Lignin as a reactive reinforcing filler for water-blown rigid biofoam composites from soy oil-based polyurethane

In this study, lignin (from bioethanol production) is used as a reactive reinforcing filler. A novel soy-based polyurethane biofoam (BioPU) from two polyols (soybean oil-derived polyol SOPEP and petrochemical polyol Jeffol A-630) and poly(diphenylmethane diisocyanate) (pMDI) has been prepared by a self-rising method using water as a blowing agent with and without lignin. The BioPU samples were evaluated for mechanical and thermal properties, and density. The cell morphology of the resulting lignin reinforced biofoam was examined by scanning electron microscope (SEM) and found to be in line with the cell structure modifications induced by the reinforcing lignin. Densities of the resultant composites were increased as a result of increased lignin content. Fourier transform infrared (FTIR) spectroscopy study exhibited characteristic peaks for lignin and BioPU. Mechanical properties of the samples were improved with the increase of lignin content, and the samples with 10% lignin had the best mechanical properties. Similarly, glass transition temperature (Tg) and storage modulus around and after Tg were increased over neat biofoam without lignin. Dynamic mechanical analysis (DMA) results coincided with the improvement of mechanical properties and showed better thermal stability of the composites over the neat biofoam. Thermogravimetric analysis showed improved thermal stability of the biofoams reinforced with lignin. Therefore, this research has provided a simple method of preparing the biofoam, while exploring the potential of using lignin in polyurethane applications.

► Lignin–soy-based biofoam composites were prepared by free-rising method.
► Lignin–soy-based polyurethane was carried out to produce renewable polyurethane.
► Properties increased to the biofoam by use of reinforcement lignin powder.
► Biopolyurethane foams exhibited comparable properties to their petroleum analogs.