Production of wood adhesives from lignin-containing material

Abstract

Adhesive compositions including a lignin-containing material, a carbohydrate additive capable of converting to 5‑hydroxymethylfurfural (5‑HMF); a solvent; and an acid catalyst are described for use in the manufacture of composite articles, such as wood composite articles, methods for preparing the adhesive compositions, wood composite articles and manufacturing methods thereof.

Description

PRODUCTION OF WOOD ADHESIVES FROM LIGNIN-CONTAINING MATERIALCROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to and the benefit of PCT Application No. PCT / US25 / 61094, filed December 23, 2025, and U.S. Provisional Patent Application No.63 / 738,393, filed December 23, 2024, the entire contents of which are incorporated by reference herein.FIELD

[0002] The invention is directed to adhesive compositions prepared from lignin-containing material and a carbohydrate additive for use in the manufacture of composite articles, methods for preparing the adhesive compositions, composite articles and manufacturing methods thereof.BACKGROUND

[0003] Adhesive compositions are used to manufacture a wide range of composite products, including plywood, oriented strand board (OSB), particleboard, and medium- and high-density fiberboard. Common wood adhesives include urea-formaldehyde (UF), melamine-urea-formaldehyde (MUF), phenol-formaldehyde (PF) resins, and polymeric methylene diphenyl diisocyanate (pMDI). While these systems offer established processing windows, UF and related formaldehyde-based adhesives raise regulatory and sustainability concerns due to free formaldehyde content and potential emissions, and PF typically requires elevated press temperatures and longer cure times. The use of pMDI avoids formaldehyde but remains petrochemical-based and presents handling and cost considerations. Accordingly, there is continuing interest in bio-based adhesive technologies that provide fast cure, robust wet and dry performance, and reduced dependence on petroleum-derived or formaldehyde-containing chemistries.

[0004] Lignin, the most abundant renewable aromatic polymer in lignocellulosic biomass, has long been investigated as a partial or full replacement for phenol in PF-type resins or as a bio-derived adhesive component. However, lignin obtained by conventional pulping or extraction processes often possess high molecular weight and a reduced number of reactive sites due to interunit C-C condensation (e.g., at the P-O-4 benzylic position), leading to high viscosity, slower cure, and lower crosslink density when formulated as binders. Strategies have emerged to stabilize the native P-O-4 linkages during extraction by protecting the benzylic diol functionality — e.g., by acetal or ketal formation with aldehydes or ketones — thereby suppressing undesired condensationand preserving a more reactive, lower-molecular-weight lignin that can subsequently self-crosslink under heat and / or acid. In parallel, it has been shown that protected lignin (e.g., formaldehyde-protected lignin) can directly function as an adhesive and particularly a wood adhesive.

[0005] Lignin-based adhesives, particularly those relying on phenolic condensation chemistry, exhibit promising initial adhesion but often suffer from reduced crosslink density due to limited reactive sites and their oligomeric character. Accordingly, wood composites formed using conventional lignin-based adhesives can deliver lower breaking loads due to insufficient penetration into wood under industrial plywood press conditions. In formaldehyde-protected lignin systems intended to mimic traditional PF condensation, additional challenges arise, including potential formaldehyde emissions, reliance on relatively strong acid catalysts, and multi-step protect! on / extracti on processes.

[0006] Accordingly, there is a need for improved lignin-based adhesives that enhance crosslinking during cure to meet or exceed wood failure criteria, while being environmentally friendly and maintaining high bio-based content.SUMMARY

[0007] The invention relates to an adhesive composition that includes a lignin-containing material, such a lignocellulosic biomass or lignin, and a carbohydrate additive capable of converting to 5-hydroxymethylfurfural (5-HMF). The adhesive composition further includes a solvent and an acid catalyst. In some aspects, the carbohydrate additive is selected from the group consisting of fructose, glucose, high fructose com syrup, sucrose diformyl glucose, and mixtures thereof. The lignin-containing material may include protected lignin, such as formaldehyde-protected lignin or 5-hydroxymethylfurfural-protected lignin, or unprotected lignin.

[0008] The acid catalyst of the adhesive composition is selected from the group consisting of paratoluenesulfonic acid, methane sulfonic acid, sulfuric acid, 2-ethenylbenzenesulfonic acid, hydrochloric acid, trifluoroacetic acid, nitric acid, hydrobromic acid, hydroiodic acid, perchloric acid, phosphoric acid, hydrofluoric acid, formic acid, lignosulfonic acid, zinc chloride, aluminum chloride, iron (III) chloride, palladium chloride, boron trifluoride etherate, boron trifluoride, aluminum trifluoride, zirconium tetrachloride, and silicon tetrabromide, and combinations thereof. In certain aspects, the acid catalyst is present in at least 5 wt.% of the adhesive composition.

[0009] The solvent of the adhesive composition is selected from the group consisting of glycerol, glycerol formal, and propylene carbonate, gamma valerolactone, diformylxylose (DFX), levulinic acid, Cyrene™ (dihydrolevoglucosenone), dimethyl isosorbide, high boiling point carboxylicacids, esters, lactones, carbonates, ethers, ethyl acetate, ethanol, isopropanol, methanol, and combinations thereof.

[0010] The adhesive composition may further include 0 to 50 wt.% of one or more auxiliary additives, selected from the group consisting of a non-polar co-solvent, a polar co-solvent, a formaldehyde donor, a defoamer, a viscosity modifier, a rheology modifier, a formaldehyde scavenger, a plasticizer, a filler, a flame retardant, a lubricant, a softening agent, a pigment, a biocide, a latent acid donor, a surfactant, a dispersant, a latex, a hydrophobic agent, a neutralizing agent, and a tackifier. In some aspects, the adhesive composition is free of added formaldehyde.

[0011] The adhesive composition includes:• 10 to 30 wt.% of the lignin-containing material;• 5 to 20 wt.% of the carbohydrate additive;• 5 to 15 wt.% of the acid catalyst; and• 15 to 50 wt.% of the solvent.

[0012] Further aspects of the invention relate to a composite article prepared from at least one wood substrate and the adhesive composition according to the invention. The composite article may be, for example, plywood, a laminated veneer layer (LVL) product, laminated glulam beam, mass timber, oriented strand board (OSB), cross-laminated timber (CLT), particle board, medium density fiberboard (MDF), impregnated paper, or paper board. Composite articles prepared in accordance with the invention exhibit a wood failure (%) of at least 80% and a breaking loading of at least 90 psi, measured according to Voluntary Product Standard PS 1-22 (published by U.S. Department of Commerce on October 2, 2023).

[0013] Further aspects of the invention are directed to a process for manufacturing a composite article comprising the steps of: applying the adhesive composition of the invention to a substrate to form a coated substrate; and pressing the substrate at an elevated temperature and for a time sufficient to cure the adhesive composition and form the composite article.

[0014] The invention is further directed to a process for preparing a protected lignin-containing material comprising the steps of:• combining a lignin-containing material with a carbohydrate additive capable of converting to 5 -hydroxy methylfurfural (5-HMF), a solvent, and an acid catalyst to form a dispersion;• dehydrating the carbohydrate additive using the acid catalyst under reaction conditions to form 5-hydroxymethylfurfural;• reacting lignin in the lignin-containing material with the 5-hydroxymethylfurfural under reaction conditions to form a protected lignin dispersion containing 5- hydroxymethylfurfural-protected lignin,• optionally neutralizing the protected lignin dispersion, and• removing all or a portion of the solvent from the protected lignin dispersion to yield a protected lignin-containing material containing 5- hydroxymethylfurfural protected lignin.

[0015] The protected lignin-containing material prepared in the above process may then be used to produce an adhesive composition by blending the protected lignin-containing material with a solvent and at least 5 wt.% of an acid catalyst.

[0016] The invention is further directed to a process for manufacturing a wood composite. The process includes combining a lignin-containing material with a carbohydrate additive capable of converting to 5-hydroxymethylfurfural (5-HMF), a solvent, and an acid catalyst under reactive conditions, thereby dehydrating the carbohydrate additive and generating 5-hydroxymethylfurfural in situ, forming a wood adhesive composition; applying the wood adhesive composition to a substrate to form a coated substrate; and pressing the substrate at an elevated temperature and for a time sufficient to cure the wood adhesive and form the composite article.

[0017] Numerous other aspects, advantages, and / or features of the general inventive concepts will become more readily apparent from the following detailed description of exemplary embodiments and from the accompanying drawings being submitted herewith.DETAILED DESCRIPTION

[0018] The invention is directed to adhesive compositions formed from a lignin-containing material, such as lignocellulosic biomass or extracted or separated lignin, and a carbohydrate additive selected from fructose, glucose, diformyl glucose, sucrose, high fructose corn syrup, and mixtures thereof, and to methods for preparing such compositions. The compositions address the problem of low crosslink density in conventional lignin-based adhesives by leveraging in situ carbohydrate-derived furanic chemistry and / or aldehydic functionality to promote or enhance crosslinking under hot-press conditions, thereby improving bond strength in use. The adhesive compositions are suitable for manufacturing composite articles, and the invention further relates to such composite articles and methods of their manufacture.ADHESIVE COMPOSITION

[0019] The adhesive composition of the invention includes or is prepared from a lignincontaining material and at least one carbohydrate additive. The lignin-containing material mayinclude lignocellulosic biomass or lignin that has been extracted or separated from lignocellulosic biomass via an extraction or separation process.Lignocellulosic Biomass

[0020] Lignocellulosic biomass refers to a plant-derived material comprising an integrated matrix of cellulose, hemicellulose, and lignin, optionally with minor components such as extractives, proteins, ash, and moisture. Representative sources include virgin lignocellulosic materials (plants, bushes, trees, etc.); waste lignocellulosic materials (low value by-products from industrial processes or consumer use); and energy crops (e.g., switchgrass, miscanthus). For example, the lignocellulosic biomass may comprise or derive from hard woods, soft woods, wood fibers, seeds, endocarps, nuts, nutshells, sugarcane bagasse, corn stover, straw, hemp, kudzu, cotton stalk, wheat, bamboo, jute, flax, grasses (switchgrass, elephant grass and the like), cereal grasses, coffee grounds, discards (from sawmills, paper mills, construction, and the like), etc. The lignocellulosic material is preferably from trees such as birch, beech, poplar, cedar, Douglas fir, cypress, firs, juniper, kauri, larch, pine, hemlock, redwood, spruce, yew, eucalyptus, bamboo, and walnut (including walnut shell flower).

[0021] The lignocellulosic biomass may encompass a raw or processed form of the biomass. The lignocellulosic biomass may be cut, sawn, chipped, or ground to a desired form using means known in the art. The lignocellulosic biomass may be in the form of chips, flakes, fibers, pellets, granules, shivers, dust, flour, etc. The lignocellulosic biomass may be used “as is” or may be mixed with a solvent, water, or an aqueous solvent forming a slurry or dispersion for use in subsequent steps of a process of the invention. A slurry or dispersion of lignocellulosic biomass may be agitated, for example by stirring or sonication, to break down the lignocellulosic biomass prior to or after combining it with a protecting agent and solvent to form a biomass dispersion.

[0022] As mentioned, various forms of lignocellulosic biomass may be used. By way of example, suitable forms include: (i) strands in which individual strips are about 20-25 mm wide and 100-150 mm long; (ii) wood particles screened in the range of about 1.6 mm (1 / 16 in) to 6.4 mm (1 / 4 in); (iii) chips and flakes having characteristic dimensions of about 5-50 mm; (iv) fibers with typical lengths from about 0.5 mm to 20 mm; and (v) wood flours or dusts having a median particle size (D50) of about 10-500 pm, with a D90 not exceeding about 1,000 pm. In some aspects, the lignocellulosic biomass used to prepare the adhesive is in a particle or flour form to facilitate homogeneous dispersion and controlled rheology in the adhesive composition.

[0023] In some aspects, particularly when preparing adhesive compositions or biomass dispersions, the lignocellulosic biomass is used in the form of particles having a size of less thanabout 1 mm. In preferred embodiments, the lignocellulosic biomass is in the form of a powder having a particle size of less than about 200 mesh. In more preferred embodiments, the lignocellulosic biomass has a particle size of less than about 325 mesh. Finer particle sizes may facilitate more uniform dispersion of the lignocellulosic biomass in the biomass dispersion and more effective protection of lignin P-O-4 linkages.

[0024] Lignocellulosic biomass comprises lignin. Lignin is a class of naturally occurring polymer which acts as a binder in wood and other lignocellulosic plants. Lignin is, therefore, a renewable resource. The following linkages have been reported in lignin. See Solihat, N.N.; Sari, F.P.; Falah, F.; Ismayati, M.; Lubis, M.A.R.; Fatriasari, W.; Santoso, E.B.; Syafii, W. Lignin as an Active Biomaterial: A Review. J. Sylva Lestari 2021, 9, 1-22.

[0025] Lignin units attached to adjacent units in ring positions 2, 3, 5, or 6 (see formula below) are referred to as “condensed units,” and consequently units lacking connection to other units in these positions are “uncondensed.” See Lundquist, K., and Parkas, J. "Different types of phenolic units in lignins," BioRes. 6(2), 920-926, (2011); Yang, G., Gong, Z., Luo, X. et al. Bonding wood with biomass powders as wood adhesives. Nature 621, 511-515 (2023).According to Li Shuai’s group, “different condensation degrees, as reflected, inversely, by the molar yields of the resulting aromatic monomers from their hydrogenolysis.” Yang, G., Gong, Z., Luo, X. et al. Bonding wood with uncondensed lignins as adhesives. Nature 621, 511-515 (2023).

[0026] As shown in the structure above, uncondensed or partially condensed lignin has more available active sites, specifically on the 2, 3, 5, 6 position of the aromatic ring. Condensed lignin will have reacted with a majority of these active sites likely due to the condensation between the P-O-4 aryl ether and the various positions of the aromatic ring. This causes the loss of the primary hydroxyl groups associated with the P-O-4 aryl ether positions. These changes can be observed by HSQC-NMR and CNMR when comparing lignin extracted with and without the use of a protecting agent. This can be further evidenced by GPC, when comparing lignin extracted with and without the use of a protecting group. Lastly, according to Li Shuai (W02023 / 208015A1), different degrees of condensation can be observed by monomer yield after hydrogenolysis, where higher condensed lignin results in lower monomer yield.Protected Lignocellulosic Biomass

[0027] Naturally occurring lignocellulosic biomass contains unprotected, native lignin, and lignocellulosic biomass-containing protected lignin can be prepared through a protection reaction using a protecting reagent, for example, an aldehyde or ketone, to form acetals or ketals and yield protected lignin. The protection reaction converts the P-O-4 benzylic hydroxyls to stable derivatives, so that the P-O-4 linkage is maintained and the benzylic position is rendered less reactive toward C-C coupling. Such protection prevents lignin condensation during processing under specific conditions (e.g., elevated temperature and / or particular pH). “Protected lignin” refers specifically to lignin bearing protective groups on its P-O-4 linkages. For example, “aldehyde-protected lignin” refers to lignin in which the P-O-4 linkages are protected by an aldehyde (e.g., formaldehyde). By contrast, “lignin” or “unprotected lignin” refers to natural lignin in which the benzylic diol functionality of P-O-4 linkages has not been chemically protected and the P-O-4 linkages remain non-condensed, i.e., not transformed into C-C coupled condensation products at the benzylic position.

[0028] Lignocellulosic biomass that contains protected lignin is referred to as “protected lignocellulosic biomass.” In some aspects, protected lignocellulosic biomass is prepared by a method that includes combining a lignocellulosic biomass with a protecting reagent in a solvent to form a biomass dispersion; and reacting the lignin in the dispersion with the protecting reagent in the presence of a catalyst under reaction conditions effective to protect lignin P-O-4 linkages, thereby forming a protected biomass dispersion. The method may further include neutralizing theprotected biomass dispersion; and / or removing all or a portion of the solvent to yield a protected lignocellulosic biomass.

[0029] Suitable protecting reagents known in the art are aldehydes, ketones, carbonates, boric acid, and boronic acids (R-B-(OH)2), and the like. Such protecting reagents include, for example, formaldehyde, paraformaldehyde, formaldehyde diethyl acetal, acetaldehyde, paraldehyde, paraacetaldehyde, p-phthalaldehyde, propionaldehyde, butyraldehyde, acetaldehyde, propionaldehyde, isobutyraldehyde, glyoxylic acid, dialdehyde, cyclopropanecarboxaldehyde, isobutyraldehyde, pivaldehyde, tolualdehyde, benzaldehyde, 2-hydroxyacetaldehyde, 2-chloroacetaldehyde, 2-bromoacetaldehyde, 2-iodoacetaldehyde, 2-hydroxyacetaldehyde, ethanedial (also known as glyoxal or oxalaldehyde), oxoethanoic acid (also known as 2-oxo-acetic acid or glyoxylic acid), 2,2,2-trichloroacetaldehyde, 4-hydroxy-3,4-dimethoxybenzaldehyde (syringaldehyde), 4-hy doxy-3 -methoxybenzaldehyde (vanillin), 2-hydroxybenzaldehyde (salicylaldehyde), 2-chlorobenzaldehyde, 2-bromobenzaldehyde, 2-iodobenzaldehyde, 3 -hydroxybenzaldehyde, 3 -chlorobenzaldehyde, 3 -bromobenzaldehyde, 3-iodobenzaldehyde, 4-hydroxybenzaldehyde, 4-chlorobenzaldehyde, 4-bromobenzaldehyde, 4-iodobenzaldehyde, 2,4-dichlorobenzaldehyde, 2,4-dibromobenzaldehyde, 2,4-diiodobenzaldehyde, 2-nitrobenzaldehyde, 4-nitrobenzaldehyde, 2,4-dinitrobenzaldehyde, 2,4,6-trinitrobenzaldehyde, 2-formylbenzoic acid, 4-formylbenzoic acid, and terephthalaldehyde, furfural, acetone, butanone, boric acid, and boronic acids (R-B-(OH)2, where R is a Ci-Ce alkyl, a Cs-Cs cycloaliphatic group, or a phenyl group), ketoacids / ketoester (pyruvic acid, levulinic acid, oxaloacetic acid, 2-oxoglutaric acid), 2-methoxyproane, 2,2-dimethoxypropane, and mixtures of such protecting reagents.

[0030] A protecting reagent may be used “neat” or as a solution or dispersion of the protecting reagent. When a solution or dispersion of the protecting reagent, the solvent may be the same or different than the solvent used to form the biomass dispersion and preferably is the same as or miscible with that solvent. Exemplary solutions of a protecting reagent which may be used include, but are not limited to, aqueous formaldehyde solutions, formaldehyde, diformylxylose (DFX) solutions, and formaldehyde levulininc acid solutions, where the protecting agent is present in 1-65 wt.%, for example, in 5-60 wt.%, 10-55 wt.%, or 30-55 wt.%. In some circumstances, the protecting agent itself may also be the solvent.

[0031] The solvent used in the protection reaction may be, but is not limited to, water, an aqueous solvent containing one or more co-solvents or an organic solvent. While water is preferred, cosolvents may be added to solubilize or disperse components in the lignocellulosicbiomass and / or the protecting reagent used in a process. A co-solvent may be added in any amount desired but is typically used in amounts up 50 wt.%. Suitable co-solvents and / or organic solvents which may be used include but are not limited to tetrahydrofuran (THF), 2-methyl tetrahydrofuran (2-methyl THF), formaldehyde diethyl acetal (FDEA), diformyl xylose, 1,4-di oxane, di oxolane, glycerol, glycerol formal, ketoacids / ketoester (levulinic acid, pyruvic acid, levulinic acid, oxaloacetic acid, 2-oxoglutaric acid), dimethylisosorbide, EDEA, acetone, cyclic ethers, cyclic carbonates, dialkyl carbonate, a diaryl carbonate, cyclic esters, gamma valerolactone, non-cyclic ethers, methanol, ethanol, ethers, nitriles, dimethoxyethane, toluene, dimethyl carbonate, diethyl carbonate, heptane, monoglyme, diglyme, carboxylic acids (formic), carboxamides, lactones, sulfoxides, ethanol, methanol, maleic acid solution, 5-sulfosalylic acid solution, 1,4-epoxybutane, 4-methylbutyrolactone, formic acid butanol, acetic acid, butanone, and mixtures thereof.

[0032] The amount of solvent used to form a biomass dispersion should be sufficient to allow mixing of the lignocellulosic biomass and the protecting reagent. Preferably, the amount of solvent should allow the biomass dispersion to be stirred or otherwise mixed during the protection reacting. The amount of solvent in the biomass dispersion may be, for example, in the range of 1-to 20-times the amount of lignocellulosic biomass, on a weight-weight basis, in the biomass dispersion, or in the range of 1- to 10-times, or 5- to 15-times.

[0033] The protection reaction may be acid or base catalyzed depending on the protecting group, as known to those skilled in the art. Accordingly, the catalyst used in the protection reaction can be an acid catalyst or a base catalyst. Suitable acid catalysts include, but are not limited to, sulfuric acid, methanesulfonic acid 2-ethenylbenzenesulfonic acid, -toluenesulfonic acid ( TSA), hydrochloric acid, trifluoroacetic acid, nitric acid, hydrobromic acid, hydroiodic acid, perchloric acid, phosphoric acid, hydrofluoric acid, formic acid, oxalic acid, terephthalic acid, lignosulfonic acid, zinc chloride, aluminum chloride, iron (III) chloride, palladium chloride, boron trifluoride etherate, boron trifluoride, aluminum trifluoride, zirconium tetrachloride and silicon tetrabromide. Suitable base catalysts include, but are not limited to, metal hydroxides (sodium hydroxide, potassium hydroxide, lithium hydroxide, cesium hydroxide), metal oxides (magnesium oxide, calcium oxide, barium oxide), metal alkoxides (sodium methoxide, potassium methoxide), triethylamine (TEA), pyridine, l,8-Diazabicyclo[5.4.0]undec-7-ene (DBU), 1,5-Diazabicyclo[4.3.0]non-5-ene (DBN), quinuclidine, morpholine, proline, 1, 1,3,3-Tetram ethylguanidine (TMG), and l,4-diazobicyclo[2.2.2]octane (DABCO). The catalyst content in the mixture of the protection reaction may be in the range of 1-50 wt.%, more optimally from2-10 wt.%. The catalyst may be added as an aqueous solution, which may include the same solvent as used to make the biomass dispersion.

[0034] The protection reaction may be carried out at temperatures of 50 °C -350 °C, more optimally 80 °C-220 °C or 200 °C -300 °C. Typical reaction times range from 0.1-10 hours, more optimally 4-6 hours. The reaction may take place in a batch or continuous reactor such as a continuous flow or plug flow reaction.

[0035] During the protection reaction, the reaction conditions may be chosen such that cellulose in the lignocellulosic material is hydrolyzed during the protection reaction, for example, by adding acid. This hydrolysis may take place during the reaction with the protecting reagent or in a subsequent step before or after the optional neutralization of the protected biomass dispersion.

[0036] After the protection reaction step, the protected biomass dispersion may be neutralized and, optionally, cooled or allowed to cool to room temperature. Neutralization of the reaction mixture may be done as appropriate as known in the art by adding a base, such as sodium hydroxide, or an acid, such as sulfuric acid. Alternatively, the protected biomass dispersion may be neutralized by distilling off or washing out the acid or base catalyst.

[0037] Following the protection reaction and / or the optional neutralization steps, all or a portion of the solvent may be removed to yield a protected lignocellulosic biomass in solid or semi-solid form. The solvent may be removed by means known in the art, such as, for example, vacuum drying, rotary evaporation, distillation, lyophilization, ambient or heated drying, phase separation, draining, filtration, and the like. Additional solvents may be added prior to solvent removal to achieve better removal of the solvent used in the dispersion and / or excess protecting reagent or catalyst. When the solvent is removed by draining or filtration, the protected biomass product may be washed to remove entrained catalyst and / or solvent and further dried if desired. A washing step may serve to neutralize the protected biomass. Any filtrate and / or washings may be recycled for use in a subsequent process of the invention. The solvent removal step and any subsequent washing may also act to remove excess protecting reagent, for example formaldehyde, that is present in the protected biomass dispersion. The resulting protected lignocellulosic biomass may be milled and / or sieved to a desired particle size.

[0038] The protected lignocellulosic biomass may be used in the preparation of an adhesive composition according to the invention. For some protecting reagents, post-protection processing of the lignocellulosic biomass may deprotect some or all of the P-O-4 or other hydroxyl functionality in the biomass without loss of its adhesive or other properties. Such deprotected lignocellulosic biomass are still considered “protected lignocellulosic biomass” of the invention.The terms “protected lignocellulosic biomass”, “protected lignocellulosic biomass dispersion”, and “lignocellulosic biomass product containing protected lignocellulosic material” refers to a biomass, a dispersion, or a lignocellulosic material prepared using a process of the invention which reacts a biomass dispersion with a protecting reagent.

[0039] In some aspects, the lignin-containing material is lignin, rather than lignocellulosic biomass. The lignin may be separated or extracted from lignocellulosic biomass and protected through a protection reaction using a protecting reagent, as described above. The resulting protected lignin is self-crosslinking upon exposure to heat and / or acid. WO 2023 / 208015 Al, for example, describes a method for derivatizing and extracting lignin from a biomass and using the extracted, protected lignin in wood adhesive.

[0040] The lignin-containing material may be present in the adhesive composition in an amount ranging from 1 wt.% to 99 wt.% based on the total weight of the composition, including, for example from 5 wt.% to 90 wt.%, from 8 wt.% to 85 wt.%, from 10 wt.% to 80 wt.%, from 12 wt.% to 70 wt.%, from 15 wt.% to 60 wt.%, from 18 wt.% to 55 wt.%, from 20 wt.% to 50 wt.%, from 22 wt.% to 45 wt.%, from 25 wt.% to 40 wt.%, and from 27 wt.% to 35 wt.%, including any endpoints and subranges therebetween. In certain aspects, the adhesive composition may include from 10 wt.% to 30 wt.%, or at least 20 wt.% of the lignin-containing material, based on the total weight of the composition.Carbohydrate Additive

[0041] The adhesive composition of the invention further includes at least one carbohydrate additive as a cross-linking agent (referred to herein as a “co-crosslinking agent”) and / or as a protecting reagent.

[0042] The carbohydrate additive is a carbohydrate that is capable of converting to 5-hydroxymethylfurfural (5-HMF) via dehydration under certain conditions. In some aspects, the dehydration occurs under thermal and acidic conditions, such as at 50 - 150 °C and a pH of less than 3. Suitable carbohydrate additives that form 5-HMF include a hexose (such as an aldohexose or ketohexose), sucrose, cellulose, hemicellulose, starch, pectin, and the like. Exemplary carbohydrate additives include, fructose, glucose, sucrose, high fructose corn syrup, diformyl glucose (DFG), and mixtures thereof. Fructose is typically the preferred starting material for producing 5-HMF and it dehydrates rapidly under heat and acidic conditions, whereas glucose generally first isomerizes to fructose before dehydrating to 5-HMF. The conversion of fructose and glucose to 5-HMF is illustrated below.glucose fructose 5-hy roxymethyifurtural (HMF

[0043] 5-HMF is a white or yellow, low-melting solid that is highly soluble in water and in a variety of organic solvents. Structurally, 5-HMF comprises a furan ring bearing an aldehyde group at the 2-position and a hydroxymethyl group at the 5-position.

[0044] Under thermal and acidic conditions, 5-HMF can further polymerize or condense in situ to form crosslinked furan networks, commonly referred to as humins, as illustrated below.

[0045] Based on the conversion of the carbohydrate additive to 5-HMF and subsequent humin formation under thermal and acidic conditions, it has been found that the carbohydrate additive can be included in a curing system as a co-crosslinker hot press crosslinking reactions. Specifically, when a carbohydrate additive is present in a curing system, such as one involving phenolic condensation with lignin, during hot-press curing (e.g., about 120 °C to 200 °C) and in the presence of an acid catalyst, the carbohydrate additive converts to 5-HMF, which subsequently huminizes, participates in acetal formation with lignin benzylic diols, and interlinks with existing crosslinking chemistry, thereby increasing overall crosslink density and enhancing bond strength. Carbohydrate additive-containing systems exhibit faster cure and higher breaking loads relative to analogous formulations lacking the carbohydrate additive.

[0046] It is important to note that it is the carbohydrate additive that is introduced into the adhesive composition, and not a pre-formed 5-HMF and / or humin compound. Any humin / furanic structures present in the adhesive composition arise in situ during cure. Without wishing to be bound by theory, the in situ generation of 5-HMF and humin from the carbohydrate additiveincreases cure rate and crosslink density by enabling furanic polymer growth and facilitating covalent integration with existing crosslinking chemistry. Accordingly, in some aspects, the adhesive composition is free of pre-formed 5-HMF and / or pre-formed humin compounds.

[0047] The carbohydrate additive co-crosslinker may be present in the adhesive composition in an amount ranging from 1 wt.% to 99 wt.% based on the total weight of the composition, including, for example from 2 wt.% to 75 wt.%, from 5 wt.% to 65 wt.%, from 8 wt.% to 50 wt.%, from 10 wt.% to 45 wt.%, from 12 wt.% to 40 wt.%, from 15 wt.% to 35 wt.%, from 18 wt.% to 30 wt.%, from 20 wt.% to 30 wt.%, from 5 wt.% to 30 wt.%, and from 5 wt.% to 20 wt.%, including any endpoints and subranges therebetween.

[0048] In certain aspects, in addition to or as an alternative to the use of 5-HMF generated by dehydration of a carbohydrate additive as a co-crosslinker, the in situ generated 5-HMF may be used as a protecting reagent to prepare 5-HMF-protected lignin or a lignocellulosic biomass comprising 5-HMF-protected lignin (i.e., 5-HMF-protected lignocellulosic biomass). Methods for preparing 5-HMF-protected lignin and 5-HMF-protected lignocellulosic biomass correspond to the protection process described herein for producing protected lignin and protected lignocellulosic biomass using various protecting reagents and auxiliary reagents (e.g., catalysts, solvents).

[0049] By way of example, a process for preparing 5-HMF-protected lignocellulosic biomass comprises: combining a lignocellulosic material with fructose, an acid catalyst (e.g., / ?TSA), and a solvent to form a biomass dispersion; dehydrating the carbohydrate additive under the catalyzed reaction conditions to generate 5-HMF; and reacting the lignin in the dispersion with the 5-HMF to form a protected biomass dispersion containing 5-HMF-protected lignin. The process may further include steps of: neutralizing the protected biomass dispersion and / or removing all or a portion of the solvent following the protection step. A representative reaction scheme depicting conversion of fructose to 5-HMF and subsequent acetal formation on lignin to yield 5-HMF-protected lignin is illustrated below.

[0050] The carbohydrate additive protecting reagent may be present in the adhesive composition in an amount ranging from 1 wt.% to 99 wt.% based on the total weight of the composition, including, for example from 2 wt.% to 85 wt.%, from 8 wt.% to 75 wt.%, from 10 wt.% to 65 wt.%, from 12 wt.% to 55 wt.%, from 15 wt.% to 45 wt.%, from 17 wt.% to 40 wt.%, from 18 wt.% to 35 wt.%, from 20 wt.% to 30 wt.%, from 5 wt.% to 40 wt.%, and from 5 wt.% to 20 wt.%, including any endpoints and subranges therebetween.Catalyst

[0051] The adhesive composition further includes at least one acid catalyst, base catalyst, acetal deprotecting agent, or ring opening reagent to catalyze crosslinking reactions during cure. The acid catalyst, base catalyst, acetal deprotecting agent, or ring opening reagent may be present in an amount of 1-30 wt.% of the adhesive composition, or in amounts of 2-20 wt. %, or 5-15 wt. %. Exemplary acid catalysts include, but are not limited to, para-toluenesulfonic acid (pTSA), methane sulfonic acid, sulfuric acid, 2-ethenylbenzenesulfonic acid, hydrochloric acid, trifluoroacetic acid, nitric acid, hydrobromic acid, hydroiodic acid, perchloric acid, phosphoric acid, hydrofluoric acid, formic acid, lignosulfonic acid, zinc chloride, aluminum chloride, iron (III) chloride, palladium chloride, boron trifluoride etherate, boron trifluoride, aluminum trifluoride, zirconium tetrachloride, and silicon tetrabromide. Suitable base catalysts include, but are not limited to, metal hydroxides (sodium hydroxide, potassium hydroxide, lithium hydroxide, cesium hydroxide), metal oxides (magnesium oxide, calcium oxide, barium oxide), metal alkoxides (sodium methoxide, potassium methoxide), tri ethylamine (TEA), pyridine, 1,8-Diazabicyclo[5.4.0]undec-7-ene (DBU), l,5-Diazabicyclo[4.3.0]non-5-ene (DBN), quinuclidine, morpholine, proline, 1,1,3,3-Tetramethylguanidine (TMG), and l,4-diazobicyclo[2.2.2]octane (DABCO). Exemplary acetal deprotecting agents and ring opening reagents include the acid and base catalysts just mentioned but also include, and are not limited to, water, methyl tritiate, boron trifluoride etherate, 1,6-diaminohexane, ethylenediamine, thenyldiamine, trimethylhexamethylenediamine, and tripelennamine, polyethylenimine, and other reagents known in the art to ring open an acetal or a cyclic carbonate.Solvent

[0052] The solvent used in the adhesive compositions may be the same as that employed in a lignin protection reaction or other solvents commonly used in wood adhesives. Typical solvents include, without limitation, water; glycerol; glycerol formal; propylene carbonate; gamma-valerolactone; diformylxylose (DFX); levulinic acid; Cyrene™(dihydrolevoglucosenone); dimethyl isosorbide; high-boiling carboxylic acids; esters; lactones; carbonates; ethers; ethyl acetate; ethanol; isopropanol; and methanol.

[0053] When a protected lignocellulosic biomass is first prepared and subsequently formulated into an adhesive composition, at least a portion of the solvent used during the lignin protection reaction may be retained and serve as the solvent in the adhesive composition. In embodiments where an organic solvent such as 2-methyl THF is used in the protection process, it is generally desirable to remove substantially all of that solvent and introduce a new solvent suitable for the adhesive formulation. In contrast, when water or an aqueous solvent system is used, a greater fraction of the solvent may be retained in the adhesive composition.Optional Curable Resin

[0054] Optionally, the adhesive composition may also contain a curable resin. A curable resin may be present in 0-15 wt. % of the composition or in amounts such as 0.5-12 wt.%, 1-10 wt.%, 2-7 wt. %, and 4-6 wt. %. Curable resins may function as co-binders or co-curatives with the lignincontaining material. A curable resin includes but is not limited to a curable resin selected from the group consisting of formaldehyde-based resin, furfural -based resin, glyoxal-based resin, glyoxylic acid-based resin, propionaldehyde-based resin, isocyanate-based resin, epoxy-based resin, a cyclic acetal-based resin, or combinations thereof. In certain aspects, the curable resin is a novolac resin. In some aspects, the curable resin is selected from the group consisting of diformylxylose (DFX)-novolac resin, diformyl glucose (DFG)-novolac resin, triformyl sorbitol (TFS)-novolac resin, diformylpentaerythritol (DFP)-novolac resin, and combinations thereof.Auxiliary Additives

[0055] The adhesive composition may further include auxiliary additives known in the art for wood adhesives. Exemplary auxiliary additives include, without limitation, non-polar and polar co-solvents; formaldehyde donors (e.g., diformyl xylose (DFX), Cyrene™, extracted formaldehyde protected lignin (FPL)); defoamers; viscosity and rheology modifiers (e.g., polyvinyl alcohol (PVOH)); formaldehyde scavengers; plasticizers; fillers; flame retardants; lubricants; softening agents; pigments; biocides; latent acid donors; surfactants; dispersants; latexes; hydrophobes; neutralizing agents (e.g., MgO, CaO); and tackifiers. When a formaldehyde scavenger is included, the adhesive composition may be heated after addition to about 50°C -100 °C for approximately 5-30 minutes to reduce free formaldehyde.

[0056] When present, the auxiliary additives may be included in amounts up to 50 wt.% of the adhesive composition. For example, the auxiliary additives may be present in the adhesivecomposition in an amount of from 0.01 to 50 wt.%, from 0.01 to 40 wt.%, from 0.01 to 30 wt.%, or from 0.01 to 20 wt.%, based on the total weight of the adhesive composition.

[0057] In one aspect, the invention provides an adhesive composition comprising, consisting essentially of, or consisting of: a protected lignin-containing material; a carbohydrate additive selected from fructose, glucose, high fructose com syrup, diformyl glucose, and mixtures thereof; an acid catalyst; and a solvent. The acid catalyst is present at least at 5 wt.% of the adhesive composition. The protected lignin-containing material may comprise, consist essentially of, or consist of an aldehyde-protected lignin, such as formaldehyde-protected lignin, or 5-HMF-protected lignin. The carbohydrate additive is preferably fructose, and the acid catalyst is preferably / ?TSA. The solvent may comprise one or more of water, propylene carbonate (PC), glycerol, and alcohols. The composition may further include additives such as polyvinyl alcohol (PVOH). In some embodiments, the composition is free of added formaldehyde.

[0058] In representative embodiments corresponding to this aspect, the adhesive composition comprises, consists essentially of, or consists of: about 10 to 30 wt.% of the protected lignincontaining material; about 5 to 20 wt.% of the carbohydrate additive; about 5 to 15 wt.% of the acid catalyst; about 15 to 50 wt.% of the solvent; and 0 to 50 wt.% of one or more auxiliary additives as disclosed above, based on the total weight of the adhesive composition.

[0059] The compositions of the first aspect employ a protected lignin backbone (e.g., formaldehyde-protected lignin) in combination with a carbohydrate additive, preferably fructose, and an acid catalyst. During hot-pressing, the carbohydrate additive dehydrates to 5-HMF, which further polymerizes to furanic / humin networks and can form acetals with benzylic diols on lignin, co-crosslinking with the protected lignin matrix. This dual-curing (phenolic / acetal plus furanic) mechanism increases crosslink density and accelerates cure, yielding higher wood failure at shorter press times, elevated breaking loads, and robust wet-condition performance, while enabling reduced or zero added formaldehyde and maintaining high bio-based content.

[0060] In a second aspect, the invention provides an adhesive composition comprising, consisting essentially of, or consisting of: a lignin-containing material; a carbohydrate additive selected from fructose, glucose, high fructose com syrup, diformyl glucose, and mixtures thereof; an acid catalyst; and a solvent. In certain embodiments, the composition is free of added formaldehyde. In further embodiments, the composition is free of protected lignin.

[0061] In representative embodiments corresponding to this aspect, the adhesive composition comprises, consists essentially of, or consists of: about 10 to 30 wt.% of the lignin-containing material about 5 to 20 wt.% of the carbohydrate additive; about 5 to 15 wt.% of the acid catalyst;about 15 to 50 wt.% of the solvent; and 0 to 50 wt.% of one or more auxiliary additives as disclosed above, based on the total weight of the adhesive composition.

[0062] The compositions of the second aspect utilize unprotected lignin-containing material in combination with a carbohydrate additive, preferably fructose, and an acid catalyst to drive in situ formation of 5-HMF during hot-pressing cure. The generated 5-HMF further polymerizes to furanic / humin networks and can form acetals with benzylic diols on native lignin, thereby co-crosslinking the biomass matrix without prior protect! on / extracti on steps. This carbohydrate-assisted curing mechanism increases crosslink density and accelerates cure, delivering higher wood failure at shorter press times, increased breaking loads, improved wet-condition durability, and the ability to meet performance targets with high bio-based content and without added formaldehyde.

[0063] In a third aspect, the invention provides an adhesive composition comprising, consisting essentially of, or consisting of: a 5-HMF -protected lignocellulosic biomass or a 5-HMF -protected lignin; an acid catalyst; and a solvent. In certain embodiments, the composition is free of added formaldehyde.

[0064] In representative embodiments corresponding to this aspect, the adhesive composition comprises, consists essentially of, or consists of: about 10 to 30 wt.% of the 5-HMF -protected lignocellulosic biomass or 5-HMF -protected lignin; about 5 to 15 wt.% of the acid catalyst; about 15 to 50 wt.% of the solvent; and 0 to 50 wt.% of one or more auxiliary additives as disclosed above, based on the total weight of the adhesive composition.

[0065] Without wishing to be bound by theory, the adhesive compositions of the third aspect derive their performance from a protected lignin backbone in which benzylic diol sites at P-O-4 linkages are acetalized with 5-HMF. This protection stabilizes the lignin during preparation and storage by suppressing premature condensation, while introducing furanic moieties that are chemically poised for cure. Under hot-press conditions in the presence of an acid catalyst, a portion of the 5-HMF acetals can participate in acid-catalyzed condensation reactions, including limited deprotection that regenerates benzylic reactivity, formation of additional acetals with neighboring lignin hydroxyls, and furanic polymer growth from 5-HMF units to yield humin-like networks. These concurrent pathways crosslink the lignin matrix through benzylic acetal bridges and furanic linkages, increasing crosslink density and producing a robust, thermoset adhesive bond. Technically, this manifests as faster cure to target wood failure at industrial press temperatures, higher breaking loads consistent with denser networks, improved resistance tomoisture conditioning, and the ability to meet performance targets without added formaldehyde while maintaining high bio-based content and practical formulation viscosity.

[0066] The adhesive composition may be prepared using methods known in the art, for example, by blending all components to make a paste, suspension, or solution, depending on the degree of solvating effects of the liquid components on the protected biomass. In the case of a paste application, the liquid component(s), such as water, would be added and then the lignocellulosic biomass component would be shear-mixed in, creating a paste. To form an emulsion, auxiliary additives, such as, dispersing, bodying agents, surfactants, detergents, or thickener could be added to the liquid portion prior to biomass powder addition. In the case of a solution, the lignincontaining material may be dissolved in the solvent.COMPOSITE ARTICLE

[0067] The adhesive composition is suitable for manufacturing a composite article and in particular, composite articles comprising substrates formed of lignocellulose material (i.e., wood particles, wood fibers, straw, hemp, cotton stalk, wheat, bamboo, jute, flax, hard woods, soft woods, grasses, etc.), paper, fiberglass, cellulose, metal, sand, polymer materials, synthetic materials, and the like.

[0068] Exemplary composite articles made from the present adhesive compositions include oriented strand board (OSB), particleboard, flake board, medium or high-density fiberboard, waferboard, plywood, laminated veneer layer (LVL), laminated glulam beam, mass timber, crosslaminated timber (CLT), medium density overlay (MDO), high density overlay (HDO), an overlaid weather barrier, high pressure laminates (HPL), or thermally fused laminates (TFL), impregnated paper, paper board, and the like.

[0069] In any of the various composite article manufacturing processes set forth below, the adhesive composition disclosed herein may be applied or otherwise associated with one or more substrates as a one-part composition, meaning that the adhesive composition includes the catalyst within the composition. Alternatively, the adhesive composition is provided as a two-part system wherein the lignin-containing material / carbohydrate additive / optional additive mixture and the acid catalyst are combined shortly before application, or are applied separately. In such systems with separate applications, the mixture and the catalyst may be added as separate coatings, beads, extrudate, and the like, with pressure and / or heat applied to promote mixing of the components and initiate curing.

[0070] The adhesive composition (inclusive of the one-part composition or two-part system) may be applied to the substrate in an amount in the range of 0.5 wt.% to 20 wt.% based on the totalweight of the coated substrate, including, for example, 1 wt.% to 15 wt.%, 1.5 wt.% to 10 wt.%, 2 wt.% to 8 wt.%, and 2.5 wt.% to 7 wt.%, including all endpoints and sub-ranges therebetween.

[0071] According to a first aspect, a composite article may be produced by applying an adhesive composition to a substrate, such as by coating, blending, or spraying the substrate with the adhesive composition, thereby forming a coated substrate (also referred to as a “first” substrate). As mentioned above, the substrate may comprise wood or wood particles, fiberglass, paper, glass particles or beads, lignocellulose, cellulose, metal, sand, polymer, synthetic materials, and the like. The adhesive composition may be applied to or blended with the substrate materials using any known method, such as by blender, roll coater, curtain coater, dip coater, spray booth, extruder, and the like. Alternatively, the adhesive composition may be provided as a two-part system that is combined shortly before application or applied as separate streams. The resulting composite may include two or more layers of adhesive composition.

[0072] The coated substrate may then be pressed between one or more plates at an elevated temperature sufficient to initiate curing of the adhesive composition and for a time sufficient to complete curing, thereby forming the composite article. Conventional processes for compressing a coated substrate are generally carried out by hot pressing along with heat transfer from hot surfaces. The press pressure during hot pressing may be between about 100 psi and about 220 psi, including, for example, between about 130 psi and about 210 psi, and between about 140 psi and about 190 psi. The temperature at which the coated substrate is pressed may be at least about 60 °C for at least about 2 minutes, such as, for example, a temperature of about 60 °C to about 250 °C, including, for example, about 100 °C to about 125 °C for about 2-15 minutes. In representative embodiments, cure temperatures may be achieved at about 80 °C to about 150 °C, with catalyst selection and loading adjusted to reach targeted gel times. Optionally, the coated substrate can be pre-pressed (e.g., cold pressed) prior to hot pressing. For example, the article may be pre-pressed for a period of time, such as about 1 minute to about 60 minutes at ambient temperature prior to hot pressing, including, for example, a pre-pressing period of about 1 minute to about 20 minutes, or about 1 minute to about 10 minutes.

[0073] In other processes, such as a glulam beam manufacture, the coated substrate is pressed via a radio frequency (RF) press, where the coated substrate is pressed at a pressure of about 100 psi to about 210 psi, including, for example, pressures between about 115 psi to about 200 psi, and about 125 psi to about 180 psi. While being pressed, the radio frequency heats up the adhesive composition, promoting cure. The adhesive may reach temperatures of about 35 °C to about 150 °C, including, for example, temperatures of about 60 °C to about 140 °C, and about 100 °C toabout 130 °C. The composite may be pressed for a period of time sufficient to cure and adhere the composite layers, such as for a period of about 2 to about 10 minutes. In such applications, the wood substrate may comprise, for example, Douglas Fir (DF), Southern Yellow pine (SYP), bamboo, oak, maple, larch, spruce, and the like.

[0074] Alternatively, in some systems, the coated substrate may be pressed and cured at ambient temperatures.

[0075] The composite article may comprise one or more additional substrates, such that the first substrate with the adhesive composition coated thereon, is pressed using a second substrate. The second substrate may optionally be pre-coated with the adhesive composition, prior to the pressing step. The first substrate and one or more additional substrates may comprise the same material, or may comprise different materials. In any aspect, at least one of the first substrate and one or more additional substrates comprise a cellulose material.

[0076] The composite article formed in accordance with the above method may comprise, for example, plywood, a laminated veneer layer (LVL) product, laminated glulam beam, mass timber, oriented strand board (OSB), cross-laminated timber (CLT), particle board, medium density fiberboard (MDF), or the like. When specifically manufacturing particle board, medium density fiberboard (MDF), or oriented strandboard (OSB), the coated substrate is formed by blending the adhesive composition with a lignocellulosic material. The lignocellulosic material may comprise, for example, wood chips, wood fiber, wood powder, or wood flour.

[0077] According to a second aspect, a composite article may be produced by saturating or impregnating a substrate with the adhesive composition. Such an application method may be used with any substrate discussed above, but finds particular application in the production of fiberglass and paper substrates. The substrate may be saturated or impregnated with the adhesive composition according to any known method, such as, for example, by placing the substrate in a resin bath and submerging the substrate therein, by applying the adhesive composition in such a way as to allow the adhesive to bleed through the substrate thickness, or a combination thereof. For example, the adhesive composition may be placed in a saturating pan and heated to about 20-25°C. A substrate is then passed through the pan and excess composition is squeezed or otherwise removed from the substrate using any known means, such as a nip roll.

[0078] The saturated or impregnated substrate is then allowed to cure, such as by placing the saturated or impregnated substrate in an oven at an appropriate temperature (i.e., 100 °C-150°C) to cure the adhesive composition, forming a composite article. The oven further reduces the volatile content of the saturated substrate to below 5%, and preferably below 3%. The compositearticle may comprise, for example, medium density overlay (MDO), high density overlay (HDO), an overlaid weather barrier, high pressure laminates (HPL), or thermally fused laminates (TFL).

[0079] According to a third aspect, a composite article may be produced by pressure infusing lumber or wood veneer with the adhesive composition. The lignin-containing material / carbohydrate additive / optional additive mixture is first mixed with the acid catalyst at about 25 - 35°C to provide a single phase, homogenous composition. The composition may then be loaded into an infusion chamber containing the lumber. Exemplary species of wood lumber include Douglas Fir, Southern Yellow Pine, spruce, larch, maple, oak, bamboo, or a mixture of. The infusion chamber is then sealed and pressure is applied in the range of 50 psi to 150 psi for a period of time, such as 1-2 hours. The pressure may then be reduced down to atmospheric pressure, and the remaining composition is removed and can be recycled. Once the composition is removed from the infusion chamber, the lumber is removed and set to a pre-cure state at 35 - 55°C for a period of time, such as between 5 and 24 hours. The pre-cure state may be a partially cured or “B-staged” state, whereby the adhesive composition is heated to a tackifying temperature without cross-linking, such that the adhesive composition will adhere the lumber or wood veneer, but remains uncured. B-staging a product allows the product to be initially produced and adhered in one location, with final curing taking place at a second location at a later date. B-staged products have increased flexibility and are often easier to transport and install before being fully cured.

[0080] Once the pre-cured lumber or wood veneer is ready to fully cure, it may be thermally cured at a temperature sufficient to cure the infused adhesive composition, thereby forming the composite article. Thermal cure can be accomplished in either an oven or Radio Frequency (RF) cured. Such composite articles may include pressure treated lumber or pressure treated veneer.

[0081] In some aspects, the composite article exhibits a wood failure (%) of at least 80% and a breaking loading of at least 90 psi, measured according to Voluntary Product Standard PS 1-22 (published by U.S. Department of Commerce on October 2, 2023).

[0082] In some aspects, the composite article meets the standards set forth in ASTM D2559 and CSA 0112.9-10.EXAMPLES

[0083] The following examples are included for the purposes of illustration, and do not limit the scope of the general inventive concepts described herein.Test Methods

[0084] The following examples utilized the test methods as provided below, unless stated otherwise.

[0085] The autoclave vacuum pressure (AVP) test was conducted according to Voluntary Product Standard PS 1-22 (published by U.S. Department of Commerce on October 2, 2023). For each sample, the panels were cut into three equal sized 1” x 3” chips for testing and the average of the three samples is provided in the test results below. Plywood shall be considered as meeting Exposure 1 adhesive bond requirements of this Standard if all test specimens taken from individual panels average 80% wood failure or greater, when tested in accordance with Section 6.1.3. Exterior Plywood shall be considered as meeting the adhesive bond requirements of this Standard if all test specimens taken from individual panels average 85% wood failure or greater when tested in accordance with Section 6.1.3.

[0086] Gel permeation chromatography (GPC) was used to perform molecular weight analyses on protected lignocellulosic biomass samples. This test was conducted on an Agilent Infinity II 1260 instrument. DMSO was used as the mobile phase and polystyrene sulfonate standards were used to generate a calibration curve. Test samples were dissolved in DMSO and then filtered through a 0.2 micrometer syringe filter to remove any insoluble material before injecting into the instrument.Example 1: Adhesives Containing Formaldehyde-Protected Lignocellulosic Biomass and a Carbohydrate Additive

[0087] Example 1(a). Preparation of formaldehyde-protected lignocellulosic biomass (FPLB) Based on total formulation weight, 155.6 g walnut shell flour (WF-7, supplied by The Willamette Valley Company, LLC), 131.4 g formaldehyde (53.2% aq. 86.8 g sulfuric acid (96.6 % t / .), 948.6 g water, and 55.1 g methanol were added to a reaction flask. The contents were heated to 95 °C for 5 hours and then cooled to 40°C. 143.8 g of sodium hydroxide (50% aq.) was added to the reaction flask to neutralize, while stirring. Flask contents were heated to 42-50 °C, under vacuum to distill off MeOH and / or methylal and / or formaldehyde (61.4 g total distillate) over 52 minutes. The reaction flask contents were filtered through Whatman 3 filter paper and washed with 2134.5 g of DI water divided into three portions and until the pH of the rinse was 6. The wet cake containing protected lignocellulosic material was lyophilized overnight to obtain the FPLB product as a dry powder.

[0088] Example 1(b). Formulation of adhesive samples. Adhesive samples 1.1 to 1.3 were formulated at ambient temperature by blending the FPLB product prepared above in Example 1(a) with propylene carbonate (PC), polyvinyl alcohol (PVOH, 11% aq.)., glycerol, TS A, water, and, where indicated, a carbohydrate additive, as listed in Table 1. Sample 1.1 contained no carbohydrate additive. Samples 1.2 to 1.3 included a carbohydrate additive: fructose and diformyl1glucose (DFG), respectively. The component loadings (wt.% based on total adhesive) are shown in Table 1.Table 1.

[0089] Example 1(c). Plywood bonding testing. A series of three-ply plywood panels were fabricated using 3” x 3” x 1 / 8” Douglas fir veneers and adhesive samples 1.1 to 1.3 at a 30-lb / l 000 sq.ft, spread rate. The assemblies were hot-pressed at 150 °C under 190 psi for press times of 3, 4, 5, and 6 minutes. The bonded specimens were subjected to AVP tests. After testing, the fracture surfaces were evaluated for wood failure (WF, %) and breaking loads (psi). The testing results are illustrated in Table 2.Table 2.

[0090] As shown in Table 2, the control adhesive (Sample 1.1), which lacks carbohydrate additive, does not reach the 80% WF threshold at the tested press times. The fructose-containing formulation with 7.0 wt.% / ?TSA (Sample 1.2) exhibits the best overall performance, achieving WF% at or above 83% and breaking loads at or above 103 psi across the press time range of 3 to 6 minutes. The high breaking loads observed for the fructose-containing samples may be attributed to increased crosslink density arising from in situ dehydration of fructose to 5-HMF andsubsequent humin network formation that co-crosslinks with the FPLB. Samples incorporating DFG (Panels 9-12) show some improvement over the panels without DFG (Panels 1-4), but do not meet target performance of 80% wood failure.Example 2: Adhesives Containing 5-HMF-Protected Lignocellulosic Biomass

[0091] Example 2(a). Preparation of 5-HMF-protected lignocellulosic biomass (HPLB). Based on total formulation weight, 13.3 wt.% walnut shell flour (WF-7, supplied by The Willamette Valley Company, LLC), 26.6 wt.% fructose, 4.9 wt.% sulfuric acid (50% acq), and 55.2 wt.% water were charged to a reactor and agitated at 95 °C for 1 hour. During the reaction, fructose dehydrated to 5-HMF in presence of the sulfuric acid catalyst, which reacted with lignin hydroxyls to form a reaction mixture. The reaction mixture was filtered and washed with water to provide a HPLB product in 95% yield.

[0092] The HPLB was analyzed by GPC, giving Mn = 257 and Mw = 897. The relatively low molecular weights demonstrate successful suppression of lignin condensation to high-molecular-weight Kraft-type lignin, as well as limited self-condensation of fructose / 5-HMF to insoluble humin networks.

[0093] Example 2(b). Formulation of adhesive sample. An adhesive sample (2.1) was prepared by blending the HPLB produced in Example 2(a) with propylene carbonate (PC), polyvinyl alcohol (PVOH, 11% aq. glycerol, TS A, and water. Component loadings (wt.% based on total adhesive) are shown in Table 3.Table 3.

[0094] Example 2(c). Plywood bonding testing. A series of three-ply plywood panels were fabricated using 3” x 3” x 1 / 8” Douglas fir veneers and adhesive sample 2.1 at a 30-lb spread rate. The assemblies were hot-pressed at 150 °C under 190 psi for press times of 4, 5, 6, and 7 minutes. The bonded specimens were subjected to AVP tests. After testing, the fracture surfaces were evaluated for WF (%) and the breaking loads (psi) were recorded. The testing results are illustrated in Table 4.Table 4.

[0095] As shown in Table 4, the HPLB-based adhesive exhibited excellent bonding performance at press times between 6 and 7 minutes, achieving high breaking loads up to 140 psi while maintaining greater than 85% WF. This Example demonstrates that fructose can be utilized as a precursor to 5-HMF, which reacts with the lignocellulosic biomass to generate a 5-HMF protected lignin component that serves as an effective wood adhesive under hot-press conditions.Example 3: Adhesives Containing Unprotected Lignin and a Carbohydrate Additive

[0096] Example 3(a). Formulation of adhesive samples. In this Example, a series of adhesive samples (3.1 through 3.8) were prepared at room temperature by blending walnut shell flour (WF-7, supplied by The Willamette Valley Company, LLC) with polyvinyl alcohol (PVOH, 11% aq. glycerol, / ?TSA, fructose, water, optional southern yellow pine (SYP, less than 200 mesh), and optional diformyl glucose (DFG), in the weight percentages shown in Table 5. Sample 3.1 contained no carbohydrate additives. The remaining samples included fructose and, in certain formulations, DFG as carbohydrate additives / co-crosslinkers.Table 5. (wt.%)

[0097] Example 3(b). Plywood bonding testing. A series of three-ply plywood panels were fabricated using 3” x 3” x 1 / 8” Douglas fir veneers and adhesive samples 3.1 to 3.8 at a 30-lb spread rate. The assemblies were hot-pressed at 150 °C under 190 psi for press times of 5, 6, and 8 minutes. The bonded specimens were subjected to AVP tests. After testing, the fracture surfaces were evaluated for WF (%). The testing results are illustrated in Table 6.Table 6.

[0098] The AVP testing results in Table 6 demonstrate that inclusion of fructose in unprotected lignocellulosic biomass-based adhesive formulations greatly improves bonding performance across press times. The improved performance may be attributed to increased crosslink density arising from in situ dehydration of fructose to 5-HMF under hot-press conditions and subsequent polymerization to humin networks that co-crosslink with the lignin, thereby enhancing boding strength.Example 4(a). SYP Treatment

[0099] 152.0 g of Southern Yellow Pine (SYP), ground to < 20 mesh (large particles), 132.5 g of Formaldehyde (53% aq. Solution), 84 g of Sulfuric Acid (96.6% aq. Solution), 676.30 g of water, and 304.2 g of MeOH were charged to a reaction flask. The contents were heated to 80°C while stirring and held at temperature for 5 hours before cooling to room temperature. The reaction flask was heated to 55°C and 310 g of distillate were collected over 25 min. The reaction contents were cooled to room temperature and washed with 2154 g of water and filtered over Whatman 3 filter paper. The protected biomass filter cake was then lyophilized, and 122.65 g of protected lignocellulosic product was collected.Example 4(b). Wood Adhesive and Plywood Panels

[0100] The protected lignocellulosic biomass product of Example 4(a) was used to prepare a wood adhesive composition according to the formulation described in Table 7. All components, excluding the pTSA and Dead-Burned MgO P98-30, were first mixed until thoroughly combined. Then the pTSA was then added and mixed for 1 minute, and then the MgO was mixed quickly until evenly dispersed and immediately prior to gluing on a 3 in x 3 in, 3-ply plywood assembly. Plywood panels were pressed immediately following glue application and assembly of plys. Finally, the plywood panels were cut into three 1-inch sections and tested for breaking strength and percent wood failure following vacuum pressure soaks, per the PS 1-22 standard. The adhesiveapplication rates, press conditions, and bond performance results are described in Table 8.Table 7. Example 4(b) Wood AdhesiveTable 8. Example 4(b) Plywood Press Conditions and PerformanceExample 5(a). Southern Yellow Pine Treatment

[0101] Southern Yellow Pine (SYP) veneers were ground to a particle size of less than 200 mesh (small particle size). 68.35 g of ground SYP, 160.27 g of formaldehyde (53% aq. solution), 47.8 g of sulfuric acid (50% aq. solution), and 484.65 g of water were added to a reaction flask. The reaction contents were heated to reflux (97.5°C) while stirring and held at temperature for 5 hours before cooling to room temperature. The reaction contents were filtered through a Whatman 3 filter paper. The filter cake was mixed with 300 g of DI water and filtered again. This step was repeated twice more with 400 g of water and then with 406 g of water. The product was dried in a desiccator under vacuum and 48 g of protected lignocellulose product was obtained.Examples 5(b) and 5(c). Wood Adhesive and Plywood Panels

[0102] The protected lignocellulosic biomass product of Example 5(a) was used to prepare wood adhesive compositions according to the formulations described in Table 9. All components, excluding the 70% pTSA solution, were first mixed until thoroughly combined. Then the 70% pTSA solution was added and mixed for 1 minute immediately prior to gluing on a 3 in x 3 in, 3-ply plywood assembly. Plywood panels were pressed immediately following glue application and assembly of plys. Finally, the plywood panels were cut into three 1-inch sections and tested for wet shear breaking strength and percent wood failure following vacuum pressure soaks, per the PS 1-22 standard. The adhesive application rates, press conditions, and bond performance results are described in Table 10.Table 9. Examples 5(b) and 5(c) Wood AdhesiveTable 10. Examples 5(a) and 5(b) Plywood Press Conditions and PerformanceExample 6(a). SYP, WF-5, and Xylose Combined Treatment

[0103] 10.6 g of SYP, ground to <200 mesh, 10.6 g of WF-5, 112.8 g of formaldehyde (53% aq.), 8.24 g of sulfuric acid (96.6% aq.), 89.08 g of Water, and 24.13 g of xylose were charged to a reaction flask. The contents were heated to reflux (93.9°C) while stirring and held at temperature for 4 hours. The temperature was decreased to 75°C and 91.71 g of Denatured Ethanol was charged to the reaction flask. The reaction was held at 75°C for one hour before distilling off ethanol and the reaction products of ethanol and formaldehyde. The reaction flask was cooled over an ice bath and then contents were filtered through a Whatman 3 filter paper. The filer cake was rinsed with 24 g of cold water before lyophilizing. 21.3g of protected biomass products were obtained.Example 6(b). Gluings

[0104] The protected lignocellulosic biomass product of Example 6(a) was used to prepare a wood adhesive composition according to the formulation described in Table 11. All components, excluding the 70% pTSA solution, were first mixed until thoroughly combined. Then the 70% pTSA solution was added and mixed for 1 minute immediately prior to gluing on a 3 in x 3 in, 3-ply plywood assembly. Plywood panels were pressed immediately following glue application and assembly of plys. Finally, the plywood panels were cut into three 1-inch sections and tested for wet shear breaking strength and percent wood failure following vacuum pressure soaks, per the PS 1-22 standard. The adhesive application rates, press conditions, and bond performance results are described in Table 12.Table 11. Example 6(b) Wood AdhesiveTable 12. Example 6(b) Plywood Press Conditions and Performance

[0105] The terminology as set forth herein is for description only and should not be construed as limiting the disclosure as a whole. All references to singular characteristics or limitations of the present disclosure shall include the corresponding plural characteristic or limitation, and vice versa, unless otherwise specified or clearly implied to the contrary by the context in which the reference is made. Unless otherwise specified, “a,” “an,” “the,” and “at least one” are used interchangeably. Furthermore, as used in the description and the appended claims, the singular forms “a,” “an,” and “the” are inclusive of their plural forms, unless the context clearly indicates otherwise.

[0106] To the extent that the term “includes” or “including” is used in the description or the claims, it is intended to be inclusive in a manner similar to the term “comprising” as that term is interpreted when employed as a transitional word in a claim. Furthermore, to the extent that the term “or” is employed (e.g., A or B) it is intended to mean “A or B or both.” When intending to indicate “only A or B but not both” then the term “only A or B but not both” will be employed. Thus, use of the term “or” herein is the inclusive, and not the exclusive use.

[0107] All combinations of method or process steps as used herein can be performed in any order, unless otherwise specified or clearly implied to the contrary by the context in which the referenced combination is made.

[0108] Unless otherwise indicated, all numbers expressing quantities of ingredients, chemical and molecular properties, reaction conditions, and so forth used in the specification and claims are to be understood as being modified in all instances by the term “about.” Accordingly, unless indicated to the contrary, the numerical parameters set forth in the specification and attached claims are approximations that may vary depending upon the desired properties sought to beobtained by the present exemplary aspects. At the very least, each numerical parameter should be construed in light of the number of significant digits and ordinary rounding approaches.

[0109] All ranges and parameters, including but not limited to percentages, parts, and ratios, disclosed herein are understood to encompass any and all sub-ranges assumed and subsumed therein, and every number between the endpoints. For example, a stated range of “1 to 10” should be considered to include any and all sub-ranges beginning with a minimum value of 1 or more and ending with a maximum value of 10 or less (e.g., 1 to 6.1, or 2.3 to 9.4), and to each integer (1, 2, 3, 4, 5, 6, 7, 8, 9, and 10) contained within the range.

[0110] The methods of the invention can comprise, consist of, or consist essentially of the essential elements of the disclosure as described herein, as well as any additional or optional element described herein, or which is otherwise useful in adhesive compositions and composite products produced therefrom.

Claims

CLAIMSWhat is claimed is:

1. An adhesive composition, comprising:a lignin-containing material;a carbohydrate additive capable of converting to 5-hydroxymethylfurfural (5-HMF); a solvent; andan acid catalyst.

2. The adhesive composition of claim 1, wherein the carbohydrate additive is selected from the group consisting of fructose, glucose, high fructose corn syrup, sucrose diformyl glucose, and mixtures thereof.

3. The adhesive composition of claim 1 or claim 2, wherein the lignin-containing material is lignocellulosic biomass or lignin.

4. The adhesive composition of any one of claims 1 to 3, wherein the carbohydrate additive is fructose.

5. The adhesive composition of any one of claims 1 to 4, wherein the lignin-containing material comprises protected lignin.

6. The adhesive composition of claim 5, wherein the protected lignin is formaldehyde-protected lignin.

7. The adhesive composition of claim 5, wherein the protected lignin is 5-hydroxymethylfurfural-protected lignin.

8. The adhesive composition of any one of claims 1 to 7, wherein the lignin-containing material comprises an unprotected lignin.

9. The adhesive composition of any one of claims 1 to 8, wherein the acid catalyst is selected from the group consisting of para-toluenesulfonic acid, methane sulfonic acid, sulfuric acid, 2-ethenylbenzenesulfonic acid, hydrochloric acid, trifluoroacetic acid, nitric acid, hydrobromic acid,hydroiodic acid, perchloric acid, phosphoric acid, hydrofluoric acid, formic acid, lignosulfonic acid, zinc chloride, aluminum chloride, iron (III) chloride, palladium chloride, boron trifluoride etherate, boron trifluoride, aluminum trifluoride, zirconium tetrachloride, and silicon tetrabromide, and combinations thereof.

10. The adhesive composition of any one of claims 1 to 9, wherein the acid catalyst is present at least 5 wt.% of the adhesive composition.

11. The adhesive composition of any one of claims 1 to 10, wherein the solvent is selected from the group consisting of glycerol, glycerol formal, and propylene carbonate, gamma valerolactone, diformylxylose (DFX), levulinic acid, Cyrene™ (Dihydrolevoglucosenone), dimethyl isosorbide, high boiling point carboxylic acids, esters, lactones, carbonates, ethers, ethyl acetate, ethanol, isopropanol, methanol, and combinations thereof.

12. The adhesive composition of any one of claims 1 to 11, wherein the adhesive composition further includes 0 to 50 wt.% of one or more auxiliary additives.

13. The adhesive composition of claim 12, wherein the one or more auxiliary additives are selected from the group consisting of a non-polar co-solvent, a polar co-solvent, a formaldehyde donor, a defoamer, a viscosity modifier, a rheology modifier, a formaldehyde scavenger, a plasticizer, a filler, a flame retardant, a lubricant, a softening agent, a pigment, a biocide, a latent acid donor, a surfactant, a dispersant, a latex, a hydrophobic agent, a neutralizing agent, and a tackifier.

14. The adhesive composition of any one of claims 1 to 13, wherein the composition is free of added formaldehyde.

15. The adhesive composition of any one of claims 1 to 14, wherein the composition includes:10 to 30 wt.% of the lignin-containing material;5 to 20 wt.% of the carbohydrate additive;5 to 15 wt.% of the acid catalyst; and15 to 50 wt.% of the solvent.

16. A composite article prepared from at least one wood substrate and the adhesive composition according to any one of claims 1 to 15.

17. The composite article of claim 16, wherein the composite article is plywood, a laminated veneer layer (LVL) product, laminated glulam beam, mass timber, oriented strand board (OSB), cross-laminated timber (CLT), particle board, medium density fiberboard (MDF), impregnated paper, or paper board.

18. The composite article of claim 16 or claim 17, wherein the composite article exhibits a wood failure (%) of at least 80% and a breaking loading of at least 90 psi, measured according to Voluntary Product Standard PS 1-22 (published by U.S. Department of Commerce on October 2, 2023).

19. A process for manufacturing a composite article comprising the steps of:applying the adhesive composition of any one of claims 1 to 15 to a substrate to form a coated substrate; andpressing the substrate at an elevated temperature and for a time sufficient to cure the adhesive composition and form the composite article.

20. A process of claim 19, wherein the composite article is plywood, a laminated veneer layer (LVL) product, laminated glulam beam, mass timber, oriented strand board (OSB), crosslaminated timber (CLT), particle board, medium density fiberboard (MDF), impregnated paper, or paper board.

21. A process for preparing a protected lignin-containing material, comprising the steps of:combining a lignin-containing material with a carbohydrate additive capable of converting to 5 -hydroxy methylfurfural (5-HMF), a solvent, and an acid catalyst to form a dispersion;dehydrating the carbohydrate additive using the acid catalyst under reaction conditions to form 5-hydroxymethylfurfural;reacting lignin in the lignin-containing material with the 5-hydroxymethylfurfural under reaction conditions to form a protected lignin dispersion containing 5-hydroxymethylfurfural-protected lignin,optionally neutralizing the protected lignin dispersion, andremoving all or a portion of the solvent from the protected lignin dispersion to yield a protected lignin-containing material containing 5- hydroxymethylfurfural protected lignin.

22. The process according to claim 21, wherein the carbohydrate additive is selected from the group consisting of fructose, glucose, high fructose com syrup, sucrose, diformyl glucose, and mixtures thereof.

23. An adhesive composition, comprising:the protected lignin-containing material prepared according to the process of claim 21 or 22;a solvent; andat least 5 wt.% of an acid catalyst.

24. The adhesive composition of claim 21, wherein the composition is free of added formaldehyde.

25. The adhesive composition of claim 23 or claim 24, wherein the composition includes:10 to 30 wt.% of the lignin-containing material;5 to 15 wt.% of the acid catalyst; and15 to 50 wt.% of the solvent.

26. The adhesive composition of any one of claims 23 to 25, wherein the acid catalyst is selected from the group consisting of para-toluenesulfonic acid, methane sulfonic acid, sulfuric acid, 2-ethenylbenzenesulfonic acid, hydrochloric acid, trifluoroacetic acid, nitric acid, hydrobromic acid, hydroiodic acid, perchloric acid, phosphoric acid, hydrofluoric acid, formic acid, lignosulfonic acid, zinc chloride, aluminum chloride, iron (III) chloride, palladium chloride, boron trifluoride etherate, boron trifluoride, aluminum trifluoride, zirconium tetrachloride, and silicon tetrabromide, and combinations thereof.

27. The adhesive composition of any one of claims 23 to 26, wherein the solvent is selected from the group consisting of glycerol, glycerol formal, and propylene carbonate, gamma valerolactone, diformylxylose (DFX), levulinic acid, Cyrene™ (Dihydrolevoglucosenone),dimethyl isosorbide, high boiling point carboxylic acids, esters, lactones, carbonates, ethers, ethyl acetate, ethanol, isopropanol, methanol, and combinations thereof.

28. The adhesive composition of any one of claims 23 to 27, wherein the composition further includes 0 to 50 wt.% of one or more auxiliary additives.

29. The adhesive composition of claim 28, wherein the one or more auxiliary additives are selected from the group consisting of a non-polar co-solvent, a polar co-solvent, a formaldehyde donor, a defoamer, a viscosity modifier, a rheology modifier, a formaldehyde scavenger, a plasticizer, a filler, a flame retardant, a lubricant, a softening agent, a pigment, a biocide, a latent acid donor, a surfactant, a dispersant, a latex, a hydrophobic agent, a neutralizing agent, and a tackifier.

30. A process for manufacturing a wood composite comprising the steps of:combining a lignin-containing material with a carbohydrate additive capable of converting to 5-hydroxymethylfurfural (5-HMF), a solvent, and an acid catalyst under reactive conditions, thereby dehydrating the carbohydrate additive and generating 5-hydroxymethylfurfural in situ, forming a wood adhesive composition;applying the wood adhesive composition to a substrate to form a coated substrate; and pressing the substrate at an elevated temperature and for a time sufficient to cure the wood adhesive and form the composite article.

31. The process according to claim 30, wherein the carbohydrate additive is selected from the group consisting of fructose, glucose, diformyl glucose, sucrose, high fructose corn syrup, and mixtures thereof,

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