New insights into orientation differences between skin and core regions of polyacrylonitrile fibers during pre-stabilization with the stretching process

In the study, a model to systematically evaluate the differences between the orientation of polyacrylonitrile (PAN) chains both in skin and core regions during pre-stabilization with the stretching process is proposed. Consequently, there are few influences on changes in the orientation of PAN chains in core regions. By contrast, when the stretching ratios is under 1.05, the chains in skin regions mainly undergo orientation, facilitating the simultaneous progress of the crystallization and cyclization reaction. However, at the stretching ratio range from 1.05 to 1.20, there may be other types of deformations, which results in a gradual increase of the crystallinity and remarkable depression of the stabilization reactions. As the stretching ratios greater than 1.20, the crystallinity and the orientation degrees drop due to overly imposed stress. The mechanical properties of stabilized PAN fibers strongly depend on the orientation degree in quasicrystals of PAN chains in skin regions.