Sustainable production and evaluation of bio-based flame-retardant PU foam via liquefaction of industrial biomass residues

Abstract

The utilization of low-cost renewable feedstock, such as furfural residue and crude glycerol, presents great potential for advancing the bio-based polymer industry. Firstly, this study explored the feasibility of using furfural residue liquefaction in the presence of crude glycerol to synthesize biopolyols. The optimal conditions for liquefaction were determined to be 220 ℃, 3 h, with a 7% sodium hydroxide loading and 9% biomass loading. The hydroxyl and acid numbers of prepared biopolyols were found to be comparable to those of commercial polyols, which were 460 mg KOH/g and 2.25 mg KOH/g, respectively. Subsequently, newly bio-based flame-retardant polyurethane (PU) foam was produced using obtained biopolyols, isocyanate, and flame retardants. The foam demonstrated a compressive strength of 286 kPa and a density of 0.050 g·cm−3, with its thermal conductivity measured at 0.032 W·m−1·K−1. To enhance the flame retardant and insulation properties of the PU foam, 2% of modified hollow silica (Kh-SiO2) was incorporated. PU foams produced under optimal conditions exhibited a limiting oxygen index of 27.25%, demonstrating exceptional fire-retardant characteristics. Cone calorimetry tests revealed that the PU composites had a 45.7% lower peak heat release rate and a 35.7% lower smoke release rate than neat PU foam. Additionally, the synchronous thermal analyzer (STA) revealed that the PU foam exhibited potential thermal insulation performance. This study provides a technically feasible and sustainable approach to valorize furfural residue and crude glycerol for producing biopolyols and flame-retardant insulation PU foam.