| By the analysis structure and performance of PAN precursors,oxidized fiber and carbon fibers,find the performance factor of PAN-based carbon fibers.1.the structure factor of pan precursors.Strength increases with molecular weight increased;on the contray,small molecular weight has small strength, but It does not affect the elongation at break significantly. Higher isotactic stereoregular, Higher crystallinity or high degree of orientation all to get high modulus and high strength carbon fiber. Small grain size had no obvious effect on the tensile modulus, but to a certain extent, it can effectively increase the modulus; PAN precursor within the larger and more holes, the more unfavorable to improve performance; In the skin-core structure of the PAN precursor, the greater the proportion of the cortex and the more dense core, the higher strength and modulus; Groove, crack, the impurity and adhesion between monofilament have more severe decrease in performance; At the micro structure, the more network structure of PAN precursor or the more spherical structure of the carbon fiber, the higher the intensity; the more layered structure of PAN precursor or the more band structure of carbon fiber, the more the higher the modulus.2.Spinning process factors.The higher purity of raw materials, the more favorable to access to high-quality fiber; Appropriately, increase in reaction temperature, lower second and third monomer ratio, increase the degree of polymerization, controlling the amount of initiator, solvent concentration and reasonable adjustments, will help improve fiber performance; Reduce the coagulation bath temperature, increase the depth of the coagulation bath can help reduce defects and access to high-performance fibers; Dry and wet spinning better than dry or wet; Drafting help to improve orientation, reduce the lattice distortion, and reduce pore size and number. With the drafting the fiber crystallinity and grain size increases, the intensity increase, but elongation at break decrease; When drawing bath temperature is low, increasing rate appropriately in stretch is beneficial to improve the modulus, strength may increase too; Increasing the stretch ratio Improve the fiber strength;Stretching in saturated steam environment under pressure is better;Multi-level stretching and adding excellent additives to optimize the performance; Appropriately increasing the washing temperature, extending time of washing and densification can improve strength and decrease elongation at break; Improve the densification temperature and wetting treatment helps to improve performance; Increasing ratio of spinneret length to diameter is conducive to quality pan precursor; Improve the pre-oxidation temperature, extended pre-oxidation time, the finer fiber number to improve the strength and lower elongation at break; Using a gradient in temperature and applying tension will help to improve performance; With the heat treatment temperature in carbonization, strength and modulus begin to increase gradually and begin to decline until 1500℃.At the same time Hereditary structure of polyacrylonitrile -based carbon fiber was concluded:1. The skin-core structure of pan precursor:Epidermis has Cylindrical lamellar structure which has been retained from the precursor to the pre-oxidation, to carbonization into Scale structure of the lamellar stack; Osteoporosis of the core has been retained to carbonation completely; The molecular chain, strip of the endothecium changes samdwich in the pre-oxidation, become the band structure in the carbonization; Samdwich in the pan precursor forms annular layer encircle a centre after pre-oxidation, changes into a spherical structure after carbonization;2. Tropism degree of pan precursor:It determines the fabric tropism in pre-oxidation and carbonization, which was retained.3. The shape of filamentary cross-section:There are rounded, random circular, radial, concentric circular, They can be shown evidently at the end of the process of pre-oxidation and carbonization4. Internal and surface defects:Internal cavities and surface grooves can not be eliminated by pre-oxidation and carbonization, can be reduced or thinning treatment in each process only. |
