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Rigid polyurethane foams were synthesized using a renewable polyol from the simple physical mixture of castor oil and crude glycerol. The effect of the catalyst (DBTDL) content and blowing agents in the foams' properties were evaluated. The use of physical blowing agents (cyclopentane and n-pentane) allowed foams with smaller cells to be obtained in comparison with the foams produced with a chemical blowing agent (water). The increase of the water content caused a decrease in density, thermal conductivity, compressive strength, and Young's modulus, which indicates that the increment of CO₂ production contributes to the formation of larger cells. Higher amounts of catalyst in the foam formulations caused a slight density decrease and a small increase of thermal conductivity, compressive strength, and Young's modulus values. These green foams presented properties that indicate a great potential to be used as thermal insulation: density (23-41 kg·m -3 ), thermal conductivity (0.0128-0.0207 W·m -1 ·K -1 ), compressive strength (45-188 kPa), and Young's modulus (3-28 kPa). These biofoams are also environmentally friendly polymers and can aggregate revenue to the biodiesel industry, contributing to a reduction in fuel prices., Competing Interests: The authors declare no conflict of interest.

Polyurethane foams from bio-based polyols have been studied to produce sustainable and eco-friendly materials from biomass industrial wastes. Semi-rigid polyurethane foams were synthesized from physical mixtures of kraft lignin, castor oil and residual glycerol. The influence of different lignin contents (10, 12.5, 15, 17.5, 20, 25, 30 and 40%) on the foam properties was evaluated. An increase in the density and a decrease in the thermal stability were observed upon an increasing amount of lignin. The foam synthesized with 17.5% lignin showed better dimensional and thermal properties as well as the best cell homogeneity and this formulation was chosen for further investigation of the effects of the castor oil content, isocyanate/hydroxyl molar ratio (NCO/OH) and the blowing agent type. Increased foam densities and compressive strengths were observed with increased castor oil content in the foams. Similar results were observed upon increasing the NCO/OH molar ratio due to the higher amount of crosslinking reactions. The evaluation of the blowing agent effect showed that using cyclopentane and n -pentane, the foams showed higher densities and lower compressive strengths in comparison to the foams synthesized with the chemical blowing agent (water). This result can be explained by the faster volatilization of these organic blowing agents, producing smaller cells in comparison to the CO 2 generated by the reaction of water with isocyanate. Green polyurethane foams with good properties and industrial interest were produced using a mixture of residual raw materials (glycerol and lignin) and castor oil as bio-based polyols. [ABSTRACT FROM AUTHOR]