Nucleation Effects of Nanoparticles on Microcelluar Polystyrene Foams

Introduction Microcellular foams with cell sizes less than 10 μm and cell densities larger than 10cells/cm [1] are gaining commercial importance as lightweight structural materials. The idea of introducing small bubbles in solid polymers was first proposed by Num P. Suh [2] in 1890s and the rationale was that if the bubbles are even smaller than the critical flaws in the polymer matrix and can be introduced in a sufficient number, the material density could be reduced while maintaining the essential mechanical properties. However, in order to drive the nucleation of a myriad of microcells, a high thermal insatiability is required, which in turn requires the stringent operation conditions such as high pressure, high pressure drop rate, and low foaming temperature [3, . In this context, nucleating agents (nucleants) such as talc [5-6] are used to reduce the nucleation energy and produce microcellular foams under relative milder conditions. More recently, nanoparticles such as nanoclay have been studied as foaming nucleants as well. Compared to micro-sized nucleants, nanoparticles offer unique properties such as a high aspect ratio and large surface area, which are valuable for controlling both the foam structures and foam properties . In this study, we explored the use of carbon nanofibers (CNFs) as the nucleants to produce polytstyrene (PS) microcellular foams. Supercritical CO2 was chosen as the blowing agent because it is low cost, non-toxic, nonflammable and environmentally benign. Considering different particle dispersion, surface curvature and surface energy, the nucleation efficiency of CNF was compared to that of nanoclay, which has been studied in our previous work.