Lignosulfonate/APP IFR and its flame retardancy in lignosulfonate-based rigid polyurethane foams

Abstract

Lignin containing substantial aromatic rings and high content of carbon has been employed as carbonizing agent to investigate the flame retardancy in the lignin/ammonium polyphosphate (APP) intumescent flame retardant (IFR) system. In addition, owing to the abundant phenolic and aliphatic hydroxyl groups, lignosulfonate, which is considered as a renewable aromatic macropolyols, substituted part of diethylene glycol (DEG) and copolymerized with isocyanate to produce lignosulfonate-based rigid polyurethane (LRPU) foams. Thermal stability was characterized by thermogravimetric analysis (TGA), and flame retardancy was investigated by limiting oxygen index (LOI) and cone calorimetry testing (CCT). Lignosulfonate increases thermal stability of LRPU foams and LRPU containing 15 wt% of lignosulfonate based on DEG (L15RPU) give rise to the best thermal stability. When 15% of lignosulfonate incorporated in the LRPU, reduced the heat release rate (HRR) and total heat release (THR) value 21 kW/m2 and 13 MJ/m2, respectively, and postponed 96 s time-to-peak carbon monoxide production than that of pure DEG rigid polyurethane (RPU) foam, the LOI values increased progressively with lignosulfonate content increasing. These results showed that lignosulfonate polyol may substitute polyol to produce lignosulfonate-based RPU foam and the presence of lignosulfonate could improve the flame retardancy. The mass loss gradually decreases with increasing APP addition, and the highest char yield was obtained from LRPU5 foam which at the lignosulfonate-to-APP ratio is 1:5. At the lignosulfonate-to-APP ratio of 1:5, the LOI value increased over 30%, and the HRR value reduced and the time-to-peak HRR postponed significantly. In addition, LRPU5 foams give rise to the lowest effect heat combustion (EHC) value, less smoke, and carbon monoxide (CO) production. Lignosulfonate acts as carbonizing agent in the lignosulfonate/APP IFR system, and the best fire retardancy is obtained at 1:5 of lignosulfonate-to–APP ratio.