Preparation of bio-based rigid polyurethane foam using hydrolytically depolymerized Kraft lignin via direct replacement or oxypropylation

Bio-based rigid polyurethane (BRPU) foams were successfully produced using hydrolytically depolymerized Kraft lignin (DKL, with Mw ∼1700 g/mole, aliphatic hydroxyl number: 365 mgKOH/g) as bio-polyols at high percentage of bio-contents i.e., 50 wt.%. BRPU foams were prepared via two routes, i.e., replacing PPG400 or sucrose polyol directly with DKL, and oxypropylation of DKL. The reference and BRPU foams were characterized in terms of their physical, mechanical and thermal properties. All BRPU foams exhibit good compressive strengths as well as compression modulus, compared with reference foams. The compression moduli of the foams decrease in the following order: BRPU foam with oxypropylated-DKL (10986.0 kPa) > BRPU foam with 50 wt.% sucrose polyol and 50 wt.% DKL (5152.0 kPa) > sucrose polyol reference foam (2086.0 kPa) > BRPU foam with 50 wt.% PPG400 and 50 wt.% DKL (1016.0 kPa) > PPG400 reference foam (789.1 kPa). Thermal conductivity of BRPU foams varied between 0.029 and 0.038 W/m K, with the lowest being of foam from oxypropylated-DKL, making it suitable for utilization as an insulation material.