Research on lignin-modified flexible polyurethane foam and its application in sound absorption

Lignin is a sustainable biomass resource with abundant hydroxyl groups that holds great promise for use as a feedstock for polyurethane foam production. Therefore, the flexible polyurethane foams (FPUFs) were prepared using the oxidized alkali lignin (OAL) as the matrix to enhance its compatibility. The OAL was obtained under the following conditions of 60 °C, 80 min treatment, a ratio of hydrogen peroxide to lignin of 1.2:1, and a ratio of iron hydroxide to lignin of 0.01. It was demonstrated that incorporating OAL enhanced the density, compressive strength, sound-absorbing performance and degradability of foam composites. The compressive strength was also improved by more than five times than that of blank foam under the optimal conditions, reaching 0.11 MPa. The thermogravimetric analysis (TGA) revealed that the foam composite containing 30 % modified lignin content exhibited the highest thermal stability. The results of solvent resistance testing demonstrated the durability of the foam composites in both water and solvents. Lignin-modified polyurethane foam exhibited an acoustic absorption coefficient above 0.2 across a wide frequency range, with the highest value reaching 0.84, meeting the conventional requirements for sound absorption materials (α > 0.2). The results suggested that this environmentally friendly preparation method was feasible for producing high-performance polyurethane foams, which was appropriate for the production of sound absorption boards for industry, transportation by train and automobile.