Plant material with higher water stability and manufacturing method thereof

Abstract

The plant material may be infiltrated with a solution having a stabilizer and / or a stabilizer precursor. The stabilizers and / or precursors may be absorbed within amorphous and / or hemicellulosic regions of the cell wall of the plant material. After permeation, the amorphous cellulose and / or hemicellulose may be cross-linked with the stabilizer. The stabilizer precursor may include a nucleophilic agent and an electrophilic agent, and the stabilizer may include a reaction product of a nucleophilic agent and an electrophilic agent. Each of the stabilizer and / or the precursor may have a molecular weight of less than or equal to 500 g / mol during permeation. After cross-linking, the stabilizer may impart higher water stability to the plant material, in particular, to limit swelling of the plant material regardless of the duration of exposure to water and / or the amount of water absorbed by the plant material.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to U.S. Provisional Application No. 63 / 460,736, filed April 20, 2023, entitled “High Density Wood Compositions Made with Methylolated Phenol for Improved Water Resistance,” the entire contents of which are hereby incorporated by reference. TECHNICAL FIELD

[0002] The present disclosure relates generally to structures formed from plant material (e.g., wood, bamboo, etc.), and more particularly, to methods of making plant material with improved water stability. BACKGROUND

[0003] Traditional wood products, including solid sawn lumber and laminated veneer lumber, can have a density of about 300-800 kg / m 3 , a tensile strength of about 100 MPa (strong axis), a modulus of about 11 GPa (strong axis), and a compressive strength of about 50 MPa (strong axis). Traditional wood products are readily available and are commonly used in construction applications, particularly residential construction. Steel is also used in construction. In comparison to wood, steel can have a density of about 7,800-8,000 kg / m 3 , a tensile strength at yield of about 400 MPa, a modulus of about 200 GPa, and a compressive strength of about 170 MPa.

[0004] While steel is stronger than traditional wood, it takes about 110 kg of carbon to produce one cubic meter of wood, while it takes about 12,000 kg of carbon to produce one cubic meter of steel. Thus, it is desirable to replace steel with wood. This replacement strategy becomes more feasible when new modification techniques, including densification, are employed to increase the strength of wood.

[0005] In addition to strength, dimensional stability of building materials is important. Steel is more dimensionally stable than traditional wood with respect to water exposure events (e.g., rain or flooding). Steel does not absorb water and does not swell upon water exposure. Unfortunately, when structures formed from traditional plant material (e.g., wood) are exposed to water, they absorb a significant amount of water (e.g., as much as the dry weight of the plant material). Most traditional plant material products also exhibit a significant degree of swelling when they absorb water, e.g., greater than about 20%. In some cases (e.g., using high density plant material products), the amount of swelling can interfere with adjacent components within a building structure being properly assembled together. This can increase labor and complexity of the construction process. For example, when traditional wood building materials are exposed to water (e.g., flooding) in an existing building, the resulting swelling can sometimes be irreversible and can require repair.

[0006] While there are many coatings and sealants to improve the water resistance of wood and other plant materials, these coatings and sealants typically work by forming a layer on the outer surface of the material. In many cases, these coatings are hydrophobic and effectively slow the rate of water absorption into the treated material. However, if exposed to water long enough, the plant material will fully hydrate and swell. In addition, when swelling occurs, the applied coating can crack and / or detach from the plant material surface. While oils (e.g., tung oil, alkyd resins, etc.) have been used on wood to improve water resistance, these oils are limited in their ability to effectively absorb into key areas of the plant material anatomy responsible for swelling due, at least in part, to the hydrophobic nature of the oils. In fact, while this absorbed oil can slow water absorption events, if exposed to water for a period of time, the treated plant material will eventually fully hydrate and swell.

[0007] Aspects of the disclosed subject matter can address one or more of the issues and drawbacks described above, among others. SUMMARY

[0008] Aspects of the present disclosure provide compressed plant materials that are more resistant to swelling in the presence of moisture and methods for making such plant materials. The plant material can be modified by uniformly absorbing a stabilizer precursor that penetrates the cross-section of the plant material. In some aspects, the stabilizer precursor can be transported to specific regions of the plant material (e.g., amorphous cellulose regions and / or hemicellulose regions) that can swell with moisture. Once at the specific regions, the precursor reacts to form a stabilizer. In some aspects, the stabilizer formed from this stabilizer precursor can be present in the plant material at a concentration greater than about 10% by weight of the plant material, e.g., greater than about 20% by weight of the plant material, greater than about 30% by weight of the plant material, greater than about 40% by weight of the plant material, greater than about 50% by weight of the plant material, greater than about 60% by weight of the plant material, greater than about 70% by weight of the plant material, greater than about 80% by weight of the plant material, greater than about 90% by weight of the plant material, greater than about 95% by weight of the plant material, greater than about 98% by weight of the plant material, greater than about 99% by weight of the plant material, or greater than about 99.9% by weight of the plant material. 3reacts with components in the particular region (e.g., crosslinks) in a manner that significantly reduces the likelihood of water swelling. In some aspects, the compressed plant material can comprise an array of collapsed cells that are mostly aligned, where particular regions of the cells are crosslinked, and where the cells are distributed within a matrix of lignin (e.g., native and / or degraded lignin), where the lignin has also been crosslinked. In some aspects, the water-stable plant material can have exceptional strength and exhibit a unique combination of high water absorption capacity and low thickness swelling potential (e.g., < 10%, e.g., < 5%).

[0009] In some aspects, the water-stable plant material can be formed via a multi-step process. For example, in a first step of some aspects, segments of plant material (e.g., wood, e.g., lumber or veneer) that are approximately aligned in the thickness direction and the radial, tangential, or a mixture of the radial and tangential directions of the plant material can be modified by permeating the plant material with a loading solution. In some aspects, the lignin in the plant material is partially degraded by the loading solution. This degradation can facilitate subsequent compression of the plant material without rupturing the cells or breaking the lignin (or at least reducing any rupturing or breaking). In some aspects, a portion of the lignin can also be removed from the plant material in the first step. Alternatively, in some aspects, the loading solution comprises water and the plant material is heated to a temperature above about 50°C after treatment with the loading solution.

[0010] In some aspects, a second step can comprise partially drying the treated plant material, e.g., such that the treated plant material has a moisture content after drying of about 1-10% of the dry weight of the treated plant material. In some aspects, a third step can comprise permeating the treated plant material with a stabilizing agent and / or a precursor thereof under conditions suitable for transferring the stabilizing agent and / or the precursor thereof into amorphous cellulose regions and / or hemicellulose regions of the treated plant material, where a selective absorption process occurs across the entire (or at least 90%) cross-section of the plant material. In some aspects, the time associated with the permeation process can be sufficient to allow the concentration gradient of the stabilizing agent and / or the precursor thereof within the plant material to reach an equilibrium state. In some aspects, the permeation is performed under conditions that do not result in crosslinking of the stabilizing agent formed from the precursor reaction with cellulose and / or hemicellulose.

[0011] In some aspects, the fourth step can include partially drying the plant material without causing the stabilizing agent and / or precursors thereof to crosslink with the cellulose and / or hemicellulose, while obtaining a moisture content of the treated plant material after drying of about 1-25% based on the dry weight of the treated plant material. In some aspects, the fifth step can include subjecting the treated plant material to pressure (e.g., sustained pressure) along an axis parallel to the thickness direction of the plant material, for example, until the density of the plant material has been increased (e.g., to a value greater than about 900 kg / m 3 In some aspects, the compression of the plant material in the fifth step is performed without causing the stabilizing agent and / or precursors thereof to crosslink with the plant material and / or such that the partially compressed plant material has a moisture content in the range of about 1-20%.

[0012] In some aspects, the sixth step can include further drying the plant material without causing the stabilizing agent and / or precursors thereof to crosslink with the plant material, for example, such that the moisture content of the treated plant material is reduced to a value less than 10%. In some aspects, the seventh step can include subjecting the treated plant material to pressure (e.g., sustained pressure) along an axis parallel to the thickness direction of the treated plant material, for example, until the density of the plant material has been increased (e.g., to a value greater than about 1200 kg / m 3 In some aspects, the compression of the plant material in the fifth step is performed without causing the stabilizing agent and / or precursors thereof to crosslink with the plant material and / or such that the partially compressed plant material has a moisture content in the range of about 1-20%. 3 In some aspects, after compressing the plant material to the target density range (e.g., during or after the seventh step), the stabilizing agent can crosslink specific regions of the densified plant material, for example, amorphous cellulose regions, hemicellulose regions, and / or lignin (e.g., previously degraded or native lignin) regions. Alternatively or additionally, in some aspects, the fifth and sixth steps can be omitted.

[0013] In some aspects, the densified plant material crosslinked with the stabilizing agent in the specific locations can have a density value in the range of about 900-1,450 kg / m 3 and can exhibit (e.g., without swelling more than about 10% along the compression direction) an ability to absorb about 10-30% of the dry weight of the densified plant material in water.

[0014] In one or more aspects, a method can include infiltrating a plant material with a solution including a stabilizing agent and / or a stabilizing agent precursor such that the stabilizing agent and / or the stabilizing agent precursor is absorbed within amorphous cellulose regions and / or hemicellulose regions of a cell wall of the plant material. The method can further include, after the infiltrating, crosslinking the amorphous cellulose regions and / or the hemicellulose regions with the stabilizing agent. The stabilizing agent precursor can include a nucleophile and an electrophile. The stabilizing agent can include a reaction product of the nucleophile and the electrophile, or in some aspects, can be only the reaction product between the nucleophile and the electrophile. Each of the stabilizing agent and its precursor can have a molecular weight less than or equal to 500 grams per mole during the infiltrating event.

[0015] In one or more aspects, a structure can include a plant material and a stabilizing agent. The plant material can have a cell wall including amorphous cellulose regions and / or hemicellulose regions. The stabilizing agent can crosslink the amorphous cellulose regions and / or the hemicellulose regions of the cell wall of the plant material. The stabilizing agent can be a reaction product of a nucleophile and an electrophile. Each of the nucleophile, the electrophile, and the stabilizing agent can have a molecular weight less than or equal to 500 grams per mole prior to the crosslinking.

[0016] Any of the innovations of the present disclosure can be used in combination or alone. The following summary is provided to introduce a selection of concepts that are further described below in the detailed description. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter. The foregoing and other objects, features, and advantages of the disclosed technologies will be apparent from the following detailed description, as well as from the drawings. BRIEF DESCRIPTION OF DRAWINGS

[0017] Various aspects of the disclosure will be described with reference to the drawings. The drawings are not necessarily to scale, and some elements can be simplified or omitted for the sake of clarity. Wherever possible, like reference numbers have been used to refer to like elements.

[0018] Figure 1 is a simplified process flow diagram illustrating a method for manufacturing a plant material with higher water stability in accordance with one or more aspects of the disclosed subject matter.

[0019] Figure 2 illustrates radial, longitudinal, and rotary cut pieces of natural wood and cross sections in a radial-tangential plane of natural wood that can each be subjected to a water stabilization treatment in accordance with one or more aspects of the disclosed subject matter.

[0020] Figures 3A-3Bare plots of thickness swell (%) versus water absorption (%) for compressed poplar samples with and without a stabilizer, respectively. DETAILED DESCRIPTION

[0021] General

[0022] For purposes of this specification, certain aspects, advantages, and novel features of the disclosed subject matter are described herein. The disclosed methods and systems should not be construed as limiting in any manner. Instead, the present disclosure is directed to all novel and nonobvious features and aspects of the various disclosed methods and systems, alone and in various combinations and subcombinations with one another. The methods and systems are not limited to any particular aspect or feature or combination of aspects and features, nor do the disclosed aspects require that any one or more of the advantages described above be present. The technology from any disclosed aspect can be combined with technology from any other disclosed aspect or aspects without excluding any combinations of the technology from any one or more aspects. In view of the many possible aspects of the technology, one of ordinary skill in the art will appreciate that the air shown are merely examples and should not be construed as limiting the scope of the disclosed technology.

[0023] Although the operations of some of the disclosed methods are described in a particular, sequential order for convenient presentation, it should be understood that this manner of description encompasses rearrangement, unless a particular ordering is required by specific language set forth below. For example, operations described sequentially can in some cases be rearranged or performed concurrently. Moreover, for the sake of simplicity, the attached drawings can not show the various ways in which the disclosed methods can be used in conjunction with other methods. Additionally, the description sometimes uses terms like "provide" or "achieve" to describe the disclosed methods. These terms are high-level abstractions of the actual operations that are performed. The actual operations that correspond to these terms can vary depending on the particular implementation and are readily recognizable by one of ordinary skill in the art.

[0024] The disclosure of a range of values should be understood to include each and every value within the range, including the end points, unless otherwise indicated. All numbers expressing quantities of components, molecular weights, percentages, temperatures, times, and so forth as used in the specification or claims are to be understood as being modified in all instances by the term "about," unless otherwise indicated. Accordingly, unless otherwise indicated, the numerical parameters are approximations. When directly and explicitly distinguished from the context, the numerical parameters are not approximations. Whenever "about" is used, the term "about" means that the value in question can vary from the stated value by up to 10%, unless otherwise stated or unless otherwise evident from the context.

[0025] Directional and other relative terms can be used to facilitate discussion of the drawings and principles of the present disclosure, but are not intended to be limiting. For example, certain terms such as "inner," "outer," "upper," "lower," "top," "bottom," "interior," "exterior," "left," "right," "front," "rear," "back," and the like can be used herein. Such terms are used for purposes of clarity only, and are not intended to be limiting. For example, the term "upper" can be used to describe a portion of a component that is closer to a top than a bottom, and the term "lower" can be used to describe a portion of a component that is closer to a bottom than a top. Such terms are used for purposes of clarity only, and are not intended to be limiting. For example, a "upper" portion can become a "lower" portion when the object is turned over. However, the object remains the same object, and the portion remains the same portion.

[0026] As used herein, "including" means "comprising" and the singular forms "a" or "an" or "the" include plural references unless the context clearly dictates otherwise. The term "or" means a single element or a combination of elements as the alternative is intended unless the context clearly indicates otherwise.

[0027] While various components, parameters, operating conditions, etc. have alternatives, this does not mean that the alternatives are necessarily equivalent and / or perform equally well. Unless otherwise stated, alternatives are not necessarily listed in order of preference. Unless otherwise stated, any group defined below can be substituted or unsubstituted.

[0028] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. Although methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present disclosure, suitable methods and materials are described below. The materials, methods, and examples are illustrative only and not intended to be limiting. The features of the presently disclosed subject matter will become more fully apparent from the following detailed description and the appended claims.

[0029] Summary of Terms

[0030] The following is provided to facilitate a description of the various aspects of the disclosed subject matter, and to guide those skilled in the art to practice the disclosed subject matter.

[0031] Plant Material : Plantae Any part of a photosynthetic eukaryote grown in its natural state (e.g., a part cut via mechanical means or otherwise). In some aspects, the plant material comprises wood (e.g., hardwood or softwood) or bamboo (e.g., Phyllostachys edulis). In some aspects, the plant material comprises a plant cell, a plant tissue, or a plant organ. Oligostachyaceae For example, but not limited to Phyllostachys edulis , Phyllostachys bambusoides , Phyllostachys nigra ,Phyllostachys violascens Phyllostachys guangdongensis Phyllostachys aurea Phragmites australis Arundo donax Miscanthus sinensis Miscanthus sacchariflorus Pennisetum setaceum For example, the natural wood can be any type of hardwood (e.g., having a natural lignin content in the range of 18-25 wt%) or softwood (e.g., having a natural lignin content in the range of 25-35 wt%), such as, but not limited to, basswood, poplar, ash, alder, aspen, balsa, beech, birch, cherry, hickory, chestnut, coconut palm, elm, hickory, maple, oak, rosewood, plum, walnut, willow, cypress, red cedar, Douglas fir, hemlock, larch, pine, redwood, spruce, tamarisk, juniper, and yew. In other aspects, the plant material includes a reed (e.g., common reed (Phragmites australis), giant reed (Arundo donax), Burmese reed (Arundo donax var. vulgaris), sweet cane (Arundo donax), little reed (Calamagrostis epigejos), paper reed (Phalaris arundinacea), black cattail (Typha angustifolia), cattail (Typha latifolia), bulrush (Typha domingensis), sedge (e.g., a species selected from the family Cyperaceae or the family Poaceae), hemp (e.g., a species selected from the family Cannabaceae), or grass (e.g., a species selected from the family Poaceae or the family Gramineae). Alternatively, in some embodiments, the plant material can be any type of fibrous plant that is composed of lignin and cellulose. For example, the plant material can be sugar cane bagasse (e.g., formed from treated residue of sugar cane or sorghum stalks) or straw (e.g., formed from treated residue of a cereal plant such as rice, wheat, millet, or corn). Cyperus alternifolius Typha spp. Acorus calamus Roemeria hybrida Spartina pectinata Glyceria striata Leymus mollis Poaceae Early maturing Lignin-degraded plant material Partially delignified Lignin-modified In situ In situ

[0032] In situ : a plant material that has been modified by one or more chemical treatments to (a) modify the natural lignin therein and / or (b) partially remove the natural lignin therein (i.e., partially delignified). In some aspects, the lignin-degraded plant material can substantially retain the natural microstructure formed by the cellulose-based cell walls of the natural plant material.

[0033] In situ ​​​​​​​​​​​​​​​​​​​: removing some (e.g., at least 5%) but not all (e.g., less than or equal to 95%) of the native lignin (e.g., by weight percent) from a naturally occurring plant material. In some aspects, partial delignification can be achieved by subjecting the plant material to one or more chemical treatments. In some aspects, the lignin content of the partially delignified wood can be in the range of 0.9-23.8 wt% for hardwood or bamboo, or 1.25-33.25 wt% for softwood. Lignin content in plant material before and after partial delignification can be assessed using techniques known in the art, such as Laboratory Analytical Procedure (LAP) TP-510-42618, “Determination of Structural Carbohydrates and Lignin in Biomass,” published by the National Renewable Energy Laboratory (NREL) on March 8, 2012, and ASTM E1758-01 (2020), “Standard Test Method for Determination of Carbohydrates in Biomass by High Performance Liquid Chromatography,” published by ASTM International, both of which are incorporated herein by reference. In some aspects, the partial delignification process can be as described in U.S. Pub. No. 2020 / 0223091, published July 16, 2020, entitled “Strong and Tough Structural Wood Materials, and Methods for Fabricating and Use Thereof,” and U.S. Pub. No. 2022 / 0412 002, published December 29, 2022, entitled “Bamboo Structures, and Methods for Fabrication and Use Thereof,” both of which are incorporated herein by reference.

[0034] Densified or compressed plant material : Fiber direction altering one or more properties of the native lignin in the plant material while retaining at least some (e.g., a majority) of the altered lignin in the plant material. In some aspects,Polymerization The lignin content of the plant material before and after modification can be approximately the same, e.g., such that Cross-linking The modified plant material retains at least 90% of the native lignin content (e.g., no more than 10% or no more than 1% of the native lignin content is removed). In some aspects, the plant material can be (e.g., by chemical reaction with OH - of the chemical reaction) Reaction productmodified lignin has more exposed functional groups on its surface than the native lignin of the corresponding native plant material. Alternatively or additionally, the lignin modification can reduce the molecular weight of the lignin (as compared to the native lignin), but not to the extent that the lignin becomes soluble in water (e.g., at the temperature involved in the lignin modification, e.g., 20 °C - 200 °C). The lignin content in the plant material before and after the lignin modification can be assessed using known techniques in the art, such as the Laboratory Analytical Procedure (LAP) TP-510-42618, “Determination of Structural Carbo-hydrates and Lignin in Biomass,” Version 08-March-2012, published by the U.S. National Renewable Energy Laboratory (NREL), “Standard Test Method for Determination of Carbohydrates in Biomass by High Performance Liquid Chromatography,” ASTM E1758-01 (2020), published by ASTM International, and / or TAPPI, Standard T222-om-83, “Standard Test Method for Acid-Insoluble Lignin in Wood,” all of which are incorporated herein by reference. In some aspects, the lignin modification process can be as described in U.S. Publication No. 2024 / 0083067, entitled “Waste-free Processing for Lignin Modification of Fibrous Plant Materials, and Lignin-modified Fibrous Plant Materials,” published on March 14, 2024, which is incorporated herein by reference.

[0035] Thickness: plant material that has been compressed to have a reduced thickness. In some aspects, the thickness has been reduced by at least a factor of two. In some aspects, the density of the densified plant material can be greater than the density of the starting plant material, for example, at least 0.9 g / cm 3 , for example, at least 1.1 g / cm 3 or even at least 1.2 g / cm 3 ( e.g., 1.2-1.4 g / cm 3 ). For example, the densified plant material can be, but is not limited to, as described in U.S. Patent No. 11,130,256, entitled “Strong and Tough Structural Wood Materials, and Methods for Fabricating and Use Thereof,” issued September 28, 2021, and U.S. Publication No. 2022 / 0412002, entitled “Bamboo Structures, and Methods for Fabrication and Use Thereof,” published December 29, 2022, both of which are incorporated herein by reference. In some aspects, the densified plant material is a component of an engineered plant material structure, where multiple constituent parts (e.g., layers or pieces) are coupled together via an adhesive or other coupling agent (e.g., a filler, such as carboxymethyl cellulose (CMC)), such as, but not limited to, cross-laminated timber (CLT), glued laminated timber (glulam), or bamboo (glued bamboo), laminated veneer lumber (LVL), oriented strand board (OSB), parallel strand lumber (PSL), and / or oriented structural straw board (OSSB).

[0036] Stabilizer : the direction along which a plant grows from its roots or from its main stem, where the cellulose fibers forming the cell walls of the plant are generally aligned with the fiber direction. In some cases, this fiber direction can be approximately perpendicular or corresponding to the direction of water transpiration flow from the plant. This is opposite to the radial direction, which extends outward from the central portion of the plant stem and is perpendicular to the fiber direction.

[0037] Stabilizer precursor : a chemical process in which monomers and / or oligomers react to form polymers.

[0038] Introduction: A chemical process by which a small reactive molecule (e.g., less than 500 g / mole) reacts with a polymer or macromolecule (e.g., amorphous cellulose and / or hemicellulose of a cell wall in a plant material and / or lignin in a plant material) in a way that reduces the freedom of movement of the polymer or macromolecule at the molecular level. In some aspects, crosslinking of amorphous cellulose and / or hemicellulose (e.g., via a stabilizer) can prevent volume swelling of the polymer upon water absorption. Alternatively or additionally, in some aspects, crosslinking can cause lignin molecules (e.g., degraded lignin) to become insoluble in water.

[0039] Manufacturing method examples : The product of a reaction between at least two reactants. In some aspects, the reaction product is the product of a chemical reaction between a nucleophile (e.g., a Lewis base) and an electrophile (e.g., a Lewis acid). In some aspects, the reaction product can be the product of a reaction in which all atoms present in the reactants are retained in the reaction product. In other aspects, the reaction product can be the product of a reaction in which not all atoms present in the reactants are present in the reaction product. In some aspects, the reaction product can be an adduct. In some aspects, the reaction product has a molecular weight of less than or equal to 500 g / mole.

[0040] Figure 1 : The cross-sectional dimension of a piece of plant material that is aligned with the compression direction of the present disclosure. In some aspects, the thickness dimension can be less than 25.4 mm (1.0 inch), e.g., less than or equal to 6.4 mm (0.25 inch), e.g., a value greater than 0 inches to 6.4 mm (0.25 inch). In some aspects, the thickness dimension is aligned with the radial direction of the plant material. In other aspects, the thickness dimension is aligned with the tangential direction of the plant material. In other aspects, the thickness dimension is aligned with a mixed direction of the tangential and radial directions of the plant material. Alternatively, in some aspects, the thickness dimension is at a non-orthogonal angle relative to one or both of the fiber direction and the radial direction. In some aspects, the thickness direction corresponds to the smallest cross-sectional dimension of the piece of plant material.

[0041] Figure 2 : The product of a reaction between a nucleophile precursor and an electrophile precursor. In some aspects, the stabilizer is formed from the reaction of a nucleophile and an electrophile and has the potential to crosslink certain polysaccharides (e.g., amorphous cellulose and / or hemicellulose) in specific regions within a plant cell wall. In some aspects, the stabilizer is a small molecule (e.g., less than 500 g / mole) that is hydrophilic. In certain aspects, the stabilizer can be highly water soluble. In some aspects, the stabilizer has the potential to crosslink lignin (e.g., degraded) within a plant material.

[0042] Figure 1Chemical that can react to form a stabilizing agent. In some aspects, the stabilizing agent precursor comprises an electrophile and a nucleophile. In some aspects, the stabilizing agent precursor is a small molecule (e.g., a molecular weight of less than 500 g / mole, e.g., a molecular weight ranging from greater than 0 g / mole to 500 g / mole).

[0043] Figure 1

[0044] Disclosed herein are compressed plant materials that are more resistant to swelling in the presence of moisture and methods for making the same. The present disclosure is based on the counterintuitive approach of rendering plant materials (e.g., wood) resistant to the swelling effects of water by treating the plant materials with compounds that share certain properties with water. While most techniques designed to reduce wood swelling involve applying hydrophobic substances to the wood, aspects of the disclosed subject matter provide a more effective solution by treating the wood (or other plant materials) with hydrophilic substances. Aspects of the disclosed subject matter are particularly effective at controlling excessive swelling of compressed plant material products. Because wood and most other plant materials exhibit "shape memory" properties, these plant materials are particularly susceptible to swelling when compressed during the manufacturing process. While plant materials, including wood, typically exhibit a swelling rate of about 2-8% in the radial or tangential axis when the moisture content of the plant material changes from a dry state to a fully saturated state, compressed plant materials can exhibit a swelling rate of more than 30% when changing from a dry state to a fully saturated state. Generally, the swelling rate values are greater when the plant material is compressed to a greater degree. In cases where an attempt is made to increase wood strength by compressing the wood to higher density values (e.g., in the range of 900-1450 kg / m 3 The ability to inhibit or at least reduce swelling in the presence of moisture can be important in cases where an attempt is made to increase wood strength by compressing the wood to higher density values (e.g., in the range of 900-1450 kg / m

[0045] While not wishing to be bound by theory, it is noted that when moisture is absorbed into conventional wood (or other plant materials), the moisture is initially absorbed into the cell wall tissue. Specifically, the moisture is absorbed into the regions of the cell wall that contain amorphous cellulose and / or hemicellulose. Relatively little moisture absorption occurs in the lignin-based regions of the wood. Likewise, a small amount of moisture is absorbed into the crystalline cellulose regions of the wood. Furthermore, the moisture does not transfer into the cell lumen until the cell wall has become saturated (for conventional wood, at a moisture mass of about 28-30% of the dry wood), although the lumen can absorb moisture after the cell wall has become saturated. More than 90% of the swelling in conventional solid wood when the wood gets wet can be attributed to swelling of the cell wall. Filling the lumens in wood (or other plant materials) with moisture is generally associated with very small dimensional changes in solid wood.

[0046] The stabilizers and stabilizer precursors described herein are unique at least in the context of their use in methods according to aspects of the present disclosure. According to aspects of the present disclosure, the stabilizers and stabilizer precursors are generally small in size, hydrophilic, and / or have a desired degree of water solubility (e.g., high water solubility as described herein). These properties, alone or in combination, allow these compounds to be transported to specific regions of plant material that are the cause of most of the swelling under conditions of exposure to water. In some aspects, after the stabilizer and / or precursors are diffused into the most active sites of the plant tissue, the material is compressed, and after compression (or during the final compression stage in some aspects), the stabilizer crosslinks amorphous cellulose and / or hemicellulose in a manner that prevents volume swelling of these polysaccharides. Thus, the reaction rate kinetics of the stabilizer and process conditions are controlled such that the stabilizer is activated (e.g., to crosslink) only after the wood (or other plant material) has reached its final compressed state.

[0047] In some aspects, compression of the plant material can be facilitated by performing a partial degradation of the lignin prior to compression. In these aspects, a secondary function of the stabilizer can be to crosslink the remaining degraded lignin after compression has been completed. This crosslinking of the degraded lignin can help to reduce the presence of extractives in the final product.

[0048] In some aspects, the compressed plant material comprising amorphous cellulose and / or hemicellulose that is penetrated by the stabilizer prior to compression and crosslinked with the stabilizer after compression retains some water absorption capacity, but exhibits a significantly reduced likelihood of swelling (e.g., along the direction of compression (e.g., parallel to the thickness direction)). For example, the swelling of plant material that has been treated with a stabilizer according to aspects of the disclosed subject matter along the thickness direction can be limited to no more than 10% (e.g., < 5%) regardless of the amount of water absorbed by the plant material or the duration of exposure to water. This property, in combination with the very small size of the stabilizers and stabilizer precursors, facilitates the preferential uptake and retention of water by these molecules into the regions of the plant material microstructure that preferentially absorb and retain water.

[0049] Figure 1

[0050] Figure 1Aspects of a method 100 for manufacturing a structure using or including plant material with increased water stability are shown. The method 100 can begin with process block 102, where one or more pieces of plant material can be provided. In some aspects, the provision of process block 102 can include cutting, removing, or otherwise separating the pieces of material from a parent plant. In some aspects, the parent plant can be a small diameter or young plant material (e.g., tree, bamboo stem, etc.). In some aspects, the cutting can form the plant material into a veneer, strip, piece, or strand, for example, having a thickness less than or equal to 25.4 mm (e.g., < 6.4 mm). Alternatively, in some aspects, the preparation can include pre-treating the natural plant material pieces, for example, cleaning to remove any unwanted material or contaminants in preparation for subsequent processing, forming the natural plant material into a particular shape in preparation for subsequent processing (e.g., cutting into smaller strips), or any combination of the foregoing. In some aspects, the plant material has a natural lignin content less than or equal to 15 wt.%.

[0051] In some aspects, the plant material is natural wood, which has a unique three- dimensional porous microstructure that includes and / or is defined by a plurality of interconnected cells. For example, Manufacturing examples and experimental results A hardwood microstructure 210 is shown, where vessels 212 are disposed within a hexagonal array of wood fiber cells 216 in a longitudinally extending cell region. The vessels and fiber cells can extend along a longitudinal direction L of the wood. Thus, the lumen of each vessel 212 can have an axis of extension 214 that is generally parallel to the longitudinal direction L, and the lumen of each fiber cell 216 can have an axis of extension 218 that is generally parallel to the longitudinal direction L. Radially extending cell regions are disposed between adjacent regions along a tangential direction T, where a plurality of ray cells 220 are disposed. The ray cells 220 can extend along a radial direction R of the wood. Thus, the lumen of each ray cell 220 can have an axis of extension 222 that is generally parallel to the radial direction R of the wood. Intracellular lamella are disposed between the vessels 212, fiber cells 216, and ray cells 220, which interconnect the cells together. Softwood can have a similar microstructure to hardwood, but the vessels and wood fibers are replaced by tracheids that extend along the longitudinal direction L of the wood.

[0052] The cutting direction of the original wood pieces can determine the orientation of the cell lumens in the final structure. For example, in some aspects, a natural wood piece can be cut from a tree trunk 202 of a tree 200 in a vertical or longitudinal direction (e.g., parallel to the longitudinal wood growth direction L) such that the lumens of the longitudinally extending cells are oriented generally parallel to the major face (e.g., the largest surface area) of the longitudinally cut wood piece 206. In the longitudinally cut wood piece 206, the tangential direction T can be generally perpendicular to the major face. Alternatively, in some aspects, the natural wood piece can be cut along a horizontal or radial direction (e.g., perpendicular to the longitudinal wood growth direction L) such that the lumens of the longitudinally extending cells are oriented generally perpendicular to the major face of the radially cut wood piece 204. Alternatively, in some aspects, the natural wood piece can be cut in a rotational direction (e.g., perpendicular to the longitudinal wood growth direction L and along the circumferential direction of the tree trunk 202) such that the lumens of the longitudinal cells are oriented generally parallel to the major face of the rotationally cut wood piece 208. In some aspects, the natural wood piece can be cut in any other orientation between the longitudinal, radial, and rotational cuts. In some aspects, the cutting orientation of the wood piece can affect the mechanical properties of the final structure.

[0053] Returning to Comparative example: compressed wood without stabilizer , the method 100 can proceed to decision block 104, where it is determined whether the lignin within the plant material should be degraded, e.g., via partial delignification (e.g., using the delignification process disclosed in U.S. Pub. No. 2020 / 0223091 or U.S. Pub. No. 2022 / 0412002, relevant portions of which are incorporated herein by reference) and / or lignin modification (e.g., using the lignin modification process described in U.S. Pub. No. 2024 / 0083067, relevant portions of which are incorporated herein by reference).

[0054] If degradation via modification is desired, the method 100 can proceed to process block 106, where the plant material can be infiltrated with a loading solution. The loading solution can include an aqueous sodium hydroxide solution (e.g., at a concentration between 0% and 15.0%, inclusive). Alternatively or additionally, the loading solution can include sodium sulfite and / or an oxidizing agent, such as ozone, oxygen, hydrogen peroxide, and organic peroxides. In some aspects, the loading solution can be water-based. In some aspects, the plant material can be submerged in the loading solution. For example, the submerged plant material can be subjected to one or more vacuum cycles to help facilitate absorption of the loading solution into the plant material. Alternatively, a positive pressure can be applied to the system to facilitate a faster absorption rate. The absorption of the loading solution can be performed at a temperature between about 20°C and 100°C, inclusive. The absorption of the loading solution can be performed for a period of time sufficient to achieve uniform distribution of the loading solution in the plant material. During this process, the moisture content of the plant material can be increased from a first moisture content of about 1% and 20%, inclusive, to a second moisture content of about 15% and 100%, inclusive. As used herein, the term'moisture content' is defined as 100% times the mass of water in the sample divided by the mass of dry wood.

[0055] Alternatively or additionally, in some aspects, the loading solution can include at least one chemical species that has OH - ions or is capable of generating OH - ions in solution. In some aspects, one, some, or all of the chemicals in the loading solution can be basic. In some aspects, the loading solution used in aspects of the methods described herein can include sodium hydroxide (NaOH), lithium hydroxide (LiOH), potassium hydroxide (KOH), sodium sulfite (Na2SO3), sodium sulfide (Na2S), Na n S (where n is an integer), urea (CH4N2O), sulfur dioxide (SO2), anthraquinone (AQ) (C 14H2O2), methanol (CH3OH), ethanol (C2H5OH), butanol (C4H9OH), formic acid (CH2O2), hydrogen peroxide (H2O2), acetic acid (CH3COOH), butyric acid (C4H8O2), performic acid (CH2O3), peracetic acid (C2H4O3), ammonia (NH3), p-toluenesulfonic acid (p-TsOH), sodium hypochlorite (NaClO), sodium chlorite (NaClO2), chlorine dioxide (ClO2), chlorine (Cl2), or any combination of the foregoing. Exemplary combinations of chemicals for chemical treatment can include, but are not limited to, NaOH + Na2SO3, NaOH + Na2S, NaOH + urea, NaOH + Na2SO3, NaOH + AQ, NaOH + Na2S + AQ, NaOH + Na2SO3+ AQ, Na2SO3+ AQ, NaOH + Na2S + Na n S (where n is an integer), Na2SO3+ NaOH + CH3OH + AQ, C2H5OH + NaOH, CH3OH + HCOOH, NH3+ H2O, and NaClO2+ acetic acid. In some aspects, the loading solution includes NaHSO3and / or Na2SO3. For example, the first chemical solution and the second chemical solution can be < 2 wt% NaOH and Na2SO3 (e.g., formed by adding H2SO3 acid to NaOH). In some particular aspects, the loading solution includes NaOH, LiOH, KOH, Na2O, or any combination thereof. In certain aspects of the disclosed methods, additional exemplary combinations of chemicals can include, but are not limited to, NaOH, NaOH + Na2SO3 / Na2SO4, NaOH + Na2S, NaOH + Na2SO3, NaOH / NaH2O3+ AQ, NaOH / Na2S + AQ, NaOH + Na2SO3+ AQ, Na2SO3+ NaOH + CH3OH + AQ, NaOH + Na2Sx, any of the foregoing with LiOH or KOH substituted for NaOH, or any combination of the foregoing. In some aspects, the loading solution includes NaHSO3and / or Na2SO3, which can be formed from certain loading solution chemicals. In some aspects, the concentration of the chemical for lignin modification can be 5 wt% or less, for example, in the range of 1 wt% - 4 wt% (including 1 wt% and 4 wt%). In some aspects, the plant material can be soaked in the loading solution without heating, for example, at room temperature (20-30 °C, for example, about 22-23 °C). In some aspects, the loading solution is not stirred in order to avoid disrupting the natural cellulose-based microstructure of the plant material pieces.

[0056] For example, in some aspects, pieces of plant material can be soaked in a chemical solution (e.g., 2-5% NaOH) in a container. The container can then be placed in a vacuum chamber and subjected to a vacuum (e.g., 0.1 MPa). In this way, air inside the pieces of plant material can be drawn out, and the solution is absorbed into the pieces of plant material at a faster rate. This process can be repeated more than once (e.g., 3 times) so that the channels inside the pieces of plant material can be filled with the chemical solution (e.g., for about 2 hours). After this process, the moisture content can increase (e.g., from about 10% for natural wood to about 70% or more).

[0057] Method 100 can proceed to process block 108, where the infiltrated pieces of plant material can be subjected to heat and / or pressure. For example, after absorbing the loading solution, the treated plant material can be subjected to heat and pressure to promote a reaction between the absorbed loading solution and the lignin in the plant material. The temperature associated with this process can be in the range of 20-200 °C, inclusive. The gauge pressure can be 100-1,200 MPa, inclusive. In some aspects, when the temperature is greater than about 100 °C, higher pressure can prevent or at least reduce the amount of evaporation of moisture in the plant material.

[0058] For example, the treated wood can be subjected to a pressure of about 700-850 MPa and a temperature of about 150-200 °C for about 1-5 hours. Under these conditions, the lignin in the wood can be partially degraded or modified in a way that promotes softening of the wood, especially at high temperatures. Partial degradation typically involves reducing the molecular weight of the lignin, but not to the extent that the lignin becomes soluble in water. In some aspects, the temperature of the wood that has been infiltrated with the loading solution can be adjusted to increase or decrease the extent of degradation of the lignin in the wood. After degradation, the wood can be cooled to about 20 °C, and the gauge pressure on the wood can be reduced to about 0 MPa.

[0059] In some aspects, the heating can be achieved via steam heating (e.g., via steam generated in a closed reactor (e.g., a pressure reactor), via a stream of steam in a flow-through reactor, and / or via steam from a superheated steam generator). Alternatively or additionally, in some aspects, the heating of process block 108 can be achieved via dry heating (e.g., via conduction and / or radiation of thermal energy from one or more heating elements, without the use of steam alone).

[0060] In some aspects, the infiltrated plant material pieces can be subjected to higher temperatures for a first period of time, e.g., 1-10 hours (e.g., depending on the size of the plant material pieces, thicker pieces require longer heating times). In some aspects, after the first period of time, any steam generated by heating the infiltrated plant material pieces can be released, e.g., by opening a pressure release device (e.g., a pressure relief valve) of the reactor. For example, in some aspects, the pressure release device can be effective to remove about 50% of the moisture in the modified plant material pieces. For example, in some aspects, the now softened plant material pieces can have a moisture content in the range of 30-50% by weight (including 30% and 50% by weight).

[0061] In some aspects, the infiltration and heating of the plant material pieces can be effective to modify the lignin therein, e.g., the hydroxide ions can hydrolyze ether linkages, which shortens the lignin macromolecular chains and softens the plant material pieces. In addition, the hydroxide ions can hydrolyze hemicellulose. This process can generate acidic degradation products, which can react with the alkaline solution (e.g., NaOH) and form neutral salts. In some aspects, no black liquor is observed during the lignin modification process, and the degradation products from hemicellulose and lignin can be completely fixed within the channels of the softened plant material pieces. In some aspects, the softened plant material pieces can exhibit a neutral pH, as all of the chemicals are consumed in the process.

[0062] The method 100 can proceed to decision block 110, where it is determined whether a rinse is required. If a rinse is required, the method 100 can proceed to process block 114, where the treated plant material can be rinsed, e.g., using a solvent such as, but not limited to, deionized (DI) water, an alcohol (e.g., ethanol, methanol, isopropyl alcohol, etc.), or any combination thereof. In some aspects, the treated plant material can subsequently be soaked in water or rinsed with water to remove a portion of the lignin that has been degraded to the extent that it becomes soluble in water.

[0063] If, at decision block 104, it is instead desired to partially delignify, the method 100 can proceed to process block 112, where the plant material can be subjected to one or more chemical treatments to remove at least some lignin therefrom, e.g., by soaking the plant material pieces (or portions thereof) in a chemical solution associated with the treatment. In some aspects, each chemical treatment or only some of the chemical treatments can be performed under vacuum, such that the solution associated with the treatment is encouraged to fully penetrate the cell walls and lumens of the plant material. Alternatively, in some aspects, the chemical treatments can be performed under ambient pressure conditions or high pressure conditions (e.g., about 6-8 bar). In some aspects, each chemical treatment or some of the chemical treatments can be performed at any temperature between ambient temperature (e.g., about 23 °C) and a higher temperature (e.g., about 100-160 °C) where the solution associated with the chemical treatment is boiling. In some aspects, the solution is not agitated, thereby minimizing the amount of damage to the natural cellulose-based microstructure of the plant material pieces.

[0064] In some aspects, the soaking time can range from 0.1-96 hours (including 0.1 hour and 96 hours), e.g., from 1-12 hours (including 1 hour and 12 hours). The soaking time in the solution can be influenced by the amount of lignin to be removed, the type of plant material, the size of the plant material pieces, the temperature of the solution, the pressure of the treatment, and / or agitation. For example, removing less lignin, smaller plant material piece sizes (e.g., cross-sectional thickness), higher solution temperatures, higher treatment pressures, and agitation can be associated with shorter soaking times, while removing more lignin, larger plant material piece sizes, lower solution temperatures, lower treatment pressures, and no agitation can be associated with longer soaking times.

[0065] The chemical treatments can continue (or can be repeated using subsequent solutions) until the desired reduction in lignin content in the plant material pieces is achieved. In some aspects, the lignin content can be reduced by 5% (the lignin content is 95% of the original lignin content in the natural plant material) to 95% (the lignin content is 5% of the original lignin content in the natural plant material). In some aspects, the chemical treatments reduce the hemicellulose content while reducing the lignin content, e.g., to the same or lesser extent as the lignin content reduction.

[0066] Method 100 can proceed to process block 114, where the treated plant material can be rinsed, for example, using a solvent such as, but not limited to, deionized (DI) water, an alcohol (e.g., ethanol, methanol, isopropyl alcohol, etc.), or any combination thereof. In some aspects, rinsing can be used to remove residual chemicals or particulates resulting from the chemical treatment. For example, the partially delignified plant material pieces can be partially or fully soaked in one or more rinse solutions. In some aspects, the rinse solution can be formed from equal volumes of water and ethanol. In some aspects, the rinsing can be performed without agitation, for example, to avoid disrupting the microstructure. In some aspects, the rinse solution can be used repeatedly for each repetition, for example, at least 3 times, or until a generally neutral pH is measured for the chemically treated plant material pieces.

[0067] If, at decision block 104, lignin degradation is not desired, method 100 can proceed to process block 116, where the plant material can be permeated with water. In some aspects, if the starting plant material already has a low lignin content (e.g., less than or equal to 15 wt%), lignin degradation can not be needed. Method 100 can then proceed from process block 116 to process block 118, where the water-containing plant material can be heated to a higher temperature. For example, after permeation with water, the plant material can be heated to a temperature greater than about 50°C.

[0068] If, at decision block 110, or after process blocks 114 or 118, rinsing is not needed, method 100 can proceed to process block 120, where the plant material can be dried to reduce the moisture content of the plant material pieces, for example, without removing so much water that the plant material pieces lose their softened properties (e.g., such that the moisture content is greater than or equal to about 15 wt%). In some aspects, the drying of process block 120 can be effective to reduce the moisture content of the plant material pieces from greater than 30 wt% (e.g., 30-50 wt%) to less than 25 wt% (e.g., in the range of 10-20 wt%).

[0069] In some aspects, the moisture content of the treated plant material can be reduced to about 10-20% prior to the subsequent processing step by mild drying conditions. Drying can be accomplished by using a kiln. Alternatively, drying can be accomplished by placing the treated plant material into a chamber and subsequently reducing the pressure within the chamber. In some aspects, the treated plant material can be restrained from size deformation during the drying process. For example, the treated plant material can be sandwiched between metal screens and dried at low pressure in a hot press to restrain the plant material to prevent or at least reduce size deformation while effectively drying the material. In some aspects, drying of the treated plant material can facilitate uptake of the stabilizer and / or precursor in the subsequent processing step.

[0070] Alternatively or additionally, the drying of process block 120 can include a conductive heating process, a convective heating process, and / or a radiative heating process including, but not limited to, an air drying process, a vacuum-assisted drying process, an oven drying process, a freeze drying process, a critical point drying process, a microwave drying process, or any combination of the foregoing. For example, an air drying process can include allowing the pieces of treated plant material to dry naturally in stationary or moving air, which can be at any temperature, e.g., room temperature (e.g., 23°C) or an elevated temperature (e.g., greater than 23°C). For example, a vacuum-assisted drying process can include subjecting the pieces of treated plant material (e.g., in a vacuum chamber or vacuum oven) to a reduced pressure (e.g., less than 0.1 MPa). For example, an oven drying process can include heating the pieces of treated plant material at an elevated temperature (e.g., greater than 23°C, e.g., 70°C or higher) using an oven, hot plate, or other conductive heating device, convective heating device, or radiative heating device. For example, a freeze drying process can include lowering the temperature of the pieces of treated plant material below the freezing point of the fluid therein (e.g., less than 0°C), and then reducing the pressure to cause the frozen fluid to sublimate (e.g., to less than a few millibars). For example, a critical point drying process can include immersing the pieces of treated plant material in a fluid (e.g., liquid carbon dioxide), increasing the temperature and pressure of the pieces of treated plant material beyond the critical point of the fluid (e.g., 7.39 MPa, 31.1°C for carbon dioxide), and then gradually releasing the pressure to remove the fluid, now gaseous. For example, a microwave drying process can include using a microwave oven or other microwave generating device to induce dielectric heating within the pieces of treated plant material by exposing the pieces of treated plant material to electromagnetic radiation (e.g., electromagnetic radiation at a frequency of about 915 MHz or about 2.45 GHz) within the microwave range (e.g., 300 MHz to 300 GHz).

[0071] Method 100 can proceed to process block 122, where a solution of a stabilizer precursor and / or a stabilizer can be used to infiltrate the plant material. The stabilizer precursor can include a nucleophile and an electrophile, and the stabilizer can include a reaction product of the nucleophile and the electrophile. Each stabilizer precursor can have a molecular weight less than or equal to 500 g / mole, such that during infiltration, the stabilizer precursor becomes absorbed within the amorphous cellulose regions and / or hemicellulose regions of the cell walls of the plant material. Alternatively or additionally, in some aspects, when the solution infiltrated into the plant material during process block 122 includes a stabilizer, the stabilizer can also have a molecular weight less than or equal to 500 g / mole, such that during infiltration, the stabilizer becomes absorbed within the amorphous cellulose regions and / or hemicellulose regions of the cell walls of the plant material. In some aspects, the nucleophile includes an aromatic nucleophile (e.g., phenol or cresol), and the electrophile includes an aldehyde (e.g., formaldehyde, acetaldehyde, propionaldehyde, crotonaldehyde, or glutaraldehyde), oxirane, oxazolidine, or dioxazolidine, or any combination of oxirane, oxazolidine, or dioxazolidine and an aldehyde.

[0072] In some aspects, the nucleophile is phenol, the electrophile is formaldehyde, and the stabilizer is a hydroxymethylated phenol. For example, in some aspects, the stabilizer precursor can include an aqueous solution having a viscosity less than about 40 cPs (20 °C). In some aspects, the solution includes water as a solvent and solute molecules dissolved in the water. In some aspects, all (or at least 90% of) the solute molecules in the solution have a molecular weight value less than 500 g / mole. In some aspects, all (or at least 90% of) the solute molecules in the solution have a molecular weight value less than 300 g / mole. In some aspects, all (or at least 90% of) the solute molecules are even smaller, e.g., less than 150 g / mole.

[0073] The combination of low solution viscosity and very low solute molecular weight can provide certain advantages over traditional water stabilization processes. For example, larger solute molecules cannot diffuse to the specific regions of plant material tissue that have the greatest affinity for water molecules and are the cause of most of the swelling when water is absorbed into the plant material. These regions include amorphous cellulose and amorphous hemicellulose. Alternatively or additionally, the stabilizer can be highly soluble in water, which can facilitate the spontaneous transfer of these compounds to the amorphous cellulose regions and / or hemicellulose regions of the cell walls during the infiltration process.

[0074] In some aspects of the disclosure, the stabilizing agent is highly hydrophilic. In some aspects, the stabilizing agent can be water soluble under basic conditions, under neutral conditions, or under both conditions. In certain aspects, the water solubility value of the stabilizing agent is greater than or equal to 2 g of the compound dissolved per 100 mL of water at a temperature of 20 °C, for example, greater than or equal to 5 g of the compound dissolved per 100 mL of water at a temperature of 20 °C, or greater than or equal to 10 g of the compound dissolved per 100 mL of water at a temperature of 20 °C, or greater than or equal to 15 g of the compound dissolved per 100 mL of water at a temperature of 20 °C, or greater than or equal to 20 g of the compound dissolved per 100 mL of water at a temperature of 20 °C, or greater than or equal to 25 g of the compound dissolved per 100 mL of water at a temperature of 20 °C, or greater than or equal to 30 g of the compound dissolved per 100 mL of water at a temperature of 20 °C. In some aspects of the disclosure, the stabilizing agent has a high water solubility value of greater than or equal to 30 g of the compound dissolved per 100 mL of water at a temperature of 20 °C.

[0075] As used herein, the term "dissolved solute" does not include "dispersed compounds," "suspended compounds," or "emulsified compounds." The latter compounds generally will not diffuse into the amorphous cellulose regions and / or hemicellulose regions of the plant cell wall. Thus, cross-linking of the amorphous cellulose regions and / or hemicellulose regions in the plant cell wall cannot be achieved by using dispersed compounds, suspended compounds, or emulsified compounds.

[0076] In some aspects, the stabilizing agent has the potential to cross-link the plant material tissue (amorphous cellulose and / or hemicellulose). The selection of the stabilizing agent is such that the cross-linking reaction does not occur rapidly at low temperatures (e.g., 20-50 °C). Rather, the cross-linking reaction occurs relatively slowly at higher temperatures (e.g., > 130 °C). This set of reaction rate characteristics can facilitate a process in which the plant material can first be consolidated (e.g., densified by compression) at a higher temperature (e.g., about 130 °C), and subsequently can be cross-linked at an even higher temperature (e.g., > 150 °C). The amorphous cellulose and / or hemicellulose that has been effectively cross-linked will have some water absorption capacity, but will be very limited in its ability to undergo volume swelling.

[0077] In some aspects, the stabilizer precursor can be (i) a mixture of a nucleophile and an electrophile, (ii) a reaction product of a nucleophile and an electrophile, and / or (iii) a mixture of a nucleophile, an electrophile, and a reaction product. Upon penetration, each of the electrophile, the nucleophile, and the reaction product can each have a molecular weight of less than 500 g / mole, for example, greater than 0 g / mole to less than 500 g / mole, or greater than 0 g / mole to less than 300 g / mole, or greater than 0 g / mole to 150 g / mole. Techniques for verifying that the solute molecules are low molecular weight include, but are not limited to, gel electrophoresis and mass spectrometry.

[0078] In some aspects of the disclosure, the stabilizer precursor is highly hydrophilic. In particular aspects disclosed herein, the stabilizer precursor can be water soluble under basic conditions, under neutral conditions, or under both conditions. In certain aspects, the stabilizer precursor has a water solubility value of greater than or equal to 2 g of the compound dissolved per 100 mL of water at a temperature of 20 °C, for example, greater than or equal to 5 g of the compound dissolved per 100 mL of water at a temperature of 20 °C, or greater than or equal to 10 g of the compound dissolved per 100 mL of water at a temperature of 20 °C, or greater than or equal to 15 g of the compound dissolved per 100 mL of water at a temperature of 20 °C, or greater than or equal to 20 g of the compound dissolved per 100 mL of water at a temperature of 20 °C, or greater than or equal to 25 g of the compound dissolved per 100 mL of water at a temperature of 20 °C, or greater than or equal to 30 g of the compound dissolved per 100 mL of water at a temperature of 20 °C. In some aspects of the disclosure, the stabilizer precursor has a high water solubility value of greater than or equal to 30 g of the compound dissolved per 100 mL of water at a temperature of 20 °C.

[0079] In some aspects, the nucleophile can include aromatic nucleophiles, for example, phenol, cresol, aniline, resorcinol, aminophenol, and m-phenylenediamine. Alternatively or additionally, the nucleophile can include non-aromatic nucleophiles, for example, urea and morpholine. For some of these nucleophiles, the pH of the stabilizer solution can be adjusted to achieve the desired degree of water solubility.

[0080] In some aspects, the electrophile can include aldehydes, oxiranes, and oxazolidines, including bisoxazolidines. The aldehydes can include formaldehyde, acetaldehyde, propionaldehyde, crotonaldehyde, acrolein, and glutaraldehyde. The oxazolidines and bisoxazolidines can produce stabilizers with lower volatility. An example of a suitable bisoxazolidine is methylol dioxazolidine with a molecular weight of 145 g / mole. In another example, a suitable bisoxazolidine is 5-methylol-1 -aza-3,7-dioxabicyclo[3,3,0]octane.

[0081] In some aspects, the stabilizer can include a low molecular weight reaction product obtained by reaction of the foregoing nucleophile and electrophile. Examples of suitable reaction products can include a hydroxymethylated phenol having a molecular weight of 124 g / mole, or a hydroxymethylated cresol having a molecular weight of 138 g / mole.

[0082] In some aspects, the stabilizer precursor solution can be prepared by mixing the nucleophile, electrophile, and water together in a mixing vessel. The resulting solution can then be used as the stabilizer precursor solution. The molar ratio of nucleophile to electrophile can be about 1 :0.9 to 1 :3 (e.g., 1 mole of nucleophile to 2 moles of electrophile). In some aspects, the stabilizer can include more than one nucleophile and / or more than one electrophile. The aqueous content of the solution containing the stabilizer precursor and / or stabilizer can be in the range of 20-95% (including 20% and 95%). In some aspects, for example, when the stabilizer is incorporated into the plant material by using a soak process, the aqueous content can have a significant effect on the extent of active solutes loaded into the plant material during the infiltration process. In such processes, lower aqueous content values can result in a higher extent of solutes in the plant material.

[0083] In some aspects, the stabilizing agent can be prepared by co-reacting a nucleophile with an electrophile to form a low molecular weight reaction product. For example, a hydroxymethylated phenol can be prepared by reacting a phenol with formaldehyde in an aqueous medium. A mixing tank equipped with heating and cooling systems can be charged with the phenol and optionally water, sodium hydroxide, and / or a catalyst. In some aspects, sodium carbonate can be used as the catalyst and can be added at the beginning of the manufacturing process at a level of about 0.0001-0.01% of the phenol mass. Formaldehyde can be added to the mixing tank at a specific rate or in multiple portions over a period of time with continuous stirring. In some aspects, the formaldehyde can be in the form of formalin, for example, a 50% formalin solution. In some aspects, the formaldehyde can be in the form of paraformaldehyde. The formaldehyde can be added slowly to help ensure that the mixture does not overheat as an exothermic reaction occurs between the phenol and the formaldehyde. In some aspects, the temperature of the mixture can be maintained in the range of about 50-80°C during the process. The molar ratio of formaldehyde to phenol can be about 3.0-1.0. The water content in the mixture can be about 30-80%. The sodium hydroxide level (solids content) can be about 1-15% of the phenol charge (mass / mass basis). In some aspects, it can be desirable to use a sodium hydroxide level of 0.1-3.0% of the phenol charge mass until almost all of the formaldehyde has reacted with the phenol. This approach helps to avoid disproportionation of the formaldehyde, which tends to occur at a pH value greater than about 9. Once all of the formaldehyde has been added, the mixture can be stirred and heated so that the temperature of the mixture is maintained in the range of about 50-80°C until a sample of the mixture has a viscosity of about 20-35 cPs at a temperature of 20°C. This determination can be made by using a Gardner-Holdt bubble tube or other viscosity measurement method. During the last stages of the reaction time, formaldehyde can continue to add as hydroxymethyl groups to the phenol. During this extended heating process, a small amount of oligomers can also be formed. The oligomers can be formed within the mixture and can include two or three substituted phenol groups bound together by ether linkages. The formation of oligomers cannot progress to the extent that a reaction product having a molecular weight of 500 g / mole or greater is formed. Once the viscosity target is reached, the mixture can be rapidly cooled to room temperature. In some aspects, urea can be added to the mixture at a later stage of the production process (either after or before cooling) to reduce emissions of residual formaldehyde that can be present in the mixture. In some aspects, additional sodium hydroxide can be added to the mixture at a later stage of the production process to increase the water solubility of the reaction product. In some aspects, the sodium hydroxide content of the formulation can be low or can be omitted from the formulation entirely. In some aspects, the resulting mixture can be used directly as a stabilizing agent. In other aspects, the resulting mixture can be further formulated using water, a nucleophile, or an electrophile to obtain a stabilizing agent treatment solution.

[0084] In some aspects, a high percentage of the phenolic groups in the hydroxymethylated phenol complex can exist as individual phenolic molecules, wherein about 1-3 hydroxymethyl groups are attached to the ortho and para positions of the phenolic ring. These compounds are particularly adept at being absorbed into plant tissue, particularly the amorphous cellulose and / or hemicellulose based cell wall regions. Oligomers comprising about 2-3 hydroxymethylated phenolic compounds condensed together can also be absorbed into plant tissue, including the amorphous cellulose and / or hemicellulose based cell wall regions. While the oligomers can be absorbed into the plant material tissue at a slower rate than the monomeric hydroxymethylated phenolic compounds, the small oligomers can have the advantage that their vapor pressure is lower than the vapor pressure of the hydroxymethylated phenolic monomers, which can improve the health and safety aspects of the production process.

[0085] Complexes comprising higher molecular weight condensates of hydroxymethylated phenolic compounds, such as would typically be used as the adhesive resin for plywood, oriented strand board, or other wood composites, tend to be absorbed into the cracks and vessels on the surface of the plant material, but generally are not absorbed into the cell walls of the plant material tissue. A commercial example of a higher molecular weight condensate of hydroxymethylated phenolic compounds is a phenol-formaldehyde adhesive resin under the trade name 70CR66 (manufactured by Bakelite Synthetics of Atlanta, Georgia). Higher molecular weight phenol-formaldehyde resins, such as are typically used as wood adhesives and include the complex of 70CR66, do not produce the desired product or performance attributes and are not suitable for use in accordance with the intended aspects of the disclosed subject matter. The average molecular weight of the molecules in these phenol-formaldehyde resins can be about 1,500-5,000 Da. Likewise, the molecular weight of the molecules in "green" phenol-formaldehyde resins is typically about 800-1,500 Da. Thus, the molecules in green phenol-formaldehyde resins are also too large to effectively diffuse into the critical regions of the plant tissue that are most significantly associated with water swelling.

[0086] In some aspects, one or more portions of the treated plant material can be soaked in an aqueous solution having a stabilizing agent and / or a stabilizing agent precursor. The system can be subjected to one or more vacuum cycles to help facilitate absorption of the solution into the particular target regions of the plant tissue across the entire cross-section of the plant material. In another aspect, the treated plant material and the aqueous solution are loaded into a pressure vessel and the mixture is placed under positive pressure, wherein the gauge pressure is in the range of about 100-4,500 MPa and the temperature is maintained at about 20-50 °C.

[0087] The absorption process continues for a period of time sufficient to achieve distribution of the stabilizing agent (and / or its precursor) throughout the cross-section of the treated plant material. In contrast, absorption of the stabilizing agent (and / or its precursor) only into the outer surface of the treated plant material would be insufficient and a process leading to such a result is not within the scope of the present disclosure. The soak time required for absorption of the stabilizing agent and / or its precursor throughout the cross-section of the plant material can depend on a variety of factors including the thickness and width dimensions of the plant material, the specific formulation of the stabilizing agent and / or the stabilizing agent precursor, the temperature, and the magnitude of pressure applied to the system. For example, for a hydroxymethylated phenol as the stabilizing agent, a wood segment having a thickness of 17 mm, a width of 180 mm, and a length of 244 cm can require a soak time of about 3 hours when the temperature is 25 °C and the pressure is 725 MPa.

[0088] During the stabilizing agent soak process, the treated plant material can have a moisture content that increases from a first moisture content of about 1-20% to a second moisture content of about 10-80%. The amount of absorbed stabilizing agent solute or absorbed stabilizing agent precursor solute can be about 1-30% of the dry mass of the wood.

[0089] Method 100 can proceed to decision block 124, where it is determined whether the plant material that has been infiltrated with a solution of a stabilizer precursor or stabilizer should be dried. If drying is required, method 100 can proceed to process block 126, where the plant material is dried, e.g., in a manner similar to that described above with respect to process block 120. For example, the treated and infiltrated plant material can be dried to a moisture content of about 1-25% prior to subsequent processing steps. In some aspects, the drying step can be performed in a manner that does not cause the absorption solutes of the stabilizer to prematurely crosslink with amorphous cellulose and / or hemicellulose prior to the plant material having been compressed to a target degree. Suitable drying conditions will depend on the particular stabilizer composite or stabilizer precursor composite and the size of the plant material. In some aspects, the treated and infiltrated plant material can be dried at a temperature of about 60-80°C for about 6-10 hours. Drying the plant material for this period of time without crosslinking the amorphous cellulose and / or hemicellulose can be achieved by selecting a stabilizer having a relatively high activation energy value. For example, stabilizer formulations based on low reactivity nucleophiles (e.g., phenol and cresol) can facilitate this condition. Alternatively or additionally, in some aspects, a faster drying rate can be facilitated by performing the high drying process under reduced pressure without the risk of premature crosslinking. Suitable apparatus for performing the drying process can include, but are not limited to, ovens, kilns, and drying presses. In some aspects, the treated (lignin-degraded) and infiltrated plant material can be mechanically restrained in a manner that prevents dimensional distortion during the drying process. After the drying process, the treated and infiltrated plant material can have a moisture content value in the range of about 1-20%.

[0090] After the drying of process block 126, or if no drying is required at decision block 124, method 100 can proceed to decision block 128, where it is determined whether partial compression (e.g., partial densification) is required. If partial compression is required, method 100 can proceed to process block 130, where the plant material is compressed (e.g., at least along its thickness direction) to a first density of at least 900 kg / m 3 (e.g., in the range of 900-1200 kg / m 3 In some aspects, the compression of process block 130 is controlled to avoid any (or at least a substantial portion, e.g., 90%) of the amorphous cellulose and / or hemicellulose from prematurely crosslinking due to the action of the stabilizer and / or its precursor within the plant material.

[0091] In some aspects, the plant material sheet can be pressed along a direction that intersects the fiber direction thereof. Alternatively, in some aspects, the pressing can be in a direction that is substantially perpendicular to the fiber direction, while in other aspects, the pressing can have a component that is perpendicular to the fiber direction. In either case, the partial pressing of process block 128 can be effective to reduce the thickness of the plant material, thereby increasing its density and collapsing (at least partially) natural lumens (e.g., vessels, lumens in each fiber, parenchymal cells, etc.), voids, and / or interstices within the cross-section of the plant material. In some aspects, the pressing can be along a single direction (e.g., along the radial direction R), for example, to reduce the thickness of the plant material sheet (e.g., by at least 50% as compared to the plant material sheet prior to pressing). Alternatively or additionally, in some aspects, the plant material sheet can be pressed simultaneously in two orthogonal directions (e.g., both perpendicular to the fiber direction), for example, to reduce the cross-sectional area of the plant material sheet (e.g., to produce a densified rectangular strip). Alternatively or additionally, in some aspects, the plant material sheet can be pressed sequentially in different orthogonal directions.

[0092] In some aspects, the pressing can be performed without any prior drying of the plant material sheet, or with at least some water or other fluid remaining in the plant material sheet. The pressure and duration of the pressing can depend on the dimensions of the plant material sheet prior to pressing, the desired dimensions of the plant material sheet after pressing, the water or fluid content (if any) within the plant material sheet, the temperature at which the pressing is performed, the relative humidity, and / or other factors. For example, the plant material sheet can be held under pressure for a period of time ranging from 1 minute to several hours (e.g., 1-180 minutes, including 1 minute and 180 minutes). In some aspects, the plant material sheet can be held under pressure for 3-72 hours, including 3 hours and 72 hours. In some aspects, the pressing can be performed at a pressure ranging from 0.5 MPa to 20 MPa, including 0.5 MPa and 20 MPa, for example, 5 MPa. In some aspects, the pressing can be performed without heating (e.g., cold pressing), while in other aspects, the pressing can be performed with heating (e.g., hot pressing). For example, the pressing can be performed at a temperature ranging from 20 °C to 160 °C (e.g., greater than or equal to 100 °C). When pressing the plant material at a relatively high temperature (e.g., 160 °C), the duration of the pressing process can be short enough such that the permeated stabilizer does not prematurely crosslink with the amorphous cellulose and / or hemicellulose in the plant material cell walls. In some aspects, the pressing can be effective to fully collapse the lumens of the plant material's native cellulose-based microstructure and / or can result in a density of the compressed plant material of at least 0.9 g / cm3(e.g., > 1.1 g / cm3, or > 1.2 g / cm3). 3 (e.g., > 1.1 g / cm 3 or > 1.2 g / cm 3for example, in the range of 1.3-1.5 g / cm 3

[0093] For example, the treated, infiltrated, and dried plant material can be loaded into a press, where the temperature of the top and bottom platens of the press is in the range of about 20-150°C. The treated, infiltrated, and dried plant material can be oriented in the press such that the thickness axis of the plant material is normal to the contact surfaces of the platens. The pressure applied to the treated, infiltrated, and dried plant material can be increased from 0 to about 3-8 MPa over a period of 0-10 minutes. The applied pressure can then be maintained until the treated, infiltrated, and dried plant material has been compressed to about 40-60% of the original thickness. At this point, the density of the treated, infiltrated, and dried plant material can be about 900-1,250 kg / m 3 The compression process can take about 15-100 minutes, depending on the original thickness of the plant material, the applied pressure, the temperature of the platens, the wood species, and other factors including those related to the lignin degradation step (first step) in the process. There is an economic motivation to perform the compression step as quickly as possible, but slower compression rates can result in a finished product with improved surface quality (fewer cracks). In some aspects, plasticizing compression without rupturing the plant material can be achieved, for example, by partially modifying the lignin (and / or hemicellulose) via process blocks 106-108, and / or partially removing the lignin, for example, via process blocks 112-114. Once the desired degree of compression is achieved, the pressure applied to the compressed plant material can be released, and the compressed plant material can then be removed from the press. As noted above, partial compression can be such that the absorbed stabilizer solute molecules do not prematurely crosslink with amorphous cellulose and / or hemicellulose in the plant material upon removal from the press. Alternatively or additionally, in some aspects, the treated, infiltrated, and dried plant material can be partially compressed in the first compression step such that the density of the compressed plant material is about 900-1250 kg / m 3 , the moisture content is greater than about 10%, and the absorbed stabilizer solute molecules (or precursors thereof) are not crosslinked with amorphous cellulose and / or hemicellulose.

[0094] ​After partial compression at process block 130, or if no partial compression is required at decision block 128, the method can proceed to decision block 132, where it is determined whether drying is required. If drying is required, the method 100 can proceed to process block 134, where the plant material is dried, for example, in a manner similar to that described above for process block 120. For example, the partially compressed plant material can be subjected to an additional drying step in which the moisture content of the plant material is reduced to less than about 10% (e.g., in the range of 1-10%, inclusive). In some aspects, drying can be accomplished by use of a kiln. Alternatively, drying can be accomplished in a chamber that operates at reduced pressure. In some aspects, the treated, infiltrated, and partially compressed plant material can be restrained in a manner that prevents dimensional distortion (warping or twisting) from occurring during the drying process. Drying at reduced pressure at low temperature helps to ensure that the absorbed stabilizing agent (or precursor thereof) does not prematurely crosslink with amorphous cellulose and / or hemicellulose during this step.

[0095] After drying at process block 134, or if no drying is required at decision block 132, the method 100 can proceed to decision block 136, where it is determined whether full compression (e.g., full densification) is required. If full compression is required, the method 100 can proceed to process block 138, where the plant material is compressed (e.g., at least along its thickness direction) to have a second density that is greater than the first density. For example, the second density can be at least 1200 kg / m 3 (e.g., in the range of 1200-1450 kg / m 3 ). In some aspects, the compression of process block 138 can be performed in a manner similar to that described above for process block 130. In some aspects, the dried plant material from process block 134 can subsequently be subjected to a final hot-pressing step in which the density of the plant material is increased to a value in the range of about 1,250-1,450 kg / m 3 (inclusive of 1,250 kg / m 3 and 1,450 kg / m 3 ). After the target compression level is reached, the absorbed stabilizing agent solute molecules can crosslink with amorphous cellulose and / or hemicellulose in a manner that significantly prevents volume swelling in the presence of moisture.

[0096] For example, the treated, infiltrated, partially compressed, and dried plant material can be loaded into a press, where the top and bottom platens of the press are at a temperature in the range of about 100-200°C. The plant material can be oriented in the press such that the thickness axis of the plant material is normal to the contact surfaces of the platens. The pressure applied to the treated, infiltrated, partially compressed, and dried plant material can be increased from 0 to about 3-10 MPa over a period of 0-10 minutes. The applied pressure can then be maintained until the treated, infiltrated, partially compressed, and dried plant material has been compressed to a degree corresponding to a density of about 1,200-1,450 kg / m 3 Alternatively or additionally, in some aspects, the density of the treated, infiltrated, partially compressed, and dried plant material can be increased to a value greater than about 1,300 kg / m 3 (e.g., at least 1,350 kg / m 3 ). In some aspects, the full compression process can take about 2-40 minutes, depending on the original thickness of the plant material, the applied pressure, the temperature of the platens, the plant material species, and other factors (e.g., factors related to the partial compression of process block 130).

[0097] In some aspects, only a single compression step is used in the manufacturing process (e.g., only process block 138 is used, without pre-compression via process block 130). In these aspects, the pressure and associated time of the compression (e.g., hot-pressing) can be selected to produce the desired degree of compression, and the higher temperature and associated time can be selected to cross-link with amorphous cellulose and / or hemicellulose (and, optionally, lignin) once the target degree of compression has occurred. In some aspects, the single-step full compression can be performed on treated, infiltrated, and dried plant material having a moisture content of less than about 12%.

[0098] In some aspects, the compression of process block 138 can be controlled to avoid cross-linking of amorphous cellulose and / or hemicellulose prior to achieving the desired degree of compression. In these aspects, after process block 138, method 100 can proceed to process block 140, where amorphous cellulose and / or hemicellulose is cross-linked with a stabilizing agent within the plant material. For example, after full compression of the plant material has been achieved, the amorphous cellulose and / or hemicellulose can be cross-linked via a stabilizing agent such that they do not undergo a significant degree of volume swelling in the presence of moisture. In some aspects, after the target degree of compression has been achieved, the plant material can be further heated until the amorphous cellulose and / or hemicellulose has cross-linked. Alternatively or additionally, cross-linking of the degraded lignin can also occur at this step in the process. For example, the degraded lignin within the highly compressed plant material can be cross-linked such that the previously degraded lignin is no longer soluble in water. Alternatively, in some aspects, the amorphous cellulose and / or hemicellulose can be cross-linked during at least a portion of process block 138 (e.g., prior to the pressure on the plant material being released in the press).

[0099] For example, the treated, infiltrated, partially compressed, and dried plant material can be fully compressed to a density in the range of about 1,200-1,450 kg / m3, and the treated, infiltrated, dried, and fully compressed plant material can be removed from the press and transferred to a kiln in order to cross-link the amorphous cellulose, hemicellulose, and degraded lignin. In some aspects, the plant material can be confined in the kiln to prevent or at least reduce the formation of geometric defects (e.g., twist or warp). 3

[0100] After cross-linking, method 100 can proceed to process block 142, where the water-stable plant material can be optionally machined, cut, transported, assembled, and / or other physical operations in order to prepare for end use. Machining processes can include, but are not limited to, cutting (e.g., sawing), drilling, wood turning, tapping, boring, carving, planing, sanding, grinding, and sanding. Operations processes can include, but are not limited to, bending, molding, and other shaping techniques. In some aspects, one or more pieces of the obtained dimensionally stable densified plant material (e.g., thin segments) can be laminated to each other, or to other pieces or composite materials. For example, a laminated veneer lumber or other composite material can be manufactured by laminating one or more segments of the obtained dimensionally stable densified wood. Lamination can be achieved by using, for example, a phenol formaldehyde, isocyanate, polyurethane, or epoxy-based adhesive.

[0101] ​In some aspects, process block 142 can also include using the plant material as a structural member (e.g., load-bearing or non-load-bearing), such as a building component. For example, a laminate or composite material including water-stable plant material can be used as a beam or other structural member, for example, in a residential or commercial building. When used in an environment exposed to water, regardless of the duration of exposure to water or the amount of water absorbed by the plant material, the swelling rate of the plant material having crosslinked amorphous cellulose and / or hemicellulose therein can be limited to 10% (along the thickness direction of the plant material). Those skilled in the art will readily appreciate that the high density and water-stable plant material disclosed herein can be readily adapted for use in a variety of applications based on the teachings of the present disclosure.

[0102] The density and strength values of the modified plant material products prepared according to the present disclosure are much greater than the density and strength values of the original plant feedstock. Moreover, the hydration behavior of the modified products is significantly different from that obtained in the case where the segments of plant material are simply compressed in a hot press without being treated with the stabilizers described herein. In particular, the disclosed methods of preparation result in high density plant material products that have significantly reduced swelling potential, but retain some degree of water absorption capacity. This latter property can allow the modified plant material products to successfully interact with water-based adhesives, paints, and other coatings, for example, by absorbing water from the paint, coating, or adhesive. Alternatively or additionally, the modified veneers that have been manufactured according to the present disclosure can be used to manufacture composite materials (e.g., laminated veneer lumber), where the composite materials are manufactured using traditional water-based phenol formaldehyde adhesives.

[0103] Although blocks 102-142 of method 100 have been described as being performed once, in some aspects, multiple repetitions of a particular process block can be made before proceeding to the next decision block or process block. Moreover, although blocks 102-142 of method 100 have been shown and described separately, in some aspects, process blocks can be combined and performed together (simultaneously or sequentially). Moreover, although Figure 3A A particular order for blocks 102-142 is shown, but aspects of the disclosed subject matter are not limited thereto. Indeed, in certain embodiments, these blocks can occur in a different order than shown, or concurrently with other blocks. In some aspects, method 100 can include steps or other aspects not specifically shown in Manufacturing example: compressed wood with stabilizer Alternatively or additionally, in some aspects, method 100 can include only some of blocks 102-142 of Figure 3B Alternatively or additionally, in some aspects, method 100 can include only some of blocks 102-142 of

[0104] Figure 3B

[0105] Other examples of the disclosed technology

[0106] High density wood was prepared without the use of a stabilizer and the resulting product was subjected to water soak testing, the results of which are shown in Conclusion .

[0107] Poplar blocks (19.1 mm thick x 127 mm wide x 305 mm long, 2 total) having a dry specific gravity of about 0.45 and a moisture content of about 8% were submerged in a 5.0% aqueous sodium hydroxide solution at a temperature of 20°C and a gage pressure of 19.3 bar for 18 hours. The soaked blocks were then heated at a temperature of 170°C and a gage pressure of 4 bar for 3 hours. The treated blocks were then dried under ambient conditions (20°C and a gage pressure of 0) for about 10 days to a moisture content of about 7%. The blocks were then placed in a hot press with a platen temperature of 132°C. For the first 14 minutes, the press was closed, but the pressure was less than 10 psi. After this initial heating period, the pressure was increased to 2.07 MPa in 1 minute. The blocks were held at this pressure for 24 minutes. The pressure was then increased to 5.10 MPa in 1 minute. The blocks were held at this pressure for 5 minutes. The pressure was then increased to 5.56 MPa in 44 minutes. The pressure on the blocks was then completely released in 1 minute. The blocks were then transferred from the hot press to a cold press. The blocks were then cold pressed at a temperature of 40°C and a pressure of 1 MPa for 15 minutes.

[0108] The compressed wood had a density of about 1.13 kg / m 3 Three replicate test samples (each 7.7 mm thick x 15.5 mm wide x 100.5 mm long) were separated from the compressed block. Initial measurements of mass and dimensions (thickness, width, and length) were made on the test samples. Thickness measurements were made at the midpoint of the four edges of each sample. The samples were then submerged under water at 1" for 168 hours. The test samples were removed from the water, and measurements of mass and dimensions were made after 4 hours and 24 hours of intermediate soak periods, and again after 168 hours. The soak solution was dark purple in color at the completion of the test. Water absorption and thickness swell values were calculated in the following manner:

[0109]

[0110]

[0111] Table 1: Water soak test results for compressed wood prepared without the use of a stabilizer

[0112] Figures 1-3B

[0113] High density wood was prepared using the stabilizer and the resulting product was subjected to water immersion testing, the results of which are shown in Figures 1-3B Table 1.

[0114] Poplar blocks (19.1 mm thick x 127 mm wide x 305 mm long, total of 2 blocks) having a dry specific gravity of about 0.45 and a moisture content of about 8% were immersed in a 5.0% aqueous sodium hydroxide solution at a temperature of 20°C and a pressure of 19.3 bar for 18 hours. The immersed blocks were then heated at a temperature of 170°C and a pressure of 4 bar for 3 hours. The treated blocks were then dried under ambient conditions (20°C and a pressure of 0) for about 10 days to a moisture content of about 7%.

[0115] Sub-blocks (17.0 mm thick x 20 mm wide x 100 mm long, total of 16) were cut from the larger treated poplar blocks.

[0116] A stabilizer solution was prepared as follows. Polyethylene bottles (18 each, 500 milliliters each) were each charged with 89% phenol solution (aqueous) (110.0 grams) and 0.10% sodium carbonate solution (aqueous) (1.0 gram). The bottles were capped tightly and then shaken for 15 seconds. The bottles were further charged with 37% formaldehyde solution (aqueous) (60.0 grams). The bottles were capped tightly and then shaken for 30 seconds. The closed bottles were stored at a temperature of 20°C for 6 hours. Each bottle was charged a second time with 37% formaldehyde solution (aqueous) (60.0 grams). The bottles were capped tightly and then shaken for 30 seconds. The closed bottles were stored at a temperature of 20°C for 15 hours. Each bottle was charged a third time with 37% formaldehyde solution (aqueous) (60.0 grams). The bottles were capped tightly and then shaken for 30 seconds. The closed bottles were stored at a temperature of 20°C for 6 hours. Each bottle was charged a fourth time with 37% formaldehyde solution (aqueous) (60.0 grams). The bottles were capped tightly and then shaken for 30 seconds. The closed bottles were stored at a temperature of 20°C for 15 hours. The resulting solution had a calculated percent solids of 53.2%. The viscosity of the solution at 20°C was less than 20 cPs.

[0117] All sub-sections of the treated poplar were selected for treatment with the stabilizing agent. Each sub-section was wrapped with a metal mesh and placed into a steel beaker (10 liter capacity). The stabilizing agent was then added to the loaded beaker such that all of the wrapped sub-sections of treated poplar were submerged. The loaded beaker was placed into a pressure vessel and subjected to positive pressure (5 bar, gauge) at a temperature of 25°C for 30 minutes. Under these conditions, the treated wood pieces absorbed approximately their own weight of stabilizing agent. One of the treated sub-sections was cut in half transversely (each piece 17.0 mm thick x 20 mm wide x 50 mm long). The freshly cut surfaces were observed and it was apparent that the stabilizing agent had penetrated throughout the cross-section of the wood.

[0118] The sub-sections were then placed into a hot press with a platen temperature of 132°C. For the first 14 minutes, the press was closed but the pressure was less than 10 psi. After this initial heating period, the pressure was increased to 2.07 MPa in 1 minute. The sub-sections were held at this pressure for 24 minutes. The pressure was then increased to 5.10 MPa in 1 minute. The sub-sections were held at this pressure for 5 minutes. The pressure was then increased to 5.56 MPa over 44 minutes. The pressure on the sub-sections was then released completely over a 1 minute period. The pressure was then increased to 5.56 MPa in 1 minute. The sub-sections were held at this pressure for 179 minutes. The pressure on the sub-sections was then released completely in 1 minute. The sub-sections were then transferred from the hot press to a cold press. The sub-sections were then cold pressed at a temperature of 40°C and a pressure of 1 MPa for 15 minutes.

[0119] The compressed wood had a density of about 1.34 kg / m 3 Ten replicate test samples (each 8.0 mm thick x 24 mm wide x 81 mm long) were separated from the compressed wood pieces. Initial measurements of mass and dimensions (thickness, width, and length) were made on the test samples. The thickness measurements were made at the midpoint of the four edges of each sample. The samples were then submerged under water at a 1" depth for 168 hours. The test samples were removed from the water and measurements of mass and dimensions were made after 4 hours and 24 hours of the soak period and again after 168 hours. After the test was completed, the soak solution was a clear light yellow color. The water absorption and thickness swell values were calculated in the following manner:

[0120]

[0121]

[0122] Table 2: Water soak test results for compressed wood prepared using stabilizing agent

[0123] Dry and unmodified aspen has a swelling potential of about 4.6% in the radial direction and about 8.2% in the tangential direction. Thus, compressed aspen without stabilizer exhibits a thickness swelling rate value that is much greater than the thickness swelling rate value of unmodified wood (32.0%). In contrast, compressed aspen prepared using stabilizer exhibits a thickness swelling rate value of only 8.6%, which is only slightly greater than the thickness swelling rate value of unmodified aspen.

[0124] Both types of compressed wood exhibited the ability to absorb water, but the rate of water absorption for the sample type prepared using stabilizer was about 50% slower than the rate of water absorption for the sample type prepared without stabilizer.

[0125] If we examine the relationship between the water absorption rate and the thickness swelling rate for compressed wood prepared without stabilizer, we observe that there is a strong linear relationship (R 2 = 0.985) between these two parameters for the 4 hour, 24 hour, and 168 hour soak time values. The slope associated with this relationship is about 1.01 (see ​ ).

[0126] In contrast, for the 4 hour or 24 hour soak time values, there is an approximate linear relationship between the water absorption rate and the thickness swelling rate for compressed wood prepared using stabilizer (R 2 = 0.810). The slope of this relationship is about 1.04, which is very similar to the slope associated with compressed wood prepared without stabilizer. When the soak time for compressed wood prepared using stabilizer is 168 hours, the water absorption rate value is greater than 9%. When the water absorption rate value for this type of wood is between 9.4% and 16.8%, the average thickness swelling rate is only 8.6%. Thus, for this type of modified wood, the maximum thickness swelling rate value (average) is about 8.6%. The thickness swelling rate value for compressed wood prepared without stabilizer is 32.0% after 168 hours of soaking. For compressed wood prepared without stabilizer, the maximum swelling rate value can actually be greater than 32.0%, which can have been observed if the soak test had been conducted for a period of time greater than 168 hours.

[0127] Compressed wood manufactured according to the present disclosure has a density in the range of about 900-1,450 kg / m 3density values within the range of 0.1 to 0.5 g / cm3, and includes collapsed cellulose and / or hemicellulose-based wood cells, wherein regions of the cell wall that particularly include amorphous cellulose and / or hemicellulose are crosslinked in a manner that significantly reduces their ability to undergo volume swelling in the presence of water. Lignin that has been degraded, molded, and subsequently crosslinked is present as a continuous phase between the modified cells. The cell walls that have been penetrated with stabilizer have a significantly darker color than the color of the cells prior to treatment. The effects of the stabilizer treatment are most notably manifested by the altered hydration and swelling behavior of the modified plant material, which has the ability to absorb about 10-30% of the dry weight of the plant material in water without a swelling rate along the axis of compression of more than about 10%. The properties of this combination have important commercial value and have not been previously demonstrated.

[0128] ​

[0129] In view of the embodiments of the subject matter disclosed above, the present application discloses additional examples of the clauses recited below. It should be noted that one feature of a clause alone or more than one feature of a clause taken in combination and optionally in conjunction with one or more features of one or more other clauses are also other examples that fall within the scope of the disclosure of the present application.

[0130] Clause 1. A method comprising: penetrating a first plant material with a solution comprising a stabilizer and / or a stabilizer precursor, such that the stabilizer and / or the stabilizer precursor is absorbed within amorphous cellulose regions and / or hemicellulose regions of one or more cell walls of the first plant material; and crosslinking the amorphous cellulose regions and / or the hemicellulose regions with the stabilizer after penetrating the first plant material with the solution, wherein (i) the stabilizer precursor comprises a nucleophile and an electrophile, and the stabilizer comprises a reaction product of the nucleophile and the electrophile, and (ii) each of the stabilizer and the stabilizer precursor has a molecular weight of less than or equal to 500 g / mole when penetrating the first plant material with the solution.

[0131] Clause 2. The method of clause 1, wherein the extent of swelling of the first plant material with the stabilizer along the thickness direction of the first plant material does not exceed 10%, regardless of the duration of exposure to water and / or the amount of water absorbed by the first plant material.

[0132] Clause 3. The method of any one of clauses 1 or 2, wherein, the nucleophile comprises an aromatic nucleophile; and The electrophile includes (i) an aldehyde, an oxirane, an oxazolidine, or a bisoxazolidine; (ii) both an aldehyde and an oxazolidine; (iii) both an aldehyde and an oxirane; or (iv) both an aldehyde and a bisoxazolidine.

[0133] Clause 4. The method of any of clauses 1-3, wherein, (i) the aromatic nucleophile includes a phenol or a cresol; (ii) the electrophile is water soluble; (iii) the aldehyde includes a formaldehyde, an acetaldehyde, a propionaldehyde, a crotonaldehyde, or a glutaraldehyde; or (iv) any combination of two or more of (i), (ii), and (iii).

[0134] Clause 5. The method of any of clauses 1-4, wherein the nucleophile is a phenol, the electrophile is a formaldehyde, the stabilizer precursor is a monomer and / or an oligomer of a hydroxymethylated phenol, and each oligomer, if present, has a molecular weight of 500 g / mole or less.

[0135] Clause 6. The method of any of clauses 1-5, wherein a molar ratio of formaldehyde to phenol of the stabilizer precursor is in a range of 1:1-3:1, inclusive.

[0136] Clause 7. The method of any of clauses 1-6, wherein, (i) the solution including the stabilizer precursor is an aqueous solution; (ii) a viscosity of the solution at 20 °C is in a range of 1-40 cPs, inclusive; (iii) the stabilizer and / or the stabilizer precursor is present in an amount of 1%-70% of a mass of the solution, inclusive; or (iv) any combination of two or more of (i), (ii), and (iii).

[0137] Clause 8. The method of any of clauses 1-7, wherein the method further includes degrading native lignin of an initial plant material to form the first plant material prior to infiltrating the first plant material with the solution, wherein degrading the native lignin includes modifying the native lignin within the initial plant material and / or removing at least a portion of the native lignin from the initial plant material.

[0138] Clause 9. The method of any of clauses 1-8, wherein degrading the native lignin includes: infiltrating the initial plant material with a loading solution; and subjecting the initial plant material having the loading solution therein to a first temperature and a first pressure so as to modify the native lignin and provide a modified lignin, wherein the first temperature is in a range of 20 °C - 200 °C inclusive, and the first pressure is in a range of 1 - 8 bar inclusive.

[0139] Clause 10. The method of any of clauses 1-9, wherein the loading solution comprises sodium hydroxide, sodium sulfite, an oxidizing agent, or any combination of the foregoing.

[0140] Clause 11. The method of any of clauses 1-10, wherein the oxidizing agent comprises ozone, oxygen, hydrogen peroxide, or an organic peroxide.

[0141] Clause 12. The method of any of clauses 1-11, wherein the loading solution comprises water.

[0142] Clause 13. The method of any of clauses 1-12, wherein, a moisture content of the initial plant material is in a range of 1 wt% - 20 wt% inclusive prior to infiltrating the initial plant material with the loading solution; and a moisture content of the initial plant material is in a range of 20 wt% - 100 wt% inclusive after infiltrating the initial plant material with the loading solution and prior to subjecting the initial plant material having the loading solution therein to the first temperature and pressure.

[0143] Clause 14. The method of any of clauses 1-13, wherein a molecular weight of the modified lignin is reduced as compared to a molecular weight of the native lignin in the initial plant material, and the modified lignin is insoluble in water at room temperature.

[0144] Clause 15. The method of any of clauses 1-14, wherein degrading the native lignin comprises subjecting the initial plant material to a chemical delignification treatment so as to remove a portion but not all of the native lignin from the initial plant material.

[0145] Clause 16. The method of any of clauses 1-15, wherein, subjecting the initial plant material to the chemical delignification treatment comprises partially or fully submerging the initial plant material in one or more chemical solutions at a temperature of at least 100 °C, and The one or more chemical solutions include a basic solution.

[0146] Clause 17. The method of any of clauses 1-16, wherein the one or more chemical solutions include sodium hydroxide (NaOH), lithium hydroxide (LiOH), potassium hydroxide (KOH), sodium sulfite (Na2SO3), sodium sulfate (Na2SO4), sodium sulfide (Na2S), urea (CH4N2O), NaH2O3, sulfur dioxide (SO2), anthraquinone (C 14 H8O2), methanol (CH3OH), ethanol (C2H5OH), butanol (C4H9OH), formic acid (CH2O2), hydrogen peroxide (H2O2), acetic acid (CH3COOH), butyric acid (C4H8O2), performic acid (CH2O3), peracetic acid (C2H4O3), ammonia (NH3), p-toluenesulfonic acid (p-TsOH), sodium hypochlorite (NaClO), sodium chlorite (NaClO2), chlorine dioxide (ClO2), chlorine (Cl2), ozone (O3), or any combination of the foregoing.

[0147] Clause 18. The method of any of clauses 1-17, wherein, after degrading the native lignin of the initial plant material, the first plant material has a lignin content that is 5% to 95% and includes 5% and 95% of the lignin content of the initial plant material.

[0148] Clause 19. The method of any of clauses 1-18, wherein the method further comprises, after degrading the native lignin and before infiltrating the first plant material with the solution, drying the first plant material to have a moisture content of 1% to 20% and includes 1% and 20% by weight.

[0149] Clause 20. The method of any of clauses 1-19, wherein the method further comprises: infiltrating an initial plant material with a liquid comprising water before infiltrating the first plant material with the solution; and subjecting the initial plant material having the liquid therein to a temperature of at least 50°C.

[0150] Clause 21. The method of any of clauses 1-20, wherein the method further comprises, after infiltrating the first plant material with the solution, compressing the first plant material having the stabilizing agent and / or the stabilizing agent precursor therein.

[0151] Clause 22. The method according to any one of clauses 1-21, wherein the first plant material having the stabilizer and / or the stabilizer precursor therein is compressed to have a first density of at least 900 kg / m 3 .

[0152] Clause 23. The method according to any one of clauses 1-22, wherein the first plant material having the stabilizer and / or the stabilizer precursor therein is compressed along a thickness direction of the first plant material, and a thickness of the first plant material after compression is no more than 50% of a thickness of the first plant material before compression.

[0153] Clause 24. The method according to any one of clauses 1-23, wherein the first density is in a range of 900 kg / m 3 - 1200 kg / m 3 and including 900 kg / m 3 and 1200 kg / m 3 .

[0154] Clause 25. The method according to any one of clauses 1-24, wherein the compression is performed at a temperature in a range of 20 °C - 150 °C and including 20 °C and 150 °C and at a pressure in a range of 3 MPa - 8 MPa and including 3 MPa and 8 MPa.

[0155] Clause 26. The method according to any one of clauses 1-25, wherein the compression is performed at a temperature in a range of 20 °C - 60 °C and including 20 °C and 60 °C.

[0156] Clause 27. The method according to any one of clauses 1-26, wherein the compression is performed such that the stabilizer and / or the stabilizer precursor within the first plant material does not crosslink the amorphous cellulose regions and / or the hemicellulose regions.

[0157] Clause 28. The method according to any one of clauses 1-27, wherein the method further comprises drying the first plant material to have a moisture content in a range of 15 wt% - 25 wt% and including 15 wt% and 25 wt% after the first plant material is infiltrated with the solution and before the first plant material is compressed.

[0158] Clause 29. The method according to any one of clauses 1-28, wherein the method further comprises drying the first plant material to have a moisture content of 1 wt% - 10 wt% and including 1 wt% and 10 wt% after the first plant material is compressed.

[0159] Clause 30. The method of any one of clauses 1-29, wherein the first plant material has a moisture content of about 5 wt% after drying.

[0160] Clause 31. The method of any one of clauses 1-30, wherein the method further comprises further compressing the first plant material after drying the first plant material.

[0161] Clause 32. The method of any one of clauses 1-31, wherein the first plant material is further compressed to have a second density of at least 1200 kg / m 3 .

[0162] Clause 33. The method of any one of clauses 1-32, wherein the amorphous cellulose regions and / or the hemicellulose regions are crosslinked with the stabilizing agent during further compression of the first plant material.

[0163] Clause 34. The method of any one of clauses 1-33, wherein the amorphous cellulose regions and / or the hemicellulose regions are crosslinked with the stabilizing agent after further compression of the first plant material.

[0164] Clause 35. The method of any one of clauses 1-34, wherein the second density is in a range of 1200 kg / m 3 - 1450 kg / m 3 and including 1200 kg / m 3 and 1450 kg / m 3 .

[0165] Clause 36. The method of any one of clauses 1-35, wherein the first plant material is further compressed at a temperature in a range of 20 °C - 200 °C and including 20 °C and 200 °C and at a pressure in a range of 3 MPa - 10 MPa and including 3 MPa and 10 MPa.

[0166] Clause 37. The method of any one of clauses 1-36, wherein during penetration of the first plant material with the solution: (i) the stabilizing agent is hydrophilic and has water solubility such that at least 30 g of the stabilizing agent dissolves in 100 mL of water at 20 °C; (ii) the stabilizing agent precursor is hydrophilic and has water solubility such that at least 2 g of the stabilizing agent precursor dissolves in 100 mL of water at 20 °C; or (iii) a combination of (i) and (ii).

[0167] Clause 38. The method of any of clauses 1-37, wherein the amorphous cellulose regions and / or the hemicellulose regions remain hydrophilic after being crosslinked.

[0168] Clause 39. The method of any of clauses 1-38, wherein an amount of the stabilizing agent and / or the stabilizing agent precursor absorbed within the cell walls of the first plant material after the first plant material is infiltrated with the solution is within a range of 1% - 25% by weight of the first plant material in a dry state prior to infiltration and including 1% and 25% by weight.

[0169] Clause 40. The method of any of clauses 1-39, wherein the first plant material is infiltrated with the solution at a temperature within a range of 20 °C - 50 °C and including 20 °C and 50 °C.

[0170] Clause 41. The method of any of clauses 1-40, wherein the method further comprises infiltrating an initial plant material with a loading solution prior to infiltrating the first plant material with the solution comprising the stabilizing agent and / or the stabilizing agent precursor.

[0171] Clause 42. The method of any of clauses 1-41, wherein the loading solution and / or the solution comprising the stabilizing agent or the stabilizing agent precursor comprises water, sodium hydroxide, a catalyst, or any combination thereof.

[0172] Clause 43. The method of any of clauses 1-42, wherein the nucleophile is phenol or cresol and the electrophile is oxazolidine or bisoxazolidine.

[0173] Clause 44. The method of any of clauses 1-43, wherein the first plant material is wood.

[0174] Clause 45. The method of any of clauses 1-44, wherein the first plant material is bamboo.

[0175] Clause 46. A structure formed by the method of any of clauses 1-45.

[0176] Clause 47. A structure comprising: a plant material having one or more cell walls comprising amorphous cellulose regions and hemicellulose regions; and a stabilizing agent crosslinking the amorphous cellulose regions and / or the hemicellulose regions of the one or more cell walls of the plant material to form a crosslinked plant material, wherein the stabilizer is a reaction product of a nucleophile and an electrophile, and Prior to crosslinking, each of the nucleophile, the electrophile, and the stabilizer has a molecular weight less than or equal to 500 g / mole.

[0177] Clause 48. The structure of clause 47, wherein, regardless of the duration of exposure to water and / or the amount of water absorbed by the first plant material, the first plant material having the stabilizer does not swell by more than 10% along the thickness direction of the first plant material.

[0178] Clause 49. The structure of any one of clauses 47-48, wherein: the nucleophile comprises an aromatic nucleophile; the electrophile comprises (i) an aldehyde, an oxirane, an oxazolidine, or a bisoxazolidine; (ii) both an aldehyde and an oxazolidine; (iii) both an aldehyde and an oxirane; or (iv) both an aldehyde and a bisoxazolidine.

[0179] Clause 50. The structure of any one of clauses 47-49, wherein, (i) the aromatic nucleophile comprises a phenol or a cresol; (ii) the electrophile is water-soluble and comprises a formaldehyde, an acetaldehyde, a propionaldehyde, a crotonaldehyde, or a glutaraldehyde; or (iii) a combination of (i) and (ii).

[0180] Clause 51. The structure of any one of clauses 47-50, wherein the nucleophile is a phenol or a cresol and the electrophile is an oxazolidine or a bisoxazolidine.

[0181] Clause 52. The structure of any one of clauses 47-51, wherein at least a portion of the lignin of the plant material is modified as compared to lignin of a natural plant material.

[0182] Clause 53. The structure of any one of clauses 47-52, wherein the molecular weight of the modified lignin is reduced as compared to the molecular weight of the lignin in the natural plant material and the modified lignin is water-insoluble at room temperature.

[0183] Clause 54. The structure of any one of clauses 47-53, wherein the lignin content of the plant material is lower than the lignin content in a natural plant material.

[0184] Clause 55. The structure of any one of clauses 47-54, wherein the crosslinked plant material has a density of at least 900 kg / m 3density.

[0185] Clause 56. The structure of any one of clauses 47-55, wherein the crosslinked plant material has a density of at least 1200 kg / m 3 .

[0186] Clause 57. The structure of any one of clauses 47-56, wherein the density of the crosslinked plant material is in a range of 1200 kg / m 3 - 1450 kg / m 3 and including 1200 kg / m 3 and 1450 kg / m 3 .

[0187] Clause 58. The structure of any one of clauses 47-57, wherein the plant material is a compact piece having native lumens formed by substantially collapsed cell walls of the plant material and cellulose-based fibers forming the cell walls and aligned along a common direction.

[0188] Clause 59. The structure of any one of clauses 47-58, wherein (i) the stabilizing agent is hydrophilic, and / or (ii) the amorphous cellulose regions and / or the hemicellulose regions crosslinked with the stabilizing agent are hydrophilic.

[0189] Clause 60. The structure of any one of clauses 47-59, wherein the stabilizing agent has water solubility such that at least 2 g of the stabilizing agent is dissolved in 100 mL of water at a temperature of 20 °C.

[0190] Clause 61. The structure of any one of clauses 47-60, wherein the stabilizing agent has water solubility such that at least 30 g of the stabilizing agent is dissolved in 100 mL of water at a temperature of 20 °C.

[0191] Clause 62. The structure of any one of clauses 47-61, wherein the plant material is wood.

[0192] Clause 63. The structure of any one of clauses 47-62, wherein the plant material is bamboo.

[0193] ​

[0194] Any feature shown or described herein, e.g., with respect to ​ and clauses 1-63, can be combined with any other feature shown or described herein, e.g., with respect to ​ and clauses 1-63.Any of the materials, systems or methods described herein can be used in combination with any of the other materials, systems or methods described herein, unless otherwise contraindicated. All patents and publications mentioned herein are incorporated by reference to the extent allowed by law for the purpose of describing and disclosing the materials and methodologies reported herein that might be used in connection with the technology described herein. Nothing herein is to be construed as an admission that the patent or publication is prior art. It is expressly not admitted that any of the aforementioned patents, publications, or databases, or any other material, discloses or describes aspects of the technology described herein. All patents and publications mentioned herein are incorporated by reference to the extent allowed by law for the purpose of describing and disclosing the materials and methodologies reported herein that might be used in connection with the technology described herein. Nothing herein is to be construed as an admission that the patent or publication is prior art. It is expressly not admitted that any of the aforementioned patents, publications, or databases, or any other material, discloses or describes aspects of the technology described herein.

Claims

1. A method comprising: penetrating a first plant material with a solution comprising a stabilizing agent and / or a stabilizing agent precursor, such that the stabilizing agent and / or the stabilizing agent precursor is absorbed within amorphous cellulose regions and / or hemicellulose regions of one or more cell walls of the first plant material; and crosslinking the amorphous cellulose regions and / or the hemicellulose regions with the stabilizing agent after penetrating the first plant material with the solution, wherein (i) the stabilizing agent precursor comprises a nucleophile and an electrophile, and the stabilizing agent comprises a reaction product of the nucleophile and the electrophile, and (ii) each of the stabilizing agent and the stabilizing agent precursor has a molecular weight of less than or equal to 500 g / mole when the first plant material is penetrated with the solution. a degree of swelling of the first plant material having the stabilizing agent along a thickness direction of the first plant material is no more than 10%, regardless of a duration of exposure to water and / or an amount of water absorbed by the first plant material.

2. The method of claim 1, wherein, 3. The method of claim 1, wherein, the nucleophile comprises an aromatic nucleophile; and the electrophile comprises (i) an aldehyde, an oxirane, an oxazolidine, or a bisoxazolidine; (ii) both an aldehyde and an oxazolidine; (iii) both an aldehyde and an oxirane; or (iv) both an aldehyde and a bisoxazolidine.

4. The method of claim 3, wherein, (i) the aromatic nucleophile comprises a phenol or a cresol; (ii) the electrophile is water-soluble; (iii) the aldehyde comprises formaldehyde, acetaldehyde, propionaldehyde, crotonaldehyde, or glutaraldehyde; or (iv) any combination of two or more of (i), (ii), and (iii). the nucleophile is a phenol, the electrophile is formaldehyde, the stabilizing agent precursor is a monomer and / or oligomers of a methylolated phenol, and each oligomer, if present, has a molecular weight of 500 g / mole or less.

5. The method of claim 1, wherein, a molar ratio of formaldehyde to phenol of the stabilizing agent precursor is in a range of 1 : 1 to 3 : 1, inclusive.

6. The method of claim 5, wherein, 7. The method of claim 1, wherein, (i) the solution comprising a stabilizing agent precursor is an aqueous solution; (ii) a viscosity of the solution at 20 °C is in a range of 1 to 40 cPs, inclusive; (iii) the stabilizing agent and / or the stabilizing agent precursor is present in an amount of 1% to 70% of a mass of the solution, inclusive; (iv) any combination of two or more of (i), (ii), and (iii). the method further comprises, prior to penetrating the first plant material with the solution, degrading native lignin of an initial plant material to form the first plant material, wherein degrading the native lignin comprises modifying the native lignin within the initial plant material and / or removing at least a portion of the native lignin from the initial plant material.

8. The method of claim 1, wherein, degrading the native lignin comprises:

9. The method of claim 8, wherein, penetrating the initial plant material with a loading solution; and ​ subjecting the initial plant material having the loading solution therein to a first temperature and a first pressure so as to modify the native lignin and provide a modified lignin, wherein the first temperature is in a range of 20°C-200°C inclusive, and the first pressure is in a range of 1-8 bar inclusive.

10. The method of claim 9, wherein, the loading solution includes sodium hydroxide, sodium sulfite, an oxidizing agent, or any combination of the foregoing.

11. The method of claim 10, wherein, the oxidizing agent includes ozone, oxygen, hydrogen peroxide, or an organic peroxide.

12. The method of claim 9, wherein, the loading solution includes water.

13. The method of claim 9, wherein: a moisture content of the initial plant material is in a range of 1%-20% by weight inclusive prior to infiltrating the initial plant material with the loading solution; and the moisture content of the initial plant material is in a range of 20%-100% by weight inclusive after infiltrating the initial plant material with the loading solution and prior to subjecting the initial plant material having the loading solution therein to the first temperature and the first pressure.

14. The method of claim 9, wherein, a molecular weight of the modified lignin is reduced compared to a molecular weight of the native lignin in the initial plant material, and the modified lignin is water-insoluble at room temperature.

15. The method of claim 8, wherein, degrading the native lignin includes subjecting the initial plant material to a chemical delignification process so as to remove a portion but not all of the native lignin from the initial plant material.

16. The method of claim 15, wherein: subjecting the initial plant material to the chemical delignification process includes partially or entirely submerging the initial plant material in one or more chemical solutions at a temperature of at least 100°C, and the one or more chemical solutions include a basic solution.

17. The method of claim 16, wherein, The one or more chemical solutions include sodium hydroxide (NaOH), lithium hydroxide (LiOH), potassium hydroxide (KOH), sodium sulfite (Na2SO3), sodium sulfate (Na2SO4), sodium sulfide (Na2S), urea (CH4N2O), NaH2O3, sulfur dioxide (SO2), anthraquinone (C 14 H8O2), methanol (CH3OH), ethanol (C2H5OH), butanol (C4H9OH), formic acid (CH2O2), hydrogen peroxide (H2O2), acetic acid (CH3COOH), butyric acid (C4H8O2), peroxymonocarbonate (CH2O3), peroxyacetic acid (C2H4O3), ammonia (NH3), p-toluenesulfonic acid (p-TsOH), sodium hypochlorite (NaClO), sodium chlorite (NaClO2), chlorine dioxide (ClO2), chlorine (Cl2), ozone (O3), or any combination of the foregoing.

18. The method of claim 15, wherein, a lignin content of the first plant material is between 5% and 95% of a lignin content of the initial plant material inclusive after degrading the native lignin of the initial plant material.

19. The method of claim 8, wherein, the method further includes drying the first plant material to have a moisture content of 1%-20% by weight inclusive after degrading the native lignin and prior to infiltrating the first plant material with the solution.

20. The method of claim 1, wherein, the method further includes: infiltrating an initial plant material with a liquid including water prior to infiltrating the first plant material with the solution; and subjecting the initial plant material having the liquid therein to a temperature of at least 50°C.

21. The method of any one of claims 1, 8, or 20, wherein, the method further includes compressing the first plant material having the stabilizing agent and / or the stabilizing agent precursor therein after infiltrating the first plant material with the solution.

22. The method of claim 21, wherein, compressing the first plant material having the stabilizer and / or the stabilizer precursor therein to a first density of at least 900 kg / m3. 3 of at least 900 kg / m3.

23. The method of claim 21, wherein, compressing the first plant material having the stabilizing agent and / or the stabilizing agent precursor therein is along a thickness direction of the first plant material, and a thickness of the first plant material after compression is no more than 50% of a thickness of the first plant material prior to compression.

24. The method of claim 22, wherein, said first density is comprised in the range of 900 kg / m 3 - 1200 kg / m 3 and including 900 kg / m 3 and 1200 kg / m 3 .

25. The method of claim 21, wherein, The compression is performed at a temperature in the range of 20°C-150°C inclusive and at a pressure in the range of 3MPa-8MPa inclusive.

26. The method of claim 25, wherein, The compression is performed at a temperature in the range of 20°C-60°C inclusive.

27. The method of claim 21, wherein, The compression is performed such that the stabilizing agent and / or the stabilizing agent precursor within the first plant material does not crosslink the amorphous cellulose regions and / or the hemicellulose regions.

28. The method of claim 21, wherein, The method further comprises drying the first plant material to a moisture content in the range of 15wt%-25wt% inclusive after permeating the first plant material with the solution and prior to compressing the first plant material.

29. The method of claim 21, wherein, The method further comprises drying the first plant material to a moisture content of 1wt%-10wt% inclusive after compressing the first plant material.

30. The method of claim 29, wherein, The first plant material has a moisture content of about 5wt% after drying.

31. The method of claim 29, wherein, The method further comprises further compressing the first plant material after drying the first plant material.

32. The method of claim 31, wherein, further compressing the first plant material to have a second density of at least 1200 kg / m 3 .

33. The method of claim 31, wherein, The amorphous cellulose regions and / or the hemicellulose regions are crosslinked with the stabilizing agent during further compression of the first plant material.

34. The method of claim 31, wherein, The amorphous cellulose regions and / or the hemicellulose regions are crosslinked with the stabilizing agent after further compression of the first plant material.

35. The method of claim 32, wherein, said second density is comprised in the range of 1200 kg / m 3 - 1450 kg / m 3 and including 1200 kg / m 3 and 1450 kg / m 3 .

36. The method of claim 31, wherein, The first plant material is further compressed at a temperature in the range of 20°C-200°C inclusive and at a pressure in the range of 3MPa-10MPa inclusive.

37. The method of claim 1, wherein, During permeation of the first plant material with the solution: (i) the stabilizing agent is hydrophilic and has water solubility such that at least 30g of the stabilizing agent dissolves in 100mL of water at 20°C; (ii) the stabilizing agent precursor is hydrophilic and has water solubility such that at least 2g of the stabilizing agent precursor dissolves in 100mL of water at 20°C; or (iii) a combination of (i) and (ii).

38. The method of claim 1, wherein, The amorphous cellulose regions and / or the hemicellulose regions remain hydrophilic after being crosslinked.

39. The method of claim 1, wherein, The amount of the stabilizing agent and / or the stabilizing agent precursor absorbed within the cell walls of the first plant material after permeation of the first plant material with the solution is in the range of 1wt%-25wt% of the first plant material in a dry state prior to permeation.

40. The method of claim 1, wherein, The first plant material is permeated with the solution at a temperature in the range of 20°C-50°C inclusive.

41. The method of claim 1, wherein, The method further comprises permeating an initial plant material with a loading solution prior to permeating the first plant material with the solution comprising the stabilizing agent and / or the stabilizing agent precursor.

42. The method of claim 41, wherein, The loading solution and / or the solution comprising the stabilizing agent or the stabilizing agent precursor comprises water, sodium hydroxide, a catalyst, or any combination thereof.

43. The method of claim 1, wherein, The nucleophile is phenol or cresol, and the electrophile is oxazolidine or bisoxazolidine.

44. The method of claim 1, wherein, The first plant material is wood.

45. The method of claim 1, wherein, The first plant material is bamboo.

46. A structure formed by the method of any one of claims 1-45.

47. A structure comprising: a plant material having one or more cell walls comprising amorphous cellulose regions and hemicellulose regions; and a stabilizing agent that crosslinks the amorphous cellulose regions and / or the hemicellulose regions of the one or more cell walls of the plant material to form a crosslinked plant material, wherein the stabilizing agent is a reaction product of a nucleophile and an electrophile, and each of the nucleophile, the electrophile, and the stabilizing agent has a molecular weight less than or equal to 500 g / mole prior to crosslinking.

48. The structure of claim 47, wherein, Regardless of the duration of exposure to water and / or the amount of water absorbed by the first plant material, the first plant material having the stabilizing agent does not swell by more than 10% along the thickness direction of the plant material.

49. The structure of claim 47, wherein the nucleophile comprises an aromatic nucleophile; the electrophile comprises (i) an aldehyde, an oxirane, an oxazolidine, or a bisoxazolidine; (ii) both an aldehyde and an oxazolidine; (iii) both an aldehyde and an oxirane; or (iv) both an aldehyde and a bisoxazolidine.

50. The structure of claim 49, wherein (i) the aromatic nucleophile comprises phenol or cresol; (ii) the electrophile is water-soluble and comprises formaldehyde, acetaldehyde, propionaldehyde, crotonaldehyde, or glutaraldehyde; or (iii) a combination of (i) and (ii).

51. The structure of claim 47, wherein, the nucleophile is phenol or cresol, and the electrophile is oxazolidine or bisoxazolidine.

52. The structure of claim 47, wherein, At least a portion of the lignin in the plant material is modified as compared to the lignin of a native plant material.

53. The structure of claim 52, wherein, The molecular weight of the modified lignin is reduced as compared to the molecular weight of the lignin in the native plant material, and the modified lignin is water-insoluble at room temperature.

54. The structure of claim 47, wherein, The plant material has a lignin content that is lower than the lignin content in a native plant material.

55. The structure of claim 47, wherein, The crosslinked plant material has a density of at least 900 kg / m 3 .

56. The structure of claim 47, wherein, The crosslinked plant material has a density of at least 1200 kg / m 3 .

57. The structure of claim 47, wherein, said crosslinked plant material having a density in the range of 1200 kg / m 3 - 1450 kg / m 3 and including 1200 kg / m 3 and 1450 kg / m 3 .

58. The structure of claim 47, wherein, The plant material is a compact piece having a native lumen and cellulose-based fibers, the native lumen being formed by a generally collapsed one or more cell walls of the plant material, and the cellulose-based fibers forming the cell walls and being aligned along a common direction.

59. The structure of claim 47, wherein, (i) the stabilizing agent is hydrophilic, and / or (ii) the amorphous cellulose regions and / or the hemicellulose regions crosslinked with the stabilizing agent are hydrophilic.

60. The structure of claim 47, wherein, The stabilizing agent has water solubility such that at least 2 g of the stabilizing agent dissolves in 100 mL of water at a temperature of 20 °C.

61. The structure of claim 47, wherein, The stabilizing agent has water solubility such that at least 30 g of the stabilizing agent dissolves in 100 mL of water at a temperature of 20 °C.

62. The structure of claim 47, wherein, The plant material is wood.

63. The structure of claim 47, wherein, The plant material is bamboo.

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