Flame-retardant performance of a novel lignin-based rigid polyurethane foam prepared from pulping black liquor

To improve the flame retardancy of rigid polyurethane foam (RPUF), black liquor lignin-based rigid polyurethane foam (LRPUF) was prepared in this work through a one-step foaming method using lignin and inorganic salt in black liquor lignin as the structural modifier and the additive flame retardant, respectively. Effect of the addition of carbon dioxide treated black liquor lignin (CBL) on the structure and flame retardancy of LRPUF, as well as the flame flame-retardant mechanism of LRPUF, were investigated. The limiting oxygen index (LOI) test and cone calorimetric tests showed that compared to the RPUF, the LOI of LRPUF with 40 wt% CBL increased from 18.9 % to 21.3 %, and the peak heat release rate, total heat release, and total smoke production decreased by 19.5 %, 25.3 %, and 20.5 %, respectively, indicating that the addition of CBL improved the flame retardancy of LRPUF. The flame-retardant mechanism was investigated by analyzing the structure and components of the char residue. We found that a dense protective layer, consisted of char residue and a considerable amount of sodium sesquicarbonate on the surface of the char residue, was formed after combustion. This study provided a novel strategy for the resource utilization of black liquor lignin.