Comparisons of polycarbonate and polycarbonate/carbon nanotube nanocomposites and their microcellular foams prepared using supercritical carbon dioxide

Polycarbonate (PC)/multi-walled carbon nanotube (CNT) nanocomposites were prepared using a Haake internal mixer. The neat PC and nanocomposites were further soaked under supercritical CO₂ (scCO₂) atmosphere for various periods to develop microcellular foams. Morphological results confirmed the fine dispersion of CNTs in the composites, resulting in superior thermal stability (44 °C increase at 5 wt% loss) and dynamic storage modulus (22 % increase at 75 °C) compared with the neat PC. The composites exhibited a rheological percolation threshold at 2 wt% CNT loading. The microcellular structure of foamed samples revealed that longer soaking periods (≤2 h) in scCO₂ resulted in larger cell sizes, and higher CNT loadings caused higher cell densities at similar soaking periods. Foaming-induced PC crystals were verified through differential scanning calorimetry and X-ray diffraction. More crystals (up to 38 %) were developed with increasing soaking time. The added CNT facilitated the crystallization of PC and obtained crystals with higher stability. The two-melting phenomenon exhibited by the foams represented the melting of the originally less-stable crystals and heating-annealed crystals. The neat PC foams or low CNT-loaded composite foams demonstrated improved thermal stability compared with their unfoamed counterparts.