Environment-friendly flame-retardant cold-pressing adhesive, preparation method and application thereof

Abstract

The present application relates to a kind of environment-friendly flame-retardant cold-pressing adhesive and its preparation method.The raw materials of the environment-friendly flame-retardant cold-pressing adhesive include 14-21 parts of modified hydrosol, 5-15 parts of magnesium sulfate, 25-35 parts of magnesium chloride, 95-105 parts of magnesium oxide and 0.001-0.01 parts of boric acid by weight.The modified hydrosol is prepared by oxidation crosslinking reaction of propylene hard monomer and hydrosol precursor in the presence of oxidant and crosslinking agent.The adhesive obtained by compounding modified hydrosol with magnesium oxychloride and magnesium oxysulfate inorganic glue has the advantages of high mechanical and bonding strength, good water resistance, and good flame-retardant effect.The modified hydrosol provided by the present application has crosslinking network and abundant hydroxyl and carboxylic acid groups, which gives the adhesive excellent permeability and bonding strength.Magnesium oxychloride inorganic glue enhances the mechanical strength of the adhesive, and magnesium oxysulfate inorganic glue enhances the water resistance of the adhesive.The present application also relates to a plywood containing the above-mentioned environment-friendly flame-retardant cold-pressing adhesive and its preparation method.

Description

Technical Field

[0001] This invention relates to the field of engineered wood products technology, and in particular to an environmentally friendly flame-retardant cold-pressed adhesive and its preparation method, as well as plywood containing the same and its preparation method. Background Technology

[0002] Plywood is a three- or multi-layered sheet material made by rotary cutting logs into veneers or slicing timber into thin sheets, and then gluing them together with adhesives. As the most produced and used engineered wood product, it has wide applications in furniture manufacturing, construction, and packaging. Currently, over 10 million tons of adhesives are consumed annually in plywood manufacturing, with aldehyde resins accounting for over 90% of the usage. These adhesives release free formaldehyde during production and use, posing a health hazard. Furthermore, like wood, plywood is a flammable material, posing a fire risk. Therefore, it is necessary to develop formaldehyde-free and flame-retardant wood adhesives for plywood production, which has significant development potential.

[0003] Among existing inorganic adhesives, magnesium oxysulfate cementitious materials are cementing systems formed by mixing active magnesium oxide and magnesium sulfate solutions in a certain proportion. They possess a series of advantages, including simple preparation process, light weight, fast setting speed, environmental friendliness, fire resistance, and good compatibility with wood. However, the relatively low strength and weak interfacial bonding with wood limit their application in the field of engineered wood products. Summary of the Invention

[0004] To address the aforementioned problems, one objective of this invention is to provide an environmentally friendly flame-retardant adhesive with high mechanical and adhesive strength, and its preparation method. This environmentally friendly flame-retardant adhesive comprises a magnesium sulfate / magnesium oxychloride / water-soluble composite system, possessing advantages such as high mechanical and adhesive strength, good water resistance, and good flame-retardant effect.

[0005] Another objective of this invention is to provide a plywood comprising the above-mentioned environmentally friendly flame-retardant adhesive with high mechanical strength and high bonding strength, and a method for preparing the same.

[0006] Therefore, in a first aspect, the present invention provides an environmentally friendly flame-retardant cold-pressed adhesive, the raw materials of which, by weight, include:

[0007]

[0008] The modified hydrosol is prepared by an oxidative crosslinking reaction of propylene hard monomers and hydrosol precursors in the presence of an oxidant and a crosslinking agent.

[0009] To address the existing problems of low mechanical strength in magnesium oxychloride inorganic adhesives, poor water resistance in magnesium oxychloride inorganic adhesives, and weak interfacial bonding between inorganic adhesives and wood, this invention utilizes a modified hydrosol to compound magnesium oxychloride and magnesium oxychloride inorganic adhesives. The modified hydrosol provided by this invention possesses a cross-linking network and abundant hydroxyl and carboxylic acid groups, endowing the adhesive with excellent permeability and bonding strength. The magnesium oxychloride inorganic adhesive enhances the mechanical strength of the adhesive, while the magnesium oxychloride inorganic adhesive enhances its water resistance. Furthermore, the complex ion and chelation competition during hydration and hardening in this compound system allows the introduction of the modified hydrosol to slow down water loss, facilitating the formation of more reinforcing phase crystal materials. Simultaneously, the modified hydrosol, through physical filling and film-forming effects, can reduce water absorption and increase strength of the two inorganic adhesive components during the hydration and hardening process. The synergistic effect of these three components results in an adhesive with high mechanical and bonding strength, good water resistance, and good flame retardant properties.

[0010] As a specific embodiment of the present invention, the hydrosol precursor is selected from at least one of hyaluronic acid, gelatin, chitosan and sodium alginate.

[0011] In a specific embodiment of the present invention, the number-average molecular weight of the hydrocolloid precursor is 2.0 × 10⁻⁶. 4 ~4.0×10 4 g / mol.

[0012] In a specific embodiment of the present invention, the number-average molecular weight of the gelatin is 2.4 × 10⁻⁶. 4 ~3.6×10 4 The number-average molecular weight of the hyaluronic acid is 4.5 × 10 g / mol. 4 ~6.5×10 4 g / mol.

[0013] As a specific embodiment of the present invention, the oxidant is selected from at least one of hydrogen peroxide, sodium hypochlorite, and perchloric acid.

[0014] As a specific embodiment of the present invention, the propylene-based hard monomer is selected from at least one of acrylic acid, methacrylic acid, and acrylonitrile.

[0015] As a specific embodiment of the present invention, the mass ratio of the propylene hard monomer to the hydrosol precursor is 1:0.75 to 4, preferably 1:1 to 2.5.

[0016] As a specific embodiment of the present invention, the amount of the oxidant is 0.5% to 1.0% of the mass of the propylene hard monomer.

[0017] As a specific embodiment of the present invention, the amount of the crosslinking agent is 1% to 3% of the mass of the propylene hard monomer.

[0018] As a specific embodiment of the present invention, the crosslinking agent is selected from at least one of cationic polyacrylamide, carboxylated polyacrylamide, and hydroxy polyacrylamide.

[0019] In a specific embodiment of the present invention, the number-average molecular weight of the crosslinking agent is 2.5 × 10⁻⁶. 6 ~3.5×10 6 g / mol.

[0020] In a specific embodiment of the present invention, the number-average molecular weight of the cationic polyacrylamide is 3 × 10⁻⁶. 6 ~3.4×10 6 g / mol.

[0021] As a specific embodiment of the present invention, the preparation method of the modified hydrosol includes the following steps:

[0022] S1. Add propylene hard monomers and crosslinking agents to the aqueous solution of the hydrosol precursor, and then add an oxidizing agent to obtain a mixed solution;

[0023] S2. Heat the mixed solution to a first temperature, maintain it at the first temperature for pre-reaction, then raise the temperature to a second temperature, maintain it at the second temperature for oxidative cross-linking reaction to obtain a modified hydrosol solution.

[0024] In a specific embodiment of the present invention, in step S1, the mixed solution is obtained under conditions of 40 to 60°C.

[0025] In a specific embodiment of the present invention, the first temperature is 50-70°C.

[0026] In a specific embodiment of the present invention, the pre-reaction time is 2 to 4 hours.

[0027] In a specific embodiment of the present invention, the second temperature is 80-95°C.

[0028] In a specific embodiment of the present invention, the crosslinking reaction time is 0.25 to 2 hours.

[0029] As a specific embodiment of the present invention, the preparation method of the modified hydrosol includes the following steps:

[0030] S10. A mixture of 5-15 wt% aqueous solution of the hydrosol precursor, propylene hard monomer and cationic polyacrylamide is stirred evenly in a constant temperature water bath at 25-50℃ to obtain a mixed solution.

[0031] S20. Add a hydrogen peroxide solution with a mass fraction of 5-15 wt% to the mixed solution obtained in step S10, and continue stirring;

[0032] S30. Heat the mixed solution obtained in step S20 to 50-70℃ and keep it at that temperature for 2-4 hours. Then raise the temperature to 80-95℃ and react for 0.25-2 hours to allow the reaction system to undergo a full oxidative cross-linking reaction, thereby obtaining a modified hydrosol solution.

[0033] In a specific embodiment of the present invention, in step S10, the stirring rate is 300-350 r / min and the time is 20-40 min.

[0034] In a specific embodiment of the present invention, in step S20, the stirring rate is 300-350 r / min and the time is 5-20 min.

[0035] Therefore, in a second aspect, the present invention provides a method for preparing the above-mentioned environmentally friendly flame-retardant cold-pressed adhesive, comprising the following steps: first mixing modified hydrosol, magnesium sulfate, magnesium chloride, and magnesium oxide, and then adding boric acid for a second mixing; preferably, the temperatures of the first mixing and the second mixing are independently 20-40°C.

[0036] Therefore, in a third aspect, the present invention provides a plywood bonded using the above-described environmentally friendly flame-retardant cold-press adhesive or the environmentally friendly flame-retardant cold-press adhesive prepared by the above-described preparation method.

[0037] Therefore, in a fourth aspect, the present invention provides a method for preparing plywood, comprising the following steps:

[0038] (1) Veneer preparation: Making veneers from wood;

[0039] (2) Apply adhesive to the veneer: Apply the above-mentioned environmentally friendly flame-retardant cold-pressed adhesive or the environmentally friendly flame-retardant cold-pressed adhesive prepared by the above-mentioned preparation method evenly to both sides of the veneer in step (1).

[0040] (3) Assembly and cold pressing: The veneers after gluing in step (2) are assembled and cold pressed;

[0041] (4) Board curing.

[0042] As a specific embodiment of the present invention, step (1) further includes: drying the veneer to a moisture content of 5-10 wt%.

[0043] In a specific embodiment of the present invention, in step (2), the amount of adhesive applied to one side of the veneer is 200-300 g / m². 2 .

[0044] As a specific embodiment of the present invention, in step (3), the conditions for assembling the blank include: following the principles of odd number of layers, symmetry, and interlayer texture arrangement.

[0045] As a specific embodiment of the present invention, the cold pressing conditions include: a temperature of 10 to 35°C, a pressure of 1.0 to 1.5 MPa, and a time of 24 to 72 hours.

[0046] As a specific embodiment of the present invention, the conditions for curing the board include: curing at 20-70°C for 2-7 days.

[0047] Beneficial effects:

[0048] This invention provides an environmentally friendly, flame-retardant, cold-pressed adhesive that addresses the shortcomings of existing magnesium oxychloride inorganic adhesives, such as low mechanical strength, poor water resistance, and weak interfacial bonding between inorganic adhesives and wood. This invention utilizes a modified hydrosol compounded with magnesium oxychloride and magnesium oxychloride inorganic adhesives. The modified hydrosol provided by this invention possesses a cross-linked network and abundant hydroxyl and carboxylic acid groups, endowing the adhesive with excellent permeability and bonding strength. The magnesium oxychloride inorganic cementitious material enhances the mechanical strength of the adhesive, while the magnesium oxychloride inorganic adhesive enhances its water resistance. The synergistic effect of these three components results in an adhesive with high mechanical and bonding strength, good water resistance, and a good flame-retardant effect.

[0049] The environmentally friendly flame-retardant cold-pressed adhesive provided by this invention improves the mechanical strength of the adhesive by blending magnesium oxychloride and magnesium oxysulfide. The cross-linking network between the acrylic hard monomers and the water-soluble adhesive in the modified water-soluble adhesive combines with wood and magnesium ions to enhance the adhesive's permeability, bonding strength and moisture resistance.

[0050] The environmentally friendly flame-retardant cold-pressed adhesive provided by this invention has the advantages of high mechanical and bonding strength, and the preparation process is simple. It releases no formaldehyde during production and use, and also has the advantages of being healthy and environmentally friendly. As a wood adhesive, it also endows plywood with flame-retardant properties and moisture resistance.

[0051] The environmentally friendly flame-retardant cold-press adhesive provided by this invention can be applied to boards at room temperature without hot pressing, thus saving energy and protecting the environment.

[0052] The plywood provided by this invention has excellent physical and mechanical properties, flame retardant properties, and moisture resistance. Furthermore, it is free of volatile formaldehydes, which can avoid harming the environment. This further improves the added value and applicability of the plywood, and its promotion prospects are promising. Attached Figure Description

[0053] Figure 1 This is a schematic diagram of the internal structure of the plywood prepared according to Embodiment 1 of the present invention. Detailed Implementation

[0054] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments are merely illustrative of the invention and should not be considered as specific limitations thereof. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0055] In the examples, the number-average molecular weight of the gelatin was 3.0 × 10⁻⁶ 4 The number-average molecular weight of cationic polyacrylamide is 3.2 × 10⁻⁶. 6 The number-average molecular weight of hyaluronic acid is 5.4 × 10 g / mol. 4 g / mol.

[0056] Example 1

[0057] The preparation of environmentally friendly flame-retardant cold-pressed adhesives is carried out according to the following steps:

[0058] (1) Weigh 100g of gelatin aqueous solution (concentration of 10wt%), 4.3g of acrylic acid monomer and 0.086g of cationic polyacrylamide, and stir at 320r / min for 30min in a constant temperature water bath at 50℃ to fully dissolve and mix the above components to obtain a mixed solution.

[0059] (2) Take 430 μL of 10 wt% hydrogen peroxide aqueous solution and add it to the mixed solution obtained in step (1), and stir at 320 r / min for 10 min.

[0060] (3) Heat the mixed solution obtained in step (2) to 70°C and keep it at that temperature for 2 hours. Then raise the temperature to 80°C and keep it at that temperature for 1 hour to allow the acrylic monomer to fully participate in the oxidative crosslinking reaction. After the reaction is completed, cool the solution to room temperature to obtain a pale yellow solution.

[0061] (4) 100g of the modified hydrosol solution (concentration of 14.4wt%) obtained in step (3) is stirred with 10g of magnesium sulfate, 30g of magnesium chloride and 100g of magnesium oxide at a speed of 320r / min for 30min, and then 1.0mg of boric acid is added to obtain the environmentally friendly flame retardant adhesive.

[0062] Example 2

[0063] The preparation of environmentally friendly flame-retardant cold-pressed adhesives is carried out according to the following steps:

[0064] (1) Weigh 100g of hyaluronic acid aqueous solution (concentration of 10wt%), 4.3g of acrylic acid monomer and 0.086g of cationic polyacrylamide, and stir at 320r / min for 30min in a constant temperature water bath at 50℃ to fully dissolve and mix the above components to obtain a mixed solution.

[0065] (2) Take 430 μL of 10 wt% hydrogen peroxide aqueous solution and add it to the mixed solution obtained in step (1), and stir at 320 r / min for 10 min.

[0066] (3) Heat the mixed solution obtained in step (2) to 70°C and keep it at that temperature for 2 hours. Then raise the temperature to 80°C and keep it at that temperature for 1 hour to allow the acrylic monomer to fully participate in the oxidative crosslinking reaction. After the reaction is completed, cool the solution to room temperature to obtain a pale yellow solution.

[0067] (4) 100g of the modified hydrosol solution (concentration of 14.4wt%) obtained in step (3) is stirred with 10g of magnesium sulfate, 30g of magnesium chloride and 100g of magnesium oxide at a speed of 320r / min for 30min, and then 1.0mg of boric acid is added to obtain the environmentally friendly flame retardant adhesive.

[0068] Example 3

[0069] The preparation of environmentally friendly flame-retardant cold-pressed adhesives is carried out according to the following steps:

[0070] (1) Weigh 100g of sodium alginate aqueous solution (concentration of 10wt%), 4.3g of acrylic acid monomer and 0.086g of cationic polyacrylamide, and stir at 320r / min for 30min in a constant temperature water bath at 50℃ to fully dissolve and mix the above components to obtain a mixed solution.

[0071] (2) Take 430 μL of 10 wt% hydrogen peroxide aqueous solution and add it to the mixed solution obtained in step (1), and stir at 320 r / min for 10 min.

[0072] (3) Heat the mixed solution obtained in step (2) to 70°C and keep it at that temperature for 2 hours. Then raise the temperature to 80°C and keep it at that temperature for 1 hour to allow the acrylic monomer to fully participate in the oxidative crosslinking reaction. After the reaction is completed, cool the solution to room temperature to obtain a pale yellow solution.

[0073] (4) 100g of the modified hydrosol solution (concentration of 14.4wt%) obtained in step (3) is stirred with 10g of magnesium sulfate, 30g of magnesium chloride and 100g of magnesium oxide at a speed of 320r / min for 30min, and then 1.0mg of boric acid is added to obtain the environmentally friendly flame retardant adhesive.

[0074] Example 4

[0075] The preparation of environmentally friendly flame-retardant cold-pressed adhesives is carried out according to the following steps:

[0076] (1) Weigh 100g of gelatin aqueous solution (concentration of 10wt%), 10g of acrylic monomer and 0.15g of cationic polyacrylamide, and stir at 320r / min for 30min in a constant temperature water bath at 50℃ to fully dissolve and mix the above components to obtain a mixed solution.

[0077] (2) Take 430 μL of 10 wt% perchloric acid aqueous solution and add it to the mixed solution obtained in step (1), and stir at 320 r / min for 10 min;

[0078] (3) Heat the mixed solution obtained in step (2) to 70°C and keep it at that temperature for 2 hours. Then raise the temperature to 80°C and keep it at that temperature for 1 hour to allow the acrylic monomer to fully participate in the oxidative crosslinking reaction. After the reaction is completed, cool the solution to room temperature to obtain a pale yellow solution.

[0079] (4) 100g of the modified hydrosol solution (concentration of 20.2wt%) obtained in step (3) is stirred with 10g of magnesium sulfate, 35g of magnesium chloride and 105g of magnesium oxide at a speed of 320r / min for 30min, and then 2.0mg of boric acid is added to obtain the environmentally friendly flame retardant adhesive.

[0080] Comparative Example 1

[0081] The difference from Example 1 is that no modification of the hydrosol was performed. The following steps were performed: 100g of gelatin aqueous solution (concentration of 10wt%) was weighed and stirred with 10g magnesium sulfate, 30g magnesium chloride and 100g magnesium oxide at a speed of 320r / min for 30min. Then 1.0mg of boric acid was added to obtain the adhesive.

[0082] Comparative Example 2

[0083] The difference from Example 1 is that the hydrosol modification only involves the addition of cationic polyacrylamide and not hydrogen peroxide. The following steps were followed:

[0084] (1) Weigh 100g of gelatin aqueous solution (concentration of 10wt%), 4.3g of propylene hard monomer and 0.086g of cationic polyacrylamide, and stir at 320r / min for 30min in a constant temperature water bath at 50℃ to fully dissolve and mix the above components to obtain a mixed solution.

[0085] (2) Heat the mixed solution obtained in step (1) to 70°C and keep it at that temperature for 2 hours, then raise the temperature to 80°C and react for 1 hour.

[0086] (3) Stir 100g of the mixed solution obtained in step (2) (concentration of 14.4wt%) with 10g of magnesium sulfate, 30g of magnesium chloride and 100g of magnesium oxide at a speed of 320r / min for 30min, and then add 1.0mg of boric acid to obtain the adhesive.

[0087] Comparative Example 3

[0088] The difference from Example 1 is that the hydrosol modification only involves the addition of hydrogen peroxide and not cationic polyacrylamide. The following steps were followed:

[0089] (1) Weigh 100g of gelatin aqueous solution (concentration of 10wt%) and 4.3g of acrylic acid monomer, and stir at 320r / min for 30min in a constant temperature water bath at 50℃ to fully dissolve and mix the above components to obtain a mixed solution;

[0090] (2) Take 430 μL of 10 wt% hydrogen peroxide aqueous solution and add it to the mixed solution obtained in step (1), and stir at 320 r / min for 10 min.

[0091] (3) Heat the mixed solution obtained in step (2) to 70°C and keep it at that temperature for 2 hours. Then raise the temperature to 80°C and keep it at that temperature for 1 hour to allow the acrylic monomer to fully participate in the oxidative crosslinking reaction. After the reaction is completed, cool the solution to room temperature to obtain a pale yellow solution.

[0092] (4) 100g of the modified hydrosol solution (concentration of 14.4wt%) obtained in step (3) is stirred with 10g of magnesium sulfate, 30g of magnesium chloride and 100g of magnesium oxide at a speed of 320r / min for 30min, and then 1.0mg of boric acid is added to obtain the environmentally friendly flame retardant adhesive.

[0093] Comparative Example 4

[0094] The difference from Example 1 is that the mass of magnesium oxide is changed from 100g to 90g.

[0095] Comparative Example 5

[0096] The difference from Example 1 is that the mass of boric acid was changed from 1 mg to 0.5 mg.

[0097] Application Example 1

[0098] The preparation of plywood is carried out according to the following steps:

[0099] (1) Use a rotary cutter to cut eucalyptus wood into veneers with a thickness of 2.0mm±0.2mm, dry them to a moisture content of 8wt%, and cut them into a size of 1200mm×600mm.

[0100] (2) Veneer application: The adhesives prepared in Examples 1-4 and Comparative Examples 1-4 were mixed and evenly applied to both sides of the veneer. The amount of adhesive applied to one side of the veneer was 250 g / m². 2 ;

[0101] (3) The single boards obtained in step (2) are assembled according to the principle of odd number of layers, symmetry and interlayer texture, and then cold-pressed at room temperature (25℃) and 1.2MPa cold pressing pressure for 48h;

[0102] (4) Curing of plywood: After depressurization, the plywood is cured at 70°C for 2 days, and then cured at room temperature for 5 days. Each plywood is designated as P1-4 (corresponding to Examples 1-4) and DP1-5 (corresponding to Examples 1-5).

[0103] Mechanical strength, moisture resistance, and flame retardant properties of boards P1-4 and DP1-5 were tested respectively. The test methods and results are as follows:

[0104] (1) Static bending strength and modulus of elasticity test: The static bending strength and modulus of elasticity of the board are tested in accordance with GB / T 17657-2022 "Test Methods for Physical and Chemical Properties of Wood-based Panels and Decorative Wood-based Panels", where the span is 20 times the thickness of the board.

[0105] (2) Moisture Resistance Test: Referring to GB / T 17657-2022 "Test Methods for Physical and Chemical Properties of Wood-based Panels and Decorative Wood-based Panels", the 24-hour water absorption thickness swelling rate and Class II immersion peel performance of the plywood were tested. The 24-hour water absorption thickness swelling rate (TS-24h) was measured by immersing a 50mm × 50mm sample in room temperature water for 24 hours, and the smaller the TS-24h, the less water absorption swelling the plywood had, indicating better moisture resistance. The Class II immersion peel test involved immersing a 75mm × 75mm sample in 65℃ water for 3 hours, followed by heat treatment in a 65℃ oven for 3 hours. The adhesive layers of the plywood were then observed for delamination and cracking, and the crack length on one side of the adhesive layer was recorded. In this test, samples with cracks exceeding 25mm on one side were considered unqualified.

[0106] (3) Flame retardant performance test: Refer to GB / T 2406.2-2009 "Determination of burning behavior of plastics by oxygen index method" to test the oxygen index of the board. The higher the oxygen index, the better the flame retardant performance. According to production practice, the oxygen index (LOI) of plywood is more than 35% (≥35%), which indicates that the flame retardant effect is good. The oxygen index is less than 35% but more than 30% (30%≤LOI<35%), which indicates that there is a certain flame retardant effect, but the flame retardant effect is weak. The oxygen index is less than 30% (<30%) and is recorded as a combustible material.

[0107] Table 1 Test results of each group of plywood

[0108]

[0109]

[0110] Table 1 shows that experimental groups P1 to P4 all exhibit good static bending strength, high elastic modulus, low water absorption thickness swelling rate, good impregnation peel performance, and excellent flame retardant oxygen index performance. The plywood prepared in control group DP1 has low bonding strength and poor moisture resistance (water absorption thickness swelling rate and impregnation peel performance). It is believed that, without modification of the organic cementitious material, the organic components themselves did not form a cross-linked structure, resulting in strong hygroscopicity, leading to low overall bonding strength between the adhesive and the veneer, and poor moisture resistance (water absorption thickness swelling rate and impregnation peel performance). The plywood prepared in control group DP2 also has poor overall performance. It is believed that, without necessary oxidation treatment of the organic components, the organic components have poor activity and did not form a good three-dimensional cross-linked structure during high-temperature heat treatment, thus resulting in poor overall performance. The plywood prepared in control group DP3 also has poor overall performance. Unwilling to be limited by theory, it is believed that the lack of necessary cross-linking treatment for the organic components resulted in poor water resistance. During high-temperature heat treatment, the oxidation of the hydrosol components caused the end groups to oxidize. Due to the absence of cross-linking components, the system did not form a good three-dimensional cross-linked structure, resulting in poor overall performance. The plywood prepared in the control group DP4 showed poor moisture resistance and flame retardancy. Unwilling to be limited by theory, it is believed that the reduced content of inorganic adhesive components led to the failure of the overall adhesive to form a good gel phase. The large amount of free magnesium chloride resulted in strong hygroscopicity and poor moisture resistance. The lack of a good inorganic cementitious skeleton also led to poor flame retardancy of the plywood. The plywood prepared in the control group DP5 showed a decrease in overall strength and a deterioration in water resistance. Unwilling to be limited by theory, it is believed that the low boric acid content led to low system viscosity and high free water content, which intensified penetration on the veneer surface, disrupting the original component ratio of the system, thus leading to a decrease in the overall strength and a deterioration in water resistance of the plywood.

[0111] The above description of the embodiments is provided to enable those skilled in the art to understand and apply the present invention. It will be apparent to those skilled in the art that various modifications can be easily made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the embodiments described herein, and any improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the invention should be within the protection scope of the present invention.

Claims

1. An environmentally friendly flame-retardant cold-pressing adhesive, characterized in that, By weight parts, its raw materials include: Modified hydrosol 14~21 parts, Magnesium sulfate 5~15 parts, Magnesium chloride 25~35 parts, Magnesium oxide 95~105 parts, Boric acid 0.001~0.01 parts, Wherein, the modified hydrosol is prepared by oxidative crosslinking reaction of acrylic hard monomer and hydrosol precursor in the presence of oxidizing agent and crosslinking agent; The hydrosol precursor is selected from at least one of hyaluronic acid, gelatin, chitosan and sodium alginate; The acrylic hard monomer is selected from at least one of acrylic acid, methacrylic acid and acrylonitrile; The mass ratio of the acrylic hard monomer to the hydrosol precursor is 1:0.75~4; The crosslinking agent is selected from at least one of cationic polyacrylamide, carboxylated polyacrylamide and hydroxyl polyacrylamide.

2. The adhesive according to claim 1, wherein The number average molecular weight of the hydrosol precursor is 2.0 x 10 4 6.5 x 10 4 g / mol.

3. The adhesive according to claim 2, wherein The number average molecular weight of the gelatin is 2.4 x 10 4 The number average molecular weight of the gelatin is 2.4 x 10 4 The number average molecular weight of the hyaluronic acid is 4.5 x 10 4 The number average molecular weight of the hyaluronic acid is 4.5 x 10 4 The number average molecular weight of the hyaluronic acid is 4.5 x 10 4. The adhesive according to any one of claims 1 to 3, characterized in that, The oxidizing agent is selected from at least one of hydrogen peroxide, sodium hypochlorite and perchloric acid; and / or, The mass ratio of the acrylic hard monomer to the hydrosol precursor is 1:1~2.5; and / or, The amount of the oxidizing agent is 0.5%~1.0% of the mass of the acrylic hard monomer; and / or, The amount of the crosslinking agent is 1%~3% of the mass of the acrylic hard monomer.

5. The adhesive according to any one of claims 1 to 3, wherein The number average molecular weight of the crosslinking agent is 2.5 x 10 6 3.5 x 10 6 g / mol.

6. The adhesive of claim 5, wherein The cationic polyacrylamide has a number average molecular weight of 3 x 10 6 3.4 x 10 6 g / mol.

7. The adhesive according to any one of claims 1 to 3, wherein The preparation method of the modified hydrosol includes the following steps: S1, adding acrylic hard monomer and crosslinking agent in the hydrosol precursor aqueous solution, and then adding oxidizing agent to obtain a mixed solution; S2, heating the mixed solution to a first temperature, pre-reacting at the first temperature, and then heating to a second temperature, and crosslinking at the second temperature to obtain a modified hydrosol solution.

8. The adhesive according to claim 7, characterized in that The first temperature is 50~70℃, and / or the pre-reaction time is 2~4 h, and / or the second temperature is 80~95℃, and / or the crosslinking reaction time is 0.25~2 h.

9. A process for the preparation of the environmentally friendly flame retardant cold press moulding adhesive as claimed in any one of claims 1 to 8, wherein, Including the following steps: Mixing the modified hydrosol, magnesium sulfate, magnesium chloride and magnesium oxide first, and then adding boric acid for second mixing.

10. The method of claim 9, wherein, The temperature of the first mixing and the second mixing is independently 20~40℃.

11. A plywood, characterized by Using the environmentally friendly flame-retardant cold-pressing type adhesive of any one of claims 1-8 or the environmentally friendly flame-retardant cold-pressing type adhesive prepared by the preparation method of claim 9 or 10 for gluing.

12. A method of producing a plywood, characterized by, Including the following steps: (1) Single board preparation: wood is made into single board; (2) Single board sizing: evenly coating the environmentally friendly flame-retardant cold-pressing type adhesive of any one of claims 1-8 or the environmentally friendly flame-retardant cold-pressing type adhesive prepared by the preparation method of claim 9 or 10 on both sides of the single board of step (1); (3) Assembly and cold pressing: the single board after sizing in step (2) is assembled and cold pressed; (4) Board curing.

13. The production method according to claim 12, characterized by, Step (1) further includes: drying the single board to a moisture content of 5~10wt%; and / or In step (2), the sizing amount of the single side of the veneer is 200-300 g / m 2 ; and / or In step (3), the assembly conditions include: according to the odd number of layers, the symmetry and the interlayer texture arrangement principle; and / or, the cold pressing conditions include: temperature 10~35℃, pressure 1.0~1.5MPa, time 24~72h; In step (4), the board curing conditions include: curing at 20~70℃ for 2~7 days.

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