Study On Wet-Sping Of Btda-TDI/MDI Ternary Copolyimide Fiber

BTDA-TDI/MDI ternary copolyimide was polycondensated from 3,3',4,4'-benzophenone tetracarboxylic dianhydride (BTDA) and methylphenylene diamine (TDI)+methylene diamine (MDI). In the mid'80s, a polyimide fiber named P84(?) has been produced by the Austrian company Lenzing AG based on this co-polyimide. This fiber was widely used as protective materials, packing materials, high-temperature filtration materials, conveyance lining materials and so on for their good resistance to high temperatures, outstanding chemical resistance, good irradiation-resistant and thermostability. BTDA-TDI/MDI ternary copolyimide fibers prepared by wet spinning with N-Methyl-2-pyrrolidone as solvent were studied in this article. In this article we studied the die-swell properties of copolyimide/NMP solutions, the coagulation mechanism of wet-spinning polyimide fibers prepared from BTDA-TDI/MDI terpolymer, effect of heat treatment conditions on structure and properties of copolyimide fibers.The die-swell behavior of copolyimide solution was studied on a capillary-rheometer by photographic method. Extrusion die-swell ratio (B) was measured under different die specification and extrusion conditions. Die length/diameter ratio (L/D) was varied from 1 to 9. Extrusion conditions included temperatures of solutions from 15℃to 60℃, extrusion pressures from 0.2MPa to 0.5MPa, and filter gauze layers. The results showed that B increases with the increase of pressures, but decreases with the increase of temperature, the die length/diameter ratio and the number of filter gauze layer.The mutual diffusion of solvent and non-solvent in the process of wet-pinning poses a great effect on the structure and properties of PI as spun fibers. The measure and calculation of diffusion coefficients was the key point on the diffusion during the coagulation process. In this paper, the amount of solvent NMP and non-solvent H2O in the proto fiber is measured by Component Analysis. Here the calculation formula of diffusion coefficients of solvent and coagulant was based on the Fick Second Law. The effects of coagulation conditions on diffusion coefficients the ratio were studied and dynamic principle during the coagulation process was revealed preliminarily. It was found that the diffusion coefficients of solvent and coagulant both increased continuously with the increase of jet stretch ratio or the bath temperature, and was lower in 70% bath concentration than 60% and 80%, and then the curve showed a trend upwards. The ratio of diffusion coefficients (Ds/DN) showed the same trend.In the experiment, the fiber was produced in-40%,-50% and-60% negative tensile conditions respactively. Combining the results of static fixed-length heat treatment and dynamic heat treatment, the effect of the temperature on the fiber was discussed.340℃was consided to be the optimum temperature. Finally the fiber with a best breaking strength of 1.76cn/dtex was obtained in the conditions as follow: 340℃,365℃,390℃and draw ratio 1 to 3.5, air or N2. The influence of drawing process parameters on mechanical properties was analyzed by computer software fitting and interpolation.