Flexible polyurethane foams produced from industrial residues and castor oil

[Display omitted] •Use of industrial waste and by-products.•Black liquor applied in the reaction without previous modifications.•Glycerolysis product as biopolyol for polyurethane foam synthesis.•Flexible polyurethane foams with high mechanical strength. This study presents the development and characterization of polyurethane foams synthesized with biopolyols obtained using an industrial residue, the black liquor (BL), and glycerol (GL), in two grades of purity: high purity (P.A.), and crude (blond) from biodiesel production. For the biopolyol synthesis, GL with different purity grades and BL (0 and 15 wt.%) were reacted with castor oil. The glycerolysis with BL was performed without the use of catalyst due to the high basicity of black liquor, which was used without prior purification, reducing the use of chemical inputs. The biopolyols produced were characterized and applied to obtain polyurethane foams (PUFs) using water as a chemical blowing agent. The foams were evaluated by Fourier transform infrared spectroscopy, scanning electron microscope, apparent density, insoluble fraction, thermogravimetric analysis and mechanical resistance. The results showed that the biopolyol source and amount of blowing agent influenced the morphology of the foam, and therefore, the mechanical behavior of the polymeric material. The biopolyol produced with the black liquor and glycerol P.A. (BP-1) presented the highest hydroxyl index (593 mg KOH/g) and the foams obtained showed apparent densities in the range of 14.6–75.9 kg/m³. Thereby, this work has shown that it is possible to prepare biopolyols that can be used in the production of polyurethane foams from the use of black liquor and other renewable materials.