Polystyrene Foams as Core Materials Used in Vacuum Insulation Panel

Abstract

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.

Vacuum insulated panels for sustainable buildings: a review of research and applications

“…[64] demonstrated that PUR-core VIPs have worst performance because of high outgassing rates. [29] showed that the use of low density polyethylene with polystyrene at some temperatures may provide thermal conductivities as low as 6.5 mW/mK, which, however, is still higher than those demonstrated by silica VIPs. [32] proposed by using double envelopes and three-sided sealing envelopes with getters with PUR foams as cores for VIPs.…”

“…In recent years, research interest in VIPs increased, as the studies covered such topics as thermal conductivity and gas pressure in VIPs [23][24][25][26], analytical and optimisation models [27,28], application of various materials in VIP manufacturing [1,[29][30][31][32] and applications of VIPs in building construction became growing areas of research [3,20,33,34].…”

Thermal conductivity analysis of a new sub-micron sized polystyrene foam

“…By using equation (6), the relationship between the calculated values of k g as function of density is presented in Figure 5. The extrapolated, dashed line in Figure 5 for small densities q reaches, as expected, the thermal conductivity k g of still air, around 26 mW/mÁK.…”

“…The search for lightweight, nanometric, pore materials at low production costs and with suitable mechanical properties has been a challenge for the scientific community. [4][5][6][7][8][9][10][11][12] Nanostructured foam materials can efficiently suppress gas conduction (by the so called Knudsen effect 13 ) thus being less sensitive to the inherent internal gas pressure increase in VIPs. The recent development of polymeric foams has yielded results especially in terms of cell size reduction, but its corresponding foam densities still remain too high.…”

“…On the other hand, the production of nanocellular foams with expansion ratios larger than 10 is extremely difficult due to the high chance of enlarging cell sizes. 5,7 Wong and Hung 6 tried to make evacuated PS foams using CaCO 3 to open the pores. However, the PS foam had cell sizes of about 200 mm.…”