Outgassing of rigid open-celled polyurethane foam used in vacuum insulation panels under vacuum condition

Rigid open-celled polyurethane foam is the main type of core material in vacuum insulation panels (VIPs). The formulation and manufacturing process of the foam are experimentally analyzed, and the factors that affect cell structure and heat insulation performance are discussed. Vacuum level in VIPs is one of the most important factors contributing to the heat insulation performance of VIPs. By the throughput method, outgassing properties of the core material of open-celled PU foam are investigated. Outgassing has a great negative influence on vacuum level in VIPs. The specific outgassing rate of the foam is tested not only at room temperature but also at low and high temperatures. It has been found that the specific outgassing rate is large, and has a decreasing trend with decreasing temperature. In a log-log plot of specific outgassing rate versus time, the decay exponent alpha ranges from 0.62 to 0.8 with temperature changes from -20 to 70 degrees C. At room temperature, pressure in VIPs used in refrigerators will reach more than 300Pa due to outgassing in its service life, if there are no getters adopted. After the foam is baked at 120 degrees C for 15 min, the specific outgassing rate is greatly reduced.