Environment-friendly flame-retardant cold-pressed adhesive as well as preparation method and application thereof

Abstract

The invention relates to an environment-friendly flame-retardant cold-pressed adhesive and a preparation method thereof. The environment-friendly flame-retardant cold-pressed adhesive is prepared from the following raw materials in parts by weight: 14 to 21 parts of modified hydrosol, 5 to 15 parts of magnesium sulfate, 25 to 35 parts of magnesium chloride, 95 to 105 parts of magnesium oxide and 0.001 to 0.01 part of boric acid, and the modified hydrosol is prepared by carrying out oxidation cross-linking reaction on a propylene hard monomer and a hydrosol precursor in the presence of an oxidizing agent and a cross-linking agent. The adhesive obtained by compounding the modified hydrosol with magnesium oxychloride and magnesium oxysulfate inorganic glue has the advantages of high mechanical and bonding strength and good water resistance, and has a relatively good flame-retardant effect. The modified hydrosol provided by the invention has a cross-linked network and rich hydroxyl and carboxylic acid groups, so that the adhesive is endowed with excellent permeability and bonding strength, the mechanical strength of the adhesive is enhanced by the magnesium oxychloride inorganic glue, and the water resistance of the adhesive is enhanced by the magnesium oxysulfate inorganic glue. The invention further relates to plywood containing the environment-friendly flame-retardant cold-pressed adhesive and a preparation method of the plywood.

Description

Technical Field

[0001] The invention relates to the technical field of artificial boards, and in particular to an environmentally friendly flame-retardant cold-pressed adhesive and a preparation method thereof, a plywood containing the same and a preparation method thereof. Background Art

[0002] Plywood is a three-layer or multi-layer board material made by peeling wood segments into veneers or planing wood blocks into veneers, and then gluing them together with adhesives. As the most produced and used man-made board, it is widely used in furniture manufacturing, construction, packaging and other fields. At present, more than 10 million tons of adhesives are consumed annually in the plywood manufacturing process, and aldehyde resins are widely used with a proportion of more than 90%. This type of adhesive will release free formaldehyde during production and use, which is harmful to human health. At the same time, this type of man-made board is a combustible material like wood, and there is a fire hazard. Therefore, it is necessary to develop wood adhesives that are free of formaldehyde and have flame retardant effects to prepare plywood, which has great development prospects.

[0003] Among the existing inorganic adhesives, magnesium oxysulfide gelling material is a gelling system formed by mixing active magnesium oxide and magnesium sulfate solution in a certain proportion, which has a series of advantages such as simple preparation process, light weight, fast coagulation speed, green environmental protection, fire resistance and good compatibility with wood. However, the magnesium oxysulfide gelling material is also limited in its application in the field of artificial boards due to its low strength and weak interface bonding with wood. Summary of the invention

[0004] In view of the above problems, one of the purposes of the present invention is to provide an environmentally friendly flame-retardant adhesive with high mechanical strength and high bonding strength and a preparation method thereof. The environmentally friendly flame-retardant adhesive comprises a magnesium sulfate / magnesium oxychloride / hydrosol composite system, has the advantages of high mechanical and bonding strength, good water resistance, and good flame retardant effect.

[0005] Another object of the present invention is to provide a plywood having high mechanical strength and high bonding strength and comprising the above-mentioned environmentally friendly flame-retardant adhesive and a preparation method thereof.

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

[0007]

[0008] The modified hydrosol is prepared by oxidative crosslinking reaction of acrylic hard monomer and hydrosol precursor in the presence of oxidant and crosslinking agent.

[0009] In view of the low mechanical strength of the existing magnesium oxysulfide inorganic adhesive, the poor water resistance of magnesium oxychloride inorganic adhesive, and the weak interface bonding problem of inorganic glue and wood, the present invention is compounded with magnesium oxychloride and magnesium oxysulfide inorganic glue by modified hydrosol. The modified hydrosol provided by the present invention has a cross-linked network and abundant hydroxyl and carboxylic acid groups, which gives the adhesive excellent permeability and bonding strength. The magnesium oxychloride inorganic glue enhances the mechanical strength of the adhesive, and the magnesium oxysulfide inorganic glue enhances the water resistance of the adhesive. In addition, there is a complex ion and chelate competition in the hydration hardening in the composite system. The introduction of the modified hydrosol can slow down the loss of water and help to form more reinforced phase crystalline materials. At the same time, the modified hydrosol can reduce the water absorption and improve the strength of the two inorganic glue components in the hydration hardening process through physical filling and film-forming effects. The three cooperate with each other, and the resulting adhesive has the advantages of high mechanical and bonding strength, good water resistance, and has a good flame retardant effect.

[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] As a specific embodiment of the present invention, the number average molecular weight of the hydrosol precursor is 2.0×10 4 ~4.0×10 4 g / mol.

[0012] As a specific embodiment of the present invention, the number average molecular weight of the gelatin is 2.4×10 4 ~3.6×10 4 g / mol, and the number average molecular weight of the hyaluronic acid is 4.5×10 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 acrylic 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 acrylic hard monomer to the hydrosol precursor is 1:0.75-4, preferably 1:1-2.5.

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

[0017] As a specific implementation of the present invention, the amount of the cross-linking agent is 1% to 3% of the mass of the propylene hard monomer.

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

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

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

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

[0022] S1, adding an acrylic hard monomer and a cross-linking agent to a hydrosol precursor aqueous solution, and then adding an oxidant to obtain a mixed solution;

[0023] S2, heating the mixed solution to a first temperature, maintaining it at the first temperature for a preliminary reaction, and then heating it to a second temperature, maintaining it at the second temperature for an oxidative cross-linking reaction to obtain a modified hydrosol solution.

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

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

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

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

[0028] As a specific embodiment of the present invention, the cross-linking reaction time is 0.25 to 2 hours.

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

[0030] S10, stirring an aqueous solution of a hydrosol precursor having a mass fraction of 5 to 15 wt %, an acrylic hard monomer and a cationic polyacrylamide in a constant temperature water bath at 25 to 50° C. to obtain a mixed solution;

[0031] S20, adding a 5-15wt% hydrogen peroxide solution into the mixed solution obtained in step S10, and continuing stirring;

[0032] S30, heating the mixed solution obtained in step S20 to 50-70°C for 2-4 hours, and then heating to 80-95°C for 0.25-2 hours to allow the reaction system to undergo sufficient oxidative crosslinking reaction to obtain a modified hydrosol solution.

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

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

[0035] To this end, 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: a first mixing of the 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 to 40°C.

[0036] To this end, in a third aspect, the present invention provides a plywood, which is bonded using 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.

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

[0038] (1) Veneer preparation: making wood into veneer;

[0039] (2) Gluing the veneer: evenly coating 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 on both sides of the veneer in step (1);

[0040] (3) Assembling and cold pressing: assembling and cold pressing the veneer sheets after gluing in step (2);

[0041] (4) Board maintenance.

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

[0043] As a specific embodiment of the present invention, in step (2), the glue application amount on one side of the veneer is 200 to 300 g / m 2 .

[0044] As a specific embodiment of the present invention, in step (3), the conditions for assembling the blanks 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: temperature of 10-35° C., pressure of 1.0-1.5 MPa, and time of 24-72 h.

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

[0047] Beneficial effects:

[0048] The environmentally friendly flame-retardant cold-pressed adhesive provided by the present invention aims at the problems of low mechanical strength of the existing magnesium oxysulfide inorganic adhesive, poor water resistance of the magnesium oxychloride inorganic adhesive, and weak interface bonding between the inorganic adhesive and wood. The present invention uses a modified hydrosol to compound magnesium oxychloride and magnesium oxysulfide inorganic glue. The modified hydrosol provided by the present invention has a cross-linked network and abundant hydroxyl and carboxylic acid groups, which give the adhesive excellent permeability and bonding strength. The magnesium oxychloride inorganic gelling material enhances the mechanical strength of the adhesive, and the magnesium oxysulfide inorganic glue enhances the water resistance of the adhesive. The three cooperate with each other, and the obtained adhesive has the advantages of high mechanical and bonding strength, good water resistance, and good flame retardant effect.

[0049] The environmentally friendly flame-retardant cold-pressed adhesive provided by the present invention improves the mechanical strength of the adhesive by blending magnesium oxychloride and magnesium oxysulfide, and the cross-linked network between the acrylic hard monomer and the hydrosol in the modified hydrosol is combined with wood and magnesium ions to enhance the permeability, bonding strength and moisture resistance of the adhesive.

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

[0051] The environmentally friendly flame-retardant cold-pressed adhesive provided by the present invention can be applied in the form of panels at room temperature without the need for hot pressing, thereby being energy-saving and environmentally friendly.

[0052] The plywood provided by the present invention has excellent physical and mechanical properties, flame retardant properties, moisture resistance, and no volatile formaldehydes, which can avoid harm to the environment, further improving the added value and application scope of the plywood, and having good promotion prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] Figure 1 This is a schematic diagram of the internal structure of the plywood prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0054] The technical scheme of the present invention is further described below by specific embodiments. Those skilled in the art should understand that the embodiments are only to help understand the present invention and should not be regarded as specific limitations of the present invention. If specific conditions are not specified in the embodiments, they are carried out according to conventional conditions or conditions recommended by the manufacturer. If the manufacturer of the reagents or instruments is not specified, they are all conventional products that can be obtained commercially.

[0055] The number average molecular weight of gelatin in the embodiment is 3.0×10 4 The number average molecular weight of cationic polyacrylamide is 3.2×10 6 g / mol, and the number average molecular weight of hyaluronic acid is 5.4×10 4 g / mol.

[0056] Example 1

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

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

[0059] (2) adding 430 μL of a 10 wt % hydrogen peroxide aqueous solution to the mixed solution obtained in step (1), and stirring at a speed of 320 r / min for 10 min;

[0060] (3) heating the mixed solution obtained in step (2) to 70° C. for 2 h and then heating to 80° C. for 1 h to allow the acrylic acid monomer to fully participate in the oxidative crosslinking reaction. After the reaction, cooling to room temperature to obtain a light yellow solution;

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

[0062] Example 2

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

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

[0065] (2) adding 430 μL of a 10 wt % hydrogen peroxide aqueous solution to the mixed solution obtained in step (1), and stirring at a speed of 320 r / min for 10 min;

[0066] (3) heating the mixed solution obtained in step (2) to 70° C. for 2 h and then heating to 80° C. for 1 h to allow the acrylic acid monomer to fully participate in the oxidative crosslinking reaction. After the reaction, cooling to room temperature to obtain a light yellow solution;

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

[0068] Example 3

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

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

[0071] (2) adding 430 μL of a 10 wt % hydrogen peroxide aqueous solution to the mixed solution obtained in step (1), and stirring at a speed of 320 r / min for 10 min;

[0072] (3) heating the mixed solution obtained in step (2) to 70° C. for 2 h and then heating to 80° C. for 1 h to allow the acrylic acid monomer to fully participate in the oxidative crosslinking reaction. After the reaction, cooling to room temperature to obtain a light yellow solution;

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

[0074] Example 4

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

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

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

[0078] (3) heating the mixed solution obtained in step (2) to 70° C. for 2 h and then heating to 80° C. for 1 h to allow the acrylic acid monomer to fully participate in the oxidative crosslinking reaction. After the reaction, cooling to room temperature to obtain a light yellow solution;

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

[0080] Comparative Example 1

[0081] The difference from Example 1 is that the hydrosol is not modified. The following steps are performed: 100 g of gelatin aqueous solution (concentration is 10 wt%) is weighed, and 10 g of magnesium sulfate, 30 g of magnesium chloride, and 100 g of magnesium oxide are stirred at a speed of 320 r / min for 30 min, and then 1.0 mg of boric acid is added to obtain an adhesive.

[0082] Comparative Example 2

[0083] The difference from Example 1 is that only cationic polyacrylamide is added to the hydrosol modification without adding hydrogen peroxide. The following steps are performed:

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

[0085] (2) heating the mixed solution obtained in step (1) to 70° C. for 2 h and then heating to 80° C. for 1 h;

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

[0087] Comparative Example 3

[0088] The difference from Example 1 is that only hydrogen peroxide is added to the hydrosol modification without adding cationic polyacrylamide. The following steps are performed:

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

[0090] (2) adding 430 μL of a 10 wt % hydrogen peroxide aqueous solution to the mixed solution obtained in step (1), and stirring at a speed of 320 r / min for 10 min;

[0091] (3) heating the mixed solution obtained in step (2) to 70° C. for 2 h and then heating to 80° C. for 1 h to allow the acrylic acid monomer to fully participate in the oxidative crosslinking reaction. After the reaction, cooling to room temperature to obtain a light yellow solution;

[0092] (4) 100 g of the modified hydrosol solution (concentration of 14.4 wt%) obtained in step (3) was stirred with 10 g of magnesium sulfate, 30 g of magnesium chloride, and 100 g of magnesium oxide at a speed of 320 r / min for 30 min, and then 1.0 mg of boric acid was 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 100 g to 90 g.

[0095] Comparative Example 5

[0096] The difference from Example 1 is that the mass of boric acid is 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) using a rotary cutter to peel the eucalyptus wood into veneers with a thickness of 2.0 mm ± 0.2 mm, drying to a moisture content of 8 wt %, and cutting to a size of 1200 mm × 600 mm;

[0100] (2) Gluing of veneers: The adhesives prepared in Examples 1-4 and Comparative Examples 1-4 were respectively selected and mixed, and the mixed adhesives were evenly coated on both sides of the veneers. The glue application amount on one side of the veneer was 250 g / m 2 ;

[0101] (3) assembling the veneer obtained in step (2) according to the principle of odd number of layers, symmetry and interlayer texture arrangement, and then cold pressing at room temperature (25° C.) and 1.2 MPa cold pressing pressure for 48 hours;

[0102] (4) Board curing: The plywood after pressure relief was cured at 70° C. for 2 days and then cured at room temperature for 5 days. The boards were denoted as P1-4 (corresponding to Examples 1-4, respectively) and DP1-5 (corresponding to Examples 1-5, respectively).

[0103] The mechanical strength, moisture resistance and flame retardancy of the panels P1-4 and DP1-5 were tested respectively. The test methods and test results are as follows:

[0104] (1) Test of static bending strength and elastic modulus: Refer to GB / T 17657-2022 "Test methods for physical and chemical properties of wood-based panels and veneer wood-based panels" to test the static bending strength and elastic modulus of the board, where the span is 20 times the thickness of the board.

[0105] (2) Moisture resistance test: Refer to GB / T 17657-2022 "Test methods for physical and chemical properties of wood-based panels and veneer wood-based panels" to test the 24h water absorption thickness expansion rate and Class II immersion peeling performance of the board. The 24h absorption thickness expansion rate (TS-24h) is to immerse a 50mm×50mm board in water at room temperature and test the expansion degree of the board after 24 hours. The smaller the TS-24h, the smaller the water absorption expansion of the board and the better the moisture resistance. The Class II immersion peeling test is to immerse a 75mm×75mm sample in 65℃ water for 3 hours, and then heat treat it in a 65℃ oven for 3 hours. Observe whether the glue layers of the plywood are debonded or cracked, and record the crack length of one side of the glue layer. In this test, samples with a single-side crack exceeding 25mm are recorded as unqualified.

[0106] (3) Flame retardant performance test: Refer to GB / T 2406.2-2009 "Determination of Combustion 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 exceeding 35% (≥35%) indicates a good flame retardant effect. The oxygen index below 35% and above 30% (30% ≤ LOI <35%) indicates a certain flame retardant effect, but the flame retardant effect is weak. The oxygen index below 30% (<30%) is recorded as combustible material.

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

[0108]

[0109]

[0110] As shown in Table 1, the test groups P1 to P4 all have good static bending strength, high elastic modulus, low water absorption thickness expansion rate, good immersion peeling performance, and excellent flame retardant oxygen index performance. The plywood prepared by the control group DP1 has low bonding strength and poor moisture resistance (water absorption thickness expansion rate and immersion peeling performance). Without wishing to be limited by theory, it is believed that since the organic gelling material has not been modified, the organic component itself has not formed a cross-linked structure, so it has strong hygroscopicity, resulting in low bonding strength between the adhesive and the veneer as a whole, and poor moisture resistance (water absorption thickness expansion rate and immersion peeling performance). The overall performance of the plywood prepared by the control group DP2 is also poor. Without wishing to be limited by theory, it is believed that since the organic component has not been subjected to necessary oxidation treatment, the activity of the organic component is poor, and a good three-dimensional cross-linked structure is not formed during the high-temperature heat treatment, so the overall performance is also poor. The overall performance of the plywood prepared by the control group DP3 is poor. Without wishing to be limited by theory, it is believed that due to the lack of necessary cross-linking treatment of the organic components, the water resistance of the organic components is poor. During the high-temperature heat treatment, the double oxidation oxidation causes the end group of the hydrosol component to oxidize. Due to the lack of cross-linking components, the system does not form a good three-dimensional cross-linking structure, so the overall performance is poor. The plywood prepared by the control group DP4 has poor moisture resistance and flame retardancy. Without wishing to be limited by theory, it is believed that due to the reduction in the component content of the inorganic glue, the overall adhesive does not form a good gel phase, and a large amount of free magnesium chloride leads to strong hygroscopicity and poor moisture resistance; due to the lack of a good inorganic gel skeleton, the flame retardancy of the plywood is also poor. The overall strength of the plywood prepared by the control group DP5 is reduced and the water resistance is deteriorated. Without wishing to be limited by theory, it is believed that due to the low boric acid content, the system viscosity is small, the free water is high, the penetration on the surface of the veneer is aggravated, and the component ratio of the original system is destroyed, thus resulting in a reduction in the overall strength of the plywood and deterioration of water resistance.

[0111] The above description of the embodiments is to facilitate the understanding and application of the present invention by those skilled in the art. It is obvious that those skilled in the art can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative work. Therefore, the present invention is not limited to the embodiments herein, and 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 present invention should be within the protection scope of the present invention.

Claims

1. An environmentally friendly flame-retardant cold-pressed adhesive, characterized in that: By weight, the raw materials include: The modified hydrosol is prepared by oxidative crosslinking reaction of acrylic hard monomer and hydrosol precursor in the presence of oxidant and crosslinking agent.

2. The adhesive according to claim 1, characterized in that: The hydrosol precursor is selected from at least one of hyaluronic acid, gelatin, chitosan and sodium alginate; Preferably, the number average molecular weight of the hydrosol precursor is 2.0×10 4 ~6.5×10 4 g / mol; More preferably, the number average molecular weight of the gelatin is 2.4×10 4 ~3.6×10 4 g / mol; the number average molecular weight of the hyaluronic acid is 4.5×10 4 ~6.5×10 4 g / mol.

3. The adhesive according to claim 1 or 2, characterized in that: The oxidant is selected from at least one of hydrogen peroxide, sodium hypochlorite and perchloric acid; and / or, The acrylic hard monomer is selected from at least one of acrylic acid, methacrylic acid and acrylonitrile; and / or, The mass ratio of the acrylic hard monomer to the hydrosol precursor is 1:0.75-4, preferably 1:1-2.5; and / or, The amount of the oxidant is 0.5% to 1.0% of the mass of the propylene hard monomer; and / or, The amount of the crosslinking agent used is 1% to 3% of the mass of the propylene hard monomer.

4. The adhesive according to any one of claims 1 to 3, characterized in that: The cross-linking agent is selected from at least one of cationic polyacrylamide, carboxylated polyacrylamide and hydroxy polyacrylamide; Preferably, the number average molecular weight of the cross-linking agent is 2.5×10 6 ~3.5×10 6 g / mol; More preferably, the number average molecular weight of the cationic polyacrylamide is 3×10 6 ~3.4×10 6 g / mol.

5. The adhesive according to any one of claims 1 to 4, characterized in that: The preparation method of the modified hydrosol comprises the following steps: S1, adding an acrylic hard monomer and a cross-linking agent to a hydrosol precursor aqueous solution, and then adding an oxidant to obtain a mixed solution; S2, heating the mixed solution to a first temperature, maintaining it at the first temperature for a preliminary reaction, and then heating it to a second temperature, maintaining it at the second temperature for an oxidative cross-linking reaction to obtain a modified hydrosol solution.

6. The adhesive according to claim 5, characterized in that: The first temperature is 50-70° C., and / or the pre-reaction time is 2-4 hours, and / or the second temperature is 80-95° C., and / or the cross-linking reaction time is 0.25-2 hours.

7. A method for preparing the environmentally friendly flame-retardant cold-pressed adhesive according to any one of claims 1 to 6, characterized in that: The following steps are involved: The modified hydrosol, magnesium sulfate, magnesium chloride and magnesium oxide are first mixed, and then boric acid is added for second mixing; preferably, the temperatures of the first mixing and the second mixing are independently 20 to 40°C.

8. A plywood, characterized in that: The bonding is performed using the environmentally friendly flame retardant cold-pressed adhesive described in any one of claims 1 to 6 or the environmentally friendly flame retardant cold-pressed adhesive prepared by the preparation method described in claim 7.

9. A method for preparing plywood, characterized in that: The following steps are involved: (1) Veneer preparation: making wood into veneer; (2) Gluing the veneer: uniformly coating the environmentally friendly flame-retardant cold-pressed adhesive described in any one of claims 1 to 6 or the environmentally friendly flame-retardant cold-pressed adhesive prepared by the preparation method described in claim 7 on both sides of the veneer in step (1); (3) Assembling and cold pressing: assembling and cold pressing the veneer sheets after gluing in step (2); (4) Board maintenance.

10. The preparation method according to claim 9, characterized in that: Step (1) further comprises: drying the veneer to a moisture content of 5 to 10 wt %; and / or In step (2), the glue application amount on one side of the veneer is 200-300 g / m 2 ; and / or In step (3), the conditions for the assembly include: following the principles of odd number of layers, symmetry and interlayer texture arrangement; and / or, the conditions for the cold pressing include: temperature of 10 to 35° C., pressure of 1.0 to 1.5 MPa, and time of 24 to 72 h; In step (4), the curing conditions of the plate include: curing at 20 to 70° C. for 2 to 7 days.

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