Lignin-Derived Polyurethane for Eco-Friendly Building Insulation Material Application

Over the last decade, the United States Department of Energy (DOE), the European Union (EU), and industrial interests have significantly advanced the use of bio-derived materials for polyurethanes as the climate crisis persists. Aligned with the goal to extract and sequester atmospheric carbon, sustainable forms of polyurethane (PU) foam insulation are consequently being developed to ultimately replace current practices dependent on the extraction of geologic carbon. Lignin, a renewable resource, has proven to yield a wide variety of products including polymeric materials, nanomaterials, fine chemicals, and biofuels; previous studies have shown the naturally occurring polymer can successfully act as a substitute for the polyol component in PU foam. However, the lignin industry has not yet invested enough research into designing a product better suited to the PU industry. Some key properties of technical lignin, such as -OH concentration and molecular weight, are frequently not optimized to enhance lignin-PU morphological, thermal, and mechanical properties. Therefore, in this experiment, lignin-based polyurethane foam was synthesized by substituting poly(ethylene glycol) (PEG) with hot water extracted Ashwood lignin at 30 – 70%. ³¹P nuclear magnetic resonance (NMR) was used to investigate the chemical structure of the lignin, after which molecular weight was determined using gel permeation chromatography (GPC). Thermal conductivity tests proved the lignin-PU foam exhibited comparable thermo-insulation capabilities to pure-PEG PU foam, while bulk density testing showed the lignin-PU foam possessed similar density as well. Scanning electron microscope (SEM) analysis was performed to examine the internal structures of the foams. Interactions between the lignin and PU components were analyzed using Fourier-transform infrared (FTIR) spectroscopy. Future research will explore using THF-soluble lignin to better disperse the polymer during production and fully employ its chemical properties in PU foam.