Preparation of flame retardant polyurethane foam from crude glycerol based liquefaction of wheat straw

Both wheat straw and crude glycerol are low-cost renewable feedstocks which could be promising for the production of biobased polymers. In this study, biopolyols were first prepared through liquefaction of wheat straw in crude glycerol. Effects of reaction temperature, catalyst loading, reaction time, biomass loading, and fatty acid amount on the liquefaction of wheat straw were investigated and the synthesized biopolyols were characterized. With 10 % wheat straw loading and 6% sodium hydroxide as the catalyst at 240 °C for 4 h, 89 % of what straw conversion yield can be reached. The synthesized biopolyols had a hydroxyl number of 612 mg KOH/g and an acid number of 1.3 mg KOH/g. The flame retardant PU foams were then prepared from the biopolyols and isocyanate in the presence of 25 % flame retardants including dimethyl methylphosphonate (DMMP) and expandable graphite (EG). When the mass ratio of DMMP to EG was 2:1, the limiting oxygen index value of PU foams reached 26.2 %, and vertical burning tests showed that flame-retardant PU foams can pass the V-0 rating. Fire behavior results indicated that the incorporation of DMMP and EG into the biobased PU foams can effectively reduce the smoke release and improve the smoke suppression performance, and the peak heat release rate and the peak smoke production release of the flame-retardant PU foam decreased by 40.0 % and 25.0 % compared with neat PU foam, respectively. Meanwhile, the compressive strength and the thermal conductivity of the flame-retardant PU foam were 283 kPa and 0.0295 W m−1 K−1, respectively. These results showed that the bio-based PU foam has great potential as flame retardant insulation material. This study provides a novel method for the production of flame-retardant PU foams through liquefaction of wheat straw in crude glycerol.