Shape-Stabilized Phase Change Material by a Synthetic/Natural Hybrid Composite Foam with Cell-Wall Pores

Improving energy efficiency of buildings reduces energy costs and helps meet the ever increasing world energy demand. Innovative building design requires high-performance structural materials with mechanical integrity, energy efficiency, and sustainability. Here, we report a polyurethane/lignin hybrid structural composite with cell-wall pores for the shape stabilization of an organic phase change material (PCM) as an active energy component in buildings. Sub-50 μm pores on the cell wall of the lignin-based rigid polyurethane (LRPU) foam, which were barely seen in ordinary RPU foams, enabled the very high loading and retention of n-eicosane as the organic PCM, yielding a PCM loading of 93% with negligible loss after extensive drying at 80 °C for 25 days. After 253 cycles of heating and cooling between 10 and 70 °C, the PCM-LRPU composite foams exhibited 213.8 and 205.8 J/g as stored and released energy, respectively. The compressive strength of PCM-LRPU composite foams was found to be 1460 kPa at 10% strain, which outperformed the required compressive strength of polyurethane insulation in structural panels. The thermal profile analysis of PCM-LRPU foams as a model-building envelope confirmed the excellent thermal performance of the hybrid composite foams, which would reduce the temperature fluctuation and peak energy demand of buildings. This rigid, synthetic/natural hybrid composite foam with the cell-wall pores in a closed-cell structure would be useful for shape-stabilized PCM serving not only as thermal energy storage but also as loading-bearing components in buildings.