Method for reinforcing and modifying wood through solvent-free and low-viscosity bio-based bi-crosslinking curing epoxy resin and application

Abstract

The invention belongs to the field of wood enhancement and modification, and discloses a method for enhancing and modifying wood through solvent-free and low-viscosity bio-based bi-crosslinking curing epoxy resin for wood enhancement and modification. The bio-based epoxy resin is synthesized from bio-based dicarboxylic acid itaconic acid and epichlorohydrin through esterification reaction, the synthesis steps are simple, the viscosity is low, raw materials are green in source and free of solvent, and the bio-based epoxy resin is environment-friendly resin. A comonomer is introduced to further reduce the viscosity and regulate the crosslinking density of an epoxy crosslinking network, a low-viscosity and high-permeability double-crosslinking curing system based on a sulfydryl-ene / sulfydryl-epoxy reaction is constructed, hydroxyl groups formed in the curing process and hydroxyl groups in wood form hydrogen-bond interaction, physical filling and chemical crosslinking synergism is achieved, and the curing effect is good. And the density of the wood is greatly improved, meanwhile, the dimensional stability and the mechanical property of the wood are improved, and good application prospects are achieved.

Description

Technical Field

[0001] The invention belongs to the field of wood reinforcement and modification, and particularly relates to a method for reinforcing and modifying wood by using a solvent-free, low-viscosity bio-based double-crosslinked cured epoxy resin. Background Art

[0002] Wood is a porous natural polymer material that is lightweight, strong, has excellent processing performance, beautiful texture, is green and environmentally friendly, and renewable. It is widely used in various fields such as construction, home furnishing, and decoration. However, wood still has defects such as low density, loose material, and poor dimensional stability, which bring corresponding safety hazards. Therefore, it is necessary to carry out functional improvement of wood to improve its material and optimize its performance.

[0003] Impregnation modification is one of the effective methods to improve the mechanical strength of wood and reduce shrinkage and swelling. Low-viscosity resin is used to enter the cell cavity or cell wall for physical filling or chemical cross-linking to achieve the purpose of strengthening. Epoxy resin itself has relatively excellent mechanical properties and bonding properties and is gradually used for wood modification. Currently, most epoxy resins used for wood modification are derived from fossil raw materials or have certain toxicity, high viscosity, are not environmentally friendly, and difficult to penetrate. Therefore, the preparation of a new type of solvent-free, low-viscosity bio-based epoxy resin is not only green in source, but also improves the dimensional stability and mechanical properties of wood. The cross-linked network structure formed by the curing of the resin can solve the defects of poor permeability and easy loss of traditional impregnation agents, which is a more comprehensive means of improving wood functionalization.

[0004] Lv Shaoyi et al. (Lv Shaoyi, Fu Feng, Li Shanming, et al. Structure and properties of microwave-expanded Scots pine wood filled with epoxy resin [J]. Wood Science and Technology, 2022, 36(02): 48-53.) used microwaves to pretreat Scots pine to produce new macro cracks in the wood, and then filled epoxy resin into the cracks and fissures of microwave-expanded wood by vacuum pressure impregnation, which improved the density and mechanical properties of the modified material. However, the experimental process not only destroyed the structure of the wood itself, but the commercial epoxy resin used had a high viscosity (3000±500mPa·s) and was not environmentally friendly.

[0005] Li Zhibin et al. (Li Zhibin, Ying Qiao, Yuan Xinbing, et al. Performance and modification mechanism of fast-growing wood modified by epoxy soybean oil acrylate impregnation [J]. Polymer Materials Science and Engineering, 2022, 38(11): 49-57.) used epoxy soybean oil acrylate to impregnate and modify fir, Larix gmelinii and poplar. The performance of modified fir was the most obvious, and its mechanical properties and water absorption properties were greatly improved. However, due to the high viscosity and limited permeability of epoxy soybean oil acrylate, benzene organic solvents were used for dilution during the impregnation process. The volatilization of organic solvents can easily cause environmental pollution and be harmful to the human body, which is not in line with the concept of green environmental protection.

[0006] Wang Dongyue et al. (Wang Dongyue. Preparation of quaternized waterborne epoxy resin system and its effect on wood properties [D]. Zhejiang A&F University, 2022.) prepared quaternized waterborne epoxy resin by chemical modification of epoxy prepolymers with different functionalities, and obtained modified materials by vacuum pressure impregnation. The density, mechanical strength and dimensional stability of the modified materials were improved, and the quaternized waterborne epoxy resin could be better fixed inside the wood. However, waterborne epoxy resin uses water as solvent, and the preparation process of quaternized waterborne epoxy resin is relatively complicated, involving multi-step reactions and a variety of required raw materials.

[0007] Xu Hongjun et al. (Xu Hongjun, Chen Changbiao, Xiao Jiahao, et al. Effect of chitosan quaternary ammonium salt modified waterborne epoxy resin on wood dimensional stability and anticorrosion and antifungal properties [J / OL]. Journal of Forestry Engineering, 2025, 1-10.) used chitosan quaternary ammonium salt to modify waterborne epoxy resin, and used the vacuum-pressure impregnation method to impregnate it into the wood to undergo a curing and cross-linking reaction. The shrinkage and swelling rates of the modified treated materials were lower than those of the untreated materials, which significantly improved the wood's ability to resist deformation. However, during the compounding process, as the content of chitosan quaternary ammonium salt increased, the viscosity of the system increased, more resin was only filled in the cell cavity, and the changes in the volume increase rate and anti-swelling rate of the wood were not obvious.

[0008] Chinese patent publication CN 117507079 A uses epoxy resin to enhance and modify phenolic resin, mixes them, and performs vacuum pressure impregnation treatment on fast-growing wood, so that the resin material can fill the fiber gaps of the fast-growing wood, play a dense and reinforcing role, thereby enhancing the dimensional stability of the fast-growing wood and avoiding the defects of cracking and easy corruption of the fast-growing wood. However, the release of harmful substances such as free formaldehyde in phenolic resin does not conform to the concept of green environmental protection, and the modification cost is high.

[0009] Chinese patent authorization text CN 112250576 B uses hydrogenated rosin and maleic anhydride as main raw materials, and prepares bifunctional reactive rosin resin REMG through epoxy ring opening, esterification and other methods. REMG is dissolved in anhydrous ethanol, and an initiator is added to prepare an impregnation solution. Because the flexible chain segment in the molecule contains two double bonds, the cross-linking degree of REMG is increased, and the bonding strength between the resin and the wood is improved. However, it is inevitable to use alcohol solvents, which are easy to remain or volatilize and cause pollution, and maleic anhydride is acidic and will affect the stability of the modified material to a certain extent.

[0010] Chinese patent publication CN 114633330A firstly performs hot pressing on softened wood, and then impregnates and modifies the wood with a low-viscosity epoxy component, an organic solvent, a curing agent, and an accelerator to obtain ultra-high-strength wood. This process effectively controls the compression layer, thereby achieving the regulation of the macroscopic distribution of the modifier and achieving different types of mechanical load enhancement. However, the weight gain rate of the modified material is low, the raw material diversity in the preparation process and the use of acetone, tetrahydrofuran or anhydrous ethanol as a diluent are not environmentally friendly and the curing time is too long. Summary of the invention

[0011] In order to overcome the shortcomings and deficiencies of the above-mentioned prior art, the primary purpose of the present invention is to provide a method for impregnating and reinforcing modified wood with a solvent-free, low-viscosity bio-based double-crosslinked epoxy resin. This method effectively solves the problem that most modifiers have complicated synthesis steps, the viscosity of traditional epoxy resins is high, it is difficult to penetrate wood evenly and effectively, the source is not green and it relies on organic solvents, and provides an efficient, convenient, green and environmentally friendly way to functionalize wood.

[0012] Another object of the present invention is to provide modified wood prepared by the above method.

[0013] Another object of the present invention is to provide the application of the modified wood in the fields of construction, furniture, decoration and so on.

[0014] The purpose of the present invention is achieved through the following solutions:

[0015] A method for impregnating and reinforcing modified wood with a solvent-free, low-viscosity bio-based double-crosslinked epoxy system comprises the following steps:

[0016] (1) Itaconic acid and epichlorohydrin are used as raw materials, a ring-opening esterification reaction occurs under the action of a catalyst and nitrogen protection, and then a base is added for a ring-closing reaction to obtain a low-viscosity bio-based epoxy resin;

[0017] (2) mixing and stirring the low-viscosity bio-based epoxy resin, curing agent and comonomer of step (1) to obtain a composite impregnation liquid, and then immersing the wood in the composite impregnation liquid, vacuum impregnating, and then pressurizing, and after depressurizing, washing the impregnation liquid remaining on the surface of the wood with water, and letting it stand to air dry;

[0018] (3) The wood after being air-dried in step (2) is heated and cured to obtain a solvent-free, low-viscosity bio-based epoxy resin double-crosslinked cured reinforced modified material.

[0019] The molar ratio of itaconic acid to epichlorohydrin in step (1) is 1:10 to 1:13;

[0020] The catalyst described in step (1) is a phase transfer catalyst, preferably at least one of tetrabutylammonium bromide, benzyltrimethylammonium chloride, benzyltrimethylammonium bromide, tetramethylammonium bromide, etc., more preferably tetrabutylammonium bromide; the amount of the catalyst used is such that 0.01 to 0.03 mmol of the catalyst is added for every 1 mmol of itaconic acid.

[0021] The ring-opening esterification reaction in step (1) is carried out at 90-100° C. for 1-3 hours; preferably, the reaction is carried out at 90° C. for 90 minutes and then the temperature is raised to 100° C. for 30 minutes.

[0022] The alkali-adding ring-closure reaction described in step (1) refers to cooling to 40-60° C. and then adding alkali to react for 1-2 hours, wherein the alkali is preferably an aqueous sodium hydroxide solution, preferably a 40-50wt% aqueous sodium hydroxide solution, and the amount of the alkali is such that 1-4 mol of sodium hydroxide is added to 1 mol of itaconic acid.

[0023] After the ring-closing reaction in step (1) is completed, a post-treatment operation is also included, which is specifically as follows: after the reaction solution is cooled to 25-30° C., it is washed with water for 3-5 times, and then the excess epichlorohydrin and water are removed by reduced pressure distillation. The low-viscosity bio-based epoxy resin is obtained after sealed storage.

[0024] The curing agent described in step (2) is at least one of bis(3-mercaptopropionic acid)ethylene glycol, trimethylolpropane tris(3-mercaptopropionate), and pentaerythritol tetra(3-mercaptopropionic acid) ester; and the comonomer is at least one of glycidyl methacrylate, 1,4-butanediol diglycidyl ether, and glycerol triglycidyl ether.

[0025] The amounts of the low viscosity bio-based epoxy resin, curing agent and comonomer described in step (2) satisfy: the mass ratio of the low viscosity bio-based epoxy resin to the comonomer is 5:5 to 7:3; the molar amount of the thiol group of the curing agent: (the molar amount of the epoxy group of the low viscosity bio-based epoxy resin + the molar amount of the epoxy group of the comonomer + the molar amount of the carbon-carbon double bond of the low viscosity bio-based epoxy resin + the molar amount of the carbon-carbon double bond of the comonomer) is 1:0.8 to 1:1.2;

[0026] The wood in step (2) is preferably dried to absolute dryness before being placed in the compound impregnation solution. The wood is preferably sawn to 200mm×10mm×10mm, 20mm×20mm×20mm, and then dried after being polished.

[0027] The wood described in step (2) is preferably at least one of poplar and fir.

[0028] The amounts of the wood and the compound impregnating liquid in step (2) are such that the impregnating liquid can immerse the wood.

[0029] The vacuum impregnation described in step (2) refers to vacuuming to -0.05 to -0.1 MPa and maintaining it for 0.5 to 1 hour; the pressurization treatment refers to pressurizing to 0.4 to 0.8 MPa and maintaining it for 1 to 4 hours.

[0030] The air-drying described in step (2) is preferably performed by standing at room temperature for 6-12 hours.

[0031] The heating and curing described in step (3) refers to heating and curing at 80-150°C for 4-6 hours to achieve a double cross-linking curing reaction, preferably gradient heating and curing in a forced air drying oven, specifically heating at 100°C for 1 hour, 120°C for 2 hours, and 140°C for 2 hours.

[0032] In step (3), after the resin is completely cured, the wood needs to be transferred to a constant temperature and humidity chamber for equilibrium, wherein the constant temperature and humidity chamber is preferably a constant temperature and humidity chamber at 25° C. and 65% RH.

[0033] Step (3) is to introduce a comonomer to further reduce the viscosity of the epoxy resin on the basis of maintaining the low viscosity of the bio-based epoxy resin, regulate the cross-linking density of the epoxy curing system, construct a high-permeability double-crosslinked epoxy curing system based on the thiol-ene / thiol-epoxy reaction and immerse it in the wood. By utilizing the fact that the molecular structure of the bio-based epoxy resin contains both double bonds and epoxy groups, the double-crosslinked curing of the thiol-epoxy nucleophilic addition and the thiol-olefin Michael addition reaction inside the wood is realized. The hydroxyl groups formed during the curing process generate hydrogen bonds with the hydroxyl groups of the three major elements inside the wood, and the physical filling and cross-linking synergistic effect of the resin and the wood is utilized to improve the density, dimensional stability and mechanical properties of the wood. The viscosity of the bio-based epoxy resin and the high-permeability double-crosslinked epoxy curing system based on the thiol-ene / thiol-epoxy reaction is between 20 and 300 mPa·s, and the permeability in the wood is good, the drug loading rate is high, and the modification effect is significant.

[0034] A modified wood prepared by the method.

[0035] The above modified wood is used in the fields of construction, furniture, decoration and decoration.

[0036] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0037] The present invention uses bio-based dicarboxylic acid itaconic acid and epichlorohydrin to synthesize bio-based epoxy resin through esterification reaction. The synthesis steps are simple, the viscosity is low, the raw material source is green and solvent-free, and it is an environmentally friendly resin. The viscosity is further reduced by introducing a comonomer, and the cross-linking density of the epoxy cross-linking network is regulated to construct a low-viscosity and high-permeability double cross-linking curing system based on mercapto-ene / mercapto-epoxy reaction. The synthesis process is simple, time-consuming, solvent-free, and has excellent stability, good permeability, high drug loading rate, and significant modification effect.

[0038] The bio-based epoxy resin and the high-permeability double-crosslinked epoxy curing system based on mercapto-ene / mercapto-epoxy reaction used in the present invention have viscosities ranging from 20 to 300 mPa·s, and have good permeability in wood, high drug loading rate, and significant modification effect.

[0039] The present invention adopts a solvent-free, low-viscosity, high-permeability dual-crosslinking curing system based on mercapto-ene / mercapto-epoxy reaction, improves the crosslinking density of the epoxy system by copolymerizing monomers, utilizes mercapto groups to react with double bonds and epoxy groups to form a crosslinking network structure inside the wood, and hydroxyl groups formed during the curing process form hydrogen bonds with hydroxyl groups inside the wood. The synergistic effect of physical filling and chemical crosslinking not only greatly improves the density of the wood, but also improves the dimensional stability and mechanical properties of the wood, and has good application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 Infrared spectrum for structural characterization of low viscosity bio-based epoxy resin.

[0041] Figure 2 Graph showing the viscosity of the mixed impregnation liquid obtained in step (5) of Examples 1 to 3 (ie, Examples 1-3) and the comparative example.

[0042] Figure 3 Graph showing the drug loading rates of the modified materials obtained in Examples 1 to 3 (ie, Examples 1-3) and the comparative example.

[0043] Figure 4 The scanning electron microscope images are cross-sections of pure wood and modified wood of Example 3 (ie, Example 3).

[0044] Figure 5 It is a density diagram of the modified wood of Examples 1 to 3 (ie Examples 1-3) and the comparative example.

[0045] Figure 6 It is a graph showing the water absorption rate of pure wood, modified wood of Examples 1 to 3 (ie, Examples 1-3) and comparative example.

[0046] Figure 7 It is a graph of the anti-swelling coefficient of pure wood, Examples 1 to 3 (ie Examples 1-3) and the modified wood of the comparative example.

[0047] Figure 8 The graphs are of bending strength and elastic modulus of pure wood, modified wood of Examples 1 to 3 (i.e., Examples 1-3), and comparative examples.

[0048] Fig. 9 This is a graph showing the impact strength of pure wood, modified wood from Examples 1 to 3 (ie, Examples 1-3), and comparative examples. DETAILED DESCRIPTION

[0049] The present invention is further described in detail below in conjunction with the examples and drawings, but the embodiments of the present invention are not limited thereto. If specific conditions are not specified in the examples, they are carried out according to conventional conditions or conditions recommended by the manufacturer. If the manufacturer of the reagents or instruments used is not specified, they are all conventional products that can be purchased commercially.

[0050] Example 1

[0051] (1) Itaconic acid and epichlorohydrin in a molar ratio of 1:10 and a catalyst tetrabutylammonium bromide (the molar ratio of itaconic acid to catalyst is 1:0.01) are added to a three-necked flask equipped with a mechanical stirrer, a condenser and a nitrogen gas device, and the temperature is gradually raised to 90°C for reaction for 90 minutes, and then the reaction temperature is raised to 100°C for reaction for 30 minutes.

[0052] (2) The reaction solution was cooled to 60° C., a 40 wt % sodium hydroxide solution (the molar ratio of itaconic acid to sodium hydroxide was 1:2) was added, and the reaction was maintained at 60° C. for 2 h.

[0053] (3) Cool to room temperature, add deionized water to wash 5 times, remove excess epichlorohydrin and water by rotary evaporation, pour out and seal for storage, and obtain a low-viscosity itaconic acid-based epoxy resin.

[0054] (4) The poplar boards were sawn into 200 mm × 10 mm × 10 mm (mainly used as mechanical property specimens) and 20 mm × 20 mm × 20 mm (mainly used as density, dimensional stability and water absorption performance specimens), polished, and dried in an oven at 103 °C until absolutely dry.

[0055] (5) Low viscosity bio-based epoxy resin, curing agent trimethylolpropane tris(3-mercaptopropionate), and comonomer glycidyl methacrylate are mixed evenly to obtain a mixed impregnation solution, which is allowed to stand for use. The mass ratio of comonomer glycidyl methacrylate to low viscosity bio-based epoxy resin is 3:7, and the molar amount of mercapto group of the curing agent is: (molar amount of epoxy group of low viscosity bio-based epoxy resin + molar amount of epoxy group of comonomer + molar amount of carbon-carbon double bond of low viscosity bio-based epoxy resin + molar amount of carbon-carbon double bond of comonomer) = 1:1.

[0056] (6) The wooden board of step (4) is completely immersed in the mixed impregnation liquid of step (5), and then the vacuum degree is evacuated to -0.1 MPa and maintained for 0.5 h; then the pressure is increased to 0.6 MPa and maintained for 2 h. After the pressure is released, the wooden board is taken out and wiped dry, and then left to air dry at room temperature for 12 h.

[0057] (7) The impregnated sample was placed in a forced air drying oven with a gradient of 100°C / 1h, 120°C / 2h, and 140°C / 2h. After the resin was completely cured, the sample was transferred to a constant temperature and humidity chamber (25°C, 65% RH) for equilibrium to obtain impregnated reinforced modified wood.

[0058] Example 2

[0059] (1) Itaconic acid and epichlorohydrin in a molar ratio of 1:10 and a catalyst tetrabutylammonium bromide (the molar ratio of itaconic acid to the catalyst is 1:0.01) are added to a three-necked flask equipped with a mechanical stirrer, a condenser and a nitrogen gas device, and the temperature is gradually raised to 90°C for reaction for 90 minutes, and then the reaction temperature is raised to 100°C for reaction for 30 minutes.

[0060] (2) The reaction solution was cooled to 60° C., a 40 wt % sodium hydroxide solution (the molar ratio of itaconic acid to sodium hydroxide was 1:2) was added, and the reaction was maintained at 60° C. for 2 h.

[0061] (3) Cool to room temperature, add deionized water to wash 5 times, remove excess epichlorohydrin and water by rotary evaporation, pour out and seal for storage, and obtain a low-viscosity itaconic acid-based epoxy resin.

[0062] (4) Saw the poplar board into 200 mm × 10 mm × 10 mm, 20 mm × 20 mm × 20 mm, grind and polish it, and put it into an oven at 103°C to dry it.

[0063] (5) A low-viscosity bio-based epoxy resin, a curing agent trimethylolpropane tris(3-mercaptopropionate) and a comonomer 1,4-butanediol diglycidyl ether are mixed uniformly to obtain a mixed impregnation solution, which is allowed to stand for use, wherein the mass ratio of the comonomer 1,4-butanediol diglycidyl ether to the low-viscosity bio-based epoxy resin is 3:7; the molar amount of the mercapto group of the curing agent: (the molar amount of the epoxy group of the low-viscosity bio-based epoxy resin + the molar amount of the epoxy group of the comonomer + the molar amount of the carbon-carbon double bond of the low-viscosity bio-based epoxy resin + the molar amount of the carbon-carbon double bond of the comonomer) = 1:1.

[0064] (6) The wooden board of step (4) is completely immersed in the mixed impregnation liquid of step (5), and then the vacuum degree is evacuated to -0.1 MPa and maintained for 0.5 h; then the pressure is increased to 0.6 MPa and maintained for 2 h. After the pressure is released, the wooden board is taken out and wiped dry, and then left to air dry at room temperature for 12 h.

[0065] (7) The impregnated sample was placed in a forced air drying oven with a gradient of 100°C / 1h, 120°C / 2h, and 140°C / 2h. After the resin was completely cured, the sample was transferred to a constant temperature and humidity chamber (25°C, 65% RH) for equilibrium to obtain impregnated reinforced modified wood.

[0066] Example 3

[0067] (1) Itaconic acid and epichlorohydrin in a molar ratio of 1:10 and a catalyst tetrabutylammonium bromide (the molar ratio of itaconic acid to the catalyst is 1:0.01) are added to a three-necked flask equipped with a mechanical stirrer, a condenser and a nitrogen gas device, and the temperature is gradually raised to 90°C for reaction for 90 minutes, and then the reaction temperature is raised to 100°C for reaction for 30 minutes.

[0068] (2) The reaction solution was cooled to 60° C., a 40 wt % sodium hydroxide solution (the molar ratio of itaconic acid to sodium hydroxide was 1:2) was added, and the reaction was maintained at 60° C. for 2 h.

[0069] (3) Cool to room temperature, add deionized water to wash 5 times, remove excess epichlorohydrin and water by rotary evaporation, pour out and seal for storage, and obtain a low-viscosity itaconic acid-based epoxy resin.

[0070] (4) Saw the poplar board into 200 mm × 10 mm × 10 mm, 20 mm × 20 mm × 20 mm, grind and polish it, and put it into an oven at 103°C to dry it.

[0071] (5) A low-viscosity bio-based epoxy resin, a curing agent, trimethylolpropane tris(3-mercaptopropionate), and a comonomer, propylene glycol triglycidyl ether, are uniformly mixed to obtain a mixed impregnation solution, which is allowed to stand for use. The mass ratio of the comonomer, propylene glycol triglycidyl ether, to the low-viscosity bio-based epoxy resin is 3:7, and the molar amount of the thiol group of the curing agent is: (the molar amount of the epoxy group of the low-viscosity bio-based epoxy resin + the molar amount of the epoxy group of the comonomer + the molar amount of the carbon-carbon double bond of the low-viscosity bio-based epoxy resin + the molar amount of the carbon-carbon double bond of the comonomer) = 1:1.

[0072] (6) The wooden board of step (4) is completely immersed in the mixed impregnation liquid of step (5), and then the vacuum degree is evacuated to -0.1 MPa and maintained for 0.5 h; then the pressure is increased to 0.6 MPa and maintained for 2 h. After the pressure is released, the wooden board is taken out and wiped dry, and then left to air dry at room temperature for 12 h.

[0073] (7) The impregnated sample was placed in a forced air drying oven with a gradient of 100°C / 1h, 120°C / 2h, and 140°C / 2h. After the resin was completely cured, the sample was transferred to a constant temperature and humidity chamber (25°C, 65% RH) for equilibrium to obtain impregnated reinforced modified wood.

[0074] Comparison examples

[0075] (1) Itaconic acid and epichlorohydrin in a molar ratio of 1:10 and a catalyst tetrabutylammonium bromide (the molar ratio of itaconic acid to the catalyst is 1:0.01) are added to a three-necked flask equipped with a mechanical stirrer, a condenser and a nitrogen gas device, and the temperature is gradually raised to 90°C for reaction for 90 minutes, and then the reaction temperature is raised to 100°C for reaction for 30 minutes.

[0076] (2) The reaction solution was cooled to 60° C., a 40 wt % sodium hydroxide solution (the molar ratio of itaconic acid to sodium hydroxide was 1:2) was added, and the reaction was maintained at 60° C. for 2 h.

[0077] (3) Cool to room temperature, add deionized water to wash 5 times, remove excess epichlorohydrin and water by rotary evaporation, pour out and seal for storage, and obtain a low-viscosity itaconic acid-based epoxy resin.

[0078] (4) Saw the poplar board into 200 mm × 10 mm × 10 mm, 20 mm × 20 mm × 20 mm, grind and polish it, and put it into an oven at 103°C to dry it.

[0079] (5) A low-viscosity bio-based epoxy resin and a curing agent, trimethylolpropane tris(3-mercaptopropionate), are mixed uniformly to obtain a mixed impregnation solution, which is allowed to stand for use, wherein the molar amount of the mercapto group of the curing agent: (the molar amount of the epoxy group of the low-viscosity bio-based epoxy resin + the molar amount of the carbon-carbon double bond of the low-viscosity bio-based epoxy resin) = 1:1.

[0080] (6) The wooden board of step (4) is completely immersed in the mixed impregnation liquid of step (5), and then the vacuum degree is evacuated to -0.1 MPa and maintained for 0.5 h; then the pressure is increased to 0.6 MPa and maintained for 2 h. After the pressure is released, the wooden board is taken out and wiped dry, and then left to air dry at room temperature for 12 h.

[0081] (7) The impregnated sample was placed in a forced air drying oven with a gradient of 100°C / 1h, 120°C / 2h, and 140°C / 2h. After the resin was completely cured, the sample was transferred to a constant temperature and humidity chamber (25°C, 65% RH) for equilibrium to obtain bio-based epoxy resin impregnated modified wood.

[0082] Figure 1 The infrared spectrum of the low viscosity bio-based epoxy resin structure is shown in Figure 1, where IA is itaconic acid and EIA is low viscosity bio-based epoxy resin. It can be seen from the figure that the low viscosity bio-based epoxy resin was successfully synthesized in Examples 1 to 3 of the present invention and the comparative example.

[0083] Figure 2The viscosity of the mixed impregnation liquid obtained in step (5) of Examples 1 to 3 and the comparative example. It can be seen from the figure that the viscosity of the epoxy curing system is between 25 and 300 mPa·s, and the viscosity of the curing system in Examples 1-3 is between 25 and 150 mPa·s, both of which belong to the category of low viscosity.

[0084] Figure 3 The drug loading rate diagram of the modified wood obtained in Examples 1 to 3 and the comparative example, wherein the drug loading rate = (m 1 -m 0 ) / m 0 ×100%,m 0 is the absolute dry mass of wood before impregnation treatment, m 1 is the quality of the modified wet wood after impregnation. It can be seen from the figure that the modified wood has a higher drug loading rate and the impregnation liquid has a higher permeability.

[0085] Figure 4 The scanning electron microscope images of the cross sections of pure wood and the modified wood of Example 3 show that the dual-crosslinked cured epoxy resin successfully penetrates into the wood and fills the ducts and cell cavities of the wood, that is, the dual-crosslinked cured epoxy resin can be fixed inside the wood.

[0086] Figure 5 The density diagram of the modified wood of Examples 1 to 3 and the comparative example, wherein the density ρ = m / V, m is the absolute dry mass of the wood sample (g), and V is the absolute dry volume of the wood sample (cm 3 ). It can be seen that the density of the modified material is improved compared with pure wood and the modified material of the comparative example.

[0087] The modified wood was immersed in deionized water at 25°C (the initial mass was tested before immersion), and the mass was tested after immersion for 6 hours, 1 day, 2 days, 4 days, 8 days, 12 days, 20 days and 30 days. The water absorption rate at each stage was calculated by the formula and a curve was drawn. Water absorption rate = (w 1 -w 0 ) / w 0 ×100%,w 1 is the mass of modified wood after immersion, W 0 is the initial mass of modified wood. Figure 6 The water absorption curves of the modified wood of Examples 1 to 3 and the comparative example show that the water absorption of the modified wood is greatly reduced compared with that of the pure wood, thereby improving the dimensional stability of the wood.

[0088] Soak the wood sample in deionized water until it is saturated with water, and record V 1 V is the volume of the wood sample when it is saturated with water. 0 is the volume of the wood sample when it is absolutely dry. 1 -V 0) / V 0 ×% to calculate the moisture expansion coefficient. The moisture expansion coefficient of unmodified wood is recorded as β1, and the moisture expansion coefficient of modified wood is recorded as β2. The anti-moisture expansion coefficient (ASE) is calculated using the formula ASE(%) = (β1-β2) / β1×100%. Figure 7 is the anti-swelling coefficient (ASE) of the modified materials of Examples 1 to 3 and the comparative example. The larger the ASE value, the better the dimensional stability of the modified material. It can be seen that the ASE value shows an increasing trend.

[0089] Figure 8 The graphs are the bending strength and elastic modulus of pure wood and the modified wood of Examples 1 to 3 and Comparative Examples. As the functional groups of the comonomer that can participate in the reaction increase, the double-crosslinked cured epoxy resin impregnation modification improves the strength of the wood.

[0090] Fig. 9 This is a graph showing the impact strength of pure wood, modified wood from Examples 1 to 3, and comparative examples. It can be seen that the toughness of the modified material is significantly improved.

[0091] Table 1 Properties of different modified materials

[0092]

[0093] Table 2 Water absorption of different modified materials

[0094]

[0095] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be equivalent replacement methods and are included in the protection scope of the present invention.

Claims

1. A method for impregnating and reinforcing modified wood with a solvent-free, low-viscosity bio-based double-crosslinked epoxy system, characterized in that The following steps are involved: (1) Itaconic acid and epichlorohydrin are used as raw materials, a ring-opening esterification reaction occurs under the action of a catalyst and nitrogen protection, and then a base is added for a ring-closing reaction to obtain a low-viscosity bio-based epoxy resin; (2) mixing and stirring the low-viscosity bio-based epoxy resin, curing agent and comonomer of step (1) to obtain a composite impregnation liquid, and then immersing the wood in the composite impregnation liquid, vacuum impregnating, and then pressurizing, and after depressurizing, washing the impregnation liquid remaining on the surface of the wood with water, and letting it stand to air dry; (3) The wood after being air-dried in step (2) is heated and cured to obtain a solvent-free, low-viscosity bio-based epoxy resin double-crosslinked cured reinforced modified material.

2. The method for impregnating and reinforcing modified wood using a solvent-free, low-viscosity bio-based double-crosslinked epoxy system according to claim 1, characterized in that: The molar ratio of itaconic acid to epichlorohydrin in step (1) is 1:10 to 1:13; The catalyst described in step (1) is a phase transfer catalyst, preferably at least one of tetrabutylammonium bromide, benzyltrimethylammonium chloride, benzyltrimethylammonium bromide, tetramethylammonium bromide, etc.; the amount of the catalyst used is such that 0.01 to 0.03 mmol of catalyst is added for every 1 mmol of itaconic acid.

3. The method for impregnating and reinforcing modified wood with a solvent-free, low-viscosity bio-based double-crosslinked epoxy system according to claim 1, characterized in that: The ring-opening esterification reaction in step (1) is carried out at 90 to 100° C. for 1 to 3 hours; The alkali-adding ring-closure reaction described in step (1) refers to adding alkali to react for 1 to 2 hours after cooling to 40 to 60° C., wherein the alkali is an aqueous sodium hydroxide solution, and the amount of the alkali used is such that 1 to 4 mol of sodium hydroxide is added to 1 mol of itaconic acid.

4. The method for impregnating and reinforcing modified wood using a solvent-free, low-viscosity bio-based double-crosslinked epoxy system according to claim 1, characterized in that: The curing agent described in step (2) is at least one of bis(3-mercaptopropionic acid)ethylene glycol, trimethylolpropane tris(3-mercaptopropionate), and pentaerythritol tetra(3-mercaptopropionic acid) ester; and the comonomer is at least one of glycidyl methacrylate, 1,4-butanediol diglycidyl ether, and glycerol triglycidyl ether.

5. The method for impregnating and reinforcing modified wood with a solvent-free, low-viscosity bio-based double-crosslinked epoxy system according to claim 1, characterized in that: The amounts of the low viscosity bio-based epoxy resin, curing agent and comonomer described in step (2) satisfy: the mass ratio of the low viscosity bio-based epoxy resin to the comonomer is 5:5 to 7:3; the molar amount of the thiol group of the curing agent: (the molar amount of the epoxy group of the low viscosity bio-based epoxy resin + the molar amount of the epoxy group of the comonomer + the molar amount of the carbon-carbon double bond of the low viscosity bio-based epoxy resin + the molar amount of the carbon-carbon double bond of the comonomer) is 1:0.8 to 1:1.

2.

6. The method for impregnating and reinforcing modified wood with a solvent-free, low-viscosity bio-based double-crosslinked epoxy system according to claim 1, characterized in that: The wood in step (2) is dried to absolute dryness before being placed in the compound impregnation solution; The wood in step (2) is at least one of poplar and fir.

7. The method for impregnating and reinforcing modified wood with a solvent-free, low-viscosity bio-based double-crosslinked epoxy system according to claim 1, characterized in that: The vacuum impregnation described in step (2) refers to vacuuming to -0.05 to -0.1 MPa and maintaining it for 0.5 to 1 hour; the pressurization treatment refers to pressurizing to 0.4 to 0.8 MPa and maintaining it for 1 to 4 hours.

8. The method for impregnating and reinforcing modified wood with a solvent-free, low-viscosity bio-based double-crosslinked epoxy system according to claim 1, characterized in that: The heat curing described in step (3) refers to heat curing at 80-150° C. for 4-6 hours.

9. A modified wood prepared according to the method according to any one of claims 1 to 8.

10. Use of the modified wood according to claim 9 in the fields of construction, furniture, and decoration.

Images