Application of a Twin-Screw Extruder with an Ultra-High Length-to-Diameter Ratio in the Dry-Jet Wet Spinning Process of Polyacrylonitrile Nascent Fibers

The quality of nascent fiber is the primary factor determining the performance of polyacrylonitrile (PAN)-based carbon fibers. This work presented a novel twin-screw extruder (TSE) with an ultra-high screw length-to-diameter (L/D) ratio for the dry-jet wet spinning process of high-quality PAN nascent fibers. The TSE with an ultra-high L/D ratio of up to 150 enabled the homogeneous mixing of PAN powder and dimethyl sulfoxide (DMSO), resulting in improved dope concentration of up to 30 wt %, improved molecular chain disentanglement, and reduced void formation. Orthogonal experiments were conducted to analyze the influence of dope concentration, barrel temperature, and screw speed on the properties of the PAN nascent fibers. Especially, three L/D ratios of 64, 96, and 150 were established to clarify the influence of the L/D ratio. It was found that with the increase in the L/D ratio from 64 to 150, the average tensile strength and modulus of the PAN nascent fibers were improved by 42.1 and 67.2%, respectively, and the crystallinity was increased by 45.5%. The PAN nascent fibers produced using the TSE with the ultra-high L/D ratio were found to have dense and smooth surfaces and fewer microvoid defects. It demonstrated the innovativeness and potential industrial application of the ultra-high L/D technique in the manufacturing of high-quality PAN-based carbon fibers.(figure