Preparation Of Polyimide Fibers And Study On Its Structure And Properties

Polyimide (PI) fiber is one of the high-performance fibers which have high mechanical properties and excellent thermal stability, along with good irradiation resistance and electrical properties, so it can be widely used in many special fields, such as fire protection, aircraft and aerospace industries and military fields. However, limited by some reason about technique and economy, only a few PI have been used to produce PI fibers in semi-commercial quantities up to now.In this paper, a kind of polyamic acid (PAA) has been synthesized, with NMP as the solvent, from pyromellitic dianhydride (PMDA) and 4,4'-oxydianiline (ODA) using solution polycondensation. The chemical structure of the solution has been characterized by FTIR. In order to obtain a PAA solution suitable for spinning, studies are concerntrated on the effects of molar ratios of the monomers and the molecular distribution on intrinsic viscosity.The standard of choosing the coagulation bath were made by testing the coagulation value and the length of gel which indicate the coagulation rate .Water, methanol, and ethanol which mixed or independent were used as the candidate for the coagulation bath. The as-spun PAA fibers were prepared using the choosing bath, the effects of the spining method and the character of the solution and the technics of the spinning on the mechanical properties of fiber and its morphology are discussed. Through controlling these factors, PAA fibers with good mechanical properties and solid cross-section are prepared.Two processes were applied to transform the PAA into PI fibers, which are chemical treatment and heat treatment. The results of two processes on the morphology and its mechanical properties are compared, and then the heat...