New bio-based polyurethane (PU) foams synthesized using crude glycerol-based biopolyol and humin-based byproducts from biomass hydrolysis

Exploring novel applications for solid waste in industrial production reduces the production cost of polyurethane (PU) foams, which is of great significance for sustainable development. In this study, crude glycerol was utilized to synthesize bio-based polyols via a one-pot method. Around 45 % of the glycerol components present in crude glycerol underwent esterification or transesterification reactions, resulting in the formation of polyhydroxy compounds. The synthesized polyol had a hydroxyl number of 406 mg KOH/g, a viscosity of 1092 mPa·s, and an acid number of 1.9 mg KOH/g, rendering it suitable for the preparation of rigid polyurethane foams. Humin-based residues (FRR, referring to residues from hydrolysis of furfural residue, and GR, referring to residues from hydrolysis of glucose) were further incorporated for the first time to reinforce bio-based PU foams. The effects of various fillers content (0, 1 %, 3 %, 5 %, 7 %, and 10 %) on the mechanical properties, morphology, thermal insulation properties, and thermal stability of PU foams were investigated. At an FRR level of 7 %, the maximum compressive strength reached 0.1536 MPa, representing an increase of 28.30 %. Similarly, when GR levels were set at 5 %, the maximum compressive strength was found to be 0.1581 MPa, reflecting an increase of 32.08 %. The addition of GR filler had a greater impact on enhancing compression strength, potentially due to its spherical and uniform particle shape, which could facilitate better dispersion within the polyols. The PU foam synthesized in this study showed comparable performance to those using cellulose-based fillers. Furthermore, the thermal conductivity of all foams containing fillers was lower than 0.0350 W/(m·K). The thermal gravimetric analysis demonstrated that the addition of humins as filler effectively enhanced the stability of the foam. As indicated from FT-IR and XPS analysis, urethane bonds were successfully formed, while the hydroxyl group on the surface of humins potentially enhanced the consumption of the –NCO group. The foams produced in this study exhibited highly favorable thermal insulation properties, while also offering superior economic and environmental benefits.