Abstract
Efforts are continually being made to improve the insulation efficiency of appliance foam to reduce dependency on fossil fuels and to meet federally mandated product energy use requirements. These efforts have become even more important due to impending elimination of chlorofluorocarbons (CFCs) as the blowing agent for polyurethane and polyisocyanurate foams. Conversion to hydrochlorofluorocarbons (HCFCs) or hydrofluorocarbons (HFCs) generally leads to decreased insulation value of foams and therefore, decreased overall energy efficiency for the appliances.
The effects of incorporating carbon black to reduce thermal conductivity of HCFC-141b blown appliance foams are discussed. The work was jointly carried out by Miles Inc. and the Center for Applied Engineering. Studies previously conducted at the Center had demonstrated that carbon black is well suited for use in rigid insulating foams, particularly in urethane-modified isocyanurates. The Celotex Corporation has now commercialized this technology in the building insulation market.
Improvements of 6-9% in initial k-factors were observed when carbon black dispersed in polyols or isocyanates was used either in TDI- or PMDI-based appliance systems. The use of carbon black in HCFC-141b blown systems has the potential to produce foams with insulation values equivalent to CFC-11 blown production foams.
The very fine particle size and inert character of commercially available carbon blacks allow loadings up to 12% by weight in foam polymer. Since the dispersions can result in excessively high viscosities, efforts were also directed towards modifying formulations to improve flow characteristics. Various approaches were taken to optimize carbon black loading in reactants as well as to facilitate processing in the foam process equipment.
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