Double synergistic modification method and device for regenerated wood

Abstract

The invention relates to a double synergistic modification method and device for regenerated wood, and belongs to the technical field of wood modification. The method comprises the following steps: carrying out vacuum impregnation treatment on wood in MUF resin modified liquid, carrying out heating curing treatment, carrying out vacuum impregnation treatment on the wood in liquid paraffin modified liquid, and then carrying out heating curing treatment to obtain the dual modified wood. Tests show that compared with unmodified wood, the tensile strength of the double-modified wood is improved by 31.27%, the 24-hour water absorption rate is reduced to 43.9%, the loss rate of the modifier is controlled to be 3.1% or below, and the water repellency rate is improved by 65%. The technical bottlenecks of weak interface bonding force and non-uniform permeation of the traditional modified wood are solved in a breakthrough manner, the modified wood is particularly suitable for structure enhancement treatment of fast-growing cedarwood, poplar and regenerated wood, and an efficient and environment-friendly modification solution is provided for green building wood components and historic building repair materials; and an innovative solution is provided for promoting efficient utilization of wood resources and development of green buildings.

Description

Technical Field

[0001] This invention relates to the field of wood impregnation modification, and provides a method and apparatus for dual synergistic modification of recycled wood. Background Technology

[0002] Timber, as a renewable resource, has wide applications in construction, furniture, and other fields. However, natural timber has problems such as insufficient mechanical properties and susceptibility to moisture absorption and deformation, which limit its use in load-bearing structures and high-humidity environments.

[0003] Resin impregnation modification (such as phenolic resin, melamine-urea-formaldehyde resin, etc.) is a common method to improve wood properties, significantly enhancing its bending strength, hardness, and corrosion resistance. However, traditional resin impregnation modification still faces two major technical bottlenecks: First, the resin loss rate is high. In humid or water-soaked environments, the resin easily dissolves from the wood pores, leading to a gradual decline in the modification effect. Studies have shown that after long-term water immersion, the resin loss rate of MUF resin-impregnated wood can reach over 15%, resulting in a 20%–30% decrease in mechanical properties. Second, the improvement in volume stability is limited. Although the resin can partially fill the cavities of wood fiber walls, its effect on inhibiting the hygroscopic expansion of cell walls is insufficient, with a swelling rate still as high as 5%–8%, making it difficult to meet the dimensional stability requirements of high-precision wooden components.

[0004] Existing technologies have attempted to modify resins by combining them with hydrophobic materials, such as CN112497356A which uses a composite impregnation of phenolic resin and organosilicon. However, research has found that this process still faces two major technical bottlenecks: interfacial compatibility issues: the rigid framework formed after resin curing and the flexible hydrophobic material have weak interfacial bonding due to polarity differences, making them prone to delamination under alternating temperature and humidity conditions. A 24-month aging test showed that the composite layer peeling rate reached over 35%; and penetration gradient conflict: high-viscosity resins preferentially occupy large pores during vacuum impregnation, while subsequent hydrophobic materials have difficulty penetrating into micropores due to surface tension differences, resulting in uneven distribution of the modified layer and severely restricting performance improvement.

[0005] To address the aforementioned problems, the innovation of this invention lies in its innovative approach of overcoming technical barriers through a specific process design, proposing a dual impregnation synergistic strengthening strategy. Paraffin wax, with its excellent hydrophobicity and dimensional stability, forms a dense, waterproof barrier on both the wood matrix and the surface of the cured resin, effectively preventing moisture intrusion and reducing resin loss. Simultaneously, paraffin wax fills micropores not fully covered by the resin, further inhibiting moisture absorption and deformation of the wood. This resin-paraffin double vacuum impregnation process achieves both mechanical strengthening of the modified wood and a significant improvement in its volumetric stability and durability. Summary of the Invention

[0006] The purpose of this invention is to solve at least one technical problem in the background art, and to provide a method and special equipment for strengthening wood by dual impregnation modification with MUF resin and liquid paraffin, which is particularly suitable for strengthening wood used in building structures.

[0007] Compared with the traditional double impregnation process, the inventiveness of this invention lies in: discovering the regulatory effect of alkaline resin treatment on the surface potential of wood; revealing the hydrogen bond bridging mechanism of glycerol and polyvinyl alcohol at the resin-paraffin interface, breaking through the interfacial compatibility problem of composite materials with different polarities; at the same time, through the design of mesoporous channels and gradient curing process, the interpenetration of the double modified materials is realized, so that the performance produces a synergistic effect of 1+1>2.

[0008] To achieve the above objectives, the technical solution of this invention mainly includes a dedicated vacuum impregnation device and a dual impregnation modification process. Taking the "gradient vacuum-cyclic impregnation" process as an innovation point, and using the modification form of "chemical cross-linking + physical reinforcement", the mechanical properties and durability of the product are improved, and the overall performance of wood is comprehensively improved.

[0009] This invention provides a method for dual synergistic modification of recycled wood, comprising the following steps: (1) Wood is vacuum impregnated in MUF resin modification liquid and then heated and cured to obtain pre-modified wood; (2) The pre-modified wood is vacuum impregnated in liquid paraffin modification solution and then heated and cured to obtain double-modified wood.

[0010] Preferably, in step (1), the wood is selected from at least one of recycled laminate, recycled logs, and wood-plastic composites. More preferably, the wood is dried to a moisture content of no more than 12%. More preferably, according to GB 50005—2017 and GB / T28986—2012, the properties of the recycled laminate can broadly represent the standards for structural timber used in construction: that is, a porosity of 25%~40%, a moisture content of 8%~12%, and an air-dry density range of 0.75~1.20 g / cm³. 3 Lightweight wood and boards.

[0011] Preferably, in steps (1) and (2), the wood or preliminarily modified wood is kept under a vacuum of not less than -0.09 MPa for 0.5-1 hours before vacuum impregnation to remove air from the wood.

[0012] Preferably, in step (1), the MUF resin modification solution includes a basic MUF resin modification solution, which includes MUF resin (melamine-urea-formaldehyde resin) and deionized water. The mass fraction of MUF resin in the basic MUF resin modification solution is 8% to 16%, more preferably 12%. At this concentration, the best performance improvement can be achieved with the smallest possible weight gain. Too low a concentration will result in poor modification effect, while too high a concentration will result in excessive weight gain and loss of modification solution, as well as increased cost. Furthermore, the solid content of the MUF resin is 40-60%, more preferably 50%; Furthermore, the pH of the MUF resin modified solution is 7.5-8.

[0013] More preferably, the MUF resin modification solution also contains a modifier, preferably polyvinyl alcohol, and the amount of polyvinyl alcohol added is preferably 1-10 wt% of the effective solid component of the MUF resin. And / or, the MUF resin modified liquid further includes an additive, preferably ammonium chloride, and the amount of ammonium chloride added is preferably 3% of the mass of the MUF resin.

[0014] More preferably, in step (1), the MUF resin preparation method includes: adding formaldehyde solution to a reaction vessel, adjusting the pH to 7.5-9.0, and heating to 60-80℃; adding urea and melamine in batches at a molar ratio of 1:0.3-0.5, and reacting for 1-3 hours; adding polyvinyl alcohol (PVA) as a modifier, accounting for 1-10 wt% of the MUF resin solids (MUF resin solids refer to the solid portion in MUF resin with a solid content of 40-60%); cooling to 40-50℃, adjusting the pH to 4.5-6.0, and continuing the reaction until the viscosity reaches 200-500 mPa·s; concentrating, dehydrating, and drying to obtain MUF resin with a solid content of 40-60%; Furthermore, the concentration of the formaldehyde solution is 30 wt%; Furthermore, after adding formaldehyde, the pH is adjusted with sodium hydroxide; Furthermore, the urea is added in two equal batches, with the first batch containing 50% and the second batch containing 50%. Furthermore, after cooling to 40-50℃, the pH is adjusted with citric acid; Furthermore, the reaction temperature is controlled with an accuracy of ±2℃; Furthermore, the drying process employs segmented temperature control to prevent heat-sensitive damage to the resin; Furthermore, the dehydrated and dried MUF resin is added to a pulverizer and crushed, then sieved through a 50-mesh sieve to obtain solid powder.

[0015] More preferably, in step (1), the MUF resin preparation process is as follows: 30wt% formaldehyde solution is added to a reaction vessel, the pH is adjusted to 7.5-9.0 with sodium hydroxide, the temperature is raised to 60-80℃, urea and melamine are added in batches at a molar ratio of 1:0.3-0.5, and after reacting for 1-3 hours, polyvinyl alcohol modifier is added, the solution is slowly cooled to 40-50℃, and the pH is adjusted to 4.5-6.0. The reaction continues until the viscosity reaches 200-500 mPa·s, and the solution is concentrated and dehydrated to a solid content of 40-60%. The dried solid is then pulverized by a pulverizer and passed through a 50-mesh sieve to obtain MUF resin powder. More preferably, the concentration, dehydration, and drying process includes drying at 60℃ for at least 4 hours, and then slowly drying at a temperature higher than room temperature to a constant weight.

[0016] Preferably, in steps (1) and (2), the vacuum degree of vacuum impregnation is not less than -0.09MPa, more preferably -0.095~-0.1MPa; Furthermore, the vacuum impregnation time is 1-3 hours; more preferably 2-3 hours. Furthermore, the temperature of the impregnation solution in the vacuum impregnation is 20-50°C; more preferably, the temperature in step (1) is 20-30°C, and the temperature in step (2) is 40°C. Furthermore, during vacuum impregnation, the impregnation liquid should cover the top of the wood by at least 2 cm; Furthermore, after vacuum impregnation, the vacuum pressure is slowly released to atmospheric pressure and maintained for 120 minutes.

[0017] Preferably, in step (1), the conditions for heat curing are: heating at 103±3℃ for 2~3 hours; Furthermore, the heat curing treatment includes two stages: the first stage involves heating at 60±3℃ until all moisture is removed, followed by curing at 103±3℃; more preferably, heating at 60±3℃ for 4-5 hours, and the second stage involves heating at 103±3℃ for 2-3 hours. During the heat curing process, the MUF resin undergoes a condensation reaction with the wood matrix, removing water and formaldehyde to form a complex three-dimensional cross-linked structure, which provides support and toughening to the wood matrix. This invention innovatively proposes a gradient curing process, enabling the MUF resin to form 50-200nm mesoporous channels within the wood cell walls, promoting the penetration of paraffin molecules and establishing hydrogen bond bridging interfaces. This achieves a synergistic effect between the chemical cross-linking of the resin and the physical sealing of paraffin.

[0018] Preferably, in step (1), stress release is performed after modification. During stress release, the material needs to be cured for 24 hours under standard conditions, namely 23±2℃ and 50% relative humidity.

[0019] Preferably, in step (2), the liquid paraffin modification solution includes solid paraffin, deionized water, glycerol, emulsifier and modifier, wherein the mass fraction of solid paraffin in the liquid paraffin modification solution is 8%~16%, more preferably 12%; Furthermore, the amount of glycerol added to the liquid paraffin modification solution is 1-3% of that of the solid paraffin; it is used to increase fluidity. Furthermore, the emulsifier is polyvinyl alcohol, and the amount added to the liquid paraffin modified liquid is 1-5% of the solid paraffin, more preferably 3%, and it is added simultaneously with glycerol; it plays an emulsifying role and accelerates the solubility of water and oil. Furthermore, the modifier is OP-10, with a mass fraction of 1-5 wt%, more preferably 2-5 wt%, in the liquid paraffin modification solution. By adding OP-10 and an emulsifier, some polar groups are introduced, and during heat curing, the non-polar paraffin and the polar groups in the wood are connected through secondary bonds formed by these polar groups.

[0020] More preferably, the liquid paraffin modification liquid has the following composition: solid paraffin accounts for 12% of the mass of the liquid paraffin modification liquid, deionized water accounts for 85% of the mass of the modification liquid, surfactant OP-10 is added at 3wt% of the mass of the modification liquid, and glycerol and emulsifier polyvinyl alcohol are added, each accounting for 3wt% of the mass of solid paraffin.

[0021] Preferably, in step (2), the preparation method of the liquid paraffin modified liquid includes: heating solid paraffin to 50~65℃ to melt, maintaining this temperature, adding deionized water, glycerol and emulsifier, stirring until completely dissolved to form a homogeneous system; adding modifier, continuing to stir for 30-90 minutes, preferably at a speed of 500-1500 rpm; cooling to room temperature to obtain a stable, non-stratified liquid paraffin modified liquid.

[0022] Preferably, in step (2), the conditions for heat curing are: curing at 103±3℃, more preferably curing time is 5-10h, and even more preferably 6h. The liquid paraffin modified liquid penetrates and coats the wood and cured MUF resin surfaces to form a paraffin film with a thickness of 1-10 μm.

[0023] Preferably, the wood obtained by the method is suitable for the wood industry, including but not limited to the fields of solid wood furniture and wood structure buildings.

[0024] The present invention also provides a vacuum impregnation modification apparatus, which is applicable to any of the above-mentioned dual synergistic modification methods for recycled wood. The apparatus includes a vacuum impregnation tank, a vacuum pump, and a modification liquid storage container, wherein: The vacuum impregnation tank includes a tank body and a top cover. A modification vessel is installed inside the tank body. The top of the modification vessel is connected to the internal space of the tank body. The modification vessel is used to place wood and modification liquid so that the wood can be modified here. A vacuum gauge is installed on the top cover to detect the vacuum level inside the tank. The vacuum pump is connected to the vacuum impregnation tank via a gas guide pipe. A valve is installed on the gas guide pipe to perform vacuum extraction and release treatment on the vacuum impregnation tank and control the vacuum level. The modified liquid storage container is connected to the vacuum impregnation tank via a liquid guide pipe, thereby guiding the modified liquid in the container to the vacuum impregnation tank; a valve is installed on the liquid guide pipe to control the flow of the modified liquid.

[0025] Preferably, the top cover is provided with an air outlet and a liquid inlet. The air guide pipe is connected to the vacuum impregnation tank space through the air outlet, and the liquid guide pipe is connected to the vacuum impregnation tank space through the liquid inlet. More preferably, the air outlet and the liquid inlet are located at opposite ends of the top cover, and the distance between them should be no less than half the diameter of the top cover, so as to avoid mutual interference between airflow and liquid.

[0026] Preferably, the valve is a ball valve and is located at one end of the air or liquid guide tube near the top cover. The air and liquid intake speeds can be adjusted by adjusting the valve opening angle. More preferably, the ball valve port adopts a quick-connect interface, which facilitates connection of the conduit and makes operation and subsequent maintenance convenient.

[0027] Preferably, the modified vessel is located at the lower end of the interior of the container. This ensures stability while avoiding proximity to the air outlet, which could cause interference between the liquid and the airflow.

[0028] Preferably, the inlet end of the liquid guide tube is located inside the modified liquid storage container, and the outlet end extends through the top cover to the modified vessel at the lower end of the container, thereby ensuring that the modified liquid uniformly submerges the wood sample. More preferably, the inlet end of the liquid guide tube is equipped with a porous suction device to control the liquid inlet rate and uniformity, ensuring uniform liquid absorption and preventing excessively rapid liquid inlet. The end of the air guide tube near the top cover is equipped with a porous interface to ensure uniform air intake when a vacuum is released.

[0029] Preferably, the modified liquid storage container is equipped with a constant temperature water bath device for maintaining the temperature of the modified liquid. More preferably, the modified liquid storage container contains a modified liquid, including MUF resin modified liquid and liquid paraffin modified liquid, and the appropriate modified liquid is selected for storage according to the actual modification steps.

[0030] Preferably, the vacuum impregnation tank is further provided with a protective device on the outside. The protective device includes a shock-absorbing pad at the bottom of the tank to buffer vibration and impact, and a spring base at the bottom of the shock-absorbing pad to provide elastic support and further absorb vibration.

[0031] In this invention, a synergistic modification mechanism is employed. Firstly, a gradient penetration mechanism: the alkaline pretreatment of MUF resin protonates some of the hydroxyl groups in the wood fibers, forming a negatively charged surface. This promotes the electrostatic adsorption of the cationic paraffin emulsion, increasing the penetration depth of the secondary impregnation. By impregnating with resin first and then paraffin, the nanoscale pores formed by MUF curing serve as paraffin molecule transport channels, achieving a gradient interpenetrating structure of the two materials. Secondly, an interfacial coupling effect: glycerol and polyvinyl alcohol in the paraffin emulsion act as co-solvents and emulsifiers. Their hydroxyl groups form a hydrogen bond network with the amino groups of the MUF resin, thus acting as a bridge between paraffin and wood. This indirectly enhances the adhesion between paraffin, wood, and resin, not only improving and stabilizing the mechanical strength of the secondary impregnated material but also enhancing the volume stability and durability of the modified wood.

[0032] The synergistic modification mechanism of this invention is as follows: The surface of the MUF cross-linked resin block contains hydroxymethyl and amino groups. During the heating and curing process, these groups react with the hydroxymethyl, carboxyl, and hydroxyl groups on the surface of wood cellulose and hemicellulose, removing hydroxyl and hydroxymethyl groups and combining with hydrogen to generate water, formaldehyde, ammonia, and other substances. The cured resin forms a strong covalent bond with the wood, forming a wood-resin cross-linked structure. The cured resin, with its high toughness and plasticity, strengthens the wood through effective bonding. Simultaneously, the reaction between the resin and the resin-wood structure reduces the number of hydrophilic groups in the modified wood, thus lowering its water adsorption level. Paraffin wax, mainly composed of long-chain alkanes, is a non-polar substance, while the main components of wood are cellulose, hemicellulose, and lignin, which contain a large number of polar groups. High temperatures alter the surface properties of the wood, making paraffin wax adhere more easily. Paraffin wax fills the pores of the wood, forming a physical barrier to prevent moisture penetration. In addition, emulsifiers such as polyvinyl alcohol or co-solvents such as glycerol are added during the processing. These substances may contain polar groups, which can act as a bridge between paraffin and wood, forming hydrogen bonds or other secondary bonds, thereby indirectly enhancing the adhesion between paraffin and wood.

[0033] Compared to other modification systems that introduce hydrophobic materials, the "chemical crosslinking + physical isolation" modification system of this invention solves the problem of weak interfacial bonding within the modified material, enabling a stronger bond between the resin and the hydrophobic material within the wood. This not only allows for a more stable enhancement of mechanical properties but also enables the modified material to remain within the wood for a longer period, significantly improving volume stability and durability.

[0034] Compared with existing technologies, the beneficial effects of this invention are: this invention not only solves the industry problem of the difficulty in balancing the "strength and environmental protection" of wood, but also breaks through the application limitations of wood in extreme environments. It is particularly suitable for high-end solid wood furniture, wood structure buildings and ancient building restoration, etc., enabling ordinary fast-growing wood to reach the performance indicators of high-quality hardwood, and providing an innovative solution for promoting the efficient use of wood resources and the development of green buildings. Attached Figure Description

[0035] Figure 1 This is a schematic diagram of a vacuum impregnation modification device according to the present invention. Wherein, 1-vacuum impregnation device; 2-vacuum impregnation tank; 3-vacuum pump; 4-modification liquid storage container; 5-liquid guide pipe; 6-protective device; 7-tank body; 8-top cover; 9-modification vessel; 10-vacuum gauge; 11-valve; 12-MUF resin modification liquid; 13-liquid paraffin modification liquid; 14-air guide pipe; 15-constant temperature water bath device; 16-porous liquid aspirator; 17-spring base; 18-shockproof pad; 19-wood.

[0036] Figure 2 The diagram schematically illustrates the compressive strength, tensile strength, water absorption, and loss rate of unmodified wood (Comparative Example 4), wood modified only with paraffin emulsion (Comparative Example 3), wood modified only with MUF resin (Comparative Example 2), and wood double-impregnated with MUF resin and paraffin (Comparative Example 1).

[0037] Figure 3 The diagram schematically illustrates the changes in bending strength, hardness, swelling rate, water repellency, and modulus of elasticity over time for unmodified wood (Comparative Example 4), wood modified only with paraffin emulsion (Comparative Example 3), wood modified only with MUF resin (Comparative Example 2), and wood double-impregnated with MUF resin and paraffin (Comparative Example 1).

[0038] Figure 4 The images schematically show the scanning electron microscope (SEM) microstructures of unmodified wood (Comparative Example 4), wood modified only with paraffin emulsion (Comparative Example 3), wood modified only with MUF resin (Comparative Example 2), and wood double-impregnated with MUF resin and paraffin (Comparative Example 1). Detailed Implementation

[0039] To better clarify and understand the objectives, process solutions, and advantages of this invention, the technical solutions and implementation methods of this invention will be further described clearly, completely, and in detail below through specific embodiments and in conjunction with the accompanying drawings. It should be understood that the embodiments described in this invention are implemented under the premise of the technical solutions of this invention, providing detailed implementation methods and specific operating procedures, but are only some embodiments of this invention, not all embodiments. The specific implementation methods described are limited to illustrating and explaining this invention and do not limit this invention. Based on the embodiments of this invention, all other implementation methods obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0040] Unless otherwise specified, the experimental methods and conditions used in the embodiments of this invention are conventional methods and conditions. The materials, reagents, instruments, and equipment used in the embodiments, unless otherwise specified, are all conventional substances or equipment known to those skilled in the art and can be obtained commercially or prepared by conventional methods. The reaction conditions described in the invention's content can all achieve the stated reactions and obtain the desired products. Due to space limitations, some embodiments are listed below to further illustrate the advantages of the technical solution of this invention.

[0041] This invention provides a vacuum impregnation modification apparatus, the apparatus comprising a vacuum impregnation tank, a vacuum pump, and a modification liquid storage container, wherein: The vacuum impregnation tank includes a tank body and a top cover. A modification vessel is installed inside the tank body. The top of the modification vessel is connected to the internal space of the tank body. The modification vessel is used to place wood and modification liquid so that the wood can be modified here. A vacuum gauge is installed on the top cover to detect the vacuum level inside the tank. The vacuum pump is connected to the vacuum impregnation tank via a gas guide pipe. A valve is installed on the gas guide pipe to perform vacuum extraction and release treatment on the vacuum impregnation tank and control the vacuum level. The modified liquid storage container is connected to the vacuum impregnation tank via a liquid guide pipe, thereby guiding the modified liquid in the container to the vacuum impregnation tank; a valve is installed on the liquid guide pipe to control the flow of the modified liquid.

[0042] According to one aspect of the invention, the top cover is provided with an air outlet and a liquid inlet, and the air guide pipe communicates with the vacuum impregnation tank space through the air outlet, and the liquid guide pipe communicates with the vacuum impregnation tank space through the liquid inlet. According to yet another aspect of the invention, the air outlet and the liquid inlet are located at opposite ends of the top cover, and the distance between them should be no less than half the diameter of the top cover, to avoid mutual interference between the airflow and the liquid.

[0043] According to one aspect of the invention, the valve is a ball valve and is disposed at one end of the air or liquid guide tube near the top cover. The air and liquid inlet speeds can be adjusted by adjusting the valve opening angle. More preferably, the ball valve port adopts a quick-connect interface, which facilitates connection of the conduit and is convenient for operation and subsequent maintenance.

[0044] According to one aspect of the invention, the modified vessel is located at the lower end of the interior of the container. This ensures stability while avoiding proximity to the air outlet, which could cause interference between the liquid and the airflow.

[0045] According to one aspect of the invention, the inlet end of the liquid guide tube is located inside the modified liquid storage container, and the outlet end extends through the top cover to the modified vessel at the lower end of the container, thereby ensuring that the modified liquid uniformly submerges the wood sample. According to another aspect of the invention, the inlet end of the liquid guide tube is provided with a porous suction device to control the liquid inlet rate and uniformity, ensuring uniform suction and preventing excessively rapid liquid inlet. The end of the air guide tube near the top cover is provided with a porous interface to ensure uniform air intake when a vacuum is released.

[0046] According to one aspect of the present invention, the modified liquid storage container is equipped with a constant temperature water bath device for maintaining the temperature of the modified liquid. According to another aspect of the present invention, the modified liquid storage container contains a modified liquid, including MUF resin modified liquid and liquid paraffin modified liquid, with the appropriate modified liquid selected for placement based on the actual modification steps.

[0047] According to one aspect of the invention, a protective device is further provided on the outside of the vacuum impregnation tank. The protective device includes a shock-absorbing pad disposed at the bottom of the tank body for buffering vibration and impact, and a spring base disposed at the bottom of the shock-absorbing pad for providing elastic support and further absorbing vibration.

[0048] The following is a further technical solution: According to one aspect of the present invention, the barrel body is a stainless steel barrel body, and the top cover is a rubber top cover, more preferably made of epoxy resin with good sealing properties, with an annular sealing groove on the edge to form an airtight connection with the barrel body, having excellent airtightness, high rigidity and good shock absorption ability, and is not easily deformed under vacuum conditions.

[0049] According to one aspect of the present invention, the top cover thickness is ≥40mm, and the vacuum gauge installed on the top cover is a high-precision shockproof vacuum gauge. The vacuum gauge is filled with silicone oil to avoid vibration affecting the vacuum value observation. The scale range of the shockproof vacuum gauge is -0.1MPa to 0MPa, and the reading error is ≤1%.

[0050] According to one aspect of the invention, the coatings inside the vacuum impregnation tank and on the surface of the modified vessel must be able to withstand a weakly alkaline environment and be able to be used for a long time without corrosion.

[0051] According to one aspect of the present invention, the bottom of the modified vessel is designed with a guide groove to facilitate the uniform distribution of the modified liquid, and the wall thickness is about 3~8mm.

[0052] According to one aspect of the invention, the volume of the vacuum impregnation tank is not less than twice that of the modified vessel, ensuring sufficient operating space.

[0053] According to one aspect of the present invention, the liquid guide tube is made of rubber material resistant to weak acids and alkalis, and the inner diameter is designed to be 8-10 mm to ensure a moderate liquid flow rate.

[0054] This invention also provides a method for dual synergistic modification of recycled wood, which can be carried out using the aforementioned apparatus. Specifically, the method includes the following steps: (1) Wood is vacuum impregnated in MUF resin modification liquid and then heated and cured to obtain pre-modified wood; (2) The preliminarily modified wood is vacuum impregnated in liquid paraffin modification solution and then heated and cured to obtain modified wood.

[0055] The following is a further technical solution: According to one aspect of the present invention, wood that has been initially modified with MUF resin modification liquid forms a mesoporous structure of 50-200 nm after the MUF resin is cured, and paraffin molecules penetrate into the wood cell wall through the mesoporous channels to form a composite reinforcing layer.

[0056] According to one aspect of the present invention, in step (2): the preliminarily modified wood is placed back into the cleaned vacuum impregnation modification device, and the modification liquid is replaced with liquid paraffin modification liquid and the impregnation operation is repeated once or more. The difference is that after the vacuum impregnation is completed and the vacuum is released, the wood is wrapped with an oil-absorbing cloth and left to stand for 10-60 minutes, more preferably 20 minutes, to absorb excess paraffin emulsion. Then the wood is placed in a vacuum drying oven and the paraffin emulsion is directly dried and cured at a temperature of 103±3℃, so that it becomes a solid film again, covering the surface and gaps of the wood.

[0057] According to one aspect of the present invention, a step-by-step vacuum is used during the evacuation process. Specifically, the procedure in the step-by-step vacuum stage is as follows: the vacuum level is reduced to -0.05 MPa within 5 minutes, maintained for 15 minutes to expel air from large pores, and then the evacuation continues for 30 minutes to -0.090 MPa to -0.1 MPa.

[0058] According to one aspect of the present invention, the modified liquid injection stage in steps (1) and (2) is as follows: the injection speed is controlled by means of the pressure difference and the opening angle of the gas valve. When injecting the modified liquid, such as 12% MUF solution, the liquid temperature is controlled at 25±1℃ and the injection speed is about 50mL / min.

[0059] According to one aspect of the present invention, the process for the pressure recovery to atmospheric pressure stage is as follows: by controlling the opening and closing of the gas valve, the gradient pressure release can be controlled, and a three-stage recovery to atmospheric pressure can be carried out. The pressure release rate is about 0.005 MPa / min. After each pressure release stage, the pressure is maintained for 5-10 minutes, and then the pressure is held stable for 120 minutes.

[0060] According to one aspect of the present invention, the post-treatment process of heat curing is as follows: in step (1), the evaporation of water and curing of the modified MUF resin liquid are controlled by segmented heating, and the evaporation temperature and curing temperature are 60±3℃ and 103±3℃, respectively, and the drying time is 4h and 2h, respectively. In step (2), the paraffin wax is cured by constant temperature evaporation at 103±3℃, and the drying time is 6h.

[0061] Specifically, the present invention will be further illustrated by the following specific examples.

[0062] In this example of the invention, MUF resin modified liquid (12) and liquid paraffin modified liquid (13) are prepared by the following method and process: MUF resin modification solution: Approximately 280g of 30% formaldehyde solution was added to a three-necked flask, and the pH was adjusted to 8.2 with 5% NaOH solution. The temperature was raised to 60℃, and 120g of 60% urea solution and 48g of 99% analytical grade melamine were added sequentially in a molar ratio of approximately 1:0.3. After reacting for 2 hours, the temperature was lowered to 45℃, and 3.8g of PVA powder was added. The pH was adjusted to 5.3 with citric acid, and the reaction continued until the viscosity reached 350 mPa·s. The mixture was vacuum dehydrated to a solid content of 52%, pulverized, and passed through a 50-mesh sieve to obtain MUF resin powder. 12% by mass of the MUF resin powder was dissolved in deionized water, and 3% by mass of NH4Cl was added to obtain the MUF resin modification solution.

[0063] Liquid paraffin modified solution: Heat 60g of solid paraffin to 60℃, add 2.4g of OP-10, 1.8g of glycerol and 1.8g of polyvinyl alcohol, and slowly add 494g of deionized water; stir at 1200rpm for 60 minutes, maintain emulsification at 60℃, and finally cool to 25℃ to obtain a stable emulsion.

[0064] like Figure 1As shown, in this embodiment, the special vacuum impregnation device includes: a vacuum impregnation tank (2): a stainless steel tank (7) with a wall thickness of 6mm, the inner surface of which is polished, the tank volume is 5L, and the modified container (9) is placed inside. A rubber top cover (8): made of epoxy resin, with silicone sealing rings embedded at the edges, and locked and sealed with the tank body through a sealing groove. Ball valves (11) are installed on the air outlet and liquid inlet on both sides of the top cover, and the distance between the two ball valves is 2 / 3 of the diameter of the top cover. A vacuum pump (3): with a pumping speed of 4.2m³ / h and an ultimate vacuum of 1.5Pa, equipped with a silencer and an oil mist filter. A gas guide pipe and a liquid guide pipe: with an inner diameter of 10mm, a multi-hole liquid suction device with a hole diameter of 0.5mm is installed at one end of the liquid guide pipe, and a multi-hole air inlet hood is connected to one end of the gas guide pipe. A protective device (6): four stainless steel springs are installed at the bottom, and a 20mm thick polyurethane anti-vibration pad with a hardness of 50 Shore A is laid on top of the springs.

[0065] The vacuum impregnation modification method using MUF resin modified liquid is as follows: Take a batch of wood (in this example, recycled laminate is used), cut it, and clean its surface. The initial moisture content is approximately 10%~12%. Dry the wood by placing it in a vacuum drying oven to remove the wood's internal moisture and weigh the sample to constant weight. Place the wood in the modification vessel of the vacuum impregnation tank, close the valve of the liquid delivery tube (liquid valve), open the valve of the gas delivery tube (gas valve), close and lock the top cover; start the vacuum pump, evacuate to -0.095MPa~-0.1MPa and maintain for 60 minutes to remove air from the wood, then close the gas valve. Insert the liquid delivery tube into the bottom of the prepared modified liquid, open the liquid delivery valve, and inject 12% MUF resin modified liquid (25℃ by mass) into the modification vessel using air pressure until the modified liquid exceeds the top of the wood by at least 2cm and does not exceed 2 / 3 of the vessel's volume. Then close the liquid delivery valve and continue to maintain the vacuum for 120 minutes to allow the resin to fully impregnate. After impregnation, slowly open the air valve. After the gradient release of vacuum is complete, maintain the pressure for 120 minutes. Remove the specimen, absorb the residual liquid on the surface with filter paper, and perform a staged curing process on the wood: place it in a vacuum drying oven at 60±3℃ for 4 hours to evaporate the moisture to an absolutely dry state, and then maintain an absolute weight. Subsequently, increase the temperature to 103±3℃ and continue drying for 2 hours to heat-cure the MUF resin. Finally, cure at room temperature for 24 hours to release stress, thus completing the initial impregnation.

[0066] The vacuum impregnation method of liquid paraffin modified liquid is as follows: After the wood has been initially impregnated with MUF resin, it is placed back into the modification vessel, the vacuum pump is started, and the vacuum is gradually reduced to -0.09MPa; the liquid paraffin modified liquid is replaced, the liquid guide valve is opened, and 12% mass fraction paraffin emulsion at 45℃ (this temperature maintains the stability of the paraffin emulsion and avoids crystallization and precipitation of solids) is drawn from the modified liquid storage container. After the liquid surface completely covers the wood, it is impregnated under pressure for 120 minutes; the vacuum is gradually and slowly released, the wood is taken out and the excess liquid on the surface is drained; the curing process is carried out at 103℃ for 6 hours to finally obtain double-impregnated modified wood.

[0067] Test methods and standards: The test methods used in the specific embodiments all adopt valid national standards. The tensile strength of wood is tested according to standard GB / T 1938-2009; the compressive strength is tested according to standard GB / T 1935-2009; the water absorption rate is tested according to standard GB / T 1934.1-2009; the bending strength is tested according to standard GB / T 1936.1-2009; the bending modulus of elasticity is tested according to standard GB / T 1936.2-2009; and the hardness of wood is tested according to standard GB / T 1941-2009.

[0068] The weight gain rate is calculated as follows:

[0069] WPG – weight gain rate, % M 1 — Oven-dried mass of the specimen after immersion, g; M 0 — Oven-dry weight of the specimen before immersion, in g.

[0070] The formula for calculating the anti-swelling rate is as follows:

[0071] Where ASE represents water absorption and swelling resistance, % A c —Wet swelling rate before modification, % A 0 — Unmodified swelling rate, %.

[0072] The formula for calculating the wet expansion rate is as follows:

[0073] Where A represents the moisture expansion rate, % l —Linear dimensions of the specimen in air-dried or water-saturated state, in mm; l 0 — Insulated dimensions of the specimen, mm.

[0074] Loss rate: The loss rate of the modifier is calculated using the following formula:

[0075] Where LA represents the churn rate, %m 0 represents the oven-dry mass before modification, in grams; m 1 represents the oven-dry mass after modification, in grams; m 2 represents the oven-dried weight after immersion in water, in g. SEM images were obtained using a Zeiss scanning electron microscope. Specific Implementation Example (I):

[0077] To fully verify the innovation of the "resin-paraffin dual impregnation synergistic modification" process of this invention, the following examples are presented, with recycled laminate as the test substrate. The dual impregnation modified wood mentioned above is the baseline example, namely Example 1.

[0078] Example 2 is as follows: the MUF impregnation time is changed to 1.5 hours, the paraffin impregnation time is 1 hour, and the rest is the same as in Example 1.

[0079] Example 3 involves changing the initial modification and curing process to direct curing at 103℃ for 6 hours, thus eliminating the 60℃ stage. The rest is the same as in Example 1.

[0080] Example 4 involves modifying the liquid paraffin modification liquid formula by removing the addition of polyvinyl alcohol and glycerol, while maintaining the same procedures as Example 1.

[0081]

[0082] The tensile strength improvement rates of Examples 2 and 3 show that their tensile strength improvement effects are not as good as those of Example 1, while their loss rate and water absorption rate are higher. The experiment indicates that changing the impregnation time in the impregnation process results in incomplete penetration of the modified liquid, failing to achieve the maximum improvement effect. Changing the segmented curing method in the impregnation process leads to excessively high curing temperatures, causing micro-cracks in the wood, thus increasing water absorption and loss rates. Example 4 shows similar water absorption and tensile strength improvement effects compared to Example 1, but its loss rate is higher. This is because the absence of polyvinyl alcohol and glycerol results in weak interfacial bonding of the modified material, making it more susceptible to hydrolysis and loss. Specific Implementation Example (II):

[0084] To fully verify the optimal concentration of the modifying solution in the "resin-paraffin dual impregnation synergistic modification" process of this invention, the following examples are presented, with recycled laminate as the test substrate. Three different concentrations of modifying solution (8%, 12%, and 16%) were prepared using the MUF resin and paraffin emulsion mixing method mentioned above, as detailed in Table 2. Single-factor, three-level experiments were conducted on five indicators, and the results are shown in Tables 3 and 4. The effects of different concentrations of modifying solution on the weight gain, swelling resistance, and mechanical strength of the wood were compared to optimize the concentration. The loss rate and weight gain rate were positively normalized by subtracting their values ​​from 100% to determine the optimal mass fraction and formulation of the modifying solution.

[0085] Specific implementation examples are shown in Table 2:

[0086] The five indicators are shown in the table below:

[0087]

[0088] It can be seen that the weight gain rate of wood increases with the increase of the concentration of the two modifying solutions. However, different modifying solutions have different weight gain thresholds. When the weight gain rate reaches this threshold, even if the concentration of the modifying solution is further increased, the weight gain rate will not increase significantly. Within the weight gain rate threshold, there is a range in which the mechanical strength reaches its peak. Beyond this range, even if the weight gain rate is increased, the mechanical strength will not increase significantly, but will instead decrease. Among them, liquid paraffin shows the largest decrease in tensile and compressive strength when the weight gain rate is large. The swelling resistance of the two modifying solutions follows roughly the same pattern: the swelling resistance increases with the increase of the weight gain rate, but decreases slightly after reaching a certain range. In terms of loss rate, the loss rate of paraffin emulsion increases with the increase of the weight gain rate, and the closer the weight gain rate is to the maximum weight gain rate, the higher the loss rate. This is because the amount of the modifying solution solidified inside the wood is limited. Modified molecules that fail to solidify in the cell walls or fiber tubes, due to the lack of significant interaction with the wood matrix, are largely lost or hydrolyzed under the action of water molecules. In summary, a concentration of 12% can obtain the optimal modification effect.

[0089] Specific comparison examples:

[0090] The same batch of recycled laminates was divided into four groups, one of which was referred to as Comparative Example 1, namely Example 1. One group consisted of MUF resin modification without secondary paraffin impregnation, and was referred to as Comparative Example 2. One group, referred to as Comparative Example 3, underwent only paraffin impregnation modification without MUF resin impregnation. One group consists of wood materials that do not undergo this modification process, namely the recycled laminate in Example 1 that has not undergone any modification, referred to as Comparative Example 4.

[0091] The four groups of wood were subjected to tests including compressive strength, tensile strength, bending strength, hardness, volume stability, 24-hour water absorption, 24-hour loss rate, and immersion durability, and observed under a scanning electron microscope.

[0092]

[0093] like Figure 2 , 3As shown in the figure and in conjunction with the table above, the results show that the mechanical properties of Comparative Example 3 not only did not improve but actually decreased slightly. This is because the non-rigid paraffin film is difficult to enhance the mechanical properties of wood, but it significantly reduced the water absorption rate, mainly because the paraffin film isolates most of the moisture transport. Comparative Example 2, due to the toughening effect of the internally cured resin on the wood, showed a significant increase in tensile strength, but no increase in compressive strength. However, the modified material hydrolyzes in a moist environment and has many pores, resulting in a high water absorption and loss rate. Comparative Example 1 not only showed a greater increase in tensile strength than MUF resin, but also a significant increase in compressive strength, and a significant decrease in water absorption and loss rate of modified material. This is because, based on the "chemical cross-linking" of the resin, the "physical isolation and filling" of the hydrophobic material was carried out, which greatly improved the volume stability and durability while ensuring mechanical properties. In addition, the interfacial connection between the paraffin and MUF resin system is more stable than that of ordinary systems due to the presence of secondary bonds, thus resulting in higher mechanical properties than single resin modification.

[0094] The bending strength diagram shows that Comparative Example 2 shows the highest improvement in bending strength, approximately 11.05%, while Comparative Example 3 shows the worst effect. Wood generally follows the plane section assumption when bending, exhibiting both tensile and compressive stresses, with tension at the bottom and compression at the top. MUF resin enhances both the longitudinal uniaxial tensile and compressive strength of the wood structure, thus correspondingly improving the bending strength. Comparative Example 1 shows that although the introduction of paraffin slightly reduced the improvement in bending strength, it still represents a significant improvement compared to Comparative Example 4. Specifically, Comparative Example 1 has a compressive strength close to the 30 MPa required for high-quality hardwood and a density of 0.76 g / cm³. 3 It exceeds the requirement of premium hardwood by 0.75 g / cm³. 3 It meets some of the requirements for high-quality hardwood.

[0095] The hardness improvement rate of the modified material is related to the hardness of the impregnated modified material itself. Figure 3 In -b, B represents the hardness of the sample before modification, and A represents the hardness of the sample after modification. Comparative Example 2 shows that the MUF resin has a larger molecular weight fraction, and during modification, it forms a plastic resin block with higher hardness after heating and curing. This block has a certain filling effect on the pores of the wood, thus significantly improving the hardness. However, the hardness improvement in Comparative Example 1 is slightly lower than that in Comparative Example 2. Combining the degree of hardness improvement in Comparative Example 3, it can be seen that MUF resin plays a dominant role in improving the hardness of the secondary impregnation modified material. The paraffin emulsion modified material forms a non-rigid film after curing and cannot effectively improve the hardness. Therefore, the introduction of paraffin emulsion has little effect on the hardness improvement.

[0096] The volumetric stability of wood was characterized by the anti-swelling rate (ASE) and the water repellency rate (RWA). Comparative Example 3 showed the greatest contribution to the improvement in volumetric stability after modification, with an anti-swelling rate of 81% and a water repellency rate of 60%. Comparative Example 2 was less effective than Comparative Example 3. The effect of Comparative Example 1 on volumetric stability was roughly between the two, and its volumetric stability performance was closer to that of the optimal Comparative Example 3. In some parameters, such as the anti-swelling rate, Comparative Example 1 was even superior to Comparative Example 3.

[0097] As can be seen from the SEM images, the paraffin film covers the cured resin and crystals, which improves the disadvantage of moisture easily penetrating into cracks and gaps, greatly reduces the contact between cell walls and moisture, and improves volume stability.

[0098] In addition, the loss of elastic modulus after immersion in water was used to characterize the durability of the modified wood. In the initial stage of immersion, the elastic modulus decreased as the modified material gradually hydrolyzed in water, and some of the fully cured modified material dissolved. As the modified material dissolved, the solution reached equilibrium, and the change in elastic modulus tended to stabilize. Paraffin wax, being a hydrophobic material, is extremely difficult to dissolve in water; only some redundant paraffin wax flowed out of the wood with the water, resulting in a smaller decrease in elastic modulus. In Comparative Example 1, the decrease in elastic modulus was significantly smaller than in Comparative Example 2, and the trend was closer to that of Comparative Example 3. This is because the paraffin film blocked the contact between the modified material and water, significantly reducing the hydrolysis process.

[0099] like Figure 4 As shown in the SEM images, Comparative Example 4 exhibits thinner micropore walls, no thickened filler, a greater number of hollow pores, mostly circular, providing numerous water inflow and outflow channels, and allowing direct contact between the surface hydrophilic groups and the environment. Comparative Example 3 shows a distinct organic film on the wood matrix surface, but still retains many hollow pores, indicating that paraffin wax has limited filling effect on these pores. Comparative Example 2 shows resin coverage on the wood fiber vessel walls and lignin surface, enhancing the surface toughness of the wood and reducing contact between the wood matrix and the environment; however, some pores and resin cracks remain on the surface, indicating that water transport channels still exist. Comparative Example 1 shows the wood matrix and MUF resin surface covered by an organic paraffin film, filling and repairing pores and cracks, thus significantly reducing water flow channels. Furthermore, the paraffin film coats the resin, reducing the contact area between the resin and external moisture, decreasing the loss rate of the modified material, and significantly improving durability.

[0100] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the present invention in any way. Other variations and modifications may be made without departing from the technical solutions described in the claims.

Claims

1. A method for dual synergistic modification of recycled wood, characterized in that, Includes the following steps: (1) Wood is vacuum impregnated in MUF resin modification liquid and then heated and cured to obtain pre-modified wood; (2) The pre-modified wood is vacuum impregnated in liquid paraffin modification solution and then heated and cured to obtain double-modified wood.

2. The method for dual synergistic modification of recycled wood according to claim 1, characterized in that, In step (1), the MUF resin modified solution includes a basic MUF resin modified solution, which includes MUF resin and deionized water, with the mass fraction of MUF resin in the basic MUF resin modified solution being 8%~16%; a modifier is also added, which is polyvinyl alcohol, and the amount of polyvinyl alcohol added is 1-10 wt% of the solid mass of MUF resin; an additive is also included, which is ammonium chloride, and the amount of ammonium chloride added is 3% of the MUF resin. In step (2), the liquid paraffin modification solution includes solid paraffin, deionized water, glycerol, emulsifier and modifier. The mass fraction of solid paraffin in the liquid paraffin modification solution is 8%~16%, the amount of glycerol added to the liquid paraffin modification solution is 1-3% of the solid paraffin, the emulsifier is polyvinyl alcohol, the amount added to the liquid paraffin modification solution is 1-5% of the solid paraffin, and the modifier is OP-10, the mass fraction of the liquid paraffin modification solution is 1-5 wt%.

3. The method for dual synergistic modification of recycled wood according to claim 2, characterized in that, In step (1), the MUF resin preparation method includes: adding formaldehyde solution to a reaction vessel, adjusting the pH to 7.5-9.0, and heating to 60-80℃; adding urea and melamine in batches at a molar ratio of 1:0.3-0.5, and reacting for 1-3 hours; adding a modifier; cooling to 40-50℃, adjusting the pH to 4.5-6.0, and continuing the reaction until the viscosity reaches 200-500 mPa·s; concentrating, dehydrating, and drying to obtain MUF resin with a solid content of 40-60%; The preparation method of MUF resin modified solution includes: dissolving MUF resin in deionized water, adding additives, and obtaining MUF resin modified solution; In step (2), the preparation method of the liquid paraffin modified liquid includes: heating solid paraffin to 50~65℃ to melt, maintaining this temperature, adding deionized water, glycerol and emulsifier, stirring until completely dissolved to form a homogeneous system; adding modifier, continuing to stir for 30-90 minutes at a speed of 500-1500 rpm; cooling to room temperature to obtain a stable, non-stratified liquid paraffin modified liquid.

4. The method for dual synergistic modification of recycled wood according to claim 3, characterized in that, In steps (1) and (2), the vacuum degree of vacuum impregnation is not less than -0.09MPa, the vacuum impregnation time is 1-3h, the temperature of the impregnation liquid is 20-50℃, and after the vacuum impregnation is completed, the vacuum pressure is slowly released to normal pressure and maintained for a certain period of time.

5. The method for dual synergistic modification of recycled wood according to claim 4, characterized in that, In step (1), the heat curing process includes two stages: the first stage is to heat at 60±3℃ until there is no moisture, and then cure at 103±3℃.

6. The method for dual synergistic modification of recycled wood according to claim 4, characterized in that, In step (2), the conditions for heat curing treatment are: curing at 103±3℃.

7. The method for dual synergistic modification of recycled wood according to claim 4, characterized in that, In step (1), stress release is performed after modification. During stress release, the material needs to be cured under standard conditions for 24 hours.

8. A vacuum impregnation modification apparatus, characterized in that, The apparatus described herein is applicable to a dual synergistic modification method for recycled wood according to any one of claims 1-7, the apparatus comprising a vacuum impregnation tank, a vacuum pump, and a modified liquid storage container, wherein: The vacuum impregnation tank includes a tank body and a top cover. A modification vessel is placed inside the tank body, and the top of the modification vessel communicates with the internal space of the tank body. A vacuum gauge is installed on the top cover. The vacuum pump is connected to the vacuum impregnation tank space through a gas guide pipe, and a valve is installed on the gas guide pipe. The modified liquid storage container is spatially connected to the vacuum impregnation tank via a liquid guide pipe; a valve is installed on the liquid guide pipe.

9. The vacuum impregnation modification apparatus according to claim 8, characterized in that, The top cover is equipped with an air outlet and a liquid inlet. The air guide pipe is connected to the vacuum impregnation tank space through the air outlet, and the liquid guide pipe is connected to the vacuum impregnation tank space through the liquid inlet.

10. The vacuum impregnation modification apparatus according to claim 8, characterized in that, The modified liquid storage container is equipped with a constant temperature water bath device.

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