Dispersion Methodology for Technical Lignin into Polyester Polyol for High-Performance Polyurethane Insulation Foam

Abstract

The incorporation of lignin into rigid polyurethane foam (RPUF) has been explored for the last two decades for replacing petrochemical polyols and producing sustainable highperformance insulation materials. However, to date, the issues associated with the dispersion of technical lignin in the commonly used polyols for RPUF have highly limited the improvement in mechanical and thermal insulation performance. This study reports the enhanced dispersion of kraft lignin (KL) up to 75 wt % in the glycerol-substituted aromatic polyester polyol blend. The influence of significantly well-dispersed KL on RPUF in terms of loading levels, the viscosity of the polyol, the microstructure, and the thermal and mechanical properties of RPUF is discussed. The KL incorporated (0.5−6.0 wt %) in polyol afforded a remarkable reduction in thermal conductivity (32%−34%) of the resultant RPUF with minimal variation in density and insignificant change in compressive strength. The scale of this improvement, to the best of our knowledge, has not been reported to date in ligninincorporated RPUF systems. Furthermore, the presence of the KL in the RPUF also resulted in a mild improvement in the flame retardance performance. This study provides insights into producing KL-incorporated RPUF for thermal insulation application.

Lignin-Based Low-Density Rigid Polyurethane/Polyisocyanurate Foams

“…Up to 50% loading, no significant difference was found for lignin-based foams compared to the control for cell perimeter and diameter, while the cell strut width showed no significant difference from the control at any lignin loading percentage. Overall, the cell diameter of our control and lignin-based foams (∼0.2 mm) was smaller than in previous studies, using 0–6% lignin loading in low-density rigid PUR foam (∼0.5 mm) . All cell size results were comparable to other biobased polyols used in low-density rigid PUR/PIR foam formulations, our previous research, and ASTM specifications…”

“…The apparent density of rigid foams is known to have a logarithmic correlation affecting most other foam properties outside the 30–60 kg/m 3 low-density range. ,,, The densities of lignin-based foams ranged from 41 to 54 kg/m 3 (Table ), falling within the low-density foam range, making the effect of density on foam properties insignificant. The increased density, compared to the control (35 kg/m 3 ), in lignin-based foams is likely caused by the use of solid lignin, which can delay foaming times (Figure ), increase polyol blend viscosity (Table ), and increase the degree of foam crosslinking. − ,, Even so, all lignin-based foams had suitable apparent densities for rigid insulation and structural applications indicated by ASTM D7425 and E1730. , …”

“…Cream times for these foams ranged from 166 to 290 s and end of rise times ranged from 445 to 451 s . Both studies incorporated less actual lignin as polyol replacement (6–40%) and used energy-intensive lignin dispersion/modification methods (≥6 h processing times). , …”

“…The 100% lignin-based foam outperformed various ligninbased low-density rigid PUR foams in reaction time. Haridevan et al 51 dispersed up to 6% kraft lignin powder (356 hydroxyl value) in an 80/20 mixture of commercial aromatic polyester polyol/glycerol polyol and formulated low-density rigid PUR foams. 51 The 6% lignin polyol dispersion-based foam had a 240 s tack-free time 51 while our 100% lignin-based foam was 70% lower (Figure 2).…”

“…Haridevan et al 51 dispersed up to 6% kraft lignin powder (356 hydroxyl value) in an 80/20 mixture of commercial aromatic polyester polyol/glycerol polyol and formulated low-density rigid PUR foams. 51 The 6% lignin polyol dispersion-based foam had a 240 s tack-free time 51 while our 100% lignin-based foam was 70% lower (Figure 2). The cream and end of rise times of 100% lignin-based foam were even superior to the liquefied lignin polyol by over 95 and 80%, respectively.…”