Laboratory and roofing exposures of cellular plastic insulation to verify a model of aging
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abstract
The Montreal Protocol made industry alter the technology for manufacturing cellular plastics by eliminating the use of chlorofluorocarbons as blowing agents. This has resulted in new foam products with alternative blowing agents. Now, the industry faces a challenge to ensure good, long-term performance of these products. To this end, the Society of the Plastics Industry of Canada and the National Research Council Canada have taken up the challenge to develop appropriate evaluation methods.A test methodology for evaluating long-term thermal performance has already been developed and applied to sprayed polyurethane foams. This methodology includes measurements of material characteristics such as nitrogen diffusion coefficient, extinction coefficient for IR radiation, concentration of blowing agent, foam morphology and aging curves measured on thin slices cut from different locations in the foam (surfaces and cores). Information from these tests serve as the input to an extrapolative model of heat and mass transfer (model of aging) that can predict the long-term performance of foam insulation.Currently, this methodology for evaluating long-term performance is being applied to board-stock products such as extruded polystyrenes, polyurethanes, polyisocyanurates, and phenolics. Several Canadian and US manufacturers have produced materials which are being exposed in laboratory as well as on a test roof. Thermal properties of these specimens are being continuously monitored and the data gathered from these two exposures are used to verify the applicability of the model.This paper reports interim findings from the SPI/NRC investigation. Even though the investigation is not yet completed, it appears that the extrapolative aging model may become an important tool for evaluating long-term thermal resistance (LTTR) of cellular plastics.
