Effect of Draw Ratio on the Morphologies and Properties of BPDA/PMDA/ODA Polyimide Fibers

3,3,4,4-Biphenyltetracarboxylic dianhydride/pyromellitic dianhydride/4,4-oxydianiline(BPDA/PMDA/ ODA) polyimide copolymer fibers with different draw ratios were prepared from the imidization of polyacrylic acid(PAA) fibers via a dry-jet wet-spinning process. Their morphologies, microcrystal orientations, thermal stabilities, and mechanical properties were investigated via scanning electron microscopy(SEM), wide angle X-ray diffraction(WAXD), thermogravimetric analysis(TGA), and tensile experiments. In order to acquire fibers with better mechanical performance, we aimed at obtaining the optimal draw ratio. Drawing during thermal imidization resulted in a decreased diameter of fiber from 25.8 μm to 16.9 μm corresponding to draw ratio from 1 to 3.5. WAXD results show that the degree of the orientation of the undrawn sample is 64.1%, whereas that of the drawn sample is up to 82%. The as-spun fiber and those with different draw ratios all exhibit high thermal stabilities, i.e., the temperature at a mass loss of 5% can reach as high as 570 ℃. The tensile strengths and tensile modulus of the fibers increase with the draw ratios, and the maximum tensile strength and modulus are 0.90 and 12.61 GPa, respectively.