The Role of Barriers in Reducing the Aging of Foam Panels

Abstract

Although most closed cell foams incorporate barriers at the surface, most of these barriers have been found to do little, if anything, to improve the long term performance of foams The cause of the barrier failures will be explained in terms of the author's previous research.

The advantage of properly applied barriers can be shown by use of the MIT aging model along with measured values of diffusion coefficients. The model shows that the time averaged insulation performance can be substantially enhanced by use of proper use of barriers. For example, a foam panel filled with CO₂ having proper bar riers on the top and bottom surface has an equivalent average R-value over the time span of decades when compared to a CFC filled panel without facers.

Means to measure the performance of a barrier when applied to a foam panel m- clude a qualitative dye technique. The dye technique allows the existence of open pathways at the interface of a foam and barrier to be easily visualized. Early test work with the dye technique indicates that many barrier/foam combinations give poor per formance even when the barrier is impermeable.

Experimental means to quantitatively measure barrier-foam behavior are needed to determine the potential of new barrier foam combinations and allow the long term performance to be predicted without the need for long term aging tests. A new mea surement technique involves the use of transient tests of a foam sample with a barrier applied from the production process. The comparison of the experimental transient performance with the barrier in place and the transient performance of a similar un faced foam will allow the barrier performance to be calculated using the transient analysis applied to the test data. The quantitative results of the barrier performance will allow the long term aging of a foam sample protected by barriers to be accurately predicted.

The barrier characteristics of dense foam polymer material at the surface of the foam give a moderate improvement in aging. Imperfect barriers, e.g., with some pin holes, will give reasonable performance if properly applied to the foam.