Preparation method of laminated timber with stable size and high strength

Abstract

The invention provides a preparation method of a stable-size and high-strength laminated timber, which comprises the following steps of: mixing boric acid and choline chloride, and heating and melting at 90 DEG C to form a uniform, stable and transparent liquid, so as to obtain a deep eutectic solvent DES; the preparation method comprises the following steps: under the vacuum degree of-0.1 MPa, dipping wood veneers in DES, performing high-temperature steam sterilization treatment under the condition of 121 DEG C, assembling the veneers subjected to multi-layer treatment according to a rift-grain mode, and performing hot pressing at 160 DEG C to obtain the laminated timber with stable size and high strength. The prepared laminated timber has dimensional stability and good mechanical properties, has structural applicability of direct contact with a moisture environment, and has the advantages of mildew resistance, corrosion resistance, flame retardance and the like.

Description

Technical Field

[0001] This invention belongs to the field of wood processing technology, and specifically relates to a method for preparing dimensionally stable, high-strength laminated lumber. Background Technology

[0002] Currently, the supply and demand imbalance of timber resources in my country is becoming increasingly severe. Fast-growing timber from plantations is gradually becoming the main raw material source for the timber industry. However, this type of timber generally suffers from problems such as softness and low density, limiting its application. Dense laminated veneer lumber (DLV) is a type of structural engineered wood product developed based on the densification of plantation timber. Its density, surface hardness, and modulus of elasticity are significantly improved compared to ordinary LPV. A typical process includes veneer cutting, impregnation, drying, assembly, hot pressing, and post-treatment. To ensure the bonding strength and durability of DLV, existing processes generally rely on synthetic resin adhesives such as urea-formaldehyde and phenol-formaldehyde resins, which easily trigger the release of volatile organic compounds such as formaldehyde, posing health and environmental risks and contradicting the concept of green and sustainable development. Furthermore, improper control of process parameters can easily lead to bonding defects, delamination, or internal stress concentration, thereby affecting the yield and long-term dimensional stability. In addition, conventional products are inherently deficient in functional properties such as flame retardancy, corrosion resistance, and mildew resistance. Subsequent additional functional treatments not only increase manufacturing costs but may also cause surface cracking or deterioration of mechanical properties due to chemical treatments interfering with the material structure. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to provide a method for preparing dimensionally stable and high-strength laminated materials, which addresses the shortcomings of the prior art. The laminated materials prepared by this method have dimensional stability and good mechanical properties, are structurally suitable for direct contact with moisture environments, and have advantages such as mildew resistance, corrosion resistance, and flame retardancy.

[0004] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is: a method for preparing dimensionally stable, high-strength laminated materials, the method being as follows: Preparation of S1 and DES: Boric acid and choline chloride are mixed and heated to melt at 90°C. The mixture is stirred until a homogeneous, stable and transparent liquid is formed, which is then obtained as a eutectic solvent, denoted as DES. S2, Veneer Impregnation: Under a vacuum of -0.1 MPa, wood veneer is impregnated in DES obtained in S1 to obtain impregnated veneer; S3, Steam treatment: The impregnated veneer obtained in S2 is subjected to high-temperature steam sterilization at a temperature of 121℃ to obtain the treated veneer. S4. The processed veneers obtained in S3 are assembled in the same grain pattern and hot-pressed at a temperature of 160℃ to obtain dimensionally stable, high-strength laminated material.

[0005] This invention uses a low-melting-point solvent (DES) composed of boric acid (hydrogen bond donor) and choline chloride (hydrogen bond acceptor). The adjustable composition of the hydrogen bond donor and acceptor endows the material with multifunctional properties such as flame retardancy, mildew resistance, and corrosion resistance. By modifying the veneer and reconstructing the wood components in situ, compression densification and lamination are simultaneously achieved at high temperatures, thus preparing "compressed" laminated lumber with high dimensional stability and excellent mechanical strength.

[0006] Preferably, the molar ratio of boric acid and choline chloride in S1 is 1:1.

[0007] Preferably, the wood veneer described in S2 is made of radiata pine.

[0008] Preferably, the immersion time in S2 is 1 hour.

[0009] Preferably, the high-temperature steam sterilization process in S3 takes 1 hour.

[0010] Preferably, the hot pressing conditions in S4 are: 2MPa, 1h.

[0011] Preferably, the thickness of the dimensionally stable, high-strength laminated material described in S4 is 6 mm.

[0012] Preferably, the dimensionally stable, high-strength laminated material described in S4 has a deformation recovery rate of 4.8% to 5.5%, a static bending strength of 98 MPa to 103 MPa, an elastic modulus of 7.2 GPa to 8.1 GPa, a bonding strength of 2.8 MPa to 3.2 MPa, a boiling water bonding strength of 1.3 MPa, and possesses anti-corrosion, anti-mildew, and flame-retardant properties.

[0013] Compared with the prior art, the present invention has the following advantages: This invention pretreats wood veneers with a eutectic solvent (choline chloride + boric acid), then impregnates the wood with organic / inorganic components until densely packed. Following hot pressing (with temperature-assisted compression), the hemicellulose, amorphous cellulose, and lignin in the wood undergo in-situ depolymerization or degradation due to the eutectic solvent pretreatment. Then, with temperature-assisted compression, they condense or repolymerize to form a cross-linked network, achieving deformation fixation and aiding in the densification of the wood. The resulting laminated lumber is a "compressed" laminated lumber, unlike existing naturally dense laminated lumbers. The "compressed" laminated lumber prepared by this invention exhibits excellent dimensional stability and mechanical properties, high strength, lower deformation recovery rate (4.8%–5.5%), higher static bending strength (98 MPa–103 MPa), good elastic modulus (7.2 GPa–8.1 GPa), and dry-wet bonding strength of 2.8 MPa–3.2 MPa, and boiling water bonding strength of 1.3 MPa. MPa, preventing mechanical degradation caused by water. The "compressed" laminate prepared by this invention has structural applicability to direct contact with water environment and has advantages such as mildew resistance, corrosion resistance and flame retardancy.

[0014] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments. Attached Figure Description

[0015] Figure 1 This is the DLVL of Embodiment 1 of the present invention. 140 DLVL 160 and DLVL 180 Dry-wet bond strength diagram.

[0016] Figure 2 This is the DLVL of Embodiment 1 of the present invention. 140 DLVL 160 and DLVL 180 Boiling water bond strength diagram.

[0017] Figure 3 This is the DLVL of Embodiment 1 of the present invention. 140 DLVL 160 and DLVL 180 The graph shows the elastic modulus (left) and static bending strength (right).

[0018] Figure 4 This is the DLVL of Embodiment 1 of the present invention. 160 The mass loss of untreated NW wood after 90 days of treatment with Trametes versicolor and Gloeophyllum trabeum, and the degree of biodegradation damage after 14 days of treatment with Aspergillus niger.

[0019] Figure 5This is the DLVL of Embodiment 1 of the present invention. 160 Deformation recovery rate graph after 3 cycles of soaking-drying.

[0020] Figure 6 This is the DLVL of Embodiment 1 of the present invention. 160 A diagram of a spray gun burning test on untreated NW wood. Detailed Implementation

[0021] Example 1 The method for preparing the dimensionally stable, high-strength laminated material in this embodiment is as follows: Preparation of S1 and DES: Boric acid and choline chloride are mixed in a molar ratio of 1:1 and then heated to melt at 90°C. The mixture is stirred until a homogeneous, stable and transparent liquid is formed, which is the eutectic solvent, denoted as DES. S2, Veneer Impregnation: Under a vacuum of -0.1 MPa, a 100 mm × 50 mm × 4.5 mm wood veneer (tree species: radiata pine) was impregnated in DES obtained in S1 to obtain the impregnated veneer. S3, Steam treatment: The impregnated veneer obtained in S2 was subjected to high-temperature steam sterilization at 121℃ for 1 hour to obtain the treated veneer. S4. The treated veneers obtained in S3 are assembled in a 3-layer parallel grain pattern and hot-pressed at 160℃ and 2MPa for 1 hour to obtain a dimensionally stable, high-strength laminated material with target dimensions of 100 mm × 50 mm × 6 mm. The prepared laminated material is denoted as DLVL. 160 .

[0022] This embodiment also included hot-pressing at temperatures of 140°C and 180°C, with the resulting laminated materials denoted as DLVL. 140 DLVL 180 As a comparison.

[0023] For the prepared DLVL 140 DLVL 160 and DLVL 180 Perform performance testing.

[0024] (a) Mechanical property testing—bonding strength Internal bond strength (adhesion strength) test: Refer to section 5.3.2 of GB / T 98463—2015.

[0025] 1. Comparison of dry and wet bond strength: For DLVL140 DLVL 160 and DLVL 180 Dry-wet bonding strength was compared (drying conditions: moisture content 8-12%; cold water soaking: soaking in cold water at 30±3℃ for 2 h, followed by drying at 63±+℃ for 1 h, and then leaving at room temperature for 10 min. This process corresponds to Class III non-moisture-resistant plywood in section 5.3.2 of GB / T 98463-2015).

[0026] like Figure 1 As shown, DLVL 140 DLVL 160 and DLVL 180 The internal bond strengths in the dry state were 1.5 MPa, 3.2 MPa and 2.4 MPa, respectively; after being soaked in cold water, their strengths decreased to 1.0 MPa, 2.8 MPa and 1.3 MPa, respectively.

[0027] All samples met the minimum internal bond strength requirements (≥0.7 MPa) for Class III plywood (applicable to dry use conditions) in GB / T 9846—2015.

[0028] The results show that the preparation method of the present invention can effectively improve the mechanical properties of the material. Among them, DLVL160 not only exhibits the best internal bonding strength in the dry state but also has a high performance retention rate in the wet state, and has the potential to be applied to environments with intermittent contact with moisture.

[0029] 2. Comparison of boiling water bonding strength: For DLVL 140 DLVL 160 and DLVL 180 Comparison of boiling water bond strength (boiling water: boiling test, corresponding to Class I weather-resistant plywood in section 5.3.2 of GB / T98463-2015).

[0030] Boiling test: Refer to GB / T 17657-1999 4.15-4.2 Class I plywood. The specific steps are as follows: place the sample in boiling water and boil for 4 h, then dry it at 63±3℃ for 20 h, boil it again for 4 h, and finally take it out and cool it at room temperature for 10 min.

[0031] like Figure 2 DLVL 140 DLVL 160 and DLVL 180 After the boiling test (boiling-drying-boiling), the internal bond strength decreased in all cases, from 1.5, 3.2, and 2.4 MPa, respectively. Figure 1 The pressure dropped to 0.3 MPa, 1.3 MPa and 0.8 MPa. Figure 2 Of these, only DLVL 160 and DLVL 180 It meets the minimum internal bond strength requirement (≥0.8 MPa) for Class I plywood (weather-resistant plywood suitable for outdoor use) in GB / T 9846—2015. It is worth noting that DLVL... 160 The strength is significantly higher than the national standard limit (0.8 MPa), indicating that the material is structurally suitable for direct contact with water environments and shows its application potential as an alternative to traditional non-renewable building materials.

[0032] (II) Mechanical property testing—static bending strength and modulus of elasticity Static bending strength and modulus of elasticity test: Refer to section 5.3.4 of GB / T 98463—2015.

[0033] For DLVL 140 DLVL 160 and DLVL 180 Perform elastic modulus ( Figure 3 (Left figure) and static bending strength ( Figure 3 (Right image) Comparison (Dry: drying conditions; Wet: soaking in room temperature water for 24 hours).

[0034] To investigate the effect of hot pressing temperature on mechanical properties, DLVL with similar densities was selected. 140 DLVL 160 and DLVL 180 An evaluation was conducted. The results are as follows: Figure 3 As shown, under dry conditions, the initial elastic moduli of the three materials were 3.2 GPa, 8.1 GPa, and 5.7 GPa, respectively, indicating that as the hot-pressing temperature increased from 140°C to 180°C, the elastic modulus showed a trend of first increasing and then decreasing. After 24 hours of immersion in room temperature water, DLVL... 140 DLVL 160 and DLVL 180 The elastic moduli decreased to 1.5 GPa, 7.2 GPa and 3.4 GPa, respectively. Figure 3 (Left image).

[0035] The trend of static bending strength is consistent with that of elastic modulus: as the hot pressing temperature increases from 140°C to 180°C, DLVL... 140 The static bending strength decreased from 32 MPa to 17 MPa, DLVL 160 The pressure decreased slightly from 103 MPa to 98 MPa, while DLVL 180 The pressure then decreased significantly from 72 MPa to 28 MPa. Figure 3 (Right image).

[0036] Therefore, DLVL160 It exhibits excellent dimensional stability, and its mechanical properties (including elastic modulus and static bending strength) remain at a high level even under water immersion conditions.

[0037] (iii) Anti-corrosion and anti-mildew capabilities Preservation resistance test: The soil-wood block method was used in accordance with the national standard GB / T 13942.1−2009 "Durability of Wood - Part 1: Laboratory Test Methods for Natural Preservation Resistance" and the American Wood Protection Association standard AWPA E10-12. A 250 mL wide-mouth glass culture bottle with a screw cap was used. 110 g of air-dried 20-40 mesh soil was added to the bottle, followed by 22 mL of deionized water. The mixture was gently shaken to level the soil surface. The culture bottles were then placed in a steam autoclave and sterilized at 121℃ for 1 hour. After cooling, four pieces of wood were placed in each culture bottle, along with 4 mL of maltose solution. A 1 cm thick layer of wood was inserted between the four pieces of wood. 3 The mycelial blocks were then pre-cultured in a constant temperature and humidity incubator at 28°C and 75% relative humidity for 3 weeks. Afterwards, sterilized test samples (DLVL laminated material prepared in Example 1) were inoculated. 160 Eight replicates were set up for each group (compared to the control plate NW). Samples were removed after 12 weeks (90 days) of decay incubation, and their oven-dry weight was measured; oven-dry weight = (weight before decay × weight after decay) / weight before decay. The decay resistance grades are shown in Table 1.

[0038] Table 1 Corrosion Resistance Rating Mold prevention test: Referring to GB / T 18261-2013 "Test Method for the Efficacy of Mold Inhibitors against Wood Molds and Discoloration Fungi", samples were cut to appropriate sizes and placed in a constant temperature and humidity chamber (temperature 28°C, relative humidity 80%) for a 14-day mold prevention test under simulated indoor conditions. Six replicate samples were set up for each group. After the test, the mold situation was assessed by combining digital photography and visual observation, and the mold infection area rate (i.e., the ratio of infected area to total area) was calculated. The damage values ​​are shown in Table 2.

[0039] Table 2 Damage values ​​of the samples Figure 4The graph shows the mass loss after 90 days of treatment with Trametes versicolor (white rot fungus) and Gloeophyllum trabeum (brown rot fungus), and the damage degree after 14 days of treatment with Aspergillus niger (black mold). (NW in the graph represents veneer, i.e., untreated wood (tree species: radiata pine).

[0040] After 90 days of white rot fungus testing, NW's mass loss rate reached 43%, and its rot resistance level was Grade III, while DLVL... 160 The rot resistance rate was only 7%, with a resistance level of I; in the brown rot fungus test, the NW mass loss rate was 56%, with a resistance level of IV, and DLVL... 160 The value is 9%, and the corrosion resistance grade is Class I. The results show that DLVL... 160 It exhibits excellent corrosion resistance (Grade I) under the action of both types of decay fungi, and has strong resistance to biodegradation, which can effectively ensure its long-term stability in outdoor environments and significantly extend the service life of building materials.

[0041] After 14 days of Aspergillus niger invasion, the surface of NW was extensively covered with mold, with a damage value of 4, while DLVL... 160 With an infestation level (damage value) close to 0, virtually no mold adheres, demonstrating excellent anti-mold performance. This characteristic helps prevent indoor air pollution and the spread of microorganisms, thus contributing to the health and safety of residents in building applications.

[0042] In summary, the DLVL prepared in this embodiment... 160 It has outstanding anti-corrosion and anti-mildew capabilities.

[0043] (iv) Dimensional stability Deformation recovery test: The dried sample was completely immersed in room temperature water for 7 days, then removed and dried at 60℃ to constant weight. Six replicate samples were set up for each experiment, and the average result was taken. The formula for calculating the deformation recovery rate is as follows: SR = (t) r -t0) / (t u -t0)×100%; In the formula, t r t0 is the thickness of the dried sample after rehydration, in mm; t0 is the thickness of the dried sample after densification .... u The thickness of the dried sample before densification is shown in mm.

[0044] This test repeated the soaking-drying operation three times, i.e., soaking-drying (7 days)-soaking-drying (7 days)-soaking-drying (7 days), to examine its long-term dimensional stability.

[0045] like Figure 5 As shown, during the 7-day water immersion test, the deformation recovery rate of the material was only 4.8%, and this value remained stable during the 3 immersion-drying cycles, at 4.8%, 5.2% and 5.5%, respectively.

[0046] The results show that DLVL 160 It exhibits excellent dimensional stability and can maintain stable performance over a long period of time in harsh, humid environments.

[0047] (v) Flame retardancy The DLVL prepared in Example 1 was tested using a spray gun scorching test. 160 Flame retardancy tests were conducted on untreated wood (NW).

[0048] like Figure 6 As shown, NW was completely engulfed by flames within 40 seconds, while DLVL 160 The flame spread was significantly suppressed and no sustained combustion occurred, indicating that it has significant flame-retardant properties.

[0049] This invention pretreats wood veneer with a eutectic solvent (choline chloride + boric acid), then impregnates the organic / inorganic components into the wood interior, achieving a dense impregnation. Following hot pressing (with temperature-assisted compression), the hemicellulose, amorphous cellulose, and lignin in the wood undergo in-situ depolymerization or degradation due to the eutectic solvent pretreatment. Then, with temperature-assisted compression, they condense or repolymerize to form a cross-linked network, achieving deformation fixation and aiding in the densification of the wood. The resulting laminated lumber is a "compressed" laminated lumber, unlike existing naturally dense laminated lumber. The "compressed" laminated lumber prepared by this invention exhibits excellent dimensional stability and mechanical properties, high strength, a lower deformation recovery rate (4.8%–5.5%), higher static bending strength (98 MPa–103 MPa), good elastic modulus (7.2 GPa–8.1 GPa), and a dry-wet bonding strength of 2.8 MPa–3.2 MPa. With a boiling water bonding strength of 1.3 MPa, and to prevent mechanical degradation caused by water, the "compressed" laminated material prepared by this invention possesses structural applicability to direct contact with moisture environments and has advantages such as mildew resistance, corrosion resistance, and flame retardancy. It can partially replace non-renewable building materials such as steel, effectively alleviating the high energy consumption and high pollution problems in the alloy material preparation process, while simultaneously achieving high-value utilization of low-quality, fast-growing materials.

[0050] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention in any way. Any simple modifications, alterations, and equivalent changes made to the above embodiments based on the inventive essence shall still fall within the protection scope of the present invention.

Claims

1. A method for preparing a dimensionally stable, high-strength laminated material, characterized in that, The method is as follows: Preparation of S1 and DES: Boric acid and choline chloride are mixed and heated to melt at 90°C. The mixture is stirred until a homogeneous, stable and transparent liquid is formed, which is then obtained as a eutectic solvent, denoted as DES. S2, Veneer Impregnation: Under a vacuum of -0.1 MPa, wood veneer is impregnated in DES obtained in S1 to obtain impregnated veneer; S3, Steam treatment: The impregnated veneer obtained in S2 is subjected to high-temperature steam sterilization at a temperature of 121℃ to obtain the treated veneer. S4. The processed veneers obtained in S3 are assembled in the same grain pattern and hot-pressed at a temperature of 160℃ to obtain dimensionally stable, high-strength laminated material.

2. The method for preparing a dimensionally stable, high-strength laminated material according to claim 1, characterized in that, The molar ratio of boric acid and choline chloride in S1 is 1:

1.

3. The method for preparing a dimensionally stable, high-strength laminated material according to claim 1, characterized in that, The wood veneer described in S2 is made of radiata pine.

4. The method for preparing a dimensionally stable, high-strength laminated material according to claim 1, characterized in that, The soaking time in S2 is 1 hour.

5. The method for preparing a dimensionally stable, high-strength laminated material according to claim 1, characterized in that, The high-temperature steam sterilization process described in S3 takes 1 hour.

6. The method for preparing a dimensionally stable, high-strength laminated material according to claim 1, characterized in that, The hot pressing conditions in S4 are: 2MPa, 1h.

7. The method for preparing a dimensionally stable, high-strength laminated material according to claim 1, characterized in that, The thickness of the dimensionally stable, high-strength laminated material described in S4 is 6 mm.

8. The method for preparing a dimensionally stable, high-strength laminated material according to claim 1, characterized in that, The dimensionally stable, high-strength laminated material described in S4 has a deformation recovery rate of 4.8%–5.5%, a static bending strength of 98 MPa–103 MPa, an elastic modulus of 7.2 GPa–8.1 GPa, a bond strength of 2.8 MPa–3.2 MPa, a boiling water bond strength of 1.3 MPa, and possesses corrosion resistance, mildew resistance, and flame retardancy.

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