Abstract
Following an intermediate period using HCFCs (R-22, R-142b or R-141b), the next generation for replacing CFCs in appliance-applications is believed to be fluorinated compounds. However, per fluorinated substances have the problem of their high GWPs. Partly fluorinated, liquid compounds (e.g., R-356) are ex-pensive, and their toxicity is not yet completely understood. Partly fluorinated gaseous products (R-134a, R-227) have rather high thermal conductivities.
For these reasons, there is a tendency-at least in Europe-to go straight to an optimum solution and use blowing agents free of halogens.
Extensive studies have shown that hydrocarbons are most suitable, because they have the lowest solubility in the PUR-matrix. As a consequence, they have the best blowing efficiency and the minimum loss of mechanical properties in the foam.
It was found that cycloalkanes have a surprisingly low thermal conductivity compared to normal hydrocarbons and-because of its appropriate boiling point-cyclopentane was chosen as the best candidate.
Optimized formulations yield foams with k-factors similar to the present R-11 system.
The diffusion of cyclopentane through the PUR-matrix was found to be as slow as with R-11.
The disadvantage of cyclopentane is its flammability. However, this problem can be solved.
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