Last year, the US Environmental Protection Agency (EPA) proposed a regulation on hydrofluorocarbons (HFCs) as blowing agents for use in rigid polyurethane insulation because of their high global warming potential (GWP). This regulation has recently been finalized, and for rigid polyurethane foam refrigerator insulation it will take effect beginning in 2020. When this occurs, those manufacturers currently using HFC 245fa or HFC 134a as blowing agents will need to find a substitute. Various candidates for these blowing agents have been proposed, and each has their own set of advantages and disadvantages which have been presented at previous CPI Conferences and are well known. Those manufacturers already using cyclopentane as a blowing agent will not be required to switch blowing agents, but they may still wish to explore alternatives. In this paper we will examine the properties of polyurethane foam co-blown with a blend of cyclopentane and halogenated olefin blowing agents. By looking at the theoretical behavior of the blowing agents inside the cells of the foam, we will show how using a blend of blowing agents can improve the thermal conductivity of the foam, especially at lower temperatures. Additionally, we will show that further optimization of the foam formulation for the blends of blowing agents can lead to even lower thermal conductivities of the foam.
展开▼
