A method for preparing a self-adhesive biomass composite material

Abstract

The application discloses a preparation method of a self-adhesive biomass composite material, and relates to a preparation method of a biomass composite material.The application aims at solving the problems of low gluing strength and poor water resistance of existing glue-free gluing technology.The preparation method comprises the following steps of:preparing a self-adhesive material; and hot pressing.The application is used for the preparation of the self-adhesive biomass composite material.

Description

Technical Field

[0001] This invention relates to a method for preparing a biomass composite material. Background Technology

[0002] my country's annual production of engineered wood products is approximately 300 million cubic meters, accounting for about 50% to 60% of the world's total, ranking first globally for many consecutive years. In terms of volume, it far exceeds that of steel and plastics. Engineered wood products are made by recombining rotary-cut veneers, wood fibers, or wood shavings as basic units. They possess excellent physical and mechanical properties and good processing performance, and are widely used in furniture, flooring, cabinets, doors, windows, and other home furnishing and decorative materials, playing a vital role in national economic development and people's lives. In the past decade, with the rapid development of industries such as customized home furnishings, whole-house customization, and integrated flooring and wall systems, the average annual growth rate of engineered wood consumption in China has approached 10.6%, indicating a vast market development potential.

[0003] However, current wood-based panel production requires adhesives, leading to complex manufacturing processes and increased costs. Furthermore, approximately 90% of adhesives used in wood-based panels are formaldehyde-based resins and their modified forms, which release free formaldehyde, becoming a major source of formaldehyde and volatile organic compounds (VOCs) in indoor air. Simultaneously, the raw materials for formaldehyde-based adhesives are derived from non-renewable fossil fuels, and the organic solvents used in their synthesis also contribute VOCs, thus failing to meet the requirements of sustainable development. Currently, with the transformation of modern production and lifestyles, people spend over 80% of their time working or living indoors. The production of green and environmentally friendly wood-based panel materials is of great and far-reaching significance for creating a healthy and safe indoor living environment and achieving the green and healthy development of the wood-based panel industry and its products.

[0004] Adhesive-free bonding technology, by eliminating the use of adhesives, effectively avoids the health and environmental problems associated with traditional formaldehyde-based adhesives. However, current adhesive-free bonding technologies often require the introduction of additional fillers as crosslinking agents or sealants (such as hexamethylenediamine, furfuryl alcohol, and maleic anhydride) to improve bond strength and water resistance to meet the actual application requirements of the materials. This not only increases the number of processes and costs, but the introduced fillers may also pose environmental and human health hazards during use. In terms of performance, current adhesive-free bonding technologies suffer from low bond strength, especially poor water resistance, which greatly limits their application and makes it difficult to replace existing formaldehyde-based adhesive technologies. Summary of the Invention

[0005] This invention aims to address the problems of low bonding strength and poor water resistance in existing glueless bonding technologies, and thus provides a method for preparing self-adhesive biomass composite materials.

[0006] A method for preparing a self-adhesive biomass composite material, comprising the following steps:

[0007] I. Preparation of self-adhesive materials:

[0008] Biomass materials are immersed in an aqueous solution of sodium periodate or a mixed solution of sodium periodate and sodium chloride, and oxidized and activated for 0.5h to 24h under conditions of protection from light and a temperature of 25℃ to 90℃ to obtain self-adhesive materials.

[0009] II. Hot pressing:

[0010] The moisture content of the self-adhesive material is controlled to be 50%–70%, and then the preforms are assembled and hot-pressed to obtain a self-adhesive biomass composite material.

[0011] The beneficial effects of this invention are:

[0012] (1) The method of the present invention enables all wooden structural units of different sizes to have self-adhesive properties;

[0013] (2) The raw materials used in this invention are not limited to wood resources, but are also suitable for bamboo and agricultural waste (such as sugarcane bagasse).

[0014] (3) The present invention overcomes the defects of low bonding strength and poor water resistance of existing glueless bonding technology. The glueless artificial board material prepared under the preferred conditions has excellent bonding strength and water resistance.

[0015] (4) Since no formaldehyde is added during the preparation process, the preparation is green and there is no formaldehyde release problem. It is environmentally friendly and harmless.

[0016] (5) The self-adhesive material can be prepared by simply impregnating it during the activation treatment process. The process is simple and easy to obtain, and is convenient for industrial production.

[0017] (6) Because hot pressing is carried out under high humidity conditions, the process of drying the wood veneer before hot pressing, which is required for traditional formaldehyde adhesives, is eliminated, which greatly reduces energy consumption.

[0018] (7) The prepared glue-free biomass composite material can be recycled and reused, and has good recyclability and sustainability.

[0019] Instruction manual illustrations

[0020] Figure 1 The diagram shows the preparation of self-adhesive materials in step one of the present invention. (1) Wood, (2) Bamboo, (3) Sugarcane, (4) Veneer, (5) Fiber, (6) Wood shavings, (7) Oxidation activation, (8) Self-adhesive veneer, (9) Self-adhesive fiber, (10) Self-adhesive wood shavings.

[0021] Figure 2 This is a diagram illustrating the self-adhesive mechanism of the present invention;

[0022] Figure 3 The diagram shows the preparation of the self-adhesive biomass composite material of the present invention. (1) Orthogonal preform, (2) Grain-parallel preform, (3) Fiber preform, (4) Particleboard preform, (5) High temperature and high humidity hot pressing, (6) Adhesive-free plywood, (7) Adhesive-free veneer laminated material; (8) Adhesive-free fiberboard; (9) Adhesive-free particleboard.

[0023] Figure 4 Comparison of physical objects and scanning electron microscope images of natural beech veneer and the self-adhesive material prepared in step one of Example 1: a is a physical image of natural beech veneer, b is an electron microscope image of natural beech veneer, c is a physical image of the self-adhesive material prepared in Example 1, and d is an electron microscope image of the self-adhesive material prepared in step one of Example 1.

[0024] Figure 5 1 is the Fourier transform infrared spectrum, 2 is the self-adhesive material prepared in step one of Example 1, and 3 is natural beech veneer.

[0025] Figure 6 The curves showing the change in the degree of oxidation acetal of the self-adhesive material prepared under different oxidation times in step one of Example 1 are shown.

[0026] Figure 7 The values ​​are 1H-13C nuclear magnetic resonance spectra. a represents lignin from natural beech veneer, and b represents lignin from the self-adhesive material prepared in step one of Example 1.

[0027] Figure 8 The image shows a comparison of peeling and impregnation of the self-adhesive beech veneer laminated lumber prepared in Example 5. a is without impregnation, b is after impregnation in cold water at 25°C for 24 hours, and c is after impregnation in hot water at 73°C for 2 hours. A, B, C, and D are the four cross-sectional directions of the lumber.

[0028] Figure 9 SEM images of the self-adhesive beech wood glue-free laminated veneer lumber prepared in Example 5, a is unimpregnated, b is impregnated with hot water at 73°C for 2 hours;

[0029] Figure 10 SEM images of self-adhesive glue-free poplar fiberboard: a) is the glue-free poplar fiberboard prepared in Comparative Experiment 3, and b) is the self-adhesive glue-free poplar fiberboard prepared in Example 7.

[0030] Figure 11 These are XPS spectra, a is the full spectrum scan, and b is the C60 ... 1s Fine spectral scanning: 1 is the self-adhesive glue-free poplar fiberboard prepared in Example 7; 2 is the self-adhesive material prepared in step one of Example 7; and 3 is poplar fiber. Detailed Implementation

[0031] Specific Implementation Method 1: This implementation method provides a method for preparing a self-adhesive biomass composite material, which is carried out according to the following steps:

[0032] I. Preparation of self-adhesive materials:

[0033] Biomass materials are immersed in an aqueous solution of sodium periodate or a mixed solution of sodium periodate and sodium chloride, and oxidized and activated for 0.5h to 24h under conditions of protection from light and a temperature of 25℃ to 90℃ to obtain self-adhesive materials.

[0034] II. Hot pressing:

[0035] The moisture content of the self-adhesive material is controlled to be 50%–70%, and then the preforms are assembled and hot-pressed to obtain a self-adhesive biomass composite material.

[0036] like Figure 1 As shown, this embodiment uses wood, bamboo, straw or bagasse as raw materials, and processes them into veneers, fibers or shavings of a predetermined size through mechanical processing. Then, they are impregnated in an activator for light-proof activation to obtain biomass structural units with self-adhesive function, i.e., self-adhesive materials.

[0037] like Figure 2 As shown, in this embodiment, under high temperature and high humidity, the aldehyde group and hydroxyl group of the self-adhesive material undergo covalent cross-linking, and at the same time, some activated lignin undergoes melt remodeling, resulting in a self-adhesive biomass composite material with high bonding strength and water resistance, thus achieving high-performance glue-free bonding.

[0038] like Figure 3 As shown, self-adhesive materials are assembled under high humidity conditions (orthogonal or parallel assembly can be used when it is veneer), and then hot-pressed under high temperature and high humidity conditions to obtain self-adhesive biomass composite materials. When orthogonal assembly is used, glue-free plywood is obtained; when parallel assembly is used, glue-free veneer laminate is obtained; when fiber assembly is used, glue-free fiberboard is obtained; and when particle assembly is used, glue-free particleboard is obtained.

[0039] This embodiment involves surface activation treatment of natural biomass materials (veneer, fiber, or wood shavings). Hydroxyl groups on the biomass material's surface are converted into aldehyde groups, giving the biomass material self-adhesive properties. Simultaneously, the lignin in the biomass material is activated and partially degraded, lowering its melt-remolding temperature to obtain a self-adhesive material. Subsequently, the self-adhesive material is hot-pressed under high temperature and humidity conditions, causing covalent cross-linking between the materials, resulting in a high-strength, water-resistant self-adhesive biomass composite material (glue-free plywood, glue-free laminated veneer lumber, glue-free fiberboard, or glue-free particleboard).

[0040] The self-adhesive biomass composite material prepared in this embodiment not only has universal applicability to different sized wood structural units (veneer, fiber, or wood shavings), but also to different types of materials (wood, bamboo, straw, or bagasse). The resulting self-adhesive biomass composite material meets national requirements for engineered wood products. Specifically, the glue-free veneer engineered wood product made from wood veneer remained intact after boiling in 63°C hot water for 3 hours, exhibiting high bonding strength and excellent water resistance, meeting the requirements for Class II engineered wood products. The self-adhesive glue-free fiberboard made from bamboo and wood fibers meets the performance requirements of ordinary high-density fiberboard while also exhibiting high moisture resistance. The self-adhesive glue-free particleboard made from wood shavings and bagasse shavings meets the performance requirements of load-bearing particleboard (P3 type) used in a dry state. Furthermore, the glue-free biomass composite material prepared by this method can be recycled and reprocessed, exhibiting good recyclability and sustainability. Therefore, this method is expected to provide new ideas and solutions for replacing existing formaldehyde adhesives in the preparation of green, high-performance glue-free engineered wood products.

[0041] The beneficial effects of this embodiment are:

[0042] (1) The method of this embodiment enables the self-adhesiveness of wooden structural units of different sizes;

[0043] (2) The raw materials used in this embodiment are not limited to wood resources, but are also suitable for bamboo and agricultural waste (such as sugarcane bagasse).

[0044] (3) This embodiment overcomes the defects of low bonding strength and poor water resistance of existing glueless bonding technology. The glueless artificial board material prepared under the preferred conditions has excellent bonding strength and water resistance.

[0045] (4) Since no formaldehyde is added during the preparation process, the preparation is green and there is no formaldehyde release problem. It is environmentally friendly and harmless.

[0046] (5) The self-adhesive material can be prepared by simply impregnating it during the activation treatment process. The process is simple and easy to obtain, and is convenient for industrial production.

[0047] (6) Because hot pressing is carried out under high humidity conditions, the process of drying the wood veneer before hot pressing, which is required for traditional formaldehyde adhesives, is eliminated, which greatly reduces energy consumption.

[0048] (7) The prepared glue-free biomass composite material can be recycled and reused, and has good recyclability and sustainability.

[0049] Specific Implementation Method Two: This implementation method differs from Specific Implementation Method One in that the biomass material mentioned in step one is wood, bamboo, straw, or sugarcane bagasse. Everything else is the same as in Specific Implementation Method One.

[0050] Specific Implementation Method Three: This implementation method differs from Specific Implementation Method One or Two in that the biomass material mentioned in step one is veneer, fiber, or wood shavings. Everything else is the same as in Specific Implementation Method One or Two.

[0051] Specific Implementation Method Four: This implementation method differs from Specific Implementation Methods One to Three in the following ways: When the biomass material is veneer, the veneer length is 10cm to 100cm, the width is 10cm to 100cm, and the thickness is 0.1cm to 5cm; when the biomass material is fiber, the fiber length is 0.05cm to 0.5cm, and the width is 30μm to 50μm; when the biomass material is wood shavings, the shavings length is 0.5cm to 3.5cm, the width is 0.1cm to 0.5cm, and the thickness is 0.01cm to 0.1cm. Everything else is the same as in Specific Implementation Methods One to Three.

[0052] Specific Implementation Method Five: This implementation method differs from Specific Implementation Methods One to Four in that the concentration of the sodium periodate aqueous solution mentioned in step one is 0.01 mol / L to 1 mol / L. Everything else is the same as in Specific Implementation Methods One to Four.

[0053] Specific Implementation Method Six: This implementation method differs from Specific Implementation Methods One to Five in that the concentration of sodium periodate in the mixed solution of sodium periodate and sodium chloride in step one is 0.01 mol / L to 1 mol / L, and the concentration of sodium chloride is 0.1 mol / L to 1 mol / L. Everything else is the same as in Specific Implementation Methods One to Five.

[0054] Specific Implementation Method Seven: This implementation method differs from Specific Implementation Methods One to Six in that the pressure during hot pressing in step two is 0.5 MPa to 20 MPa. Everything else is the same as in Specific Implementation Methods One to Six.

[0055] Specific Implementation Method Eight: This implementation method differs from Specific Implementation Methods One to Seven in that the temperature during hot pressing in step two is 100℃~200℃. Everything else is the same as Specific Implementation Methods One to Seven.

[0056] Specific Implementation Method Nine: This implementation method differs from Specific Implementation Methods One to Eight in that the hot pressing time in step two is 0.5h to 6h. Everything else is the same as Specific Implementation Methods One to Eight.

[0057] Specific Implementation Method Ten: This implementation method differs from Specific Implementation Methods One to Nine in that: in step two, the hot pressing is performed for 40 to 60 minutes under conditions of 5 MPa pressure and 160°C temperature. Everything else is the same as in Specific Implementation Methods One to Nine.

[0058] The beneficial effects of the present invention are verified using the following embodiments:

[0059] Example 1:

[0060] A method for preparing a self-adhesive biomass composite material, comprising the following steps:

[0061] I. Preparation of self-adhesive materials:

[0062] Biomass materials were immersed in a mixed solution of sodium periodate and sodium chloride, and then oxidized and activated for 6 hours under conditions of darkness and temperature of 50°C to obtain a self-adhesive material.

[0063] II. Hot pressing:

[0064] The moisture content of the self-adhesive material was controlled at 50%, and then the blanks were orthogonally assembled and hot-pressed for 40 minutes under a pressure of 5 MPa and a temperature of 160℃ to obtain self-adhesive beech wood glue-free plywood.

[0065] The biomass material mentioned in step one is a beech veneer with a length of 10cm, a width of 10cm, and a thickness of 0.3cm.

[0066] In the mixed solution of sodium periodate and sodium chloride mentioned in step one, the concentration of sodium periodate is 0.05 mol / L and the concentration of sodium chloride is 0.2 mol / L.

[0067] Example 2: This example differs from Example 1 in that step one involves oxidation activation for 8 hours under conditions of darkness and a temperature of 50°C. Everything else is the same as in Example 1.

[0068] Example 3: This example differs from Example 1 in that step one involves oxidation activation for 10 hours under conditions of darkness and a temperature of 50°C. Everything else is the same as in Example 1.

[0069] Example 4: This example differs from Example 1 in that step two controls the moisture content of the self-adhesive material to be 70%. Everything else is the same as in Example 1.

[0070] Example 5: This example differs from Example 1 in that step two involves assembling the blanks along the grain; step two yields self-adhesive beech wood veneer laminated lumber. Everything else is the same as in Example 1.

[0071] Example 6: This example differs from Example 1 in that: in step 2, the moisture content of the self-adhesive material is controlled to be 70%; in step 2, the wood is assembled along the grain; in step 2, self-adhesive beech wood veneer laminated lumber without glue is obtained. Everything else is the same as in Example 1.

[0072] Example 7:

[0073] A method for preparing a self-adhesive biomass composite material, comprising the following steps:

[0074] I. Preparation of self-adhesive materials:

[0075] Biomass materials were immersed in a mixed solution of sodium periodate and sodium chloride, and then oxidized and activated for 6 hours under conditions of darkness and temperature of 50°C to obtain a self-adhesive material.

[0076] II. Hot pressing:

[0077] The moisture content of the self-adhesive material was controlled at 50%, and then the blanks were assembled and hot-pressed for 60 minutes under a pressure of 5 MPa and a temperature of 160℃ to obtain self-adhesive glue-free poplar fiberboard.

[0078] The biomass material mentioned in step one is poplar fiber with a length of 0.05cm to 0.5cm and a width of 30μm to 50μm.

[0079] In the mixed solution of sodium periodate and sodium chloride mentioned in step one, the concentration of sodium periodate is 0.05 mol / L and the concentration of sodium chloride is 0.2 mol / L.

[0080] Example 8: This example differs from Example 7 in that step two controls the moisture content of the self-adhesive material to be 70%. Everything else is the same as in Example 7.

[0081] Example 9: This example differs from Example 7 in that the biomass material mentioned in step one is bamboo fiber with a length of 0.05cm to 0.5cm and a width of 30μm to 50μm; and the self-adhesive, glue-free bamboo fiberboard is obtained in step two. Everything else is the same as in Example 7.

[0082] Example 10:

[0083] A method for preparing a self-adhesive biomass composite material, comprising the following steps:

[0084] I. Preparation of self-adhesive materials:

[0085] Biomass materials were immersed in a mixed solution of sodium periodate and sodium chloride, and then oxidized and activated for 6 hours under conditions of darkness and temperature of 50°C to obtain a self-adhesive material.

[0086] II. Hot pressing:

[0087] The moisture content of the self-adhesive material was controlled at 50%, and then the blanks were assembled and hot-pressed for 40 minutes under a pressure of 5 MPa and a temperature of 160℃ to obtain self-adhesive glue-free poplar particleboard.

[0088] The biomass material mentioned in step one consists of coarse poplar shavings with a length of 0.5cm to 3.5cm, a width of 0.1cm to 0.3cm, and a thickness of 0.015cm to 0.05cm, and fine poplar shavings with a length of 0.5cm to 3.5cm, a width of 0.1cm to 0.3cm, and a thickness of 0.01cm to 0.1cm. The coarse poplar shavings and fine poplar shavings are mixed at an oven-dry weight ratio of 2:1 before being laid.

[0089] In the mixed solution of sodium periodate and sodium chloride mentioned in step one, the concentration of sodium periodate is 0.05 mol / L and the concentration of sodium chloride is 0.2 mol / L.

[0090] Example 11: This example differs from Example 10 in that the biomass material mentioned in step one is sugarcane shavings with a length of 0.5cm to 2cm, a width of 0.1cm to 0.5cm, and a thickness of 0.01cm to 0.05cm; and the self-adhesive, glue-free sugarcane bagasse particleboard is obtained in step two. Everything else is the same as in Example 10.

[0091] Comparative Experiment 1:

[0092] Biomass material is soaked in water for 6 hours under conditions of darkness and temperature of 50°C to obtain water-soaked veneer. The moisture content of the water-soaked veneer is controlled at 50%. Then, the veneer is orthogonally assembled and hot-pressed for 40 minutes under conditions of pressure of 5MPa and temperature of 160°C to obtain beech wood glue-free plywood. The biomass material mentioned in step one is beech wood veneer with a length of 10cm, a width of 10cm and a thickness of 0.3cm.

[0093] Comparative Experiment 2: This comparative experiment differs from Comparative Experiment 1 in that the blanks are assembled along the grain to obtain beech wood laminated veneer lumber without glue. Everything else is the same as in Comparative Experiment 1.

[0094] Comparative Experiment 3: This comparative experiment differs from Comparative Experiment 1 in that: hot pressing was performed for 60 minutes; the biomass material used was poplar fiber with a length of 0.05cm to 0.5cm and a width of 30μm to 50μm; resulting in glue-free poplar fiberboard. Everything else was the same as in Comparative Experiment 1.

[0095] Comparative Experiment 4: This comparative experiment differs from Comparative Experiment 1 in that: hot pressing was performed for 60 minutes; the biomass material used was bamboo fiber with a length of 0.05cm to 0.5cm and a width of 30μm to 50μm; resulting in glue-free bamboo fiberboard. Everything else was the same as in Comparative Experiment 1.

[0096] Comparative Experiment 5: This comparative experiment differs from Comparative Experiment 1 in that the biomass materials used are coarse poplar shavings with a length of 0.5cm–3.5cm, a width of 0.1cm–0.3cm, and a thickness of 0.015cm–0.05cm, and fine poplar shavings with a length of 0.5cm–3.5cm, a width of 0.1cm–0.3cm, and a thickness of 0.01cm–0.1cm. The coarse and fine poplar shavings are mixed at an oven-dry weight ratio of 2:1 before being laid out, resulting in glue-free poplar particleboard. Everything else is the same as in Comparative Experiment 1.

[0097] Comparative Experiment Six: This comparative experiment differs from Comparative Experiment One in that the biomass material used is sugarcane shavings with a length of 0.5cm to 2cm, a width of 0.1cm to 0.5cm, and a thickness of 0.01cm to 0.05cm; resulting in a glue-free sugarcane bagasse particleboard. Everything else is the same as in Comparative Experiment One.

[0098] Comparative Experiment 7: This comparative experiment differs from Example 1 in that the moisture content of the self-adhesive material is controlled at 30% in step two. Everything else is the same as in Example 1.

[0099] Figure 4 Comparison of physical specimens and scanning electron microscope (SEM) images of natural beech veneer and the self-adhesive material prepared in step one of Example 1. a) is a physical image of the natural beech veneer; b) is an SEM image of the natural beech veneer; c) is a physical image of the self-adhesive material prepared in Example 1; d) is an SEM image of the self-adhesive material prepared in step one of Example 1. As can be seen from the physical images of the natural veneer and the self-adhesive material, the surface color of the veneer darkens under the action of the activator. Furthermore, the comparison of the SEM images of the natural veneer and the self-adhesive material shows that the original structure is maintained after activation, indicating that activation does not damage the material.

[0100] Figure 5 The figure shows Fourier transform infrared spectra, where 1 represents the self-adhesive material prepared in step one of Example 1, and 2 represents natural beech veneer. As can be seen from the figure, the activated self-adhesive material exhibits a high optical density at 1735 cm⁻¹. -1 The C=O peak at the veneer showed a significant change compared to the natural veneer, indicating that the activation treatment converted the hydroxyl groups on the veneer surface into more reactive aldehyde groups.

[0101] The activation time in step one of Example 1 was adjusted to 2 hours to 10 hours; Figure 6 The figure shows the variation curves of the oxidation acetal degree of the self-adhesive material prepared under different oxidation times in step one of Example 1. As can be seen from the figure, the degree of oxidation increases with the extension of oxidation time, and the content of aldehyde groups is higher.

[0102] Figure 7The figures show the 1H-13C nuclear magnetic resonance spectra, where a represents the lignin of natural beech veneer, and b represents the lignin of the self-adhesive material prepared in step one of Example 1. As can be seen from the figures, the chemical shift (δ... C / δ H 45-95 / 2.8-5.3) and (δ C / δ H (98-132 / 6.45-9.75) represent the aliphatic and aromatic regions, respectively. Natural lignin is a three-dimensional macromolecule composed of phenylpropane units of varying structures linked by ether and carbon-carbon bonds. 1 H- 13 Methoxy groups (δ¹⁺ γ ... C / δ H The signal at 56.27 / 3.75) was weakened compared to natural lignin. Meanwhile, oxidized lignin showed a lower chemical shift at δ. C / δ H 111.47 / 7.00、δ C / δ H 115.26 / 6.7 and δ C / δ H The signal at 119.48 / 6.76 is significantly reduced, indicating that lignin has undergone structural changes due to oxidation, which may be attributed to the oxidation of lignin's methoxy groups to benzoquinone. (The chemical shift δ...) C / δ H 72.56 / 4.83 and δ C / δ H The signal observed at 86.72 / 4.10 also weakened significantly after oxidation, indicating that lignin was partially degraded after oxidation, forming small molecular structural units.

[0103] Table 1 Performance of Self-Adhesive Beech Glue-Free Plywood

[0104] Dry bond strength (MPa) Wet bond strength at 63℃ (MPa) Comparative Experiment 1 0.33 0.00 (30 min) Comparative Experiment 7 0.30 0.00(3h) Example 1 1.86 0.96(3h) Example 2 1.25 0.54(3h) Example 3 1.12 0.52(3h) Example 4 0.96 0.32(3h) GB / T9846-2015 0.70 0.70(3h)

[0105] As shown in Table 1, the bonding strength was 1.86 MPa when the oxidation time was 6 hours, and it remained as high as 0.93 MPa after boiling in hot water at 63°C for 3 hours (Example 1), meeting the national standard (0.7 MPa) and demonstrating excellent bonding and water resistance. When the veneer oxidation times were 8 hours (Example 2) and 10 hours (Example 3), the dry strengths of the resulting glue-free plywood were 1.25 MPa and 1.12 MPa, respectively, and the wet strengths were 0.54 MPa and 0.52 MPa, respectively. In contrast, the dry bonding strength of untreated natural veneer was only 0.33 MPa, and it would boil in hot water at 63°C for 30 minutes, failing to meet the national standard for service strength (Comparative Experiment 1).

[0106] The reason for the above phenomenon is that during the hot pressing process, the hydroxyl groups on the adjacent interfaces of the unactivated natural veneer only generate hydrogen bonds. The bonding strength provided by this weak intermolecular force is low and it is easily destroyed by water molecules, so it cannot meet the usage standards.

[0107] Meanwhile, it was found that moisture content plays a crucial role in the bonding strength and water resistance of glue-free plywood. When the moisture content is approximately 50%, ideal high strength and high water resistance can be achieved (Example 1). At a lower moisture content of 30%, the dry bonding strength is 0.30 MPa (Comparative Experiment 7). When the moisture content is too high (70%), the bonding strength decreases to 0.90 MPa, while the wet strength is 0.32 MPa (Example 4). The experimental results indicate that the synergistic effect of activation and high humidity conditions gives glue-free plywood excellent bonding performance and high water resistance.

[0108] This is because the high-humidity hot pressing of glueless plywood can generate strong covalent cross-linking, resulting in higher dry and wet strength. On the other hand, if the moisture content is too low, the interfacial reaction will be incomplete, causing a decrease in bonding strength, while if the moisture content is too high, the moisture will be difficult to remove, resulting in a significant decrease in bonding strength.

[0109] Table 2 Performance of Self-Adhesive Beech Glue-Free Laminated Veneer Lumber

[0110]

[0111]

[0112] As shown in Table 2, the self-adhesive beech veneer laminated lumber of Example 5 exhibits high strengths in both the vertical and horizontal loading directions, measuring 10.02 MPa and 10.14 MPa respectively, both meeting the national standard requirements of 5.5 MPa and 6.5 MPa. In contrast, the beech veneer laminated lumber prepared from unactivated natural veneer showed strengths of only 4.92 MPa and 5.46 MPa (Comparative Experiment 2), failing to meet the national standard requirements. Furthermore, the comparative results show that the elastic modulus and static bending strength of the self-adhesive beech veneer laminated lumber of Example 5 are 17569.65 MPa and 145.2 MPa respectively, exceeding the national standard requirements of 15500.00 MPa and 67.50 MPa, demonstrating excellent mechanical properties. The static bending strength and modulus of elasticity of the unactivated beech glue-free laminated veneer lumber were 14369.03 MPa and 47.63 MPa, respectively (Comparative Experiment 2), which were far lower than those of the self-adhesive beech glue-free laminated veneer lumber and failed to meet the requirements of the national standard, thus failing to meet the requirements for use.

[0113] The water resistance of the self-adhesive beech glue-free laminated veneer lumber prepared in Example 5 was tested in accordance with the standard GB / T 20241-2006 Laminated Veneer Lumber. Figure 8 The images show a comparison of peeling and impregnation of the self-adhesive beech veneer laminated lumber prepared in Example 5. a) is before impregnation, b) is after impregnation in cold water at 25°C for 24 hours, and c) is after impregnation in hot water at 73°C for 2 hours. A, B, C, and D are the four cross-sectional orientations of the lumber. It can be clearly observed that no peeling of the adhesive interface was observed at any cross-section of the self-adhesive beech veneer laminated lumber after complete impregnation in cold water for 24 hours and after impregnation in hot water at 73°C for 2 hours, demonstrating excellent water resistance.

[0114] Figure 9 The image shows an SEM image of the self-adhesive beech wood laminated veneer lumber prepared in Example 5. Image a shows the unimpregnated lumber, and image b shows the lumber after being impregnated in hot water at 73°C for 2 hours. The dashed line represents the bonding interface. As can be seen from the image, even after being impregnated in hot water at 73°C for 2 hours, the bonding interface of the self-adhesive beech wood laminated veneer lumber remains very dense, and no cracking was observed. This demonstrates the excellent water resistance of the self-adhesive wood laminated veneer lumber.

[0115] In contrast, beech veneer laminated lumber made from unactivated natural veneers peeled off completely after being immersed in cold water at 25°C for only 30 minutes.

[0116] Table 3 Performance of Self-Adhesive Glue-Free Poplar (Bamboo) Fiberboard

[0117]

[0118]

[0119] According to the relevant testing requirements of the national standard GB / T 31765-2015 High-Density Fiberboard, the performance of glue-free fiberboard was tested, as shown in Table 3. It can be seen that the static bending strength and modulus of elasticity of the self-bonded glue-free poplar fiberboard prepared in Example 7 are 51.03 MPa and 8320.73 MPa, respectively, far exceeding the national standard requirements of 38.00 MPa and 3900.00 MPa. In contrast, the static bending strength and modulus of elasticity of the glue-free wood fiberboard prepared in Comparative Experiment 3 are only 30.22 MPa and 3516.23 MPa, respectively, far lower than those of the self-bonded fiberboard, and fail to meet the national standard requirements. Furthermore, the self-bonded glue-free poplar fiberboard prepared in Example 7 has an extremely high internal bond strength of 1.72 MPa, far exceeding the national standard requirements, while the glue-free wood fiberboard prepared in Comparative Experiment 3 only has a strength of 0.20 MPa, failing to meet the requirements. Regarding water resistance, the self-adhesive, glue-free poplar fiberboard prepared in Example 7 had a 24-hour thickness swelling rate of only 7.06%, lower than the national standard requirement of 16%. In contrast, the glue-free wood fiberboard prepared in Comparative Experiment 3 had a 24-hour thickness swelling rate of 55.26%, more than three times higher than the national standard requirement.

[0120] Bamboo fiber possesses a high aspect ratio and excellent mechanical properties, making it a superior raw material for fiberboard production. Self-adhesive bamboo fiber was obtained by treating bamboo fiber in the same way as wood fiber. The resulting self-adhesive bamboo fiberboard exhibits high strength and high water resistance (Example 9). Its static bending strength and modulus of elasticity are 42.30 MPa and 6257.02 MPa, respectively, significantly higher than the 7.31 MPa and 1310.22 MPa of untreated natural bamboo fiberboard (Comparative Experiment 4), meeting national standards. Furthermore, the internal bond strength of the self-adhesive bamboo fiberboard reaches 1.44 MPa, also significantly higher than the 0.17 MPa of natural bamboo fiberboard, meeting national standards. Regarding water resistance, the self-adhesive bamboo board exhibits a 45.37% improvement in water resistance compared to natural bamboo board. Its 24-hour thickness swelling rate after water absorption is only 7.14%, even lower than that of self-adhesive wood fiberboard.

[0121] The improved mechanical strength and water resistance are attributed to the dense physical and chemically covalently cross-linked structure generated after the activated fibers are hot-pressed. This is confirmed by SEM and XPS analysis of the self-adhesive-free poplar fiberboard. Figure 10SEM images of self-adhesive glue-free poplar fiberboard are shown. Image a shows the glue-free fiberboard prepared in Comparative Experiment 3, and image b shows the self-adhesive glue-free poplar fiberboard prepared in Example 7. As can be seen from the images, the internal structure of the self-adhesive glue-free fiberboard is denser than that of the natural fiber glue-free fiberboard. This is due to the partial degradation of lignin through oxidation, resulting in a lower melting and plasticizing temperature of lignin. Activated lignin can fill the gaps between fibers under hot-pressing temperatures to achieve better water resistance.

[0122] Figure 11 These are XPS spectra, a is the full spectrum scan, and b is the C60 ... 1s Fine spectral scanning shows that 1 is the self-adhesive glue-free poplar fiberboard prepared in Example 7, 2 is the self-adhesive material prepared in step one of Example 7, and 3 is poplar fiber. As can be seen from the figure, the decrease in C=O bond content and the increase in CO bond content indicate that ester bonds have been formed between the oxidized fibers.

[0123] Table 4 Performance of Self-Adhesive Glue-Free Poplar (Bagasse) Particleboard

[0124]

[0125] According to the national standard GB / T 4897-2015 Particleboard, relevant performance tests were conducted on glue-free particleboard. As shown in Table 4, the self-adhesive glue-free poplar particleboard prepared from self-adhesive shavings (Example 10) has a static bending strength and modulus of elasticity of 28.40 MPa and 2345.33 MPa, respectively, which meet the national standard requirements of 15 MPa and 2200.00 MPa. In contrast, the glue-free particleboard prepared from natural shavings (Comparative Experiment 5) has a static bending strength and modulus of elasticity of only 5.61 MPa and 1123.56 MPa, respectively, failing to meet the national standard requirements. The internal bond strength of the self-adhesive glue-free poplar particleboard prepared from self-adhesive shavings is 0.47 MPa, higher than the 0.16 MPa of the self-adhesive glue-free poplar particleboard in Comparative Experiment 5, and also meets the national standard requirements. Regarding water resistance, the 24-hour thickness swelling rate of self-adhesive poplar particleboard made from self-adhesive wood shavings was 14.28%, lower than the national standard requirement of 22%. In contrast, the 24-hour thickness swelling rate of glue-free particleboard made from natural wood shavings was 34.28%, higher than the national standard requirement, and therefore failed to meet the usage requirements.

[0126] Sugarcane bagasse is one of the most abundant agricultural wastes. By converting waste sugarcane bagasse into self-adhesive sugarcane bagasse shavings, the prepared self-adhesive glue-free sugarcane bagasse particleboard (Example 11) exhibits mechanical properties that even surpass those of glue-free fiber particleboard. Its static bending strength and modulus of elasticity are 21.93 MPa and 4572.88 MPa, respectively, and its internal bond strength is 0.50 MPa, all higher than the performance of the self-adhesive glue-free sugarcane bagasse particleboard in Comparative Experiment 6, and meeting the requirements of national standards. More notably, the 24-hour thickness swelling rate of the self-adhesive glue-free sugarcane bagasse particleboard in Example 11 is only 6.11%, far lower than the 27.15% of the self-adhesive glue-free sugarcane bagasse particleboard in Comparative Experiment 6, and also lower than that of self-adhesive wood glue-free particleboard, demonstrating high water resistance.

Claims

1. A method for preparing a self-adhesive biomass composite material, characterized in that... It is done in the following steps: I. Preparation of self-adhesive materials: Biomass materials are immersed in a mixed solution of sodium periodate and sodium chloride, and oxidized and activated for 0.5h to 24h under conditions of darkness and temperature of 50℃~90℃ to obtain self-adhesive materials. The biomass material is veneer, fiber, or wood shavings; When the biomass material is a veneer, the veneer length is 10cm to 100cm, the width is 10cm to 100cm, and the thickness is 0.1cm to 5cm; when the biomass material is fiber, the fiber length is 0.05cm to 0.5cm, and the width is 30μm to 50μm; when the biomass material is wood shavings, the wood shavings length is 0.5cm to 3.5cm, the width is 0.1cm to 0.5cm, and the thickness is 0.01cm to 0.1cm. The concentration of sodium periodate in the mixed solution of sodium periodate and sodium chloride is 0.01 mol / L to 1 mol / L, and the concentration of sodium chloride is 0.1 mol / L to 1 mol / L. II. Hot pressing: The moisture content of the self-adhesive material is controlled at 50% to 70%. Then, the preforms are assembled and hot-pressed for 0.5 to 6 hours under the conditions of hot pressing pressure of 0.5 MPa to 5 MPa and hot pressing temperature of 160℃ to 200℃ to obtain the self-adhesive biomass composite material.

2. The method for preparing a self-adhesive biomass composite material according to claim 1, characterized in that... The biomass material mentioned in step one is wood, bamboo, straw, or sugarcane bagasse.

3. The method for preparing a self-adhesive biomass composite material according to claim 1, characterized in that... In step two, the hot pressing is carried out for 40 to 60 minutes under the conditions of a pressure of 5 MPa and a temperature of 160°C.

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