Zero ODP,Zero GWP,Halogen-Free,and Low K-factor Azeotropes as Blowing Agents for Isocyanate-Based Foams

Due 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 C₅-C₇ hydrocarbon and a compound selected from the group consisting of C₂-C₄ carboxylic acid esters, C₃-C₄ ketones, and C₄ 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.