Flame-Retarded, Rigid PUR Foams with a Low Thermal Conductivity

Abstract

This paper examines and discusses various ways of reducing the initial thermal conductivity value of PUR foams and slowing down the rate at which it rises. The initial value for thermal conductivity is shown to depend basically on cell size, and not on the type of raw materials system. In order to obtain a low initial value, the cells of the foam must be as small as possible. In order to investigate the rate at which thermal conductivity increases-in other words the ageing phenomenon—both the pressure and the composition of gas in the cells were determined. Two factors are shown to be responsible for increasing ther mal conductivity: 1. Permeation of air 2. Reduced R11 concentration of the gas in the cells as a result of ad- or absorption to the cell structure During the investigation period of 12 months, however, there was virtually no measurable reduction in R11 concentration in the foam. It was found that different raw materials had a considerable effect on air permea tion in the cells. Foams containing the following components exhibit little air permeation: toluene diisocyanate, aromatic aminopolyethers, phosphoros and halogen-containing flame retardants. An attempt was made to calculate thermal con ductivity from the change in the composition of gas in the cells. The calculations were then compared with actual measurements. With our new foam we couldn't find a loss of chlorofluorocarbon in the ageing process.