Preparation and properties of room temperature foaming lignin-based non-isocyanate polyurethane foams

The preparation and application of biomass-based non-isocyanate polyurethane (NIPU) is an essential and meaningful hot topic research work in the field of polyurethane industry, due to its advantages of sustainability of raw materials and no highly toxic isocyanate used in the synthesis. Lignin, as the second most renewable natural polymer on earth, was used in this paper to synthesize lignin-based non-isocyanate polyurethane (L-NIPU) resins. Subsequently, L-NIPU foams were prepared by self-foaming at room temperature with the addition of maleic acid as an initiator and glutaraldehyde as a cross-linker, and their properties were investigated. Results show that L-NIPU foams are lightweight (0.11-0.18 g/cm³), have low thermal conductivity (0.033-0.04 W/m·K), and have excellent compressive strength. When the addition of maleic acid and glutaraldehyde is respectively 18 % and 25 % (based on L-NIPU resin quality), the compressive strength can be as high as 0.5 MPa, and the thermal conductivity is only 0.03559 W/m·K, so it can be used as an insulating board in buildings. In addition, FT-IR and XPS analyses showed that maleic acid and glutaraldehyde can react with the amino group in L-NIPU to form a cross-linked network structure, which ensures the favorable mechanical properties of the foam.