Polyimide fibers prepared by dry-spinning process: imidization degree and mechanical properties

Polyimide fibers were prepared by dry spinning a polyamic acid solution to get the precursor fibers and then the precursor fibers were transferred into the polyimide fiber by heat treatment. The imidization degree (ID) of the precursor fibers obtained at various spinning conditions was investigated using FTIR and TGA analysis. As a result, the IDs of the precursor fibers increased with elevating spinning temperature. Meanwhile, the IDs measured by FTIR and TGA were much higher than the values from our model prediction. The tensile strength of precursor fibers exhibited a slight dependency on IDs. On the other hand, the complete imidization and hot stretching led to a great improvement in the mechanical properties. Subglass transition and glass transition of the stretched polyimide fibers were observed in DMA, and the activation energy of these transitions was 346 and 981 kJ mol−1, respectively.