Tough and moldable green composite wood and preparation method thereof

Abstract

The invention discloses tough and moldable green composite wood and a preparation method thereof. The composite wood is based on natural wood, after lignin is partially removed, a cellulose solvent system is used for activating, swelling and slightly dissolving a fiber skeleton, then a regenerated cellulose solution is poured, gelation is carried out to enable a whole cellulose network to be tightly crosslinked and fixed, and finally washing and drying are carried out to obtain the composite wood. And the moldable wood with high strength and high toughness is obtained. According to the wood obtained through the method, in the final drying process or in the low-humidity state such as short-time wetting after a sample is prepared, high-curvature special-shaped machining such as right-angle machining and wave machining can be achieved, and the wood is rapidly dried to keep the structure stable. The technology is simple, the processing time is short, and the prepared wood has the low-humidity moldability performance and the dry-state high toughness performance and can be widely applied to the fields of sustainable structural parts, formed decorating parts, functional composite materials and the like.

Description

Technical Field

[0001] This invention pertains to wood modification and functionalization, specifically relating to a strong, moldable, green composite wood and its preparation method. Background Technology

[0002] Natural wood, as a renewable structural material, has good specific strength and lightweight properties. However, its processability and strength are often limited by the content of lignin and hemicellulose, resulting in problems such as high rigidity and low plasticity, which limit its processing cost and application.

[0003] The tensile strength parallel to the grain of traditional wood is typically only tens of MPa, about 1 / 20th that of steel. Traditional wood reinforcement methods often employ synthetic resin impregnation (such as phenolic resin PF and urea-formaldehyde resin UF) or hot-pressing densification processes, which can significantly improve strength and dimensional stability. However, these methods suffer from problems such as high environmental burden, lack of ability to process irregular shapes, and low processing efficiency. CN115503066A reports the use of sodium hydroxide / sodium sulfite chemical treatment combined with hot pressing to obtain high-performance densified wood with a tensile strength parallel to the grain of approximately 600 MPa (about 11 times that of logs). This achieves some success in improving mechanical properties, but the resulting material is still a rigid or semi-rigid structure with poor moldability and limited freedom in shape design.

[0004] Wood shaping typically employs hydrothermal treatment and high-frequency medium heating, which carries the risk of wood cracking and results in wood with poor mechanical properties and limited bending curvature. Among existing moldable wood technologies, CN115698091A achieves folding in a wet state by partially deligninating and rehydrating the wood, but requires a prolonged water impact to reach 100% humidity after thorough drying, increasing processing complexity and cost, and making it unsuitable for rapid industrial processing. Zhou et.ACSNano 202317(23),23524-23534 reported that water-plastic wood can achieve irregular wood shaping, but it also suffers from problems such as complex processes, long processes, and slow drying after high humidity deformation. A process for achieving wood bending by combining delignification / softening has been disclosed, such as Chinese patent CN112157751A, which describes a preparation method that uses N,N-dimethylacetamide and LiCl to treat wood micro and nanofibers to expand and slip, making them easy to bend. However, the deformation scale of wood is limited, and the humidity must be maintained at 30%-100% to ensure the structural integrity of the deformation process.

[0005] Therefore, existing technologies still struggle to simultaneously achieve efficient irregular-shaped processing with low moisture content and high strength and toughness, especially under conditions of moisture content below 35% and thickness above 1.0 mm, it is difficult to achieve both plastic deformation and a high fracture strength of over 200 MPa after drying. How to simultaneously achieve mechanical properties and plasticity remains a pressing problem to be solved. Summary of the Invention

[0006] Purpose of the invention: The purpose of this invention is to provide a strong and tough green composite wood with moldability, solving the problems of existing wood and high-performance wood being rigid and difficult to deform and process; another purpose of this invention is to provide a method for preparing this strong and tough, moldable green composite wood, which does not require exogenous additives and has a simple preparation process that can be mass-produced.

[0007] Technical Solution: The strong and moldable green composite wood of this invention is based on natural wood and is composed of a partially lignin-removed natural wood fiber matrix and a regenerated cellulose network. The green composite wood exhibits moldability and high tensile strength when the moisture content is not less than 9%. The strong and moldable green composite wood structure is a fiber network structure with natural wood as the matrix. The fibers generated from partial lignin removal and micro-dissolution are tightly cross-linked with regenerated nanofibers under environmental induction, ultimately resulting in a green composite wood with a dense skeleton, tightly filled internal wood fibers, and tight inter-fiber bonding.

[0008] Preferably, "moldable" refers to the ability to mold wood from a curvature of 0 mm under conditions of a moisture content of not less than 9% and a thickness of not more than 10 mm. -1 From a flat state to a curvature of 1587m -1 Plastic deformation in a bending state; plastic deformation that can achieve the maximum curvature is manifested by the ability to fold 180°.

[0009] More preferably, the strong, moldable green composite wood can achieve a curvature of 0m under conditions of 9%-36.3% moisture content and 1.0-10mm thickness. -1 The flat state to the curvature is at least 1587m -1 Plastic bending in a bending state.

[0010] Preferably, the breaking strength of the green composite wood is 230.2 to 378.2 MPa.

[0011] More preferably, the green composite wood has a breaking elongation of 4.53 to 6.23%.

[0012] The preparation method of the strong, tough, moldable, green composite wood of the present invention includes the following steps:

[0013] (1) Natural wood is pretreated with delignification to obtain pretreated wood;

[0014] (2) After washing and drying the pretreated wood, it is placed in a cellulose solvent system to activate and dissolve it, thus obtaining activated slightly soluble wood;

[0015] (3) Take out the activated micro-dissolved wood vacuum impregnation regenerated cellulose solution;

[0016] (4) It is placed in an environment isolated from moisture to gel, and after drying, green composite wood is obtained.

[0017] Preferably, the natural wood in step (1) is coniferous or broad-leaved wood with a thickness of 1.0 mm to 10 mm.

[0018] In a further preferred embodiment, the cellulose material in step (1) is pulverized before being dissolved.

[0019] Preferably, the solvent system used for delignification in step (1) is one or more of sodium hydroxide solution, sodium sulfite solution, sodium hypochlorite solution, and hydrogen peroxide solution; the treatment time is 12h-72h; and the temperature is 45-100℃.

[0020] Preferably, the cellulose solvent system in step (2) is a lithium chloride / NN dimethylacetamide system.

[0021] Further preferred, the drying method in step (2) includes multiple methods such as baking, natural air drying, and freeze drying.

[0022] More preferably, the environment described in step (2) is an oven.

[0023] In a further preferred embodiment, before activation and dissolution, the wood is placed in a solvent system and impregnated under pressure in a vacuum environment for 3-10 minutes to allow the solvent system to penetrate the entire wood uniformly.

[0024] More preferably, in step (2), the activation temperature of the wood in the N,N dimethylacetamide solution is 150°C.

[0025] -170℃, time for 1h-3h; then lithium chloride and NNN dimethylacetamide were added in a mass ratio of 1:9-1:11, and the wood was dissolved in the lithium chloride / NN dimethylacetamide solution at a temperature of 95℃-110℃ for 1h-3h.

[0026] Preferably, the cellulose source in the regenerated cellulose solution used in step (3) includes wood fiber, bamboo fiber, hemp fiber, cotton fiber, and cellulose containing plant fibers including paper, cellulose powder, and wood powder.

[0027] Preferably, the regenerated cellulose solution used in step (3) is a lithium chloride / NN dimethylacetamide solution, with a cellulose mass fraction of 1%-10%. To prepare the regenerated cellulose solution, a certain amount of cellulose is first placed in the NN dimethylacetamide solution and activated at 150℃-170℃ for 1h-24h. Then, the temperature is adjusted to 95℃-110℃ to dissolve for 2h-24h, and the solution is allowed to stand at room temperature to obtain the regenerated cellulose solution.

[0028] More preferably, the vacuum environment in step (3) is a sealed container with a vacuum degree of -0.09 to 0.01 MPa.

[0029] More preferably, the vacuum impregnation in step (3) can employ a multi-step vacuuming-restoration atmospheric pressure cycle to enhance permeability.

[0030] More preferably, the regenerated cellulose solution in step (3) is left to stand for no less than 6 hours.

[0031] More preferably, the vacuum impregnation time in step (3) is not less than 10 minutes.

[0032] Preferably, the gelation time in step (4) is 3h-24h.

[0033] More preferably, the gelation temperature range in step (4) is 25℃-85℃.

[0034] More preferably, the drying method in step (4) is natural environment drying or hot pressing drying, with a hot pressing temperature of 25℃-85℃ and a pressure not exceeding 20MPa.

[0035] Preferably, in step (4), the product is placed in a mold for shaping during the drying process, or it is stamped and shaped after drying.

[0036] Preferably, the moisture content of the wood in the shaping process described in step (4) is not less than 9%.

[0037] More preferably, the wood used in the shaping process of step (4) has low humidity, with a moisture content of 9%-36.3%.

[0038] This invention relates to a strong, tough, and moldable green composite wood produced by constructing a continuous cellulose network in partially delignified wood and introducing regenerated cellulose to induce interpenetration. The introduced cellulose solution increases the overall hydrogen bond density, strengthens the inter-chain forces of cellulose, and, combined with gelation-induced microfiber bonding, improves structural continuity and interfacial adhesion. Simultaneously, this material exhibits excellent plasticity at low humidity. The well-integrated lignocellulose and the infused regenerated cellulose can undergo hydrogen bond slippage, allowing for stamping or complex bending of irregular structures under low-humidity conditions, such as during the molding stage or after brief wetting, while maintaining good dimensional stability. Therefore, this invention features a simple process, short processing time, and environmentally friendly product, achieving a synergistic improvement in wood structural continuity, dry strength and toughness, and molding potential, endowing wood with moldability similar to thermoplastic materials.

[0039] Beneficial Effects: Compared with existing technologies, this invention has the following significant advantages: The strong, tough, and moldable green composite wood material prepared by this invention significantly improves the tensile and bending strength and other mechanical properties of wood while achieving rapid irregular-shaped processing capabilities for wood of a certain thickness. The tensile strength along the grain can reach 230.2–378.2 MPa, which is 4.2–7.0 times higher than that of ordinary wood. It can achieve bending and other deformations under low humidity and quickly dry and fix the structure, enabling it to meet the application requirements of high-strength structural materials. This green wood material, with its low forming moisture content, short-term wet formability, and ability to maintain high strength in a dry state, will simplify processes and significantly save energy, showing obvious application advantages in furniture, lightweight structures, and functional panels. Attached Figure Description

[0040] Figure 1 This is a picture of the tough, moldable green composite wood material obtained in Example 1, after irregular processing.

[0041] Figure 2 This is a picture of the tough, moldable green composite wood material obtained in Example 2, after irregular processing.

[0042] Figure 3 This is a comparison image of deformation of blank wood.

[0043] Figure 4 This is a scanning electron microscope image of the tensile cross section of the strong, moldable green composite wood prepared in Example 1.

[0044] Figure 5 This is a scanning electron microscope image of the side of the strong, moldable green composite wood obtained in Example 1 after a tensile fracture.

[0045] Figure 6 The image shows a bending electron microscope image of the strong, moldable green composite wood prepared in Example 1.

[0046] Figure 7 The tensile mechanical properties curves of the wood obtained in Example 1 and Comparative Example 1 are shown. Detailed Implementation

[0047] The technical solution of the present invention will be further described below with reference to the accompanying drawings.

[0048] Example 1: A method for preparing a strong, tough, moldable, green composite wood material is as follows:

[0049] (1) Soak 100mm×100mm×2mm dry natural linden wood in 300g of an aqueous solution of 10% sodium hydroxide and 5% sodium sulfite, and place it in a 95℃ environment for delignification for 12h.

[0050] (2) Remove the residual solution after washing and air dry naturally to obtain partially delignified wood. Soak it in 200g DMAc, vacuum impregnate for 5min, activate at 165℃ for 1h, cool to 105℃, add 20g LiCl and stir to dissolve for 1.5h.

[0051] (3) Soak 10.8g of dry cotton fiber in 350g of DMAc solution, activate it in an environment of 165℃ for 1h, cool it down to 105℃, add 35g of LiCl and stir to dissolve for 1h, and leave it at room temperature in the absence of air for 5 days to obtain a fully soluble regenerated cellulose solution with a cotton pulp fiber mass fraction of 3%.

[0052] (4) Take out the activated slightly soluble wood and place it in the regenerated cellulose solution. Transfer it to a vacuum environment and impregnate it under pressure of -0.09MPa for 20 minutes.

[0053] (5) Place the treated cellulose in a 60℃ oven for 12 hours to allow for dense regeneration and cross-linking. Wash and dry to obtain a strong, moldable, green composite wood material. After a brief 15-second immersion in water, it can achieve high deformation without cracking in all directions, including along and perpendicular to the wood fiber grain, under low humidity conditions (15% moisture content). It can achieve right angles and wavy shapes (curvature 125m). -1 It undergoes deformation processing such as folding and drying, and retains its structure.

[0054] The resulting strong, moldable, green composite wood bending and shaping products are as follows: Figure 1 As shown. The thickness is 1.12mm, the tensile strength along the grain reaches 378.2MPa, and the tensile strain is 6.23%. This naturally dried, tough, moldable green composite wood has a moisture content of 8.10%. The material possesses excellent plastic deformation capabilities and can be processed and deformed in low-moisture conditions (it is bendable and foldable, with a maximum bending curvature of 1587m). -1 Afterwards, it should be dried rapidly to maintain structural stability. See the tensile stress-strain curve for wood. Figure 5 Compared with ordinary linden wood (54.1 MPa, 1.38%) and delignified linden wood, its strength is increased by approximately 7.0 times and 2.9 times, respectively.

[0055] Figure 2 The images show scanning electron microscope (SEM) images and magnified details of the tensile fracture section along the grain of the strong, tough, and moldable green composite wood material prepared in Example 1. It can be seen that the regenerated cellulose, which is fully impregnated between the wood fiber skeleton and inside the cell wall, is tightly cross-linked with the partially delignin-removed fiber skeleton and presents a stacked state. The cellulose network is interwoven and solidified with the original wood fibers, which greatly enhances the interfacial bonding force between the fibers in the composite structure and improves the tensile strength and toughness. Figure 3The scanning electron microscope image of its side tear shows that the natural wood retains the highly oriented structure of cellulose fibers. The regenerated cellulose network is distributed throughout the wood pores and between the pores, giving the wood a composite structure with high strength and high toughness. When the wood deforms under low humidity, the dense hydrogen bonds break and recombine in time through the efficient transfer of water molecules, realizing the relative slippage between fibers, thereby achieving plastic deformation and irregular shape processing.

[0056] Example 2

[0057] (1) Soak 100mm×100mm×5mm dry natural linden wood in 300g of an aqueous solution of 10% sodium hydroxide and 5% sodium sulfite, and place it in a 92℃ environment for delignification for 24h.

[0058] (2) Remove the residual solution after washing and air dry naturally to obtain partially delignified wood. Soak it in 300g DMAc, vacuum impregnate for 5min, activate at 165℃ for 1h, cool to 105℃, add 30g LiCl and stir to dissolve for 2h.

[0059] (3) Soak 10.8g of dry cotton fiber in 350g of DMAc solution, activate it in an environment of 165℃ for 1h, cool it down to 105℃, add 35g of LiCl and stir to dissolve for 1h, and leave it at room temperature in the absence of air for 5 days to obtain a fully soluble regenerated cellulose solution with a cotton pulp fiber mass fraction of 3%.

[0060] (4) Take out the activated slightly soluble wood and place it in the regenerated cellulose solution. Transfer it to a vacuum environment and impregnate it under pressure of -0.08MPa for 30 minutes.

[0061] (5) Place it in a 60℃ oven to allow the cellulose to be densely regenerated and crosslinked for 20 hours, then wash and dry to obtain a strong, tough, moldable green composite wood material.

[0062] The resulting strong, moldable, green composite wood, such as Figure 2 As shown, the thickness is 2.19 mm, the tensile strength along the grain reaches 365.2 MPa, and the tensile strain is 5.65%. Even in a low-humidity state with a moisture content of 19%, it can achieve high deformation without cracking in all directions, including along and perpendicular to the wood fiber grain, achieving right angles and wavy shapes (curvature 125 mm). -1 (e.g., deformation processing, and maintaining the structure after drying.)

[0063] Example 3

[0064] (1) Soak 100mm×50mm×10mm dry natural linden wood in 400g of an aqueous solution of 10% sodium hydroxide and 5% sodium sulfite, and place it in a 95℃ environment for delignification for 72h.

[0065] (2) Remove the residual solution after washing and air dry naturally to obtain partially delignified wood. Soak it in 300g DMAc, vacuum impregnate for 10min, activate at 165℃ for 1h, cool to 105℃, add 30g LiCl and stir to dissolve for 3h.

[0066] (3) Soak 7.14g of dry cotton fiber in 350g of DMAc solution, activate it in an environment of 165℃ for 1h, cool it down to 105℃, add 35g of LiCl and stir to dissolve for 1h, and leave it at room temperature in the absence of air for 5 days to obtain a fully soluble regenerated cellulose solution with a cotton pulp fiber mass fraction of 2%.

[0067] (4) Take out the activated slightly soluble wood and place it in the regenerated cellulose solution. Transfer it to a vacuum environment and impregnate it under pressure of -0.09MPa for 30 minutes.

[0068] (5) Place it in a 60℃ oven to allow the cellulose to be densely regenerated and crosslinked for 20 hours, then wash and dry to obtain a strong, tough, moldable green composite wood material.

[0069] The resulting strong, moldable, green composite wood has a thickness of 6.58 mm, a tensile strength parallel to the grain of 352.1 MPa, and a tensile strain of 5.21%. Even under low humidity conditions with a minimum moisture content of 36.3%, it can achieve high deformation without cracking in all directions, including along and perpendicular to the wood fiber grain.

[0070] Example 4

[0071] (1) Soak 100mm×50mm×3mm dry natural linden wood in 300g of an aqueous solution of 10% sodium hydroxide and 5% sodium sulfite, and place it in a 95℃ environment for delignification for 12h.

[0072] (2) Remove the residual solution after washing and air dry naturally to obtain partially delignified wood. Soak it in 200g DMAc, vacuum impregnate for 5min, activate at 165℃ for 1.5h, cool to 105℃, add 20g LiCl and stir to dissolve for 1.5h.

[0073] (3) Crush 14.58g of dry waste paper and soak it in 350g of DMAc solution. Activate it in an environment of 165℃ for 1h, cool it down to 105℃, add 35g of LiCl and stir to dissolve for 2h. Place it at room temperature in the absence of air for 24h to obtain a regenerated cellulose solution with a fiber mass fraction of 4%.

[0074] (4) Take out the activated slightly soluble wood and place it in the regenerated cellulose solution. Transfer it to a vacuum environment and impregnate it under pressure of -0.08MPa for 30 minutes.

[0075] (5) Place it in a 25℃ oven to allow the cellulose to be densely regenerated and crosslinked for 24 hours, then wash and dry to obtain a strong, tough, moldable green composite wood material.

[0076] The resulting strong, moldable, green composite wood has a thickness of 1.8 mm, a tensile strength parallel to the grain of 320.0 MPa, and a tensile strain of 4.73%. Even in a low-humidity state with a moisture content of 13%, it can achieve high deformation in all directions, both parallel and perpendicular to the wood fiber grain, without cracking.

[0077] Example 5

[0078] (1) Soak 100mm×50mm×3mm dry natural linden wood in 200g of an aqueous solution of 15% sodium hydroxide and 7.5% sodium sulfite, and place it in a 95℃ environment for delignification for 12h;

[0079] (2) Remove the residual solution after washing and dry it in an oven at 60°C to obtain partially delignified wood. Soak it in 200g DMAc and activate it at 165°C for 1h. Cool it down to 105°C and add 20g LiCl and stir to dissolve for 1.5h.

[0080] (3) Soak 5.33g of dried bamboo fiber in 350g of DMAc solution, activate it in an environment of 165℃ for 1h, cool it down to 105℃, add 35g of LiCl and stir to dissolve for 1h, and place it at room temperature in the absence of air for 3 days to obtain a fully soluble regenerated cellulose solution with a bamboo fiber mass fraction of 1.5%.

[0081] (4) Take out the activated slightly soluble wood and place it in the regenerated cellulose solution. Transfer it to a vacuum environment and impregnate it under pressure of -0.07MPa for 20min.

[0082] (5) Place it in a 25℃ oven to allow the cellulose to be densely regenerated and crosslinked for 24 hours, then wash and dry to obtain a strong, tough, moldable green composite wood material.

[0083] The resulting strong, moldable green composite wood has a thickness of 2.38 mm, a tensile strength parallel to the grain of 254.2 MPa, and a tensile strain of 4.61%. It can achieve high deformation without cracking in all directions, including along and perpendicular to the wood fiber grain, even under low humidity conditions with a moisture content of 15%.

[0084] Example 6

[0085] (1) Soak 100mm×50mm×3mm dry natural poplar wood in 300g of an aqueous solution of sodium hydroxide with a mass fraction of 8% and sodium sulfite with a mass fraction of 4%, and place it in an environment of 95℃ for delignification for 12h.

[0086] (2) Remove the residual solution after washing and air dry naturally to obtain partially delignified wood. Soak it in 200g DMAc, vacuum impregnate for 5min, activate at 165℃ for 1h, cool to 105℃, add 20g LiCl and stir to dissolve for 1.5h.

[0087] (3) Soak 10.8g of dried hemp fiber in 350g of DMAc solution, activate it in an environment of 165℃ for 1h, cool it down to 105℃, add 35g of LiCl and stir to dissolve for 1h, and place it at room temperature in the absence of air for 3 days to obtain a fully soluble regenerated cellulose solution with a mass fraction of 3% of hemp fiber.

[0088] (4) Take out the activated slightly dissolved wood and place it in the regenerated cellulose solution. Transfer it to a vacuum environment and impregnate it under pressure of -0.06MPa for 20 minutes.

[0089] (5) Place it in a 60℃ oven to allow the cellulose to be densely regenerated and crosslinked for 24 hours, then wash and dry to obtain a strong, tough, moldable green composite wood material.

[0090] The resulting strong, moldable green composite wood has a thickness of 2.30 mm, a tensile strength parallel to the grain of 288.5 MPa, and a tensile strain of 6.01%. Even in a low-humidity state with a moisture content of 18.2%, it can achieve high deformation without cracking in all directions, including along and perpendicular to the wood fiber grain.

[0091] Example 7

[0092] (1) Soak 100mm×50mm×3mm dry natural poplar wood in 300g of an aqueous solution of 10% sodium hydroxide and 5% sodium sulfite, and place it in a 95℃ environment for delignification for 8h.

[0093] (2) Remove the residual solution after washing and freeze-dry to obtain partially delignified wood. Soak it in 200g DMAc at 165℃ for 1.5h, cool it down to 105℃, add 20g LiCl and stir to dissolve for 1.5h.

[0094] (3) Soak 10.8g of dried wood powder in 350g of DMAc solution, activate it in an environment of 165℃ for 1h, cool it down to 105℃, add 35g of LiCl and stir to dissolve for 2h, and leave it at room temperature in the absence of air for 3 days to obtain a fully soluble regenerated cellulose solution with a wood fiber mass fraction of 3%.

[0095] (4) Take out the activated slightly dissolved wood and place it in the regenerated cellulose solution. Transfer it to a vacuum environment and impregnate it under pressure of -0.09MPa for 15min.

[0096] (5) Place it in a 60℃ oven to allow the cellulose to be densely regenerated and crosslinked for 12 hours, then wash and dry to obtain a strong, tough, moldable green composite wood material.

[0097] The resulting strong, moldable green composite wood has a thickness of 2.32 mm, a tensile strength parallel to the grain of 322.2 MPa, and a tensile strain of 4.66%. It can achieve high deformation without cracking in all directions, including parallel and perpendicular to the wood fiber grain, even in a low-humidity state with a moisture content of 17.5%.

[0098] Example 8

[0099] (1) Soak 100mm×100mm×2mm dry natural pine wood in 200g of NaClO aqueous solution with a mass fraction of 10% and place it in a 50℃ environment for delignification for 12h;

[0100] (2) Remove the residual solution after washing and freeze-dry to obtain partially delignified wood. Soak it in 200g DMAc, vacuum impregnate for 5min, activate at 165℃ for 1.5h, cool to 105℃, add 20g LiCl and stir to dissolve for 1.5h.

[0101] (3) Soak 10.8g of dry cellulose powder in 350g of DMAc solution, activate it in an environment of 165℃ for 1h, cool it down to 105℃, add 35g of LiCl and stir to dissolve for 1h, and leave it at room temperature in the absence of air for 2 days to obtain a fully dissolved regenerated cellulose solution with a cellulose mass fraction of 3%.

[0102] (4) Take out the activated slightly soluble wood and place it in the regenerated cellulose solution. Transfer it to a vacuum environment and impregnate it under pressure of -0.09MPa for 10 minutes.

[0103] (5) Place it in a 60℃ oven to allow the cellulose to be densely regenerated and crosslinked for 12 hours, then wash and dry to obtain a strong, tough, moldable green composite wood material.

[0104] The resulting strong, moldable green composite wood has a thickness of 1.44 mm, a tensile strength parallel to the grain of 301.9 MPa, and a tensile strain of 5.89%. Even in a low-humidity state with a moisture content of 18.2%, it can achieve high deformation without cracking in all directions, including along and perpendicular to the wood fiber grain.

[0105] Example 9

[0106] (1) Soak 100mm×100mm×1mm dry natural linden wood in 200g of NaClO aqueous solution with a mass fraction of 10% and place it in an environment of 45℃ for delignification for 8h;

[0107] (2) Remove the residual solution after washing and air dry naturally to obtain partially delignified wood. Soak it in 200g DMAc, vacuum impregnate for 5min, activate at 165℃ for 1h, cool to 105℃, add 20g LiCl and stir to dissolve for 1h.

[0108] (3) Soak 38.9g of dry cotton fiber in 350g of DMAc solution, activate it in an environment of 165℃ for 1h, cool it down to 105℃, add 35g of LiCl and stir to dissolve for 2h, and leave it at room temperature in the absence of air for 5 days to obtain a fully dissolved regenerated cellulose solution with a cellulose mass fraction of 10%.

[0109] (4) Take out the activated slightly soluble wood and place it in the regenerated cellulose solution. Transfer it to a vacuum environment and impregnate it under pressure of -0.09MPa for 10 minutes.

[0110] (5) Place it in an 85℃ oven to allow the cellulose to be densely regenerated and crosslinked for 3 hours, then wash and dry to obtain a strong, tough, moldable green composite wood material.

[0111] The resulting strong, moldable, green composite wood has a thickness of 0.74 mm, a tensile strength parallel to the grain of 230.2 MPa, and a tensile strain of 4.53%. Even in a dry state with a moisture content of 9.0%, it can achieve high deformation without cracking in all directions, including along and perpendicular to the wood fiber grain.

[0112] Example 10

[0113] (1) Soak 100mm×50mm×2mm dry natural linden wood in 300g of aqueous solution containing 75% formic acid and 3% hydrogen peroxide, and place it in an environment of 70℃ for delignification for 8h;

[0114] (2) Remove the residual solution after washing and air dry naturally to obtain partially delignified wood. Soak it in 200g DMAc, vacuum impregnate for 5min, activate at 165℃ for 3h, cool to 105℃, add 20g LiCl and stir to dissolve for 1.5h.

[0115] (3) Soak 10.8g of dried wood fiber in 350g of DMAc solution, activate it in an environment of 165℃ for 1h, cool it down to 105℃, add 35g of LiCl and stir to dissolve for 3h, and place it at room temperature in the absence of air for 5 days to obtain a fully dissolved regenerated cellulose solution with a wood fiber mass fraction of 3%.

[0116] (4) Take out the activated slightly soluble wood and place it in the regenerated cellulose solution. Transfer it to a vacuum environment and impregnate it under pressure of -0.09MPa for 10 minutes.

[0117] (5) Place it in an 80℃ oven to allow the cellulose to be densely regenerated and crosslinked for 12 hours, then wash and dry to obtain a strong, tough, moldable green composite wood material.

[0118] The resulting strong, moldable green composite wood has a thickness of 1.02 mm, a tensile strength parallel to the grain of 241.0 MPa, and a tensile strain of 6.02%. Even in a low-humidity state with a moisture content of 14.5%, it can achieve high deformation without cracking in all directions, including along and perpendicular to the wood fiber grain.

[0119] Comparative Example 1

[0120] Everything else is the same as in Example 1, except that:

[0121] Step (2) Remove the residual solution from the wood washing process and air dry it naturally to obtain partially delignified wood, which is the final wood material.

[0122] The obtained wood has a thickness of 1.65 mm, a tensile strength parallel to the grain of 129.1 MPa, a tensile strain of 1.30%, and a moisture content of 6.52%. It is malleable under high humidity conditions (134% moisture content) after being soaked in water for 12 hours; however, below 80% moisture content, the wood exhibits significant cracking during bending. The tensile stress-strain curve of the obtained wood can be found in [reference needed]. Figure 5 .

[0123] Comparative Example 2

[0124] Everything else is the same as in Example 1, except that:

[0125] After obtaining partially delignified wood, without going through the activation and dissolution process in step (2), it is directly placed in a regenerated cellulose solution, impregnated under vacuum of -0.09MPa for 20 minutes, and then crosslinked in an oven at 60℃ for 12 hours. After washing and drying, the wood material is obtained.

[0126] The resulting wood was 1.72 mm thick, with a tensile strength parallel to the grain of 150.9 MPa, a tensile strain of 3.50%, and a moisture content of 7.31%. It was malleable under high humidity conditions (84.2% moisture content) after being soaked in water for 12 hours. However, when the moisture content was below 80%, the wood developed fine cracks during bending.

[0127] Comparative Example 3

[0128] Everything else is the same as in Example 1, except that:

[0129] After obtaining the wood activated and dissolved in step (2), it is directly placed in water for cross-linking for 12 hours, and then washed and dried to obtain the wood material.

[0130] The resulting wood was 1.68 mm thick, with a tensile strength parallel to the grain of 207.4 MPa, a tensile strain of 3.93%, and a moisture content of 7.75%. It was malleable under high humidity conditions (87.2% moisture content) after being soaked in water for 12 hours. However, when the moisture content was below 70%, the wood developed fine cracks during bending.

[0131] Comparative Example 4

[0132] Everything else is the same as in Example 1, except that:

[0133] The regenerated cellulose solution impregnation process in step (3) is omitted, and the subsequent treatments remain unchanged to obtain wood material.

[0134] The resulting wood was 1.60 mm thick, with a tensile strength parallel to the grain of 245.2 MPa, a tensile strain of 3.50%, and a moisture content of 7.22%. It was malleable when soaked in water for 12 hours at a high humidity of 95% moisture content; however, when the moisture content was below 70%, the wood developed fine cracks during bending.

[0135] Comparative Example 5

[0136] Everything else is the same as in Example 1, except that:

[0137] The regenerated cellulose solution impregnation process in step (3) was carried out at room temperature and pressure for 20 minutes. Subsequent treatments remained unchanged, and wood material was obtained.

[0138] The resulting wood was 1.72 mm thick, with a tensile strength parallel to the grain of 220.0 MPa, a tensile strain of 3.00%, and a moisture content of 7.55%. It was malleable under high humidity conditions (89.2% moisture content) after being soaked in water for 12 hours. However, when the moisture content was below 70%, obvious cracks appeared during bending.

[0139] Comparative Example 6

[0140] Everything else is the same as in Example 1, except that:

[0141] The delignification pretreatment process in step (1) and the activation and dissolution process in step (2) are omitted, and the remaining treatments remain unchanged to obtain wood material.

[0142] The obtained wood has a thickness of 1.91 mm, a tensile strength parallel to the grain of 62.3 MPa, a tensile strain of 2.15%, and a moisture content of 7.51%. It exhibits high brittleness, showing signs of bending and brittle fracture, whether under low humidity conditions or after being soaked in water for 12 hours at a high humidity level of 100.3%.

[0143] Comparative Example 7

[0144] Everything else is the same as in Example 1, except that:

[0145] The delignification pretreatment process in step (1) and the vacuum impregnation process of regenerated cellulose solution in steps (3) and (4) are omitted, and the remaining treatments remain unchanged to obtain wood material.

[0146] The obtained wood has a thickness of 1.86 mm, a tensile strength parallel to the grain of 71.0 MPa, a tensile strain of 2.33%, and a moisture content of 6.66%. It exhibits high brittleness, showing signs of bending and brittle fracture, whether under low humidity conditions or after being soaked in water for 12 hours at a high humidity level of 79.5%.

[0147] Comparative Example 8

[0148] Everything else is the same as in Example 1, except that:

[0149] The delignification pretreatment process in step (1) is omitted, and the subsequent treatments remain unchanged to obtain wood material.

[0150] The obtained wood has a thickness of 1.84 mm, a tensile strength parallel to the grain of 89.0 MPa, a tensile strain of 1.37%, and a moisture content of 7.37%. It exhibits high brittleness, showing signs of bending and brittle fracture, whether under low humidity conditions or after being soaked in water for 12 hours at a high humidity level of 92.8%.

[0151] Comparative Example 9

[0152] Everything else is the same as in Example 1, except that:

[0153] Step (4) After taking out the soaked wood, place it directly in water for cross-linking for 12 hours, wash and dry to obtain wood material.

[0154] The resulting wood has a thickness of 1.57 mm, a tensile strength parallel to the grain of 224.4 MPa, a tensile strain of 4.44%, and a moisture content of 7.14%. It can be bent and shaped under high humidity conditions (84.6% moisture content) after being soaked in water for 12 hours. However, under the same low humidity conditions as in Example 1, it is prone to irregular cracks along the fiber direction when bent.

[0155] Comparing Example 1 and Comparative Example 1, it can be seen that if only the wood is treated with delignification, although the lignin that maintains the stiffness is removed from the wood structure, it can complete the irregular shape processing under high humidity. The drying process causes the treated wood fibers to shrink and become dense, thereby improving the strength. However, the connection between the fibers is not tight enough, and there is a lack of sufficient hydrogen bond density, resulting in many defects. Stable bending and other deformations cannot be achieved under low humidity, which also leads to a lack of significant improvement in tensile stress. Comparing Example 1 and Comparative Examples 4-5, it can be seen that the regenerated cellulose solution needs to be vacuum impregnated to fully fill the wood skeleton for cross-linking, so as to achieve efficient water molecule transfer and hydrogen bond breaking and recombination. Comparing Example 1 and Comparative Examples 6-8, it can be seen that if the wood does not undergo the delignification step, the rigid lignin components will maintain the high brittleness of the wood in the cell walls of the wood fibers. Later micro-dissolution and impregnation with regenerated cellulose solution cannot affect the lignin. Although the resulting structure achieves improved strength and toughness due to fiber cross-linking, the deformation capacity is not improved. Comparing Example 1 and Comparative Example 9, it can be seen that if the treated wood is gelled and shaped in a high humidity environment, the cellulose regeneration in the process is too rapid, the cross-linking network is not tight enough and voids are easy to appear. As a result, the final wood strength is not as good as the tightly cross-linked state in low humidity, and multiple micro-cracks and other defects are easy to appear when deformed in low humidity.

Claims

1. A strong, moldable, green composite wood, characterized in that, The green composite wood is based on natural wood and is composed of a partially lignin-free natural wood fiber matrix and a regenerated cellulose network. The green composite wood has moldability and high tensile strength when the moisture content is not less than 9%.

2. The strong, moldable, green composite wood according to claim 1, characterized in that, Moldability refers to the ability of wood to change from a curvature of 0m under conditions of a moisture content of not less than 9% and a thickness of not more than 10mm. -1 From a flat state to a curvature of 1587m -1 Plastic deformation in a bending state; plastic deformation that can achieve the maximum curvature is manifested by the ability to fold 180°.

3. The strong, moldable, green composite wood according to claim 1, characterized in that, The fracture strength of the green composite wood is 230.2–378.2 MPa.

4. A method for preparing the strong, tough, moldable green composite wood according to claim 1, characterized in that, Includes the following steps: (1) Natural wood is pretreated with delignification to obtain pretreated wood; (2) After washing and drying the pretreated wood, it is placed in a cellulose solvent system to activate and dissolve it, thus obtaining activated slightly soluble wood; (3) Take out the activated micro-dissolved wood vacuum impregnation regenerated cellulose solution; (4) It is placed in an environment isolated from moisture to gel, and after drying, green composite wood is obtained.

5. The method for preparing the strong, tough, moldable green composite wood according to claim 4, characterized in that, The natural wood mentioned in step (1) is coniferous or broad-leaved wood with a thickness of 1.0mm-10mm.

6. The method for preparing the strong, tough, moldable green composite wood according to claim 4, characterized in that, In step (1), the solvent system used for delignification is one or more of sodium hydroxide solution, sodium sulfite solution, sodium hypochlorite solution, and hydrogen peroxide solution; the treatment time is 12h-72h; and the temperature is 45-100℃.

7. The method for preparing the strong, tough, moldable green composite wood according to claim 4, characterized in that, The cellulose solvent system in step (2) is a lithium chloride / NN dimethylacetamide system.

8. The method for preparing the strong, tough, moldable green composite wood according to claim 4, characterized in that, The cellulose sources in the regenerated cellulose solution used in step (3) include wood fiber, bamboo fiber, hemp fiber, cotton fiber, and cellulose containing plant fibers, including paper, cellulose powder, and wood flour.

9. The method for preparing the strong, tough, moldable green composite wood according to claim 4, characterized in that, The regenerated cellulose solution used in step (3) is a lithium chloride / NN dimethylacetamide solution with a cellulose mass fraction of 1%-10%.

10. The method for preparing the strong, tough, moldable green composite wood according to claim 4, characterized in that, The gelation time in step (4) is 3h-24h.

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