A lightweight high-strength wood and a method for preparing the same

Abstract

The application discloses light high-strength wood and a preparation method thereof. The light high-strength wood has a porous microstructure formed by closely arranging hollow tubular wood cell units, and the wood cell wall is a dense and high-strength unit composed of nanocellulose fibers and lignin. The wood density is about 0.35-0.72 g·cm ‑3 , and the specific strength is 246-444 MPa·g·cm ‑3 . The preparation method comprises the following steps: firstly, removing part of lignin in the wood in situ; secondly, filling a filler into the pore channel and cavity structure of the wood; thirdly, performing radial pressure drying after the filler is solidified; and finally, obtaining the light high-strength wood by removing the filler. The modified high-strength wood of the application greatly retains the porous characteristics of natural wood, maintains the low-density characteristics of the wood, and greatly improves the mechanical properties such as the absolute strength and specific strength of the wood. The application is a high-efficiency cell wall modification method and can be applied to large-scale industrial production.

Description

Technical Field

[0001] This invention relates to a method for preparing hollow porous wood, and more particularly to a lightweight high-strength wood and its preparation method. Background Technology

[0002] The main component of natural wood, nanocellulose fibers, possesses extremely high theoretical mechanical strength (2-3 GPa). However, short-chain molecules such as lignin and hemicellulose, which act as binders in wood, limit its mechanical properties to some extent. Simultaneously, the porous structure, including cell cavities, vessels, and mesopores, endows wood with a macroscopically low density. Furthermore, influenced by the natural growth characteristics of wood and the external environment, these porous structures manifest as numerous mechanical defects in the material's structure. Currently, specific modification treatments of natural wood to create new wood products with superior structure and enhanced performance have become a trend in new materials science research.

[0003] To address the issue of low mechanical strength in natural wood, existing technologies employ hot-pressing to densify the wood, artificially closing structural defects such as cracks between wood cells and increasing the hydrogen bond density, thereby significantly enhancing its strength. However, this hot-pressing densification process sacrifices the wood's lightweight advantage by increasing its density.

[0004] Chinese patent CN113696291A discloses a method for improving wood properties through mild furfuryl alcohol modification and synergistic densification treatment. This method involves impregnating wood with furfuryl alcohol followed by hot pressing to increase wood strength. However, the increased strength is not solely due to the hot-pressing densification process; it also relies on the deformation-fixing effect of furfuryl alcohol and furfuryl alcohol resin on the densified wood. Removing these resins would inevitably lead to springback deformation. Furthermore, the furfuryl alcohol and furfuryl alcohol resin solidify within the wood after hot-pressing and drying, making them impossible to remove. This residual furfuryl alcohol resin further increases the density of the densified wood and prevents lightweight modification. Therefore, existing wood hot-pressing densification modification methods cannot simultaneously achieve both lightweighting and strength improvement in wood.

[0005] In addition, existing technologies also combine wood with other materials, such as injecting metal into the porous structure of wood, to obtain composite materials with enhanced structure and function. However, due to issues such as material compatibility, these methods are difficult to apply on a large scale.

[0006] In summary, current known physicochemical modification methods, while improving the mechanical properties of wood, struggle to maintain its porous nature, thus making it difficult to obtain lightweight and high-strength wood. Summary of the Invention

[0007] Purpose of the Invention: The purpose of this invention is to provide a lightweight, high-strength wood, solving the problem that existing densified wood cannot simultaneously achieve both lightweight and strength improvement. Another purpose of this invention is to propose a method for preparing lightweight, high-strength wood, addressing how to arrange and surround densified cell wall structures in situ in space to form micron-scale cavities and channels.

[0008] Technical solution: The present invention provides a lightweight and high-strength wood, comprising a porous microstructure in which the position of wood cells remains unchanged while the cell walls are compressed, with an average compression rate of 30-70% for the wood cell walls.

[0009] Because of the large differences in cell wall thickness in wood, there are also significant differences in cell wall thickness in different parts of the same piece of wood; in addition, there are also significant differences in cell wall thickness between different types of wood. Taking into account the differences in cell wall compression between different types of wood and the differences in cell wall compression between different parts of the same type of wood, the average compression rate of wood cell walls in this invention is in the range of 30-70%, more preferably 30-45%.

[0010] Preferably, the type of wood includes broadleaf wood or coniferous wood.

[0011] Preferably, the density of the wood is 0.31-0.72 g·cm³. -3 .

[0012] The aforementioned lightweight, high-strength wood retains the multi-level structure and porous characteristics of natural wood to the greatest extent. Through partial removal of lignin and compression of the cell wall, it utilizes the hydrogen bond breaking and recombination behavior between cellulose chains in the cell wall to significantly increase the density of hydrogen bonds, thereby achieving a strengthening and toughening effect. Furthermore, this modified wood exhibits excellent flexural strength, tensile strength, impact strength, high porosity, and low density.

[0013] To prepare the above-mentioned lightweight and high-strength wood, the present invention provides the following preparation method:

[0014] (1) Remove lignin from the cell walls of wood to obtain intermediate 1;

[0015] (2) Intermediate 2 is obtained by filling the cavity and pores of intermediate 1 with organic solvent; the organic solvent is a liquid solvent with a melting point of less than 150°C and a viscosity of less than 200 mPa·s.

[0016] (3) After drying intermediate 2 at room temperature, radial pressure is applied;

[0017] (4) After depressurization, remove the organic solvent in intermediate 2 to obtain lightweight and high-strength wood.

[0018] Preferably, in step (1), the method for removing lignin is as follows: immersing the wood in at least one of a strong alkaline solution, a sodium hypochlorite solution, and a hydrogen peroxide solution and heating it for 30 min to 12 h. For example, it can be immersed first in a strong alkaline solution or a sodium hypochlorite solution, and then immersed in a hydrogen peroxide solution. The removal of short-chain molecules such as lignin and hemicellulose from the wood through these solutions provides space for the long-chain cellulose molecules to entangle and connect, thus forming denser hydrogen bonds.

[0019] Preferably, the strong alkaline solution is a mixed alkaline solution of sodium hydroxide with a concentration of 5-15 wt% and sodium sulfite with a concentration of 2-3 wt%; the sodium hypochlorite solution is an aqueous solution of sodium hypochlorite with a concentration of 3-7%; and the hydrogen peroxide solution is an aqueous solution of hydrogen peroxide with a volume percentage concentration of 10-40%.

[0020] Preferably, the organic solvent in step (2) includes one or more of paraffin, paraffin derivatives, rosin, and rosin derivatives. The viscosity of the organic solvent during filling is less than 200 mPa·s, which can ensure that the liquid solvent has good fluidity, and the melting point of the organic solvent is below the cellulose transition temperature of 150°C, so it does not react chemically with cellulose; at the same time, these organic solvents can be removed by other organic solvents.

[0021] Preferably, the method for removing organic solvents in step (4) is to remove organic solvents by soaking and stirring with aromatic hydrocarbons or alcohols. The infusion and filling of organic solvents such as paraffin wax in the radial compression of wood plays a supporting and protective role in the overall porous structure of the wood, so that the wet wood will not undergo severe deformation and crushing due to pressure, thus forming ultra-lightweight and high-strength structural wood.

[0022] Preferably, the aromatic hydrocarbon is one or more of toluene, xylene, trimethylbenzene, and tetramethylbenzene; the alcohol is one or more of methanol, ethanol, propanol, and butanol. After completing their supporting function, the organic solvents such as paraffin are removed by the corresponding aromatic hydrocarbons or alcohols, preserving the original micron-scale cavities and channels of the wood, thus reducing the density of the denser wood while increasing its strength.

[0023] Preferably, the filling method in step (2) includes one or more of vacuum filling, pressurized filling, and vacuum filtration filling, and the radial pressurization method in step (3) includes pressurized filling and / or vacuum filling. The pressure of pressurized filling is 3-15 MPa, and the treatment time is 5-30 min. The pressure of vacuum filling is less than 200 Pa, and the treatment time is 5-30 min. The step of radially pressurizing wood and gradually drying and dehydrating it is a process of regulating the microstructure of wood cell walls. By directionally compressing the cell walls, the hydrogen bond density within the cell walls increases significantly, enhancing the interaction between cellulose chains in wood cells and reducing structural defects between cell walls, thereby giving the wood higher overall mechanical strength.

[0024] Beneficial Effects: Compared with existing technologies, this invention has the following significant advantages: This invention not only maintains the hollow structure of natural wood and reduces the density of modified wood, but also significantly improves the strength of the wood, achieving a balance between lightweighting and strength enhancement. The lightweight, high-strength wood obtained by this invention possesses natural chemical components, with bending strength increased by 1.8-4.1 times, tensile strength increased by 1.9-4.6 times, specific strength increased by 1.6-3.8 times, and density approximately 0.31-0.61 g·cm³. -3 The entire preparation process largely preserves the natural cavity and pore structure of wood, and only regulates the composition and microstructure of the wood cell wall. It is a highly efficient cell wall modification method that is suitable for large-scale industrial production. Attached Figure Description

[0025] Figure 1 This is a scanning electron microscope (SEM) cross-sectional image of the lightweight, high-strength wood prepared in Example 1.

[0026] Figure 2 This is a scanning electron microscope cross-sectional image of the lightweight, high-strength wood prepared in Example 1;

[0027] Figure 3 This is a scanning electron microscope (SEM) cross-sectional image of the vascular bundles of the lightweight, high-strength wood prepared in Example 1.

[0028] Figure 4 The images show the cross-sectional morphology of wood at different preparation stages in Example 1, where (a) is the wood intermediate after paraffin infusion and (b) is the lightweight high-strength wood after paraffin removal.

[0029] Figure 5 The tensile stress-strain curve of the lightweight, high-strength wood prepared in Example 1 is shown.

[0030] Figure 6 This is a comparison diagram of the changes in cell wall thickness of the lightweight, high-strength wood prepared in Example 1. Detailed Implementation

[0031] The technical solution of the present invention will be further described below with reference to the accompanying drawings.

[0032] Example 1: As Figure 1-3 As shown, a lightweight, high-strength wood comprises a porous microstructure composed of in-situ compressed wood cell walls. The in-situ compressed natural wood cell wall structure is arranged and surrounds each other in space to form micron-scale cavities and channels, preserving the original pore structure of natural wood.

[0033] The preparation method of lightweight, high-strength wood is as follows:

[0034] (1) Partial removal of lignin from wood cell walls: The cut linden wood was immersed in a mixed alkaline solution (a mixed aqueous solution containing 5 wt% sodium hydroxide and 2 wt% sodium sulfite) and heat-treated at 98°C for 12 h, and then placed in a 30% hydrogen peroxide aqueous solution and heat-treated at 50°C for 0.5 h to obtain intermediate 1;

[0035] (2) Fill the cavity and pores of intermediate 1 with organic solvent: The preheated wet linden wood is immersed in liquid paraffin (viscosity 90-110 mPa·s) at 90-100℃, vacuum treated (vacuum degree 40 Pa, treatment time 20 min) and pressurized (pressure 10 MPa, treatment time 20 min) to obtain intermediate 2;

[0036] (3) After drying intermediate 2 at room temperature, radial pressure is applied. Radial pressure is applied using both vacuum treatment (vacuum degree of 40 Pa, treatment time of 20 min) and pressure treatment (pressure of 10 MPa, treatment time of 20 min).

[0037] (4) After depressurization, intermediate 2 was immersed in toluene at a constant temperature of 70℃ and magnetically stirred for 36 hours to remove paraffin wax and obtain modified linden wood. The average compression rate of the wood cell walls of the modified linden wood was 34%, the bending strength reached 225 MPa, the tensile strength reached 255 MPa, and the density was 0.60 g·cm³. -3 The specific strength reaches 425 MPa·g·cm. -3 Compared to natural linden wood, its bending strength is increased by 4.1 times, its tensile strength by 4.6 times, and its specific strength by 3.8 times. Figure 5 and Figure 6 As shown, Figure 6 show Figure 5 The enhanced properties of medium-modified wood are due to cell wall compression strengthening, while the basic structure remains unchanged.

[0038] Example 2: Everything else is the same as in Example 1, except that:

[0039] Cut pine wood was immersed in a mixed alkaline solution (containing 15 wt% sodium hydroxide and 3 wt% sodium sulfite) and heat-treated at 90°C for 8 hours. It was then placed in a 40% (v / v) hydrogen peroxide aqueous solution and heat-treated at 40°C for 1 hour. The preheated, moist pine wood was then subjected to vacuum and pressure treatment to fill the pores with liquid paraffin. After drying the samples at room temperature, radial pressure was applied using both vacuum treatment (90 Pa, 30 min) and pressure treatment (15 MPa, 5 min). After depressurization, the wood was immersed in xylene at 60°C with stirring for 24 hours to remove the paraffin, resulting in lightweight, high-strength wood. The modified pine wood exhibited an average cell wall compression rate of 33%, a bending strength of 210 MPa, a tensile strength of 240 MPa, and a density of 0.63 g·cm³. -3 The specific strength reaches 381 MPa·g·cm. -3 Compared to natural pine wood, its bending strength is increased by 3 times, its tensile strength by 3.2 times, and its specific strength by 2.9 times.

[0040] Example 3: Everything else is the same as in Example 1, except that:

[0041] The cut balsa wood was heat-treated at 80°C for 1.5 hours in a 10% (v / v) hydrogen peroxide aqueous solution. After preheating, the wet balsa wood was then vacuum-treated and pressurized at 130-140°C to fill its pores with liquid rosin (viscosity 95-115 centistokes). After drying the samples at room temperature, radial pressurization was applied simultaneously using both vacuum treatment (100 Pa, 20 min) and pressurization (3 MPa, 30 min). After depressurization, the samples were immersed in ethanol at 60°C for 48 hours with stirring to remove the rosin, yielding lightweight, high-strength wood. The modified balsa wood exhibited an average cell wall compression rate of 47%, a bending strength of 77 MPa, a tensile strength of 86 MPa, and a density of 0.35 g·cm³. -3 The specific strength reaches 246 MPa·g·cm. -3 Compared to natural balsa wood, its bending strength is increased by 2.6 times, its tensile strength by 2.7 times, and its specific strength by 1.3 times.

[0042] Example 4: Everything else is the same as in Example 1, except that:

[0043] Cut fir wood was immersed in a 5 wt% sodium hypochlorite aqueous solution and heat-treated at 95°C for 6 hours, followed by heat treatment in a 25% (v / v) hydrogen peroxide aqueous solution at 65°C for 1 hour. The preheated, moist fir wood was then subjected to vacuum and pressure treatment to fill the pores with liquid paraffin. After drying the samples at room temperature, radial pressure was applied simultaneously using both vacuum treatment (190 Pa, 30 min) and pressure treatment (12 MPa, 15 min). After depressurization, the samples were immersed in trimethylbenzene at 80°C for 24 hours with stirring to remove the paraffin. This yielded lightweight, high-strength wood. The modified fir wood exhibited an average cell wall compression rate of 32%, a flexural strength of 216 MPa, a tensile strength of 247 MPa, and a density of 0.56 g·cm³. -3 The specific strength reaches 441 MPa·g·cm. -3 Compared to natural cedar wood, its bending strength is increased by 3.8 times, its tensile strength by 3.9 times, and its specific strength by 2.6 times.

[0044] Example 5: Everything else is the same as in Example 1, except that:

[0045] Cut poplar wood was immersed in a 3wt% sodium hypochlorite aqueous solution and heat-treated at 98℃ for 8 hours, followed by heat treatment in a 35% hydrogen peroxide aqueous solution at 75℃ for 2.5 hours. The preheated, moist poplar wood was then subjected to vacuum and pressure treatment to fill its pores with liquid rosin. After drying the samples at room temperature, radial pressure was applied simultaneously using both vacuum treatment (30 Pa, 5 min) and pressure treatment (8 MPa, 20 min). After depressurization, the samples were immersed in methanol at 50℃ for 36 hours with stirring to remove the rosin. This yielded lightweight, high-strength wood. The modified poplar wood exhibited an average cell wall compression rate of 42%, a bending strength of 232 MPa, a tensile strength of 249 MPa, and a density of 0.57 g·cm³. -3 The specific strength reaches 437 MPa·g·cm. -3 Compared to natural poplar wood, its bending strength is increased by 3.3 times, its tensile strength by 3.4 times, and its specific strength by 2.6 times.

[0046] Example 6: Everything else is the same as in Example 1, except that:

[0047] Cut pine wood was immersed in a mixed alkaline solution (containing 10 wt% sodium hydroxide and 2.5 wt% sodium sulfite) and heat-treated at 98°C for 8 hours. It was then placed in a 15% (v / v) hydrogen peroxide aqueous solution and heat-treated at 95°C for 3 hours. The preheated, moist pine wood was then vacuum-treated and pressurized to fill the pores with liquid rosin. After drying the samples at room temperature, radial pressurization was applied using a pressure treatment method (15 MPa for 30 minutes). After depressurization, the samples were immersed in isopropanol at 45°C with stirring for 36 hours to remove the rosin. This yielded lightweight, high-strength wood. The modified pine wood exhibited an average cell wall compression rate of 32%, a bending strength of 212 MPa, a tensile strength of 237 MPa, and a density of 0.64 g·cm³. -3 The specific strength reaches 370 MPa·g·cm. -3 Compared to natural pine wood, its bending strength is increased by 3.0 times, its tensile strength by 3.2 times, and its specific strength by 2.9 times.

[0048] Example 7: The rest is the same as Example 1, except that:

[0049] Cut beech wood was immersed in a 7wt% sodium hypochlorite aqueous solution and heat-treated at 98℃ for 8 hours, followed by heat treatment in a 30% (v / v) hydrogen peroxide aqueous solution at 55℃ for 3 hours. The preheated, moist beech wood was then filtered and pressurized to fill the pores with liquid rosin. After drying the sample at room temperature, radial pressurization was performed using a vacuum treatment method (30 Pa, 30 min). After depressurization, the sample was immersed in butanol at 75℃ for 36 hours with stirring to remove the rosin. This yielded lightweight, high-strength wood. The modified beech wood exhibited an average cell wall compression rate of 43%, a bending strength of 215 MPa, a tensile strength of 213 MPa, and a density of 0.72 g·cm³. -3 The specific strength reaches 312 MPa·g·cm. -3 Compared to natural beech wood, its bending strength is increased by 2.0 times, its tensile strength by 2.3 times, and its specific strength by 1.9 times.

[0050] Comparative Example 1: Everything else was the same as in Example 1, except that the step of partially removing lignin from the wood cell walls was omitted, and steps (2)-(4) were performed directly. The modified wood cell walls had an average compression rate of 90%, a bending strength of 120 MPa, a tensile strength of 98 MPa, and a density of 0.51 g·cm³. -3 The specific strength reaches 192 MPa·g·cm. -3 Compared to natural linden wood, its bending strength is increased by 1.1 times, its tensile strength by 1.2 times, and its specific strength by 1.2 times.

[0051] It is evident that the strength and cell wall compression rate of the modified wood prepared in Comparative Example 1 are not as good as those in Example 1. The main reason is that when the lignin in the cell wall is not removed, there is not enough space in the cell wall for subsequent compression strengthening. As a result, after removing the paraffin and other fillers, the cell wall is not compressed and strengthened. Macroscopically, the improvement effect of various indicators of the modified wood compared with natural wood is not obvious.

[0052] Comparative Example 2: The rest is the same as Comparative Example 1, except that the paraffin removal step is not performed, only steps (1)-(3) are performed. The average compression rate of the modified linden wood cell wall is 35%, the bending strength of the modified linden wood reaches 222 MPa, the tensile strength reaches 253 MPa, and the density is 1.21 g·cm³. -3 The specific strength reaches 209 MPa·g·cm. -3 Compared to natural linden wood, its bending strength is increased by 4 times, its tensile strength by 4.5 times, and its specific strength by 3.2 times.

[0053] As can be seen, the strength and cell wall compressibility of the modified wood prepared in Comparative Example 2 are comparable to those in Example 1. However, because the paraffin wax inside the wood pores was not removed, the density of the modified wood is higher. Paraffin wax itself has no binding or deformation-fixing effect, so filling with paraffin wax does not improve the strength of the modified wood. Retaining paraffin wax not only does not help improve the strength but also significantly increases the density of the modified wood.

Claims

1. A method of producing lightweight high-strength wood, characterized by, The method comprises the following steps: (1) removing lignin in cell wall of wood to obtain intermediate 1; (2) filling the cavities and pores of intermediate 1 with organic solvent to obtain intermediate 2; the organic solvent is a liquid solvent with a melting point less than 150℃ and a viscosity less than 200 mPa·s; the organic solvent comprises one or more of paraffin, paraffin derivative, rosin, and rosin derivative; (3) drying intermediate 2 at room temperature and then performing radial pressure; (4) removing the organic solvent in intermediate 2 after pressure relief to obtain light-weight high-strength wood.

2. The method of claim 1, wherein the wood is selected from the group consisting of pine, fir, spruce, hemlock, aspen, poplar, and combinations thereof. In step (1), the method for removing lignin comprises immersing wood in at least one of a strong alkali solution, a sodium hypochlorite solution, and a hydrogen peroxide solution and heating for 30 min to 12 h.

3. The method of claim 2, wherein the wood is treated with a solution of 0.1% to 1% of the compound of formula (I) in water. The strong alkali solution is a mixed alkali solution with a sodium hydroxide concentration of 5-15 wt% and a sodium sulfite concentration of 2-3 wt%; the sodium hypochlorite solution is a sodium hypochlorite aqueous solution with a concentration of 3-7%; and the hydrogen peroxide solution is a hydrogen peroxide aqueous solution with a volume percentage concentration of 10-40%.

4. The method of producing a lightweight high-strength wood according to claim 1, wherein In step (4), the method for removing the organic solvent comprises soaking and stirring with aromatic hydrocarbon or alcohol to remove the organic solvent.

5. The method of claim 4, wherein the wood is treated with a solution of 0.1% to 1% of the compound of formula (I) in water. The aromatic hydrocarbon is one or more of toluene, xylene, trimethylbenzene, and tetramethylbenzene; and the alcohol is one or more of methanol, ethanol, propanol, and butanol.

6. The method of producing a lightweight high-strength wood according to claim 1, wherein In step (2), the filling method comprises one or more of vacuum filling, pressure filling, and suction filtration; and in step (3), the radial pressure method comprises pressure filling and / or vacuum filling, the pressure filling has a pressure of 3-15 MPa and a treatment time of 5-30 min, and the vacuum filling has a pressure lower than 200 Pa and a treatment time of 5-30 min.

7. The lightweight high-strength wood prepared according to the method of claim 1, wherein The wood has a porous microstructure in which the wood cells are unchanged and the cell walls are compressed, and the average compression rate of the wood cell walls is 30-70%.

8. The lightweight high strength wood product of claim 7, wherein, The wood can be broad-leaved wood or coniferous wood.

9. The lightweight, high-strength wood product of claim 7, wherein the wood product has a density of less than 0.5 g / cm3. The density of the lightweight high-strength wood is 0.31-0.72 g-cm -3 .

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