Biobased polyurethane foam insulation from microwave liquefaction of woody underbrush

Abstract

Yaupon holly is one of the most widespread woody underbrush species in the southeastern United States, and it can undermine forest health and safety due to its biofuel-like nature during catastrophic wildfires. Yaupon holly was subjected to microwave liquefaction to produce biobased polyurethane (PU) foam insulation. Liquefaction parameters were optimized and summarized as follows: 1) particle size was controlled in the range of 16- to 40- mesh; 2) both the ratios of glycerol to ethylene glycol and liquid to solid were set at 3:1; 3) the reaction process was conducted at 160 °C for 10 min and catalyzed by 1.5% sulfuric acid. The optimal liquefaction conversion yield was 94.9%. The Fourier transform infrared spectra (FTIR) indicated the successful liquefaction and dissolution of wood essential components, i.e. hemicellulose, cellulose, and lignin. The optimal liquefaction product with solid residue was used directly to produce biofoams. With an increased isocyanate index, the thermal insulation properties, mechanical properties, and thermal stability of biofoams increased. Therefore, a promising biobased PU foam was obtained at an isocyanate index of 150. The density, thermal conductivity, Young’s modulus, and compressive stress of the promising biofoam were 18.5 kg·m-3, 0.033 W·m-1·K-1, 176.7 kPa, and 15.4 kPa, respectively.