Improvement of the thermal conductivity of micronized nanocellular poly(methyl-methacrylate) (PMMA) by adding infrared blockers

Abstract

Micronized nanocellular polymers show great potential to be used as core materials for vacuum insulation panels due to their reduced thermal conductivity under vacuum. However, as a result of their nanocellular structure, these materials are characterized by thermal radiation contributions higher than 4 mW/(m·K). This work studies how to further enhance their thermal insulation behavior by adding infrared blockers to reduce thermal radiation. Three different opacifiers (titanium(IV) oxide, graphene nanoplatelets, and silicon carbide) are used in different contents (2.5, 5, 10, 15, and 20 wt%). The obtained powders are characterized to determine the apparent density, the particle size distribution, and the thermal conductivity. The addition of infrared blockers leads to an increase in apparent density which is also related to the opacifier’s particle size. For each infrared blocker, there is an optimum concentration to achieve the minimum thermal conductivity. Finally, compacted panels are produced to analyze their behavior as VIP cores by measuring thermal conductivity under vacuum conditions. A minimum thermal conductivity of 9.6 mW/(m·K) is obtained for the compacted panel containing 10 wt% of silicon carbide, a reduction of 2 mW/(m·K) regarding the sample without opacifier.