Characterization of the Flexural Properties of Vapor-Grown Carbon Nanofiber/Vinyl Ester Nanocomposites by Experimental Design

The effects of four critical formulation and processing factors on the flexural moduli and strengths of vapor-grown carbon nanofiber (VGCNF)/vinyl ester (VE) nanocomposites were investigated using a mixed-level full factorial experimental design. The factors included vapor-grown carbon nanofiber (VGCNF) type (pristine, surface-oxidized), use of a dispersing agent (no, yes), mixing method (ultrasonication, high-shear mixing, and a combination of both), and VGCNF weight fraction (0.00, 0.25, 0.50, 0.75, and 1.00 parts per hundred parts resin (phr)). Response surface models were developed to predict flexural moduli and strengths as a function of VGCNF weight fraction. The use of surface-oxidized carbon nanofibers, a dispersing agent, and high-shear mixing at 0.48 phr of VGCNF gave an average increase of 19% in the flexural modulus over that of the neat VE. High-shear mixing with 0.60 phr of VGCNF resulted in a remarkable 49% increase of nanocomposite flexural strength. This study highlights the use of design of experiments and response surface modeling to both predict and optimize nanocomposite mechanical properties.