Preparation method of novel polyethyleneimine grafted high-toughness furfuryl alcohol modified wood

Abstract

The invention relates to the technical field of wood processing, and discloses a preparation method of novel polyethyleneimine grafted high-toughness furfuryl alcohol modified wood. The water-soluble polyethyleneimine and the furfuryl alcohol prepolymer are subjected to Schiff base reaction to graft and modify the furfuryl alcohol resin, so that the crosslinking density of the furfuryl alcohol resin is effectively reduced, and the problem of high brittleness of furfuryl alcohol modified wood is solved. Compared with traditional furfuryl alcohol modified wood, the toughness of the furfuryl alcohol modified wood prepared through the method is improved by 90%, and meanwhile the size stability of the wood is greatly improved. The method is mild in reaction condition, the prepared furfuryl alcohol modified wood has the color close to that of natural wood, and the furfuryl alcohol modified wood can be applied to the fields of building structures and decoration.

Description

Technical Field

[0001] The present invention relates to the technical field of wood processing, and more specifically, to a method for preparing a novel polyethyleneimine-grafted high-toughness furfuryl alcohol-modified wood. Background Art

[0002] Furfuryl alcohol modification is a wood modification method with good application prospects. Through impregnation treatment, furfuryl alcohol is introduced into the wood interior and in-situ polymerized into furfuryl alcohol resin, thereby significantly reducing the hydrophilicity of the cell wall and improving the dimensional stability of the wood. In addition, furfuryl alcohol-modified wood can also play a role in resisting termites, decay fungi, and molds. There are many existing furfuryl alcohol modification methods. Patent CN107599086A impregnates wood by compounding furfuryl alcohol with ammonium dihydrogen phosphate. While the wood has good flame retardancy, its dimensional stability, flexural modulus of elasticity and other properties are also improved to a certain extent. Patent CN104552516B uses a compound of citric acid and oxalic acid as a catalyst to modify wood or bamboo in various forms, improving the dimensional stability, hygroscopicity and other properties of the wood.

[0003] However, a major drawback of furfuryl alcohol-modified wood is the decline in the mechanical properties of the modified wood, especially the significant decline in toughness. Epmeier et al. (2004) demonstrated that the impact toughness of furfurylated wood decreased by 75%, and the WPG was 48%. The brittleness of furfuryl alcohol-modified wood not only limits its application in building structures, but also affects its machining performance, resulting in an increase in dust during the cutting process. In order to expand the application range of furfuryl alcohol-modified wood, it is urgent to optimize and upgrade the traditional furfuryl alcohol modification technology to improve the toughness of the modified wood.

[0004] To enhance the toughness of the modified wood, researchers usually copolymerize or graft aliphatic flexible molecules with furfuryl alcohol to reduce the crosslinking density of the furfuryl alcohol resin. Lv Jianxiong et al. (2021) crosslinked epoxy soybean oil with furfuryl alcohol, and the toughness of the wood was effectively improved. In addition, Yang Tiantian crosslinked hyperbranched polymers with furfuryl alcohol, and the impact toughness increased by 50%. The prior art CN 109333719 A uses a combination of furfuryl alcohol and polyvinyl alcohol to develop a mixed modifier to improve the waterproofness, stability and impact toughness of furfuryl alcohol resin-modified wood. The prior art CN 118205060 A mixes glycerol, diisopropanolamine and carboxylic acid for reaction to obtain a hyperbranched polyester amide prepolymer, and formulates a furfuryl alcohol modification solution with furfuryl alcohol, maleic anhydride and sodium tetraborate. The furfuryl alcohol / acrylamide modifier of the prior art CN 119260875 A is prepared from furfuryl alcohol, maleic anhydride, borax, acrylamide and a solvent. However, the above methods are all difficult to effectively control the color of the modified wood, and the resulting modified wood often has a darker color and a decrease in aesthetics. Summary of the Invention

[0005] The present invention aims to overcome the defects of the above-mentioned prior art, such as the inability to regulate the color of wood while enhancing the toughness of wood, and provides a novel polyethyleneimine-grafted high-toughness furfuryl alcohol modification solution.

[0006] Another object of the present invention is to provide a preparation method of a novel polyethyleneimine-grafted high-toughness furfuryl alcohol modification solution.

[0007] Another object of the present invention is to provide an application of a novel polyethyleneimine-grafted high-toughness furfuryl alcohol modification solution.

[0008] Another object of the present invention is to provide a novel polyethyleneimine-grafted high-toughness furfuryl alcohol modified wood.

[0009] Another object of the present invention is to provide a preparation method of a novel polyethyleneimine-grafted high-toughness furfuryl alcohol modified wood.

[0010] To solve the above technical problems, the technical solution of the present invention is as follows:

[0011] A novel polyethyleneimine-grafted high-toughness furfuryl alcohol modification solution, the components of which include maleic anhydride, polyethyleneimine, and furfuryl alcohol prepolymer.

[0012] Further, the components of the furfuryl alcohol prepolymer include furfuryl alcohol, and the molar ratio of furfuryl alcohol to polyethyleneimine in the novel polyethyleneimine-grafted high-toughness furfuryl alcohol modification solution is 1-2:1-4.

[0013] Preferably, the molar ratio of furfuryl alcohol to polyethyleneimine in the novel polyethyleneimine-grafted high-toughness furfuryl alcohol modification solution is 1-2:1-2.

[0014] Further, the molecular weight of polyethyleneimine is 300-3000.

[0015] Preferably, the molecular weight of polyethyleneimine is 300-800.

[0016] Preferably, the molecular weight of polyethyleneimine is 800.

[0017] Polyethyleneimine is a cationic polymer. When its molecular chain is too large and there are too many branched chains, it will repel furfuryl alcohol, resulting in a decrease in the reactivity between the two. In addition, the higher the molecular weight of polyethyleneimine, the poorer the permeability. Using polyethyleneimine with too high a molecular weight to react with wood will cause the overall molecular weight of the polymer to be too high to be impregnated into the interior of the wood, affecting the wood properties.

[0018] Further, the furfuryl alcohol prepolymer is prepared from a furfuryl alcohol solution with a mass fraction of 40%-80%.

[0019] Preferably, in the furfuryl alcohol solution with a mass fraction of 40% to 80%, ethanol or methanol is used as the solvent.

[0020] Preferably, the furfuryl alcohol prepolymer is prepared from a 40% furfuryl alcohol solution.

[0021] A preparation method of the novel polyethyleneimine-grafted high-toughness furfuryl alcohol modified liquid includes the following steps: stirring and reacting a furfuryl alcohol solution with a mass fraction of 40% to 80% and a catalyst in a solvent to obtain a furfuryl alcohol prepolymer; after uniformly stirring maleic anhydride and the furfuryl alcohol prepolymer in a solvent, mixing them uniformly with polyethyleneimine to obtain the novel polyethyleneimine-grafted high-toughness furfuryl alcohol modified liquid.

[0022] Preferably, the mass ratio of the catalyst to the furfuryl alcohol solution is 1:10.

[0023] Preferably, in the novel polyethyleneimine-grafted high-toughness furfuryl alcohol modified liquid, the total mass fraction of the solute is 15% to 40%.

[0024] Preferably, after the obtained prepolymer is fully filtered through a sieve to remove the catalyst, the furfuryl alcohol prepolymer is obtained and stored in a refrigerator at 4 to 6 °C.

[0025] Furthermore, the solvent includes methanol and ethanol; the catalyst includes cation exchange resin.

[0026] Preferably, the solvent is ethanol, and the cation exchange resin is a strong acid type cation exchange resin.

[0027] Preferably, the strong acid type cation exchange resin is a sulfonic acid type cation exchange resin.

[0028] During the prepolymerization process of furfuryl alcohol, due to the removal of hydroxyl groups, its solubility in water decreases. Among organic solvents, the solubility parameters of methanol and ethanol are closest to that of furfuryl alcohol, and they have good solubility for furfuryl alcohol and its polymers. The higher the concentration of furfuryl alcohol, the greater the polymerization rate and the higher the possibility of forming high polymers. In addition to acting as a solvent, ethanol or methanol can effectively limit the further polymerization of furfuryl alcohol oligomers into polymers with a larger molecular weight. At this time, the molecular weight range of the furfuryl alcohol polymer in the furfuryl alcohol prepolymer is 98 to 1400.

[0029] In the process of preparing the furfuryl alcohol prepolymer in the present invention, a heterogeneous catalyst is used. After the preparation of the prepolymer is completed, the heterogeneous catalyst can be separated from the solution. During the subsequent storage process, the furfuryl alcohol prepolymer is at room temperature, and at this time, there is no acid catalyst and high temperature condition to promote the polymerization of furfuryl alcohol. In addition, ethanol or methanol can limit the further polymerization of oligomers to form high polymers. Therefore, compared with the prepolymer prepared by a homogeneous catalyst, the storage period can be extended.

[0030] Application of a novel polyethyleneimine-grafted highly tough furfuryl alcohol modification solution for preparing furfuryl alcohol-modified wood.

[0031] A novel polyethyleneimine-grafted highly tough furfuryl alcohol-modified wood is prepared by the novel polyethyleneimine-grafted highly tough furfuryl alcohol modification solution.

[0032] Further, the wood includes coniferous wood and broad-leaved wood;

[0033] Preferably, the wood further includes softwood plantation wood.

[0034] Preferably, the coniferous wood includes Chinese fir, poplar, masson pine, paulownia, and the broad-leaved wood includes eucalyptus and birch.

[0035] A preparation method of the novel polyethyleneimine-grafted highly tough furfuryl alcohol-modified wood includes the following steps: placing a wood raw material in the novel polyethyleneimine-grafted highly tough furfuryl alcohol modification solution for impregnation; after standing, curing, and drying, the novel polyethyleneimine-grafted highly tough furfuryl alcohol-modified wood is obtained.

[0036] Preferably, standing is carried out to remove the solvent.

[0037] Preferably, the impregnation time can select appropriate vacuum degree, pressure, and pressurization time according to actual situations such as wood species and sample thickness to ensure uniform distribution of the furfuryl alcohol solution in the wood cell wall;

[0038] Preferably, gradient drying is adopted, and each stage is heat-insulated for 2 h;

[0039] Preferably, the wood to be treated is placed in an anhydrous and dry sealed impregnation tank for impregnation; the sealed impregnation tank is evacuated to a negative pressure and maintained in a vacuum state for 30 min, then pressurized to 0.8 MPa, taken out after holding the pressure for 3 h; the impregnated sample is wiped dry on the surface, placed at room temperature for 24 h to remove most of the ethanol, the sample is wrapped with aluminum foil paper and cured at 103 °C for 3 h, the aluminum foil paper is removed and the sample is cooled to room temperature, and the sample is placed at 40, 60, 80, and 103 °C in sequence for drying to absolute dryness.

[0040] On the basis of effectively controlling the molecular weight of furfuryl alcohol oligomers, the present invention innovatively uses the side reaction in the furfuryl alcohol polymerization process - the crosslinking of the carbonyl group generated by the ring-opening reaction with flexible amine compounds, effectively eliminating the main chromophore (carbonyl group), and successfully regulating the color of the modified wood. On this basis, the introduction of polyethyleneimine reduces the crosslinking density of the resin, and the compounding of the two cationic polymers also leads to the occurrence of microphase separation during the polymerization process, which is beneficial to crack passivation and thus improves the toughness of the wood, expanding the practical application of the modified wood.

[0041] Compared with the prior art, the beneficial effects of the technical solution of the present invention are:

[0042] 1. Effectively regulate the color of modified wood. The modified wood prepared by the present invention has a lighter color. With the addition of polyethyleneimine, the lower the furfuryl alcohol content, the more obvious the improvement in the lightness of the wood.

[0043] 2. Significantly improve the toughness and impact resistance of wood

[0044] The addition of polyethyleneimine promotes the Schiff base reaction and reduces the cross-linking density of furfuryl alcohol resin, thereby improving the toughness of the wood. Compared with the traditional method, the toughness improvement of the present invention can reach 90.57%. Most of the fibers of the modified wood in the present invention appear in the toughness section and show significant plastic deformation, indicating that the modified wood has good impact resistance.

[0045] 3. Improve the dimensional stability. The weight gain rate of the modified wood in the present invention can reach 70.21%, and the volume expansion rate is as low as 6.22%. The equilibrium moisture content decreases compared with the untreated wood, which helps to reduce swelling and deformation and improve the long-term stability.

[0046] 4. Enhance the mechanical properties and improve the bending strength and elastic modulus. The bending strength and elastic modulus of the modified wood are significantly improved compared with the untreated wood, and it is suitable for structural and high-strength application scenarios. Description of the Drawings

[0047] Figure 1 are the weight gain rate and volume expansion rate of different specimens;

[0048] Figure 2 are the equilibrium moisture content of different specimens;

[0049] Figure 3 are the bending strength and elastic modulus of different specimens;

[0050] Figure 4 are the flexibility and toughness of different specimens;

[0051] Figure 5 are the scanning electron microscope photos of the impact fracture surface;

[0052] Figure 6 are the photos and color difference values of the surfaces of different specimens;

[0053] Figure 7 is the molecular weight distribution of the furfuryl alcohol prepolymer of Comparative Example 3. Detailed Embodiments

[0054] The present invention will be further described below in conjunction with the drawings of the specification and specific embodiments, but 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.

[0055] Unless otherwise specified, the reagents and materials used in the following examples are all commercially available.

[0056] Example 1

[0057] S1. Specimen preparation: a) Prepare specimens of artificial Cunninghamia lanceolata with dimensions of 20mm×20mm×20mm (T×R×L) and 10mm×10mm×160mm (T×R×L); b) Place 40 parts of furfuryl alcohol and 60 parts of absolute ethanol in a 60°C water bath and stir well. When the solution temperature rises to 60°C, add 10 parts of cation exchange resin (sulfonic acid group), stir and react for 12 h, separate the product from the cation exchange resin to obtain furfuryl alcohol prepolymer (the molecular weight range of furfuryl alcohol polymer is 98 - 1400), and store it under low temperature conditions; c) Dry in an oven at 103°C until it reaches absolute dryness.

[0058] S2. Preparation of furfuryl alcohol modified solution. Specific steps: First, place 30.9 parts of absolute ethanol and 1.7 parts of maleic anhydride in a beaker and stir well. After maleic anhydride is completely dissolved, pour 64.2 parts of furfuryl alcohol prepolymer into the beaker and stir evenly. Subsequently, weigh 3.2 parts of polyethyleneimine (molecular weight 800) in another beaker, quickly transfer the homogeneous solution to this beaker, and stir well with a glass rod until polyethyleneimine is dissolved to obtain furfuryl alcohol modified solution (the molar ratio of furfuryl alcohol to polyethyleneimine is 2:1).

[0059] S3. Vacuum pressure impregnation with furfuryl alcohol. Specific steps: First, place the specimens in a closed reaction kettle, evacuate to negative pressure, maintain the vacuum state for 30 min, then introduce the furfuryl alcohol modified solution into the reaction kettle under negative pressure, pressurize to 0.8 MPa, and keep the pressure for 3 h. Wipe the residual solution on the material surface with absorbent paper, place it at room temperature and let it stand for 1 d to remove most of the ethanol.

[0060] S4. Wood curing and drying: Wrap the samples with aluminum foil paper and cure at 103°C for 3 h. Remove the aluminum foil paper and cool the samples to room temperature. Place the samples at 40, 60, and 80°C in sequence and dry for 2 h each to remove most of the ethanol, and then dry the samples to absolute dryness at 103°C.

[0061] Example 2

[0062] The technical solution of Example 2 is similar to that of Example 1, except that in the preparation of the furfuryl alcohol modified solution in S2 of Example 2, the furfuryl alcohol prepolymer is 60 parts, polyethyleneimine is 6 parts (molecular weight 800), absolute ethanol is 32.3 parts, and maleic anhydride is 1.7 parts (the molar ratio of furfuryl alcohol to polyethyleneimine is 1:1).

[0063] Example 3

[0064] The technical scheme of Example 3 is similar to that of Example 1, except that in Example 3, anhydrous ethanol is replaced by methanol; the mass fraction of the furfuryl alcohol solution after furfuryl alcohol and methanol are evenly stirred in S1 is 80%; in the configuration of S2 furfuryl alcohol modified liquid, furfuryl alcohol prepolymer is 50 parts, polyethyleneimine is 10 parts (molecular weight is 800), anhydrous ethanol is 38.3 parts, and maleic anhydride is 1.7 parts (the molar ratio of furfuryl alcohol and polyethyleneimine is 1:2).

[0065] Example 4

[0066] The technical scheme of Example 4 is similar to that of Example 1, except that, in the configuration of S2 furfuryl alcohol modified liquid in Example 4, furfuryl alcohol prepolymer is 15 parts, polyethyleneimine is 24 parts (molecular weight is 300), anhydrous ethanol is 59.3 parts, and maleic anhydride is 1.7 parts (the molar ratio of furfuryl alcohol and polyethyleneimine is 1:4).

[0067] Example 5

[0068] The technical scheme of Example 5 is similar to that of Example 1, except that the molecular weight of polyethyleneimine is 3000.

[0069] Control group

[0070] Untreated wood was dried at 103°C until it was absolutely dry, and standard specimens of wood of different sizes were prepared.

[0071] Comparative Example 1

[0072] The technical scheme of Comparative Example 1 is similar to that of Example 1, except that the specific steps for preparing the S2 furfuryl alcohol modified liquid in Comparative Example 1 are as follows: 23.3 parts of anhydrous ethanol and 1.7 parts of maleic anhydride are placed in a beaker and stirred thoroughly, and after the maleic anhydride is fully dissolved, 75 parts of furfuryl alcohol prepolymer are poured into the beaker and stirred thoroughly.

[0073] Comparative Example 2

[0074] S1. Sample preparation: a) Cunninghamia lanceolata was made into samples of 20 mm × 20 mm × 20 mm (T × R × L) and 10 mm × 10 mm × 160 mm (T × R × L); b) it was dried in an oven at 103°C to absolute dryness. At the same time, a furfuryl alcohol aqueous solution with a mass concentration of 30% was prepared at room temperature of 22-25°C.

[0075] S2. Preparation of furfuryl alcohol modified liquid. Specific steps: First, 68.3 parts of water and 1.7 parts of maleic anhydride are placed in a beaker and stirred thoroughly. After the maleic anhydride is fully dissolved, 30 parts of furfuryl alcohol are poured into the beaker and stirred thoroughly.

[0076] The technical solutions S3 and S4 are consistent with those in Example 1.

[0077] Comparative Example 3

[0078] A furfuryl alcohol prepolymer was prepared. The specific steps were similar to those in Example 1, except that 85 parts of furfuryl alcohol and 15 parts of absolute ethanol were placed in a water bath at 60°C and stirred well.

[0079] Performance Test

[0080] 1. Weight gain percentage (WPG) and bulking efficiency (BE)

[0081] The weight gain percentage and bulking efficiency can respectively reflect the content of furfuryl alcohol resin entering the whole wood and the wood cell wall. By measuring the dimensions and mass of the samples before and after furfuryl alcohol modification, the weight gain percentage and bulking efficiency of the wood can be calculated according to formula (1) and formula (2) respectively.

[0082]

[0083] Where m0 and m1 are the oven-dry masses of the samples before and after furfuryl alcohol modification, respectively, in g.

[0084]

[0085] Where V0 is the oven-dry volume of the sample before furfuryl alcohol modification, in mm 3 ; V1 is the oven-dry mass of the sample before furfuryl alcohol modification, in mm 3 .

[0086] 2. Modulus of rupture (MOR) and modulus of elasticity (MOE)

[0087] The modulus of elasticity and modulus of rupture of the samples were tested using a three-point bending test method with reference to GB / T1936.1 and GB / T1936.2. The sample size was 10 mm × 10 mm × 160 mm (R × T × L), the indenter diameter was 30 mm, the support span was 130 mm, and the constant loading speed was 8 mm / min. The test termination condition was that the stress attenuation amplitude reached 90%.

[0088] 3. Evaluation method for wood bending toughness and flexibility

[0089] To explore the effect of the concentration of the furfuryl alcohol modification solution on the toughness of modified Chinese fir, based on the three-point bending test in this study, a method proposed in the literature (Habibi et al., 2015; Wei Xin, 2022) was used to calculate the bending toughness and flexibility of the wood before and after modification. The bending toughness was calculated by formula (3).

[0090]

[0091] 4. Determination of surface color parameters

[0092] At the micro level, a portable color difference meter is used to obtain the surface color parameters of the specimen, and three main parameters in the CIEL*a*b* standard colorimetric system defined by the International Commission on Illumination are obtained, namely L* (lightness), a* (red-green index), and b* (yellow-blue index). Specifically: L* represents the degree of light and dark (the larger the value, the brighter), a* represents the red-green chromaticity index (the larger the value, the more the color tends to red), and b* represents the yellow-blue chromaticity index (the larger the value, the more the color tends to yellow).

[0093] Analysis and explanation

[0094] As Figure 1 shown, compared with Comparative Example 1, the weight gain rate of Example 1 increased from 51.57% to 55.63%, and the volume increase rate decreased from 9.71% to 7.24%; the weight gain rate of Example 2 was 64.51%, an increase of 25.09% compared with Comparative Example 1; the volume increase rate was 6.37%, a decrease of 34.34% compared with Comparative Example 1. In addition, the weight gain rate of Example 3 increased to 70.21%, an increase of 36.13% compared with Comparative Example 1, and the volume increase rate decreased to 6.22%, a decrease of 35.39% compared with Comparative Example 1. In addition, the weight gain rate and volume increase rate of Examples 4 and 5 both decreased slightly. The decrease in the weight gain rate indicates that part of the agent was wasted. In Example 4, due to the excessive addition amount of PEI, the viscosity of the modified liquid increased, which may lead to a decrease in the permeability of the modified liquid to wood, resulting in a decrease in the weight gain rate and volume increase rate of the wood. The formulation of Example 5 is similar to that of Example 1, and the only difference is that polyethyleneimine with a molecular weight of 3000 is used. It can be found that the weight gain rate and volume increase rate of Example 5 decreased compared with Example 1, which may be due to the fact that after the crosslinking of PEI and furfuryl alcohol, the molecular weight of the polymer is too large, resulting in a decrease in the permeability to the wood cell wall and even the wood cell cavity. In the present invention, polyethyleneimine with an appropriate molecular weight crosslinks with the furfuryl alcohol prepolymer. On the one hand, the occurrence of the Schiff base reaction causes an increase in the molecular weight of the polymer, which is difficult to penetrate into the wood cell wall while being able to penetrate into the interior of the wood; on the other hand, the volatility of the furfuryl alcohol prepolymer further decreases, and the curing rate increases. Therefore, the modified wood obtained by the present invention can obtain a higher weight gain rate and a lower volume increase rate.

[0095] As Figure 2As shown, compared with the untreated materials (control group), the equilibrium moisture contents of the examples all decreased, indicating that the hygroscopicity of the modified wood obtained by the present invention decreased. Among them, the equilibrium moisture contents of Example 1, Example 2, Example 3 and Example 4 decreased by 52.4%, 34.8%, 16.9% and 8.0% respectively. This is mainly related to the hydrophilicity of polyethyleneimine. Compared with Example 1, the higher the content of polyethyleneimine in Example 2, Example 3 and Example 4, the slightly stronger the hygroscopicity of the wood. In addition, the equilibrium moisture content of Example 5 decreased by 36.6% compared with the control group, and the hygroscopicity was slightly stronger than that of Example 1. In Example 5, part of the furfuryl alcohol prepolymer reacted with higher molecular weight PEI, resulting in too high molecular weight of some polymers, which was difficult to penetrate into the interior of the wood. At this time, the mainly low molecular weight furfuryl alcohol prepolymer entered the interior of the wood. Although the hydrophilicity of PEI had a smaller impact on the hygroscopicity of the wood than that of Example 1, the deposition of furfuryl alcohol resin in the wood cell wall also decreased accordingly, and the overall response degree of the wood to moisture increased. This shows that adding an appropriate amount of polyethyleneimine with a suitable molecular weight will not cause waste of the agent and will not affect the hygroscopic performance of the wood such as Figure 3 It can be found that after adding a small amount of polyethyleneimine, the flexural strength and elastic modulus of Example 1 are significantly improved compared with the control group. There is no significant change in the flexural strength and elastic modulus of Example 2, Example 3 and Example 4 compared with the control group. This is due to the increase in the addition amount of polyethyleneimine and its strength being lower than that of the furfuryl alcohol resin. The flexural strength and elastic modulus of Example 5 decreased compared with Example 1, which is due to the decrease in the amount of polyethyleneimine and furfuryl alcohol prepolymer entering.

[0096] such as Figure 4 As shown, after adding polyethyleneimine, the flexibility and toughness of Examples 1-3 are both improved, and the flexibility increases with the increase in the addition amount of polyethyleneimine. Compared with Comparative Example 1, the flexibilities of Examples 1-5 increased by 33.50%, 57.64%, 58.13%, 87.6% and 15.2% respectively. In addition, the toughness of Examples 1-5 also increased to varying degrees. Among them, the toughness of Example 1 reached the maximum, increasing by 90.57% compared with Comparative Example 1. Examples 2, 3, 4 and 5 increased by 51.98%, 53.20%, 54.5% and 17.4% respectively compared with Comparative Example 1. This shows that adding an appropriate amount of polyethyleneimine with a suitable molecular weight can effectively improve the toughness of furfuryl alcohol modified wood.

[0097] such as Figure 4As shown, after adding polyethyleneimine, the flexibility and toughness of Examples 1-3 are both improved, and the flexibility increases with the increase of the polyethyleneimine addition amount. Compared with Comparative Example 1, the flexibility of Examples 1-3 is improved by 33.50%, 57.64% and 58.13% respectively. In addition, the toughness of Examples 1-3 also shows different degrees of improvement. Among them, the toughness of Example 1 reaches the maximum, which is improved by 90.57% compared with Comparative Example 1. Examples 2 and 3 are improved by 51.98% and 53.20% respectively compared with Comparative Example 1. This shows that adding an appropriate amount of polyethyleneimine can effectively improve the toughness of furfuryl alcohol modified wood.

[0098] Scanning electron microscope observations showed the impact fracture surfaces of the control group, Comparative Example 1 and Example 3. There was no obvious fiber pull-out in the cross-section SEM image of Comparative Example 1, and the flatness and smoothness of the fracture surface indicated that no signs of plastic deformation were found, belonging to brittle fracture. In the control group and Example 3, the flatness of the port and surface decreased, and most of the fibers appeared on the toughness cross-section showing significant plastic deformation phenomena, indicating that the material had good toughness, impact resistance and ductility. This shows that after adding polyethyleneimine, the toughness of furfuryl alcohol is effectively improved, exceeding that of natural wood.

[0099] It can be seen from Figure 6 that Comparative Example 2 has the lowest lightness, and the lightness of Comparative Example 1 is slightly improved compared with Comparative Example 2, which may be due to the slightly lower polymerization degree of furfuryl alcohol in the ethanol system compared with the water system. Ethanol, as a chain transfer agent, can reduce the chain polymerization of furfuryl alcohol, and the cross-linking density of furfuryl alcohol resin may decrease. In addition, with the addition of polyethyleneimine, the lightness of Examples 1-3 has been significantly improved. This is because the content of furfuryl alcohol decreases, and the chromophore C=O in the furfuryl alcohol resin is consumed.

[0100] Figure 7 The molecular weight distribution of the furfuryl alcohol prepolymer in Comparative Example 3 was determined by gel permeation chromatography. The results showed that Mw = 3406, Mn = 933, and PD = 3.65, indicating that the sample had a wide molecular weight distribution. In Comparative Example 3, the ethanol concentration was too low, and a large amount of oligomers were easily converted into high polymers (some reached 100000), making the reaction difficult to control and the polymer molecular weight distribution too wide to be impregnated into the wood interior. In addition, when the ethanol concentration is too high, the formation of oligomers will also become slow, so the relative content between the two needs to be reasonably adjusted.

[0101] Obviously, the above 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 implementation manners here. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the claims of the present invention.

Claims

1. A novel highly tough furfuryl alcohol modified solution grafted with polyethyleneimine, characterized in that, Its components include maleic anhydride, polyethyleneimine, and furfuryl alcohol prepolymer.

2. The novel high-toughness furfuryl alcohol modified liquid grafted with polyethyleneimine according to claim 1, characterized in that, The furfuryl alcohol prepolymer is prepared from a furfuryl alcohol solution with a mass fraction of 40% to 80%.

3. The novel polyethyleneimine-grafted highly tough furfuryl alcohol modified liquid according to claim 1, characterized in that, The components of the furfuryl alcohol prepolymer include furfuryl alcohol, and the molar ratio of furfuryl alcohol to polyethyleneimine in the furfuryl alcohol modification solution is 1 to 2:1 to 4.

4. The novel high-toughness furfuryl alcohol modified liquid grafted with polyethyleneimine according to claim 1, wherein, The molecular weight of polyethyleneimine is 300 to 3000.

5. A preparation method of the novel polyethyleneimine-grafted high-toughness furfuryl alcohol modified liquid according to any one of claims 1 to 4, characterized in that, It includes the following steps: stirring and reacting a furfuryl alcohol solution with a mass fraction of 40% to 80% and a catalyst in a solvent to obtain a furfuryl alcohol prepolymer; after stirring maleic anhydride and the furfuryl alcohol prepolymer evenly in a solvent, mixing them evenly with polyethyleneimine to obtain a novel polyethyleneimine-grafted high-toughness furfuryl alcohol modification solution.

6. The preparation method of the novel polyethyleneimine-grafted high-toughness furfuryl alcohol modified liquid according to claim 5, characterized in that, The solvent includes methanol and ethanol; the catalyst includes cation exchange resin.

7. Use of the novel polyethyleneimine-grafted high-toughness furfuryl alcohol modified liquid according to any one of claims 1 to 4, characterized in that, It is used for preparing furfuryl alcohol-modified wood.

8. A novel high-toughness furfuryl alcohol-modified wood grafted with polyethyleneimine, characterized in that, It is prepared from the novel polyethyleneimine-grafted high-toughness furfuryl alcohol modification solution according to any one of claims 1 to 4.

9. The novel high-toughness furfuryl alcohol-modified wood grafted with polyethyleneimine according to claim 8, wherein, The wood includes softwood and hardwood.

10. A method for preparing the novel polyethyleneimine-grafted highly tough furfuryl alcohol-modified wood according to any one of claims 8 to 9, characterized in that, It includes the following steps: immersing wood raw materials in the novel polyethyleneimine-grafted high-toughness furfuryl alcohol modification solution; After standing, curing, and drying, novel polyethyleneimine-grafted high-toughness furfuryl alcohol-modified wood is obtained.

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