Carbon nanofibers were modified using 4-aminobenzoic acid and 5-benzimidazole carboxylic acid to obtain carbon nanofibers functionalized aminobenzoyl (CNF-aminobenzoyl) and carbon nanofibers functionalized benzimidazole (CNF-benzimidazole), respectively. The functionalized CNFs were incorporated into a PBI matrix to prepare nanocomposite membranes and additionally, to analyze their addition effects on several properties. The use of CNFs was intended to replace CNTs which are much costly due to their complicated fabrication using arc discharge and laser ablation. Compared to pristine CNF and CNF-aminobenzoyl, CNF-benzimidazole provided higher mechanical reinforcement due to its better compatibility with the PBI matrix. CNF-benzimidazole reinforced PBI at a loading of 0.3 wt% was able to enhance the tensile stress by 24% to 86.84 MPa, as compared to pristine PBI with a tensile stress of 70.31 MPa. This better compatibility was also seen in SEM results for the nanocomposite membranes. Furthermore, each of membranes was doped with phosphoric acid to provide proton conductivity. The highest acid doping level was 12.27 and the highest value for proton conductivity at 160oC under anhydrous condition was 0.21 S/cm. This was achieved by CNF-benzimidazole/PBI nanocomposite membrane at a loading of 0.3 wt%.

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