Study Of 1,4-benzenediamine/4,4'-diamino Diphenyl/pyromellitic Dianhydride Polyimide Fiber

As one of high-performance fibers, polyimide fiber has excellent mechanical properties, radiation-resistance and heat-stabilities. It is widely using under circumstances such as space industry, atomic energy industry, military industry and so on. Recently, along with the great requirements of aero-area and development of its synthesis and spinning technique, more extensive attention has been payed on the research of polyimide fiber.In this paper, the third monomer 1,4- benzenediamine (PPD) was introduced into the system of pyromellitic dianhydride (PMDA) and 4, 4'-diamino diphenyl (ODA). Polyamic acid (PAA) was synthesized in N-methyl pyrrolidone (NMP) by solution polycondensation. The chemical structure of the polymer obtained was characterized by infrared spectrum. The dynamic viscosity and intrinsic viscosity were measured. Studies were mainly focused on the influences of monomer solid contents, monomer adding methods on intrinsic viscosity.In the storing process of PAA solution, the effects of adding tertiary amine, environmental temperature, averaging and storing time on dynamic viscosity or intrinsic viscosity of PAA solution was studied.By using water, alcohol, NMP and their mixed solution as coagulating bath, the coagulation value was measured as coagulating standard. Then, PAA fiber was made by wet spinning method. The influences of coagulation bath conditions, methods of modification of PAA solution, characters of PAA solution and technics parameters of spinning on PAA fiber's morphology structure and mechanicalproperties were discussed. Thereinto, coagulation bath conditions concerned on the temperature and composition of coagulation bath; Modification of PAA solution included the effects of adding acetic anhydride and tertiary amine on fiber's properties. Furthermore, the influences of PAA solution's intrinsic viscosity, solid content and drawn condition in spinning process were also studied for finding the best spinning parameters of PAA solution.For preparation of PI fiber, three methods were used.They were chemical imization, heat imization and chemical-heat imization. The three methods were compared for the mechanical performance and the heat imization method was choosen. In heat imization method, the influences of treating temperature, treating atomospheres (vacuum, nitrogen, air),exerting force, temperature holding time and heat-setting conditions (time, temperature and force) on PI fiber's performance were all studied. By the tests of mechanical properties, scanning electron microscope (SEM), differential scanning calorimetry (DSC), thermal gravity analysis (TGA), x-ray diffraction (XRD), the structure and performance of PAA and PI fibers were characterized. Finally, PI fibers with better mechanical performance were prepared when the ratio of PPD and ODA was 4/6 or 3/7, the tensile strength and initial modulus were 5.21cN/dtex, 160cN/dtex and 5.0 cN/dtex, 145 cN/dtex, respectively; Meanwhile, the PI fibers had excellent heat performace, their decomposition temperatures were 500℃and remaining weights of 800℃were about 60%.