Thermal Measurement of In-Situ and Thin-Specimen Aging of Experimental Polyisocyanurate Roof Insulation Foamed with Alternative Blowing Agents

    Published: Jan 1991

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    This paper reports apparent thermal conductivity (k) values from field and laboratory aging tests on a set of industry-produced, experimental polyisocyanurate (PIR) laminated boardstock foamed with hydrochlorofluorocarbons (HCFCs) as alternatives to chlorofluorocarbons (CFCs). The PIR boards were blown with five gases: CFC-11, HCFC-123, HCFC-141b, and 50/50 and 65/35 blends of HCFC-123/ HCFC-141b.

    The k-values were determined at mean temperatures from 0 to 50°C (30 to 120°F) using techniques that meet ASTM C 1114 (Thin Heater Apparatus) and ASTM C 518 (Heat Flow Meter Apparatus) test methods. Results on laminate boards with facers provide an independent laboratory check on the increase in k observed for field exposure in the ORNL Roof Thermal Research Apparatus (RTRA). The observed laboratory increase in k was between 8% and 11% for all three blowing agent foams for a 240 day field exposure in the RTRA.

    A thin-specimen aging procedure established the long-term thermal resistance of gas-filled foams. Thin specimens were planed from the industry-produced boardstock foams and aged at 24 and 65°C for up to 300 days.

    An exponential dependency of k with the quantity (diffusion coefficient X time)½/thickness, provided effective diffusion coefficients for air components into the foams and blowing agent out of the foams. The foams blown with alternative blowing agents exhibited k-values 8 to 16% (average 12.7%) above CFC-11 foams under similar conditions.

    Field exposures were conducted on specimens under single ply EPDM membranes in the RTRA for over 400 days. Hourly averages of panel temperature and heat flux were analyzed to obtain k as a function of mean temperature on a week by week basis. The k-values derived from the field data provided effective diffusion coefficients for air components in the foam, which were greater than those obtained from the thin-specimen aging procedure at 24°C by 20 to 70%, but were less than the 65°C aging values by 20 to 80%.

    The relative performance of test specimens of HCFC-141b under a black and under a white membrane is reported. The field data suggests that the percent increase in k over that of the foam blown with CFC-11 is, after one year of aging, 4.3% for HCFC-123 and 10.2% for HCFC-141b. This leads to the same ordering of foams as derived from the thin-specimen analysis.


    polyisocyanurate foams, alternative blowing agents, thermal conductivity, thin-specimen aging, diffusion coefficients, field exposure aging, roof insulation, in-situ performance, gas-filled foams, CFC-11 and HCFC blown foams, thin heater apparatus, heat flow meter apparatus, aging, roof thermal research apparatus

    Author Information:

    Christian, JE
    Oak Ridge National Laboratory, Oak Ridge, TN

    Courville, GE
    Oak Ridge National Laboratory, Oak Ridge, TN

    Graves, RS
    Oak Ridge National Laboratory, Oak Ridge, TN

    Linkous, RL
    Oak Ridge National Laboratory, Oak Ridge, TN

    McElroy, DL
    Oak Ridge National Laboratory, Oak Ridge, TN

    Weaver, FJ
    Oak Ridge National Laboratory, Oak Ridge, TN

    Yarbrough, DW
    Oak Ridge National Laboratory, Oak Ridge, TN

    Paper ID: STP16345S

    Committee/Subcommittee: C16.30

    DOI: 10.1520/STP16345S

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