Abstract
With the traditional use of CFC-11 blown polyurethane foam for refrigerator insulation there has been limited need for interaction between the PU producers on the one hand and the producers of plastics used for liner materials on the other hand.
Taking into consideration their ozone depletion potential (ODP) and global warming potential (GWP) there is wide acceptance that HCFC-123 and -141b are the nearest “drop in” substitutes known today for CFC-11 replacement.
However, this has major implications as these new blowing agents are significantly more aggressive requiring novel approaches in terms of material choice for monolithic and/or co-extruded sheet to retain the optimum sheet thickness, productivity and economics of current materials.
This paper first of all summarises the current status of developments towards the reduction and eventual elimination of CFC-11 from rigid polyurethane foam systems used for the insulation of domestic refrigerators and freezers. It then addresses the problems of liner/alternative blowing agent interactions using tests which attempt to bridge the classical laboratory tests whilst acknowledging the ultimate need to run full scale processing, assembly and functional performance trials at refrigerator manufacturers.
Key parameters covered include thermal conductivity, its ageing, carbon dioxide permeability and adhesion between the polyurethane foam and the plastic liner.
Physical attack of the liners is studied employing two qualitative testa One involves an unconstrained situation with profiled vacuum formed liner in contact with HCFC blown foams; the other uses a prototype tool which incorporates shelf support and mullion in a restrained mode with an aluminium tool. New liner materials and combinations which are compatible with HCFC blown foams are identified as a result of this work.
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