The thermal conductivity of isocyanate-based rigid cellular plastics: A technique for predicting the 25 year values

摘要

This paper reviews the factors determining the thermal conductivity of isocyanate-based rigid cellular plastics. It provides research data obtained from a programme conducted at Salford University, UK, to establish the basis of a method based on an accelerated procedure for the determination of the thermal conductivity of these products which can be assumed to apply, without taking into account production variation, to a product over its 50 year life. The latter is used to correspond to the term ''reasonable economic life'' used in the EU Construction Products Directive. The data is limited to products principally expanded with HCFC 141b and n-pentane blowing agents but the authors believe, although proof will be necessary, that the method has a good chance to be acceptable for all future products which are expanded principally with a gas which is shown to remain, for the most part, in the cells over its reasonable economic life and for which the gaseous composition of the cell gas is changed only by dilution, to varying degrees, by the ingress of air. In essence the ingress of air is accelerated by ageing the test specimen in air at 70 degrees C for 25 weeks. The paper also discusses the merits of various other procedures claiming to produce ''realistic aged thermal conductivity values''. Finally it provides evidence that the products made with these new blowing agents have similar thermal conductivities and similar thermal conductivity ageing characteristics to their CFC blown counterparts.