Rheology, Spinnability, and Fiber Properties of AB-Benzimidazole Solutions in Polyphosphoric Acid

This study examines the rheology and fiber formation of poly(2,5(6)-benzimidazole) (ABPBI) solutions in polyphosphoric acid (PPA) at 12.5 wt%. These solutions exhibit typical features of associative polymer systems, such as pronounced shear thinning and high elasticity. The activation energy of the viscous flow increases with the polymer concentration, reaching 29 kJ/mol at 12.5 wt%, but remains significantly lower than in phosphoric acid solutions. This indicates more efficient solvation and chain mobility in PPA. A comparison with two superbasic solvent systems further highlights the critical role of the solvent nature in flow mechanisms and associative interactions. Model coagulation experiments revealed how the non-solvent composition controls the fiber morphology and solidification. Under optimized conditions, homogeneous monolithic fibers with good mechanical performance were obtained. These findings provide new insight into the physicochemical principles of ABPBI fiber formation and establish PPA as a promising solvent for producing high-performance fibers.