A preparation method for reinforced and toughened wood based on carbon quantum dots

Abstract

The present invention belongs to the technical field of wood modification, and specifically relates to a method for preparing reinforced and toughened wood based on carbon quantum dots. The preparation method comprises the following steps: treating a test material with a carbon quantum dot modification liquid by vacuum pressure impregnation; then sealing the ends of the wood with a capping material and leaving it at room temperature for a period of time; and finally, placing the wood in a drying oven or a drying kiln for heating and drying, thereby obtaining a carbon quantum dot modified material. The carbon quantum dots are surface ion-modified carbon quantum dots; and the concentration of the carbon quantum dot modification liquid is 0.1 to 5% (by mass percentage). The carbon quantum dot preparation method of the present invention is simple, has no solid by-products, and is time-efficient. The present invention uses carbon quantum dots to directly modify wood, has a simple preparation process, a low concentration of modification liquid, and is low-cost, and can be widely promoted and applied. The prepared modified material can increase the absolute value of cell wall crystallinity and achieve expansion of the cell cavity. Under the premise that the overall size and mass of the wood do not change much, the dimensional stability, strength, and toughness of the wood are simultaneously improved, and the strength-to-weight ratio of the wood is improved.

Description

Technical Field

[0001] The invention relates to a preparation method of reinforced and toughened wood based on carbon quantum dots, belonging to the technical field of wood modification. Background Art

[0002] The information disclosed in this background technology section is only intended to enhance understanding of the overall background of the invention and should not necessarily be regarded as an admission or any form of suggestion that the information constitutes the prior art already known to those skilled in the art.

[0003] Wood is a renewable, recyclable, and ecologically sound material, highly valued for its aesthetically pleasing texture, high strength-to-weight ratio, and ease of processing. It is a top choice for construction, furniture, and a variety of other applications. However, hemicellulose, a primary component of wood, is highly hygroscopic, resulting in dimensional instability, deformation, and cracking, and can lead to microbial degradation such as mold and decay. Therefore, to avoid these problems, wood modification is necessary.

[0004] Currently, modification methods that can simultaneously improve both the strength and dimensional stability of wood include resin impregnation (phenolic resins, etc.), monomer impregnation (furfuryl alcohol, 1,3-dimethylol-4,5-dihydroxyethylene urea, etc.), and cross-linking modification (glutaraldehyde, etc.). These methods have demonstrated good results in terms of dimensional stability and mechanical properties (such as surface hardness and compressive strength), but the toughness of most modified materials decreases to varying degrees. For example, in phenolic resin modification, when the density of the modified material increases by 15%, the toughness decreases by 43%. When the weight gain rate of the furfuryl alcohol modified material reaches 70%, the impact toughness of the wood decreases by 57%. This adverse effect is also observed in furfuryl alcohol modified materials with lower weight gain rates. After modification with a concentration of glutaraldehyde of 0.4M, the toughness of the wood decreases by more than 60%. In addition, the performance improvement effect of these modified materials is often inseparable from the weight gain rate, resulting in a significant decrease in the strength-to-weight ratio of the modified material compared to unmodified wood, losing the unique advantage of wood's inherent high strength-to-weight ratio.

[0005] Carbon quantum dots (CQDs) are a type of zero-dimensional carbon nanomaterial, primarily composed of C, H, and O elements. They possess excellent hydrophilicity, low toxicity, and a wide range of synthetic raw materials and simple synthesis methods. Studies have shown that CQDs can significantly alter the physical and chemical structure of wood cellulose. Furthermore, surface ion modification helps enhance the hydrogen bonding between carbon quantum dots and wood components. The inherent properties of CQDs and their modification of cellulose make surface ion-modified CQDs a reasonable choice as modifiers in this study. Therefore, this study used surface ion-modified carbon quantum dots to directly modify wood. By regulating the microstructure of the cell wall, the absolute value of the crystallinity of the wood cell wall and the expansion of the cell cavity were increased, achieving a simultaneous improvement in the dimensional stability, strength, and toughness of the wood and improving the strength-to-weight ratio of the wood, while maintaining minimal changes in the overall size and mass of the wood. Summary of the Invention

[0006] The purpose of the present invention is to prepare lightweight, high-strength and high-toughness wood, and to achieve simultaneous improvement in the dimensional stability, strength and toughness of the wood without much change in the overall size and quality of the wood. A method for strengthening and toughening wood based on carbon quantum dots is provided, comprising the following steps:

[0007] Step 1: Preparation of a carbon quantum dot modification solution. The carbon quantum dots can be prepared using the method of patent application number 202411000022.8, entitled "An ion-based carbon quantum dot and its application in resin curing." Using polybasic organic acid and fluoroborate as raw materials, after fully dissolving them by ultrasound, they are placed in a microwave oven and heated for 3 to 10 minutes to obtain surface ion-modified carbon quantum dots. Then, the carbon quantum dots and ultrapure water are mixed in a certain proportion to obtain a carbon quantum dot modification solution.

[0008] Step 2: Processing and characterization of wood: select wood without bark. If it is a heartwood species, try to select the sapwood part. Saw the wood into test pieces of a certain size.

[0009] Step 3: Vacuum impregnation of the wood with the carbon quantum dot-modified solution. After impregnation, wipe any excess modifier from the surface with a paper towel. To facilitate the entry of the modifier into the cell walls and prevent rapid moisture migration at the ends, the ends of the wood are sealed and left at room temperature for a period of time to diffuse and air-dry. The wood is then dried in a drying oven to obtain a carbon quantum dot-modified material. The modified material exhibits improved physical and mechanical properties, including impact toughness, flexural strength and elastic modulus, compressive strength, and dimensional stability.

[0010] Preferably, in step 1, the concentration of the carbon quantum dot modification solution is 0.1% to 5% by mass.

[0011] Preferably, in step 2, broad-leaved wood, such as poplar, oak, eucalyptus, etc., is included, and coniferous wood, such as fir, radiata pine, Scots pine, etc. is also included.

[0012] Preferably, in the step 3, the specific method of vacuum pressure impregnation is to first perform vacuum treatment for 30 to 60 minutes under a vacuum degree of 0 to -0.1 MPa, and then introduce the carbon quantum dot modification liquid, and then perform pressure treatment for 60 to 120 minutes under a pressure of 0 to 2 MPa. Further preferably, the vacuum degree is -0.05 to -0.1 MPa and the pressure is 0.5 to 2 MPa.

[0013] Preferably, in step 3, after the wood is subjected to vacuum pressure impregnation treatment and before drying, the end-sealing material is one or more of tin foil, tin foil tape, epoxy resin, and polyethylene glycol, and the room temperature placement time is 24 to 72 hours.

[0014] Preferably, in step 3, the drying procedure is to first treat at 40-80°C for 1-6 hours, then treat at 80-105°C for 9-24 hours, remove the end-capping material, and finally dry at 80°C to absolute dryness;

[0015] A carbon quantum dot modified material prepared by the above method.

[0016] The beneficial effects of the present invention are:

[0017] The carbon quantum dots of the present invention are simple to prepare, have no solid byproducts, and are time-efficient. The carbon quantum dots of the present invention are ion-modified, with surfaces rich in hydroxyl, carboxyl, and fluoroborate anions and cations, which enhance hydrogen bonding between the carbon quantum dots and wood components.

[0018] The present invention uses carbon quantum dots to directly modify wood, has a simple preparation process, low concentration of the modified liquid, low cost, and can be widely promoted and applied.

[0019] The modified material of the present invention maintains its unique advantage of high strength-to-weight ratio without much change in the overall size and quality of the wood, thereby achieving simultaneous improvement in the dimensional stability, strength and toughness of the wood, and can increase the absolute value of the crystallinity of the wood cell wall and the expansion of the wood cell cavity. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 Schematic diagram of the bending strength and elastic modulus of the comparative example and Examples 1, 2, and 3.

[0021] Figure 2 Schematic diagram of the compressive strength along the grain of the comparative example and Examples 1, 2, and 3.

[0022] Figure 3 It is a schematic diagram of the impact toughness of the comparative example and Examples 1, 2, and 3.

[0023] Figure 4 Schematic diagram of the strength-to-weight ratio of the comparative example and Examples 1, 2, and 3.

[0024] Figure 5 Schematic diagram of dimensional stability of Examples 1, 2, and 3. DETAILED DESCRIPTION

[0025] The present invention will be further described below with reference to the accompanying drawings and specific embodiments. The embodiments provide detailed implementation methods and specific operating processes, but the protection scope of the present invention is not limited to the following embodiments.

[0026] Example 1

[0027] Preparation of the carbon quantum dot modification solution: 3 parts citric acid and 1 part sodium borofluoride were used as raw materials. After thorough sonication, the solution was heated in a microwave oven for 5 minutes to obtain surface-ion-modified carbon quantum dots. A 0.5% concentration of the carbon quantum dot modification solution was prepared by stirring with a glass rod, yielding a homogeneous, light yellow, clear solution.

[0028] Wood processing and characterization: Populus cathayana was selected and sawn into test pieces with dimensions of 20 mm (axial) × 20 mm (tangential) × 20 mm (radial), 80 mm (axial) × 10 mm (tangential) × 4 mm (radial), and 30 mm (axial) × 20 mm (tangential) × 20 mm (radial).

[0029] Vacuum impregnation of wood: Vacuum treatment is carried out for 45 minutes at a vacuum degree of -0.1MPa, followed by the introduction of the carbon quantum dot modification liquid, followed by a pressure treatment at a pressure of 0.5MPa for 90 minutes. After impregnation, excess modifier is wiped off the surface with a paper towel. To promote the entry of the modifier into the cell wall and prevent excessive movement of moisture at the ends, both ends of the wood are sealed with tin foil and left at room temperature for 24 hours to diffuse and air dry. The wood is then dried in a drying oven: first at 80°C for 1 hour, then at 105°C for 10 hours. The tin foil is removed, and finally, the wood is dried at 80°C to absolute dryness to obtain a carbon quantum dot modified material.

[0030] Example 2

[0031] Preparation of a carbon quantum dot modification solution: 3 parts citric acid and 1 part sodium fluoroborate were used as raw materials. After thorough sonication, the solution was heated in a microwave oven for 5 minutes to obtain surface-ion-modified carbon quantum dots. A 1% concentration of the carbon quantum dot modification solution was prepared by stirring with a glass rod, resulting in a homogeneous, pale yellow, clear solution. The wood was then vacuum-impregnated as in Example 1.

[0032] Example 3

[0033] Preparation of a carbon quantum dot modification solution: 3 parts citric acid and 1 part sodium fluoroborate were used as raw materials. After thorough sonication, the solution was heated in a microwave oven for 5 minutes to obtain surface-ion-modified carbon quantum dots. A 2% concentration of the carbon quantum dot modification solution was prepared by stirring with a glass rod, resulting in a homogeneous, pale yellow, clear solution. The wood was then vacuum-impregnated as in Example 1.

[0034] Comparative Example

[0035] Untreated wood was dried at 103°C until absolutely dry, and physical and mechanical test specimens of the above dimensions were prepared.

[0036] The weight gain, volumetric expansion, and density change rates of Examples 1, 2, and 3 after modification are shown in Table 1. After modification with carbon quantum dots, the weight gain and volumetric expansion rates of the wood were relatively small, indicating that the overall size and quality of the wood did not change significantly. The density of Example 1 remained essentially unchanged, while the density of Examples 2 and 3 increased slightly, demonstrating that the modified material retains the lightweight advantage of wood.

[0037] Table 1 Weight gain rate, volume increase rate and density change rate of Examples 1, 2 and 3

[0038]

[0039]

[0040] Figure 1 This is a schematic diagram of the flexural strength and elastic modulus of the comparative example and Examples 1, 2, and 3. It can be seen that the flexural strength does not change much, while the elastic modulus is significantly improved, up to 70%. This shows that carbon quantum dot modification effectively improves the stiffness of wood. This is mainly because carbon quantum dots cross-link cellulose, making the cell wall structure more compact and able to withstand greater forces without being easily deformed.

[0041] Figure 2 3 is a schematic diagram of the compressive strength along the grain of the comparative example and Examples 1, 2, and 3. It can be seen that the compressive strength along the grain is significantly improved, indicating that the carbon quantum dot modification can effectively improve the strength of the wood. This is mainly because the hydrogen bonds between the carbon quantum dots and cellulose cause the cellulose to cross-link, thereby changing the cell wall structure of the wood.

[0042] Figure 3 The impact toughness of the comparative example and Examples 1, 2, and 3 is shown in the figure. It shows a significant improvement in impact toughness, demonstrating that the present invention can effectively improve both the strength and toughness of wood. This is primarily due to the carbon quantum dots cross-linking the cellulose, reducing the distance between microfibrils and densifying the cell wall. This differs from conventional cell wall expansion, which increases the distance between microfibrils and hinders stress transmission and transfer.

[0043] Figure 4 Schematic diagram of the strength-to-weight ratio of the comparative example and embodiments 1, 2, and 3. It can be seen from the figure that the strength-to-weight ratio is significantly improved, indicating that the present invention not only improves the strength and toughness of wood, but also improves the strength-to-weight ratio of wood.

[0044] Figure 52 is a schematic diagram of the dimensional stability of Examples 1, 2, and 3. It can be seen that the carbon quantum dot modified materials can improve the dimensional stability of wood, and the dimensional stability of Example 3 is better. This is due to the larger capacity increase rate of Example 3.

Claims

1. A method for preparing reinforced and toughened wood based on carbon quantum dots, characterized in that: Using polybasic organic acid and fluoroborate as raw materials to obtain surface ion-modified carbon quantum dots; mixing the carbon quantum dots and water in a certain proportion to obtain a carbon quantum dot modified solution; Then, the carbon quantum dot modified liquid is treated with the wood by vacuum pressure impregnation method, and after treatment, the ends of the wood are sealed with a sealing material and left at room temperature for a period of time; finally, the wood is placed in a drying oven or a drying kiln for heating and drying to obtain a carbon quantum dot modified material.

2. The method for preparing carbon quantum dot reinforced and toughened wood according to claim 1, wherein: Calculated by mass percentage, the concentration of the carbon quantum dot modification liquid is 0.1-5%.

3. The method for preparing carbon quantum dot reinforced and toughened wood according to claim 1, wherein: The vacuum pressure impregnation method is to first perform vacuum treatment for 30 to 60 minutes at a vacuum degree of 0 to -0.1 MPa, then introduce the carbon quantum dot modification liquid, and then perform pressure treatment for 60 to 120 minutes at a pressure of 0 to 2 MPa.

4. The method for preparing carbon quantum dot reinforced and toughened wood according to claim 1, wherein: The end-capping material is one or more of tinfoil, tinfoil tape, epoxy resin, and polyethylene glycol, and the storage time at room temperature is 24 to 72 hours.

5. The method for preparing carbon quantum dot reinforced and toughened wood according to claim 1, wherein: The drying procedure is to first treat at 40-80°C for 1-6 hours, then treat at 80-105°C for 9-24 hours to remove the end-capping material, and finally dry at 40-80°C to constant weight.

6. A wood prepared by the method for preparing reinforced and toughened wood based on carbon quantum dots according to any one of claims 1 to 5.

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