Valorization of hydrolysis lignin for polyols and rigid polyurethane foam

The objectives of this study are to produce polyols through hydrothermal liquefaction of hydrolysis lignin (HL), a by-product of pre-treatment processes in cellulosic ethanol plants, in 50/50 (v/v) water-ethanol mixture under N ₂ atmosphere at 250°C for 1 h, and to use these polyols to prepare rigid polyurethane (PU) foam. Bio-based PU (BPU) foam was prepared with 30% and 50% liquefied HL (LHL) replacing PPG400 and sucrose polyols. The foam samples were analyzed in terms of their physical, mechanical, and thermal characteristics for potential use as an insulation material. Foam samples prepared at 0% LHL from sucrose polyol were, however, found to have lower density and thermal conductivity; their mechanical properties were inferior (1030 kPa) to those of a foam sample prepared from PPG400 and glycerol (compressive modulus ∼9199 kPa). Replacement of sucrose polyol with LHL both at 30% and 50% replacement ratios improved the foam sample's compressive modulus (∼3313±25 kPa) and strength (∼216±31 kPa and 303±79 kPa @ 10% and 20% deformations respectively) while maintaining lower thermal conductivity (0.036±0.001 W/mK). Replacing PPG400 by LHL in the foam, however, resulted in inferior mechanical properties and higher densities.