Lignin-Based Rigid Polyurethane Foam Reinforced with Pulp Fiber: Synthesis and Characterization

Petroleum-based polyol was replaced with different amounts of lignin (8.33–37.19% w/w) to prepare lignin-based rigid polyurethane foam (LRPF). The LRPF containing 37.19% lignin was further reinforced with different weight ratios (1, 2, and 5 wt %) of pulp fiber. The resulting foams were evaluated by their chemical structure, cellular structure, density, compressive strength, and thermal property. Fourier transform infrared (FT-IR) and 13C CP/MAS NMR spectra indicated that typical urethane linkages in LRPF were formed. Scanning electron microscope (SEM) results showed that the cell shape is significantly affected by the lignin and pulp fiber contents, which resulted in inhomogeneous, irregular, and large cell shapes and further decreased the densities of the LRPF. Mechanical results suggested that the compressive strength of the LRPF decreased with the increase in lignin content, but the additional pulp fiber had no significant effect on the compressive strength. Thermogravimetric analysis results demonstrated that the introduction of lignin led to high "carbon residue", but the introduction of pulp fiber would slightly improve the thermal stability of the LRPF.