Preparation method of low-moisture-absorbing and flame-retardant plywood and the prepared plywood

Abstract

The present application relates to the technical field of flame-retardant materials, and particularly relates to a preparation method of low-hygroscopic flame-retardant plywood and the prepared plywood. The preparation method of low-hygroscopic flame-retardant plywood comprises the following steps: S1, providing a plywood as a base material plate; S2, coating magnesium sulfide oxide adhesive on two surfaces of the base material plate to obtain a sizing base material plate; S3, providing two veneers; S4, assembling the veneers in the order of veneer-sizing base material plate-veneer to obtain a board blank of low-hygroscopic flame-retardant plywood; and S5, cold pressing and hot pressing the board blank in sequence to obtain the low-hygroscopic flame-retardant plywood. The low-hygroscopic flame-retardant plywood is prepared by using the magnesium sulfide oxide flame-retardant adhesive, the problem of moisture absorption and corrosion of metal connecting parts existing in the traditional wet-process flame-retardant plywood is solved, and the low-hygroscopic flame-retardant plywood can be used only in the facing layer of the flame-retardant plywood, so that the cost can be effectively reduced.

Description

Technical Field

[0001] This invention relates to the field of flame retardant materials technology, specifically to a method for preparing low moisture absorption and flame retardant plywood and the resulting plywood. Background Technology

[0002] According to GB20286-2006 "Requirements and Marking for Combustion Performance of Flame-Retardant Products and Components in Public Places," all plywood used in public gathering places and densely populated areas such as schools, shopping malls, and entertainment venues must undergo flame-retardant treatment to achieve a certain flame-retardant rating. There are two conventional processes for preparing flame-retardant plywood: one is to impregnate the veneer with a flame retardant, then apply glue and press it into boards. This process requires a high amount of flame retardant, and the treated veneer is prone to moisture absorption, corroding metal connectors such as light steel keels. The other process involves adding a flame retardant to the adhesive, then applying glue and pressing it into boards. This process requires multiple layers of flame retardant, increasing costs, and the flame-retardant effect is not ideal for thin boards of 9-12mm.

[0003] Inorganic adhesives are characterized by flame retardancy and smoke suppression, good bonding performance, formaldehyde-free and environmentally friendly properties, and reasonable raw material costs, making them one of the ideal adhesives for producing fire-retardant plywood. However, inorganic adhesives have poor interfacial compatibility with wood, and the adhesive solution is relatively thin, making application difficult. Appropriate application processes, pressing and curing parameters, and raw material ratios are needed to improve the interfacial compatibility between inorganic adhesives and wood, extend the application time, and thus improve the bonding performance of inorganic adhesives. Chinese invention patent application CN 116574452 A discloses a water-resistant magnesium oxychloride inorganic adhesive for plywood. This adhesive, as a plywood adhesive, does not contain formaldehyde or other volatile organic compounds, but it is relatively thin, making it difficult to operate on a roller gluer, resulting in poor coating performance. Furthermore, a large coating amount is required to consistently achieve a B1 flame retardant rating, and the boards are prone to glue seepage. Summary of the Invention

[0004] This invention aims to solve the above-mentioned problems by providing a method for preparing low-moisture-absorption, flame-retardant plywood. The plywood prepared by this method solves the problems of moisture absorption and corrosion of metal connectors inherent in traditional wet-process flame-retardant plywood, while simultaneously achieving a stable flame-retardant rating of B1.

[0005] The technical solution of the present invention to solve the above problems is as follows:

[0006] A method for preparing low moisture absorption and flame-retardant plywood includes the following steps:

[0007] S1. Provide a plywood as the base material board;

[0008] S2. Apply magnesium oxysulfate adhesive to both sides of the substrate board to obtain an adhesive-coated substrate board;

[0009] S3 provides two single boards;

[0010] S4. Assemble the blanks in the order of veneer-adhesive substrate board-veneer to obtain a blank of low moisture absorption and flame retardant plywood.

[0011] S5. The slab is subjected to cold pressing and hot pressing in sequence to obtain low moisture absorption and flame retardant plywood.

[0012] As a preferred embodiment of the above technical solution, the cold pressing process conditions are: unit pressure 0.8~3.0MPa, time 20~48h; the hot pressing process conditions are: unit pressure 0.2~0.5Mpa, hot pressing temperature 40~50℃, hot pressing time 3~10min.

[0013] As a preferred embodiment of the above technical solution, the thickness of the substrate board is 3-25mm, and the material is selected from any one of poplar, eucalyptus, pine, and paulownia.

[0014] As a preferred embodiment of the above technical solution,

[0015] As a preferred embodiment of the above technical solution, the thickness of the veneer is 0.2 to 0.5 mm, and it is selected from either reconstituted decorative veneer or natural veneer.

[0016] In the above technical solution of the present invention, the thickness of the single board is between 0.2 and 0.5 mm. If the single board layer is too thin, it is easy to cause glue penetration.

[0017] As a preferred embodiment of the above technical solution, the magnesium sulfate-oxygenate adhesive comprises, by weight fraction: 40-60 parts magnesium sulfate heptahydrate, 100-150 parts lightly calcined magnesium oxide, 20-40 parts carboxylated styrene-butadiene emulsion, 10-30 parts boron-based flame retardant, 5-20 parts thickener, 2-8 parts isocyanate, 1-2 parts citric acid, and 80-120 parts water.

[0018] In the above-mentioned technical solution of the present invention, the acid radical ions in citric acid combine with magnesium ions, which can effectively reduce the porosity of magnesium oxysulfate adhesive and improve its water resistance.

[0019] Isocyanates are polar and highly reactive, and can easily cross-link with some active sites, and can also form hydrogen bonds. They can not only improve the bonding strength of magnesium oxysulfate adhesives, but also significantly shorten the curing time of the adhesives.

[0020] Carboxylated styrene-butadiene emulsion has good flowability and filling properties, which can be incorporated into magnesium oxysulfate adhesives to reduce porosity, increase density, and thus improve the strength of magnesium oxysulfate flame-retardant adhesives. In addition, carboxylated styrene-butadiene emulsion can coat the surface of magnesium oxysulfate crystal structure and form a protective film. The encapsulation effect of this film prevents direct contact between magnesium oxysulfate cement and moisture, greatly improving the water resistance of magnesium oxysulfate cement. At the same time, carboxylated styrene-butadiene emulsion, as an intermediate medium, improves the compatibility between the adhesive and wood, thereby further improving the bonding strength.

[0021] The addition of thickeners can effectively increase the viscosity of magnesium oxysulfate adhesives, which can improve coating performance and prevent excessive penetration of the adhesive, thus avoiding over-penetration.

[0022] The addition of flame retardants can effectively improve the flame retardant properties of magnesium oxysulfate adhesives, thereby ensuring a stable flame retardant rating of B1 while reducing the coating amount, thus reducing costs and improving production efficiency.

[0023] As a preferred embodiment of the above technical solution, the preparation method of the magnesium sulfate-oxygenate adhesive is as follows: magnesium sulfate heptahydrate and water are added to a stirring vessel and stirred until dissolved. Then, citric acid, isocyanate, carboxylated styrene-butadiene emulsion, lightly calcined magnesium oxide, thickener and flame retardant are added in sequence, and stirring is continued until the mixture is homogeneous to obtain the magnesium sulfate-oxygenate flame retardant adhesive.

[0024] As a preferred embodiment of the above technical solution, the carboxylated styrene-butadiene emulsion has a viscosity of 130–150 mPa·s, a pH value of 6.0–7.0, and a solid content of 45–55%.

[0025] As a preferred embodiment of the above technical solution, the thickener is selected from at least one of flour, polyacrylamide, and hydroxymethyl cellulose.

[0026] As a preferred embodiment of the above technical solution, the flame retardant is selected from at least one of borax, boric acid, and zinc borate.

[0027] Another object of the present invention is to provide a low moisture absorption and flame retardant plywood prepared by the above method.

[0028] In summary, the present invention has the following beneficial effects:

[0029] 1. This invention uses magnesium oxysulfate flame retardant adhesive to prepare low moisture absorption and flame retardant plywood, which solves the problems of moisture absorption and corrosion of metal connectors in traditional wet flame retardant plywood. It only needs to be used on the surface layer of flame retardant plywood, which can effectively reduce costs.

[0030] 2. This invention uses carboxylated styrene-butadiene emulsion to modify magnesium oxysulfate adhesive, which effectively improves the bonding strength and water resistance of magnesium oxysulfate adhesive. By adding a thickener, the problems of insufficient adhesive viscosity causing difficulties in adhesive application and adhesive penetration in magnesium oxysulfate adhesive are effectively solved.

[0031] 3. This invention uses boron-based flame retardants to improve the flame retardant properties of magnesium oxysulfate adhesives, ensuring stable flame retardant performance up to B1 level while reducing the coating amount;

[0032] 4. This invention uses low-temperature hot pressing to hot press low-moisture-absorbing and flame-retardant plywood, which can ensure the surface of the low-moisture-absorbing and flame-retardant plywood is flat and shorten the production cycle. Detailed Implementation

[0033] To more clearly demonstrate the objectives and technical advantages of this invention, the technical solution of this invention will be described in detail below. Obviously, the described embodiments are only a part of the embodiments of the invention, and not all of them. Based on the embodiments in this utility model, any embodiments obtained by those skilled in the art without inventive effort are within the scope of protection of this invention.

[0034] Unless otherwise specified, all materials, equipment, and instruments used in the following embodiments are commercially available. In this invention, "parts" refers to parts by weight.

[0035] Example 1

[0036] A method for preparing low moisture absorption and flame retardant plywood includes the following steps:

[0037] I. Preparation of magnesium oxysulfate adhesive

[0038] By weight, 40 parts magnesium sulfate heptahydrate and 80 parts water are added to a mixing vessel in sequence. After stirring and dissolving, 1 part citric acid, 2 parts diphenylmethane diisocyanate, 20 parts carboxylated styrene-butadiene emulsion, 100 parts lightly calcined magnesium oxide, 10 parts boric acid, 1 part polyacrylamide, and 15 parts flour are added in sequence. Stirring is continued until homogeneous to obtain magnesium sulfate-oxygenate adhesive.

[0039] II. Preparation of Low Moisture Absorption and Flame Retardant Plywood

[0040] 1) Apply the above-mentioned magnesium oxysulfate adhesive to both sides of a 9mm thick plywood substrate made of 7 layers of rotary-cut eucalyptus veneer, with an adhesive application rate of 300g / m² on each side. 2 The adhesive substrate board is obtained;

[0041] 2) Provide two identical engineered wood veneers and assemble them in the order of engineered wood veneer-glued substrate board-engineered wood veneer to obtain a blank of low moisture absorption and fire retardant plywood.

[0042] 3) The slab is subjected to cold pressing and hot pressing in sequence to obtain low moisture absorption and flame retardant plywood; the process conditions for cold pressing are: unit pressure 0.8MPa, time 24h; the process conditions for hot pressing are: unit pressure 0.3MPa, hot pressing temperature 40℃, hot pressing time 3min.

[0043] Example 2

[0044] A method for preparing low moisture absorption and flame retardant plywood includes the following steps:

[0045] I. Preparation of magnesium oxysulfate adhesive

[0046] By weight, 45 parts magnesium sulfate heptahydrate and 90 parts water were added to a mixing vessel in sequence. After stirring and dissolving, 1 part citric acid, 4 parts diphenylmethane diisocyanate, 25 parts carboxylated styrene-butadiene emulsion, 110 parts lightly calcined magnesium oxide, 10 parts boric acid, 5 parts borax, 2 parts hydroxymethyl cellulose, and 15 parts flour were added in sequence. The mixture was stirred until homogeneous to obtain magnesium sulfate-oxygenate adhesive.

[0047] II. Preparation of Low Moisture Absorption and Flame Retardant Plywood

[0048] 1) Apply the above-mentioned magnesium oxysulfate adhesive to both sides of a 9mm thick plywood substrate made of 7 layers of rotary-cut eucalyptus veneer, with an adhesive application rate of 300g / m² on each side. 2 The adhesive substrate board is obtained;

[0049] 2) Provide two identical engineered wood veneers and assemble them in the order of engineered wood veneer-glued substrate board-engineered wood veneer to obtain a blank of low moisture absorption and fire retardant plywood.

[0050] 3) The slab is subjected to cold pressing and hot pressing in sequence to obtain low moisture absorption and flame retardant plywood; the process conditions for cold pressing are: unit pressure 0.8MPa, time 24h; the process conditions for hot pressing are: unit pressure 0.3MPa, hot pressing temperature 40℃, hot pressing time 3min.

[0051] Example 3

[0052] A method for preparing low moisture absorption and flame retardant plywood includes the following steps:

[0053] I. Preparation of magnesium oxysulfate adhesive

[0054] By weight, 55 parts magnesium sulfate heptahydrate and 100 parts water were added to a mixing vessel in sequence. After stirring and dissolving, 2 parts citric acid, 6 parts diphenylmethane diisocyanate, 30 parts carboxylated styrene-butadiene emulsion, 120 parts lightly calcined magnesium oxide, 20 parts zinc borate, 1 part hydroxymethyl cellulose, and 20 parts flour were added in sequence. Stirring was continued until homogeneous to obtain magnesium sulfate-oxygenate adhesive.

[0055] II. Preparation of Low Moisture Absorption and Flame Retardant Plywood

[0056] 1) Apply the above-mentioned magnesium oxysulfate adhesive to both sides of a 9mm thick plywood substrate made of 7 layers of rotary-cut eucalyptus veneer, with an adhesive application rate of 250g / m² on each side. 2 The adhesive substrate board is obtained;

[0057] 2) Provide two identical Okoume veneers and assemble them in the order of Okoume veneer - adhesive substrate board - Okoume veneer to obtain a blank of low moisture absorption and flame retardant plywood.

[0058] 3) The slab is subjected to cold pressing and hot pressing in sequence to obtain low moisture absorption and flame retardant plywood; the process conditions for cold pressing are: unit pressure 0.8MPa, time 24h; the process conditions for hot pressing are: unit pressure 0.3MPa, hot pressing temperature 40℃, hot pressing time 3min.

[0059] Comparative Example 1

[0060] A method for preparing plywood includes the following steps:

[0061] I. Preparation of magnesium oxysulfate adhesive

[0062] By weight, 40 parts magnesium sulfate heptahydrate and 80 parts water are added to a mixing vessel in sequence. After stirring and dissolving, 1 part citric acid, 2 parts diphenylmethane diisocyanate, 100 parts lightly calcined magnesium oxide, 10 parts zinc borate, 1 part polyacrylamide, and 15 parts flour are added in sequence. Stirring is continued until uniform to obtain magnesium sulfate-oxygenated adhesive.

[0063] II. Preparation of Low Moisture Absorption and Flame Retardant Plywood

[0064] 1) Apply the above-mentioned magnesium oxysulfate adhesive to both sides of a 9mm thick plywood substrate made of 7 layers of rotary-cut eucalyptus veneer, with an adhesive application rate of 250g / m² on each side. 2 The adhesive substrate board is obtained;

[0065] 2) Provide two identical engineered wood veneers and assemble them in the order of engineered wood veneer - adhesive substrate board - engineered wood veneer to obtain a plywood blank;

[0066] 3) The slab is subjected to cold pressing and hot pressing in sequence to obtain low moisture absorption and flame retardant plywood; the process conditions for cold pressing are: unit pressure 0.8MPa, time 24h; the process conditions for hot pressing are: unit pressure 0.3MPa, hot pressing temperature 40℃, hot pressing time 3min.

[0067] Comparative Example 2

[0068] A method for preparing plywood includes the following steps:

[0069] I. Preparation of magnesium oxysulfate adhesive

[0070] By weight, 40 parts magnesium sulfate heptahydrate and 80 parts water are added to a mixing vessel in sequence. After stirring and dissolving, 1 part citric acid, 2 parts diphenylmethane diisocyanate, 20 parts carboxylated styrene-butadiene emulsion, 100 parts lightly calcined magnesium oxide, 1 part polyacrylamide, and 15 parts flour are added in sequence. Stirring is continued until homogeneous to obtain magnesium sulfate-oxygenate adhesive.

[0071] II. Preparation of Plywood

[0072] 1) Apply the above-mentioned magnesium oxysulfate adhesive to both sides of a 9mm thick plywood substrate made of 7 layers of rotary-cut eucalyptus veneer, with an adhesive application rate of 250g / m² on each side. 2 The adhesive substrate board is obtained;

[0073] 2) Provide two identical engineered wood veneers and assemble them in the order of engineered wood veneer - adhesive substrate board - engineered wood veneer to obtain a plywood blank;

[0074] 3) The slab is subjected to cold pressing and hot pressing in sequence to obtain plywood; the process conditions for cold pressing are: unit pressure 0.8MPa, time 24h; the process conditions for hot pressing are: unit pressure 0.3MPa, hot pressing temperature 40℃, hot pressing time 3min.

[0075] Comparative Example 3

[0076] A method for preparing plywood includes the following steps:

[0077] I. Preparation of magnesium oxysulfate adhesive

[0078] By weight, 30 parts magnesium sulfate heptahydrate and 80 parts water are added to a mixing vessel in sequence. After stirring and dissolving, 1 part citric acid, 2 parts diphenylmethane diisocyanate, 20 parts carboxylated styrene-butadiene emulsion, 100 parts lightly calcined magnesium oxide, and 10 parts boric acid are added in sequence. Stirring is continued until homogeneous to obtain magnesium sulfate-oxygenate adhesive.

[0079] II. Preparation of Low Moisture Absorption and Flame Retardant Plywood

[0080] 1) Apply the aforementioned magnesium oxysulfate adhesive to both sides of a 9mm thick plywood substrate made of 7 layers of rotary-cut eucalyptus veneer. However, due to the adhesive being too thin, it could not be applied onto the glue rollers. The process was discontinued.

[0081] Comparative Example 4

[0082] Preparation of flame-retardant plywood

[0083] Urea-formaldehyde resin adhesive was applied to both sides of a 9mm thick flame-retardant plywood substrate, with a coating amount of 250g / m². 2The plywood is assembled with engineered wood veneer, and then cold-pressed and hot-pressed to produce wet-process fire-retardant plywood. The cold-pressing process conditions are: unit pressure 0.6 MPa, time 40 min; the hot-pressing process conditions are: unit pressure 0.7 MPa, hot-pressing temperature 120℃, hot-pressing time 10 min.

[0084] The method for preparing the flame-retardant plywood substrate is as follows:

[0085] 1) Immerse 7 eucalyptus rotary-cut veneers in a saturated ammonium molybdate aqueous solution until fully saturated, then remove them, wipe off the surface water stains, rinse them with clean water, and then send them to a wood drying equipment to dry until the moisture content is about 10% to obtain flame-retardant veneers.

[0086] 2) Coat 7 flame-retardant veneers with urea-formaldehyde resin adhesive, with a coating amount of 200g / m². 2 Then, according to the longitudinal and transverse directions, 7 layers of blanks are assembled;

[0087] 3) The flame-retardant plywood used as the substrate is obtained by cold pressing and hot pressing in sequence; the process conditions for cold pressing are: unit pressure 0.6MPa, time 40min; the process conditions for hot pressing are: unit pressure 0.7MPa, hot pressing temperature 120℃, hot pressing time 10min.

[0088] Comparative Example 5

[0089] Preparation of flame-retardant plywood

[0090] I. Preparation of Flame-Retardant Adhesives

[0091] By weight, take 35 parts of ammonium polyphosphate flame retardant, 30 parts of flour, and 100 parts of urea-formaldehyde resin adhesive and mix them evenly to obtain a flame retardant adhesive.

[0092] Preparation of flame-retardant plywood

[0093] 1) Apply the above-mentioned flame-retardant adhesive to both sides of a 9mm thick plywood substrate made of 7 layers of rotary-cut eucalyptus veneer, with an adhesive application rate of 250g / m² on each side. 2 The adhesive substrate board is obtained;

[0094] 2) Provide two identical engineered wood veneers and assemble them in the order of engineered wood veneer - adhesive substrate board - engineered wood veneer to obtain a plywood blank;

[0095] 3) The slab is subjected to cold pressing and hot pressing in sequence to obtain plywood; the process conditions for cold pressing are: unit pressure 0.6MPa, time 40min; the process conditions for hot pressing are: unit pressure 0.7MPa, hot pressing temperature 120℃, hot pressing time 10min.

[0096] The combustion performance of Examples 1-3 and Comparative Examples 1-5 was tested according to GB / T 20284-2006 "Single Combustion Test of Building Materials or Products". Table 1 shows the test results of the combustion performance of Examples 1-3 and Comparative Examples 1-5.

[0097] Table 1. Combustion performance test results of Examples 1-3 and Comparative Examples 1-5

[0098]

[0099]

[0100] As shown in Table 1, the low-moisture-absorbing flame-retardant plywoods obtained in Examples 1-3 all meet the national standard requirement of B1(B) in terms of combustion performance. Comparing the combustion performance test results of Example 1 with Comparative Example 2, it can be seen that the addition of boron-based flame retardants can effectively improve the combustion performance of low-moisture-absorbing flame-retardant plywoods, enabling them to stably meet the B1(B) level requirement. Compared with Comparative Example 1, it can be seen that the addition of carboxylated styrene-butadiene emulsion and thickener improves the bonding strength and coating performance of the plywood. The improved bonding strength also helps to improve the overall combustion performance of the plywood. The synergistic effect of boron-based flame retardants, carboxylated styrene-butadiene emulsion, and thickener enables the low-moisture-absorbing flame-retardant plywoods to stably meet the B1(B) level in terms of combustion performance. Compared with Comparative Example 5, the flame-retardant plywood prepared by coating only the engineered wood veneer and the plywood substrate with conventional flame-retardant adhesives in Example 1 does not meet the B1(C) level requirement in terms of combustion performance. This shows that the use of magnesium oxysulfate flame-retardant adhesives can significantly improve the flame-retardant performance.

[0101] According to GB / T 17657-2013 "Test Methods for Physical and Chemical Properties of Wood-based Panels and Decorative Wood-based Panels", "Accelerated Determination Method for Metal Corrosion Rate in Contact with Preservative-treated Wood", and LY / T 3036-2018 "Test Method for Hygroscopicity of Flame-retardant Wood Materials", the surface bonding strength, impregnation peeling, metal corrosion rate, and hygroscopicity of Examples 1-3 and Comparative Examples 1-5 were tested respectively. Table 2 shows the test results of the physical and chemical properties of Examples 1-3 and Comparative Examples 1-5.

[0102] Table 2. Physicochemical property test results of Examples 1-3 and Comparative Examples 1-5

[0103]

[0104]

[0105] As shown in Table 2, the physicochemical performance test results of Examples 1-3 all meet the national standard requirements for impregnation peel performance and surface bonding strength. However, Comparative Example 1 fails to meet the national standard for impregnation peel performance and surface bonding strength. This is because the carboxylated styrene-butadiene emulsion has good fluidity and filling effect, which can advance the initial setting time of the magnesium oxysulfate adhesive. The carboxylated styrene-butadiene emulsion fills the magnesium oxysulfate adhesive, reducing porosity and improving water resistance. Simultaneously, the carboxylated styrene-butadiene emulsion also forms a thin film in the magnesium oxysulfate adhesive, coating the surface and enhancing bonding strength. Comparative Example 3 did not add a thickener, resulting in an excessively thin adhesive that could not be applied on the roller gluer. Comparative Example 4 is a wet-process fire-retardant plywood. As shown in Table 2, the metal corrosion rate and hygroscopicity of Example 1 are much lower than those of Comparative Example 4. Excessive metal corrosion rate and hygroscopicity can lead to corrosion of metal connectors and mold growth on the board surface, seriously endangering life and property safety over time.

Claims

1. A method for preparing low-moisture-absorbing and flame-retardant plywood, comprising the following steps: S1. Provide a plywood as the base material board; S2. Apply magnesium oxysulfate adhesive to both sides of the substrate board to obtain an adhesive-coated substrate board; S3 provides two single boards; S4. Assemble the blanks in the order of veneer-adhesive substrate board-veneer to obtain a blank of low moisture absorption and flame retardant plywood. S5. The slab is subjected to cold pressing and hot pressing in sequence to obtain low moisture absorption and flame retardant plywood. The cold pressing process conditions are: unit pressure 0.8~3.0 MPa, time 20~48h; the hot pressing process conditions are: unit pressure 0.2~0.5 MPa, hot pressing temperature 40~50℃, hot pressing time 3~10min. The magnesium sulfate-oxygenated adhesive comprises, by weight fraction: 40-60 parts magnesium sulfate heptahydrate, 100-150 parts lightly calcined magnesium oxide, 20-40 parts carboxylated styrene-butadiene emulsion, 10-30 parts boron-based flame retardant, 5-20 parts thickener, 2-8 parts isocyanate, 1-2 parts citric acid, and 80-120 parts water; The preparation method of the magnesium sulfate-oxygenate adhesive is as follows: magnesium sulfate heptahydrate and water are added to a stirring tank and stirred until dissolved. Then, citric acid, isocyanate, carboxylated styrene-butadiene emulsion, lightly calcined magnesium oxide, thickener and boron flame retardant are added in sequence and stirred until uniformly mixed to obtain the magnesium sulfate-oxygenate adhesive.

2. The method for preparing a low-moisture-absorbing, flame-retardant plywood according to claim 1, characterized in that: The thickness of the substrate board is 3~25 mm, and the material is selected from any one of poplar, eucalyptus, pine and paulownia.

3. The method for preparing a low-moisture-absorbing, flame-retardant plywood according to claim 1, characterized in that: The thickness of the veneer is 0.2~0.5 mm, and it is selected from either reconstituted decorative veneer or natural veneer.

4. The method for preparing a low-moisture-absorbing, flame-retardant plywood according to claim 1, characterized in that: The carboxylated styrene-butadiene emulsion has a viscosity of 130-150 mPa·s, a pH value of 6.0-7.0, and a solid content of 45-55%.

5. The method for preparing a low-moisture-absorbing, flame-retardant plywood according to claim 1, characterized in that: The thickener is selected from at least one of flour, polyacrylamide, and hydroxymethyl cellulose.

6. The method for preparing a low-moisture-absorbing, flame-retardant plywood according to claim 1, characterized in that: The boron-based flame retardant is selected from at least one of borax, boric acid, and zinc borate.

7. Low moisture absorption and flame retardant plywood prepared by the method according to any one of claims 1 to 6.

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