Effect of Blowing-Agent Depletion on Thermal Conductivity During Accelerated Thermal Aging of Polyisocyanurate Foams

Polyisocyanurate (PIR) insulation boards are widely used in buildings because of their low thermal conductivity, however their long-term performance is affected by aging. This study investigates the effect of accelerated thermal aging at +70 °C on the thermal conductivity and gas composition of pentane-blown PIR boards. Thermal conductivity was monitored over time, while changes in blowing-agent composition were analyzed using gas chromatography/mass spectrometry (GC/MS). Thermal conductivity increased from 0.0201–0.0211 W/(m·K) to 0.0243–0.0247 W/(m·K), corresponding to an increase of approximately 18–22%, with the most pronounced changes occurring during the first 40–50 days before stabilizing. GC/MS identified isopentane, cyclopentane, and pentane as the main gases in the foam cells, with isopentane as the dominant component. Accelerated aging caused a progressive decrease in blowing-agent concentration, explaining the deterioration in thermal insulation performance. Thermal outgassing proved more reliable than solvent extraction, providing higher sensitivity and reproducibility. Sample location, sample size, and outgassing temperature significantly affected the measured gas quantities, while higher outgassing temperatures improved analytical sensitivity without changing gas composition trends. The results confirm that the aging-induced increase in thermal conductivity is primarily caused by the loss of low-conductivity blowing agents, improving understanding of the long-term performance of PIR insulation materials.