Environment-friendly glue for plywood and preparation method thereof

Abstract

The invention relates to the technical field of adhesives, in particular to environment-friendly glue for plywood and a preparation method of the environment-friendly glue. The environment-friendly glue for plywood is prepared from the following preparation raw materials in parts by mass: 20 to 25 parts of light calcined magnesia, 6 to 8 parts of anhydrous magnesium chloride, 30 to 35 parts of modified potato starch, 10 to 12 parts of gelatin, 5 to 7 parts of flame retardant, 3 to 4 parts of waterproof agent, 3 to 4 parts of closed waterborne polyurethane, 0.5 to 0.6 part of preservative and 200 to 220 parts of water. The preparation method of the environment-friendly glue for the plywood has the advantages that the preparation is simple, the cost is low, and the obtained environment-friendly glue for the plywood has excellent water resistance, flame retardance and adhesive strength, is high in safety and is green and environment-friendly.

Description

Technical Field

[0001] The present application relates to the technical field of adhesives, and in particular to an environmentally friendly glue for plywood and a preparation method thereof. Background Art

[0002] Glue is a product that people often use in production work and daily life. Glue is generally a substance used to connect two objects. People will design different types of glue according to different application scenarios, so that glue can be used to bond paper, plates, metals, etc. Glue has become an indispensable part of current production and life.

[0003] For bonding between boards, such as bonding between wooden boards, people commonly use phenolic resin glue and urea-formaldehyde resin glue. Both have the advantages of high bonding strength, resistance to weak acids and alkalis, good insulation performance and low price. In addition, phenolic resin glue has good heat resistance, so phenolic resin glue and urea-formaldehyde resin glue are widely used. However, since the raw materials for preparing phenolic resin glue and urea-formaldehyde resin glue contain formaldehyde, when formaldehyde is released into the environment, it will cause harm to the human body.

[0004] In order to reduce the harm to the human body, people began to look for wood board glues that could replace phenolic resin glue and urea-formaldehyde resin glue. The emergence of magnesium glue has solved the problem of formaldehyde release. Magnesium glue is a water-solid inorganic adhesive, generally made of magnesium oxide and magnesium chloride. The preparation process does not contain formaldehyde, so the harm to the human body is reduced. However, in actual production and application, it is found that the water resistance, flame retardancy and bonding strength of magnesium glue are poor, and it is easy to fail in the environment with high humidity, which needs to be improved. Summary of the invention

[0005] The purpose of this application is to address the deficiencies of current technology and provide an environmentally friendly glue for plywood and a preparation method thereof. The preparation method of the environmentally friendly glue for plywood of the present application has the advantages of simple preparation and low cost. At the same time, the environmentally friendly glue for plywood obtained has excellent water resistance, flame retardancy and bonding strength, high safety and green environmental protection.

[0006] In the first aspect, the present application provides an environmentally friendly glue for plywood, which adopts the following technical solution: An environmentally friendly glue for plywood comprises the following raw materials by weight: 20-25 parts of light-burned magnesium oxide, 6-8 parts of anhydrous magnesium chloride, 30-35 parts of modified potato starch, 10-12 parts of gelatin, 5-7 parts of flame retardant, 3-4 parts of waterproofing agent, 3-4 parts of closed water-based polyurethane, 0.5-0.6 parts of preservative and 200-220 parts of water.

[0007] By adopting the above technical scheme, light-burned magnesium oxide and anhydrous magnesium chloride: light-burned magnesium oxide mainly plays the role of adjusting the pH value of environmentally friendly glue, increasing stability and bonding ability, while anhydrous magnesium chloride acts as a gelling agent to increase the viscosity of environmentally friendly glue and improve the adhesion of environmentally friendly glue. The two work together to make the glue have better stability and bonding ability. Modified potato starch can improve the gel strength of environmentally friendly glue and the water holding capacity of potato starch gel. This is conducive to improving the bonding strength and water resistance of environmentally friendly glue. At the same time, modified potato starch is a natural degradable polymer material with good biocompatibility and environmental friendliness, which can reduce pollution to the environment and improve the safety and environmental performance of products. Flame retardant: Graphene-modified 2-carboxyethylphenyl hypophosphorous acid as a gas source releases a large amount of non-flammable gas, dilutes the oxygen in the environment, and thus improves the flame retardant effect. Modification by γ-aminopropyltrimethoxysilane helps the combination between graphene oxide and 2-carboxyethylphenyl hypophosphorous acid, enhances the interaction between them, and improves the compatibility and dispersibility in environmentally friendly glue. Graphene oxide forms a three-dimensional mesh structure, which further enhances the flame retardant effect of environmentally friendly glue. Waterproofing agent can increase the water resistance of environmentally friendly glue, and it is not easy to be damaged even if soaked in water, and at the same time greatly improves the bonding strength of environmentally friendly glue. Closed waterborne polyurethane: The hydroxyl group on the methyl ethyl ketone oxime molecule undergoes a polycondensation reaction with the isocyanate group on the polyurethane prepolymer to prepare a closed waterborne polyurethane; the closed waterborne polyurethane prepared by methyl ethyl ketone oxime is a cross-linking agent, and the active isocyanate group is unblocked under high temperature conditions, so that it reacts with gelatin to produce a cross-linking reaction to synthesize a colloid, which can significantly improve the water resistance and bonding strength of environmentally friendly glue. Preservative: Preservative can effectively prevent the growth and reproduction of microorganisms in the glue and extend the service life of the glue. In summary, the environmentally friendly glue for plywood of the present application has the advantages of simple preparation and low cost, excellent water resistance, flame retardancy and bonding strength, high safety and green environmental protection.

[0008] Preferably, the method for preparing the modified potato starch comprises the following steps: S21, according to the mass fraction, 180 parts of wheat bran were ground through a 100 mesh sieve, mixed with 500g of water and stirred for 50min to obtain a suspension, 42 parts of α-amylase were added, and the enzymolysis time was 12h; after the enzymolysis was completed, the mixture was heated to 115°C and the enzyme was inactivated for 12min; then 230 parts of a 20g / L sodium hydroxide aqueous solution were added, and after stirring for 6h, the pH value of the system was adjusted to 4 with 30% hydrochloric acid by mass concentration, and then centrifuged at 8000rpm for 60min, the supernatant was collected, 300 parts of a 75% ethanol aqueous solution by mass concentration were added to precipitate the supernatant, and the supernatant was filtered after stirring for 40min, and the precipitate was collected, and freeze-dried at -35°C for 24h to obtain a wheat bran hydrolysate; S22. According to the mass fractions, 120 parts of potato starch are added to 83 parts of an aqueous solution of wheat bran hydrolysate having a mass concentration of 15%, stirred at 68°C for 60 minutes, then heated to 93°C, stirred for 40 minutes, cooled to 30°C, stirred for 40 minutes, and then centrifuged at 8000 rpm for 60 minutes, and then the precipitate is collected and freeze-dried at -5°C for 24 hours to obtain modified potato starch.

[0009] By adopting the above technical scheme, the role and synergistic effect of the prepared modified potato starch in the environmentally friendly glue are mainly reflected in the following aspects: 1. Improving bonding strength: Modified potato starch can improve the gel strength of environmentally friendly glue and the water holding capacity of potato starch gel through the hydrogen bond interaction between wheat bran enzymatic hydrolysate and potato starch. This is conducive to improving the bonding strength and water resistance of environmentally friendly glue. 2. Green, environmentally friendly and safe: Modified potato starch is a natural, degradable polymer material with good biocompatibility and environmental friendliness. Using modified potato starch as one of the components of the adhesive can reduce pollution to the environment and improve the safety and environmental performance of the product. 3. Reduce costs: Modified potato starch has a lower cost than other synthetic polymer adhesives and a simple preparation method.

[0010] Preferably, the flame retardant is graphene-modified 2-carboxyethylphenyl hypophosphorous acid.

[0011] Preferably, the method for preparing the graphene-modified 2-carboxyethylphenyl hypophosphorous acid comprises the following steps: S41, dispersing 150 parts of 2-carboxyethylphenylphosphorous acid and 13 parts of graphene oxide in a solution consisting of 14 parts of γ-aminopropyltrimethoxysilane, 320 parts of ethanol and 30 parts of water, according to parts by mass, to obtain a mixed solution; S42, heating the mixed solution to 43°C, stirring at a rate of 800 rpm, reacting for 10 hours, filtering, and vacuum drying at 85°C for 24 hours, grinding and sieving to obtain graphene-modified 2-carboxyethylphenylphosphorous acid with a particle size of 1-3 μm.

[0012] By adopting the above technical scheme, the prepared graphene-modified 2-carboxyethylphenyl hypophosphorous acid plays a key role as a flame retardant in environmentally friendly glue: 1. Improving the flame retardant effect: Graphene-modified 2-carboxyethylphenyl hypophosphorous acid is used as a gas source to release a large amount of non-flammable gas, dilute the oxygen in the environment, and thus improve the flame retardant effect. 2. Enhance compatibility and dispersibility: Modification by γ-aminopropyltrimethoxysilane helps the combination between graphene oxide and 2-carboxyethylphenyl hypophosphorous acid, enhances the interaction between them, and improves the compatibility and dispersibility in environmentally friendly glue. 3. Forming a three-dimensional network structure: Graphene oxide forms a three-dimensional network structure, which further improves the flame retardant effect of environmentally friendly glue.

[0013] Preferably, the waterproofing agent comprises the following raw materials, measured by weight: 50 parts of tannic acid, 38 parts of maltodextrin, 35 parts of sodium sulphate, and 45 parts of water.

[0014] Preferably, the preparation method of the waterproofing agent is to mix maltodextrin, sodium sulfate and water in proportions by mass, heat to 35°C, react for 60-70 minutes, then add tannic acid, heat to 55°C, and react for 5-6 hours to obtain the waterproofing agent.

[0015] By adopting the above technical solution, the prepared waterproofing agent can increase the water resistance of the environmentally friendly glue, and it is not easy to be damaged even if it is soaked in water, and at the same time greatly improves the bonding strength of the environmentally friendly glue.

[0016] Preferably, the method for preparing the blocked waterborne polyurethane comprises the following steps: S71. 10 g of polypropylene glycol and 5.33 g of isophorone diisocyanate after vacuum dehydration were added to a three-necked flask equipped with a thermometer, a stirrer and a glass stopper, and mixed well. Then, 0.12 g of dibutyltin laurate was added, and the mixture was reacted at 50° C. for 20 min. The mixture was heated to 70° C. and reacted for 1 h to obtain a polyurethane prepolymer. The mixture was heated to 80° C., 0.77 g of 2,2-dimethylolpropionic acid was added, and the mixture was reacted for 1 h. The mixture was then cooled to 40° C., 1.52 g of methyl ethyl ketone oxime was added, and the mixture was reacted for 2 h. Then, 0.58 g of triethylamine was added and the mixture was neutralized for 0.5 h. During the reaction, the viscosity was adjusted with acetone, and the mixture was cooled to room temperature. Finally, 20 g of distilled water was slowly added under a stirring speed of 4000 r / min, and the mixture was emulsified for 0.5 h. After the acetone was removed by vacuum distillation, a closed waterborne polyurethane emulsion was obtained. S72. The closed waterborne polyurethane emulsion is dialyzed in a dialysis bag with a molecular weight cutoff of 1000 for 24 hours to remove reactive monomers, and after purification, a closed waterborne polyurethane is obtained.

[0017] By adopting the above technical scheme, the effects of the prepared closed waterborne polyurethane are mainly reflected in the following aspects: 1. Improving water resistance: The closed waterborne polyurethane unblocks the active isocyanate group under high temperature conditions, so that it undergoes a cross-linking reaction with gelatin to synthesize a colloid, which can significantly improve the water resistance of the environmentally friendly glue. 2. Enhancing bonding strength: The closed waterborne polyurethane is used as a cross-linking agent. By unblocking the active isocyanate group under high temperature conditions, it undergoes a cross-linking reaction with gelatin to synthesize a colloid, which can significantly improve the bonding strength of the environmentally friendly glue. 3. Green, environmentally friendly and safe: The closed waterborne polyurethane is an environmentally friendly material with good biocompatibility and environmental friendliness. Using closed waterborne polyurethane as one of the components of the adhesive can reduce pollution to the environment and improve the safety and environmental performance of the product. 4. Reducing costs: The closed waterborne polyurethane has a lower cost than other synthetic polymer adhesives and is simple to prepare.

[0018] Preferably, the preservative consists of sodium benzoate and potassium sorbate in a mass ratio of 3:2.

[0019] In a second aspect, the present application provides a method for preparing environmentally friendly glue for plywood, which adopts the following technical solution: As a general technical concept, the present application also provides a method for preparing the above-mentioned environmentally friendly glue for plywood, comprising the following steps: S91. Mix light-burned magnesium oxide, anhydrous magnesium chloride, gelatin and half of water according to their weight proportions, heat and stir to obtain a mixed solution A; S92, mixing the blocked waterborne polyurethane, the flame retardant, the water repellent, the preservative, the modified potato starch and half of the water according to their weight proportions, heating and stirring, to obtain a mixed solution B; S93. Mix the mixed solution A and the mixed solution B according to their weight proportions and stir them evenly to obtain an environmentally friendly glue.

[0020] Preferably, in step S91, the heating temperature is 65-70°C, and the stirring time is 15-20 minutes; in step S92, the heating temperature is 40-45°C, and the stirring time is 15-20 minutes; and in step S93, the stirring time is 10-20 minutes.

[0021] In summary, the beneficial technical effects of this application are: 1. Improve bonding strength and water resistance: The prepared modified potato starch improves the gel strength of the environmentally friendly glue and the water holding capacity of the potato starch gel through the hydrogen bond interaction between the wheat bran enzymatic hydrolysate and the potato starch. This is conducive to improving the bonding strength and water resistance of the environmentally friendly glue. At the same time, the prepared waterproofing agent can also increase the water resistance of the environmentally friendly glue. The blocked water-based polyurethane is used as a cross-linking agent. By unblocking the active isocyanate group under high temperature conditions, it undergoes a cross-linking reaction with gelatin to synthesize a colloid, which can significantly improve the water resistance and bonding strength of the environmentally friendly glue.

[0022] 2. Green, environmentally friendly and safe: Using modified potato starch as one of the ingredients of the adhesive can reduce pollution to the environment and improve the safety and environmental performance of the product. In addition, the glue of this application does not contain substances that are harmful to the human body and the environment, such as formaldehyde, benzene and other harmful substances.

[0023] 3. Reduce costs: Modified potato starch has lower costs than other synthetic polymer adhesives and is simple to prepare.

[0024] 4. Improve the flame retardant effect: Graphene-modified 2-carboxyethylphenyl hypophosphorous acid is used as a gas source to release a large amount of non-flammable gas, dilute the oxygen in the environment, and thus improve the flame retardant effect.

[0025] 5. Wide application: The glue of the present application can not only be used for the manufacture of plywood, but also can be widely used in the fields of wood processing, furniture manufacturing, building decoration, etc. DETAILED DESCRIPTION

[0026] The embodiments of the present application will be described in detail below in conjunction with the examples, but it will be appreciated by those skilled in the art that the following examples are only used to illustrate the present application and should not be considered as limiting the scope of the present application. In the examples, if specific conditions are not specified, they are carried out according to normal conditions or the conditions recommended by the manufacturer. If the manufacturer is not specified for the reagents or instruments used, they are all conventional products that can be purchased commercially.

[0027] In the following examples and preparation examples, 1 part means 100 g.

[0028] Preparation Example 1 Preparation of modified potato starch The preparation method of modified potato starch comprises the following steps: S21, according to the mass fraction, 180 parts of wheat bran were ground through a 100 mesh sieve, mixed with 500g of water and stirred for 50min to obtain a suspension, 42 parts of α-amylase were added, and the enzymolysis time was 12h; after the enzymolysis was completed, the mixture was heated to 115°C and the enzyme was inactivated for 12min; then 230 parts of a 20g / L sodium hydroxide aqueous solution were added, and after stirring for 6h, the pH value of the system was adjusted to 4 with 30% hydrochloric acid by mass concentration, and then centrifuged at 8000rpm for 60min, the supernatant was collected, 300 parts of a 75% ethanol aqueous solution by mass concentration were added to precipitate the supernatant, and the supernatant was filtered after stirring for 40min, and the precipitate was collected, and freeze-dried at -35°C for 24h to obtain a wheat bran hydrolysate; S22. According to the mass fractions, 120 parts of potato starch are added to 83 parts of an aqueous solution of wheat bran hydrolysate having a mass concentration of 15%, stirred at 68°C for 60 minutes, then heated to 93°C, stirred for 40 minutes, cooled to 30°C, stirred for 40 minutes, and then centrifuged at 8000 rpm for 60 minutes, and then the precipitate is collected and freeze-dried at -35°C for 24 hours to obtain modified potato starch.

[0029] Preparation Example 2 Preparation of graphene-modified 2-carboxyethylphenyl hypophosphorous acid The preparation method of graphene-modified 2-carboxyethylphenyl hypophosphorous acid comprises the following steps: S41, dispersing 150 parts of 2-carboxyethylphenylphosphorous acid and 13 parts of graphene oxide in a solution consisting of 14 parts of γ-aminopropyltrimethoxysilane, 320 parts of ethanol and 30 parts of water, according to parts by mass, to obtain a mixed solution; S42, heating the mixed solution to 43°C, stirring at a rate of 800 rpm, reacting for 10 hours, filtering, and vacuum drying at 85°C for 24 hours, grinding and sieving to obtain graphene-modified 2-carboxyethylphenylphosphorous acid with a particle size of 1-3 μm.

[0030] Preparation Example 3 Preparation of waterproofing agent The waterproofing agent comprises the following raw materials by weight: 50 parts of tannic acid, 38 parts of maltodextrin, 35 parts of sodium sulphate and 45 parts of water. The preparation method of the waterproofing agent is as follows: after uniformly mixing maltodextrin, sodium sulphate and water by weight, heating to 35°C, reacting for 65 minutes, then adding tannic acid thereto, heating to 55°C, and keeping warm for 5.6 hours to obtain the waterproofing agent.

[0031] Preparation Example 4 Preparation of blocked waterborne polyurethane The preparation method of closed waterborne polyurethane comprises the following steps: S71. 10 g of polypropylene glycol and 5.33 g of isophorone diisocyanate after vacuum dehydration were added to a three-necked flask equipped with a thermometer, a stirrer and a glass stopper, and mixed well. Then, 0.12 g of dibutyltin laurate was added, and the mixture was reacted at 50° C. for 20 min. The mixture was heated to 70° C. and reacted for 1 h to obtain a polyurethane prepolymer. The mixture was heated to 80° C., 0.77 g of 2,2-dimethylolpropionic acid was added, and the mixture was reacted for 1 h. The mixture was then cooled to 40° C., 1.52 g of methyl ethyl ketone oxime was added, and the mixture was reacted for 2 h. Then, 0.58 g of triethylamine was added and the mixture was neutralized for 0.5 h. During the reaction, the viscosity was adjusted with acetone, and the mixture was cooled to room temperature. Finally, 20 g of distilled water was slowly added under a stirring speed of 4000 r / min, and the mixture was emulsified for 0.5 h. After the acetone was removed by vacuum distillation, a closed waterborne polyurethane emulsion was obtained. S72. The closed waterborne polyurethane emulsion is dialyzed in a dialysis bag with a molecular weight cutoff of 1000 for 24 hours to remove reactive monomers, and after purification, a closed waterborne polyurethane is obtained.

[0032] Example 1 An environmentally friendly glue for plywood comprises the following raw materials, measured by weight: 20 parts of light-burned magnesium oxide, 6 parts of anhydrous magnesium chloride, 30 parts of modified potato starch, 10 parts of gelatin, 5 parts of flame retardant, 3 parts of waterproofing agent, 3 parts of closed waterborne polyurethane, 0.5 parts of preservative, and 200 parts of water, wherein the flame retardant is graphene-modified 2-carboxyethylphenyl hypophosphite, and the preservative is composed of sodium benzoate and potassium sorbate in a weight ratio of 3:2.

[0033] The above-mentioned method for preparing the environmentally friendly glue for plywood comprises the following steps: S91. Mix light-burned magnesium oxide, anhydrous magnesium chloride, gelatin and half of water according to their weight fractions, heat and stir, the heating temperature is 65° C., and the stirring time is 20 minutes, to obtain a mixed solution A; S92, according to the mass fractions, the blocked waterborne polyurethane, the flame retardant, the water repellent, the preservative, the modified potato starch and one half of the water are mixed, and the mixture is heated and stirred at a temperature of 40° C. and a stirring time of 20 minutes to obtain a mixed solution B; S93. Mix the mixed solution A and the mixed solution B according to their weight fractions and stir for 10 minutes to obtain an environmentally friendly glue.

[0034] Example 2 An environmentally friendly glue for plywood comprises the following raw materials, measured by weight: 25 parts of light-burned magnesium oxide, 8 parts of anhydrous magnesium chloride, 35 parts of modified potato starch, 12 parts of gelatin, 7 parts of flame retardant, 4 parts of waterproofing agent, 4 parts of closed waterborne polyurethane, 0.6 parts of preservative, and 220 parts of water, wherein the flame retardant is graphene-modified 2-carboxyethylphenyl hypophosphite, and the preservative is composed of sodium benzoate and potassium sorbate in a weight ratio of 3:2.

[0035] The above-mentioned method for preparing the environmentally friendly glue for plywood comprises the following steps: S91. Mix light-burned magnesium oxide, anhydrous magnesium chloride, gelatin and half of water according to their weight fractions, heat and stir, the heating temperature is 70° C., and the stirring time is 15 minutes, to obtain a mixed solution A; S92, according to the mass proportions, the blocked waterborne polyurethane, the flame retardant, the water repellent, the preservative, the modified potato starch and one half of the water are mixed, and the mixture is heated and stirred at a temperature of 45° C. and a stirring time of 15 minutes to obtain a mixed solution B; S93. Mix the mixed solution A and the mixed solution B according to their weight fractions and stir for 20 minutes to obtain an environmentally friendly glue.

[0036] Example 3 An environmentally friendly glue for plywood comprises the following raw materials, measured by weight: 23 parts of light-burned magnesium oxide, 7 parts of anhydrous magnesium chloride, 33 parts of modified potato starch, 11 parts of gelatin, 6 parts of flame retardant, 3.5 parts of waterproofing agent, 3.5 parts of closed waterborne polyurethane, 0.55 parts of preservative, and 210 parts of water, wherein the flame retardant is graphene-modified 2-carboxyethylphenyl hypophosphite, and the preservative is composed of sodium benzoate and potassium sorbate in a weight ratio of 3:2.

[0037] The above-mentioned method for preparing the environmentally friendly glue for plywood comprises the following steps: S91. Mix light-burned magnesium oxide, anhydrous magnesium chloride, gelatin and half of water according to their weight fractions, heat and stir, the heating temperature is 68° C., and the stirring time is 18 minutes, to obtain a mixed solution A; S92, according to the mass fractions, the blocked waterborne polyurethane, the flame retardant, the water repellent, the preservative, the modified potato starch and one half of the water were mixed, and the mixture was heated and stirred at a temperature of 43° C. and a stirring time of 18 minutes to obtain a mixed solution B; S93. Mix the mixed solution A and the mixed solution B according to their weight fractions and stir for 15 minutes to obtain an environmentally friendly glue.

[0038] Comparative Example 1 Same as Example 3, except that an equal amount of potato starch is used instead of modified potato starch.

[0039] Comparative Example 2 The same as Example 3, except that an equal amount of 2-carboxyethylphenyl hypophosphorous acid is used instead of graphene-modified 2-carboxyethylphenyl hypophosphorous acid.

[0040] Comparative Example 3 The same as Example 3, except that the amount of waterproofing agent added is 0 parts.

[0041] Comparative Example 4 The same as Example 3, except that an equal amount of waterborne polyurethane resin AH-1704B-2 produced by Anhui Dawei Huatai New Material Technology Co., Ltd. is used instead of the blocked waterborne polyurethane.

[0042] Performance Testing 1. The environmentally friendly glue prepared in each embodiment and comparative example is used to make a three-layer poplar plywood test piece, wherein the average moisture content of the poplar board is 8.5%, the grain directions of adjacent poplar boards are perpendicular to each other, the specifications of the poplar board are 400mm×400mm×3mm, and the glue application amount is 600g / m 2 , hot pressing at 150℃ and hot pressing at a pressure of 1.5MPa for 5 minutes to obtain plywood specimens.

[0043] According to the bonding strength determination in GB / T176571999 “Test methods for physical and chemical properties of wood-based panels and veneer wood-based panels”, a universal mechanical testing machine was used to conduct a dry bonding strength test on the specimens. The test results are shown in Table 1.

[0044] According to the bonding strength determination in GB / T176571999 "Test methods for physical and chemical properties of wood-based panels and veneer wood-based panels", a universal mechanical testing machine was used to conduct a water-immersion bonding strength test on the specimens. Before the test, the specimens were placed in hot water at 63±3℃ for 3 hours, and then cooled at room temperature for 10 minutes. The test results are shown in Table 1.

[0045] According to the bonding strength determination in GB / T176571999 "Test methods for physical and chemical properties of wood-based panels and veneer wood-based panels", a universal mechanical testing machine was used to conduct a boiling water immersion bonding strength test on the specimens. Before the test, the specimens were boiled in boiling water for 4 hours, and then the specimens were separated and laid flat in an air convection drying oven at 63±3℃ for 20 hours, and then boiled in boiling water for 4 hours. After being taken out, they were cooled at room temperature for 10 minutes. The test results are shown in Table 1.

[0046] Water resistance test: Wet shear strength can also be used to measure the water resistance of environmentally friendly glue. Referring to GB / T17657-1999, the plywood specimen is immersed in hot water at 63±3℃ for 3h, taken out and cooled at room temperature for 10min, and then the wet shear strength test is carried out; 2. Sample the environmentally friendly glue for plywood prepared in Examples 1 to 3 and Comparative Examples 1 to 4, apply the environmentally friendly glue for plywood on a glass surface, dry at 150° C. for 4 minutes, obtain a strip with a thickness of 2 mm, and conduct a flame retardancy test; Flame retardancy test: Place the sample to be tested in a glass combustion tube, introduce a nitrogen-oxygen mixed flow, and record the minimum oxygen concentration required for combustion. Take the average value of five tests for each group. The test results are shown in Table 1.

[0047] Table 1 Performance test According to GB / T98462004 "National Standard for Plywood", the boiling water soaked bonding strength of Class I plywood made of poplar should be greater than or equal to 0.7MPa, and the water soaked bonding strength of Class II plywood should be greater than or equal to 0.7MPa.

[0048] Analyzing the data in Table 1, we can see that: 1) The environmentally friendly glue for plywood prepared in Examples 1 to 3 has excellent water resistance, flame retardancy and bonding strength, is highly safe and environmentally friendly.

[0049] 2) The performance comparison analysis of the environmentally friendly glue for plywood prepared in combination with Example 3 and Comparative Example 1 shows that the prepared modified potato starch can improve the gel strength of the environmentally friendly glue and the water holding capacity of the potato starch gel through the hydrogen bond interaction between the wheat bran enzymolyzate and the potato starch. This is conducive to improving the bonding strength and water resistance of the environmentally friendly glue. Modified potato starch is a natural degradable polymer material with good biocompatibility and environmental friendliness. Using modified potato starch as one of the components of the adhesive can reduce pollution to the environment and improve the safety and environmental performance of the product.

[0050] 3) The performance comparison analysis of the environmentally friendly glue for plywood prepared in combination with Example 3 and Comparative Example 2 shows that the graphene-modified 2-carboxyethylphenyl hypophosphorous acid prepared in the present application, as a flame retardant, releases a large amount of non-flammable gas, dilutes the oxygen in the environment, and thus improves the flame retardant effect. Modification by γ-aminopropyltrimethoxysilane helps the combination between graphene oxide and 2-carboxyethylphenyl hypophosphorous acid, enhances the interaction between them, and improves the compatibility and dispersibility in the environmentally friendly glue for plywood. Graphene oxide forms a three-dimensional network structure, which further improves the flame retardant effect of the environmentally friendly glue. Graphene-modified 2-carboxyethylphenyl hypophosphorous acid works together with other ingredients to improve the water resistance, flame retardancy and bonding strength of the environmentally friendly glue for plywood, while being highly safe and green.

[0051] 4) The comparative analysis of the performance of the environmentally friendly glue for plywood prepared in combination with Example 3 and Comparative Example 3 shows that the prepared waterproofing agent can increase the water resistance of the environmentally friendly glue, and it is not easily damaged even if soaked in water, and at the same time greatly improves the bonding strength of the environmentally friendly glue.

[0052] 5) The comparative analysis of the performance of the environmentally friendly glue for plywood prepared in combination with Example 3 and Comparative Example 4 shows that the blocked waterborne polyurethane prepared in the present application can significantly improve the water resistance of the environmentally friendly glue by unblocking the active isocyanate group under high temperature conditions, causing it to undergo a cross-linking reaction with gelatin to synthesize a colloid. The blocked waterborne polyurethane is used as a cross-linking agent, and can significantly improve the bonding strength of the environmentally friendly glue by unblocking the active isocyanate group under high temperature conditions, causing it to undergo a cross-linking reaction with gelatin to synthesize a colloid. The blocked waterborne polyurethane is an environmentally friendly material with good biocompatibility and environmental friendliness. Using a blocked waterborne polyurethane as one of the components of an adhesive can reduce pollution to the environment and improve the safety and environmental performance of the product.

[0053] The above embodiments are only used to explain the technical solutions of the present application rather than to limit them. Although the above embodiments provide a specific description of the present application, relevant technical personnel should understand that the specific implementation modes of the present invention can still be modified or replaced by equivalents, and any modifications and equivalent replacements that do not depart from the spirit and scope of the present application should be included in the scope of protection of the present application.

Claims

1. An environmentally friendly glue for plywood, characterized in that: The preparation raw materials include the following by weight: 20-25 parts of light-burned magnesium oxide, 6-8 parts of anhydrous magnesium chloride, 30-35 parts of modified potato starch, 10-12 parts of gelatin, 5-7 parts of flame retardant, 3-4 parts of waterproofing agent, 3-4 parts of closed water-based polyurethane, 0.5-0.6 parts of preservative and 200-220 parts of water.

2. The environmentally friendly glue for plywood according to claim 1, characterized in that: The preparation method of the modified potato starch comprises the following steps: S21, according to the mass fraction, grind 180 parts of wheat bran through a 100 mesh sieve, mix with 500g of water and stir for 50min to obtain a suspension, add 42 parts of α-amylase, and the enzymolysis time is 12h; after the enzymolysis is completed, heat to 115°C and inactivate the enzyme for 12min; then add 230 parts of a 20g / L sodium hydroxide aqueous solution, stir for 6h, adjust the pH value of the system to 4 with 30% hydrochloric acid, then centrifuge at 8000rpm for 60min, collect the supernatant, add 300 parts of a 75% ethanol aqueous solution to precipitate the supernatant, stir for 40min, filter, collect the precipitate, and freeze-dry at -35°C for 24h to obtain a wheat bran hydrolysate; S22. According to the mass fractions, 120 parts of potato starch are added to 83 parts of an aqueous solution of wheat bran hydrolysate having a mass concentration of 15%, stirred at 68°C for 60 minutes, then heated to 93°C, stirred for 40 minutes, cooled to 30°C, stirred for 40 minutes, and then centrifuged at 8000 rpm for 60 minutes, and then the precipitate is collected and freeze-dried at -35°C for 24 hours to obtain modified potato starch.

3. The environmentally friendly glue for plywood according to claim 1, characterized in that: The flame retardant is graphene-modified 2-carboxyethylphenyl hypophosphorous acid.

4. The environmentally friendly glue for plywood according to claim 3, characterized in that: The preparation method of the graphene-modified 2-carboxyethylphenyl hypophosphorous acid comprises the following steps: S41, dispersing 150 parts of 2-carboxyethylphenylphosphorous acid and 13 parts of graphene oxide in a solution consisting of 14 parts of γ-aminopropyltrimethoxysilane, 320 parts of ethanol and 30 parts of water, according to parts by mass, to obtain a mixed solution; S42, heating the mixed solution to 43°C, stirring at a rate of 800 rpm, reacting for 10 hours, filtering, and vacuum drying at 85°C for 24 hours, grinding and sieving to obtain graphene-modified 2-carboxyethylphenylphosphorous acid with a particle size of 1-3 μm.

5. The environmentally friendly glue for plywood according to claim 1, characterized in that: The waterproofing agent comprises the following raw materials, calculated by weight: 50 parts of tannic acid, 38 parts of maltodextrin, 35 parts of sodium sulphate and 45 parts of water.

6. The environmentally friendly glue for plywood according to claim 5, characterized in that: The preparation method of the waterproofing agent comprises the following steps: uniformly mixing maltodextrin, sodium sulfate and water according to their weight fractions, heating to 35° C., reacting for 60-70 minutes, adding tannic acid thereto, heating to 55° C., and reacting for 5-6 hours to obtain the waterproofing agent.

7. The environmentally friendly glue for plywood according to claim 1, characterized in that: The preparation method of the closed waterborne polyurethane comprises the following steps: S71. 10 g of polypropylene glycol and 5.33 g of isophorone diisocyanate after vacuum dehydration were added to a three-necked flask equipped with a thermometer, a stirrer and a glass stopper, and mixed well. Then, 0.12 g of dibutyltin laurate was added, and the mixture was reacted at 50° C. for 20 min. The mixture was heated to 70° C. and reacted for 1 h to obtain a polyurethane prepolymer. The mixture was heated to 80° C., 0.77 g of 2,2-dimethylolpropionic acid was added, and the mixture was reacted for 1 h. The mixture was then cooled to 40° C., 1.52 g of methyl ethyl ketone oxime was added, and the mixture was reacted for 2 h. Then, 0.58 g of triethylamine was added and the mixture was neutralized for 0.5 h. During the reaction, the viscosity was adjusted with acetone, and the mixture was cooled to room temperature. Finally, 20 g of distilled water was slowly added under a stirring speed of 4000 r / min, and the mixture was emulsified for 0.5 h. After the acetone was removed by vacuum distillation, a closed waterborne polyurethane emulsion was obtained. S72. The closed waterborne polyurethane emulsion is dialyzed in a dialysis bag with a molecular weight cutoff of 1000 for 24 hours to remove reactive monomers, and after purification, a closed waterborne polyurethane is obtained.

8. The environmentally friendly glue for plywood according to claim 1, characterized in that: The preservative is composed of sodium benzoate and potassium sorbate in a mass ratio of 3:

2.

9. A method for preparing an environmentally friendly glue for plywood according to any one of claims 1 to 8, characterized in that: The following steps are involved: S91. Mix light-burned magnesium oxide, anhydrous magnesium chloride, gelatin and half of water according to their weight proportions, heat and stir to obtain a mixed solution A; S92, mixing the blocked waterborne polyurethane, the flame retardant, the water repellent, the preservative, the modified potato starch and half of the water according to their weight proportions, heating and stirring, to obtain a mixed solution B; S93. Mix the mixed solution A and the mixed solution B according to their weight proportions and stir them evenly to obtain an environmentally friendly glue.

10. A method for preparing environmentally friendly glue for plywood according to claim 9, characterized in that: In step S91, the heating temperature is 65-70°C, and the stirring time is 15-20 minutes. In step S92, the heating temperature is 40-45°C, and the stirring time is 15-20 minutes. In step S93, the stirring time is 10-20 minutes.

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