Techniques to Assess the Various Factors Affecting the Long Term Dimensional Stability of Rigid Polyurethane Foam

Abstract

CFC blowing agents have been eliminated from virtually all polyurethane foam applications and replaced, in many cases, with the more environmentally acceptable HCFCs, or in some cases in Europe, with hydrocarbons. At the same time, the search continues for zero ozone depletion potential blowing agents and some possible candidates are HFCs, hydrocarbons and water. The physical properties such as boiling point and solubility characteristics of the new blowing agents vary widely and formulations have had to be adapted to new types of blowing agents in order to achieve acceptable processing and resultant foam properties.

One of the big limitations to adapting formulations has been the ability of the present test methods to predict performance of foam blown with the new blowing agents. Predictive tests for the dimensional stability of fully CFC-11 blown systems have proven their validity over the years. But such is not the case with foams blown with the new blowing agents. ICI developed a new, more stringent, test to predict the long term dimensional stability performance, and the results of some preliminary evaluations were presented at the last SPI meeting in Boston. This new test focuses on accelerating the normal diffusion processes that typically take place over a period of months or years.

This latest paper is directed towards gaining an additional understanding of the matrix plasticization effects of various types of blowing agents and describes a method for quantifying such an effect. It also shows how these new evaluation techniques serve as useful development tools for foam based on third generation blowing agents. Both construction and appliance systems based on PIR and PUR technology are elucidated. Some results from the long term aging of boards and refrigerator/freezer cabinets and comparison of these results with the prediction of the new dimensional stability test method are also discussed.

The results discussed here show that industry may be guided in selecting appropriate alternative blowing agents and in the development of current/future formulations and processing by more accurately comparing the long-term dimensional properties using the reliable and accurate test procedures developed in this fundamental study.