Abstract
A significant characteristic of polyurethane foams as applied in thermal insulation is their thermal ageing behaviour. The thermal conductivity of a non-encapsulated foam tends to increase with time due to an effusion of the blowing agents and an infusion of air. This causes the gas composition in the foam cells to change with time. As air has a higher thermal conductivity than the blowing agents a thermal ageing occurs. Essentially, the mechanism is that the gases permeate through the cell walls by a diffusion process. As the diffusion for some gas components is rather slow the total ageing process can take many, up to 25 or more, years for a foam panel of 50 mm thickness. However, the diffusion of carbon dioxide outwards is fast (weeks) and the inward diffusion of air can take place within one year. A typical ageing curve showing the behaviour is given in Fig. 6.1. A small initial decrease of the thermal conductivity λ due to outward C02 diffusion followed by a fast increase of thermal conductivity in the first period (air in) and a slower but still important one in the latter stages (CFC-11 out). In the first period (1–10 weeks) a dissolution of the high molecular blowing agent into the plastic matrix can also occur, leading to an increase of λ.
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© 1994 Springer Science+Business Media Dordrecht
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Hoogendoorn, C.J. (1994). Thermal ageing. In: Hilyard, N.C., Cunningham, A. (eds) Low density cellular plastics. Springer, Dordrecht. https://doi.org/10.1007/978-94-011-1256-7_6
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DOI: https://doi.org/10.1007/978-94-011-1256-7_6
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