Microfibril alignment induced by stretching fields during the dry-jet wet spinning process: Reinforcement on polyacrylonitrile fiber mechanical properties. (January 2020) - Gao, Quan
Abstract: The high-quality polyacrylonitrile (PAN) precursor fibers are indispensable for the manufacture of high-performance carbon fibers. For the purpose of regulating microfibril structures and improving fiber quality, scanning electron microscopy, high-resolution transmission electron microscopy and the nitrogen adsorption measurement were carried out to investigate the microfibril alignment evolution in PAN fibers, which was obtained by different stretching fields during dry-jet wet spinning process. The interconnected microfibrillar network forming in coagulation bath was plastically elongated and gradually developed into the oriented microfibrils while the transverse lamellae formed. Then break-reorganization of the lamellae brought the remarkable enhancement of fiber crystallinity during the hot-treatment process. Finally, the well-aligned and regular microfibrils appeared due to the deep plastic deformation. There were three stages in the total evolution of microfibril alignment: the plastic deformation of microfibrillar network, the fragmentation of the original lamella, and the formation and development of regular microfibrils. The microfibrils in PAN fibers were stacked by crystal layers in an order and tightly manner. Served as excellent reinforcing elements, aligned microfibrils could efficiently improve the fiber mechanical properties. Compared with nascent fiber, the tensile strength of PAN precursor fiber increased by 1492% and its tensile modulus enhanced by 574%. Graphical abstract: Image 1 Highlights: The interconnected network was plastically elongated and rearranged to develop into well-aligned and regular microfibrils. The well-aligned and regular microfibrils were superposed by the regular arrangement of crystal layers. Served as excellent reinforcing elements, aligned microfibrils could efficiently improve the fiber mechanical properties. PAN fibers' tensile strength increased by 1492% and tensile modulus enhanced by 574%.