Cellulose Nanofiber-Templated Synthesis of Polypyrrole-Polyaniline Core-Shell Composites

Abstract

Polypyrrole (PPy)-polyaniline (PAni) core-shell composite was synthesized by successive oxidative polymerization of pyrrole and aniline on TEMPO-oxidized cellulose nanofibers (TOCN) as a template. The weight ratio of pyrrole to TOCN was first optimized to minimize the aggregation of TOCN in the aqueous polymerization medium consisting of the monomer, TOCN, and oxidant. Use of mineral acids and metallic oxidants were avoided because they usually facilitate the aggregation of TOCNs. As a result, highly-dispersed PPy-coated TOCNs with diameters of 30 to 80 nm were obtained when the PPy-to-CN ratio was three or more. Next, aniline was polymerized on the TOCN1PPy5 (TOCNPPy with a 1:5 PPy-to-CN ratio). The PAni layer was grown on the surface of the TOCNPPy nanofibers dispersed in the oxidant solution. Increasing the aniline-to-CN ratio resulted in the dendritic morphology of PAni. The composites showed high specific surface areas and pore volumes as compared with the PPy polymerized without a template in the same concentration of monomer and oxidant. The electrical conductivity of the TOCNPPy was 3~7 S/cm, much greater than the non-template PPy. The conductivity decreased to 0.3~0.7 S/cm after coating the PAni layer.