This work examines the foam density, average cell sizes, and cell structure of four polystyrene (PS) blended with calcium carbonate (CaCO 3 ) or low density polyethylene (LDPE) at various ratios. The PS/CaCO 3 and PS/LDPE are foamed by carbon dioxide (CO 2 ) under supercritical conditions. CaCO 3 and LDPE can strongly influence the foam density, average cell sizes, and cell structure of PS foams. Based on the result of PS/CaCO 3 foams and PS/LDPE foams, the thermal conductivity of large porous PS foams as core materials used in vacuum insulation panels (VIPs) is further studied. Large porous PS foams are produced by the mixture of CO 2 and fluorocarbon or the mixture of CO 2 and nitrogen (N 2 ) as foaming agents. The content of open-cells in PS foams is affected by materials, foaming temperatures, and foaming agents. A higher content of open-cells in a porous PS foam can lead to a lower and more stable thermal conductivity of VIPs.

Foaming behaviors of four polystyrenes (PSs) filled and unfilled with various amounts of CaCO 3 using supercritical carbon dioxide were investigated. The PSs include three general purpose grades with different molecular weights (different melt index) and one high impact grade. By adjusting foaming conditions, foam density was determined for each investigated sample. In general, the sample with a lower molecular weight (i.e. higher melt index) yielded a lower foam density for the three general purpose PSs. With the addition of CaCO 3 filler, foam density would increase. The inclusion of rubber in high impact PS was found to complicate its foaming behavior. A qualitative correlation between various types of filled/unfilled PSs and foam density was found in a certain range. An optimum foaming temperature range was required to obtain low foam density for each sample. The corresponding change in matrix modulus by employing various PSs and various filler contents apparently affected the resulting foam density. Although several factors were involved in foaming conditions, the addition of CaCO 3 filler played a significant role in reducing cell size and increasing cell density of the PSs foams investigated.

This work examines the foam density of polystyrene (PS) blended with low density polyethylene (LDPE) at various ratios, and the thermal conductivity of vacuum insulation panels (VIPs) using PS/PE with filler foam as core materials. The experimental results indicate that LDPE strongly influences the foam density of PS/PE foam and the content of open-cells in PS/PE with filler foam. A higher content of open-cells in PS/PE with filler foam can lead to a lower thermal conductivity of VIP.

This work examines four polystyrene (PS) resins and PS resins with fillers. The materials are processed into sheets and then the sheets are foamed at various supercritical conditions. The morphology of the foam is studied and a large porous PS foam is also developed for a vacuum insulation panel.

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