Epoxy lignin-modified tetraethylenepentamethylene-CO2 halogen-free blown rigid polyurethane foam

Abstract

A new halogen-free blowing agent for rigid polyurethane foam, E-Lig-TEPA-CO2, was synthesized by absorbing CO2 onto tetraethylenepentamine modified with epoxy lignin. The blowing agent was modified with lignin, which introduced hydrophobic groups such as benzene rings, carbon chains, and aromatic ethers. This modification enhanced its oil affinity and compatibility in the polyol mixture. Surface tension testing showed that the surface tension of the lignin-modified blowing agent decreased from 36 to 24 mN/m. Observations through Olympus microscopy revealed that the lignin-modified blowing agent was better dispersed in the polyol mixture, with fewer air bubbles and improved compatibility. Additionally, the main raw material used for this blowing agent was low molecular weight tetraethylenepentamine, resulting in a liquid-state blowing agent. This liquid-state blowing agent inherently possessed advantages in terms of dispersibility and compatibility compared to solid-state blowing agents. Finally, self-made lignin phosphate (P-Lig), expandable graphite (EG), and dimethyl methyl phosphonate (DMMP) were added as halogen-free flame retardants. Lignin-bio-based polyol was used as partial polyol. A new type of bio-based and halogen-free blown flame-retardant rigid polyurethane foam was prepared. The resulting foam demonstrated small and evenly distributed cell structures, as well as good compression strength (224 kPa) and thermal conductivity (0.029 W/(m·k)). The limiting oxygen index of foam increased to 30.6%, reached the V-0 level during the vertical burning process, the peak heat release rate decreased to 196 Kw/m2, and high-temperature thermal stability in thermogravimetric was enhanced.