Environmentally Compatible Hybrid‐Type Polyurethane Foams Containing Saccharide and Lignin Components

AbstractSemi‐rigid polyurethane (PU) foams were prepared using lignin‐molasses‐ poly(ethylene glycol) polyols. Two kinds of lignin, kraft lignin (KL) and sodium lignosulfonate (LS), were used. Both lignin and molasses polyols were mixed with various ratios and were reacted with poly(phenylene methylene) polyisocyanate (MDI) in the presence of silicone surfactant and di‐n‐butyltin dilaurate. A small amount of water was used as a foaming agent. The apparent density of PU foams increased with increasing lignin content. The compression strength and elastic modulus linearly increase with increasing apparent density, suggesting that mechanical properties are controllable by changing reaction conditions. The PU foams were amorphous and glass transition was detected by differential scanning calorimetry. The glass transition temperature (Tg ) maintained an almost constant value, regardless of the mixing ratio. This indicates that both the phenolic group of lignin and the glucopyranose ring of molasses act as rigid components in PU crosslinking network structures, and both groups contribute to the main chain motion to the same extent. By thermogravimetry (TG), it was confirmed that PU foams are thermally stable up to around 300 °C. By differential scanning calorimetry, Tg was observed at temperatures from 80 to 120 °C.