Effect of replacing polyol by organosolv and kraft lignin on the property and structure of rigid polyurethane foam

Abstract

BackgroundLignin is one of the three major components in plant cell walls, and it can be isolated (dissolved) from the cell wall in pretreatment or chemical pulping. However, there is a lack of high-value applications for lignin, and the commonest proposal for lignin is power and steam generation through combustion. Organosolv ethanol process is one of the effective pretreatment methods for woody biomass for cellulosic ethanol production, and kraft process is a dominant chemical pulping method in paper industry. In the present research, the lignins from organosolv pretreatment and kraft pulping were evaluated to replace polyol for producing rigid polyurethane foams (RPFs).ResultsPetroleum-based polyol was replaced with hardwood ethanol organosolv lignin (HEL) or hardwood kraft lignin (HKL) from 25% to 70% (molar percentage) in preparing rigid polyurethane foam. The prepared foams contained 12-36% (w/w) HEL or 9-28% (w/w) HKL. The density, compressive strength, and cellular structure of the prepared foams were investigated and compared. Chain extenders were used to improve the properties of the RPFs.ConclusionsIt was found that lignin was chemically crosslinked not just physically trapped in the rigid polyurethane foams. The lignin-containing foams had comparable structure and strength up to 25-30% (w/w) HEL or 19-23% (w/w) HKL addition. The results indicated that HEL performed much better in RPFs and could replace more polyol at the same strength than HKL because the former had a better miscibility with the polyol than the latter. Chain extender such as butanediol could improve the strength of lignin-containing RPFs.

Characterization of Biobased Polyurethane Foams Employing Lignin Fractionated from Microwave Liquefied Switchgrass

“…The alteration in the cell structure may be due to the fact that high lignin content affected the cell nucleation process in the preparation of PU foams [30]. Similar results were also found by Pan and Saddler [17], who reported that the increase of ethanol organosolv lignin ratio in petroleum-based polyol resulted in particularly large cells (bubbles). However, this finding regarding cell diameter was quite different from Luo et al [3].…”

“…With higher lignin content (15%), the mechanical properties of the foam were decreased, probably due to the lignin macromolecules agglomerating into segments, which reduced the uniform distribution of lignin in the foam. This will result in significant changes in the cellular structure and weaken the strength of the foam [17].…”

“…The liquefied lignin was applied for the substitution of petro derived ployol to prepare flexible polyurethane foams [16]. Organosolv and Kraft lignin were used as hydroxyl sources to replace polyols for the production of PU foams [17,18]. Meanwhile, some chemical strategies such as oxypropylation [19], urethane modification [20], and liquefaction [21] were also used to modify lignin macromolecules, and the modified lignin was incorporated into the polyurethane matrix for production of high biocontent materials.…”

Characterization of Lignins Isolated from Industrial Residues and their Beneficial Uses

“…Thus, of the four lignins tested in this study, L2 was the most degraded from its original form. Lignins with a fair amount of hydroxyl (phenolic and aliphatic) and carboxyl groups can potentially replace polyols in polyurethane production (Pan and Saddler 2013). …”

Bio-Renewable Sources for Synthesis of Eco-Friendly Polyurethane Adhesives—Review

“…Most of the lignin extracted from pulp and paper operations is burned during pulp-spent liquor treatment. This offers energy recovery and regeneration of pulping chemicals with less than 2% recovered for utilization as a chemical product [137] [138]. However, the amount of lignin produced exceeds the requirements for energy generation.…”