and reduces the tensile strength. If the hole reduces the effective cross-sectional area by 23.6%, the tensile strength cannot reach the level of T300 carbon fiber. There may be two reasons for the occurrence of these large internal holes. One is that the PAN precursor itself has a large central hole, and the other is that there is a serious skin-core structure during the pre-oxidation process, and the core that does not form a trapezoidal structure during the carbonization process evaporates sharply. structure.

During the carbonization process, the fiber changes from flexibility to brittleness, and the scratched fragments cannot be retained. Therefore, surface scratches are likely to be generated during the pre-oxidation process, and then after the straight-line carbonization, the scratched debris is likely to remain in place. The cause of the scratches is undoubtedly the poor surface finish of the conveying roller, so the roller needs to be sprayed with ceramics. Grinding and polishing to remove burrs and sharp corners.