A surface-reinforced moldable wood and a method for producing the same

Abstract

The present application relates to the technical field of wood modification, and discloses a surface layer reinforced plastic wood and a preparation method thereof, which comprises the following steps: (1) soaking wood in an impregnation reagent for impregnation treatment, wherein the impregnation reagent comprises an oxidizing agent and an organic hydrogen bond acceptor; (2) compressing the wood subjected to the impregnation treatment in step (1). The surface layer reinforced plastic wood prepared by the preparation method has significantly improved mechanical strength, controllable and low density, effectively inhibited size rebound, excellent comprehensive performance, and good application prospect.

Description

Technical Field

[0001] This invention relates to the field of wood modification technology, specifically to a surface-reinforced malleable wood and its preparation method. Background Technology

[0002] Plantation-grown fast-growing forests have high yields and short rotation periods, but they also have many disadvantages, such as loose wood structure, low mechanical strength, poor rot resistance, inferior quality, and poor dimensional stability. These defects limit their industrial use. Hydrothermal compression treatment can significantly improve the quality and efficiency of wood, not only increasing its hardness, bending strength, compressive strength, and impact resistance, but also changing its shape to enrich the variety of wood products and broaden its applications. However, hydrothermally compressed wood generally faces the technical challenge of significant dimensional rebound.

[0003] Currently, CN114407150A utilizes furfuryl alcohol to reduce the number of hydroxyl groups by self-crosslinking within compressed wood or by crosslinking with wood cell wall components. Simultaneously, it occupies cell pores, hindering water penetration, reducing the hygroscopicity of compressed wood, and improving its dimensional stability. It also serves to fix the compression layer, with a water absorption thickness swelling rate of 12-38% and a moisture absorption thickness swelling rate of 3-10%. However, this method still suffers from a significantly high dimensional resilience rate and a relatively high density in the compressed wood, making it difficult to achieve synergistic optimization of dimensional stability, mechanical properties, and material density. Summary of the Invention

[0004] The purpose of this invention is to overcome the problems of low strength, high dimensional resilience, excessive density, and high transportation costs of compressed wood in the prior art, and to provide a surface-reinforced malleable wood and its preparation method. The surface-reinforced malleable wood prepared by this method has high strength, low density, and low dimensional resilience, and its comprehensive performance is more in line with the needs of practical applications.

[0005] To achieve the above objectives, a first aspect of the present invention provides a method for preparing surface-reinforced malleable wood, the method comprising the following steps: (1) The wood is soaked in an impregnation agent for impregnation treatment, wherein the impregnation agent contains an oxidant and an organic hydrogen bond acceptor; (2) Compress the wood that has been impregnated in step (1).

[0006] The second aspect of the present invention provides a surface-reinforced malleable wood prepared by the preparation method described in the first aspect.

[0007] Through the above technical solution, the present invention has at least the following beneficial effects: (1) The preparation method of the present invention achieves the dissociation and recombination of lignin by impregnating the wood, thereby simultaneously improving the dimensional stability and mechanical properties of the wood. The surface-reinforced malleable wood prepared by the preparation method of the present invention has high mechanical strength, controllable and low density, and effectively suppressed dimensional rebound rate, exhibiting excellent comprehensive performance and good application prospects.

[0008] (2) At the same time, the excess moisture in the compressed wood is removed by hot pressing, minimizing the subsequent dimensional deformation caused by changes in moisture content, and ensuring that the thickness and mechanical strength of the compressed wood are not lost during the storage process. Attached Figure Description

[0009] Figure 1 These are infrared micrographs of lignin in cross-sections of wood from Comparative Examples 1, 6, and 2. Detailed Implementation

[0010] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0011] In this invention, the compression ratio refers to (thickness of wood before hot pressing - thickness of wood after hot pressing) / thickness of wood before hot pressing.

[0012] In this invention, "absolutely dry" refers to the state in which wood is dried to constant weight, and the internal free water and bound water are basically completely removed, with the moisture content approaching zero.

[0013] In this invention, surface-reinforced malleable wood refers to a novel wood material in which the surface structure of wood is densified through chemical reagents and hot-pressing technology, giving the wood surface high strength (bending strength ≥79MPa, bending modulus of elasticity ≥6.8GPa) and strong dimensional stability (radial resilience ≤10%). The term "malleable" means that the material can undergo plastic bending, pressing, and other deformations under certain temperature, humidity, or pressure conditions, and can maintain its shape stability after molding without significant springback or cracking.

[0014] The first aspect of this invention provides a method for preparing surface-reinforced malleable wood, the method comprising the following steps: (1) The wood is soaked in an impregnation agent for impregnation treatment, wherein the impregnation agent contains an oxidant and an organic hydrogen bond acceptor; (2) Compress the wood that has been impregnated in step (1).

[0015] In this invention, the organic hydrogen bond acceptor refers to a class of organic molecules that contain atoms or groups that can accept hydrogen bonds. These atoms or groups typically have high electronegativity and lone pairs of electrons.

[0016] The inventors of this invention discovered through research that by using a specific impregnation reagent to impregnate wood, the depolymerization and recombination of lignin can be achieved. By combining this with a hot-pressing process to control the density distribution of lignin, not only can the dimensional stability of the wood be effectively improved, but its mechanical strength can also be enhanced simultaneously. At the same time, it can avoid the problem of excessive increase in wood density caused by the full compression process, and also effectively control the economic cost of production.

[0017] In this invention, there is no particular limitation on the oxidant, and common oxidants in the art can achieve the purpose of this invention.

[0018] In this invention, preferably, the oxidant is a green oxidant, which is characterized by being environmentally friendly, having mild reaction conditions, and producing few byproducts. This oxidant is widely available and cost-effective, which is beneficial for achieving green and clean production processes in industrial settings.

[0019] In this invention, preferably, the oxidant is selected from at least one of water-soluble peroxides, free radical oxidants, titanium catalytic oxidants, fatty alcohol oxidants, and organophosphorus oxidants.

[0020] In this invention, physical compression and oxidant activation of wood cell wall components promote in-situ chemical condensation, as well as efficient plasticization and reconstruction, thereby improving the permanent fixation of compressed wood.

[0021] In this invention, preferably, the content of the oxidant is 5wt%-10wt%, such as 5wt%, 5.5wt%, 6wt%, 6.5wt%, 7wt%, 7.5wt%, 8wt%, 8.5wt%, 9wt%, 9.5wt%, 10wt%, or any value or range between the above values, based on the total weight of the impregnation reagent.

[0022] More preferably, the oxidant is a water-soluble peroxide.

[0023] According to some preferred embodiments of the present invention, the oxidant is selected from hydrogen peroxide and / or peracetic acid, more preferably hydrogen peroxide.

[0024] In this invention, there is no particular limitation on the organic hydrogen bond acceptor, and common organic hydrogen bond acceptors in the art can achieve the purpose of this invention.

[0025] In this invention, preferably, the organic hydrogen bond acceptor is selected from at least one of quaternary ammonium hydrogen bond acceptors, polyol hydrogen bond acceptors, and organic acid hydrogen bond acceptors.

[0026] In this invention, preferably, the content of the organic hydrogen bond acceptor is 2wt%-5wt%, such as 2wt%, 2.5wt%, 3wt%, 3.5wt%, 4wt%, 4.5wt%, 5wt%, or any value or range between the above values, based on the total weight of the impregnation reagent.

[0027] More preferably, the organic hydrogen bond acceptor is a quaternary ammonium hydrogen bond acceptor.

[0028] According to some preferred embodiments of the present invention, the organic hydrogen bond acceptor is selected from at least one of choline chloride, citrate choline, and tartrate choline.

[0029] In this invention, preferably, in step (1), the impregnation process includes vacuum impregnation.

[0030] In this invention, there are no particular limitations on vacuum impregnation conditions and pressure impregnation conditions, as long as they can penetrate hot wood.

[0031] According to some preferred embodiments of the present invention, the vacuum impregnation conditions include: a pressure of -0.05MPa to -0.1MPa and an impregnation time of 0.5h to 2h, which are more conducive to enhancing the mechanical properties of wood.

[0032] In this invention, preferably, in step (2), the conditions for compression treatment include: temperature of 160℃-190℃, time of 20min-40min, and compression ratio of 20%-40%.

[0033] More preferably, in step (2), the conditions for the compression process include: a temperature of 175℃-185℃, such as 175℃, 176℃, 177℃, 178℃, 179℃, 180℃, 181℃, 182℃, 183℃, 184℃, 185℃, or a range consisting of any two of the above values, or any intermediate value within that range.

[0034] In this invention, preferably, the preparation method further includes: in step (1), the wood after impregnation is subjected to a first drying treatment so that the moisture content of the dried wood is 40%-50%. Controlling the moisture content of the wood within this range is more conducive to the movement of moisture and improves the uniformity of chemical reagent penetration.

[0035] According to some preferred embodiments of the present invention, the conditions for the first drying include: a drying temperature of 20°C-35°C and a drying time of 20 min-40 min.

[0036] In this invention, preferably, the preparation method further includes: subjecting the compressed wood to a second drying treatment so that the moisture content of the dried wood is 8%-12%, such as 8%, 8.5%, 9%, 9.5%, 10%, 10.5%, 11%, 11.5%, 12%, or any range of any two of the above values, or any intermediate value within that range. Controlling the moisture content of the compressed wood within this range is more beneficial to the dimensional stability of the compressed wood.

[0037] According to some preferred embodiments of the present invention, the conditions for the second drying include: a drying temperature of 90°C-110°C and a drying time of 6h-10h.

[0038] According to a particularly preferred embodiment of the present invention, the method includes the following steps: (1) completely immersing the wood in a mixed solution containing 7wt%-8wt% hydrogen peroxide and 2.5wt%-3.5wt% choline chloride, and adjusting the pressure of the sealed tank to -0.8 to -0.1MPa for immersion treatment for 0.8h-1h; (2) After soaking, the wood is dried at room temperature for 20-40 minutes to remove surface moisture (moisture content is about 40%-45%). The dried wood blocks are placed on the press plate. The temperature of the upper and lower press plates is 175℃-185℃, the preheating time is 5-7 minutes, the compression ratio is 30%-35%, and the compression time is 35-40 minutes. The compressed wood is then heated in an oven at 100℃-105℃ for 5.5-6 hours.

[0039] The second aspect of the present invention provides a surface-reinforced malleable wood prepared by the preparation method described in the first aspect.

[0040] In this invention, preferably, the hardness of the wood is 2000N-2500N, more preferably 2200N-2400N.

[0041] In this invention, preferably, the average density of the wood is 0.6 g / cm³. 3 -0.65g / cm 3 More preferably, it is 0.62 g / cm³. 3 -0.64g / cm 3 .

[0042] In this invention, preferably, the bending strength of the wood is 100MPa-140MPa, more preferably 120MPa-125MPa.

[0043] In this invention, preferably, the bending elastic modulus of the wood is 9 GPa-14 GPa, more preferably 10 GPa-14 GPa.

[0044] In this invention, preferably, the radial resilience of the wood is 0.1%-10%, more preferably 2%-5.5%.

[0045] In this invention, preferably, the moisture absorption radial resilience of the wood is 0.1%-3%, more preferably 0.4%-2.5%.

[0046] In this invention, preferably, the water absorption rate of the wood is 87%-136%, more preferably 95%-127%.

[0047] In this invention, preferably, the moisture absorption rate of the wood is 4%-14%, more preferably 9%-13%.

[0048] The present invention will be described in detail below through examples. Unless otherwise specified, the reagents and materials used in the following examples are all commercially available products purchased from regular chemical or biological reagent / material suppliers, and all reagents are of analytical grade.

[0049] In the following examples, the room temperature conditions are 23°C-27°C.

[0050] Example 1 (1) Immerse 15mm thick poplar wood completely in a mixed solution containing 7.5wt% hydrogen peroxide and 1.5wt% choline chloride, and adjust the pressure of the sealed tank to -0.1MPa for 1h of immersion treatment; (2) After soaking, the wood was dried at room temperature for 30 minutes to remove the surface moisture (moisture content of about 40%). The dried wood block was placed on the press plate. The temperature of the upper and lower press plates was 180℃. The preheating time was 5 minutes. The thickness was calibrated with a thickness gauge to determine the compression ratio of 33% with a thickness of 10mm. The press was closed and the press plate heating device was turned off. The compression time was 40 minutes. The compressed wood was then heated in an oven at 103℃ for 6 hours.

[0051] Example 2 (1) Immerse 15mm thick poplar wood completely in a mixed solution containing 7.5wt% hydrogen peroxide and 3wt% choline chloride, and adjust the pressure of the sealed tank to -0.1MPa for 1h of immersion treatment; (2) After soaking, the wood was dried at room temperature for 30 minutes to remove the surface moisture (moisture content of about 40%). The dried wood block was placed on the press plate. The temperature of the upper and lower press plates was 180℃. The preheating time was 5 minutes. The thickness was calibrated with a thickness gauge to determine the compression ratio of 33% with a thickness of 10mm. The press was closed and the press plate heating device was turned off. The compression time was 40 minutes. The compressed wood was then heated in an oven at 103℃ for 6 hours.

[0052] The average density of the wood prepared by the above steps is 0.62 g / cm³. 3 It has a moisture content of 8% and a hardness of 2364.43 N.

[0053] Example 3 (1) Immerse 15mm thick poplar wood completely in a mixed solution containing 7.5wt% hydrogen peroxide and 4.5wt% choline chloride, and adjust the pressure of the sealed tank to -0.1MPa for 1h of immersion treatment; (2) After soaking, the wood was dried at room temperature for 30 minutes to remove the surface moisture (moisture content of about 40%). The dried wood block was placed on the press plate. The temperature of the upper and lower press plates was 180℃. The preheating time was 5 minutes. The thickness was calibrated with a thickness gauge to determine the compression ratio of 33% with a thickness of 10mm. The press was closed and the press plate heating device was turned off. The compression time was 40 minutes. The compressed wood was then heated in an oven at 103℃ for 6 hours.

[0054] Example 4 Compressed wood was prepared according to the method in Example 2, except that in step (1), the impregnation time was 0.5 h.

[0055] Example 5 Compressed wood was prepared according to the method in Example 2, except that in step (1), the impregnation time was 1.5 h.

[0056] Example 6 Compressed wood was prepared according to the steps in Example 2, except that in step (1), the impregnation time was 2 hours.

[0057] Example 7 Compressed wood was prepared according to the method in Example 2, except that in step (2), the temperature of the upper and lower pressure plates of the press was 170°C.

[0058] Example 8 Compressed wood was prepared according to the method in Example 2, except that in step (2), the temperature of the upper and lower pressure plates of the press was 190°C.

[0059] Example 9 Compressed wood was prepared according to the method in Example 2, except that in step (2), the compression time was 20 min.

[0060] Example 10 Compressed wood was prepared according to the method in Example 2, except that in step (2), the compression time was 60 min.

[0061] Comparative Example 1 For untreated poplar (average density 0.44 g / cm³)3 The parameters of the sample (with a hardness of 1678.22 N) were directly measured, and the results are shown in Table 1.

[0062] Comparative Example 2 (1) Immerse 15mm thick poplar wood completely in 1.5wt% choline chloride solution and adjust the pressure of the sealed tank to -0.1MPa for 1h. (2) After soaking, the wood was dried at room temperature for 30 minutes to remove the surface moisture. The dried wood block was placed on the press plate. The temperature of the upper and lower press plates was 180℃. The preheating time was 5 minutes. The thickness was calibrated with a thickness gauge to determine the compression ratio of 33% as 10mm. The press was closed and the press plate heating device was turned off. The compression time was 40 minutes. The compressed wood was then heated in an oven at 103℃ for 6 hours.

[0063] Comparative Example 3 Compressed wood was prepared according to the method in Comparative Example 2, except that the mass concentration of the choline chloride solution was 3 wt%.

[0064] Comparative Example 4 Compressed wood was prepared according to the method in Comparative Example 2, except that the mass concentration of the choline chloride solution was 4.5 wt%.

[0065] Comparative Example 5 Compressed wood was prepared according to the method in Comparative Example 2, except that in step (1), wood with a thickness of 15 mm was completely immersed in a 7.5 wt% hydrogen peroxide solution.

[0066] Comparative Example 6 Compressed wood was prepared according to the method in Comparative Example 2, except that in step (1), wood with a thickness of 15 mm was completely immersed in water.

[0067] Test Example 1 Confocal Raman microscopy (Horiba Jobin Yvon) was used to investigate and detect the migration and distribution patterns of wood components in cross-sections of Comparative Example 1, Comparative Example 6, and Example 2. Figure 1 It can be seen that, compared with the cross-sections of untreated poplar (Comparative Example 1) and water-soaked compressed wood (Comparative Example 6), the lignin and carbohydrate complexes in the cell walls of the compressed wood (Example 2) prepared by the method of the present invention are more uniformly distributed and significantly increased.

[0068] The performance of the compressed wood prepared in the above examples and comparative examples was evaluated under the following test conditions: The standard for testing average density is GB-T 1941-2009; The test standard for flexural strength is GB-T 1936-1-2009; The test standard for flexural modulus of elasticity is GB-T 1936-2-2009; The standard for hardness testing is GB / T 1941 (2009). The standard for testing moisture content is GB / T 1931-2009.

[0069] Table 1

[0070] In this invention, the average density of the surface-reinforced malleable wood prepared in all embodiments was controlled within the range of 0.6-0.65 g / cm³. 3 Within the specified range, the hardness is in the range of 2000-2500 N, and the moisture content is in the range of 8%-12%. Compared with the untreated wood in Comparative Example 1, the wood treated by the method of the present invention can achieve a significant increase in wood hardness while maintaining a lower density.

[0071] As can be seen from the results in Table 1, the wood prepared by the embodiments of the present invention has excellent bending strength and bending modulus of elasticity.

[0072] Test Example 2 The dimensional stability of the wood prepared in the above examples and comparative examples was evaluated under the following test conditions: Water absorption thickness swelling rate (%): The thickness swelling rate of different compressed woods after soaking in water at room temperature for 10 days was measured according to the test standard GB / T 1934.2 (2009). The water absorption thickness swelling rate is the percentage increase in the radial dimension of compressed wood relative to its oven-dry radial dimension before soaking during water immersion at room temperature. Water absorption thickness swelling rate (%) = (radial dimension after water absorption - oven-dry radial dimension) / oven-dry radial dimension × 100%.

[0073] Moisture absorption thickness expansion rate (%): The thickness expansion rate of different compressed wood after being placed at 40℃ and 90% relative humidity for 10 days was measured according to the test standard GB / T 1934.2 (2009). Moisture absorption thickness expansion rate (%) = (radial dimension after moisture absorption - radial dimension after oven-dry) / radial dimension after oven-dry × 100%.

[0074] Water absorption rate (%): Measured according to test standard GB / T 1934.1 (2009). The percentage of water absorbed by compressed wood during room temperature immersion relative to its initial dry weight. The formula for calculating water absorption rate is: Water absorption rate (%) = (Weight after water absorption - Dry weight) / Dry weight × 100%.

[0075] Moisture absorption rate (%): Determined according to GB / T 1934.1-2009 test standard. Different compressed wood samples were placed in a constant temperature and humidity chamber at 40℃ and 90% relative humidity for 10 days. After the predetermined time, the samples were removed and weighed immediately. The formula for calculating the moisture absorption rate is: Moisture absorption rate (%) = (Mass after moisture absorption - Dry mass) / Dry mass × 100%.

[0076] Radial resilience (%): The compressed wood sample was completely immersed in distilled water at room temperature for 10 days. After removal, the degree of recovery of the radial dimension was measured. The calculation formula is: Radial resilience (%) = (Radial dimension after water absorption - Radial dimension after compression) / (Initial radial dimension - Radial dimension after compression) × 100%.

[0077] Moisture-absorbing radial resilience (%): The degree to which the radial dimension of compressed wood recovers relative to its compressed state after being exposed to an environment of 40℃ and 90% relative humidity until its thickness stabilizes and then dried to absolute dryness; that is, the percentage of the final absolute dry recovery relative to the compression. The calculation formula is: Moisture-absorbing radial resilience (%) = (Radial dimension after moisture absorption - Radial dimension after compression) / (Initial radial dimension - Radial dimension after compression) × 100%.

[0078] Table 2

[0079] As can be seen from the results in Table 2, the dimensional resilience of the wood prepared in each embodiment of the present invention is at a low level, indicating that the dimensional recovery phenomenon of wood under hygroscopic and water-absorbing environments is significantly suppressed, and the dimensional stability is excellent.

[0080] As can be seen from Tables 1 and 2 above, the compressed wood produced by this invention has high mechanical strength, low density, and strong dimensional stability, which improves the use value and service life of low-quality fast-growing wood, broadens the application field of fast-growing wood, and is expected to be applied in structural materials.

[0081] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A method for preparing surface-reinforced malleable wood, characterized in that, The method includes the following steps: (1) The wood is soaked in an impregnation agent for impregnation treatment, wherein the impregnation agent contains an oxidant and an organic hydrogen bond acceptor; (2) Compress the wood that has been impregnated in step (1).

2. The method according to claim 1, wherein, The oxidant is selected from at least one of water-soluble peroxides, free radical oxidants, titanium catalytic oxidants, fatty alcohol oxidants, and organophosphorus oxidants, preferably water-soluble peroxides; And / or, the organic hydrogen bond acceptor is selected from at least one of quaternary ammonium hydrogen bond acceptors, polyol hydrogen bond acceptors, and organic acid hydrogen bond acceptors, more preferably quaternary ammonium hydrogen bond acceptors.

3. The method according to claim 2, wherein, The oxidant is selected from at least one of hydrogen peroxide and / or peracetic acid; And / or, the organic hydrogen bond acceptor is selected from at least one of choline chloride, citrate choline, and tartrate choline.

4. The method according to any one of claims 1-3, wherein, Based on the total weight of the impregnation reagent, the content of the oxidant is 5wt%-10wt%; And / or, based on the total weight of the impregnation reagent, the content of the organic hydrogen bond acceptor is 2wt%-5wt%.

5. The method according to any one of claims 1-4, wherein, The impregnation process includes vacuum impregnation; Preferably, the vacuum impregnation conditions include: a pressure of -0.05MPa to 0.1MPa and an impregnation time of 0.5h to 2h.

6. The method according to any one of claims 1-5, wherein, In step (2), the compression conditions include: temperature of 160℃-190℃, time of 20min-40min, and compression ratio of 20%-40%.

7. The method according to any one of claims 1-6, wherein, The preparation method further includes: in step (1), the impregnated wood is subjected to a first drying treatment so that the moisture content of the dried wood is 40%-50%; Preferably, the conditions for the first drying include: a temperature of 20°C-35°C and a time of 20 min-40 min.

8. The method according to any one of claims 1-7, wherein, The preparation method further includes: subjecting the compressed wood to a second drying treatment so that the moisture content of the dried wood is 8%-12%; Preferably, the conditions for the second drying include: a temperature of 90℃-110℃ and a time of 6h-10h.

9. The preparation method according to any one of claims 1-8 is used to prepare surface-reinforced malleable wood.

10. The timber according to claim 9, wherein, The hardness of the wood is 2000N-2500N; And / or, the average density of the wood is 0.6 g / cm³. 3 -0.65g / cm 3 ; And / or, the bending strength of the wood is 100MPa-140MPa; And / or, the modulus of elasticity in bending of the wood is 9 GPa-14 GPa; And / or, the radial resilience of the wood to water absorption is 0.1%-10%; And / or, the moisture absorption radial resilience of the wood is 0.1%-3%; And / or, the water absorption rate of the wood is 87%-136%; And / or, the moisture absorption rate of the wood is 4%-14%.

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