Preparation of Mechanically Robust Bio-Based Polyurethane Foams Using Depolymerized Native Lignin

Abstract

Native lignin, a major structural polymer in lignocellulosic biomass, offers unique advantages as a feedstock for high-performance biobased polymeric materials. In this work, depolymerized native lignin was utilized as a polyol in the synthesis of rigid bio-based polyurethane (PU) foams. Lignin in Pinus radiata wood was subjected to a pilot-scale hydrogenolysis process to obtain a depolymerized native lignin oil that was composed of monomers, dimers, and oligomers of predominant dihydroconiferyl alcohol and 4-propyl guaiacol. These lignin-derived polyols had low molecular weight, high hydroxyl group content, and good copolyol solubility, all of which were advantageous factors in preparing PU foams. The whole lignin oil, or fractions of the oil, was incorporated into PU foams by substituting sorbitol polyether polyol at 12.5−50 wt % to boost the bio-based content. Substituting with lignin-derived polyols led to foams with similar densities and thermal properties and substantially improved compression properties. The monomeric-/dimeric-rich fraction of the lignin oil, when incorporated at 33 or 50 wt % of the polyol, led to 100 and 61% improvements in compression modulus and strength in the resulting PU foams. The dimeric polyols in the lignin oil were principally responsible for enhancing the resistance of the foam to mechanical compression. These findings provide insights into how native lignin can be valorized via a lignin-first approach to produce rigid PU foam materials with an enhanced mechanical robustness and bio-based content.

Antimicrobial Lignin-Based Polyurethane/Ag Composite Foams for Improving Wound Healing

“…There are three-dimensional structures and a large number of aromatic rings in the lignin structure, 50 which react with isocyanate and exist as hard chain segments in polyurethane. In fact, the change of the hard segment improves the mechanical properties of the polyurethane foam.…”

Pyrolytic lignin: a promising biorefinery feedstock for the production of fuels and valuable chemicals

“…[114][115][116] Other lignin applications explored in the materials literature include the partial replacement of aromatic polyols in rigid polyurethane foams and of phenol in phenol-formaldehyde resins. 91,[117][118][119] Being a particularly reactive motif, the phenol groups in PL can also serve as a handle for the engineering of advanced materials with on-demand functionalities. On the other hand, further depolymerization of PL may lead to high amounts of valuable phenolic monomers with applications as building blocks in the chemical and pharmaceutical industries, as well as energydense products with great potential as fuels.…”

Lignocellulosic Materials for the Production of Biofuels, Biochemicals and Biomaterials and Applications of Lignocellulose-Based Polyurethanes: A Review

“…In any case, lignin can provide exceptional fire resistance, crosslink density, ultraviolet stability, biodegradability, insulation, compression, antioxidant, thermal and reinforcing properties to PUs [ 200 , 238 , 241 , 244 , 245 ], as well as high availability and low cost, the reason why foams constitute one of the main formulations for lignin-based PUs, where it can act either as a polyol or as a filler. The mechanical performance is usually improved as a consequence of the more entangled generated systems [ 245 ]; however, lignin is also known to increase stiffness, and therefore brittleness, due to the aromatic and low flexible structural configuration, which has been usually reported for concentrations larger than 30 wt.% [ 241 ].…”

“…As a consequence, flexible chains like castor oil, butanediol and polypropylene oxide have been proved valuable for improving this characteristic. Another approach followed has been to depolymerise native lignin to reduce its molecular weight [ 244 ]. It is also worth mentioning that different lignin-extraction procedures, origin, biomass source, etc.…”