Preparation method of high-flame-retardant high-strength modified wood

Abstract

The invention belongs to the technical field of wood modification and flame retardance, and particularly relates to a preparation method of high-flame-retardance and high-strength modified wood. By introducing quaternized waterborne epoxy resin and a condensed phase flame-retardant system, a flame-retardant-reinforced synergistic composite structure is constructed in the wood, so that the flame-retardant property of the wood is remarkably improved while the mechanical property is maintained and improved. According to the preparation method, the industrial problem that the inflammability and the mechanical property of wood are difficult to consider at the same time is fundamentally solved, the forest fiber / epoxy resin high-strength flame-retardant material is constructed through forest fiber chemical component and microstructure regulation and control, organic / inorganic hybridization and in-situ heterogeneous compounding, the flame retardant property and the mechanical property of the wood are improved, and the flame retardant property and the flame retardant property of the wood are improved. Meanwhile, the green chemical principle is emphasized in the whole process, low-toxicity, halogen-free and renewable flame-retardant components are preferentially used, development of the green flame-retardant technology is promoted, and the national dual-carbon strategic target is met.

Description

Technical Field

[0001] This invention belongs to the field of wood modification and flame retardant technology, specifically relating to a method for preparing highly flame-retardant and high-strength modified wood. Background Technology

[0002] Fire, one of the most destructive disasters facing human society, has resulted in over 600,000 fires annually in my country over the past five years, causing thousands of deaths, thousands of injuries, and direct property losses exceeding 10 billion yuan. The flammability of decorative materials is a key contributing factor. With increasing demands for spatial aesthetics, wood-based decorative materials, due to their natural texture and warm feel, have become the preferred choice for buildings, high-speed rail carriages, and ship cabins. However, traditional wood-based decorative materials harbor significant safety hazards: their ignition point is only about 260℃, making them highly flammable when exposed to open flames or high temperatures. Furthermore, they burn rapidly with a large heat release, quickly forming a large-scale fire within minutes. To address the flammability problem of wood-based decorative materials, the industry has attempted to improve their safety through chemical flame-retardant treatments. Traditional wood flame-retardant treatments often use halogenated or phosphorus-containing chemical flame retardants. While these methods can improve flame retardancy to some extent, these flame retardants release toxic gases during combustion or gradually leach out during the product's life cycle, harming the ecological environment and human health.

[0003] Therefore, developing a new type of wood composite material that combines high flame retardancy, excellent mechanical properties, and environmental friendliness has become an urgent research direction in the fields of materials science and forestry engineering. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing highly flame-retardant and high-strength modified wood. The method provided by this invention fundamentally solves the industry problem of the difficulty in balancing the flammability and mechanical properties of wood. While improving the flame-retardant and mechanical properties of wood, the entire preparation process emphasizes the principles of green chemistry, giving priority to the use of low-toxicity, halogen-free, and renewable flame-retardant components, thus promoting the development of "green flame-retardant" technology and conforming to the national "dual-carbon" strategic goal.

[0005] To achieve the above objectives, the present invention provides the following technical solution: This invention provides a method for preparing modified wood, comprising the following steps: S1. Alkali treatment of wood: Soak the wood in a 5-10% sodium hydroxide aqueous solution. After treatment, rinse with deionized water until the pH reaches 7.0, and store in anhydrous ethanol. S2. Preparation of modified waterborne epoxy resin: Bisphenol A type epoxy resin is dissolved in anhydrous ethanol to obtain epoxy groups; diethanolamine is added to the epoxy groups and reacted for 2 h, followed by the sequential addition of polyetheramine, glacial acetic acid and deionized water to form a modified waterborne epoxy resin containing quaternary ammonium groups. S3. Preparation of condensed phase flame retardant: Montmorillonite is mixed with 4% boric acid solution and then ultrasonically centrifuged to obtain 5-10 wt% flame retardant. S4. Alkali-treated wood is placed in a mixture of modified waterborne epoxy resin and flame retardant, and after vacuum impregnation and hot pressing, high flame retardant and high mechanical property modified wood is obtained.

[0006] Preferably, the soaking conditions in step S1 are 60-80°C for 6-12 hours.

[0007] Preferably, the mass ratio of bisphenol A epoxy resin to anhydrous ethanol in step S2 is 1:1; the dissolution conditions are stirring at 65°C and 300 r / min.

[0008] Preferably, the amount of diethanolamine added in step S2 is 30% of the amount of E-44 epoxy group; the polyetheramine is added in a molar mass ratio of bisphenol A epoxy resin to polyetheramine of 4:1. Preferably, the amount of glacial acetic acid added in step S2 is equal to the total amount of amine groups in diethanolamine and polyetheramine (D230); the mass ratio of bisphenol A epoxy resin to deionized water is 1:(0.8~1.2).

[0009] Preferably, the mass ratio of boric acid to montmorillonite in step S3 is 1:(1.0~4.0); the ultrasonic centrifugation conditions are: ultrasonication for 30 min, followed by centrifugation at 9000 rpm for 10 min.

[0010] Preferably, the vacuum impregnation process in step S4 is as follows: vacuum impregnation is performed 3 to 6 times under conditions of -0.1 to -0.6 MPa, with each impregnation lasting 3 to 50 minutes.

[0011] Preferably, the hot pressing process in step S4 is as follows: the wood is placed horizontally under a hot press for hot pressing and shaping, the hot pressing temperature is 80~100℃, the pressure is 15~25 MPa, the hot pressing time is 8~12 hours, the compression rate is controlled at 65%~85%, and the density of the resulting wood is 1.6~1.9 times that of the original wood.

[0012] This invention also provides the application of the above preparation method in enhancing the flame retardancy and mechanical strength of wood.

[0013] The beneficial effects of this invention are: Compared with the prior art, the present invention has the following advantages: (1) Excellent flame retardant performance: Through the synergistic flame retardant effect of montmorillonite and boric acid, the limiting oxygen index (LOI) of the modified wood is greater than 50%, reaching the highest flame retardant level of UL-94 V-0. It can quickly self-extinguish when exposed to fire, greatly improving fire safety.

[0014] (2) Significantly enhanced mechanical strength: The modified waterborne epoxy resin forms a strong chemical bond with the wood fiber and is densified by hot pressing, so that the tensile strength of the product is as high as 184.9 MPa and the bending strength is 102.65 MPa, and the mechanical properties far exceed those of untreated wood.

[0015] (3) High environmental protection and safety: The montmorillonite-boric acid flame retardant system used is a halogen-free formula, which will not release a large amount of toxic smoke and corrosive gases when burning, which is in line with the development trend of green and environmentally friendly materials. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 (a) is a graph showing the heat release rate of Example 1 and Comparative Examples 1 and 2; (b) is a graph showing the total heat release rate of Example 1 and Comparative Examples 1 and 2; (c) is a graph showing the flue gas release rate of Example 1 and Comparative Examples 1 and 2. Figure 2 The graph shows the limiting oxygen index test results for Example 1 and Comparative Examples 1 and 2; Figure 3 The figures show the vertical combustion test results for Example 1 and Comparative Examples 1 and 2, respectively. Figure 4 (a) is a graph showing the tensile properties of Example 1 and Comparative Examples 1 and 2; (b) is a graph showing the bending properties of Example 1 and Comparative Examples 1 and 2. Detailed Implementation

[0018] This invention provides a method for preparing modified wood with high flame retardancy and high strength. By introducing quaternized waterborne epoxy resin and a condensed phase flame retardant system, a flame retardant-reinforcement synergistic composite structure is constructed inside the wood, thereby significantly improving the flame retardant performance of the wood while maintaining or improving its mechanical properties.

[0019] The preparation method of the high flame retardant and high strength modified wood of the present invention includes the following steps: (1) Alkali treatment of wood: Soak the wood in a 5-10% sodium hydroxide aqueous solution at 60-80 ℃ to remove some of the hemicellulose. Treat for 6-12 hours. After treatment, rinse the wood with deionized water until neutral (pH=7.0) and put it in anhydrous ethanol for later use. (2) Preparation of modified waterborne epoxy resin: Bisphenol A type epoxy resin (E-44) was dissolved in anhydrous ethanol (the mass ratio of E-44 to anhydrous ethanol was 1:1). The solution was dissolved under stirring at 65℃ and 300 r / min. Diethanolamine (DEA) was added, and its amount was 30% of the amount of epoxy group. After reacting for 2 hours, polyetheramine D230 was added at a molar ratio of E-44 to polyetheramine (D230) of 4:1. Then, glacial acetic acid and deionized water were added to form a waterborne epoxy resin containing quaternary ammonium groups. (3) Preparation of condensed phase flame retardant: Montmorillonite was mixed with 4% boric acid solution at 600 rpm for 5 days (the mass ratio of boric acid to montmorillonite was 1:(1.0~4.0)), and a dispersion of 5~10 wt% was obtained by sonication for 30 min and centrifugation at 9000 rpm for 10 min; (4) Place the alkali-treated wood in the modified epoxy resin and flame retardant mixture system and vacuum impregnate it 3 to 6 times under -0.1 to -0.6 MPa conditions, each lasting 3 to 50 minutes; (5) Hot pressing densification: The wood is placed horizontally under a hot press for hot pressing. The hot pressing temperature is 80~100℃, the pressure is 15~25 MPa, the hot pressing time is 8~12 hours, the compression rate is controlled at 65%~85%, and the density of the resulting wood is 1.6~1.9 times that of the original wood. After hot pressing, high flame retardant and high mechanical property modified wood is obtained.

[0020] In this embodiment of the invention, the wood can be poplar, balsa wood, linden, fir, or birch.

[0021] The purpose of the NaOH alkali treatment in this invention is not to remove lignin, but to improve the connectivity and permeability of wood pores through limited alkali treatment, creating conditions for the introduction of subsequent functional systems. This invention introduces a waterborne epoxy resin containing quaternary ammonium groups to form a chemical cross-linking network inside the wood, and combines it with hot pressing to achieve structural stability and densification.

[0022] The waterborne epoxy resin containing quaternary ammonium groups described in this invention allows the resin to not only exist as a filler or binder phase, but also to form a reinforced interfacial interaction with wood fibers. At the same time, a condensed phase flame retardant system is constructed by montmorillonite and boric acid, and it is distributed synergistically with the resin inside the wood to form a continuous and dense carbonized heat insulation layer during combustion, thereby achieving a simultaneous improvement in flame retardant performance and mechanical properties.

[0023] To further illustrate the present invention, the technical solutions provided by the present invention will be described in detail below with reference to the accompanying drawings and embodiments, but these should not be construed as limiting the scope of protection of the present invention.

[0024] Unless otherwise specified, the production processes, experimental methods, or testing methods involved in the embodiments of this invention are all conventional methods in the prior art, and their names and / or abbreviations are all conventional names in the field, which are very clear and distinct in the relevant application areas. Those skilled in the art can understand the conventional process steps based on the names and apply the corresponding equipment, and implement them according to conventional conditions or the conditions recommended by the manufacturer.

[0025] The various instruments, equipment, raw materials or reagents used in the embodiments of this invention are not subject to any special restrictions on their source. They are all conventional products that can be purchased through regular commercial channels and can be prepared according to conventional methods known to those skilled in the art.

[0026] Example 1 A method for preparing wood with both high flame retardant properties and high mechanical properties includes the following steps: (1) Soak the wood in an 80°C, 5-10% sodium hydroxide aqueous solution for alkali treatment for 10 hours. After treatment, rinse the wood with deionized water until neutral (pH=7) to remove residual chemicals and obtain alkali-treated wood. Then, store the wood in anhydrous ethanol.

[0027] (2) Weigh a certain amount of bisphenol A type epoxy resin (E-44), add an equal mass of anhydrous ethanol, and stir at 65℃ and 300 r / min until completely dissolved; add diethanolamine, the amount of which is 30% of the amount of the epoxy group of E-44, and react for 2 hours; then add polyetheramine D230 at a molar ratio of 4:1 of E-44 to polyetheramine D230 to continue the reaction; finally add glacial acetic acid (the amount of glacial acetic acid added is equal to the total amount of the amine groups in diethanolamine and polyetheramine (D230)) and deionized water (the mass ratio of bisphenol A type epoxy resin to deionized water is 1:(0.8~1.2)) to obtain a modified waterborne epoxy resin containing quaternary ammonium groups.

[0028] (3) Stir montmorillonite and 4% boric acid solution at 600 rpm for several days (the mass ratio of boric acid to montmorillonite is 1:2). After ultrasonic dispersion, the solution is centrifuged to obtain a stable dispersion system. The modified epoxy resin and flame retardant are mixed at a mass ratio of 1:3 to obtain the modified epoxy resin and montmorillonite-boric acid dispersion system. The alkali-treated wood is placed in the above modified epoxy resin and montmorillonite-boric acid dispersion system and cyclically impregnated 4 times under a negative pressure of -0.1 MPa.

[0029] (6) The impregnated wood is hot-pressed in a hot press at 80°C and 24 MPa for 10 hours to ensure that the wood is completely compacted (the compression rate is controlled at 65%~85%, and the density of the resulting wood is 1.6~1.9 times that of the original wood). During the hot pressing process, the epoxy resin undergoes cross-linking and curing and combines with the wood fiber, which significantly improves the structural density and mechanical properties, ultimately resulting in highly flame-retardant and high-strength modified wood.

[0030] The high flame-retardant, high mechanical property wood obtained in Example 1 is designated as MBW-Wood.

[0031] Comparative Example 1 To verify that the high-strength flame-retardant wood prepared in this invention possesses efficient flame-retardant and mechanical properties, untreated wood was used as a comparison.

[0032] The wood in Comparative Example 1 is labeled Nature Wood.

[0033] Comparative Example 2 To verify that the high-strength flame-retardant wood prepared by this invention has efficient flame-retardant and mechanical properties, wood impregnated only with water-based epoxy resin was used as a comparison.

[0034] The wood in Comparative Example 2 is numbered WEP-Wood.

[0035] Example 2: Application Performance Test of High Flame Retardant Properties Example 1 and Comparative Examples 1 and 2 were subjected to cone calorimetry, vertical combustion, and limiting oxygen index tests.

[0036] 2.1 Cone Calorimetry Test Using a cone calorimeter at 50 kW / m³ in air 2 The flame retardant properties of wood specimens (100 mm × 100 mm) were evaluated under an external heat flux density. The heat release rate (HRR), total heat release rate (THR), and smoke release rate (SPR) of Example 1 and Comparative Examples 1 and 2 were measured.

[0037] The results are as follows Figure 1 As shown in (a), under this heat flow condition, the heat release rates of the two flame-retardant woods, WEP-Wood and MEIW-Wood, are almost the same, while MBW-Wood significantly reduces the heat release rate of the wood. The peak Pk-HRR (Peak of Heat Release Rate) of MBW-Wood is 33.3% lower than that of Nature Wood.

[0038] like Figure 1As shown in (b), the THR gradually increases over time, and the total heat release of the three components continues to accumulate during combustion. However, the total heat release rate of MBW-Wood is significantly lower than that of WEP-Wood and MEIW-Wood. like Figure 1 As shown in (c), the SPR value of MBW-Wood is 0 or very low for most of the time, indicating that less smoke is produced. It only rises slightly in the later stage of combustion, indicating that the flame retardant treatment of the present invention has a certain effect on smoke suppression.

[0039] 2.2 Limiting Oxygen Index Test The combustion performance of wood specimens (100 mm × 6.5 mm) was evaluated using an oxygen index tester. A high oxygen index indicates that the material is not easily combustible, while a low oxygen index indicates that the material is easily combustible.

[0040] The results are as follows Figure 2 As shown, the limiting oxygen index of MBW-Wood exceeds 50%, which is significantly higher than that of WEP-Wood and MEIW-Wood, indicating that the wood prepared by this invention has good flame retardancy.

[0041] 2.3 Vertical Burning Test The combustion performance of wood specimens (100 mm × 13 mm) was evaluated using the vertical combustion method.

[0042] The results are as follows Figure 3 As shown, MBW-Wood did not show obvious burning at 1, 7, 13 and 25 s, and its vertical burning rating reached V-0, indicating that the wood has excellent flame retardant effect.

[0043] 2.4 Mechanical Performance Testing The mechanical properties of Example 1, Comparative Example 1, and Comparative Example 2 were tested using a universal testing machine.

[0044] The results are as follows Figure 4 As shown, MBW-Wood has a tensile strength of not less than 184.9 MPa and a flexural strength of not less than 102.65 MPa, which is several times higher than that of Nature Wood.

[0045] Although the above embodiments have provided a detailed description of the present invention, they are only some embodiments of the present invention, and not all embodiments. People can obtain other embodiments based on these embodiments without creative effort, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A method for preparing modified wood, characterized in that, Includes the following steps: S1. Alkali treatment of wood: Soak the wood in a 5-10% sodium hydroxide aqueous solution. After treatment, rinse with deionized water until the pH reaches 7.0, and store in anhydrous ethanol. S2. Preparation of modified waterborne epoxy resin: Bisphenol A type epoxy resin is dissolved in anhydrous ethanol to obtain epoxy groups; diethanolamine is added to the epoxy groups and reacted for 2 h, followed by the sequential addition of polyetheramine, glacial acetic acid and deionized water to form a modified waterborne epoxy resin containing quaternary ammonium groups. S3. Preparation of condensed phase flame retardant: Montmorillonite is mixed with 4% boric acid solution and then ultrasonically centrifuged to obtain 5~10 wt% flame retardant; S4. Alkali-treated wood is placed in a mixture of modified waterborne epoxy resin and flame retardant, and after vacuum impregnation and hot pressing, high flame retardant and high mechanical property modified wood is obtained.

2. The preparation method according to claim 1, characterized in that, The soaking conditions described in step S1 are 60-80℃ for 6-12 hours.

3. The preparation method according to claim 1, characterized in that, In step S2, the mass ratio of bisphenol A epoxy resin to anhydrous ethanol is 1:1; the dissolution conditions are stirring at 65°C and 300 r / min.

4. The preparation method according to claim 1, characterized in that, In step S2, the amount of diethanolamine added is 30% of the amount of E-44 epoxy group; polyetheramine is added at a molar mass ratio of 4:1 between bisphenol A type epoxy resin and polyetheramine.

5. The preparation method according to claim 1, characterized in that, The amount of glacial acetic acid added in step S2 is equal to the total amount of amine groups in diethanolamine and polyetheramine (D230) to achieve complete neutralization; the mass ratio of bisphenol A epoxy resin to deionized water is 1:(0.8~1.2).

6. The preparation method according to claim 1, characterized in that, The mass ratio of boric acid to montmorillonite in step S3 is 1:(1.0~4.0); the ultrasonic centrifugation conditions are: ultrasonication for 30 min, followed by centrifugation at 9000 rpm for 10 min.

7. The preparation method according to claim 1, characterized in that, The mass ratio of the modified epoxy resin to the flame retardant in step S4 is 1:

3.

8. The preparation method according to claim 1, characterized in that, The vacuum impregnation process described in step S4 is as follows: vacuum impregnation is performed 3 to 6 times under conditions of -0.1 to -0.6 MPa, with each impregnation lasting 3 to 50 minutes.

9. The preparation method according to claim 1, characterized in that, The hot pressing process described in step S4 is as follows: the wood is placed horizontally under a hot press for hot pressing and shaping. The hot pressing temperature is 80~100℃, the pressure is 15~25 MPa, the hot pressing time is 8~12 hours, the compression rate is controlled at 65%~85%, and the density of the resulting wood is 1.6~1.9 times that of the original wood.

10. The application of the preparation method according to any one of claims 1-9 in enhancing the flame retardancy and mechanical strength of wood.

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