Lignin wood adhesive

Abstract

Disclosed is a wood adhesive of an uncondensed lignin and an aqueous solvent. Uncondensed lignin is extracted lignin which retains a significant portion, 50% or more of the aliphatic hydroxyl functionality of the natural lignin. Also disclosed is a process for manufacturing a composite article. A process of the invention applies a wood adhesive to a substrate to form a coated substrate and presses the substrate at an elevated temperature and for a time sufficient to cure the wood adhesive and form the composite article. Exemplary composite articles include, but are not limited to, 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) and the like.

Description

[0001] LIGNIN WOOD ADHESIVE

[0002] Related Applications

[0003]

[0001] This application claims priority to and benefit of U.S. Provisional Application 63 / 693,085, filed September 10, 2024; and of European Patent Application 25175830.6, filed May 12, 2025; which are incorporated herein by reference.

[0004] Field of the Invention

[0005]

[0002] The invention relates to lignin-based adhesives and processes for using them, particularly as adhesives for wood products. The invention also provides processes for manufacturing composite articles using lignin-based adhesives.

[0006] Background

[0007]

[0003] Composite wood products are routinely used to construct walls, floors, roofs, cabinets, furniture, architectural moldings, among other products. Composite wood products are often composite wood panels, both structural and non-nonstructural panels. Common composite wood panel products are, for example, plywood, oriented strand board (OSB), particleboard (PB), and fiberboards of different densities [low density fiberboard (LDF), medium density fiberboard (MDF) and high-density fiberboard (HDF)]. At its most basic, a composite wood product is composed of wood fibers, wood chips, wood particles, or wood flour and a wood adhesive. Common wood adhesives are formaldehyde-based resins, such as urea-formaldehyde (UF), melamine-formaldehyde (MF), melamine-urea-formaldehyde (MUF) resorcinol-formaldehyde (RF), phenol-resorcinol- formaldehyde (PRF) and phenol-formaldehyde (PF) resins, and to some extent, formaldehyde-free resins, such as polymeric methylene diphenyl diisocyanate (pMDI). The formaldehyde-based resins are thermoset resins and contain a certain amount of free formaldehyde. Upon curing, formaldehyde may react with components of the resin or evaporate from the panels. There has been interest in significantly reducing or even eliminating formaldehyde in the manufacture of composite wood products.

[0008]

[0004] Lignin is a class of naturally occurring polymer which acts as a binder in wood and lignocellulosic plants. Lignin is the second most abundant natural polymer and the largest source of natural aromatic monomers. Lignin is, therefore, a renewable resource. It represents a vast, yet largely untapped, reservoir of renewable carbon with the potential to be used as a feedstock for fuels, chemicals, and materials. Currently, most lignin is produced as an industrial byproduct in pulp and paper production - such as through the Kraft process - and several million tons are generated annually, predominantly used as a low-cost fuel for energy and heat.

[0005] Lignin is rich in aromatic rings, which contribute to its mechanical strength, rigidity, and functional versatility and possesses aliphatic hydroxyl groups. With its natural origin and performance-enhancing properties, lignin holds great promise for driving eco-friendly innovation. The following linkages have been reported in lignin.

[0009] 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.

[0010]

[0006] 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 uncondensed lignins as adhesives. Nature 621, 511-515 (2023). o

[0011] According to Li Shuai's group, "different condensation degrees, as reflected, inversely, by the molar yields of the resulting aromatic monomers from their hydrogenolysis."

[0012]

[0007] Overall, as shown in the figure 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 aliphatic hydroxyl 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 / 208015 Al), different degrees of condensation can be observed by monomer yield after hydrogenolysis, where higher condensed lignin results in lower monomer yield.

[0013]

[0008] Lignin has been proposed as an ecofriendly alternative for wood adhesives used to produce composite wood products. Associating lignin with the various resin systems used in known wood adhesives has been reported. See, for example, WO 2019 / 068180 Al. These approaches, however, have utilized condensed lignin.

[0014]

[0009] With its complex structure, when lignin is extracted from a plant source, lignin undergoes a condensation reaction, forming carbon-carbon bonds making its structure even more complex and the condensed lignin less reactive - changing the lignin from its natural or native state, with a concomitant loss of hydroxyl functionality. Condensed lignin is more difficult to process and, with its decreased reactivity, has less utility and promise to be an ecofriendly alternative for wood adhesives.

[0010] There are several methods for obtaining lignin fragments. Sun et al, Bright Side of Lignin Depolymerization: Toward New Platform Chemicals, Chem. Rev. 2018, 118, 614- 678 discloses various lignin isolation methods and catalytic approaches, particularly those that preserve the P-O-4 linkages, which can significantly influence product yields and composition.

[0015] [Oil] Milled wood lignin (MWL), isolated via the Bjbrkman process, represents one of the most structurally preserved forms of lignin available for research purposes. The main advantage of this method lies in its ability to extract lignin under very mild conditions, without the harsh chemical treatments typical of industrial pulping processes. As a result, the lignin obtained retains many of its original structural features, making it ideal for fundamental research, particularly in structural analysis using techniques like NMR spectroscopy or size exclusion chromatography. Because MWL is soluble in organic solvents, it is much easier to characterize than lignin isolated through more aggressive methods. However, the process is time-consuming, non-scalable, and yields only a small fraction, typically around 1-5% of the total lignin content.

[0016]

[0012] Aldehyde Assisted Fractionation (AAF) is a more recent technique that employs aldehydes to assist in the selective extraction of lignin. This method enhances the yield of lignin fragments with desirable properties while maintaining high purity and quality. For example, WO2017 / 178513A1 discloses the production of monomers and fragments from lignin during depolymerization of lignocellulose-containing composition in the presence of an aldehyde.

[0017]

[0013] WO 2023 / 208015 Al describes a method for derivatizing and extracting lignin from a woody biomass and using the extracted, modified lignin as an adhesive. The method derivatizes the lignin prior to extraction by reacting lignin in the woody-biomass with an agent which is one or more of formaldehyde, paraformaldehyde, acetaldehyde, paraldehyde, para-acetaldehyde, propionaldehyde, butyraldehyde, benzaldehyde, furfural, acetone, and butanone to modify the lignin. This protects the P-O-4 ether linkage from cleavage during extraction of the lignin and prevents formation of carboncarbon bonds.

[0018]

[0014] There remains a need, however, for improved wood adhesives, especially ecofriendly wood adhesives. This invention answers that need.

[0019] Summary of Invention

[0020]

[0015] The invention relates to a wood adhesive comprising, consisting essentially of, or consisting of extracted lignin and an aqueous solvent. The extracted lignin has 50% or more of the aliphatic hydroxyl functionality of natural lignin. In some aspects, the extracted lignin has 55-95% of the aliphatic hydroxyl functionality, 60-90% of the aliphatic hydroxyl functionality, 70-90% of the aliphatic hydroxyl functionality, or 80-90% of the aliphatic hydroxyl functionality of natural lignin.

[0021]

[0016] The adhesive of the invention includes 10-50 wt.% of the extracted lignin, 15-45 wt.% of the extracted lignin, 17-25 wt.% of the extracted lignin, or 20-30 wt.% of the extracted lignin.

[0022]

[0017] The extracted lignin comprises a lignin fragment A comprising at least monomer units (I) and (II): wherein Ri is selected from the group consisting of methyl, ethyl, propyl, isopropyl and n-butyl. The lignin fragment A has an average aliphatic hydroxyl group content of more than 3 mmol / g.

[0023]

[0018] The adhesive of the invention may further include additives selected from the group consisting of a non-polar solvent, a polar solvent, 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 and a tackifier.

[0024]

[0019] Aspects of the invention are further directed to a process for manufacturing a composite article comprising the steps of: applying a wood adhesive 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.

[0025]

[0020] In some aspects, 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, or medium density fiberboard (MDF). In such aspects, the process further includes pressing the substrate at least 50°C for at least 2-25 minutes.

[0026]

[0021] In other aspects, the composite article is oriented strand board and the substrate is OSB flakes. In such aspects, the wood adhesive is applied such that uncondensed lignin solids contribute 1.0 to 20 wt.% to the total panel weight and the OSB flakes coated with wood adhesive are hot pressed between 100 °C to 250 °C and pressure is applied until a desired thickness is achieved.

[0027]

[0022] In yet other aspects, the composite article is plywood, and the wood adhesive is applied by coating a lignocellulosic surface at a spread rate of from 20 lbs. to lOOIbs / lOOOft2and hot pressed between 100-190 °C for 2-20 minutes.

[0028]

[0023] In other aspects, the composite article is fiberboard, and the wood adhesive is applied by coating lignocellulosic fibers such that the wood adhesive comprises 0.5-20% solid weight percent of the panel, and is pressed to cure at 60-250 °C for 2-15 min.

[0029] Description of the Figures

[0030]

[0024] Fig. 1 shows lignin linkages identification by HSQC as a function of treatment time in dioxane / HCl / water. I stands for [3-0-4 protected (monomer unit I), II for [3-0-4 unprotected (monomer unit II), III for |3-|3 linkage (i.e., carbon-carbon (C-C) bond between two lignin monomers).

[0025] Fig. 2 shows % deprotection (left axis) and quality (right axis) of lignin fragments B (at 0 hours) and lignin fragments A as a function of treatment time in dioxane / HCl / water. The arrow shows that the squares correspond to the right y axis.

[0031]

[0026] Fig. 3 shows confirmation of deprotection by PNMR before (at 6% deprotection) and after treatment in dioxane / HCl / water. x corresponds to the theoretical value, and square the actually measured value.

[0032]

[0027] Fig. 4 shows % deprotection with different solvents and different acids all at 80°C and with 3-hour reaction time

[0033]

[0028] Fig. 5 shows % deprotection (left axis) and quality (right axis) with PGME / HjSCUat 90°C as a function of reaction time. The arrow shows that the squares correspond to the right y axis.

[0034]

[0029] Fig. 6 shows % deprotection (bars) and lignin quality (squares) with time in by heating in liquid water at various temperatures in a sealed pressure vessel.

[0035]

[0030] Fig. 7 shows UV-absorption of lignin fragments A and B at a wavelength of 280nm.

[0036]

[0031] Fig. 8 shows HSQC spectra of the propionaldehyde protected lignin (degree of deprotection: 6%) (A) and the lignin fragment obtained after the treatment with PGME / H2SO4 / H2O (degree of deprotection: 75%) (B), depicting the reduction of signals corresponding to the monomer unit I and increase of the signal assigned to monomer unit II.

[0032] Fig 9. shows31P-NMR spectra of the propionaldehyde protected lignin (degree of deprotection: 6%) (A) and the lignin fragment after the treatment with PGME / H2SO4 / H2O (degree of deprotection: 83%) (B), demonstrating the increase of aliphatic hydroxyl groups after the reaction.

[0037] Description of Invention

[0038]

[0033] A wood adhesive of the invention contains an uncondensed lignin and an aqueous solvent. The lignin is an extracted lignin which retains a significant portion, 50% or more of the aliphatic hydroxyl functionality of the natural (or native) lignin. The lignin used in wood adhesives of the invention may have 55-95% of the aliphatic hydroxyl functionality, 60-90% of the aliphatic hydroxyl functionality, 70-90% of the aliphatic hydroxyl functionality, or 80-90% of the aliphatic hydroxyl functionality of the natural lignin. The terms "natural" or "native" lignin may be used interchangeably and refer to lignin in its natural state, prior to extraction.

[0039]

[0034] Extracted Lignin

[0040]

[0035] As mentioned above WO 2023 / 208015 Al describes a method for derivatizing and extracting lignin from a woody biomass. The method derivatizes the lignin prior to extraction by reacting lignin in the woody-biomass with one or more of formaldehyde, paraformaldehyde, acetaldehyde, paraldehyde, para-acetaldehyde, propionaldehyde, butyraldehyde, benzaldehyde, furfural, acetone, and butanone to modify the lignin. While this inhibits the self-condensation reaction which occurs during the lignin extraction process, the derivatization effectively creates protected hydroxyl functionality in the derivatized lignin extract.

[0041]

[0036] According to this invention, extracted lignin which retains a significant portion, 50% or more of the aliphatic hydroxyl functionality of the natural (or native) lignin may then be produced by deprotecting the hydroxyl groups.

[0042]

[0037] Various methods are known in the art for deprotecting hydroxyl groups, though not with lignin. With lignin care should be taken not to destroy the hydroxyl functionality or the linkages in the lignin and to not condense the lignin during the deprotection. One method is to react the protected lignin with acid, such as 1 N H2SO4, at an elevated temperature, for example above 100°C, e.g. at 125°C, followed by neutralization with a base, and then lyophilizing the mixture to yield an uncondensed lignin powder. The elevated temperature allows for water to evaporate during the deprotection reaction. Another method would be to bubble CO2 through an aqueous dispersion of the protected lignin extract. The carbonic acid formed from the CO2 provides the necessary acid for the deprotection. Due to the hydrophobic nature of uncondensed lignin, a wood adhesive of the invention may be an aqueous emulsion of the uncondensed lignin.

[0038] Lignin which retains a significant portion, 50% or more of the aliphatic hydroxyl functionality of the natural (or native) lignin, defined as lignin fragment A, can be produced very easily in a two- step process, where lignin fragments are first produced through aldehyde-assisted fractionation, which are then deprotected in a second step, thereby partially removing the acetal. The term lignin fragment A stands for lignin fragments that underwent the deprotecting step, i.e. have an average aliphatic hydroxyl group content of more than 3 mmol / g and comprise at least monomer units (I) and (II). The dashed lines in monomer units I and II indicate that secondary methoxy groups are present in some, but not all, instances.

[0043] Ri is selected from the group consisting of methyl, ethyl, propyl, isopropyl and n-butyl. The lignin fragments A have an average aliphatic hydroxyl group content of more than 3 mmol / g. The extracted lignin may also contain lignin fragments B, lignin fragments obtained after aldehyde- assisted fractionation, i.e. have an average aliphatic hydroxyl group content of less than 2 mmol / g. In contrast to lignin fragments A, lignin fragments B have not undergone the second step of deprotection. However, lignin fragments B may also comprise at least monomer units (I) and (II).

[0044]

[0039] The term "an average aliphatic hydroxyl group content" refers to the mean quantity of hydroxyl (-OH) groups that are bonded to aliphatic (non-aromatic) carbon atoms within the structure of lignin. In this context, it represents how many such groups are present per unit mass of lignin, expressed in millimoles per gram (mmol / g). These aliphatic hydroxyl groups are located on the side chains of lignin's phenylpropane units and differ from phenolic hydroxyl groups, which are attached directly to aromatic rings.

[0045]

[0040] This two-step process enables the straightforward production of reactive polyols. However, it was found that Ri plays a crucial role. For example, deprotecting the fragments was not possible if Ri was hydrogen (i.e., if the protection was conducted in the presence of formaldehyde) or COOH (i.e., if the protection was conducted with glyoxylic acid), as both have a tendency to self-react.

[0046] When Ri is selected from the group consisting of methyl, ethyl, propyl, isopropyl, and n-butyl, deprotection is possible without the formation of undesirable by-products. This method is straightforward, cost-effective, suitable for scaling up, and utilizes renewable resources.

[0041] The lignin fragments A accordingly have an average aliphatic hydroxyl group content of more than 3 mmol / g which enhances the reactivity of said fragments, resulting in a greater number of reactive sites available for chemical reactions. Consequently, this promotes faster and more efficient crosslinking, leading to improved mechanical properties in the final products.

[0047] Furthermore, lignin fragments A with a higher hydroxyl group content enable the production of materials with superior physical and chemical characteristics, such as increased strength, enhanced elasticity, and better thermal resistance. Additionally, these lignin fragments A contribute to optimized processing characteristics, improving the viscosity and flow behavior of the materials. This results in increased efficiency during production processes. The higher hydroxyl content also facilitates the formation of denser and more stable polymer networks, enhancing the durability and stability of the end products.

[0048]

[0042] In addition to the monomeric units I and II, both lignin fragments A and lignin fragments B can also comprise further monomeric units that are naturally occurring in lignin that are formed, for example, via P~P or 5-5 linkages. Typically, 45 to 80 % of all monomer units in the lignin fragments A and B are either monomer units I or II. Additional monomeric units may include various structures formed between coniferyl alcohol, sinapyl alcohol, and p-coumaryl alcohol, such as P~P or 5-5 linkages. The exact composition depends on the specific type of lignin. Different plant species and their respective lignin types can have varied proportions of monomeric units and linkages, resulting in distinct lignin structures and properties. During conventional lignin extraction, typically under acidic and elevated- temperature conditions, the p-O-4 linkages, which are the most abundant and reactive bonds in native lignin, are highly prone to cleavage. This cleavage leads to the formation of reactive benzylic carbocation intermediate. Once formed, this intermediate can readily undergo electrophilic aromatic substitution with other lignin units, resulting in undesired carbon-carbon (C-C) condensation reactions. These reactions form stable linkages such as p-5 or 5-5 bonds, which are not present in high abundance in native lignin but accumulate during processing. The result is a highly condensed, poorly soluble, and chemically less accessible lignin structure, which poses major challenges for downstream valorization. To prevent this, an aldehyde - such as propionaldehyde - is added during the extraction process. It reacts with the a-hydroxyl group next to the p-O-4 linkage, forming a stable cyclic acetal. This stabilizes the a-position and prevents the formation of reactive benzylic carbocations in the first place. As a result, the p-O-4 linkages remain intact, and undesired condensation reactions are largely avoided. However, naturally occurring carbon-carbon linkages in lignin, such as P~P and 5-5 bonds, are not affected by this process. These linkages are inherently more stable and do not react with the aldehyde under the conditions used in aldehyde-assisted fractionation. Therefore, there is no need to specify the "further monomeric units that are naturally occurring in lignin and are connected for example via P~P or 5-5 linkages" as they are neither affected by the aldehyde- assisted fractionation nor by the subsequent deprotection step. An extracted lignin with fragments A and B consists of 45 to 80% monomer units I and 11, preferably 60 to 75 %, while the remainder comprises other monomeric units that are naturally occurring in lignin and differ from monomeric units I and II. With the method described here, the amount of monomer unit I is reduced, while the amount of monomer unit II is increased. However, lignin fragments A always contain both monomer units I and monomer unit II.

[0049]

[0043] Lignin which retains a significant portion (50% or more) of the aliphatic hydroxyl functionality of the natural (or native) lignin having fragments A has an outstanding quality, as the number of aromatic monomers that can be produced via catalytic reductive depolymerization (which cleaves ether units in native lignin structures) per gram lignin is more than 1.4 mmol, preferably even more than 1.6 mmol per gram lignin. Such a high number of monomers per gram of lignin indicates that the lignin has undergone very limited degradation or condensation during extraction and therefore provides a greater density of reactive functional groups.

[0050]

[0044] Preferably, lignin fragments A have an average aliphatic hydroxyl group content of more than 4 mmol / g, preferably more than 6 mmol / g and even more preferably more than 7.5 mmol / g. This elevated hydroxyl content enhances reactivity by increasing the number of reactive sites, which promotes faster and more efficient crosslinking, leading to improved mechanical properties. The average aliphatic hydroxyl group content can be controlled through the method according to the present invention, allowing for a tailored average aliphatic hydroxyl group content that meets the desired properties of the final product. Furthermore, the short alkyl chain Ri of monomer unit I minimizes the risk of negatively impacting subsequent reactions.

[0051]

[0045] Especially preferred are lignin fragments A, wherein Ri in monomer unit I is ethyl, i.e,

[0052]

[0046] The dashed line in monomer unit (IA) indicates that hydroxymethyl and secondary methoxy groups are present in some, but not all, instances. The presence of propionaldehyde during aldehyde-assisted fractionation ensures effective stabilization of the resulting lignin fragments B but also allows for a very efficient deprotection step, as propionaldehyde provides an optimal balance of reactivity, selectivity, handleability, and safety. As a result, it yields lignin fragments A characterized by a high average content of aliphatic hydroxyl groups.

[0053]

[0047] Lignin fragments A preferably comprise 4 to 85 monomer units, and more preferably 5 to 50. Such lignin fragments A have an optimal reactivity, for example in polyurethane synthesis, where too few units may lack necessary cross-linking, while too many can complicate processing. Additionally, controlling the length of the fragments helps tailor the mechanical properties of the final product.

[0054]

[0048] To prepare lignin which retains a significant portion, 50% or more of the aliphatic hydroxyl functionality of the natural (or native) lignin, such as a lignin fragments A comprising at least monomer units (I) and (II) where Ri is selected from the group consisting of methyl, ethyl, propyl, isopropyl and n-butyl, the lignin fragments A have an average aliphatic hydroxyl group content of more than 3 mmol / g., involves the steps of providing acetal protected lignin fragments B comprising at least monomer units (I), and (II) obtained by aldehyde-assisted fractionation having an average aliphatic hydroxyl group content of less than 2 mmol / g, preferably less than 1.2 mmol / g, and subsequently treating the protected lignin fragments B through heterogeneous or homogeneous deprotection to obtain lignin fragments A.

[0055]

[0049] The skilled person knows how to obtain the protected lignin fragments B by aldehyde- assisted fractionation having an average aliphatic hydroxyl group content of less than 2 mmol / g, preferably less than 1.2 mmol / g. Typically they are obtained for example by providing a lignocellulose-containing composition, heating said composition under acidic conditions (for example in the presence of sulfuric acid or HCI) together with an aldehyde (such as propionaldehyde), preferably at a temperature of 60 to 90°C for 2 to 20 hours, to obtain protected lignin fragments B. They have an average aliphatic hydroxyl group content of less than 2 mmol / g, preferably less than 1.2 mmol / g. Due to the selection of Ri a very high protection rate can be obtained, which is important as it directly affects the efficiency of lignin stabilization and improves the yield and quality of the extracted lignin fragments B. Typically, lignin fragments B are separated before deprotection, for example by filtration.

[0056]

[0050] The protected lignin fragments B provided in step a) are subsequently treated through heterogeneous or homogeneous deprotection to obtain lignin fragments A. Due to this protection step, the lignin fragments B having an average aliphatic hydroxyl group content of less than 2 mmol / g, preferably less than 1.2 mmol / g are deprotected to obtain the lignin fragments A having an average aliphatic hydroxyl group content of more than 3 mmol / g. Thus, the amount of monomer unit I decreases, whereas the amount of monomer unit II increases. The process according to the present invention has no negative impact on the quality of the lignin as lignin fragments A have preferably a number of monomers per gram lignin of more than 1.4 mmol, preferably even more than 1.6 mmol per gram lignin. Preferably, the method achieves a degree of deprotection of at least 50%, more preferably at least 60%, and even more preferably at least 80%. The degree of deprotection is measured by Heteronuclear Single Quantum Coherence Spectroscopy (HSQC) and defined as follows:

[0057] Degree of deprotection: integration of the signal of monomer units (ii) X 100 Integration of the signal of monomer units (i) + monomer units (ii)

[0058]

[0051] The degree of deprotection (%) may be converted to mmol aliphatic OH / g through the following equation: y= 4.19x + 0.3, where y is mmol aliphatic OH / g and x is percent deprotection.

[0059]

[0052] Within this context, "homogeneous" refers to a state where lignin fragments B are uniformly distributed, resulting in a single-phase solution. This means that lignin fragments B are fully solubilized in an organic solvent. On the other hand, "heterogeneous" describes a system where lignin fragments B are not dissolved, leading to the presence of distinct phases. In this situation, lignin fragments B are in a solid, undissolved state, while the deprotection reaction occurs in the presence of boiling water or steam or a mixture thereof, creating a mixture of solid and liquid or solid and gas or solid, liquid and gas phases.

[0060]

[0053] Especially good results could be obtained with homogeneous deprotection that takes place in an organic solvent in the presence of water and an acid. The organic solvent facilitates the solubilization of lignin fragments B, enabling effective interaction between water and the acid, which in turn promotes the removal of the acetal group. The reaction typically takes place at a temperature between 70°C and 120°C for 0.25 to 10 hours.

[0061]

[0054] The solvent is preferably selected from the group consisting of dioxane, propylene glycol methyl ether, ethanol, isopropanol, DMSO, and DMF. Due to their excellent water miscibility, these solvents provide the effective production of lignin fragments A with a high yield. In addition, high average aliphatic hydroxyl group content could be obtained. Especially good results could be obtained with propylene glycol methyl ether. This low-toxicity solvent allows for higher temperature reactions, and offers excellent solubility of lignin fragments A and B.

[0062]

[0055] The homogenous deprotection can be conducted in the presence of an acid, preferably selected from the group consisting of HCI and H2SO4. The presence of an acid leads to a higher rate of average aliphatic hydroxyl group content. Particularly good results were achieved with HCI and H2SO4. Sulfuric acid is preferable as it does not require the use of highly corrosion resistant equipment.

[0056] Heterogenous deprotection can take place in liquid water at a pressure of at least 1 bar, preferably 4.5 to 5 bar, and ideally about 4.75 bar, thus preferably with temperatures maintained between 80°C and 180°C, preferably 140°C to 150°C. The reaction time is typically between 0.2 and 12 hours. Interestingly, in this case, no lignin dissolution is required. Furthermore, the resulting lignin fragments A have a high quality, thus having a number of monomers per gram of lignin of more than 1.8 mmol / g (see Fig. 5). The heterogenous deprotection may take place in water steam at a pressure of at least 1 bar, preferably 5 to 7 bar, and ideally about 6 bar, thus preferably with temperatures maintained between 125°C and 180°C. The reaction time is typically between 0.2 and 12 hours. A higher deprotection degree is obtained than for the deprotection in liquid water.

[0063]

[0057] A heterogenous deprotection in a liquid water / water steam mixture is also possible, for example via steam explosion. Preferably, heterogenous deprotection takes place in absence of an acid. The use of non-acidic conditions minimizes the risk of corrosion and damage to reaction vessels, leading to reduced maintenance and a longer lifespan for the apparatus. Heterogenous deprotection may also take place in absence of an organic solvent. This approach reduces environmental impact by minimizing the emission of volatile organic compounds.

[0064]

[0058] An extracted lignin which retains a significant portion, more than 50% of the aliphatic hydroxyl functionality of the natural (or native) lignin, such as one comprising lignin fragments A, serves as a reactive polyol in the preparation of materials selected from the group consisting of polyurethanes, polyester resins, composite materials, thermoset resins, and other such functional materials. Lignin fragments A boast several favorable properties, making them an attractive building block for various applications. Being biobased, they contribute to sustainability by deriving from renewable resources, which helps to reduce dependence on fossil fuels. Additionally, lignin fragments A are non-toxic, ensuring safety in applications where health and safety regulations are paramount, such as in consumer products. One of the significant advantages of lignin fragments A is their flexibility in chain length, allowing for customization based on specific requirements. This adaptability enables the formulation of materials that range from highly flexible elastomers to more rigid thermoset plastics. Furthermore, the average content of aliphatic hydroxyl groups in lignin fragments A can be tailored to achieve the desired reactivity and properties, making it possible to fine-tune the performance of the final product. By leveraging its biobased and non-toxic characteristics, lignin fragments A can also contribute to more sustainable practices within these industries.

[0065]

[0059] Wood adhesive

[0066]

[0060] A wood adhesive may contain 10-50 wt.% of an extracted lignin which retains a significant portion, 50% or more of the aliphatic hydroxyl functionality of the natural lignin, including, for example, 15-45 wt.% of the extracted lignin, 17-25 wt.% of the extracted lignin, or 20-30 wt.% of the extracted lignin. In preferred embodiments, the extracted lignin used in an adhesive of the invention may have 55-95% of the aliphatic hydroxyl functionality, 60-90% of the aliphatic hydroxyl functionality, 70-90% of the aliphatic hydroxyl functionality, or 80-90% of the aliphatic hydroxyl functionality of the natural lignin. The aqueous component may be water or a mixture of water and a polar solvent. Suitable polar solvents include, for example, glycerol, ethanol, propylene carbonate, butyl Cellosolve (TM), butyl Carbitol (TM), butanetriol, diformyl xylose (DFX), levulinic acid, Cyrene, levoglucosenone, isosorbide, 1,3-dioxolane, glycerol formal, gamma-valerolactone. A polar solvent may be present in amounts up to 20 wt. %, typically between 5 to 15 wt.% or 10 wt. %.

[0067]

[0061] A wood adhesive of the invention may also contain additives known in the art for wood adhesives. For example, a wood adhesive may contain one or more additives including, but not limited to, a non-polar solvent, a polar solvent, 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 and a tackifier. Such additives may be added in amounts known in the art, typically in individual amounts of 0.01-20 wt.% of the wood adhesive. A wood adhesive may also be a one component or a two- component system where one component is the uncondensed lignin-containing component and the other a component with accelerants or other additives for curing.

[0068]

[0062] A wood adhesive may be prepared using methods known in the art, for example, by making a paste, suspension, or solution, depending on the degree of solvating effects of the liquid components on lignin. In the case of a paste application, the liquid component(s), such as water, would be added and then the uncondensed lignin powder would be shear-mixed in, creating a paste. To form an emulsion, dispersing, bodying agents, surfactants, detergents, or thickener could be added to the liquid portion prior to uncondensed lignin addition. In the case of a solution, the extracted lignin would be dissolved in the solvent system, promoting Newtonian fluid behavior.

[0069]

[0063] A wood adhesive of the invention 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. Exemplary lignocellulose-based composites include oriented strand board (OSB), particleboard, flake board, medium or high-density fiberboard, waferboard, plywood, laminated veneer layer (LVL), laminated glulam beam, mass timber, cross-laminated timber (CLT), medium density overlay (MDO), high density overlay (HDO), an overlaid weather barrier, high pressure laminates (HPL), or thermally fused laminates (TFL), and the like.

[0064] The invention also provides a process for manufacturing a composite article. In this process, wood adhesive is applied to a substrate to form a coated substrate, which is then pressed at an elevated temperature and for a time sufficient to cure the wood adhesive and form the composite article.

[0070]

[0065] A composite article may be produced by applying a wood adhesive to a substrate, such as by coating, blending, spraying, or impregnating the substrate with the wood adhesive, forming a coated substrate such as those mentioned above. A wood adhesive 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. The resulting composite may have 2 or more layers of the wood adhesive.

[0071]

[0066] In a process of the invention the coated substrate is then pressed using one or more plates at an elevated temperature sufficient to initiate curing of the wood adhesive and for a sufficient amount of time to complete curing, 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 uncondensed lignin in the adhesive adds mass to the composite article. As is known in the art, the temperatures and pressures vary depending upon the composite article being manufactured. The press pressure during which hot pressing occurs may be between 150 psi and 210 psi, including, for example, between 170 psi and 200 psi, and between about 185 psi and 195 psi or at 190 psi. The temperature at which the coated substrate is pressed may be at least 50°C for at least 2-25 minutes, such as a temperature of 100 °C to 250 °C for at least 2-25 minutes, a temperature of 100 °C to 150 °C for at least 2-15 minutes, or , a temperature of 60 °C to 150 °C for at least 2-15 minutes including for example, 125 °C, for 2-20 minutes, 170 °C, for 10-15 minutes, or 195 °C, for 5- 15 minutes. Optionally, the coated substrate can be pre-pressed (e.g., cold pressed) prior to hot pressing. A composite article may be pre-pressed for a period of time, such as 1 minute to 60 minutes at ambient temperature prior to hot pressing, including, for example, a pre-pressing period of 1 minute to 20 minutes, or from 1 minute to 10 minutes.

[0072]

[0067] Composite articles produced by a process of the invention 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), or the like. When specifically manufacturing particle board, medium density fiberboard (MDF), or oriented strand board (OSB), the coated substrate is formed by blending the wood adhesive with a lignocellulosic material such as, for example, wood chips, wood fiber, wood powder, or wood flour.

[0068] After the pressing step, the curing of a composite article may be completed outside the press, such as by placing the pressed substrate in an oven at an appropriate temperature ( / .e., 100 °C-150 °C) to cure the wood adhesive, forming a composite article. Alternatively, such as in the case of plywood, the composite article may be "hot stacked."

[0073]

[0069] A process of the invention may be used to manufacture oriented strand board (OSB). In an OSB manufacturing process, the wood adhesive containing the extracted lignin is applied such that the extracted lignin solids contribute 1.0 to 20% of the total panel weight. The coated OSB flakes are hot pressed between 100 °C to 250 °C and pressure is applied until the desired thickness is achieved.

[0070] A process of the invention may be used to manufacture plywood. In a plywood manufacturing process the wood adhesive containing the extracted lignin is applied by coating the lignocellulosic surface at a spread rate of from 20 lbs. to lOOIbs / lOOOft2and hot pressed between 100-190 °C for 2-20 minutes.

[0074]

[0071] A process of the invention may be used to manufacture MDF / Fiberboard. In a fiberboard manufacturing process, the wood adhesive containing the extracted lignin is applied by coating the lignocellulosic fibers such that the wood adhesive comprises 0.5-20% solid weight percent of the panel, and be pressed to cure at 60-250°C for 2-15 minutes.

[0075]

[0072] A process of the invention does not necessarily require the use as a catalyst during curing of the wood adhesive, which reduces the risk of formaldehyde generation. Furthermore, press conditions are not adversely impacted by the requirement for additional energy to deprotect the lignin. More importantly, the lack of condensation of the extracted lignin in the wood adhesive preserves the structure of the natural lignin - increasing the concentration of hydroxyl groups for bonding, increasing the plasticization effect of water during the press cycle, and increasing the similarities between the uncondensed lignin within the adhesive, and the natural lignin within the wood substrate. This promotes a seamless bond with the natural lignin in the wood substrate - leading to improved properties in the panel board such as reduced thickness swell and water absorption, as well as increased Modulus of Rupture (MOR) and Modulus of Elasticity (MOE), relative to the properties achieved with conventional pMDI or PF adhesives alone. Furthermore, the presence of more hydroxyl groups on the lignin adhesive promotes additional crosslinking with small amounts pMDI or PF adhesive which could optionally be added to the lignin adhesive.

[0076]

[0073] Examples

[0077]

[0074] Characterization Methods

[0078]

[0075] Method 1: Monomer yield by hydrogenolysis

[0079]

[0076] 100 mg of the lignin in a high-pressure Parr reactor together with 100 mg of catalyst (5wt% Ru / C) and 20 mL of ethanol. The reactor was purged twice before being pressurized with 10 bars of hydrogen. The mixture was heated and maintained at 250°C for three hours. After the reaction, the reactor was cooled down to room temperature. The resulting solution was filtered and analyzed by GC-FID. The quality of the lignin is indicated in monomers per gram lignin.

[0080]

[0077] Method 2: Determination of the deprotection degree by Heteronuclear Single Quantum Coherence Spectroscopy (HSQC)

[0081]

[0078] 40 mg of lignin fragments A or B were dissolved in 0.5 mL deuterated DMSO (DMSO-d6). The spectra were recorded on a 300 MHz Bruker advance spectrometer acquiring 32 scans and setting a 2 seconds relaxation delay (dl). The signals related to aromatic syringyl and guaiacyl units were integrated and considered for the determination of the total aromatic content. Specific signals were used to quantify the relative abundance of two monomer units over the total aromatic content: propionaldehyde acetal signal (monomer unit I) and the a position of the p-aryl ether (monomer unit II) (Fig. 8). The degree of deprotection was determined by calculating the percentage of monomer unit (ii) present in the lignin fragment, according to the following equation:

[0082] Degree of deprotection: integration of the signal of monomer units (ii) X 100 integration of the signal of monomer units (i) + monomer units (ii)

[0083]

[0079] Method 3: Quantification of the hydroxyl content by Phosphorus-31 Nuclear Magnetic Resonance (31P-NMR):

[0084]

[0080] The three following solutions were prepared prior to the analysis: 1.6:1 (v / v) pyridine:chloroform-d (solution A), 19 mg / mL cyclohexanol in 1.6:1 (v / v) pyridine:chloroform-d (solution B), and 11.4 mg / mL chromium(lll)acetylacetonate in 1.6:1 (v / v) pyridine:chloroform-d (solution C). For the analysis, 30 mg sample was dissolved in a mixture consisting of 0.5 mL solution A, 0.2 mL solution B, and 50 pL solution C. Once dissolved, 50 pL 2-chloro-4, 4,5,5- tetramethyl-l,3,2-dioxaphospholane (TMPD) was added as the phosphorylating agent. The NMR spectra were recorded on a 300 MHz Bruker advance spectrometer. The aliphatic hydroxyl groups, the phenolic hydroxyl groups, and the carboxylic acids were quantified.

[0085]

[0081] Method 4: UV-absorption by UV-Vis Spectrometry

[0086]

[0082] The UV absorption profiles of various lignins were analyzed using a Thermo Fisher Evolution 220 UV- Visible Spectrophotometer. The lignin samples were dissolved in l-methoxy-2-propanol at concentrations of 0.01 g / L, 0.001 g / L, and 0.0001 g / L, and placed in a quartz cuvette with a path length of 1 cm. The wavelengths used ranged from 195 to 800 nm. The absorption of the lignin fragments A and B at 280 nm were plotted against concentration in Figure 7.

[0087]

[0083] Example 1: Acetal removal of propionaldehyde protected lignin in dioxane with hydrochloric acid at low lignin concentration

[0088]

[0084] 6 grams of propionaldehyde protected lignin (PA-lignin, extracted from beech wood, degree of deprotection: 6%, monomer yield: 1.6 mmol of monomers per grams of lignin, aliphatic hydroxyl groups: 1.7 mmol / g, phenolic hydroxyl groups: 0.9 mmol / g), was dissolved in 330 mL of 1,4 - dioxane. 60 mL of a 1 molar aqueous solution of hydrochloric acid was slowly poured into the reaction medium. The mixture was heated and maintained at 80°C for 3 hours. Then, the solution was cooled down to room temperature and an aqueous solution of 2 molar sodium hydroxide was used to increase to pH to a value of 5. 1,4 - dioxane was evaporated under reduced pressure until a slightly viscous liquid was obtained. The remaining solution was added dropwise onto water with vigorous agitation to precipitate a solid. The latter was filtered on a nylon filter (0.45 pm pore size) and dried at 50°C under reduced pressure for at least 24 hours. A powder with a pinkish color was collected (mass yield: 52%, degree of deprotection: 78%, monomer yield: 2.0 mmol of monomers per grams of lignin, aliphatic hydroxyl groups: 5.4 mmol / g, phenolic hydroxyl groups: 1.2 mmol / g) (Fig. 1 to 3).

[0089]

[0085] Example 2: Acetal removal of propionaldehyde protected lignin in dioxane with sulfuric acid at low lignin concentration

[0090]

[0086] Example 2 was carried out as Example 1, wherein the 1 molar aqueous solution of hydrochloric acid was substituted by a 1 molar aqueous solution of sulfuric acid. A powder with a pinkish color was collected (mass yield: 66%, degree of deprotection: 63%, monomer yield: 1.8 mmol of monomers per grams of lignin; Fig. 4).

[0091]

[0087] Example 3: Acetal removal of propionaldehyde protected lignin in propylene glycol methyl ether with hydrochloric acid at low lignin concentration

[0092]

[0088] Example 3 was carried out as Example 1, wherein the 1,4 - dioxane was substituted by propylene glycol methyl ether. A powder with a pinkish color was collected (mass yield: 62%, degree of deprotection: 68%; Fig. 4).

[0093]

[0089] Example 4: Acetal removal of propionaldehyde protected lignin in propylene glycol methyl ether with sulfuric acid at low lignin concentration

[0094]

[0090] 4 grams of propionaldehyde protected lignin (PA-lignin, extracted from beech wood, degree of deprotection: 6%, monomer yield: 1.6 mmol of monomers per grams of lignin, aliphatic hydroxyl groups: 1.7 mmol / g, phenolic hydroxyl groups: 0.9 mmol / g), was dissolved in 480 mL of propylene glycol methyl ether. 120 mL of a 1 molar aqueous solution of sulfuric acid was slowly poured into the reaction medium. The mixture was heated and maintained at 90°C for 2 hours. Then, the solution was cooled down to room temperature and an aqueous solution of 2 molar sodium hydroxide was used to increase the pH to a value of 5. Propylene glycol methyl ether was evaporated under reduced pressure until a slightly viscous liquid was obtained. The remaining solution was added dropwise onto water with vigorous agitation to precipitate a solid. The latter was filtered on a nylon filter (0.45 pm pore size) and dried at 50°C under reduced pressure for at least 24 hours. A powder with a purple color was collected (mass yield: 48%, degree of deprotection: 83%, monomer yield: 2.1 mmol of monomers per grams of lignin, aliphatic hydroxyl groups: 6.2 mmol / g, phenolic hydroxyl groups: 1.3 mmol / g; Fig. 5).

[0095]

[0091] Example 5: Acetal removal of propionaldehyde protected lignin in dioxane with hydrochloric acid at increased lignin concentration

[0096]

[0092] 2 grams of propionaldehyde protected lignin (PA-lignin, extracted from beech wood, degree of deprotection: 6%, monomer yield: 1.6 mmol of monomers per grams of lignin, aliphatic hydroxyl groups: 1.7 mmol / g, phenolic hydroxyl groups: 0.9 mmol / g), was dissolved in 15 mL of 1,4 - dioxane. 3 mL of a 1 molar aqueous solution of hydrochloric acid was slowly poured into the reaction medium. The mixture was heated and maintained at 80°C for 3 hours. Then, the solution was cooled down to room temperature and an aqueous solution of 50%wt sodium hydroxide was used to increase to pH to a value of 5. 1,4 - dioxane was evaporated under reduced pressure until in a slightly viscous liquid was obtained. The remaining solution was added dropwise onto water with vigorous agitation to precipitate a solid. The latter was filtered on a nylon filter (0.45 pm pore size) and dried at 50°C under reduced pressure for at least 24 hours. A powder with a pinkish color was collected (mass yield: 65%, degree of deprotection: 49%, monomer yield: 1.9 mmol of monomers per grams of lignin).

[0097]

[0093] Example 6: Acetal removal of propionaldehyde protected lignin in dioxane with higher hydrochloric acid amount at low lignin concentration

[0098]

[0094] 2 grams of propionaldehyde protected lignin (PA-lignin, extracted from beech wood, degree of deprotection: 6%, monomer yield: 1.6 mmol of monomers per grams of lignin, aliphatic hydroxyl groups: 1.7 mmol / g, phenolic hydroxyl groups: 0.9 mmol / g), was dissolved in 105 mL of 1,4 - dioxane. 45 mL of a 1 molar aqueous solution of hydrochloric acid was slowly poured into the reaction medium. The mixture was heated and maintained at 80°C for 3 hours. Then, the solution was cooled down to room temperature and an aqueous solution of 50%wt sodium hydroxide was used to increase to pH to a value of 5. 1,4 - dioxane was evaporated under reduced pressure until a slightly viscous liquid was obtained. The remaining solution was added dropwise onto water with vigorous agitation to precipitate a solid. The latter was filtered on a nylon filter (0.45 pm pore size) and dried at 50°C under reduced pressure for at least 24 hours. A powder with a dark red color was collected (mass yield: 54%, degree of deprotection: 75%, monomer yield: 1.9 mmol of monomers per grams of lignin).

[0099]

[0095] Example 7: Acetal removal of propionaldehyde protected lignin in propylene glycol methyl ether with low sulfuric acid concentration and low lignin concentration

[0100]

[0096] Example 8 was carried out as example 4, wherein the 1 molar aqueous solution of sulfuric acid, was substituted by a 0.1 molar aqueous solution of sulfuric acid, and the temperature was increased from 80°C to 100°C. A powder with a light pink color was collected (mass yield: 55%, degree of deprotection: 58%, monomer yield: 1.8 mmol of monomers per grams of lignin).

[0101]

[0097] Example 8: Acetal removal of propionaldehyde protected lignin in propylene glycol methyl ether with sulfuric acid at 120°C and high lignin concentration

[0102]

[0098] 5 grams of propionaldehyde protected lignin (PA-lignin, extracted from beech wood, degree of deprotection: 6%, monomer yield: 1.6 mmol of monomers per grams of lignin, aliphatic hydroxyl groups: 1.7 mmol / g, phenolic hydroxyl groups: 0.9 mmol / g), was dissolved in 17 mL of propylene glycol methyl ether. 3 mL of a 1 molar aqueous solution of sulfuric acid was slowly poured into the reaction medium. The mixture was heated and maintained at 120°C for 30 minutes. Then, the solution was cooled down to room temperature and an aqueous solution of 50%wt sodium hydroxide was used to increase to pH to a value of 5. Propylene glycol methyl ether was evaporated under reduced pressure until a slightly viscous liquid was obtained. The remaining solution was added dropwise onto water with vigorous agitation to precipitate a solid. The latter was filtered on a nylon filter (0.45 pm pore size) and dried at 50°C under reduced pressure for at least 24 hours. A powder with a pinkish color was collected (mass yield: 83%, degree of deprotection: 50%, monomer yield: 1.8 mmol of monomers per grams of lignin).

[0103]

[0099] Example 9: Heterogeneous acetal removal of propionaldehyde protected lignin in water

[0104]

[0100] In a pressure resistant vessel equipped with a magnetic stir bar, 0.25 grams of propionaldehyde protected lignin (PA-lignin, extracted from beech wood, degree of deprotection: 6%, monomer yield: 1.6 mmol of monomers per grams of lignin, aliphatic hydroxyl groups: 1.7 mmol / g, phenolic hydroxyl groups: 0.9 mmol / g), was dispersed in 20 mL distilled water. The reaction mixture was heated and held at 150°C (corresponding to about 4.75 bar) for 6 hours, after which the solution was cooled down to room temperature. The powder was filtered on a nylon filter (0.45 pm pore size) dried at 50°C under reduced pressure for at least 24 hours. A powder with a beige color was collected (mass yield: 52%, degree of deprotection: 25%, monomer yield: 1.9 mmol of monomers per grams of lignin, Fig. 6)

[0105]

[0101] Comparative Example 10: Heterogeneous acetal removal of formaldehyde protected lignin in water

[0106]

[0102] In a pressure resistant vessel equipped with a magnetic stir bar, 0.25 grams of formaldehyde protected lignin (FA-lignin, extracted from beech wood degree of deprotection: 2%, monomer yield: 1.6 mmol of monomers per grams of lignin, aliphatic hydroxyl groups: 1.4 mmol / g, phenolic hydroxyl groups: 0.9 mmol / g), was dispersed in 20 mL distilled water. The reaction mixture was heated and held at 140°C for 6 hours, after which the solution was cooled down to room temperature. The powder was filtered on a nylon filter (0.45 pm pore size) dried at 50°C under reduced pressure for at least 24 hours. A powder with a black color was collected (mass yield: 91%). The obtained lignin was insoluble in any organic solvent and prevented further characterization.

[0107]

[0103] Comparative Example 11: Heterogeneous acetal removal of glyoxylic acid protected lignin in water

[0108]

[0104] In a pressure resistant vessel equipped with a magnetic stir bar, 0.25 grams of glyoxylic acid protected lignin (GA-lignin, extracted from beech wood, degree of deprotection: 43%, monomer yield: 1.2 mmol of monomers per grams of lignin, aliphatic hydroxyl groups: 2.8 mmol / g, phenolic hydroxyl groups: 1.1 mmol / g), was dispersed in 20 mL distilled water. The reaction mixture was heated and held at 140°C for 6 hours, after which the solution was cooled down to room temperature. The powder was filtered on a nylon filter (0.45 pm pore size) dried at 50°C under reduced pressure for at least 24 hours. A powder with a black color was collected (mass yield: 72%). The obtained lignin was insoluble in any organic solvent and prevented further characterization.

[0109]

[0105] Example 12: Fractionation of wood to produce lignin fragments B

[0110]

[0106] 400 g of beech wood was added to a 5 L round-bottom flask equipped with an overhead stirrer and placed in an oil bath. To the flask, 1320 g of 2-methyltetrahydrofuran, 144 g of propionaldehyde, 36 g of water, and 60 g of 97% sulfuric acid were added. The reaction mixture was stirred and heated at reflux for 3 hours. After completion, the mixture was allowed to cool to room temperature and was then neutralized with 94 g of 50 wt% sodium hydroxide solution. The resulting mixture was filtered through a sintered glass Buchner funnel (P4), separating the solid cellulose pulp from the liquid mother liquor. The mother liquor was concentrated on a rotary evaporator at 55 °C under 50 mbar. After cooling to room temperature, 1050 g of antisolvent (10% ethyl acetate in hexanes) was added to the oil under stirring to precipitate the lignin. The precipitated lignin was collected by filtration through a 0.45 pm nylon membrane filter, rinsed with antisolvent, and then dried in a vacuum oven at 40 °C overnight, yielding 80 g of beige lignin powder (degree of deprotection: 6%, monomer yield: 1.6 mmol of monomers per grams of lignin, aliphatic hydroxyl groups: 1.7 mmol / g, phenolic hydroxyl groups: 0.9 mmol / g).

[0111]

[0107] Example 13: Wood Adhesive

[0112]

[0108] Samples of propionaldehyde extracted lignin were prepared with varying degrees of % aliphatic hydroxyl content (free [3-0-4 functionality). The relative amounts of free hydroxyl groups from p-O-4 linkages were quantified by the area of the beta carbon at 87-84 ppm in the13C NMR spectra. Each of lignin samples was formulated into an adhesive and used to glue veneers into plywood test panels. Each panel was assembled in a 3-ply construction using 1 / 8" Douglas Fir veneer pre-cut into 3"x3" squares. Adhesive was applied using 30 lbs. of glue mix per 1000 square feet. Each specimen was subjected to PS-1- 22 AVP (autoclave-vacuum pressure) conditioning, prior to measuring % wood failure (%WF) and shear breaking load (psi).

[0113]

[0109] Table 1 describes the adhesive formulations for each set of test panels. Adhesive examples 1 and 2 were made from lignin with 50% or more of the aliphatic hydroxyl of natural lignin.

[0114] Comparative adhesive examples 1-6 were made with lignin samples with less than 50% or more of the aliphatic hydroxyl functionality of natural lignin.

[0115]

[0110] Table 2 describes the test results from all the adhesive examples, after pressing at a pressure of 190 and a platen temperature of 125°C, for a period of 2, 4, 6, 8, and 10 minutes, followed by AVP conditioning. AVP conditioning was performed in accordance with the Structural Plywood 6.1.3.2 Vacuum-pressure test: Test specimen placed in a pressure vessel and submerged in cold tap water.

[0116] 30' vacuum at 83.5- 98.5 kPa followed by 30' pressure at 450-480 kPa. The specimen is then removed from the vessel and tested while wet by tension loading to failure in a shear testing machine. Tested samples dried for 13 hours at 150F and % of wood failure visually determined in accordance with ASTM D2566. "FIT" stands for "failed-in-test" and indicates that the samples delaminated prior to being mounted in the test rig for measurement of shear breaking load and percentage wood failure (%WF).

[0117]

[0111] Adhesive example 13-1 was the only sample that demonstrated acceptable performance at the lowest catalyst loading (see result at 10 minutes), demonstrating that the higher percentage of hydroxyl groups makes it possible to reduce the amount of catalyst, because the lignin is more reactive. Although all samples demonstrated acceptable performance at the highest catalyst loading, adhesive example 13-2 was the only sample that passed the requirement for 85% WF with a pressing time of 4 minutes. Comparative examples 13-4, -5, and-6 required longer press times to pass the same criteria. At the highest catalyst loading, and a press time of 10 minutes, adhesive example 2 demonstrated the highest breaking load and the highest % WF.

[0118]

[0112] The terminology used here serves to explain not to limit the disclosure. Unless a specific context demands otherwise, singular terms should be read to include their plural forms and vice versa, and the articles "a," "an," and "the" are interchangeable with "at least one."

[0119]

[0113] The verbs "include" and "including" are intended to be open-ended in the same way "comprise" and "comprising" are interpreted in patent claims. Likewise, the conjunction "or" should be understood as "A or B or both," unless the text expressly says, "only A or B, but not both."

[0120]

[0114] Unless the context states otherwise, any set of process steps described here can be carried out in any order.

[0121]

[0115] All numerical values— amounts, temperatures, pressures, and so on— are to be taken as "about" those numbers, interpreted in light of significant digits and ordinary rounding. A stated range such as "1 to 10" covers every sub-range and individual value between 1 and 10, for example 1 to 6.1 or 2.3 to 9.4, as well as each integer from 1 through 10.

[0122]

[0116] Each expression of the invention described here (e.g., method, composition, apparatus) may comprise, consist essentially of, or consist of the elements set out in this disclosure together with any optional features useful in an invention or in any preferred or derived embodiment.

Claims

CLAIMSThe claimed invention is:

1. A wood adhesive comprising extracted lignin and an aqueous solvent, wherein the extracted lignin has 50% or more of the aliphatic hydroxyl functionality of natural lignin.

2. A wood adhesive of claim 1, wherein the extracted lignin has 55-95% of the aliphatic hydroxyl functionality, 60-90% of the aliphatic hydroxyl functionality, 70-90% of the aliphatic hydroxyl functionality, or 80-90% of the aliphatic hydroxyl functionality of natural lignin.

3. A wood adhesive of claim 1 or claim 2 comprising 10-50 wt.% of the extracted lignin, 15-45 wt.% of the extracted lignin, 17-25 wt.% of the extracted lignin, or 20-30 wt.% of the extracted lignin.

4. A wood adhesive of any one of claims 1-3, wherein the extracted lignin comprises a lignin fragment A comprising at least monomer units (wherein Ri is selected from the group consisting of methyl, ethyl, propyl, isopropyl and n-butyl; and wherein the lignin fragment A has an average aliphatic hydroxyl group content of more than 3 mmol / g.

5. A wood adhesive of claim 4, wherein Ri is ethyl.

6. A wood adhesive of any one of claims 1-5, further comprising one or more additives selected from the group consisting of a non-polar solvent, a polar solvent, 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 and a tackifier.

7. A process for manufacturing a composite article comprising the steps of: applying a wood adhesive of any one of claims 1-6 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.

8. A process of claim 7 , 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, or medium density fiberboard (MDF).

9. A process of claim 7 or 8, wherein the substrate is pressed at least 50°C for at least 2-25 minutes.

10. A process of any one of claims 7-9, wherein the composite article is oriented strand board; the substrate is OSB flakes; the wood adhesive is applied such that uncondensed lignin solids contribute 1.0 to 20 wt.% to the total panel weight and the OSB flakes coated with wood adhesive are hot pressed between 100 °C to 250 °C and pressure is applied until a desired thickness is achieved.

11. A process of any one of claims 7-9, wherein the composite article is plywood, and wherein the wood adhesive is applied by coating a lignocellulosic surface at a spread rate of from 20 lbs. to lOOIbs / lOOOft2and hot pressed between 100-190 °C for 2-20 minutes.

12. A process of any one of claims 7-9, wherein the composite article is fiberboard, and wherein the wood adhesive is applied by coating lignocellulosic fibers such that the wood adhesive comprises 0.5-20% solid weight percent of the panel, and be pressed to cure at 60-250 °C for 2-15 min.

13. A composite article prepared by any one of claims 7-12.

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