Super-tough flame-retardant plastic mineralized composite wood as well as preparation method and application thereof

Abstract

The invention discloses super-tough flame-retardant plastic mineralized composite wood as well as a preparation method and application thereof. Natural wood is delignified, then is soaked in water for plasticizing, then is oxidized by using an oxidizing agent, cellulose hydroxyl is converted into carboxyl so as to provide mineralization nucleation sites, and in-situ mineralization of calcium carbonate in the wood is further realized in calcium salt and soluble carbonate; and finally, the density is greatly improved through water soaking and hot pressing treatment, and the mineralized composite wood is obtained. The mineralized composite wood has ultrahigh strength, high toughness, excellent flame retardance and plasticity, and the performance of the mineralized composite wood is obviously superior to that of natural wood and traditional structural materials. The preparation method provided by the invention is green and low in cost, and the obtained product is suitable for the fields of light high-strength structural materials and multifunctional composite materials, and has wide application prospects in the fields of buildings, energy sources and the like.

Description

Technical Field

[0001] This invention belongs to the field of composite material research, and specifically relates to an ultra-tough, flame-retardant, plastic mineralized composite wood, its preparation method, and its application. Background Technology

[0002] Natural wood is a renewable, low-cost material with a porous structure and unique anisotropy. It also boasts a small carbon footprint, low environmental impact, and good mechanical properties. In recent years, wood and its derived composites have been widely used as structural and functional materials in fields such as construction, energy, environment, and catalysis, and are expected to lead the development of green materials. However, the strength and stiffness of wood are significantly inferior to those of metals and polymer engineering composites. Furthermore, wood's deformation capacity is relatively limited, and its flammability greatly restricts its wider application. To enhance the competitiveness of wood in lightweight structural and functional material applications, there is an urgent need to develop a simple and scalable method to prepare novel wood-based composites that are tough, easily shaped, and possess numerous functions such as flame retardancy and electrical conductivity.

[0003] Nature has created many structural and functional materials, such as shrimp and crab shells, which possess excellent mechanical properties. Existing research has shown that these widely existing natural structural and functional materials are organic / inorganic composite materials formed by biomineralization of natural polymer organic templates. They possess unique layered and ordered structures, exhibiting extraordinary mechanical properties, such as excellent stiffness and strength. Inspired by the formation of shrimp and crab shells, in-situ mineralization of wood as an organic template to generate calcium carbonate inorganic phases holds promise for improving the mechanical properties of natural wood. However, the key to successfully mimicking the formation of shrimp and crab shells is that the wood organic template can efficiently mineralize to generate calcium carbonate, and that a stable bond can be formed between the generated calcium carbonate inorganic phase and the wood organic phase. Existing reports mainly cover two approaches to biomineralization to generate calcium carbonate: one is based on the formation of calcium carbonate from calcium salts and carbonates. The rapid formation of calcium carbonate somewhat affects the effective mineralization within the wood, and the bonding force between the generated calcium carbonate inorganic phase and the wood template organic phase is relatively weak; the other approach involves first preparing amorphous calcium carbonate (ACC), and then using ACC to diffuse into the wood interior for further mineralization to generate calcium carbonate. The challenge lies in the poor thermodynamic stability of ACC, which rapidly transforms into stable crystalline polymorphs such as calcite and aragonite, thus affecting the effectiveness of biomineralization. In contrast, naturally occurring ACC in organisms is quite stable in its surrounding environment, and this excellent stability has been shown to be related to acidic organic biomolecules, such as polyaspartic acid-rich proteins. Among these, carboxyl-rich polymers (polyaspartic acid, polyacrylic acid, etc.) have been extensively explored to prevent ACC nucleation and crystallization for efficient mineralization due to their high calcium binding efficiency. However, these carboxyl-rich polymers are often expensive, have poor biocompatibility or are non-degradable, have low efficiency in introducing pathways into wood, and lack effective bonding with the wood matrix, limiting their efficiency in guiding mineralization and their potential applications in wood mineralization.

[0004] Therefore, designing a more effective, green, and simple method to introduce a large number of carboxyl groups that promote mineralization nucleation sites, replacing the currently used carboxyl polymer stabilizers, and achieving regulated and efficient guidance of biomineralization of calcium carbonate in the wood matrix; on this basis, further enhancing the mechanical properties and multifunctionality of mineralized wood, and endowing it with high plasticity, is of great significance for better utilizing green natural materials such as wood. Summary of the Invention

[0005] In order to overcome the shortcomings of the prior art, the primary objective of this invention is to provide a method for preparing ultra-tough, flame-retardant, plastic mineralized composite wood.

[0006] Another objective of this invention is to provide an ultra-strong, tough, flame-retardant, and malleable mineralized composite wood obtained by the above-described preparation method. This mineralized composite wood is composed of a carboxyl-rich malleable wood matrix and mineralized calcium carbonate. The carboxyl-rich wood matrix provides numerous available nucleation sites for the mineralization of calcium carbonate, enabling efficient mineralization of the wood matrix and ensuring interfacial stability between the organic phase of the wood matrix and the inorganic phase of calcium carbonate. Furthermore, this type of mineralized composite wood, as a novel ultra-strong, tough, lightweight organic / inorganic composite material, possesses excellent mechanical properties, as well as multifunctional characteristics such as flame retardancy, electrical conductivity, and malleability.

[0007] Another object of the present invention is to provide the application of the above-mentioned ultra-tough, flame-retardant, plastic mineralized composite wood.

[0008] To achieve the above-mentioned objectives, the present invention adopts the following technical solution: a method for preparing ultra-strong, tough, flame-retardant, and plastic mineralized composite wood, comprising the following steps: (1) Natural wood is delignified, then washed until neutral, dried, and soaked in water to obtain plastic wood; (2) The plastic wood obtained in step (1) is subjected to oxidation treatment, washed until neutral, and dried to obtain oxidized wood rich in carboxyl groups; (3) Immerse the oxidized wood obtained in step (2) into a soluble calcium salt solution and stir to react. Then add soluble carbonate and continue stirring to react. In-situ mineralization is carried out to generate calcium carbonate. Wash and dry to obtain mineralized plastic wood. (4) The mineralized plastic wood obtained in step (3) is soaked in water and then densified by hot pressing to obtain mineralized composite wood.

[0009] The natural wood mentioned in step (1) is at least one of natural balsa wood, natural linden wood, natural beech wood, and natural walnut wood.

[0010] The delignification process described in step (1) is preferably performed by treating natural wood with an alkaline solution.

[0011] The alkaline solution is a solution containing NaOH and Na2SO3; wherein the molar ratio of NaOH to Na2SO3 is 2.0 to 5.0:1; preferably 2.5 to 4.0:1.

[0012] The concentration of NaOH in the alkaline solution is preferably 1 to 3 mol / L; more preferably 1 to 2.5 mol / L.

[0013] The concentration of Na2SO3 in the alkaline solution is preferably 0.3 to 0.8 mol / L; more preferably 0.4 to 0.7 mol / L.

[0014] The specific steps of the treatment are as follows: first, soak the natural wood in an alkaline solution, and then react at 60-120℃ for 6-48 hours.

[0015] The preferred soaking method is vacuum impregnation; the purpose is to allow the alkaline solution to fully penetrate the pores of the wood.

[0016] The vacuum impregnation conditions are preferably -70 to -90 kPa for 5 to 15 min; more preferably -80 kPa for 10 min.

[0017] The preferred reaction conditions are 100–110°C for 20–24 hours.

[0018] The preferred solvent for washing in step (1) is deionized water.

[0019] The drying conditions described in step (1) are preferably natural air drying at 20-30°C for 20-30 hours; more preferably natural air drying at 24-26°C for 20-30 hours.

[0020] The water immersion treatment conditions described in step (1) are preferably immersion at 20-30°C for 3-10 minutes; more preferably immersion at 24-26°C for 4-6 minutes; and most preferably immersion at 25°C for 5 minutes.

[0021] The preferred specific operation of the oxidation treatment in step (2) is as follows: mix the plastic wood obtained in step (1) with the oxidant solution and react under stirring; first adjust the pH of the reaction system to 10.0 to 11.0, and maintain the pH of the reaction system at 10.0 to 11.0 during the reaction process.

[0022] The preferred oxidant is TEMPO (2,2,6,6-tetramethylpiperidine oxide), NaBr (sodium bromide), and NaClO (sodium hypochlorite) in a molar ratio of 1:10-15:100-150; more preferably, it is in a molar ratio of 1:10:100.

[0023] The concentration of TEMPO in the oxidant solution is preferably 0.5–2 mmol / L, more preferably 1–1.5 mmol / L; the concentration of NaBr is preferably 5–20 mmol / L, more preferably 10–15 mmol / L; and the concentration of NaClO is preferably 50–200 mmol / L, more preferably 100–150 mmol / L.

[0024] The stirring speed is preferably 200-800 rpm; more preferably 400-600 rpm; and most preferably 500 rpm.

[0025] The pH adjuster is preferably an HCl solution or a NaOH solution.

[0026] The concentration of the HCl solution is preferably 0.1 to 0.3 mmol / L; more preferably 0.2 mmol / L.

[0027] The concentration of the NaOH solution is preferably 0.2–1.0 mmol / L; more preferably 0.5–1.0 mmol / L.

[0028] The pH value is preferably 10.4–10.6; more preferably 10.5. The preferred reaction conditions are 20–30°C for 0.5–3 hours; more preferably 20–30°C for 1–2 hours; and most preferably 24–26°C for 1–2 hours.

[0029] The preferred washing steps in step (2) are: first wash with deionized water, then soak in anhydrous ethanol, and then wash with deionized water.

[0030] The soaking time is preferably 0.5 to 10 minutes; more preferably 5 minutes.

[0031] The drying conditions described in step (2) are preferably natural air drying at 20-30°C; more preferably natural air drying at 24-26°C.

[0032] The soluble calcium salt mentioned in step (3) is preferably calcium chloride (CaCl2).

[0033] The concentration of the soluble calcium salt solution in step (3) is preferably 0.2 to 2.0 mol / L; more preferably 1.0 to 1.5 mol / L.

[0034] The stirring reaction conditions described in step (3) are preferably 20-30°C for 0.5-48 h; more preferably 20-30°C for 10-15 h; and even more preferably 24-26°C for 12 h.

[0035] The soluble carbonate mentioned in step (3) is preferably at least one of sodium carbonate (Na2CO3) or sodium bicarbonate (NaHCO3).

[0036] The amount of soluble carbonate used in step (3) is preferably calculated based on a molar ratio of carbonate ions to calcium ions of 1:1.

[0037] The preferred conditions for the continued reaction in step (3) are 20-30°C for 0.5-48 hours; more preferably 20-30°C for 10-15 hours; and most preferably 24-26°C for 12 hours.

[0038] The preferred solvent for washing in step (3) is deionized water.

[0039] The drying conditions described in step (3) are preferably natural air drying at 20-30°C for 12-48 hours; more preferably natural air drying at 24-26°C for 18-24 hours.

[0040] The preferred conditions for the water immersion treatment in step (4) are immersion at 20-30°C for 10-3 minutes; more preferably immersion at 24-26°C for 30-90 seconds; and most preferably immersion at 25°C for 60 seconds.

[0041] The hot pressing densification process described in step (4) is preferably carried out using a flat vulcanizing machine.

[0042] The preferred processing conditions are preheating at 30–50°C and normal pressure for 5–30 s; followed by hot pressing at 60–120°C and a pressure of 0.5 MPa–5 MPa, perpendicular to the wood fiber growth direction, for 5 min–12 h; more preferably, preheating at 40°C and normal pressure for 20 s; followed by hot pressing at 80–100°C and a pressure of 1 MPa–3 MPa, perpendicular to the wood fiber growth direction, for 1–2 h.

[0043] A super-tough, flame-retardant, plastic mineralized composite wood is obtained by the above preparation method.

[0044] The aforementioned ultra-tough, flame-retardant, plastic mineralized composite wood is used as a novel ultra-tough lightweight structural material and / or functional material.

[0045] The functional materials mentioned include flame-retardant materials, energy materials, and biomaterials.

[0046] The above-mentioned ultra-tough, flame-retardant, plastic mineralized composite wood is used in the construction or energy fields.

[0047] Compared with the prior art, the present invention has the following advantages and beneficial effects: (1) The preparation of plastic wood based on natural wood is not only conducive to the introduction of carboxyl groups and mineralization in wood oxidation treatment, but also realizes the hot pressing densification treatment of mineralized composite wood under mild conditions.

[0048] (2) Oxidizing the wood transforms the hydroxyl groups on the cellulose molecules of the wood matrix into carboxyl groups, which provides a large number of nucleation sites for mineralization, thus achieving efficient mineralization of the wood matrix without the addition of polyanionic compounds such as PAA. Moreover, the wood matrix itself is rich in carboxyl groups to guide mineralization, and the mineralization products form chemical bonds with the wood matrix, ensuring the interfacial bonding between the organic phase of the wood matrix and the inorganic phase of calcium carbonate.

[0049] (3) By regulating the degree of oxidation of plastic wood, the carboxyl content of the wood matrix can be regulated, thereby guiding and regulating the formation and content of mineralized calcium carbonate, realizing flexible regulation of the composition and performance of mineralized composite wood to meet different application needs.

[0050] (4) The mineralized composite wood prepared by the present invention is an organic / inorganic composite material in composition. In terms of microstructure, it is composed of closely arranged oriented cellulose nanofibers. Multi-scale hydrogen bonds are formed between the fibers, and strong interfacial bonding is generated with the inorganic mineralization layer, which endows this type of novel mineralized composite wood with super strength, super toughness and anisotropic mechanical properties.

[0051] (5) The mineralized composite wood prepared by the present invention not only has excellent mechanical properties, but also has good biocompatibility, flame retardancy, electrical conductivity and plasticity and other multifunctional properties.

[0052] (6) The super-tough flame-retardant plastic mineralized composite prepared by the present invention also has the advantages of wide availability of raw materials, low cost, mild preparation conditions and large-scale production, and is expected to have good application prospects in the fields of new high-strength and tough lightweight structural materials and functional materials. Attached Figure Description

[0053] Figure 1 Tensile stress-strain curves for natural wood, plastic wood, oxidized wood, mineralized plastic wood, and mineralized composite wood.

[0054] Figure 2 This is a photograph of a piece of mineralized malleable wood that has been shaped into a six-pointed star and the English letters JNU after being impacted by water.

[0055] Figure 3 Photographs of mineralized plastic wood (A) and load-bearing wood (B) are shown.

[0056] Figure 4 XRD patterns of natural wood, plastic wood, oxidized wood, and mineralized plastic wood.

[0057] Figure 5 The left image is a scanning electron microscope (SEM) image of a longitudinal section of natural wood, and the right image is a scanning electron microscope (SEM) image of a longitudinal section of mineralized plastic wood.

[0058] Figure 6 A comparison chart showing the flame retardant effects of natural wood, plastic wood, oxidized wood, mineralized plastic wood, and mineralized composite wood.

[0059] Figure 7 The image shows a comparison of the stress-strain curves of the mineralized plastic wood obtained in Example 6 and Comparative Example 1.

[0060] Figure 8The images show (A) of plastic wood after it has been soaked in water and (B) of dry plastic wood after it has been bent. Detailed Implementation

[0061] The present invention will now be described in further detail with reference to specific embodiments and accompanying drawings. Unless otherwise specified, all raw materials and reagents used in the present invention are commercially available and conventional. The amounts of each component used in the embodiments are expressed in parts by mass and volume; when the mass is g, the volume is mL. Unless otherwise specified, the solvent used in the solutions of the present invention is deionized water.

[0062] Example 1 A super-tough, flame-retardant, plastic, mineralized composite wood is prepared through the following steps: (1) Take natural balsa wood (size: 5 cm × 2 cm × 0.2 cm) and immerse it completely in a composite alkaline solution containing 2.0 mol / L NaOH and 0.5 mol / L Na2SO3. Vacuum impregnation treatment (vacuum degree: -80 KPa, time: 10 min) is then performed to allow the alkaline solution to fully penetrate the wood pores. The wood and solution are then transferred to a flask and treated at 100℃ for 24 hours to remove lignin. The wood is then removed, rinsed with deionized water until neutral, and then air-dried at 25℃ for 24 hours. The air-dried wood is then immersed in deionized water at 25℃ for 5 min to obtain malleable wood that can be shaped in any way.

[0063] (2) The plasticized wood was completely immersed in a mixed aqueous solution containing 1 mmol / L TEMPO, 10 mmol / L NaBr, and 100 mmol / L NaClO, with a stirring speed of 500 rpm. First, a 0.2 mmol / L HCl solution was added dropwise to adjust the pH of the mixed solution to 10.5. Then, a 0.5 mmol / L NaOH solution was slowly added dropwise during the reaction to maintain the pH of the mixed solution at approximately 10.5. After reacting at 25°C for 2 hours, the wood was removed, rinsed three times with deionized water, and then soaked in anhydrous ethanol for 5 minutes to replace any residual solution. It was then rinsed again with deionized water until neutral and air-dried at 25°C to obtain carboxyl-rich oxidized wood.

[0064] (3) Immerse the oxidized wood completely in a 1.0 mol / L CaCl2 solution and stir at 25°C for 12 hours. Add anhydrous Na2CO3 powder to the reaction solution (controlling the concentration of Na2CO3 in the mineralization mixture to 1.0 mol / L) and continue stirring for 12 hours. Remove the wood, rinse the surface repeatedly with deionized water to remove residual salt, and air dry at 25°C for 24 hours to obtain mineralized plastic wood.

[0065] (4) Soak the mineralized plastic wood in deionized water at 25°C for 1 min, and then place the wood in a flat vulcanizing machine. The preheating conditions are as follows: atmospheric pressure at 40°C for 20 s; then hot-press at 80°C and 3 MPa for 2 hours perpendicular to the direction of wood fiber orientation. Remove the wood and cool it at room temperature (25°C) to obtain mineralized composite wood.

[0066] The tensile properties of the wood before and after modification were characterized, and the results are as follows: Figure 1 As shown, the tensile strength of the mineralized composite wood after hot pressing reached 420±20 MPa, which is nearly 38 times higher than that of natural wood (10±2 MPa), and significantly better than other modified wood samples such as mineralized plastic wood (80±10 MPa), plastic wood (60±5 MPa) and oxidized wood (30±4 MPa), demonstrating excellent tensile properties.

[0067] Example 2 A super-tough, flame-retardant, plastic, mineralized composite wood is prepared through the following steps: (1) Take natural balsa wood (size: 5 cm × 2 cm × 0.2 cm) and immerse it completely in a composite alkaline solution containing 2 mol / L NaOH and 0.6 mol / L Na2SO3. Vacuum impregnation treatment (vacuum degree: -80 KPa, time: 10 min) is then performed to allow the alkaline solution to fully penetrate the wood pores. The wood and solution are then transferred to a flask and treated with delignification at 105℃ for 24 hours. The wood is then removed, rinsed with deionized water until neutral, and then air-dried at 25℃ for 24 hours. The air-dried wood is then immersed in deionized water at 25℃ for 5 min to obtain malleable wood that can be arbitrarily shaped.

[0068] (2) The plasticized wood was completely immersed in a mixed aqueous solution containing 1.5 mmol / L TEMPO, 15 mmol / L NaBr (final concentration: ), and NaClO (final concentration: 150 mmol / L), while maintaining a stirring speed of 500 rpm. First, a 0.2 mmol / L HCl solution was added dropwise to adjust the pH to 10.5. Then, during the reaction, a 1.0 mmol / L NaOH solution was slowly added dropwise to maintain the pH of the mixed solution at approximately 10.5. After reacting at 25°C for 1 hour, the wood was removed, rinsed three times with deionized water, and then soaked in anhydrous ethanol for 5 minutes to replace any residual solution. It was then rinsed again with deionized water until neutral and air-dried at 25°C to obtain carboxyl-rich oxidized wood.

[0069] (3) Immerse the oxidized wood completely in a 1.5 mol / L CaCl2 solution and stir at 25°C for 12 hours. Add anhydrous Na2CO3 powder to the reaction solution (controlling the initial concentration of Na2CO3 in the mineralization mixture to 1.0 mol / L) and continue stirring for 12 hours. Remove the wood, rinse the surface repeatedly with deionized water to remove residual salt, and air dry at 25°C for 20 hours to obtain mineralized plastic wood.

[0070] (4) Soak the mineralized plastic wood in deionized water at 25°C for 1 min. Then place the wood in a flat vulcanizing machine and preheat it under the following conditions: atmospheric pressure at 40°C for 20 s; then hot press it at 80°C and 3 MPa for 2 hours perpendicular to the direction of the wood fibers. Remove the wood and cool it at room temperature (25°C) to obtain mineralized composite wood.

[0071] The deformability of the mineralized plastic wood obtained in step (3) above was characterized, and the results are shown in the figure. Figure 2 Through manual shaping and natural air drying, flat, rectangular mineralized composite wood can be made into shapes such as hexagons, rabbits, pentagrams, the English letters JNU, and twisted waves; in principle, it can be made into any complex shape. The plasticity of mineralized composite wood stems from the pre-treatment delignification process, where the wood becomes more porous after partially removing lignin and hemicellulose. Soaking it in water for 5 minutes creates a unique wrinkled cell wall structure. This wrinkled cell wall provides ample space for compression and the ability to support high strain, allowing the material to be easily folded and shaped to achieve different structural forms. Subsequent TEMPO oxidation further softens the wood cell walls. After the final mineralization and air drying step, the internal fibers and pores of the wood shrink tightly together. Finally, air drying removes the remaining water, resulting in mineralized plastic wood with high strength and plasticity.

[0072] Example 3 A super-tough, flame-retardant, plastic, mineralized composite wood is prepared through the following steps: (1) Take natural beech wood (size: 5 cm × 2 cm × 0.2 cm) and immerse it completely in a composite alkaline solution containing 2.5 mol / L NaOH and 0.7 mol / L Na2SO3. Vacuum impregnation treatment (vacuum degree: -80 KPa, time: 10 min) is then performed to allow the alkaline solution to fully penetrate the wood pores. The wood and solution are then transferred to a flask and treated with delignification at 105℃ for 20 hours. The wood is then removed, rinsed with deionized water until neutral, and then air-dried at 25℃ for 24 hours. The air-dried wood is then immersed in deionized water at 25℃ for 5 min to obtain malleable wood that can be arbitrarily shaped.

[0073] (2) The plasticized wood was completely immersed in a mixed aqueous solution containing 1 mmol / L TEMPO, 15 mmol / L NaBr, and 150 mmol / L NaClO, while maintaining a stirring speed of 500 rpm. The pH was adjusted to 10.5 by adding 0.2 mmol / L HCl solution dropwise, and the pH was maintained at around 10.5 by slowly adding 1.0 mmol / L NaOH solution dropwise. After reacting at 25°C for 1.5 hours, the wood was removed, rinsed three times with deionized water, and then soaked in anhydrous ethanol for 5 minutes to replace the residual solution. It was rinsed again with deionized water until neutral, and then air-dried at 25°C to obtain carboxyl-rich oxidized wood.

[0074] (3) Immerse the oxidized wood completely in a 1.5 mol / L CaCl2 solution and stir at 25°C for 12 hours. Add anhydrous Na2CO3 powder to the reaction solution (controlling the concentration of Na2CO3 in the mineralization mixture to 1.0 mol / L) and continue stirring for 12 hours. Remove the wood, rinse the surface repeatedly with deionized water to remove residual salt, and air dry at 25°C for 24 hours to obtain mineralized plastic wood.

[0075] (4) Soak the mineralized plastic wood in deionized water at 25°C for 1 min. Then place the wood in a flat vulcanizing machine and preheat it under the following conditions: 40°C, normal pressure, time 20 s; then hot press it at 80°C and 3 MPa, perpendicular to the wood fiber orientation direction, for 2 hours. Remove the wood and cool it at room temperature (25°C) to obtain mineralized composite wood.

[0076] The compressive strength of the mineralized plastic wood obtained in step (3) above was characterized. Due to the rich interfacial bonding between the organic phase and the inorganic phase of calcium carbonate in the wood matrix, the mechanical strength of the air-dried mineralized plastic wood was significantly improved. Figure 3 As shown, a piece of dried mineralized wood (approximately 1 mm thick) weighing 0.43 g can easily support the weight of 3.75 kg of metal when placed on its side, which is 8720 times its own weight. Moreover, the wood does not deform after being subjected to long-term load, indicating that mineralized wood has excellent mechanical strength. This increase in strength is mainly attributed to two reasons: (1) Under natural air drying, abundant bonding forces can spontaneously form between wood fibers, making the fibers tightly bound together; (2) After mineralization, calcium carbonate is uniformly deposited inside the wood, which fully improves the internal structure of the wood and enhances its mechanical strength.

[0077] Example 4 A super-tough, flame-retardant, plastic, mineralized composite wood is prepared through the following steps: (1) Take natural linden wood (size: 5 cm × 2 cm × 0.2 cm) and immerse it completely in a composite alkaline solution containing 1 mol / L NaOH and 0.4 mol / L Na2SO3. Vacuum impregnation treatment (vacuum degree: -80 KPa, time: 10 min) is then performed to allow the alkaline solution to fully penetrate the wood pores. The wood and solution are then transferred to a flask and treated with delignification at 105℃ for 24 hours. The wood is then removed, rinsed with deionized water until neutral, and then air-dried at 25℃ for 24 hours. The air-dried wood is then immersed in deionized water at 25℃ for 5 min to obtain malleable wood that can be arbitrarily shaped.

[0078] (2) The plasticized wood was completely immersed in a mixed aqueous solution containing 1.5 mmol / L TEMPO, 15 mmol / L NaBr, and 150 mmol / L NaClO, while maintaining a stirring speed of 500 rpm. The pH was adjusted to 10.5 by adding 0.2 mmol / L HCl solution dropwise, and the pH was maintained at around 10.5 by slowly adding 1.0 mmol / L NaOH solution dropwise. After reacting at 25°C for 1 hour, the wood was removed, rinsed three times with deionized water, and then soaked in anhydrous ethanol for 5 min to replace the residual solution. It was rinsed again with deionized water until neutral, and then air-dried at 25°C to obtain carboxyl-rich oxidized wood.

[0079] (3) Immerse the oxidized wood completely in a 2.0 mol / L CaCl2 solution and stir at 25°C for 12 hours. Add anhydrous Na2CO3 powder to the reaction solution (controlling the concentration of Na2CO3 in the mineralization mixture to 1.0 mol / L) and continue stirring for 12 hours. Remove the wood, rinse the surface repeatedly with deionized water to remove residual salt, and air dry at 25°C for 18 hours to obtain mineralized plastic wood.

[0080] (4) Soak the mineralized plastic wood in deionized water at 25°C for 1 min. Then place the wood in a flat vulcanizing machine and preheat it under the following conditions: 40°C, normal pressure, time 20 s; then hot press it at 80°C and 3 MPa, perpendicular to the wood fiber orientation direction, for 2 hours. Remove the wood and cool it at room temperature (25°C) to obtain mineralized composite wood.

[0081] X-ray diffraction (XRD) was used to further analyze the crystal structure of natural wood, plastic wood, oxidized wood, and mineralized plastic wood samples. Figure 4As shown, all wood exhibits two broad diffraction peaks at 2θ=15.8° and 2θ=22.2°, corresponding to the (101) and (002) crystal planes of cellulose I, respectively. Moreover, the XRD curves of mineralized plastic wood show characteristic diffraction peaks corresponding to calcium carbonate, and the calcium carbonate generated by mineralization is mainly composed of two crystal forms: calcite and aragonite. Specifically, the strong signal peak at 2θ=28.08° corresponds to the (104) crystal plane of calcite, and the diffraction peaks at 35.28°, 38.56° and 42.44° correspond to the (110), (113) and (202) crystal planes of calcite, respectively; while diffraction peaks belonging to the (110), (114), (018) and (016) crystal planes of aragonite were observed at 24.2°, 32.9°, 46.82° and 47.86°. The crystallinity of the product can be determined by the intensity and sharpness of the XRD diffraction peaks, with sharper peaks indicating higher crystallinity. The above data indicate that mineralized plastic wood was successfully prepared by in-situ mineralization of calcium carbonate crystals using carboxyl groups on oxidized wood as nucleation sites.

[0082] Example 5 A super-tough, flame-retardant, plastic, mineralized composite wood is prepared through the following steps: (1) Take natural balsa wood (size: 5 cm × 2 cm × 0.2 cm) and immerse it completely in a composite alkaline solution containing 1 mol / L NaOH and 0.4 mol / L Na2SO3. Vacuum impregnation treatment (vacuum degree: -80 kPa, time: 10 min) is then performed to allow the alkaline solution to fully penetrate the wood pores. The wood and solution are then transferred to a flask and treated with delignification at 100°C for 20 hours. The wood is then removed, rinsed with deionized water until neutral, and then air-dried at 25°C for 24 hours. The air-dried wood is then immersed in deionized water at 25°C for 3 min to obtain malleable wood that can be arbitrarily shaped.

[0083] (2) The plasticized wood was completely immersed in a mixed aqueous solution containing 1.5 mmol / L TEMPO, 15 mmol / L NaBr, and 150 mmol / L NaClO, while maintaining a stirring speed of 500 rpm. The pH was adjusted to 10.5 by adding 0.2 mmol / L HCl solution dropwise, and the pH was maintained at approximately 10.5 by slowly adding 1.0 mmol / L NaOH solution dropwise. After reacting at 25°C for 1 hour, the wood was removed, rinsed three times with deionized water, and then soaked in anhydrous ethanol for 5 minutes to replace any residual solution. It was then rinsed again with deionized water until neutral and air-dried at 25°C to obtain carboxyl-rich oxidized wood.

[0084] (3) Immerse the oxidized wood completely in a 1.0 mol / L CaCl2 solution and stir at 25°C for 12 hours. Add anhydrous Na2CO3 powder to the reaction solution (controlling the concentration of Na2CO3 in the mineralization mixture to 1.0 mol / L) and continue stirring for 12 hours. Remove the wood, rinse the surface repeatedly with deionized water to remove residual salt, and air dry at 25°C for 18 hours to obtain mineralized plastic wood.

[0085] (4) Soak the mineralized plastic wood in deionized water at 25°C for 1 min. Then place the wood in a flat vulcanizing machine and preheat it under the following conditions: 40°C, normal pressure, time 20 s; then hot press it at 80°C and 3 MPa, perpendicular to the wood fiber orientation direction, for 2 hours. Remove the wood and cool it at room temperature (25°C) to obtain mineralized composite wood.

[0086] By observing the scanning electron microscope images of mineralized plastic wood ( Figure 5 It can be observed that, compared to natural wood, the calcium carbonate deposits grown in situ on the fibers of mineralized plastic wood are mainly composed of two crystal forms: calcite and aragonite, with calcite being the predominant form. Furthermore, due to the oxidation of TEMPO, a large number of nucleation sites are generated within the wood, allowing the mineralized calcium carbonate to be uniformly deposited in situ within the cell wall microfibers, thus optimizing the internal structure. Most importantly, the layered anisotropic structure of the wood is well preserved after calcium carbonate filling, resulting in a denser layered structure after hot pressing, significantly improving mechanical properties and effectively retardant the flame.

[0087] Example 6 A super-tough, flame-retardant, plastic, mineralized composite wood is prepared through the following steps: (1) Take natural linden wood (size: 5 cm × 2 cm × 0.2 cm) and immerse it completely in a composite alkaline solution containing 2 mol / L NaOH and 0.6 mol / L Na2SO3. Vacuum impregnation treatment (vacuum degree: -80 KPa, time: 10 min) is then performed to allow the alkaline solution to fully penetrate the wood pores. The wood and solution are then transferred to a flask and treated with delignification at 100℃ for 24 hours. The wood is then removed, rinsed with deionized water until neutral, and then air-dried at 25℃ for 24 hours. The air-dried wood is then immersed in deionized water at 25℃ for 5 min to obtain malleable wood that can be arbitrarily shaped.

[0088] (2) The plasticized wood was completely immersed in a mixed aqueous solution containing 1.5 mmol / L TEMPO, 15 mmol / L NaBr, and 150 mmol / L NaClO, while maintaining a stirring speed of 500 rpm. The pH was adjusted to 10.5 by adding 0.2 mmol / L HCl solution dropwise, and the pH was maintained at approximately 10.5 by slowly adding 1.0 mmol / L NaOH solution dropwise. After reacting at 25°C for 1.5 hours, the wood was removed, rinsed three times with deionized water, and then soaked in anhydrous ethanol for 5 minutes to replace any residual solution. It was then rinsed again with deionized water until neutral and air-dried at 25°C to obtain carboxyl-rich oxidized wood.

[0089] (3) Immerse the oxidized wood completely in a 1.0 mol / L CaCl2 solution and stir at 25°C for 12 hours. Add anhydrous Na2CO3 powder to the reaction solution (controlling the concentration of Na2CO3 in the mineralization mixture to 1.0 mol / L) and continue stirring for 12 hours. Remove the wood, rinse the surface repeatedly with deionized water to remove residual salt, and air dry at 25°C for 18 hours to obtain mineralized plastic wood.

[0090] (4) Soak the mineralized plastic wood in deionized water at 25°C for 1 min. Then place the wood in a flat vulcanizing machine and preheat it under the following conditions: 40°C, normal pressure, time 20 s; then hot press it at 80°C and 3 MPa, perpendicular to the wood fiber orientation direction, for 2 hours. Remove the wood and cool it at room temperature (25°C) to obtain mineralized composite wood.

[0091] Example 7 A super-tough, flame-retardant, plastic, mineralized composite wood is prepared through the following steps: (1) Take natural beech wood (size: 5 cm × 2 cm × 0.2 cm) and completely immerse it in a composite alkaline solution containing 1.5 mol / L NaOH and 0.4 mol / L Na2SO3. Vacuum impregnation treatment (vacuum degree: -80 KPa, time: 10 min) is then performed to allow the alkaline solution to fully penetrate the wood pores. The wood and solution are then transferred to a flask and treated with delignification at 100℃ for 24 hours. The wood is then removed, rinsed with deionized water until neutral, and then air-dried at 25℃ for 24 hours. The air-dried wood is then immersed in deionized water at 25℃ for 5 min to obtain malleable wood that can be arbitrarily shaped.

[0092] (2) The plasticized wood was completely immersed in a mixed aqueous solution containing 1.5 mmol / L TEMPO, 15 mmol / L NaBr, and 150 mmol / L NaClO, while maintaining a stirring speed of 500 rpm. The pH was adjusted to 10.5 by adding 0.2 mmol / L HCl solution dropwise, and the pH was maintained at around 10.5 by slowly adding 1.0 mmol / L NaOH solution dropwise. After reacting at 25°C for 1.5 hours, the wood was removed, rinsed three times with deionized water, and then soaked in anhydrous ethanol for 5 minutes to replace the residual solution. It was rinsed again with deionized water until neutral, and then air-dried at 25°C to obtain carboxyl-rich oxidized wood.

[0093] (3) Immerse the oxidized wood completely in a 1.0 mol / L CaCl2 solution and stir at 25°C for 12 hours. Add anhydrous Na2CO3 powder to the reaction solution (controlling the concentration of Na2CO3 in the mineralization mixture to 1.0 mol / L) and continue stirring for 12 hours. Remove the wood, rinse the surface repeatedly with deionized water to remove residual salt, and air dry at 25°C for 18 hours to obtain mineralized plastic wood.

[0094] (4) Soak the mineralized plastic wood in deionized water at 25°C for 1 min. Then place the wood in a flat vulcanizing machine and preheat it under the following conditions: 40°C, normal pressure, time 20 s; then hot press it at 100°C and 1 MPa, perpendicular to the wood fiber orientation direction, for 1.5 hours. Remove the wood and cool it at room temperature (25°C) to obtain mineralized composite wood.

[0095] Example 8 A super-tough, flame-retardant, plastic, mineralized composite wood is prepared through the following steps: (1) Take natural walnut wood (size: 5 cm × 2 cm × 0.2 cm) and completely immerse it in a composite alkaline solution containing 2 mol / L NaOH and 0.6 mol / L Na2SO3. Vacuum impregnation treatment (vacuum degree: -80 KPa, time: 10 min) is then performed to allow the alkaline solution to fully penetrate the wood pores. The wood and solution are then transferred to a flask and treated with delignification at 100℃ for 24 hours. The wood is then removed, rinsed with deionized water until neutral, and then air-dried at 25℃ for 24 hours. The air-dried wood is then immersed in deionized water at 25℃ for 5 min to obtain malleable wood that can be arbitrarily shaped.

[0096] (2) The plasticized wood was completely immersed in a mixed aqueous solution containing 1.5 mmol / L TEMPO, 15 mmol / L NaBr, and 150 mmol / L NaClO, while maintaining a stirring speed of 500 rpm. The pH was adjusted to 10.5 by adding 0.2 mmol / L HCl solution dropwise, and the pH was maintained at around 10.5 by slowly adding 1.0 mmol / L NaOH solution dropwise. After reacting at 25°C for 1.5 hours, the wood was removed, rinsed three times with deionized water, and then soaked in anhydrous ethanol for 5 minutes to replace the residual solution. It was rinsed again with deionized water until neutral, and then air-dried at 25°C to obtain carboxyl-rich oxidized wood.

[0097] (3) Immerse the oxidized wood completely in a 1.0 mol / L CaCl2 solution and stir at 25°C for 12 hours. Add anhydrous Na2CO3 powder to the reaction solution (controlling the concentration of Na2CO3 in the mineralization mixture to 1.0 mol / L) and continue stirring for 12 hours. Remove the wood, rinse the surface repeatedly with deionized water to remove residual salt, and air dry at 25°C for 24 hours to obtain mineralized plastic wood.

[0098] (4) Soak the mineralized plastic wood in deionized water at 25°C for 1 min. Then place the wood in a flat vulcanizing machine and preheat it under the following conditions: 40°C, normal pressure, time 20 s; then hot press it at 100°C and 1 MPa, perpendicular to the wood fiber orientation direction, for 1 hour. Remove the wood and cool it at room temperature (25°C) to obtain mineralized composite wood.

[0099] like Figure 6 As shown, the flammability of each group of materials was evaluated by placing the samples under an open flame. The mineralized composite wood exhibited significant self-extinguishing behavior 5 seconds after the flame was removed, maintaining structural integrity and producing only a small amount of black smoke on the material surface. In contrast, natural wood, plasticized wood, and oxidized wood showed significant combustion-supporting behavior after 5 seconds of burning and were almost completely burned after 15 seconds. The results indicate that the presence of calcium carbonate significantly enhances the flame-retardant properties of the mineralized plasticized wood and mineralized composite wood samples through multiple mechanisms, including endothermic, insulating, and oxygen-consuming effects. Furthermore, due to hot-pressing densification, the mineralized composite wood exhibited the best flame-retardant effect because the dense cellulose effectively isolates oxygen transport within the wood. These synergistic effects give the material excellent flame retardancy and self-extinguishing properties, making it highly advantageous in structural material applications.

[0100] Comparative Example 1 To investigate the effect of pH adjustment treatment on the mechanical properties of mineralized plastic wood during the wood oxidation process, the experimental procedure was as follows: (1) Same as step (1) in Example 6; (2) The plasticized wood was completely immersed in a mixed aqueous solution containing 1.5 mmol / L TEMPO, 15 mmol / L NaBr and 150 mmol / L NaClO, and the stirring speed was maintained at 500 rpm. After reacting at 25°C for 1.5 hours, the wood was removed, rinsed three times with deionized water, and then soaked in anhydrous ethanol for 5 min to replace the residual solution. It was rinsed again with deionized water until neutral, and then air-dried at 25°C to obtain oxidized plasticized wood rich in carboxyl groups. The difference between this step and step (2) in Example 6 is that the pH value was not adjusted by adding HCl solution and NaOH solution dropwise.

[0101] (3) Same as step (3) in Example 6, mineralized plastic wood without pH control during oxidation is prepared.

[0102] The tensile properties of the mineralized plastic wood obtained in Example 6 and Comparative Example 1 were measured, and the stress-strain curves obtained are shown below. Figure 7 .Depend on Figure 7 It can be seen that, compared with the tensile properties of mineralized plastic wood prepared without pH control during oxidation (Comparative Example 1), the strength and toughness of mineralized plastic wood prepared with pH control during mineralization are significantly improved, showing a substantial difference. The reason for this may be attributed to maintaining the pH of the mixed aqueous solution at around 10.5, which promotes the oxidation process of TEMPO, thereby efficiently and selectively converting the hydroxyl groups on the surface of wood cellulose into carboxyl groups, providing more nucleation sites for mineralization, and thus obtaining a high-strength and tough material combining organic and inorganic components.

[0103] Comparative Example 2 To investigate the effect of delignification treatment on the plasticity of air-dried wood after water immersion in step (1), the specific experimental procedures are as follows: (1) Take natural beech wood (size: 5 cm × 2 cm × 0.2 cm) and immerse it completely in a composite alkaline solution containing 1.5 mol / L NaOH and 0.4 mol / L Na2SO3. Vacuum impregnation treatment (vacuum degree: -80 KPa, time: 10 min) is then performed to allow the alkaline solution to fully penetrate the wood pores. The wood and solution are then transferred to a flask and treated with delignification at 100°C for 24 hours. The wood is then removed, rinsed with deionized water until neutral, and then air-dried naturally at 25°C for 24 hours. Unlike step (1) in Example 7, the delignified wood was not soaked in water after air-drying.

[0104] The plasticity of delignified wood was compared with that of wood without or after "water impact" (water soaking) treatment. The results are shown in [Figure Number]. Figure 8 After lignin removal, beech wood exhibits good plasticity when soaked in water, such as... Figure 8As shown in Figure A, it can be molded into a spiral shape without breaking. In contrast, delignified wood without a "water impact" (water soaking) process lacks plasticity and breaks after being bent 180°. Figure 8 (B in the middle).

[0105] The above embodiments are the optimal implementation methods explored by the present invention, but the implementation methods of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A method for preparing ultra-strong, tough, flame-retardant, plastic, mineralized composite wood, characterized in that... Includes the following steps: (1) Natural wood is delignified, then washed until neutral, dried, and soaked in water to obtain plastic wood; (2) The plastic wood obtained in step (1) is subjected to oxidation treatment, washed until neutral, and dried to obtain oxidized wood rich in carboxyl groups; (3) Immerse the oxidized wood obtained in step (2) into a soluble calcium salt solution and stir to react. Then add soluble carbonate and continue stirring to react. In-situ mineralization is carried out to generate calcium carbonate. Wash and dry to obtain mineralized plastic wood. (4) The mineralized plastic wood obtained in step (3) is soaked in water and then densified by hot pressing to obtain mineralized composite wood.

2. The preparation method according to claim 1, characterized in that: The delignification process mentioned in step (1) involves treating natural wood with an alkaline solution; The water immersion treatment conditions described in step (1) are immersion at 20-30℃ for 3-10 minutes; The specific operation of the oxidation treatment in step (2) is as follows: the plastic wood obtained in step (1) and the oxidant solution are mixed and reacted under stirring; the pH of the reaction system is first adjusted to 10.0 to 11.0, and the pH of the reaction system is maintained at 10.0 to 11.0 during the reaction process; The soluble calcium salt mentioned in step (3) is calcium chloride; The soluble carbonate mentioned in step (3) is at least one of sodium carbonate or sodium bicarbonate.

3. The preparation method according to claim 2, characterized in that: In the delignification process: The alkaline solution is a solution containing NaOH and Na2SO3; wherein the molar ratio of NaOH to Na2SO3 is 2.0–5.0:1; The specific steps of the treatment are as follows: first, soak the natural wood in an alkaline solution, and then react it at 60-120℃ for 6-48 hours; The water immersion treatment conditions described in step (1) are immersion at 24-26℃ for 4-6 minutes; In the aforementioned oxidation treatment: The oxidizing agent is TEMPO, NaBr and NaClO in a molar ratio of 1:10-15:100-150; The pH adjuster is an HCl solution and a NaOH solution; The reaction conditions are as follows: reaction at 20–30°C for 0.5–3 hours; The concentration of the soluble calcium salt solution mentioned in step (3) is 0.2–2.0 mol / L; The amount of soluble carbonate used in step (3) is calculated based on a molar ratio of carbonate ions to calcium ions of 1:

1.

4. The preparation method according to claim 3, characterized in that: In the delignification process: The concentration of NaOH in the alkaline solution is 1–3 mol / L; The concentration of Na2SO3 in the alkaline solution is 0.3–0.8 mol / L; The soaking method is vacuum impregnation; The reaction conditions are 100–110°C for 20–24 hours; In the aforementioned oxidation treatment: The concentration of TEMPO in the oxidant solution is 0.5–2 mmol / L; The concentration of NaBr is 5–20 mmol / L; The concentration of NaClO is 50–200 mmol / L; The concentration of the HCl solution is 0.1–0.3 mmol / L; The concentration of the NaOH solution is 0.2–1.0 mmol / L; The reaction conditions are 20–30°C for 1–2 hours.

5. The preparation method according to claim 1, characterized in that: The natural wood mentioned in step (1) is at least one of natural balsa wood, natural linden wood, natural beech wood, and natural walnut wood; The washing solvent mentioned in step (1) is deionized water; The solvent used for washing in step (3) is deionized water.

6. The preparation method according to claim 1, characterized in that: The drying conditions described in step (1) are natural air drying at 20-30℃ for 20-30 hours; The specific steps of washing described in step (2) are as follows: first wash with deionized water, then soak in anhydrous ethanol, and then wash with deionized water. The drying conditions described in step (2) are natural air drying at 20-30℃; The stirring reaction conditions described in step (3) are 20-30℃ for 0.5-48 hours; The conditions for continuing the reaction described in step (3) are 20-30℃ for 0.5-48 hours; The drying conditions described in step (3) are natural air drying at 20-30°C for 12-48 hours; The water immersion treatment conditions described in step (4) are immersion at 20-30°C for 10 seconds to 3 minutes; The hot pressing densification process described in step (4) is carried out using a flat vulcanizing machine.

7. The preparation method according to claim 6, characterized in that: The soaking time in the washing process described in step (2) is 0.5 to 10 minutes; The stirring reaction conditions described in step (3) are 20-30℃ for 10-15 hours; The conditions for continuing the reaction described in step (3) are 20-30℃ for 10-15 hours; The water immersion treatment conditions described in step (4) are immersion at 25°C for 60 seconds; The hot-press densification treatment conditions are: preheating at 30-50℃ and normal pressure for 5-30 s; then hot-pressing at 60-120℃ and pressure of 0.5 MPa-5 MPa, perpendicular to the wood fiber growth direction, for 5 min-12 h.

8. A super-tough, flame-retardant, plastic, mineralized composite wood, characterized in that: It is obtained by the preparation method according to any one of claims 1 to 7.

9. The application of the ultra-tough, flame-retardant, plastic mineralized composite wood according to claim 8 in the preparation of ultra-tough, lightweight structural materials and / or functional materials.

10. The application of the ultra-tough, flame-retardant, plastic mineralized composite wood according to claim 8 in the fields of construction or energy.

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