Effect of glass transition temperature and saturation temperature on the solid-state microcellular foaming of cyclic olefin copolymer

Effect of glass transition temperature and saturation temperature on the solid-state microcellular foaming of cyclic olefin copolymer (COC)—including CO2 solubility, diffusivity, cell nucleation, and foam morphology—were investigated in this article. COCs of low Tg (78°C) and high Tg (158°C) were studied. Solubilities are 20–50% higher in high Tg COC than in the low Tg COC across the saturation temperature range. Diffusivities are about 15% higher on average in high Tg COC for temperatures up to 50°C. A much faster increase of diffusivity beyond 50°C is observed in low Tg COC due to it being in the rubbery state. Under similar gas concentration, high Tg COC starts foaming at a higher temperature. And the foam density decreases faster in low Tg COC with foaming temperature. Also, high Tg COC foams show about two orders of magnitude higher cell nucleation density than the low Tg COC foams. The effect of saturation temperature on microcellular foaming can be viewed as the effect of CO2 concentration. Nucleation density increases and cell size decreases exponentially with increasing CO2 concentration. Uniform ultramicrocellular structure with an average cell size of 380 nm was created in high-Tg COC. A novel hierarchical structure composed of microcells (2.5 μm) and nanocells (cell size 80 nm) on the cell wall was discovered in the very low-density high-Tg COC foams. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42226.