Effect of Thermal Imidization Conditions on Polyimide Webs Derived from Poly(amic acid)/Lignin Nanofiber

This study investigates the influence of lignin incorporation on the morphology and thermal imidization behavior of electrospun polyimide nanofibers. Blending lignin with poly-(amic acid) significantly improved fiber uniformity, reducing the average fiber diameter by 46% and decreasing diameter deviation by 73% compared to neat PAA nanofibers. Both neat and lignin-containing nanofibers achieved high degrees of imidization (DOI > 90%) at 230 °C and approached 99% at 280 °C while maintaining their porous structures. Notably, lignin-containing fibers showed higher degrees of imidization than neat PAA under comparable thermal conditions. Although rapid thermal ramping led to greater optical darkening, spectroscopic and thermal analyses confirmed that the polymer backbone remained chemically stable. These findings suggest a potential approach to lignin valorization and provide a basis for fabricating polyimide nanofibers with controlled structure and thermal properties.