Preparation and properties of lignin-based flame retardant-modified polyurethane insulation materials

The fire retardant and smoke suppression performance of thermal insulation materials are crucial factors in ensuring building fire safety. In this study, based on ammonium polyphosphate (APP), a intumescent flame-retardant APP@AL (Mass ratio APP∶MDI∶AL=9∶2∶1) with core-shell structure was prepared by utilizing alkali lignin (AL) and bis(4-isocyanatophenyl) methane (MDI) for its poor interfacial compatibility and smoke suppression performance, and applied to the flame-retardant treatment of rigid polyurethane (RPU) thermal insulation materials (25wt% addition). The structure and composition of APP@AL were analyzed by SEM-EDS, XPS and FTIR, and the flame retardant and smoke suppression properties were analyzed by CONE and TG instruments. The results show that APP@AL has excellent interfacial compatibility with the RPU matrix. The compressive strength of the APP@AL-modified RPU foam is significantly increased (up to 31.8%) compared with the APP-added RPU foam and the thermal conductivity is reduced (7.0%). CONE test show that mean heat release rate and total heat release are reduced by 27.2% and 24.4%, respectively, while smoke suppression is notably enhanced (47.6% reduction in total smoke production and 57.0% reduction in total CO production). TG analysis show that the thermal stability of APP@AL flame retardant is obviously higher than that of APP, and it is more beneficial to build a stable residual char layer. In conclusion, lignin-based intumescent flame retardant has excellent flame retardant and smoke suppression effect on RPU foam insulation materials.