Effect of carbon nanotube surface modification on tensile properties of carbon fiber epoxy impregnated bundle composites

The effect of carbon nanotubes (CNTs) on the tensile properties of polyacrylonitrile (PAN)-based carbon fiber epoxy impregnated bundle composites was investigated. To grow CNTs on the carbon fibers, the following catalysts were selected: Ferrocene ([Fe(C ₅ H ₅ ) ₂ ]) catalyst applied to the bundles using chemical vapor deposition (CVD), and iron (III) nitrate nonahydrate ([Fe(NO ₃ ) ₃ •9H ₂ O]) catalyst applied by dipping the bundles in ethanol solutions of different concentrations ranging from 0.01 to 0.5 M. For bundle composites with Fe(C ₅ H ₅ ) ₂ -catalyzed CNTs, the Weibull modulus was 29% higher than the as-received state, although the tensile strength is almost unchanged. The Weibull modulus is 9–39% higher than the as-received state for Fe(NO ₃ ) ₃ •9H ₂ O catalyst solutions in the range 0.01–0.3 M, while it decreases by 22–32% for 0.4–0.5 M solutions. The tensile strength is lower in both cases; 4–7% lower for 0.01–0.3 M solutions and 14–17% lower for 0.4–0.5 M solutions. Fe(NO ₃ ) ₃ •9H ₂ O catalysts 0.1 M solutions gives the best combination of tensile strength and Weibull modulus improvement. The results also show that for each type of CNT-grafted and as-received PAN-based carbon fibers, an almost linear relation between the Weibull modulus and average tensile strength on the log-log scale is observed. This relation indicates that Fe(C ₅ H ₅ ) ₂ catalyst-grafting of CNTs gives better tensile strength and Weibull modulus results.