Single-component bio-based epoxy formaldehyde-free adhesive and preparation method thereof

Abstract

The invention discloses a single-component bio-based epoxy formaldehyde-free adhesive and a preparation method thereof, and relates to the field of adhesives for formaldehyde-free plywood production. The adhesive comprises the following raw materials in parts by weight: 10-20 parts of water, 1-2 parts of cellulose, 0-10 parts of a styrene-acrylic acid copolymer emulsion, 0.1-1 part of a wetting agent, 0.1-1 part of a dispersing agent, 10-20 parts of an acrylate copolymer emulsion, 10-20 parts of an ethylene-vinyl acetate copolymer emulsion, 10-30 parts of an epoxy emulsion, 10-30 parts of starch, 0-10 parts of a polyacrylamide solution, 1-2 parts of an accelerant and 1-2 parts of a pH regulator. 0.1-1 part of a defoaming agent; 0.1-1 part of a mildew preventive; the adhesive disclosed by the invention has the characteristics of long activation period, high bonding strength, good wood breaking effect, high adhesive film hardness, secondary activation of glue through thermal activation and the like; the method can obviously prolong the use time of the glue at the application end, fundamentally improves the pain point that the plywood is long in process time and cannot be segmented, enhances the comprehensive performance of the plywood, and can be applied to soft and hard wood base materials and compact wood.

Description

Technical Field

[0001] This invention relates to the field of adhesives for the production of formaldehyde-free plywood, and more particularly to a single-component bio-based epoxy formaldehyde-free adhesive and its preparation method. Background Technology

[0002] Formaldehyde-free plywood adhesives are key materials in the current wood industry. The mainstream adhesives include soybean glue, tannin glue, and single-component polyurethane adhesives. Soybean glue is commonly used to prepare Class II plywood, but its high viscosity and near-zero flowability require large application amounts and are prone to overflow during cold pressing, affecting not only the surface quality and performance of the plywood but also subsequent veneering and finishing processes. Tannin glue is also used to prepare Class II plywood, but its main drawback is poor initial tack, with an open time typically only half an hour. After cold pressing, the plywood has almost no initial tack, severely impacting and even limiting subsequent processes. In contrast, formaldehyde-free single-component polyurethane adhesives have similar basic physical properties and workability to traditional urea glue, offering better operability and becoming one of the most widely used choices in the production of formaldehyde-free plywood. CN102268232A provides a formaldehyde-free adhesive scheme using polyvinyl alcohol blended with styrene-acrylic emulsion for the preparation of multi-layer formaldehyde-free solid wood composite flooring. However, after coating, the rapid evaporation of moisture after aging leads to poor initial tack after cold pressing, and the polyvinyl alcohol used requires high-temperature dissolution, resulting in high energy consumption. Furthermore, the blended styrene-acrylic emulsion has poor water resistance, meaning the resulting plywood only meets the requirements for Class II plywood. CN108822793A mentions a soybean protein-based formaldehyde-free adhesive, but its poor flowability severely impacts construction efficiency, and the initial tack decreases significantly with prolonged aging. CN106336835A provides a single-component formaldehyde-free adhesive for multi-layer boards, using isocyanates thickened and end-capped with cellulose to create the formaldehyde-free adhesive. However, this solution involves a large amount of isocyanate, posing a risk of board sticking during hot pressing, directly affecting production efficiency and board-making results.

[0003] In summary, existing formaldehyde-free plywood adhesive technologies still have the following shortcomings: 1. Most adhesives have poor water resistance and cannot meet Class I standards; 2. Existing isocyanate systems have short open times, which cannot meet the long operating times required by applications (such as coating, preforming, and pre-pressing processes); 3. Some existing environmentally friendly adhesives have difficult processing. The viscosity is too high in the early stage, making it difficult to apply the adhesive. The pre-compression strength is too low in the middle stage, which cannot meet the requirements for repairing the board. In the later stage, the hot-press curing process results in serious board sticking. 4. Traditional formaldehyde-free adhesives require a long curing time, and the production and testing cycle from application to performance testing is too lengthy.

[0004] Therefore, there is an urgent need to develop a formaldehyde-free adhesive for plywood that combines excellent water resistance, suitable open time, good process adaptability, and a short curing cycle. Summary of the Invention

[0005] The purpose of this invention is to address the shortcomings of existing technologies by providing a single-component bio-based epoxy formaldehyde-free adhesive and its preparation method.

[0006] The objective of this invention is achieved through the following technical solution: In a first aspect, a one-component bio-based epoxy formaldehyde-free adhesive is provided, wherein, by weight, its raw material components include: 10-20 parts water 1-2 parts cellulose 0-10 parts of styrene-acrylic copolymer emulsion Wetting agent 0.1-1 part Dispersant 0.1-1 part 10-20 parts of acrylate copolymer emulsion 10-20 parts of ethylene-vinyl acetate copolymer emulsion 10-30 parts of epoxy emulsion 10-30 parts starch 0-10 parts of polyacrylamide solution 1-2 parts of accelerator pH adjuster 1-2 parts Defoamer 0.1-1 part 0.1-1 part of antifungal agent As a further aspect of the present invention: the styrene-acrylate copolymer emulsion has a solid content of 45-55%, a viscosity of 1000-6000 mPa.s, a pH of 3-8, and a glass transition temperature of -30℃ to -10℃.

[0007] As a further aspect of the present invention: the ethylene-vinyl acetate copolymer emulsion is Wacker's EP 736, with a solid content of 60%, a viscosity of 3500~4000 mPa.s, and a pH value of 4~6.

[0008] As a further aspect of the present invention: the polyacrylamide solution is prepared by dissolving polyacrylamide with a molecular weight of 2 million to 10 million in water, with a volume concentration of 10%, a viscosity of 20,000 mPa·s, and a pH of 3-5.

[0009] As a further aspect of the present invention, the starch is one of the following: tapioca starch, corn starch, wheat starch, etc.

[0010] As a further aspect of the present invention: the antifungal agent is a Kathon-type antifungal agent.

[0011] As a further aspect of the present invention, the accelerator is one or more alcohols such as propylene glycol, glycerol, and benzyl alcohol.

[0012] As a further aspect of the present invention: the wetting agent, dispersant, and defoamer are all commercially available and are not required to be specific.

[0013] As a further aspect of the present invention: the acrylate copolymer emulsion has a viscosity of 6000-8000 mPa·s and a solid content of 58%-60%, and is prepared by the following method: Take a certain proportion of monomers BA, St, HEC and MAA, mix them evenly at room temperature, and add them to a mixed solution consisting of 70 g water, 1.8 g A-102 and 0.8 g AHPS. Stir and emulsify to obtain a pre-emulsified monomer. Then add 100 g water, 0.35 g A-102, 1.2 g AHPS and 0.4 g APS to a reaction flask, heat to 80℃, and then add 20 g of pre-emulsified monomer. Keep the temperature and react for 20 min. Then add the remaining pre-emulsified monomer and a solution of 0.5 g APS dissolved in 5 g water dropwise at 80-84℃. The addition is completed within 2 h. Keep the temperature and react for another 1.5 h, then cool to room temperature. Add water to adjust the solid content to 40%, adjust the pH to 6.5 with ammonia, and finally filter through a 200 mesh sieve to obtain the acrylate copolymer emulsion.

[0014] As a further aspect of the present invention: the epoxy emulsion has a viscosity of 3000-5000 mPa·s and a solid content of 52-55%, and is prepared by the following method: (1) Filtration and dehydration: The cashew shell oil was filtered to remove impurities and dehydrated to a water content of less than 0.5 wt%, and then vacuum dried at 60°C for 2 h; (2) Epoxidation reaction: Cashew nut shell oil and toluene are mixed at a mass ratio of 1:1~2 and heated to 50~70℃; formic acid is slowly added dropwise, with formic acid accounting for 5-10% of the mass of cashew nut shell oil, and stirred at 600R / min for 30min; then the temperature is adjusted to 60-80℃, and 30% volume concentration of H2O2 is added dropwise to obtain the reaction solution, wherein the molar ratio of cashew nut shell oil to H2O2 is 1:0.8~1.2, and the H2O2 is added dropwise for 4-6h; (3) Product purification: Wash the reaction solution obtained in step (2) with saturated saline solution 2 to 3 times to remove residual acid and water, and then carry out vacuum distillation under experimental conditions of vacuum degree -0.09MPa and distillation temperature of 100 to 120℃ to remove toluene, and epoxidized cashew shell oil can be obtained. (4) Emulsification: Mix the epoxy cashew nut shell oil obtained in step (3) with an emulsifier. The amount of emulsifier is 8-15% of the mass of the epoxy cashew nut shell oil. Stir and heat to 50-60℃. Then slowly add deionized water. The mass ratio of epoxy cashew nut shell oil to deionized water is 1:1-2. Then stir at high speed at 2000-3000 rpm. The temperature of the emulsification process is controlled between 40-70℃. When the epoxy equivalent is 320-400, the reaction ends and the epoxy emulsion is obtained.

[0015] As a further aspect of the present invention: the pH adjuster is one or more organic acids such as oxalic acid, boric acid, and citric acid.

[0016] Secondly, the present invention also provides a method for preparing the above-mentioned single-component bio-based epoxy formaldehyde-free adhesive, comprising the following steps: S1: Weigh out the following components according to their weight percentages: 10-20 parts ethylene-vinyl acetate copolymer emulsion, 10-20 parts acrylate copolymer emulsion, 10-30 parts epoxy emulsion, 10-30 parts starch, 10-20 parts water, 1-2 parts cellulose, 0-10 parts styrene-acrylic acid copolymer emulsion, 0.1-1 parts dispersant, 0.1-1 parts wetting agent, 0-10 parts polyacrylamide solution, 1-2 parts accelerator, 1-2 parts pH adjuster, 0.1-1 parts defoamer, and 0.1-1 parts mildew inhibitor. S2: First, pour 10-20 parts water and 1-2 parts cellulose into the reactor and start stirring. Stir at 1500r / min for 20 minutes. S3: Pour 0-10 parts of styrene-acrylic acid copolymer emulsion, 10-30 parts of epoxy emulsion, 10-20 parts of ethylene-vinyl acetate copolymer emulsion and 10-20 parts of acrylate copolymer emulsion into a reaction vessel and stir at 1000-1200 r / min for 45 minutes. S4: Add 0.1-1 parts of dispersant and 0.1-1 parts of wetting agent to the reactor, then slowly add 10-30 parts of starch, and stir for 50 minutes at a speed of 600-900 r / min; S5: Then add 1-2 parts of accelerator and 1-2 parts of pH adjuster to the reactor, and stir for 20 minutes at a speed of 600-800 / min; S6: After mixing, add 0.1-1 parts of the weighed antifungal agent and 0.1-1 parts of the defoamer to the mixing tank and stir for 30 minutes at a speed of 300-500 r / min. S7: Finally, vacuum the system, stop stirring, and filter the solution to obtain a single-component bio-based epoxy formaldehyde-free adhesive product.

[0017] As a further aspect of the present invention: the starch is added at a rate of 25 kg / min in step S4.

[0018] As a further aspect of the present invention: in step S7, the vacuuming time is 60 minutes, the stirring speed is 300-500 r / min, and the filter screen used for filtration is 100 mesh.

[0019] Thirdly, the present invention also provides the application of the above-mentioned single-component bio-based epoxy formaldehyde-free adhesive in softwood and hardwood substrates and dense wood.

[0020] Compared with the prior art, the beneficial effects of the present invention are: (1) The raw materials used in the preparation process of this invention are all free of formaldehyde, have excellent environmental performance, and have good bonding strength and water resistance. They can be used for a variety of soft and hard wood substrates and have a good bonding effect on dense wood. They can meet the water resistance requirements of Class I and Class II plywood, and at the same time meet the environmental protection standards of ENF grade boards, thus avoiding the release of formaldehyde during the production process and causing harm to the environment and human health.

[0021] (2) The present invention uses bio-based modified toughened epoxy emulsion, which can generate sufficient elastic modulus after hot pressing.

[0022] (3) The viscosity range of the present invention is 15000-30000 mPa.s, and the amount of glue can be controlled arbitrarily. It can be used on any type of wood without the problems of slow cold pressing and slow drying speed or excessively thick glue film.

[0023] (4) The adhesive of the present invention can be activated by heat for a second time, and the adhesive film can also be reactivated by hot pressing after drying, thereby achieving secondary bonding and curing, which solves the problem of activity failure during production shutdown of ordinary adhesives.

[0024] (5) The adhesive of the present invention is a single-component adhesive. When hot-pressed, the polyacrylamide solution and epoxy emulsion in the adhesive cross-link with the wood, resulting in good stability, simple use, and good brushability.

[0025] (6) After the adhesive of the present invention is applied and pre-pressed, it can be continuously stacked for 24 hours in the client's environment of 0-35℃ and can still be thermally activated and cured. It also has stable performance and high elastic modulus.

[0026] (7) Good operability: the adhesive of the present invention does not require mixing with curing agent, has a long activation period, and the viscosity does not change much over time. It can be continuously stacked after pre-pressing and the strength does not decrease after hot pressing activation, which solves the problem of long process time and inability to produce continuously. Attached Figure Description Detailed Implementation

[0028] In this embodiment, the epoxy emulsion and polyacrylic acid copolymer emulsion are self-polymerized, and all other raw materials are commercially available products. The single-component bio-based formaldehyde-free epoxy adhesive prepared by this invention can be used in softwood and hardwood substrates as well as dense wood.

[0029] The present invention will be further described below through specific embodiments: The acrylate copolymer emulsion was prepared by the following method: Mix 6.2g of monomer BA, 2.3g of St, 1g of HEC, and 0.2g of MAA at room temperature until homogeneous. Add this mixture to a mixed solution of 70g of water, 1.8g of A-102, and 0.8g of AHPS and stir to emulsify for 30 minutes to obtain a pre-emulsified monomer. Then, add 100g of water, 0.35g of A-102, 1.2g of AHPS, and 0.4g of APS to a reaction flask and heat to 80℃. Add 20g of the pre-emulsified monomer and maintain the temperature at 400 rpm for 20 minutes. Then, add the remaining pre-emulsified monomer and a solution of 0.5g of APS dissolved in 5g of water dropwise at 80-84℃ over 2 hours. Maintain the temperature for another 1.5 hours and then cool to room temperature. Add water to adjust the solid content to 40%, adjust the pH to 6.5 with ammonia, and finally filter through a 200-mesh sieve to obtain the acrylate copolymer emulsion.

[0030] Epoxy emulsions are prepared by the following method: (1) Filtration and dehydration: The cashew shell oil was filtered to remove impurities and dehydrated to a water content of 0.3wt%, and then vacuum dried at 60℃ for 2h; (2) Epoxidation reaction: Cashew nut shell oil and toluene are mixed at a mass ratio of 1:1 and heated to 50~70℃; formic acid is slowly added dropwise, with formic acid accounting for 10% of the mass of cashew nut shell oil, and stirred at 600R / min for 30min; then the temperature is adjusted to 60-80℃, and 30% volume concentration of H2O2 is added dropwise to obtain the reaction solution, wherein the molar ratio of cashew nut shell oil to H2O2 is 1:0.8, and the H2O2 is added dropwise for 6h; (3) Product purification: Wash the reaction solution obtained in step (2) with saturated saline solution 2 to 3 times to remove residual acid and water, and then carry out vacuum distillation under experimental conditions of vacuum degree -0.09MPa and distillation temperature of 100 to 120℃ to remove toluene, and epoxidized cashew shell oil can be obtained. (4) Emulsification: Mix the epoxy cashew shell oil obtained in step (3) with the emulsifier. The amount of emulsifier is 15% of the mass of the epoxy cashew shell oil. Stir and heat to 50~60℃. Then slowly add deionized water. The mass ratio of epoxy cashew shell oil to deionized water is 1:1. Then stir at 2000 rpm. The temperature of the emulsification process is controlled between 40-60℃. When the epoxy equivalent is 320~380, the reaction ends and the epoxy emulsion is obtained.

[0031] Example 1: This embodiment provides a method for preparing a one-component bio-based epoxy adhesive, including the following steps: S1: Weigh out the following components according to their weight percentages: 12 parts ethylene-vinyl acetate copolymer emulsion, 10 parts acrylate copolymer emulsion, 15 parts epoxy emulsion, 30 parts starch, 18 parts water, 1 part cellulose, 10 parts styrene-acrylic acid copolymer emulsion, 0.2 parts wetting agent, 0.3 parts dispersant, 1 part polyacrylamide solution, 1 part accelerator, 1 part citric acid, 0.3 parts defoamer, and 0.2 parts mildew inhibitor. The styrene-acrylate copolymer emulsion has a solid content of 45%, a viscosity of 1000 mPa·s, a pH of 3, and a glass transition temperature of -30℃. The ethylene-vinyl acetate copolymer emulsion is Wacker's EP 736, with a solid content of 60%, a viscosity of 3500 mPa·s, and a pH of 4. The polyacrylamide solution is prepared by dissolving polyacrylamide with a molecular weight of 2 million in water, with a volume concentration of 10%, a viscosity of 20000 mPa·s, and a pH of 3. S2: First, pour the weighed water and cellulose into the reactor and start the stirring machine. Stir for 20 minutes at a speed of 1500 R / min. S3: Pour the weighed polyacrylate copolymer emulsion, epoxy emulsion, ethylene-vinyl acetate copolymer emulsion, and acrylate copolymer emulsion into the reaction vessel and stir for 45 minutes at a speed of 1000 R / min. S4: Add dispersant and wetting agent to the reactor, then slowly add starch and stir for 50 minutes at 900 R / min. S5: Then add the accelerator, citric acid, and defoamer to the reactor, and stir for 20 minutes at a speed of 600 R / min; S6: After mixing, add the weighed antifungal agent and defoamer to the mixing tank and mix for 30 minutes at a speed of 300 R / min. S7: Finally, vacuum for 60 minutes, stop stirring and filter to prepare the single-component bio-based epoxy formaldehyde-free adhesive product A1.

[0032] Example 2: This embodiment provides a method for preparing a one-component bio-based epoxy adhesive, including the following steps: S1: Weigh out the following components according to their weight percentages: 10 parts ethylene-vinyl acetate copolymer emulsion, 10 parts acrylate copolymer emulsion, 20 parts epoxy emulsion, 20 parts starch, 18 parts water, 1 part cellulose, 10 parts styrene-acrylic acid copolymer emulsion, 0.2 parts wetting agent, 0.3 parts dispersant, 1 part polyacrylamide solution, 1 part accelerator, 1 part citric acid, 0.3 parts defoamer, and 0.2 parts mildew inhibitor. The styrene-acrylate copolymer emulsion has a solid content of 55%, a viscosity of 6000 mPa·s, a pH of 8, and a glass transition temperature of -10℃. The ethylene-vinyl acetate copolymer emulsion is Wacker's EP 736, with a solid content of 60%, a viscosity of 4000 mPa·s, and a pH of 6. The polyacrylamide solution is prepared by dissolving polyacrylamide with a molecular weight of 10 million in water, with a volume concentration of 10%, a viscosity of 20000 mPa·s, and a pH of 5. S2: First, pour the weighed water and cellulose into the reactor and start the stirring machine. Stir for 20 minutes at a speed of 1500 R / min. S3: Pour the weighed polyacrylate copolymer emulsion, epoxy emulsion, ethylene-vinyl acetate copolymer emulsion, and acrylate copolymer emulsion into the reaction vessel and stir for 45 minutes at a speed of 1000 R / min. S4: Add dispersant and wetting agent to the reactor, then slowly add starch and stir for 50 minutes at 600 R / min. S5: Then add the accelerator, citric acid, and defoamer to the reactor, and stir for 20 minutes at a speed of 600 R / min; S6: After mixing, add the weighed antifungal agent and defoamer to the mixing tank and mix for 30 minutes at a speed of 300 R / min. S7: Finally, vacuum for 60 minutes, stop stirring and filter to prepare the single-component bio-based epoxy formaldehyde-free adhesive product A2.

[0033] Example 3: This embodiment provides a method for preparing a one-component bio-based epoxy adhesive, including the following steps: S1: Weigh the following components according to their weight percentages: 0 parts ethylene-vinyl acetate copolymer emulsion, 20 parts acrylate copolymer emulsion, 15 parts epoxy emulsion, 25 parts starch, 18 parts water, 1 part cellulose, 10 parts styrene-acrylic acid copolymer emulsion, 0.2 parts wetting agent, 0.3 parts dispersant, 1 part polyacrylamide solution, 1 part accelerator, 1 part boric acid, 0.3 parts defoamer, and 0.2 parts mildew inhibitor. The styrene-acrylate copolymer emulsion has a solid content of 50%, a viscosity of 4000 mPa·s, a pH of 6, and a glass transition temperature of -20℃. The ethylene-vinyl acetate copolymer emulsion is Wacker's EP 736, with a solid content of 60%, a viscosity of 3800 mPa·s, and a pH of 5. The polyacrylamide solution is prepared by dissolving polyacrylamide with a molecular weight of 5 million in water, with a volume concentration of 10%, a viscosity of 20000 mPa·s, and a pH of 4. S2: First, pour the weighed water and cellulose into the reactor and start the stirring machine. Stir for 20 minutes at a speed of 1500 R / min. S3: Pour the weighed polyacrylate copolymer emulsion, epoxy emulsion, ethylene-vinyl acetate copolymer emulsion, and acrylate copolymer emulsion into the reaction vessel and stir for 45 minutes at a speed of 1000 R / min. S4: Add dispersant and wetting agent to the reactor, then slowly add starch and stir for 50 minutes at 600 R / min. S5: Then add the accelerator, boric acid, and defoamer to the reactor, and stir for 20 minutes at a speed of 600 R / min; S6: After mixing, add the weighed antifungal agent and defoamer to the mixing tank and mix for 30 minutes at a speed of 300 R / min. S7: Finally, vacuum for 60 minutes, stop stirring and filter to prepare the single-component bio-based epoxy formaldehyde-free adhesive product A3.

[0034] Example 4: This embodiment provides a method for preparing a one-component bio-based epoxy adhesive, including the following steps: S1: Weigh out the following components according to their weight percentages: 10 parts ethylene-vinyl acetate copolymer emulsion, 15 parts acrylate copolymer emulsion, 10 parts epoxy emulsion, 30 parts starch, 20 parts water, 1 part cellulose, 10 parts styrene-acrylic acid copolymer emulsion, 0.2 parts wetting agent, 0.3 parts dispersant, 1 part polyacrylamide solution, 1 part accelerator, 1 part oxalic acid, 0.3 parts defoamer, and 0.2 parts mildew inhibitor. The styrene-acrylate copolymer emulsion has a solid content of 50%, a viscosity of 4000 mPa·s, a pH of 6, and a glass transition temperature of -20℃. The ethylene-vinyl acetate copolymer emulsion is Wacker's EP 736, with a solid content of 60%, a viscosity of 3800 mPa·s, and a pH of 5. The polyacrylamide solution is prepared by dissolving polyacrylamide with a molecular weight of 5 million in water, with a volume concentration of 10%, a viscosity of 20000 mPa·s, and a pH of 4. S2: First, pour the weighed water and cellulose into the reactor and start the stirring machine. Stir for 20 minutes at a speed of 1500 R / min. S3: Pour the weighed polyacrylate copolymer emulsion, epoxy emulsion, ethylene-vinyl acetate copolymer emulsion, and acrylate copolymer emulsion into the reaction vessel and stir for 45 minutes at a speed of 1000 R / min. S4: Add dispersant and wetting agent to the reactor, then slowly add starch and stir for 50 minutes at 800 R / min. S5: Then add the accelerator, oxalic acid, and defoamer to the reactor, and stir for 20 minutes at a speed of 600 R / min; S6: After mixing, add the weighed antifungal agent and defoamer to the mixing tank and mix for 30 minutes at a speed of 300 R / min. S7: Finally, vacuum for 60 minutes, stop stirring and filter to prepare the single-component bio-based epoxy formaldehyde-free adhesive product A4.

[0035] The single-component bio-based formaldehyde-free epoxy adhesive products prepared in the above four examples were tested as follows: (1) Activation period test: The product is sealed and placed in a constant temperature and humidity chamber at 35°C and 60% humidity for 4 hours. Then it is taken out and stirred thoroughly to make it uniform. Then it is put back into the constant temperature and humidity chamber and the viscosity change over time is tested. If the viscosity increases sharply during the test and it does not have good coating properties, it is considered unusable and has exceeded the activation period.

[0036] (2) Class II water resistance strength test: Taking amine wood and poplar wood substrate as examples: single-sided glue application, control the glue application amount to 180g / ㎡, veneer wood grain vertically cross-stacked seven layers, pressure 6MPa, cold press at room temperature for 1h, after pressure relief, place at temperature 25℃ and humidity 60% for 1 hour, then hot press at temperature 120℃ and pressure 5MPa for 15min.

[0037] (3) Curing speed test: Use 25*50mm beech wood blocks, control the glue application area to be 25*25mm, 5 blocks per group, place them in a hot press and apply a force of 2MPa, test the compressive shear strength after 5min, 10min, 15min, 20min, 25min, 35min and 45min respectively. If the strength reaches 0.75MPa or above after 15min of pressure, it is judged to have a fast curing speed. If it takes 25min of pressure to reach 0.75MPa or above, the curing time is medium. If the strength does not reach 0.75MPa after more than 25min of pressure, the curing speed is slow.

[0038] (4) Transverse elastic modulus test: Taking amine wood and poplar wood substrates as examples: single-sided glue application, controlling the glue application amount to 180g / ㎡, seven layers of veneer wood grain perpendicularly crossed, pressure 6MPa, cold pressing at room temperature for 1 hour, after pressure release, placed at 25℃ and 60% humidity for 1 hour, then hot pressing, hot pressing temperature 120℃, pressure 5MPa, hot pressing time 25min. After board preparation, the sample is cured at 25℃ and 60% humidity for 24 hours. After sample preparation, the test is carried out according to GBT 17657-2013.

[0039] (5) Dry strength test: Taking amine wood and poplar wood substrates as examples: apply glue to one side, control the glue amount to 180g / ㎡, stack seven layers of veneer with vertically intersecting wood grains, apply pressure of 6MPa, cold press at room temperature for 1 hour, after depressurization, place under conditions of 25℃ and 60% humidity for 1 hour, then hot press at 120℃, pressure of 5MPa, and hot press time of 15min. After sample preparation, prepare sample blocks according to GBT17657-2013 glue strength test method, and test the dry strength with a tensile tester.

[0040] (6) Formaldehyde content: The formaldehyde content is tested by rotary evaporation. If it is greater than 0.05 g / kg, it is considered to exceed the formaldehyde standard.

[0041] (7) Class I water resistance strength test: Taking amine wood and poplar wood substrates as examples: single-sided glue application, with glue amount controlled at 180g / ㎡, seven layers of veneer wood grain perpendicularly crossed, pressure 6MPa, cold pressing at room temperature for 1 hour, after pressure release, placed at 25℃ and 60% humidity for 1 hour before hot pressing, hot pressing temperature 120℃, pressure 5MPa, hot pressing time 15min. After sample preparation, the test was carried out according to GBT17657-2013 Class I adhesive strength test method.

[0042] The performance test data of the single-component bio-based epoxy formaldehyde-free adhesives prepared in the four examples are shown in Table 1: Table 1: Performance Test Table of Single-Component Bio-based Epoxy Formaldehyde-free Adhesives Prepared in Four Examples

[0043] Based on the above test data, the introduction of cashew nutshell oil-toughened modified epoxy emulsion can effectively improve the overall performance of the product. The prepared adhesive has advantages such as long activation period, fast curing speed, secondary activation capability, high transverse elastic modulus, high dry strength, good water resistance, formaldehyde-free, and long service life. It has a good reinforcing effect on both softwood and hardwood single-layer plywood substrates, and can effectively improve the stiffness and strength of plywood. The styrene-acrylic acid copolymer emulsion in the formula can effectively improve the water resistance of the adhesive film, thereby improving the Class I strength of the sample. The ethylene-vinyl acetate copolymer emulsion in the formula has a good wetting effect on substrates with low surface energy, which can improve the adhesion of the adhesive to low surface energy substrates such as melamine paper, thereby improving the bonding strength.

[0044] All samples in the above embodiments are formaldehyde-free, exhibiting significantly improved performance and stronger environmental friendliness compared to existing products on the market. Although preferred embodiments of the present invention have been disclosed for illustrative purposes, and the technical solutions of the present invention have been described in detail, the embodiments of the present invention are not limited to the above embodiments. Equivalent changes made to the scope and spirit of the present invention as disclosed in the appended claims are considered to fall within the technical scope of the present invention.

Claims

1. A one-component bio-based epoxy formaldehyde-free adhesive, characterized in that, The raw material components include, by weight: Water 10-20 parts Cellulose 1-2 parts Styrene-acrylic acid copolymer emulsion 0-10 parts Wetting agent 0.1-1 part Dispersing agent 0.1-1 part Acrylate copolymer emulsion 10-20 parts Ethylene-vinyl acetate copolymer emulsion 10-20 parts Epoxy emulsion 10-30 parts Starch 10-30 parts Polyacrylamide solution 0-10 parts Accelerator 1-2 parts pH adjuster 1-2 parts Defoaming agent 0.1-1 part Mildew-proof agent 0.1-1 part.

2. A one-component bio-based epoxy formaldehyde-free adhesive according to claim 1, characterized in that, The styrene-acrylate copolymer emulsion has a solid content of 45-55%, a viscosity of 1000-6000 mPa.s, a pH of 3-8, and a glass transition temperature of -30℃ to -10℃.

3. A one-component bio-based epoxy formaldehyde-free adhesive according to claim 1, characterized in that, The ethylene-vinyl acetate copolymer emulsion is EP 736 from Wacker, has a solid content of 60%, a viscosity of 3500-4000 mPa.s, and a pH of 4-6.

4. The one-component bio-based epoxy formaldehyde-free adhesive according to claim 1, characterized in that, The polyacrylamide solution is prepared by dissolving polyacrylamide with a molecular weight of 2 million to 10 million in water, has a volume concentration of 10%, a viscosity of 20000 mPa.s, and a pH of 3-5.

5. The one-component bio-based epoxy formaldehyde-free adhesive according to claim 1, characterized in that, The starch is selected from tapioca starch, corn starch, and wheat starch.

6. A single component bio-based epoxy formaldehyde-free adhesive according to claim 1, characterized in that, The mildew-proof agent is a kathon mildew-proof agent, and the accelerator is selected from propylene glycol, glycerol, and benzyl alcohol.

7. A single component bio-based epoxy formaldehyde-free adhesive according to claim 1, characterized in that, The acrylate copolymer emulsion has a viscosity of 6000-8000 mPa.s and a solid content of 58%-60%, and is prepared by the following method: 6.2g of monomer BA, 2.3g of St, 1g of HEC, and 0.2g of MAA are uniformly mixed at room temperature, then added to a mixed solution composed of 70g of water, 1.8g of A-102, and 0.8g of AHPS, and stirred and emulsified to obtain a pre-emulsified monomer; then 100g of water, 0.35g of A-102, 1.2g of AHPS, and 0.4g of APS are added to a reaction bottle, heated to 80℃, then 20g of the pre-emulsified monomer is added, and kept at temperature for 20min; then the remaining pre-emulsified monomer and 0.5g of APS dissolved in 5g of water are added dropwise at 80-84℃, and the dropwise addition is completed within 2h, then kept at temperature for 1.5h, cooled to room temperature, added with water to adjust the solid content to 40%, added with ammonia water to adjust the pH to 6.5, and finally filtered through a 200-mesh sieve to obtain the acrylate copolymer emulsion.

8. The one-component bio-based epoxy formaldehyde-free adhesive according to claim 1, characterized in that, The epoxy emulsion has a viscosity of 3000-5000 mPa.s and a solid content of 52-55%, and is prepared by the following method: (1) Filtration and dehydration: the cashew nut shell oil is filtered to remove impurities, and dehydrated to a water content of less than 0.5wt%, then vacuum dried at 60℃ for 2h; (2) Epoxidation reaction: mix cashew nut shell oil and toluene at a mass ratio of 1:1-2, heat to 50-70℃; slowly add formic acid, formic acid accounts for 5-10% of the mass of cashew nut shell oil, stir at 600R / min for 30min; adjust the temperature to 60-80℃, drop 30% volume concentration of H2O2, obtain the reaction liquid, wherein the molar ratio of cashew nut shell oil and H2O2 is 1:0.8-1.2, the drop time of H2O2 is 4-6h; (3) Product purification: wash the reaction liquid obtained in step (2) with saturated brine 2-3 times to remove residual acid and water, then perform vacuum distillation under the experimental conditions of vacuum degree-0.09MPa and distillation temperature 100-120℃ to remove toluene, thus obtaining epoxidized cashew nut shell oil; (4) Emulsification: mix the epoxidized cashew nut shell oil obtained in step (3) and emulsifier, the amount of emulsifier is 8-15% of the mass of epoxidized cashew nut shell oil, stir and heat to 50-60℃; then slowly add deionized water, the mass ratio of epoxidized cashew nut shell oil and deionized water is 1:1-2, then perform high-speed stirring at 2000-3000rpm, the emulsification process temperature is controlled between 40-70℃, when the epoxide equivalent weight is 320-400, the reaction is completed, thus obtaining an epoxy emulsion.

9. The one-component bio-based epoxy formaldehyde-free adhesive according to claim 1, characterized in that, The pH regulator is selected from oxalic acid, boric acid and citric acid.

10. A process for the preparation of one component bio-based epoxy formaldehyde-free adhesive as claimed in claim 1, characterized in that, The method comprises the following steps: S1: weigh 10-20 parts of ethylene-vinyl acetate copolymer emulsion, 10-20 parts of acrylate copolymer emulsion, 10-30 parts of epoxy emulsion, 10-30 parts of starch, 10-20 parts of water, 1-2 parts of cellulose, 0-10 parts of styrene-acrylic acid copolymer emulsion, 0.1-1 parts of dispersant, 0.1-1 parts of wetting agent, 0-10 parts of polyacrylamide solution, 1-2 parts of accelerator, 1-2 parts of pH regulator, 0.1-1 parts of defoaming agent and 0.1-1 parts of mildew-proof agent according to the weight of raw materials; S2: first pour 10-20 parts of water and 1-2 parts of cellulose into the reaction kettle and start stirring, stir at a speed of 1500r / min for 20min; S3: pour 0-10 parts of styrene-acrylic acid copolymer emulsion, 10-30 parts of epoxy emulsion, 10-20 parts of ethylene-vinyl acetate copolymer emulsion and 10-20 parts of acrylate copolymer emulsion into the reaction kettle, stir at a speed of 1000-1200r / min for 45min; S4: then add 0.1-1 parts of dispersant and 0.1-1 parts of wetting agent to the reaction kettle, and then slowly add 10-30 parts of starch, stir at a speed of 600-900r / min for 50min; the adding speed of starch is 25kg / min; S5: subsequently add 1-2 parts of accelerator and 1-2 parts of pH regulator to the reaction kettle, stir at a speed of 600-800 / min for 20min; S6: after stirring is completed, add the weighed 0.1-1 parts of mildew-proof agent and 0.1-1 parts of defoaming agent into the stirring tank, and stir at a speed of 300-500r / min for 30min; S7: Finally, vacuumize for 60 minutes, stirring speed is 300-500 r / min, stop stirring and use 100 mesh filter screen to filter, then the single-component bio-based epoxy formaldehyde-free adhesive product is prepared.

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