The distinctive nucleation of polystyrene composites with differently shaped carbon‐based nanoparticles as nucleating agent in the supercritical CO2 foaming process

Abstract

AbstractMicrocellular polystyrene (PS)/carbon‐based nanoparticle (CbN) composites were prepared by a pressure release process using supercritical CO2 as the foaming agent. Nanocomposite foams with different shapes or dimensions but with CbNs with a similar surface structure showed a quite different cell nucleation. The underlying nucleation mechanism was semi‐quantitatively analyzed by classical nucleation theory, which indicated that the energy barrier for heterogeneous nucleation was related to the shapes of the fillers. Below 80 °C and 20 MPa, the nucleation density of the composites with different fillers showed marked differences, among which the nucleation density of PS/fullerene (FE) was the highest, followed by PS/carbon nanotubes (CNTs) and PS/thermally reduced graphene (TRG). However, the difference in nucleation density of PS/CbNs decreased with increase in filler content to 0.3 wt%. With increase in foaming temperature, the PS/TRG composite foams showed the highest cell density and no cellular merging and collapsing at 100 and 120 °C. The results obtained from DSC, rheology and positron annihilation lifetime spectroscopy measurements showed that FE nanoparticles exhibited the strongest plasticization effects on the matrix followed by CNTs and TRG nanoparticles. The distinctive plasticization suggested that the shapes of CbNs have a strong influence on the interaction between the PS matrix and the nanoparticles, which could affect the energy barrier for heterogeneous nucleation. The influence of CO2 on the rheology and thermal properties of the composites was investigated using high pressure DSC and high pressure rheology measurements. The results revealed that at high temperature high viscosity became the key factor to determining the cell morphology of nanocomposite foams by preventing bubble coalescence and collapse. © 2018 Society of Chemical Industry