Study On Preparing Polyimide Fibers Via Partly Imidized And Ternary Copolymerized Method

Polyimide (PI)fiber is one of the high-performance fibers,which contains imide cycles in the mainchain of the molecule, possessing excellent mechanical properties, insulation, irradiation resistance, corrosion resistance, high or low temperature resistance. Polyimide fiber has significant foreground of industrial applications as structural or functional materials, along with good irradiation resistance and electrical properties, so it can be widely used in many special fileds, such as fire protection, electronics, aircraft and aerospace industries and military fileds. It also has drawbacks such as too high melting point at which the polymer is difficult to process, weaker adhesion, easy hydrolysis, weaker spinnability and higher cost etc. Therefore, the research for the synthesis and modification of po1yimide fiber has become important development directions.With the improvement both of the polymerization and spinning technologies, polyimide fiber have got much more attention. On the basis of previous works, this paper prepared polyimide fibers using partly imidized and ternary copolymerized method. And the mechanical property, morphology and thermal property of PI fibers was characterized. The specific steps as follows:1. The two-step process of preparing polyimide fibers was used in this paper. On the basis of pyromellitic(acid)dianhydride-4,4'-diaminodiphenylether poly(amic acid))PAA)polymerized mothod , the partly imidized ternary copoly (amic acid) was synthesized with pyromellitic(acid)dianhydride (PMDA), 4,4'-diaminodiphenylether (ODA) and p-Phenylene diamine(PPDA) via copolymerization in polar solvent Dimethylacetamide (DMAc), then the mixture of acetic anhydride and triethylamine was added into the intermediate product. It is found that the intrinsic viscosity of polymer was influenced by molar ratio of PPDA and ODA, total solid content, reaction temperature and time, molar ratio of Acetic anhydride and diamine and so on. In this paper, addition of the third monomer could change the stereostructure and symmetry, enhance the molecular chain's flexility and the spinnability of PAA solution; partly imidized mothod also enhance the spinnability.2. This paper spun the fibers from PAA solution by dry-wet spinning. The standard of choosing the coagulation bath was made by testing the coagulation value and the length of gel which indicate the coagulation rate. By SEM, IR spectrum, DMA and mechanical properties measurement, the effects of the spining method, the character of the solution and the technics of the spinning on the mechanical properties of fiber and its morphology were discussed. And in the aftertreatment process, the efforts of draw atmosphere and ratio were discussed firstly. Through controlling these factors, PAA fibers with good mechanical properties and dense cross-section were prepared.3. Three processes were applied to transform the partly imidized ternary PAA fibers into PI fibers, which are chemical treatment, heat treatment and both of them. The results of three processes on the morphology and mechanical properties of the fiber are compared. Between the chemical-heat treatments, the effort of different atmosphere, wrapping form, the heating method and temperature on the mechanical properties of PI fibers were also studied. At last the PI fibers with good mechanical properties and dense cross-section are prepared. The results obtained from IR spectrum and DSC analysis were that the imidization was about 100% when it was treated at 300℃; and the PI fiber's decomposition temperature reached 561℃.