Blowing Agents in Rigid Polyurethane Foam - Analytical Studies - Technical and Environmental Aspects
Rigid polyurethane foam is used in many different applications because of its high insulating capacity. CFC-11 has been the predominant blowing agent due to its advantageous properties, especially its low thermal conductivity. To prevent a depletion of ozone in the stratosphere and an increase in global warming, the use of CFCs and similar compounds is now being phased out. Less environmentally harmful alternatives thus have to be developed.
In order to study the performance of blowing agents their concentration and their distribution in the foam must be measured. A method for analysis of the cell gases in rigid foam was developed. Partial pressures of all gases in the cells could thus be determined as well as the amount of condensed blowing agent. Three methods involving heating and weight-loss determination were elaborated for the determination of the blowing agent distribution in rigid foam. A combustion method was also applied and a method for solvent extraction developed. Experiments were performed both on pieces of foam and on powdered foam.
The analytical methods were applied in several studies, mainly on rigid polyurethane foams blown with CFC-11, water or cyclopentane. Changes in partial pressures over time were determined and used to calculate effective diffusion coefficients of the different gases in slabs or cylinders, cut from the foam. Slabs or cylinders of different sizes are recommended for gases with widely differing diffusion coefficients. The influence of surface materials, such as the outer polyethylene casing on district heating pipes, on the rate of diffusion was measured.
Assessments were made of the amount and distribution of CFC-11 in old insulating foams. The total remaining amount of CFC-11 in old district heating pipes in Sweden was estimated at about 2000 tonnes. Treatment of polyurethane foam waste is discussed.
district heating pipes