Comprehensive research on the correlation between microstructure and mechanical properties of polyacrylonitrile-based precursor fibers prepared by wet-spinning

Polyacrylonitrile (PAN)-based precursor fibers with different mechanical properties prepared by wet-spinning and its correlation with microstructure was researched, the primary structural factors that affecting its properties were analyzed. The tensile strength and modulus of precursor fibers increased from 4.63 cN/dtex to 9.16 cN/dtex and 99.09 cN/dtex to 168.92 cN/dtex, respectively, with the increase in crystallinity from 69.29% to 87.84% and orientation degree increased from 83.95% to 93.81%, high performance precursor fibers could be achieved by decrease in the crystallite size and interlayer spacing, these aggregation structure plays a decisive role to the mechanical properties of fibers. The integrality of aggregation structure and properties could reflected by boiling water shrinkage behavior and glass transition temperature from the side. The fracture morphology of fibers with different properties were studied by scanning electron microscope (SEM) and three fracture characteristics were observed, PF1 and PF3 presented the radial extended fracture without microfibril pull out, radial cluster fracture with the pull out of microfibril for PF2, PF4-PF6, together with the axial splitting pattern in PF6, which was revealed by microfibrils/fibrils in longitudinal and transverse combined with solution etching. Precursor fibers with less voids, without serious skin-core, continuous arrangement, tightly stacked, well-developed and complete oriented microfibrils/fibrils, exhibited excellent mechanical properties. Possible fracture process was given from the perspective of aggregation structure and microfibrils/fibrils, which become dominant factors determining properties of precursor fibers. Improve the performance could be achieved by regulating surface structure and cross-sectional shape. As one of the main structural factors that determining properties, by reducing diameter could minimize the numbers and sizes of defects. The possible fracture process of interior texture and its reinforcing mechanism to properties.image