Carbon fiber is a kind of high-strength special fiber mainly composed of C element, and its molecular structure is limited to graphite. Between diamond and diamond, in recent years, it has become the focus of materials research with its excellent comprehensive performance. Carbon fiber is mainly made of precursor organic fiber carbonized at high temperature in an inert atmosphere. The chemical composition and preparation process of the precursor fiber matrix determine the structure and performance of carbon fiber. At present, the industrialized products of carbon fiber are polyacrylonitrile (PAN)-based and pitch-based carbon fibers.
As an important variety of high-performance fibers, polyimide fiber has the characteristics of diversified molecular structure design and high carbon content in addition to the aforementioned outstanding performance. In the preparation process, strict control of the polymerization ratio of dianhydride and diamine can obtain high molecular weight fibers. ). This kind of molecular structure fiber after high-temperature carbonization produces graphite with large lattice size and few defects, and high-performance carbon fiber can be obtained.
Patent CN102605477 first prepared a polyamic acid solution, and then spun into polyimide fiber. The polyimide fiber is fixed in a vacuum tube furnace, and force is applied along its axial direction, so that the fiber is in a stretched state during the heat treatment process, and the temperature is gradually increased under the protection of nitrogen. Polyimide-based carbon fiber with few defects, high carbon content, and conductive. Patent CN10276699032 performs gas or liquid phase stabilization treatment on polyimide fiber, polyimide polymer chain is cross-linked and solidified, and then the stabilized fiber is carbonized under low temperature constrained conditions in a nitrogen atmosphere, and finally high temperature graphite is performed By chemical treatment, high thermal conductivity carbon fiber with high crystallinity and high orientation was prepared.
In addition, polyimide nanofibers prepared by electrospinning can also be made into carbon nanofibers. Choi et al. first used electrospinning to prepare polyimide nanofibers, and then carbonized the fibers at a high temperature to prepare carbon nanofibers. The study showed that the residual carbon rate after carbonization was 53%. As the carbonization temperature increases, nanometer two meters The electrical conductivity of carbon fiber increased, the electrical conductivity after 220 treatment was 5.3/cm, the tensile strength was 5.0MPa, and the tensile modulus was 73.9MPa. Lee et al. 2 used electrospinning to prepare polyimide nanofibers, and further prepared carbon nanofibers after high-temperature carbonization. During the preparation process, the morphology and diameter of the final polyimide fiber are controlled by adjusting the molecular weight of the polyimide nanofiber precursor polyamic acid, the bias voltage of electrospinning, and the spinning rate to control the diameter and shape of the carbon nanofibers. The purpose of appearance. The research results show that the conductivity of carbon nanofibers prepared from polyimide nanofibers is higher than that of general carbon nanofibers. The main reason is that the carbon nanofibers prepared by this method cross each other. The electrical conductivity of carbon fiber increases. Figure 7-14 shows the morphology of carbon nanofibers prepared by applying different pressures during high-temperature carbonization of polyimide nanofibers.
Endo et al. prepared carbon nanofibers by carbonizing the mixture of PAN and polyamic acid after electrospinning at a high temperature. The research results showed that the addition of PAN reduced the viscosity of the polymer solution and increased the spinnability of the polymer; adjusting the diameter of the carbon nanofibers The properties of carbon nanofibers can be controlled. With the diameter of carbon nanofibers, the crystallinity of a single carbon nanofiber increases, resulting in an increase in the electrical conductivity and mechanical properties of carbon nanofibers.