Abstract
For several years, the polyurethanes industry has critically examined its products in order to meet all present, and possible future, US environmental regulations. Formulations have had to be adapted to new types of blowing agents in order to compare favourably with the thermal and fire performances previously achieved.
These changes have highlighted a need to understand the fundamental factors which determine the long term dimensional stability of foams. From the theoretical understanding, it is then possible to assess the validity of current test methods and to design improved tests for the prediction of long term dimensional stability with the new systems.
In this paper, the relevant fundamental factors have been examined individually. Factors which predominantly affect polymer strength, processing, diffusion of gases and plasticisation have been grouped together, and their combined effect, under different conditions and in different applications within construction, are discussed.
Furthermore, the prediction of long term behaviour via modelling is highlighted. Based on fundamental understanding and model calculations, a new test has been designed and a comparison made with standard predictive tests. The behaviour of several HCFC-141b and pentane blown foams in the test are also given.
It has been shown that the effect of the combined action of all parameters influencing the long term dimensional stability of foams has changed in new systems based on benign blowing agents, compared to conventional CFC-11 blown foams. It has also been shown that the new predictive test is better adapted and more critical than the standard test for these new systems.
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