Response surface predictions of the viscoelastic properties of vaporgrown carbon nanofiber/vinyl ester nanocomposites
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A full factorial design of experiments and response surface methodology were used to investigate the effects of formulation, processing, and operating temperature on the viscoelastic properties of vapor-grown carbon nanofiber (VGCNF)/vinyl ester (VE) nanocomposites. Factors included VGCNF type (pristine, oxidized), use of a dispersing agent (DA) (no, yes), mixing method (ultrasonication, high-shear mixing, and a combination of both), VGCNF weight fraction (0.00, 0.25, 0.50, 0.75, and 1.00 parts per hundred parts resin (phr)), and temperature (30, 60, 90, and 120C). Response surface models (RSMs) for predicting storage and loss moduli were developed, which explicitly account for the effect of complex interactions between nanocomposite design factors and operating temperature on resultant composite properties; such influences would be impossible to assess using traditional single-factor experiments. Nanocomposite storage moduli were maximized over the entire temperature range (20% increase over neat VE) by using high-shear mixing and oxidized VGCNFs with DA or equivalently by employing pristine VGCNFs without DA at 0.40 phr of VGCNFs. Ultrasonication yielded the highest loss modulus at 0.25 phr of VGCNFs. The RSMs developed in this investigation may be used to design VGCNF-enhanced VE matrices with optimal storage and loss moduli for automotive structural applications. Moreover, a similar approach may be used to tailor the mechanical, thermal, and electrical properties of nanomaterials over a range of anticipated operating environments. 2013 Wiley Periodicals, Inc.
