High Performance Polyacrylonitrile Precursor Preparation Process Optimization

Wet-spinning processes of free-radical copolymerization of acrylonitrile (AN) with methacrylate (MA) and itaconic acid (IA) were investigated. Effects of finish, dry collapse, draw in steam on structure and properties were examined by scanning electron microscopy (SEM), electron microprobe analyze (EMPA), X-ray diffraction (XRD). The denier, tensile strength, the extension at break, density, the fractional voids, boiling shrinkage, crystal ratio, crystal orientation and crystal size of experiment precursors were tested, which may prove the data for making fine denier, high strength, fine crystal size, homogeneity, high density precursor. At the same time we forecasted the denier, and optimized the extension process. Also the sequence distribution of acrylonitrile/acrylate/itaconic acid copolymers was simulated by Monte Carlo method, provided for synthesizing better sequence distribution solution.Denier is one of the important indexes for precursors. The denier can be forecast by testing polymer density and concentration, for fabricating fine precursors. We can control the wet-spinning process by assigning stretch ratio.The composition and sequence distribution of the AN/MA/IA copolymers were simulated by Monte Carlo method. The effect of comonomers on the sequence distribution of chain was discussed. When the ratio of acrylonitrile/acrylate/itaconic acid is 98:0.7:1.3, the copolymers with an ideal sequence distribution can be obtained. Dripping the second monomer IA is an efficient method to improve the uniformity of sequence distribution.Finish is the key process for spinning favoring and improving the properties of PAN precursor. The finish uptake in the precursors was controlled by two steps in order to reducing soakage, depressing tiny hole and improving the effect of dry collapse. The first finish is between the stretch in boiling water and dry collapse, thesecond is between stretching in steam and dry collapses relax. Effect of the finish on the properties of the precursors and the pre-oxidation stabilized fibers were discussed. It was found that the fibers applied with the Mod-amino silicone oil do not give fluff, broken and adhered precursors during pre-oxidation. The tensile strength and elongation at-break of the finished precursors increase greatly. The density of the pre-oxidation stabilized fibers with the finish is lower than that of the import pre-oxidation stabilized fibers. Mod-amino silicone oil can satisfy the requirements for spinning and can be used to produce high performance carbon fibers.Five hot rollers were used during dry collapse to lustrate water and obtain dry collapse. The temperature should be higher than the glass temperature of PAN precursors. To avoid hot shrink resulted from tensile force, a negative draw was provided. Density, tensile strength, extensibility at break and boiling shrinkage increase at first and then depress. Crystal size increases with elevating temperatures. Homogenization, fine crystal size and structure collapsed precursors can be obtained for 65.0s below 140℃. Improving the surface quality of the rollers and adopting new technology are favorable to fabricate high performance precursors with less surface defects.Fine deniers were made by high draw ratio in saturation high pressure steam. Relationship between the steam pressure/temperature and draw ratio, draw ratio and the precursors properties, the steam pressure and the precursors properties were investigated. When the temperature was higher than glass temperature with drawing in saturated high pressure steam, the vapor depresses glass temperature of the precursors and tensile forces was helpful for the molecule chain movement. If the pre-stretch was 4.5, vapor stress was 0.50MPa (that is 151.7℃), the denier will be thin, crystal ratio and orientation increased. The tensile strength, extension at break, density and boiling shrinkage research the optimum value at 2.8 stretch ratios. The inner stress increases with steam stretching the precursors, giving rise to theincrement of boiling shrinkage. Under the same stretch ratio the temperature increase with steam pressure increase, which may remove the inner stress and depress boiling shrinking ratio. Under high draw ratio fine denier and depressed skin-core structure are gained. Thin denier depresses the ratio of the precursors lacuna and makes structure perfect, crystal ratio and orientation increase. More flaw and cranny would decrease the precursors properties with a high draw ratio.