Non-HCFC Closed-Cell Foam Insulation

Introduction
Closed-cell foam insulations are widely used in building envelopes and appliances. Both polyisocyanurate board insulation and polyurethane refrigerator insulation owe their high thermal resistance (R-value) primarily to the low thermal conductivity of the gas used as a blowing agent to produce the foam.

Issues
Chlorofluorocarbons (CFCs) were formerly used as blowing agents, but were banned from use by the Montreal Protocol, an international plan to limit the production and ultimately the release of CFCs. Chlorofluorocarbons contain chemicals that contribute to the destruction of the ozone layer, the barrier that protects the earth from the sun's harmful ultraviolet radiation. Currently, foam insulation is blown with hydrochlorofluorocarbons such as HCFC-141b, which are less threatening to the earth's upper atmosphere, but still have ozone depletion potential. Production of this chemical for use as a blowing agent is to cease by January 1, 2003. Therefore, a new, non-ozone-depleting chemical is needed as a replacement for CFCs and HCFCs.

Objectives

  • Evaluate the long-term thermal performance of foams blown with non-HCFC blowing agents
  • Develop experimental methods and models that properly account for the aging characteristics of complete foam insulation systems

Research
Studies are underway to measure the aging characteristics (the decrease in thermal performance as air components diffuse into the cells of the foam and as the blowing agent gas diffuses out) of foam insulations blown with several alternative blowing agents. One study has looked at the thermal conductivity and aging characteristics of simulated refrigerator panels containing polyurethane foam blown with third-generation blowing agents. Four companies that supply foam to the refrigerator / freezer industry provided a set of 96 test panels containing polyurethane foam blown with HCFC-141b and with three potential non-ozone-depleting replacements. We have also been working on the development of a computational model for the aging of foam insulation with semi-permeable surface skins, which will be used to predict the aging characteristics of the refrigerator walls.

Additional studies are underway to develop a fundamental understanding of the aging processes. This includes development and validation of mathematical models of aging and measurement of basic material properties that control the aging process. Further research will continue to focus on collecting and analyzing thermal performance data for foams blown with various alternative blowing agents so that the best choice of a new blowing agent can be made.