Stretching-induced deformation of polyacrylonitrile chains both in quasicrystals and in amorphous regions during the in situ thermal modification of fibers prior to oxidative stabilization

In situ thermal stretching to modify the conformation of polyacrylonitrile (PAN) chains in quasicrystals and amorphous regions is carried out on PAN copolymer fibers prior to oxidative stabilization. Meanwhile, a model to evaluate the deformation of PAN quasicrystals and amorphous regions is proposed, in which deformation behavior (orientation or extension) and type (elastic or plastic) in the two regions are analyzed. PAN chains exhibit various deformations as a consequence of combined thermal treatment and mechanical stretching. The orientation of PAN chains occurs prior to their extension when the stretching ratio is under 1.06, however, no significant orientation but extension is observed when the deformation ratio ranges from 1.08 to 1.16. As the stretching ratio increases, elastic-dominated orientation of PAN chains is stronger in quasicrystals before 1.03 and is prominent in amorphous regions between 1.04 and 1.08. The mechanical properties of the resulting carbon fibers strongly depend on the orientation degree of PAN chains in amorphous regions.