Zero ODP, Zero GWP, Halogen-Free, and Low K-factor Azeotropes as Blowing Agents for Isocyanate-Based Foams
AbstractDue to the ozone depletion potential (ODP) problem of CFCs and HCFCs, a number of alternative physical blowing agents for isocyanate-based foams are being investigated. Among them, two representative candidates are HFCs (hydrofluorocarbons) and halogen-free, aliphatic hydrocarbons in which the major hydrocarbons are n -pentane and cyclopentane. Another accompanying problem of CFCs and HCFCs is global warming potential (GWP). This paper describes azeotropic blowing agents (hereinafter referred to as AZBs 32,33) having no halogens. The AZBs employed in this study comprise a C 5 -C 7 hydrocarbon and a compound selected from the group consisting of C 2 -C 4 carboxylic acid esters, C 3 -C 4 ketones, and C 4 ethers. These halogen-free azeotropes have advantages of zero ODP, zero GWP, and lower K -factor. The AZBs have the following advantages over HFCs and hydrocarbons: (a) they have a minimum boiling point and thus give more efficient blowing action than that of the respective individual components, resulting in lower density foams; (b) the AZBs-blown foams have lower K -factor than that of the foams blown with the respective individual blowing agents; (c) the adequate polarity of the AZBs exhibits better compatibility with foaming ingredients and results in finer celled foams than by the use of a single hydrocarbon blowing agent, e.g., cyclopentane; (d) due to the similarity of boiling points and polarity of the AZBs with those of CFC-11, the AZBs are a direct replacement for CFC-11 without any change of CFC-11-based formulations and without the use of special raw materials; (e) in general, the foam density is roughly proportional to the number of moles of blowing agent; the AZBs have lower molecular weights than CFC-11 and therefore, smaller amounts can be used. Also their costs are far less than that of CFCs or HCFCs; (f) the AZBs have zero ODP, zero GWP, and are halogen-free; therefore, there are no environmental problems. A number of the AZBs can be used as blowing agents, for example a blend of n -pentane/methyl formate at a weight ratio of 47/53. The blend has a boiling point of 21.8°C, which is almost equal to that of CFC-11. The AZBs can be used for various isocyanate-based foams, eg., flexible and rigid urethane foams, modified isocyanurate foams, urea foams, flexible and rigid integral skin foams.