Effect of Coagulation Conditions on the Radial Moduli of Polyacrylonitrile Nascent Fibers

Polyacrylonitrile (PAN) nascent fibers were spun in a mixture of dimethyl sulfoxide (DMSO) and water. As the DMSO mass fraction (W_DMSO) or temperature (T_S) of the solution increased, the crystallinity and the modulus of PAN fibers first increased and then decreased. At W_DMSO < 75% or T_S < 45 °C, increases in the W_DMSO and T_S resulted in the formation of ordered crystal structures, and the crystallinity and the modulus of the PAN fibers improved. At W_DMSO > 75% or T_S > 45 °C, increases in the W_DMSO and T_S facilitated formation of a chaotic internal structure. Furthermore, the crystallinity and modulus of the nascent fiber decreased because the aqueous DMSO solution dissolved PAN. The moduli of the PAN fibers depended strongly on the crystallinity. The fiber outer layer was the first part of the fiber to encounter the DMSO aqueous solution, and material exchange between DMSO in the fiber and water in the DMSO aqueous solution occurred more readily than in the core. This resulted in a higher degree of coagulation and a larger modulus. When W_DMSO was 75% and T_S was 45 °C, the PAN fibers had the highest crystallinity (61%), highest modulus (28.5 GPa), and smallest modulus difference (5 GPa) between the PAN fiber outer layer and core.