ABSTRACT The hierarchical microfibril/fibril architecture constitutes a key structural determinant governing the mechanical properties of polyacrylonitrile (PAN) precursor fibers. This study systematically investigated the effect of drawing ratio and temperature on the development of microfibrillar structures and the resultant mechanical properties of PAN fibers, while elucidating the underlying mechanism of fibrillation. The stretching field enhanced the fiber crystallinity, whereas increasing temperature resulted in the reduction of their crystallinity. Through analysis of the microfibril/fibrils morphology in both longitudinal and transverse directions, combined with the solution etching method, it was observed that the initially random microfibrillar network developed into lamellae structures, while the interconnected microfibrillar network became elongated and aligned along the fiber axis. The stretching field promoted the alignment and the aggregation of the microfibrils, facilitating the formation of the larger fibrils. The improved orientation and orderly stacking of microfibrils significantly contributed to the enhancement of the mechanical properties of fibers, leading to an increase in tensile strength from 79.8 to 233.9 MPa. These findings provided valuable insights into the fibrillation behavior and might support the optimization of the spinning process.
Gao et al. (Fri,) studied this question.