The Research Of Fiber Manufacture Technology To Improve The Mechanical Properties Of PSA Fiber

PSA （Polysulfonamide） fiber is a kind of high-temperature resistant fibers, which was mutually developed by Shanghai Textile Research Institute and Shanghai Synthetic Fiber Research Institute. With many years’ efforts, the industrialization of PSA fiber was realized in 2008. Based on technologies of the pilot production line, the industrialized production process for 1000 tpy plant has run through and the manufacture and the product quality become stable. As an independent research and developed fiber, the high-temperature resistant performance of PSA fiber has been recognized and indentified by clients. However, the fiber still has certain deficiencies in mechanical properties, which to some extent restricts the market competitiveness of PSA with other high-performance fibers, also hinders PSA’s fast application and promotion in the market. Therefore, it is critical to research the manufacture technology in order to improve mechanical properties of PSA fiber.With the theme how to improve the mechanical properties of PSA, the researcher designs the spinning process conditions and technology programs to improve the mechanical properties. Since spinning is the core process for a synthetic fiber production, changing the conditions of the spinning process can adjust fiber structure in a wide range, compared to polymerization process, and then it can change the physical and mechanical properties of fibers. Therefore, we can further explore potential mechanical properties of PSA by optimizing the spinning process without the change of the basic process.With the research of the rheological property of PSA spinning solution, the researcher finds that the solution is a typical pseudo-plastic fluid, which is beneficial for fiber production and application. The higher temperature rises, the more flow property increases. Nevertheless, when the temperature becomes too high （higher than 75℃）, the rheological property of dope will be unstable. With the continuous increase of the polymer concentration （solid content） and relative viscosity, the flow property will be worse. As a result, it is found that polymer concentration has a greater impact on the rheological properties of PSA solution in comparison with the other two factors.With the research of the die swell characteristics of the PSA spinning solution, the researcher finds that when the temperature for coagulation bath increases from 5℃to 15℃, the ration of die swell will increase; when temperature exceeds 15℃, die swell will reduce; with the increase of the coagulation bath concentration, polymer concentration and the relative viscosity, the ratio of the extrusion swell is constantly increasing; the higher temperature of the solution will lead to smaller extrusion swell ratio; greater spinning rate will lead to greater shear rate and higher flexibility engager, and the extrusion die swell will be more obvious.With the research of the solidification process of PSA spinning dope, the research finds that with the increase of the coagulation bath temperature, the thermal motion of molecules will speed up, the diffusion coefficients of DMAc and H₂O become bigger, and the solidification process accelerate; when the coagulation bath temperature increases from 5℃to 15℃, the cross-section of small flow won’t change a lot with consistent density; while the temperature rises to 30℃the cross-section of the small flow will appear to be and the impact of temperature change is not significant on the roundness of the cross-section; with the increase of the coagulation bath concentration, solidification process will gradually slow down, and the cross-sectional shape of sample become more and more round, homogenized and densified; the greater relative viscosity becomes, the faster the solidification process will be; the relative viscosity has no significant impact on the densification of the cross-section; with the increase of the polymer concentration, the change will be different in accordance with the solution with the solid content of 12.5% as a division, that is, when the polymer concentration is lower than the content, the solidification process will continue to slow down with the concentration increases; when the concentration is higher than 12.5%, the solidification process will continue to accelerate with the concentration increase; Besides, polymer concentration has considerable influence on the cross-sectional shape.With the research of the impact of spinning conditions on the fiber morphology and mechanical properties, the researcher finds that lower coagulation bath temperature will lead to more slowly solidification process, so that the fiber structure can get denser and the fiber will have better mechanical properties; when the coagulation bath concentration is 50%/wt, the fiber break strength reaches a maximum; it is no good for mechanical properties to over stretch or under stretch the spinneret, that is, when its value is between -5% and +5%, the mechanical properties of the fiber will be best; there is a certain fluctuation for fiber strength and elongation with the temperature change of the dope: the maximum intensity appears when the dope temperature approaches to 50℃and the maximum of elongation appears when the dope reaches 40℃;the intensity reaches a maximum when the spinning rate is 5m/min, while the fiber elongation, with the increase of spinning rate, is gradually reduced in general; when the spinning rate is 6.5m/min, the elongation reaches the minimum value; 3 times plastic draw ratio is most beneficial to the strength of the fiber. So the reasonable spinning process is as following: temperature of spinning solution should be kept at 60℃; temperature of coagulation bath is 10-15℃; concentration of coagulation bath is 50w/%; spinning-drawing rate is between -5% to+5%; plastic stretch is 2.5-3 times; spinning rate is 2.56m/min. This spinning process can basically ensure the strength of PSA fiber to 2.0cN/dtex, as long as the heat treatment process of production are reasonable, PSA’s strength will reach to 4.0cN/dtex, with the original 3.0-3.3cN/dtex it will have a greater degree of increase.With the research of different heat treatment processes, the researcher finds that the strength of fiber increases firstly and then decrease with the increase of draw ratio; when the draw ratio approaches to 1.85 times, the fiber reaches a maximum intensity, and while the fiber break elongation decreases with the improvement of tensile elongation in multiple. On the conditions that the tensile strength of oiled silk is under relaxed status, the strength can be increased by 10%, with 30 minutes’ heating in air at 260℃.