MYTHS AND FACTS SURROUNDING LONG TERM AGEING OF FOAM INSULATION

摘要

Many factors influence the thermal efficiency [lambda value or k-factor] one obtains with foams blown with any of the commercial physical blowing agents. Factors affecting a product's thermal efficiency depend on, but are not limited to, the blowing agent itself - such as the blowing agent's molecular weight, its boiling point, and its solubility in the foam matrix. Other factors depend on formulation parameters such as catalyst levels which affect speed of reaction and fineness of cell structure. Yet others depend on the mixing efficiency of the equipment used to process the foams. Finally, a great deal of the contribution depends on the amount of protection the foam receives from its immediate environment - ranging from exposed foam to foam enclosed within impermeable facers. The long term aging of foams has always been filled with myth and controversy. This has been true for every blowing agent that has been commercialized. We will try to dispel some of the myth with the results of several long term aging studies, run on ecomate? and other commercial BAs. In one study, the 5 year drift of insulation values was monitored by long term thermal value changes in comparison to unit efficiency over that span of time. This comparison pits ecomate blown foams against those made with R-134a. AGEING - Myth or Fact? The "fact" of Foam Aging [loss of thermal insulation efficiency with time] seems certain. Many prestigious research labs [such as ORNL'] have investigated the phenomenon. There have been many papers written on the subject over the years. Many countries, including the US [ASTM C-1303~(ii)] and Canada [CAN/ULC S-770~(iii)], have adopted test methods on how to measure this change. What are the consequences of this aging? It seems obvious that the thermal insulation value is critically important if one goes to the expense of putting urethane foam insulation in place...and the obvious consequence is that the insulation value that one had anticipated is slowly dissipating! So if foams age, why do they age? The common belief is that the blowing agent [BA] diffuses out of the foam over time. While this may in part be true, this author believes it to be surrounded in MYTH. The purpose of this paper is to give various types of evidence to show that the perceived "aging" of foams centers upon the infusion of moisture laden air into the foam. How does one effectively differentiate the effects of moisture infusion from those of BA diffusion?