Ternary composite catalyst for furfuryl alcohol modified wood as well as preparation method and application of ternary composite catalyst

Abstract

The invention relates to the field of wood compression densification, and discloses a ternary composite catalyst for furfuryl alcohol modified wood as well as a preparation method and application of the ternary composite catalyst. Citric acid, ammonium chloride, itaconic anhydride and borax are used as catalyst components of a ternary composite system and are added into furfuryl alcohol resin, furfuryl alcohol modified liquid with an efficient catalytic effect is obtained, the curing rate of the furfuryl alcohol resin on wood can reach 95%, and the wood modified by furfuryl alcohol has excellent mechanical properties and dimensional stability and can be applied to wood processing. The wet expansion resistance coefficient is more than 66%, and the maximum wet expansion resistance coefficient can reach 75%. The preparation method has the advantages of being simple, efficient, excellent in wood performance and the like and can be applied to actual production, and the obtained furfuryl alcohol modified compressed wood has remarkable advantages in the aspects of dimensional stability, mechanical performance and environmental change resistance and has wide application prospects.

Description

Technical Field

[0001] The present invention relates to the field of wood compression and densification, and more particularly to a ternary composite catalyst for furfuryl alcohol-modified wood, a preparation method thereof, and an application thereof. Background Art

[0002] Fast-growing plantation timber, as a renewable resource that can be cultivated on a large scale, has gradually become an important alternative source to alleviate the contradiction between timber supply and demand. my country has abundant reserves of plantation timber resources. Woods such as poplar, eucalyptus, and pine have the advantages of short growth cycles and rapid maturity, and have broad application prospects. However, plantation timber generally has inherent defects such as loose material, loose fiber structure, low density, poor mechanical strength, insufficient dimensional stability, easy moisture absorption, expansion and deformation, and pale color. These performance shortcomings have severely limited the widespread application of plantation timber in mid-to-high-end wood products, structural materials, and outdoor durable materials. There is an urgent need to improve its overall performance through effective modification methods.

[0003] Compression densification can significantly improve the physical and mechanical properties of wood, while also imparting it with excellent biological durability, including resistance to decay, mildew, and termite infestation, and thus possessing significant market application value. Furfuryl alcohol is a highly polar small molecule compound with good reactivity and permeability, and exhibits significant modification potential in the field of wood compression densification. However, furfuryl alcohol currently faces key technical bottlenecks in its industrial application. This is primarily due to the fact that furfuryl alcohol solutions are prone to spontaneous free radical polymerization reactions under room temperature storage conditions, resulting in increased system viscosity, stratification, and gelation, which seriously affects its storage stability and permeation modification effect. To prevent premature solidification during storage, traditional technologies typically rely on low-temperature storage or the addition of strong inhibitors, but this not only increases storage and transportation costs but also has a negative impact on the wood modification effect.

[0004] Prior art CN107866884A uses a composite system consisting of furfuryl alcohol, water, nano-calcium carbonate, stabilizers (such as sodium citrate, sodium phosphate, etc.), and initiators (such as itaconic anhydride, malic acid, etc.) for conventional temperature-controlled impregnation and heat curing. This solution mainly relies on a strong acid initiator (such as itaconic anhydride) to trigger the polymerization of furfuryl alcohol. The lack of a pH buffering and regulation mechanism can lead to a violent or uneven polymerization process, making it difficult to balance system stability and deep penetration. In addition, the curing temperature is as high as 150-170°C, which is not conducive to energy conservation, environmental protection, and practical industrial application.

[0005] The prior art CN104552516A uses citric acid and oxalic acid as a compound catalyst, adds borax as a stabilizer, and the modification methods include vacuum pressurization, brushing, and soaking. Although citric acid and oxalic acid are compounded to form a catalytic environment, auxiliary ion regulation components are not introduced, and the catalytic ability is weak. Especially, the curing efficiency in high-density systems such as compressed wood is limited.

[0006] Currently, there is no publicly disclosed catalyst system that can maintain the long-term stability of furfuryl alcohol solution at room temperature and can efficiently catalyze the curing of furfuryl alcohol under high-temperature conditions. Summary of the Invention

[0007] In order to overcome the defects that the catalyst system in the above-mentioned prior art cannot maintain the long-term stability of furfuryl alcohol solution at room temperature and has low catalytic efficiency for curing furfuryl alcohol, the present invention provides a ternary composite system catalyst;

[0008] Another object of the present invention is to provide a preparation method of a ternary composite system catalyst;

[0009] Another object of the present invention is to provide an application of a ternary composite system catalyst;

[0010] Another object of the present invention is to provide a furfuryl alcohol modification solution;

[0011] Another object of the present invention is to provide a furfuryl alcohol modified wood;

[0012] Another object of the present invention is to provide a preparation method of a furfuryl alcohol modified wood;

[0013] Another object of the present invention is to provide a furfuryl alcohol modified compressed wood;

[0014] Another object of the present invention is to provide a preparation method of a furfuryl alcohol modified compressed wood.

[0015] To solve the above technical problems, the technical solution of the present invention is as follows:

[0016] A ternary composite system catalyst, the components of which include citric acid, ammonium chloride, itaconic anhydride, and borax with a mass ratio of 0.2-1:0.1-0.75:0.2-1.25:0.3-2.

[0017] Preferably, it includes citric acid, ammonium chloride, itaconic anhydride, and borax with a mass ratio of 0.2-0.5:0.1-0.75:0.2-1.25:0.3-1.2.

[0018] Preferably, it includes citric acid, ammonium chloride, itaconic anhydride, and borax with a mass ratio of 0.5:0.75:0.5:0.9.

[0019] In the ternary composite catalyst of the present invention, citric acid and itaconic anhydride enhance the crosslinking between the furfuryl alcohol resin and the wood; ammonium chloride provides an acidic environment, increases the curing rate of the furfuryl alcohol during heating, and improves the dimensional stability of the modified wood; and borax enhances the stability of the furfuryl alcohol modified solution.

[0020] Furthermore, the pH of the ternary composite system catalyst is 3.5 to 4.5.

[0021] Preferably, the pH of the ternary composite system catalyst is 3.9 to 4.1.

[0022] The pH value of the ternary composite catalyst is maintained between 3.5 and 4.5, effectively promoting polymerization and enhancing the curing effect of the furfuryl alcohol resin. It also improves the curing effect of the furfuryl alcohol resin during high-temperature polymerization, protects the wood from strong acid corrosion, and is less likely to delaminate at room temperature.

[0023] A preparation method of the ternary composite system catalyst comprises the following steps: dissolving citric acid, ammonium chloride and borax in water; adding itaconic anhydride and stirring uniformly to obtain the ternary composite system catalyst.

[0024] An application of the ternary composite system catalyst is used for preparing furfuryl alcohol modified liquid.

[0025] A furfuryl alcohol modified liquid comprises the ternary composite system catalyst and furfuryl alcohol.

[0026] Furthermore, the mass ratio of the ternary composite system catalyst to furfuryl alcohol is 0.8 to 4.5:30.

[0027] A method for preparing furfuryl alcohol-modified wood is provided, which is prepared using a furfuryl alcohol-modifying liquid. The method comprises the following steps: using a vacuum pressure impregnation method to allow the furfuryl alcohol-modifying liquid to fully penetrate into a wood sample, performing a sealing and wrapping treatment on the wood sample, and curing the wood sample under heating conditions; and sequentially performing gradient drying treatments to obtain the furfuryl alcohol-modified wood.

[0028] Preferably, a vacuum pressure impregnation method is used: a completely dry wood sample is placed in a sealed reactor, evacuated for 25 minutes, and the furfuryl alcohol modification liquid is sucked into the reactor using the negative pressure. The reactor is then pressurized to 0.8 MPa with industrial nitrogen and maintained at this pressure for 2.5 hours. After the pressure is released and the sample is removed, any excess liquid remaining on the surface is wiped off with paper. The resulting wood sample is wrapped in aluminum foil and placed in a 103°C oven for curing for 3 hours. After the furfuryl alcohol resin is cured, the aluminum foil is removed and the sample is placed in a 60°C oven for drying for 2 hours, then the temperature is raised to 80°C and held for 2 hours. Finally, the sample is dried in a 103°C oven until the mass remains unchanged, thereby obtaining furfuryl alcohol-modified wood.

[0029] A furfuryl alcohol modified wood is prepared by the method for preparing the furfuryl alcohol modified wood.

[0030] A preparation method of furfuryl alcohol modified compressed wood, which is prepared by using the furfuryl alcohol modified wood, comprises the following steps: placing the furfuryl alcohol modified wood sample in a hot pressing device for segmented hot pressing treatment; and then cooling and drying to obtain the furfuryl alcohol modified compressed wood.

[0031] Preferably, the specific compression process is as follows: in the first stage, the temperature is 80 °C and the pressure approaches 0, and the wood sample is softened for 10 min; in the second stage, the temperature is raised to 100 °C within 30 min and the pressure rises to 2 MPa; in the third stage, the temperature is raised to 120 °C within 20 min and the pressure rises to 5 MPa, and is maintained at this parameter for 60 min. In the fourth stage, the temperature of the hot press is quickly lowered to 40 °C, and the sample is taken out and transferred to an oven at 103 °C until it reaches a constant weight to obtain the furfuryl alcohol modified compressed wood.

[0032] A furfuryl alcohol modified compressed wood, which is prepared by the preparation method of the furfuryl alcohol modified compressed wood.

[0033] The present invention creatively establishes a ternary composite catalytic system with a synergistic catalytic mechanism, and by limiting the component ratio and the system pH, not only shows good synergistic catalytic effect in promoting the polycondensation reaction of furfuryl alcohol, but also can significantly improve the room temperature stability of the system, avoiding problems such as catalyst stratification or premature reaction commonly seen in the prior art. Compared with the prior art in which furfuryl alcohol modified compressed wood is mostly treated by soaking at room temperature or for a short time, the present invention adopts more stringent test conditions, that is, after wet-dry cycling and then boiling water immersion treatment, it can still significantly reduce the dimensional set recovery rate of the wood, which not only proves that the modification effect penetrates to the cell wall level, but also reflects the effective fixing ability of the cross-linked structure on the compressed form of the wood, indicating that the wood after the modification treatment of the present invention has extremely high dimensional stability and structure retention ability. Therefore, the present invention shows significant technological progress and differences in the catalytic system components and their ratios, system pH control, room temperature storage performance, and dimensional stability after extreme hydrothermal treatment, and has outstanding creativity.

[0034] Compared with the prior art, the beneficial effects of the technical solution of the present invention are:

[0035] 1. High curing efficiency and stable catalytic system. The ternary composite catalytic system adopted by the present invention can significantly improve the curing efficiency of furfuryl alcohol resin in wood, and the highest curing rate reaches 95.15%, and the system is stable and does not stratify at room temperature, and has good storage performance.

[0036] 2. Significantly enhanced dimensional stability. The anti-swelling coefficient of the furfuryl alcohol-modified compressed wood of the present invention is generally higher than 66%. Among them, the radial anti-swelling coefficient is up to 78.51% at most, the tangential anti-swelling coefficient is up to 71.45% at most, and the volumetric anti-swelling coefficient is up to 74.33% at most, effectively suppressing the swelling and deformation of wood caused by moisture absorption.

[0037] 3. Comprehensive improvement in mechanical properties. The maximum flexural strength of the modified wood can reach 82.38 MPa, the elastic modulus is increased from 6.34 GPa to 8.82 GPa, and the compressive strength parallel to the grain is increased to more than 58 MPa, indicating that cell wall strengthening and resin embedding significantly enhance the overall strength and anti-deformation ability of the wood.

[0038] 4. Stable compression structure and strong anti-deformation recovery ability: At a compression ratio of 69%, after three wet-dry cycles and treatment with hot water at 95 °C for 30 minutes, the wet and dry compression recovery rates of the compressed wood are only 2.97% and 0.39% respectively, showing excellent anti-recovery stability, indicating that the cross-linked structure has a good fixing effect on compression deformation. Description of the Drawings

[0039] Figure 1 shows the color and layering of the furfuryl alcohol modification solution under different conditions;

[0040] Figure 2 shows the influence of different catalyst ratios on the curing rate of furfuryl alcohol resin-modified wood;

[0041] Figure 3 shows the influence of different ratios of catalysts on the dimensional stability of furfuryl alcohol-modified wood, the radial anti-swelling coefficient (a), the tangential anti-swelling coefficient (b), and the volumetric anti-swelling coefficient (c);

[0042] Figure 4 shows the influence of different ratios of catalysts on the flexural strength (a), elastic modulus (b), and compressive strength parallel to the grain (c) of furfuryl alcohol-modified wood

[0043] Figure 5 shows the compression set recovery rate of furfuryl alcohol-modified compressed wood (FAC-DW) with different compression ratios (CR = 37%, 54%, 69%);

[0044] Figure 6 shows the swelling rate of furfuryl alcohol-modified compressed wood with different compression ratios (CR = 37%, 54%, 69%);

[0045] Figure 7 shows the compressive strength parallel to the grain (a), flexural strength, and elastic modulus (b) of furfuryl alcohol-modified compressed wood (FAC-DW) with different compression ratios (CR = 37%, 54%, 69%). Detailed Embodiment

[0046] The present invention will be further described below in conjunction with the accompanying drawings of the specification and specific embodiments. However, the embodiments do not impose any form of limitation on the present invention. Unless otherwise specified, the reagents, methods, and equipment used in the present invention are conventional reagents, methods, and equipment in the technical field.

[0047] Unless otherwise specified, the reagents and materials used in the following examples are all commercially available.

[0048] The wood sizes used in the following embodiments include 8 / 11 / 16 mm × 48 mm × 120 mm, and the corresponding compression ratios of the obtained modified compressed wood are 37%, 54%, and 69% respectively.

[0049] Example 1 (Ratio 1)

[0050] Add citric acid, ammonium chloride, and borax to pure water, and use a magnetic stirrer to fully dissolve the solids. Then add itaconic anhydride. After complete dissolution, a ternary composite catalyst system is obtained; slowly add furfuryl alcohol and stir well to obtain a uniform light yellow solution (furfuryl alcohol modification solution, and the mass fractions of each component are: 0.5% citric acid, 0.75% ammonium chloride, 1.2% borax, 1.25% itaconic anhydride, 30% furfuryl alcohol), and the pH is 3.92.

[0051] Adopt the vacuum pressure impregnation method. Put the absolutely dry wood specimen into a closed reactor, evacuate for 25 minutes, suck in the furfuryl alcohol modification solution by the negative pressure of the reactor, and then pressurize with industrial nitrogen to 0.8 MPa and keep the pressure for 2.5 hours. After relieving the pressure and taking out the specimen, wipe off the remaining excess liquid on the surface with paper. Then wrap the wood specimen with aluminum foil and transfer it to an oven at 103 °C for curing for 3 hours. After the furfuryl alcohol resin is cured, open the aluminum foil, put the specimen into an oven at 60 °C for drying for 2 hours, and then raise the temperature to 80 °C and keep it for 2 hours. Finally, bake the specimen in an oven at 103 °C until the mass remains unchanged to obtain furfuryl alcohol modified wood.

[0052] Perform compression treatment on the wood specimen after impregnation pretreatment. The specific compression process is as follows: In the first stage, the temperature is 80 °C and the pressure approaches 0, and the wood specimen is softened for 10 minutes; in the second stage, the temperature is raised to 100 °C within 30 minutes and the pressure rises to 2 MPa; in the third stage, the temperature is raised to 120 °C within 20 minutes and the pressure rises to 5 MPa, and keep this parameter for 60 minutes. In the fourth stage, quickly lower the temperature of the hot press to 40 °C, take out the specimen, and transfer it to an oven at 103 °C for drying until a constant weight is reached to obtain furfuryl alcohol modified compressed wood.

[0053] Examples 2 - 6 (Ratios 2 - 6)

[0054] The technical solutions of Examples 2 to 6 are similar to those of Example 1, except that the mass fractions of the components in the obtained furfuryl alcohol modified solution are different, as specifically shown in Table 1.

[0055] Table 1 Mass fractions (%) and pH of the components in the obtained furfuryl alcohol modified solution

[0056]

[0057] Example 7

[0058] The technical solution of Example 7 is similar to that of Example 1, except that the mass fractions of the components in the obtained furfuryl alcohol modified solution are: 0.5% citric acid, 0.5% ammonium chloride, 2% borax, 0.5% itaconic anhydride, 30% furfuryl alcohol, and the pH is 4.50.

[0059] Example 8

[0060] The technical solution of Example 8 is similar to that of Example 1, except that the mass fractions of the components in the obtained furfuryl alcohol modified solution are: 1% citric acid, 0.1% ammonium chloride, 0.5% borax, 0.75% itaconic anhydride, 30% furfuryl alcohol, and the pH is 3.50.

[0061] Comparative Examples 1 to 5

[0062] The technical solutions of Comparative Examples 1 to 5 are similar to those of Example 1, except that the mass fractions of the components in the obtained furfuryl alcohol modified solution are different, as specifically shown in Table 2.

[0063] Table 2 Mass fractions (%) of the components in the obtained furfuryl alcohol modified solution

[0064]

[0065]

[0066] Comparative Example 6

[0067] The technical solution of Comparative Example 6 is similar to that of Example 1, except that the mass fractions of the components in the obtained furfuryl alcohol modified solution are: 1.5% citric acid, 0.75% ammonium chloride, 0.2% borax, 2% itaconic anhydride, 30% furfuryl alcohol.

[0068] Comparative Example 7

[0069] The technical solution of Comparative Example 7 is similar to that of Example 1, except that the mass fractions of the components in the obtained furfuryl alcohol modified solution are: 0.1% citric acid, 0.1% ammonium chloride, 2.5% borax, 0.2% itaconic anhydride, 30% furfuryl alcohol.

[0070] Detection method

[0071] (1) Detection of the stability of the modified solution

[0072] Store the obtained furfuryl alcohol modified solution at room temperature for 6 days and observe the color change.

[0073] (2) Calculation of curing rate

[0074] Calculate the curing rate (SR) through formula (1):

[0075]

[0076] Where, m1 is the oven-dry mass of the modified specimen, g; m2 is the mass of the specimen after vacuum impregnation, g; m0 is the oven-dry mass of the specimen before modification, g; w is the mass fraction of furfuryl alcohol in the furfuryl alcohol modified solution.

[0077] (3) Dimension stability test

[0078] Take natural Chinese fir material as the control group. Put the oven-dry specimen into a closed reaction kettle, evacuate for 40 min, suck in pure water using the pressure difference inside and outside the reaction kettle, pressurize to 1.0 MPa with industrial nitrogen, and keep the pressure for 10 h. Take out the sample, wipe off the residual water on the surface with paper, measure the dimensions of the specimen before and after treatment with a vernier caliper, and calculate the anti-swelling coefficient (ASE) through formulas (2) and (3):

[0079]

[0080] Where, V1 is the volume of the specimen after soaking in water, mm 3 ; V0 is the volume of the specimen after oven-drying, mm 3 ; a0 is the swelling coefficient of the untreated specimen, %; α1 is the swelling coefficient of the modified specimen, %; The dimension stability is characterized by the anti-swelling coefficient (ASE).

[0081] (4) Mechanical property test

[0082] Compressive strength parallel to the grain: Test using a Shenzhen Sansi universal testing machine. Place the specimen at the center position of the spherical movable support of the testing machine and break the specimen within 2 min at a constant loading speed of 3 mm / min.

[0083] Flexural strength and elastic modulus: Test using a Shenzhen Sansi universal testing machine. Adopt the three-point bending test method, with a punch diameter of 10 mm, a support span of 120 mm, and a constant loading speed of 8 mm / min. Before testing the compressive strength parallel to the grain, flexural strength and elastic modulus of the specimen, first place it in a constant temperature and humidity chamber with a relative humidity of 65 ± 5% and a temperature of 23 ± 2 °C until the equilibrium moisture content.

[0084] (5) Compression deformation recovery rate test

[0085] Taking pure water-pretreated compressed wood as the control group, after the obtained compressed wood went through 3 wet-dry cycles and was soaked in hot water at above 95 °C for 30 min, the compression set recovery rate was calculated by formula (4):

[0086]

[0087] Among them: the absolutely dry radial thickness of the compressed specimen is h0, in mm; the absolutely dry radial thickness of the Chinese fir raw material is h1, in mm; after the compressed specimen is soaked, or after soaking and being absolutely dry, the radial thickness is h2, in mm.

[0088] Analysis and Explanation

[0089] According to the results in Table 3, in Comparative Example 2, phthalic acid and ascorbic acid were used, with high reaction activity but a pH greater than 5 and poor dispersibility; in Comparative Example 4, ascorbic acid and oxalic acid were used and no buffering assistant was introduced, resulting in too fast catalytic reaction. Therefore, the color of the above comparative example systems became darker. However, the polycondensation reaction activity was too strong, and the reaction rate far exceeded the diffusion and homogeneous velocity of each component in the system, causing the separation between the polymer and the unreacted monomers, uneven polymerization, obvious stratification in the system, poor stability, and difficulty in meeting the requirements for normal temperature storage. In Comparative Example 3 and Comparative Example 5, combinations of ascorbic acid and itaconic anhydride, and citric acid and itaconic anhydride were used respectively. Although they had certain acidity, due to the lack of an effective synergistic catalytic mechanism and co-catalytic components, it was difficult for the system to form an efficient and stable catalytic environment, resulting in a slow polymerization reaction, a lighter color, and a significantly reduced catalytic efficiency. The color of the system in Comparative Example 1 was orange-red and there was no stratification, indicating that it had certain catalytic activity and stability. However, the activation ability of the phthalic acid molecular structure on the hydroxyl group was weak, the degree of polymerization reaction was limited, and it did not have the effect of synergistically promoting the curing reaction, resulting in poor comprehensive performance. In Comparative Example 6, the pH was too small, the reaction activity increased significantly, and polymerization was likely to occur in advance at normal temperature, the color quickly deepened, and polymer deposition and slight separation appeared in the lower part of the liquid, resulting in the loss of effective permeability and curing activity of the modified liquid. In Comparative Example 7, the polymerization reaction of furfuryl alcohol was not likely to occur. During storage at normal temperature, the color changed slowly and it was not easy to become turbid in the short term. However, due to the low catalytic efficiency, the polycondensation reaction of furfuryl alcohol at high temperature was insufficient, resulting in low curing degree and insufficient modification depth, and ultimately limited improvement in the mechanical properties and dimensional stability of the wood. In contrast, Examples 7 and 8 adopted a composite catalytic system composed of citric acid, itaconic anhydride, and ammonium chloride, which not only achieved sufficient reaction but also ensured system stability. The pH was controlled within the optimal polymerization range of furfuryl alcohol resin, taking into account catalytic efficiency, curing effect, and wood acid resistance, showing good compatibility and storage stability.

[0090] pH of the obtained modified liquid and color change after 6 days in Table 3

[0091] pH Color change Comparative Example 1 4.09 Orange - red, no layering Comparative Example 2 5.83 Orange - red, layering Comparative Example 3 4.99 Light yellow, no layering Comparative Example 4 4.08 Red - brown, layering Comparative Example 5 4.34 Light yellow, no layering Comparative Example 6 3.23 Orange - brown, bottom deposition Comparative Example 7 5.32 Light yellow, no layering Example 7 4.50 Light yellow deepened, no layering Example 8 3.50 Light yellow deepened, no layering

[0092] The curing rate range of the embodiments of the present invention is between 46.28% and 95.15%, generally higher than 80%. The curing rates of Embodiments 2 and 5 are slightly lower, but the lower ammonium chloride content in the catalyst system avoids the rapid curing of furfuryl alcohol on the wood surface, enabling furfuryl alcohol to penetrate into the wood interior and cure in the cell wall. The resulting modified compressed wood can achieve the same performance as other embodiments. For Comparative Example 5, after being placed at room temperature for 9 days, the furfuryl alcohol modification liquid showed a light yellow color and did not show any delamination phenomenon. However, after heating in an oven at 103 °C for 3 h, there was still no delamination phenomenon, indicating that the furfuryl alcohol resin did not cure( Figure 1 ), and the results of other comparative examples were similar to those of Comparative Example 5.

[0093] For wood modification technology, a moisture expansion coefficient exceeding 50% indicates a significant improvement in the dimensional stability of wood. The radial moisture expansion coefficients of the modified woods in Embodiments 1-6 of the present invention are all higher than 62%, with a maximum of 78.51%( Figure 3 a); the tangential moisture expansion coefficients are all higher than 65%, with a maximum of 71.45%( Figure 3 b); the volumetric moisture expansion coefficients are all higher than 66%, with a maximum of 74.33%( Figure 3 c). The above results show that under a moisture change environment, the radial and tangential dimensional changes of the modified wood are small, the stability is good, and the overall moisture resistance and deformation ability are significantly enhanced. This further demonstrates that the catalyst system of the present invention promotes the uniform penetration and curing of furfuryl alcohol resin inside the cell wall, forming a stable cross-linked structure, thereby effectively restricting the dimensional expansion of wood caused by moisture absorption.

[0094] The flexural strengths of the furfuryl alcohol-modified compressed woods of the present invention are all higher than those of the control group, with a maximum of 82.38 MPa( Figure 4 a); the elastic modulus is increased from 6.34 GPa of natural wood to a maximum of 8.82 GPa, indicating an enhanced deformation resistance of the wood( Figure 4 b); the longitudinal compressive strength is also increased from 40.6 MPa of natural wood to above 58 MPa( Figure 4 c). These results indicate that furfuryl alcohol undergoes a polycondensation reaction under the catalytic system of the present invention, and the formed three-dimensional cross-linked structure can penetrate deep into the wood cell wall interior, react with lignin and cellulose parts or form physical intercalation, thereby enhancing the cell wall strength and improving the overall density; at the same time, the cured resin network helps to disperse stress and inhibit the propagation of microcracks, further improving the mechanical properties of the wood.

[0095] Under the catalytic system of the present invention, the mild and controllable acidic environment significantly accelerates the polycondensation reaction rate of furfuryl alcohol, promotes the firm fixation of the cross-linked structure within the cell wall, and effectively inhibits the tendency of the compressed structure to recover. After undergoing severe treatments such as multiple wet-dry cycles and soaking in 95°C hot water for 30 minutes, the compressed wood still exhibits an extremely low compression deformation recovery rate. Especially in the highly dense state with a compression rate of 69%, its wet and dry set recovery rates are only 2.97% and 0.39%( Figure 5 ).

[0096] Compared with natural uncompressed wood, the tangential and volumetric swelling rates of the furfuryl alcohol-modified compressed wood of the present invention both decrease to a certain extent( Figure 6 ). Figure 7 are the longitudinal compressive strength, flexural strength and elastic modulus of furfuryl alcohol-modified compressed wood (FAC-DW) with different compression rates (CR = 37%, 54%, 69%). Compared with natural wood, the longitudinal compressive strength, flexural strength and elastic modulus of furfuryl alcohol-modified compressed wood all increase to a certain extent, and the mechanical properties improve with the increase of the compression rate.

[0097] Obviously, the above-mentioned embodiments of the present invention are merely examples for clearly illustrating the present invention, rather than limitations on the implementation manners of the present invention. For those of ordinary skill in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to enumerate all the implementation manners here. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the claims of the present invention.

Claims

1. A ternary composite system catalyst, characterized in that, Its components include citric acid, ammonium chloride, itaconic anhydride and borax with a mass ratio of 0.2-1:0.1-0.75:0.2-1.25:0.3-2.

2. The ternary composite system catalyst according to claim 1, wherein The pH of the ternary composite system catalyst is 3.5-4.

5.

3. A method for preparing the ternary composite system catalyst according to any one of claims 1 to 2, characterized in that, It includes the following steps: dissolving citric acid, ammonium chloride and borax in water; adding itaconic anhydride and stirring evenly to obtain the ternary composite system catalyst.

4. Use of the ternary composite system catalyst according to any one of claims 1 to 2, characterized in that, It is used for preparing a furfuryl alcohol modification solution.

5. A furfuryl alcohol modified liquid, characterized in that, Its components include the ternary composite system catalyst described in any one of claims 1-2 and furfuryl alcohol.

6. The furfuryl alcohol modified liquid according to claim 5, wherein The mass ratio of the ternary composite system catalyst to furfuryl alcohol is 0.8-4.5:

30.

7. A preparation method of furfuryl alcohol modified wood, characterized in that, It is prepared by using the furfuryl alcohol modification solution described in claim 5; it includes the following steps: making the furfuryl alcohol modification solution fully penetrate into the wood by the vacuum pressure impregnation method, performing a sealing and wrapping treatment on it, and curing it under heating conditions; sequentially performing gradient drying treatment to obtain furfuryl alcohol modified wood.

8. A furfuryl alcohol modified wood, which is prepared by the preparation method of the furfuryl alcohol modified wood described in claim 7.

9. A preparation method of furfuryl alcohol-modified compressed wood, characterized in that, It is prepared by using the furfuryl alcohol modified wood described in claim 8, and includes the following steps: placing the furfuryl alcohol modified wood in a hot pressing device and performing segmented hot pressing treatment; then cooling and drying to obtain furfuryl alcohol modified compressed wood.

10. A furfuryl alcohol-modified compressed wood, characterized in that, It is prepared by the preparation method of the furfuryl alcohol modified compressed wood described in claim 9.

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