Low-swelling shaving board using recycled material and preparation process thereof

Abstract

The application relates to the technical field of artificial boards, and particularly discloses a low-swelling shaving board using recycled materials and a preparation process. The low-swelling shaving board comprises an upper surface layer, a core layer and a lower surface layer which are sequentially bonded from top to bottom by an adhesive, and the core layer comprises the following raw materials in parts by weight: recycled shaving 55-65 parts, pre-composite particles 12-16 parts, pre-composite fiber network sheet 6-10 parts, hydrophobic nano-silica aerogel powder 2-4 parts, zinc borate 1.5-2.5 parts and weather-resistant adhesive 15-18 parts. Through the three-layer plywood structure and the core layer design of the specific raw material ratio, the water absorption thickness swelling rate of the recycled shaving board can be reduced, and the defect that the recycled shaving board is prone to arching and warping in the outdoor humid and cold and hot alternating environment can be reduced.

Description

Technical Field

[0001] This invention relates to the technical field of engineered wood products, and in particular to a low-absorption-expansion particleboard using recycled materials and its preparation process. Background Technology

[0002] Particleboard is an important type of engineered wood product, possessing advantages such as uniform structure, good processing performance, and low production cost. With increasingly scarce timber resources, utilizing recycled wood to produce particleboard has become a significant development direction for the engineered wood product industry. However, recycled wood particleboard still faces numerous technical challenges in practical applications.

[0003] After long-term use and weathering and aging by the external environment, the fiber structure of recycled wood has changed. The degradation of hemicellulose leads to increased hydrophilicity, and microcracks appear in the fiber cell walls, making it easier for water to penetrate. Therefore, particleboard made from recycled wood generally has a high water absorption thickness swelling rate. The 24-hour water absorption thickness swelling rate of conventional products is often above 8%, which is difficult to meet the requirements for outdoor and high humidity environments.

[0004] Furthermore, veneer particleboard is prone to warping and buckling in humid outdoor environments or under alternating hot and cold conditions. This is because wood veneer exhibits anisotropic expansion and contraction due to moisture, while the particleboard core layer is relatively isotropic. The mismatch in dimensional change rates between the two under varying humidity and temperature conditions creates interlayer shear stress. When this stress exceeds the interfacial bonding strength, warping, buckling, or even delamination occurs. While existing technologies can improve moisture resistance to some extent by adding waterproofing agents or using adhesives with better water resistance, they offer limited improvement in dimensional stability under alternating hot and cold conditions.

[0005] To address the above problems, this invention provides a low-absorption-expansion particleboard using recycled materials and its preparation process. Summary of the Invention

[0006] In order to reduce the water absorption thickness expansion rate of recycled particleboard and reduce the defects of recycled particleboard being prone to arching and warping in outdoor humid and alternating hot and cold environments, this application provides a low-absorption expansion particleboard using recycled materials and its preparation process.

[0007] Firstly, this application provides a low-absorption-expansion particleboard using recycled materials, employing the following technical solution: A low-absorption-expansion particleboard using recycled materials includes an upper surface layer, a core layer, and a lower surface layer bonded together from top to bottom by an adhesive. The core layer comprises the following raw materials in parts by weight: 55-65 parts recycled wood shavings, 12-16 parts pre-composite particles, 6-10 parts pre-composite fiber network sheet, 2-4 parts hydrophobic nano-silica aerogel powder, 1.5-2.5 parts zinc borate, and 15-18 parts weather-resistant adhesive.

[0008] In one specific implementation, the upper and lower surface layers are the same type of eucalyptus veneer or poplar veneer with a thickness of 1.5 to 3.0 mm.

[0009] In one specific implementation scheme, the pre-composite particles are prepared according to the following steps: The isocyanate-terminated polyurethane prepolymer is heated to 85-95°C to melt, and a silane coupling agent and tannic acid are added and stirred evenly to obtain an activated liquid phase; the mass ratio of the isocyanate-terminated polyurethane prepolymer, the silane coupling agent and the tannic acid is 100:(2-5):(8-15). Micron-sized carbonized wood powder and modified nano-montmorillonite are premixed at a mass ratio of (6-7):3 and put into a high-speed kneader. Under stirring, the activated liquid phase is atomized and sprayed into the kneader at a liquid-solid mass ratio of 7:(13-15). The kneader is kept at 80-90℃ for 15-25 minutes. The kneaded material is extruded into strips, cooled and brittled, then crushed and sieved to obtain pre-composite particles with a particle size of 0.5-2.0 mm.

[0010] By employing the above technical solution, after carbonization, the hydrophilic hydroxyl groups in the cell walls of micron-sized carbonized wood powder undergo extensive dehydration and condensation to form a carbon layer, which acts as a rigid framework filling the pores between large wood shavings in the core layer. Modified nano-montmorillonite blocks the permeation channels of water molecules in the core layer. Under hot-pressing conditions, the terminal -NCO groups of the isocyanate-terminated polyurethane prepolymer can simultaneously react chemically with the hydroxyl groups on the surface of recycled wood shavings, the phenolic hydroxyl groups on tannic acid, and the hydroxymethyl groups in the resin to form a chemically cross-linked polyurethane-lignin interpenetrating network. Tannic acid molecules contain a large number of catechol groups, which can form multiple reversible hydrogen bonds and covalent bonds with the surfaces of wood shaving cellulose, PU prepolymer, and OMMT. When alternating hot and cold temperatures generate stress, these hydrogen bonds can first break and dissipate energy, and then re-bond after the temperature recovers, essentially eliminating the initiation of interfacial microcracks. The four components form core-shell structured particles through a pre-composite process, and the highly active -NCO groups on the outside of the particles can directly undergo secondary chemical cross-linking with the wood shaving substrate and LPF adhesive. During the mixing process, hydrophobic nano-silica aerogel powder preferentially adheres to the liquid-air interface, spontaneously forming a nano-scale waterproof protective film that coats the outer surface of the mixed particles.

[0011] In one specific implementation, the pre-composite fiber network sheet is prepared according to the following steps: Polyester fiber and hemp fiber chopped strands are opened and mixed at a mass ratio of 8:(11-13), and a uniform fiber web is formed on an air-laid web machine. Silane coupling agent accounting for 0.8-1.2% of the total fiber weight is sprayed on the web, and the web is heat-treated at 100-105℃ for 2-3 minutes to obtain a fiber network felt. The felt is then chopped to obtain a pre-composite fiber network sheet.

[0012] By employing the above technical solution, low-melting-point polyester fibers are melted into a high-viscosity fluid at hot-pressing temperature, uniformly coated on the surface of the wood shavings and filling the micropores. After cooling, they crystallize and solidify, forming a continuous thermoplastic skeleton film. When subjected to repeated tensile and compressive stress, it undergoes ductile deformation rather than brittle fracture, uniformly dispersing stress concentration points. Short chopped hemp fibers serve as reinforcing fibers, spanning the gaps between the wood shavings and preventing relative slippage of the veneers. After the two are pre-composite to form a semi-cured network felt, each fragment contains rigid hemp fibers and thermoplastic LMPET. During hot pressing, the LMPET melts and spreads uniformly along the pre-overlapping hemp fiber network, forming a continuous, directional stress-dissipating skeleton.

[0013] In one specific implementation, the polyester fiber has a melting point of 110–120°C and a length of 2–4 mm; the chopped hemp fiber has a length of 5–8 mm.

[0014] In one specific implementation, the weather-resistant adhesive is prepared according to the following steps: The weather-resistant adhesive comprises the following raw materials in parts by weight: 30-45 parts sodium hydroxide, 45-60 parts water, 100-120 parts phenol, 190-230 parts formaldehyde solution, 8-12 parts methyl phenyl silicone resin, 5-8 parts isocyanate-terminated polyurethane prepolymer, and 4-6 parts emulsified paraffin wax with a solid content of 60%. Sodium hydroxide was dissolved in water and cooled to obtain a sodium hydroxide solution; the formaldehyde solution was divided into three portions by weight ratio (120-140):(65-80):7. Preheat the reaction vessel to 40-45℃, add molten phenol to the reaction vessel, then add sodium hydroxide solution, keep the temperature ≤50℃, add the first part of formaldehyde solution, keep the temperature ≤80℃, stir for 10 minutes, adjust the temperature to 70-75℃, add the second part of formaldehyde solution, keep the temperature ≤80℃, keep warm for 40-60 minutes, then add the third part of formaldehyde solution, keep warm at 80℃ for 10 minutes, raise the temperature to boiling, keep boiling for 10-20 minutes, cool to room temperature to obtain the modified resin solution; Add methylphenyl silicone resin, isocyanate-terminated polyurethane prepolymer, and emulsified paraffin with a solid content of 60% to the modified resin solution, and stir until homogeneous to obtain the weather-resistant adhesive.

[0015] Secondly, this application provides a process for preparing low-absorption-expansion particleboard using recycled materials, employing the following technical solution: A process for preparing low-absorption-expansion particleboard using recycled materials includes the following steps: Mixing: Divide the weather-resistant adhesive into two parts, put the recycled wood shavings into the drum mixer, add the first part of the weather-resistant adhesive, stir evenly, then add the pre-composite granules and pre-composite fiber network sheet, the second part of the weather-resistant adhesive, hydrophobic nano silica aerogel powder and zinc borate in sequence, stir evenly to obtain the core layer mixture; Core layer preparation: The core layer mixture is laid into a gradient structure board blank, and cold pre-pressed. The pre-pressing pressure is 1.5-2.5MPa and the pre-pressing time is 30-60 seconds. Then hot-pressing is performed. The total hot-pressing time is 9-12s / mm board thickness. After hot pressing, the board is aged at a temperature of 45-55℃ and a relative humidity of 35-45% for 48-72 hours. The edges are then trimmed to obtain the core layer. Composite process: Prepare an upper and lower surface layer, apply adhesive to the surfaces of the upper and lower surface layers that are to be bonded to the core layer, stack the upper surface layer, core layer and lower surface layer in sequence, and then perform hot pressing, cooling, edge trimming and sanding to obtain a low-expansion particleboard using recycled materials.

[0016] In one specific feasible implementation, the recycled wood shavings undergo the following pretreatment before use: Sugar removal treatment: Immerse the recycled wood shavings in a mixed aqueous solution for 2-4 hours to obtain sugar-removed recycled wood; the mixed aqueous solution contains 1-2% NaOH and 3-6% ethanol by mass. Moist heat flash explosion treatment: Place the desugared recycled material in a pressure vessel, introduce saturated steam, and keep it at 140-155℃ and 0.4-0.6MPa for 20-30 minutes. Depressurize to obtain the flash explosion recycled material. Vacuum impregnation hydrophobic modification: Place the flash explosion recycled material into a vacuum impregnation tank and maintain it under vacuum for 10 to 15 minutes. Then inject the modification liquid, release the vacuum, pressurize to 0.2 to 0.4 MPa, and impregnate under pressure for 15 to 20 minutes. After removal, drain and dry to a moisture content of 3.0 to 4.5% to complete the pretreatment of recycled material shavings. Based on the total weight of the modified liquid, the modified liquid comprises the following components in parts by weight: 8-12 parts potassium methylsilicate, 1-3 parts perfluorooctyltriethoxysilane, 2-4 parts nano silica sol, and 80-90 parts water.

[0017] In one specific implementation, the total thickness of the low-absorption particleboard using recycled materials is 10-30 mm, and the thickness of the core layer is 70-80% of the total thickness.

[0018] In summary, this application has the following beneficial effects: 1. This application, through the three-layer plywood structural design, the introduction of pre-composite particles, pre-composite fiber network sheets, hydrophobic nano-silica aerogel powder and weather-resistant adhesive, and the optimized preparation process, can reduce the water absorption thickness expansion rate of recycled particleboard and reduce the defects of recycled particleboard that are prone to arching and warping in outdoor humid and alternating hot and cold environments.

[0019] 2. This application achieves a synergistic unity of rigid filling, nano-maze barrier, chemical bonding anchoring and stress dissipation by precompositing micron-sized carbonized wood powder, modified nano-montmorillonite, PU prepolymer and tannic acid into core-shell structured particles, thereby eliminating the main channels for water molecule capillary penetration between inorganic fillers and organic substrates.

[0020] 3. This application achieves a synergistic effect of hot-melt crack arrest and fiber bridging reinforcement by pre-compositing low-melting-point polyester fibers and hemp fibers into a semi-cured network felt. During hot pressing, LMPET spreads evenly along the hemp fiber network to form a continuous three-dimensional stress dissipation skeleton.

[0021] 4. This application reduces the water absorption rate of recycled wood shavings through three synergistic steps: alkaline alcohol desaccharification to degrade hydrophilic hemicellulose, wet heat flash explosion to open the pores of aged fibers, and vacuum impregnation hydrophobic modification to impart hydrophobic properties to the surface. Detailed Implementation

[0022] Unless otherwise specified, all raw materials used in this application are commercially available. Recycled wood shavings are shavings from discarded wooden furniture; shaving dimensions: length 15–35 mm, width 3–8 mm, thickness 0.5–2.0 mm, moisture content: 3.0%–4.5%. Hydrophobic nano-silica aerogel powder, particle size: 10–30 μm, density: 0.08 g / cm³, water contact angle ≥130°. Zinc borate, grade: C-ZB80M. Isocyanate-terminated polyurethane prepolymer, NCO content: 8%–12%, viscosity (25℃): 2000–5000 mPa·s. Tannic acid, CAS number: 1401-55-4, purity ≥85%, moisture content ≤5%. Micron-sized carbonized wood powder, poplar wood carbonized at 200–250℃ and then pulverized, particle size 80–150 mesh, moisture content ≤3%. Modified nano-montmorillonite, grade DK10. Polyester fiber is PET fiber, fiber fineness: 2-4 D, tensile strength ≥3.0 cN / dtex. Hemp fiber chopped strands are sisal fiber, fiber fineness 15-25μm, tensile strength ≥4.5 cN / dtex. Phenol, CAS No.: 108-95-2, purity ≥99%. Formaldehyde solution, concentration: 37% aqueous solution. Methylphenyl silicone resin, grade: IOTA 6056. Emulsified paraffin wax, grade / model: AD9108. Nano-silica sol is an aqueous nano-silica dispersion with a solid content of 30±2%. Potassium methylsilicate, grade / trade name: DK-104 potassium methylsilicate. Perfluorooctyltriethoxysilane, grade KH-F823. Adhesive is MDI adhesive with grade WANNATE® CW20.

[0023] The present application will be further described in detail below with reference to embodiments and comparative examples.

[0024] Example 1

[0025] This embodiment provides a low-swell particleboard using recycled materials, comprising an upper surface layer, a core layer, and a lower surface layer bonded together from top to bottom with adhesive. Both the upper and lower surface layers are 2.2 mm thick eucalyptus veneers, and the core layer is 13.4 mm thick. The total thickness of the low-swell particleboard using recycled materials is 17.6 mm. The core layer accounts for 75% of the total thickness.

[0026] The core layer comprises the following raw materials: 60 kg of recycled wood shavings, 14 kg of pre-composite granules, 8 kg of pre-composite fiber network sheet, 3 kg of hydrophobic nano-silica aerogel powder, 2 kg of zinc borate, and 16.5 kg of weather-resistant adhesive.

[0027] The pre-composite particles are prepared according to the following steps: The isocyanate-terminated polyurethane prepolymer was heated to 90°C to melt, and KH-560 silane coupling agent and tannic acid were added and stirred until homogeneous to obtain an activated liquid phase. The mass ratio of the isocyanate-terminated polyurethane prepolymer, KH-560 silane coupling agent, and tannic acid was 100:3.5:11.5.

[0028] Micron-sized carbonized wood powder and modified nano-montmorillonite were premixed at a mass ratio of 6.5:3 and put into a high-speed kneader. Under stirring, the activated liquid phase was atomized and sprayed in at a liquid-solid mass ratio of 1:2. The mixture was kneaded at 85°C for 20 minutes. The kneaded material was then fed into an extruder, extruded into strips, cooled and brittled, crushed and sieved to obtain pre-composite particles with a particle size between 0.5 and 2.0 mm.

[0029] The pre-composite fiber network sheet is prepared according to the following steps: Polyester fibers and chopped hemp fibers were opened and mixed at a mass ratio of 2:3, and a uniform fiber web was formed on an air-laid web machine. KH-550 silane coupling agent (1.0% of the total fiber weight) was sprayed on the web, and the mixture was heat-treated at 103℃ for 2.5 minutes to obtain a fiber network felt. This felt was then shredded to obtain a pre-composite fiber network sheet. The polyester fibers had a melting point of 115℃ and a length of 3 mm; the chopped hemp fibers had a length of 6.5 mm.

[0030] Weather-resistant adhesives are prepared according to the following steps: The weather-resistant adhesive comprises the following raw materials: 37.5 kg sodium hydroxide, 52.5 kg water, 110 kg phenol, 210 kg formaldehyde solution, 10 kg methyl phenyl silicone resin, 6.5 kg isocyanate-terminated polyurethane prepolymer, and 5 kg emulsified paraffin wax with a solid content of 60%.

[0031] Sodium hydroxide was dissolved in water and cooled to obtain a sodium hydroxide solution; the formaldehyde solution was divided into three portions by weight ratio of 130:73:7.

[0032] Preheat the reaction vessel to 42.5℃, add molten phenol to the reaction vessel, then add sodium hydroxide solution, and keep the temperature ≤50℃. Add the first portion of formaldehyde solution, keep the temperature ≤80℃, stir for 10 minutes, adjust the temperature to 72.5℃, add the second portion of formaldehyde solution, keep the temperature ≤80℃, and keep warm for 50 minutes. Add the third portion of formaldehyde solution, keep warm at 80℃ for 10 minutes, raise the temperature to boiling, keep boiling for 15 minutes, and cool to room temperature to obtain the modified resin solution.

[0033] Add methylphenyl silicone resin, isocyanate-terminated polyurethane prepolymer, and emulsified paraffin with a solid content of 60% to the modified resin solution, and stir until homogeneous to obtain the weather-resistant adhesive.

[0034] This embodiment also provides a process for preparing low-absorption-expansion particleboard using recycled materials, including the following steps: Mixing: Divide the weather-resistant adhesive into two equal parts. Put the recycled wood shavings into a drum mixer, add the first part of the weather-resistant adhesive, stir for 3 minutes, and then add the pre-composite granules and pre-composite fiber network sheet, the second part of the weather-resistant adhesive, hydrophobic nano silica aerogel powder and zinc borate in sequence. Stir evenly to obtain the core layer mixture.

[0035] Core layer preparation: The core layer mixture is laid into a gradient structure board using a mechanical laying machine, and then cold pre-pressed at a pressure of 2MPa for 45 seconds. Then hot-pressed for a total time of 10.5s / mm board thickness. The hot-pressed board is then aged for 60 hours at a temperature of 50℃ and a relative humidity of 40%. After trimming the edges, the core layer is obtained.

[0036] Composite process: Prepare an upper and lower surface layer. Apply an adhesive, specifically WANNATE® CW20 MDI adhesive, to the surfaces where the upper and lower surface layers will adhere to the core layer. Stack the upper, core, and lower surface layers sequentially and hot-press them at 130°C and 3.0 MPa for 8 minutes. After cooling, trimming, and sanding, a low-expansion particleboard made from recycled materials is obtained.

[0037] Example 2

[0038] The only difference between this embodiment and Embodiment 1 is that the core layer includes the following raw materials: 55 kg of recycled wood shavings, 12 kg of pre-composite granules, 6 kg of pre-composite fiber network sheet, 2 kg of hydrophobic nano silica aerogel powder, 1.5 kg of zinc borate, and 15 kg of weather-resistant adhesive.

[0039] Example 3

[0040] The only difference between this embodiment and Embodiment 1 is that the core layer includes the following raw materials: 65 kg of recycled wood shavings, 16 kg of pre-composite granules, 10 kg of pre-composite fiber network sheet, 4 kg of hydrophobic nano-silica aerogel powder, 2.5 kg of zinc borate, and 18 kg of weather-resistant adhesive.

[0041] Example 4

[0042] The only difference between this embodiment and Example 1 is that the pre-composite particles are prepared according to the following steps: The isocyanate-terminated polyurethane prepolymer was heated to 85°C to melt, and KH-560 silane coupling agent and tannic acid were added and stirred until homogeneous to obtain an activated liquid phase. The mass ratio of the isocyanate-terminated polyurethane prepolymer, KH-560 silane coupling agent, and tannic acid was 100:2:15.

[0043] Micron-sized carbonized wood powder and modified nano-montmorillonite were premixed at a mass ratio of 2:1 and put into a high-speed kneader. Under stirring, the activated liquid phase was atomized and sprayed into the kneader at a liquid-solid mass ratio of 7:13. The mixture was kneaded at 80°C for 15 minutes. The kneaded material was then fed into an extruder, extruded into strips, cooled and brittled, crushed and sieved to obtain pre-composite particles with a particle size between 0.5 and 2.0 mm.

[0044] Example 5

[0045] The only difference between this embodiment and Example 1 is that the pre-composite particles are prepared according to the following steps: The isocyanate-terminated polyurethane prepolymer was heated to 95°C to melt, and KH-560 silane coupling agent and tannic acid were added and stirred until homogeneous to obtain an activated liquid phase. The mass ratio of the isocyanate-terminated polyurethane prepolymer, KH-560 silane coupling agent, and tannic acid was 100:5:8.

[0046] Micron-sized carbonized wood powder and modified nano-montmorillonite were premixed at a mass ratio of 7:3 and put into a high-speed kneader. Under stirring, the activated liquid phase was atomized and sprayed into the kneader at a liquid-solid mass ratio of 7:15. The mixture was kneaded at 90°C for 25 minutes. The kneaded material was then fed into an extruder, extruded into strips, cooled and brittled, crushed and sieved to obtain pre-composite particles with a particle size between 0.5 and 2.0 mm.

[0047] Example 6

[0048] The only difference between this embodiment and Example 1 is that the pre-composite fiber network sheet is prepared according to the following steps: Polyester fibers and chopped hemp fibers were loosely mixed at a mass ratio of 8:11 and formed into a uniform fiber web on an air-laid web machine. KH-550 silane coupling agent (0.8% of the total fiber weight) was sprayed on the web, and the mixture was heat-treated at 100℃ for 2 minutes to obtain a fiber network felt. This felt was then shredded to obtain a pre-composite fiber network sheet. The polyester fibers had a melting point of 110℃ and a length of 2 mm; the chopped hemp fibers had a length of 5 mm.

[0049] Example 7

[0050] The only difference between this embodiment and Example 1 is that the pre-composite fiber network sheet is prepared according to the following steps: Polyester fibers and chopped hemp fibers were loosely mixed at a mass ratio of 8:13 and formed into a uniform fiber web on an air-laid web machine. KH-550 silane coupling agent (1.2% of the total fiber weight) was sprayed on the web, and the mixture was heat-treated at 105℃ for 3 minutes to obtain a fiber network felt. This felt was then shredded to obtain a pre-composite fiber network sheet. The polyester fibers had a melting point of 120℃ and a length of 4 mm; the chopped hemp fibers had a length of 8 mm.

[0051] Example 8

[0052] The only difference between this embodiment and Example 1 is that the weather-resistant adhesive is prepared according to the following steps: The weather-resistant adhesive comprises the following raw materials: 30 kg sodium hydroxide, 45 kg water, 100 kg phenol, 190 kg formaldehyde solution, 8 kg methyl phenyl silicone resin, 5 kg isocyanate-terminated polyurethane prepolymer, and 4 kg emulsified paraffin wax with a solid content of 60%.

[0053] Sodium hydroxide was dissolved in water and cooled to obtain a sodium hydroxide solution; the formaldehyde solution was divided into three portions by weight ratio of 120:65:7.

[0054] Preheat the reaction vessel to 40°C, add the molten phenol to the reaction vessel, then add sodium hydroxide solution, and keep the temperature ≤50°C. Add the first portion of formaldehyde solution, keep the temperature ≤80°C, stir for 10 minutes, adjust the temperature to 70°C, add the second portion of formaldehyde solution, keep the temperature ≤80°C, keep warm for 40 minutes, then add the third portion of formaldehyde solution, keep warm at 80°C for 10 minutes, raise the temperature to boiling, keep boiling for 10 minutes, and cool to room temperature to obtain the modified resin solution.

[0055] Add methylphenyl silicone resin, isocyanate-terminated polyurethane prepolymer, and emulsified paraffin with a solid content of 60% to the modified resin solution, and stir until homogeneous to obtain the weather-resistant adhesive.

[0056] Example 9

[0057] The only difference between this embodiment and Example 1 is that the weather-resistant adhesive is prepared according to the following steps: The weather-resistant adhesive comprises the following raw materials: 45 kg sodium hydroxide, 60 kg water, 120 kg phenol, 230 kg formaldehyde solution, 12 kg methyl phenyl silicone resin, 8 kg isocyanate-terminated polyurethane prepolymer, and 6 kg emulsified paraffin wax with a solid content of 60%.

[0058] Sodium hydroxide was dissolved in water and cooled to obtain a sodium hydroxide solution; the formaldehyde solution was divided into three portions by weight ratio of 140:80:7.

[0059] Preheat the reaction vessel to 45°C, add molten phenol to the reaction vessel, then add sodium hydroxide solution, maintain the temperature ≤50°C, add the first portion of formaldehyde solution, maintain the temperature ≤80°C, stir for 10 minutes, adjust the temperature to 75°C, add the second portion of formaldehyde solution, maintain the temperature ≤80°C, keep warm for 60 minutes, then add the third portion of formaldehyde solution, keep warm at 80°C for 10 minutes, raise the temperature to boiling, keep boiling for 20 minutes, cool to room temperature, and obtain the modified resin solution.

[0060] Add methylphenyl silicone resin, isocyanate-terminated polyurethane prepolymer, and emulsified paraffin with a solid content of 60% to the modified resin solution, and stir until homogeneous to obtain the weather-resistant adhesive.

[0061] Example 10

[0062] The only difference between this embodiment and Embodiment 1 is that both the upper and lower surface layers are 1.5mm thick eucalyptus veneers, and the core layer is 7mm thick. The total thickness of the low-expansion particleboard using recycled materials is 10mm. The core layer is 70% of the total thickness.

[0063] Example 11

[0064] The only difference between this embodiment and Embodiment 1 is that both the upper and lower surface layers are 3.0 mm thick eucalyptus veneers, and the core layer is 24 mm thick. The total thickness of the low-expansion particleboard using recycled materials is 30 mm. The core layer accounts for 80% of the total thickness.

[0065] Example 12

[0066] The only difference between this embodiment and Embodiment 1 is the preparation process of the low-expansion particleboard using recycled materials, which includes the following steps: Mixing: Divide the weather-resistant adhesive into two equal parts. Put the recycled wood shavings into a drum mixer, add the first part of the weather-resistant adhesive, stir for 3 minutes, and then add the pre-composite granules and pre-composite fiber network sheet, the second part of the weather-resistant adhesive, hydrophobic nano silica aerogel powder and zinc borate in sequence. Stir evenly to obtain the core layer mixture.

[0067] Core layer preparation: The core layer mixture is laid into a gradient structure board using a mechanical paving machine, and then cold pre-pressed at a pressure of 1.5 MPa for 30 seconds. Then hot-pressed for a total time of 9 seconds per mm of board thickness. The hot-pressed board is then aged at 45°C and 35% relative humidity for 48 hours. After trimming the edges, the core layer is obtained.

[0068] Composite process: Prepare an upper and lower surface layer. Apply an adhesive, specifically WANNATE® CW20 MDI adhesive, to the surfaces where the upper and lower surface layers will adhere to the core layer. Stack the upper, core, and lower surface layers sequentially and hot-press them at 130°C and 3.0 MPa for 8 minutes. After cooling, trimming, and sanding, a low-expansion particleboard made from recycled materials is obtained.

[0069] Example 13

[0070] The only difference between this embodiment and Embodiment 1 is the preparation process of the low-expansion particleboard using recycled materials, which includes the following steps: Mixing: Divide the weather-resistant adhesive into two equal parts. Put the recycled wood shavings into a drum mixer, add the first part of the weather-resistant adhesive, stir for 3 minutes, and then add the pre-composite granules and pre-composite fiber network sheet, the second part of the weather-resistant adhesive, hydrophobic nano silica aerogel powder and zinc borate in sequence. Stir evenly to obtain the core layer mixture.

[0071] Core layer preparation: The core layer mixture is laid into a gradient structure board using a mechanical paving machine, and then cold pre-pressed at a pressure of 2.5 MPa for 60 seconds. Then hot-pressed for a total time of 12 seconds per mm of board thickness. The hot-pressed board is then aged at 55°C and 45% relative humidity for 72 hours. After trimming, the core layer is obtained.

[0072] Composite process: Prepare an upper and lower surface layer. Apply an adhesive, specifically WANNATE® CW20 MDI adhesive, to the surfaces where the upper and lower surface layers will adhere to the core layer. Stack the upper, core, and lower surface layers sequentially and hot-press them at 130°C and 3.0 MPa for 8 minutes. After cooling, trimming, and sanding, a low-expansion particleboard made from recycled materials is obtained.

[0073] Example 14

[0074] The only difference between this embodiment and Embodiment 1 is that, in the mixing step of the preparation process of low-expansion particleboard using recycled materials, the recycled wood shavings undergo the following pretreatment before use: Sugar removal treatment: The recycled wood shavings are immersed in a mixed aqueous solution for 3 hours to obtain sugar-removed recycled wood. The mixed aqueous solution contains 1.5% NaOH and 4.5% ethanol by mass.

[0075] Moist heat flash explosion treatment: The desugared recycled material is placed in a pressure vessel, saturated steam is introduced, and it is kept at 148℃ and 0.5MPa for 25 minutes. The pressure is then released instantly to obtain the flash explosion recycled material.

[0076] Vacuum impregnation hydrophobic modification: Place the flash explosion recycled material into a vacuum impregnation tank, evacuate to -0.085MPa, maintain the vacuum for 12.5 minutes, then inject the modification liquid, release the vacuum, pressurize to 0.3MPa, maintain the pressure for impregnation for 17.5 minutes, remove and drain, and dry to a moisture content of 3.8%, thus completing the pretreatment of the recycled material shavings.

[0077] The modified solution includes the following components: 10 kg of potassium methylsilicate, 2 kg of perfluorooctyltriethoxysilane, 3 kg of nano silica sol, and 85 kg of water.

[0078] Example 15

[0079] The only difference between this embodiment and Embodiment 1 is that, in the mixing step of the preparation process of low-expansion particleboard using recycled materials, the recycled wood shavings undergo the following pretreatment before use: Sugar removal treatment: The recycled wood shavings are immersed in a mixed aqueous solution for 2 hours to obtain sugar-removed recycled wood. The mixed aqueous solution contains 1% NaOH and 3% ethanol by mass.

[0080] Moist heat flash explosion treatment: The desugared recycled material is placed in a pressure vessel, saturated steam is introduced, and it is kept at 140℃ and 0.4MPa for 20 minutes. The pressure is then released instantly to obtain the flash explosion recycled material.

[0081] Vacuum impregnation hydrophobic modification: Place the flash explosion recycled material into a vacuum impregnation tank, evacuate to -0.085MPa, maintain the vacuum for 10 minutes, then inject the modification liquid, release the vacuum, pressurize to 0.2MPa, maintain the pressure for 15 minutes, remove and drain, and dry to a moisture content of 3.0%, thus completing the pretreatment of the recycled material shavings.

[0082] The modified solution includes the following components: 8 kg of potassium methylsilicate, 1 kg of perfluorooctyltriethoxysilane, 2 kg of nano silica sol, and 80 kg of water.

[0083] Example 16

[0084] The only difference between this embodiment and Embodiment 1 is that, in the mixing step of the preparation process of low-expansion particleboard using recycled materials, the recycled wood shavings undergo the following pretreatment before use: Sugar removal treatment: The recycled wood shavings are immersed in a mixed aqueous solution for 4 hours to obtain sugar-removed recycled wood. The mixed aqueous solution contains 2% NaOH and 6% ethanol by mass.

[0085] Moist heat flash explosion treatment: The desugared recycled material is placed in a pressure vessel, saturated steam is introduced, and it is kept at 155℃ and 0.6MPa for 30 minutes. The pressure is then released instantly to obtain the flash explosion recycled material.

[0086] Vacuum impregnation hydrophobic modification: Place the flash explosion recycled material into a vacuum impregnation tank, evacuate to -0.085MPa, maintain the vacuum for 15 minutes, then inject the modification liquid, release the vacuum, pressurize to 0.4MPa, maintain the pressure for 20 minutes, remove and drain, and dry to a moisture content of 4.5% to complete the pretreatment of the recycled material shavings.

[0087] The modified solution includes the following components: 12 kg of potassium methylsilicate, 3 kg of perfluorooctyltriethoxysilane, 4 kg of nano silica sol, and 90 kg of water.

[0088] Example 17

[0089] The only difference between this embodiment and Embodiment 1 is that poplar veneer of the same thickness is used instead of eucalyptus veneer.

[0090] Comparative Example 1 The only difference between this comparative example and Example 1 is that, in the raw materials and preparation process of the core layer, an equal amount of recycled wood shavings are used to replace the pre-composite particles.

[0091] Comparative Example 2 The only difference between this comparative example and Example 1 is that, in the raw materials and preparation process of the core layer, an equal amount of recycled wood shavings are used to replace the pre-composite fiber network sheet.

[0092] Comparative Example 3 The only difference between this comparative example and Example 1 is that, in the raw materials and preparation process of the core layer, an equal amount of recycled wood shavings are used to replace the hydrophobic nano-silica aerogel powder.

[0093] Comparative Example 4 The only difference between this comparative example and Example 1 is that, in the raw materials and preparation process of the core layer, an equal amount of melamine-modified urea-formaldehyde resin adhesive is used to replace the weather-resistant adhesive.

[0094] Performance testing The following performance tests were conducted on Examples 1-17 and Comparative Examples 1-4: According to GB / T 17657-2013 "Test Methods for Physical and Chemical Properties of Wood-based Panels and Decorative Wood-based Panels", the following were tested: 24-hour water absorption thickness expansion rate (%), peel strength between core layer and veneer (MPa), change in warpage after thermal cycling (-20℃ / 60℃, 20 times) (mm / m), and retention rate of static bending strength after water immersion at 70℃ (%). The test results are shown in Table 1.

[0095] Table 1

[0096] Combining Example 1 and Comparative Examples 1-4 with Table 1, it can be seen that compared to Example 1, Comparative Examples 1-4 exhibit significantly higher 24-hour water absorption thickness swelling rates, significantly lower core-to-veneer interface peel strength, significantly larger changes in warpage after thermal cycling (-20℃ / 60℃, 20 cycles), and significantly lower static bending strength retention after immersion in water at 70℃. This indicates that using the raw material ratio and preparation process of Example 1 can reduce the water absorption thickness swelling rate of recycled particleboard and also reduce the defects of recycled particleboard being prone to warping and buckling in outdoor humid and alternating hot and cold environments. Pre-composite particles, pre-composite fiber network sheets, hydrophobic nano-silica aerogel powder, and weather-resistant adhesives play an indispensable synergistic role in achieving low water absorption swelling, high stability, and high water resistance.

[0097] As can be seen from Examples 1-17 and Table 1, Examples 1-17 all exhibited low 24-hour water absorption thickness expansion rates, high peel strength at the core-to-veneer interface, minimal warping changes during thermal cycling (-20℃ / 60℃, 20 cycles), and high static bending strength retention rates after immersion in water at 70℃. This indicates that using the raw material ratios and process conditions within the range of Examples 1-17 can reduce the water absorption thickness expansion rate of recycled particleboard and also mitigate the defects of recycled particleboard prone to warping and buckling in outdoor humid and alternating hot and cold environments.

[0098] By comparing the test data of each embodiment, it can be seen that the data of Embodiments 14-16 are all better than those of Embodiment 1. This shows that systematic desugaring, flash explosion and hydrophobic modification treatment of recycled materials can further improve their performance.

[0099] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A low-absorption-expansion particleboard using recycled materials, characterized in that, It includes an upper surface layer, a core layer, and a lower surface layer bonded together from top to bottom by an adhesive. The core layer comprises the following raw materials in parts by weight: 55-65 parts recycled wood shavings, 12-16 parts pre-composite granules, 6-10 parts pre-composite fiber network sheet, 2-4 parts hydrophobic nano-silica aerogel powder, 1.5-2.5 parts zinc borate, and 15-18 parts weather-resistant adhesive.

2. The low-absorption-expansion particleboard using recycled materials according to claim 1, characterized in that, The upper and lower surface layers are the same type of eucalyptus veneer or poplar veneer with a thickness of 1.5 to 3.0 mm.

3. The low-absorption-expansion particleboard using recycled materials according to claim 1, characterized in that, The pre-composite particles are prepared according to the following steps: The isocyanate-terminated polyurethane prepolymer is heated to 85-95°C to melt, and a silane coupling agent and tannic acid are added and stirred evenly to obtain an activated liquid phase; the mass ratio of the isocyanate-terminated polyurethane prepolymer, the silane coupling agent and the tannic acid is 100:(2-5):(8-15). Micron-sized carbonized wood powder and modified nano-montmorillonite are premixed at a mass ratio of (6-7):3 and put into a high-speed kneader. Under stirring, the activated liquid phase is atomized and sprayed into the kneader at a liquid-solid mass ratio of 7:(13-15). The kneader is kept at 80-90℃ for 15-25 minutes. The kneaded material is extruded into strips, cooled and brittled, then crushed and sieved to obtain pre-composite particles with a particle size of 0.5-2.0 mm.

4. The low-absorption-expansion particleboard using recycled materials according to claim 1, characterized in that, The pre-composite fiber network sheet is prepared according to the following steps: Polyester fiber and hemp fiber chopped strands are opened and mixed at a mass ratio of 8:(11-13), and a uniform fiber web is formed on an air-laid web machine. Silane coupling agent accounting for 0.8-1.2% of the total fiber weight is sprayed on the web, and the web is heat-treated at 100-105℃ for 2-3 minutes to obtain a fiber network felt. The felt is then chopped to obtain a pre-composite fiber network sheet.

5. The low-absorption-expansion particleboard using recycled materials according to claim 4, characterized in that, The polyester fiber has a melting point of 110-120°C and a length of 2-4 mm; the chopped hemp fiber has a length of 5-8 mm.

6. The low-absorption-expansion particleboard using recycled materials according to claim 1, characterized in that, The weather-resistant adhesive is prepared according to the following steps: The weather-resistant adhesive comprises the following raw materials in parts by weight: 30-45 parts sodium hydroxide, 45-60 parts water, 100-120 parts phenol, 190-230 parts formaldehyde solution, 8-12 parts methyl phenyl silicone resin, 5-8 parts isocyanate-terminated polyurethane prepolymer, and 4-6 parts emulsified paraffin wax with a solid content of 60%. Sodium hydroxide was dissolved in water and cooled to obtain a sodium hydroxide solution; the formaldehyde solution was divided into three portions by weight ratio (120-140):(65-80):

7. Preheat the reaction vessel to 40-45℃, add molten phenol to the reaction vessel, then add sodium hydroxide solution, keep the temperature ≤50℃, add the first part of formaldehyde solution, keep the temperature ≤80℃, stir for 10 minutes, adjust the temperature to 70-75℃, add the second part of formaldehyde solution, keep the temperature ≤80℃, keep warm for 40-60 minutes, then add the third part of formaldehyde solution, keep warm at 80℃ for 10 minutes, raise the temperature to boiling, keep boiling for 10-20 minutes, cool to room temperature to obtain the modified resin solution; Add methylphenyl silicone resin, isocyanate-terminated polyurethane prepolymer, and emulsified paraffin with a solid content of 60% to the modified resin solution, and stir until homogeneous to obtain the weather-resistant adhesive.

7. A process for preparing low-absorption-expansion particleboard using recycled materials as described in any one of claims 1-6, characterized in that, Includes the following steps: Mixing: Divide the weather-resistant adhesive into two parts, put the recycled wood shavings into the drum mixer, add the first part of the weather-resistant adhesive, stir evenly, then add the pre-composite granules and pre-composite fiber network sheet, the second part of the weather-resistant adhesive, hydrophobic nano silica aerogel powder and zinc borate in sequence, stir evenly to obtain the core layer mixture; Core layer preparation: The core layer mixture is laid into a gradient structure board blank, and cold pre-pressed. The pre-pressing pressure is 1.5-2.5MPa and the pre-pressing time is 30-60 seconds. Then hot-pressing is performed. The total hot-pressing time is 9-12s / mm board thickness. After hot pressing, the board is aged at a temperature of 45-55℃ and a relative humidity of 35-45% for 48-72 hours. The edges are then trimmed to obtain the core layer. Composite process: Prepare an upper and lower surface layer, apply adhesive to the surfaces of the upper and lower surface layers that are to be bonded to the core layer, stack the upper surface layer, core layer and lower surface layer in sequence, and then perform hot pressing, cooling, edge trimming and sanding to obtain a low-expansion particleboard using recycled materials.

8. The preparation process of low-absorption-expansion particleboard using recycled materials according to claim 7, characterized in that, The recycled wood shavings undergo the following pretreatment before use: Sugar removal treatment: Immerse the recycled wood shavings in a mixed aqueous solution for 2-4 hours to obtain sugar-removed recycled wood; the mixed aqueous solution contains 1-2% NaOH and 3-6% ethanol by mass. Moist heat flash explosion treatment: Place the desugared recycled material in a pressure vessel, introduce saturated steam, and keep it at 140-155℃ and 0.4-0.6MPa for 20-30 minutes. Depressurize to obtain the flash explosion recycled material. Vacuum impregnation hydrophobic modification: Place the flash explosion recycled material into a vacuum impregnation tank and maintain it under vacuum for 10 to 15 minutes. Then inject the modification liquid, release the vacuum, pressurize to 0.2 to 0.4 MPa, and impregnate under pressure for 15 to 20 minutes. After removal, drain and dry to a moisture content of 3.0 to 4.5% to complete the pretreatment of recycled material shavings. Based on the total weight of the modified liquid, the modified liquid comprises the following components in parts by weight: 8-12 parts potassium methylsilicate, 1-3 parts perfluorooctyltriethoxysilane, 2-4 parts nano silica sol, and 80-90 parts water.

9. The preparation process of low-absorption-expansion particleboard using recycled materials according to claim 7, characterized in that, The total thickness of the low-absorption particleboard using recycled materials is 10-30 mm, and the thickness of the core layer is 70-80% of the total thickness.

Images