Regulation of thermal relaxation behavior and aggregation structure of polyacrylonitrile fiber

Polyacrylonitrile (PAN) fibers which formed high-elastic deformation during the spinning process, have thermal relaxation behavior in the heat conditions, such as thermal shrinkage with disorientation. The thermal relaxation behavior of PAN fibers was investigated by thermomechanical analyzer (TMA) , dynamic mechanical analyzer (DMA) , wide-angle X-ray diffraction(WAXD). And PAN fibers aggregation structure changed by tension and temperature were analyzed. The results show that the forced high-elastic deformation in PAN fibers accounts for more than 10% which leads to disorientation at high temperature. With structure rearrangement under controlled conditions, the high-elastic deformation in PAN fibers can be transferred to plastic deformation by appropriate tension and temperature imposed to fibers without orientation structure loss. By imposing tension and temperature, further improvement is achieved in the regularity of aggregation structure and the orientation of the molecular chain, crystalline structure, and dimensional stability increase by more than 50%. The crystallites of PAN based carbon fibers treated by this method are more regularly arranged along the molecular chain, and the performance has been improved effectively.