| It was based on the study of the use of industrialized production technology in this paper, and preparation of high performance PAN precursor and carbon fiber as the goal, for batch, continuous and stable. For the PAN spinning dope and dry-jet wet-spinning of PAN precursor preparation technology exploration, practice and theory was combined. Among them, the PAN spinning dope preparation process including the selection of solvents, determination of dissolving methods and solution post-processing. The dry-jet wet-spinning of PAN precursor preparation was mainly explored for the influence of spinning dope properties and first coagulation bath parameters adjustment. Most of the experimentals were mainly used by existing experiment instruments in the lab, the necessary equipments were designed and commissioned at the same time to ensure that the new methods were verified and developed, such as ultrasonic strengthening processing device and two-order twin-screw extruder, etc. Several testing instruments were involved in this paper, such as the rotating viscometer, Ubbelohde viscometer, falling ball viscometer, UV light spectrophotometer, infrared spectrometer, X-ray diffraction, scanning electron microscopy (SEM) and fiber elongation, tensile experiment of door type, dynamic light scattering (DLS) instrument, gel permeation chromatography (GPC), etc. The PAN spinning dope, PAN fiber (precursor) and carbon fiber in all kinds of characteristics were analyzed comprehensively, and the tensile strength of carbon fiber above 5500MPa was finally obtained. The technology for laboratory results transform to industrial production has played a promote and guiding role.For the PAN dissolution theory, the solvation effects between PAN chain and solvent molecules which based on the theory of solubility parameter was researched, meanwhile, the theory of solvation is the fundamental principle of polymer solution, and the solvation structure determines the performance of the solution were pointed out, respectively. Through the study of solubility parameters and the distribution, it was found that the relationship between solvent and PAN intermiscibility ability for:DMSO>DMF>DMAc, and the characteristics of performance contribution were mainly depended on the δp part. This paper puts forward the concept "solution frame" structure and its image model was set up, which to more scientific and simply explain the solvation process. Based on the theory of solution frame, the distinguish between different solvents and solution viscosity were illustrated, the basis of the solvent selection and use of mixed solvent were determined. To PAN dilute solution, the study found that hydrodynamic diameter (Dh) and intrinsic viscosity ([η]) follow as DMSO>DMF>DMAc relationship, and the concentrated solution viscosity was proportional to the intrinsic viscosity. At the same time, the DMSO system has strong stability and environment resistance for store, meanwhile, DMAc system has lower viscosity, so the spinning dope was easy to post-processing and increase polymer content. It could be combine the advantages when two kinds of solvent mixed, therefore, solvent ratio could be adjusted according to requirements of industrial production, when the rate of solvent is V(DMSO):V(DMAc)≈1.4, the mixed solution got the best balance performance.According to the dissolve theoretical research, the selected mixed solvent ratio of V(DMSO):V(DMAc)= 1.4 as mainly use, and then using different ways to the preparation of PAN concentrated solution, made every effort to get spinning dope low viscosity and high polymer content and uniformity performance. There were many ways to reduce the solution viscosity, but the premise was not change or destroy the PAN molecular structure, so this paper put forward along with all the different method of dissolving problem what should be paid attention and avoid. Swelling fully was the premise of polymer dissolves, so the ideal concentrated solution could be obtained by periodic heating mode, and ultrasonic enhanced dissolution process could promote the swelling process. The principle of ultrasonic enhanced dissolution was based on the ultrasonic cavitation effect who made the nucleuses wall oscillation periodic of local high temperature and high pressure. For PAN solution, the main factors which affecting ultrasonic intensity were the frequency and solution viscosity, the solution got low viscosity by the ultrasonic enhanced dissolved, which performance was the PAN fully swelling, but, what must pay attention to was long ultrasonic treatment time unfavorably, otherwise, it would cause PAN molecular chain break. The two-order twin-screw extruder was also studied in this paper, whose function was as a PAN concentrated solution preparation equipment, because of its continuous and good self-cleaning capacity, twin-screw extruder was more suitable for industrialized production. In this paper, a two-order twin-screw extruder was designed and commissioned, who equipped with automatic weighing feeding system, and the characteristics of thread section combination was determined according to PAN performance, the screw rotation speed and temperature distribution was studied on the effects of dissolution, and the rotation speed below 80 RPM was determined ultimately, meanwhile, periodic heat treatment was set in the dissolving process. At the same time, the screw cannot remove and restructuring easily was considered, so a cycle path was set up to strengthen the dissolution, the problem of ultrahigh viscosity and polymer content dissolve incomplete was solved. Finally, high quality spinning dope was obtained by using this equipment efficiently.For two step spinning process, the last craft of the spinning dope preparation was purification, which was also a decisive step for spinning feasibility, because impurity particles and bubbles in solution would affect normal jet process. This paper mainly studied the bubbles rapid removal of high viscosity solution, and a set of ultrasonic deaeration equipment was designed, which different with ultrasonic enhance dissolving principle, the ultrasonic deaeration was mainly based on the standing wave what made by the silo wall reflect, made the bubbles focus on nodal point and gathered, merger, escape finally. The biggest advantage of ultrasonic deaeration was focus tiny bubbles together to be big bubbles which decompression process difficult to remove, and overcome the transgression resistance what because of the liquid surface tension, thus, it could improve the efficiency and effect of deaeration greatly. Ultrasound not only produced mechanical effect but also brought cavitation effect, but it doesn’t necessary to the dissolved completely solution, so it must pay attention to the negative effect on the solution of cavitation effect, one of which was to the influence of frame structure. The cavitation effect would contribute to swelling, reduce the solution viscosity, but when the solution got low viscosity enough, or the molecular chain stretch reached a certain degree, it would due to the increase of solution frame and made the solution viscosity increase by ultrasonic continually. So it was better that standing sealed after ultrasonic deaeration process to reduce the viscosity and easy to spinning. In addition, the standing wave effect would gather the molecular with similar size of hydrodynamic volume, therefore, long time of ultrasonic deaeration process would also amplification the defect of broad molecular weight distribution because of LMW and HMW PAN were separated from each other. It was easy to swap out for LMW molecular group in the double diffusion subsequently, what caused the solute loss and the pores inside fiber which couldn’t closed. Therefore, the long time ultrasonic deaeration processing was inadvisable, instead of using intermittent approach for bubbles removal.The twin-screw extruder was used for dissolve PAN powder, the solution was treated by ultrasonic deaeration process, and got the spinning dope which suitable for the dry-jet wet-spinning process. The influences of solution viscosity on dry-jet wet-spinning process feasibility, and the first coagulation bath conditions on PAN fiber dispersion and fine denier were studied in this paper. At the same time, it was pointed out that fine denier of PAN precursor could improve the tensile strength of carbon fiber. The drop ball viscosity of 1000s around at 60℃ was determined by the experiment, which was beneficial to the dry-jet wet-spinning process goes smoothly. In order to ensure the air flow stress ability, the spinneret temperature could be changed to regulate the fluid viscosity in spinning process. The first coagulation bath concentration was 5% lower than spinning dope, and as-spun fiber draft in the bath about 4～5 times was appropriate, which were good for the PAN fiber fine denier. By the properties of PAN adjusted. By made its denier about 0.6dtex, and ensured the fine fiber dispersion ability to and the molecular chain structured, the tensile strength of carbon fiber over 5500MPa was produced ultimately, which arrived the level of T800 carbon fiber for industrial production. |
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