Bamboo powder adhesive based on green eutectic solvent driving and preparation method

Abstract

The invention relates to the technical field of bamboo powder adhesives, in particular to a bamboo powder adhesive based on green deep-eutectic solvent driving and a preparation method thereof.The bamboo powder adhesive is prepared from, by mass, 40%-50% of a functional deep-eutectic solvent, 20%-30% of bamboo powder, 0.4%-0.9% of sodium alginate, 0.2%-0.6% of nanometer titania, 0.16%-0.36% of cellulose nanowhiskers, 0.2%-0.45% of a bio-based plasticizer, ethyl alcohol and water; the functional eutectic solvent in the adhesive can induce in-situ carboxylation of the bamboo powder, so that the binding force between the bamboo powder and other materials is enhanced; meanwhile, the cohesive strength and the bonding strength of the adhesive are further improved through the synergistic effect of additives such as sodium alginate, nano titanium dioxide and cellulose nanowhiskers, the defect that a traditional biomass adhesive is poor in water resistance is overcome, and the adhesive is prepared through a special raw material formula and a preparation technology. The adhesive can still keep good adhesive performance in a humid environment, the application scene of the adhesive is effectively widened, and the adhesive has good economic benefits and competitiveness.

Description

Technical Field

[0001] The present invention relates to the technical field of bamboo powder adhesives, and in particular to a bamboo powder adhesive driven by a green deep eutectic solvent and a preparation method thereof. Background Art

[0002] Adhesives are the core material of the wood-based panel industry, but its mainstream product, urea-formaldehyde resin, causes serious health and environmental problems due to formaldehyde release and poor water resistance. Although formaldehyde-free adhesives (such as glyoxal-urea and biomass-based adhesives) have made progress, they still face new challenges: raw material toxicity (glyoxal), complex processes (tannins need to be modified with strong acids) or insufficient performance (protein adhesives have poor water resistance). Although biomass resources can replace petroleum-based raw materials, their low reactivity leads to reliance on chemical cross-linking agents, making it difficult to achieve truly green manufacturing.

[0003] Deep eutectic solvents (DES), as green solvents, provide new ideas for the high-value conversion of biomass. However, existing research has mostly focused on the extraction of cellulose or lignin using DES, ignoring its potential to induce in situ functionalization of biomass. In addition, the high viscosity and recovery problems of DES hinder its large-scale application. Summary of the Invention

[0004] In order to overcome the problems of traditional biomass adhesives such as reliance on synthetic resins, formaldehyde release and poor water resistance, a green low eutectic solvent-driven bamboo powder adhesive and its preparation method are provided. By inducing in-situ carboxylation of bamboo powder through DES and combining it with closed-loop DES recycling technology, high-value utilization of bamboo processing waste is achieved.

[0005] The technical solution of the present invention is: a bamboo powder adhesive driven by a green low eutectic solvent, which includes the following components, calculated by mass percentage: 40% to 50% functionalized low eutectic solvent, 20% to 30% bamboo powder, 0.4% to 0.9% sodium alginate, 0.2% to 0.6% nano-titanium dioxide, 0.16% to 0.36% cellulose nanowhiskers, 0.2% to 0.45% bio-based plasticizer, and ethanol and water.

[0006] Preferably, the functionalized deep eutectic solvent is prepared by mixing a quaternary ammonium salt and a dibasic aliphatic carboxylic acid in a molar ratio of 1:1-2, and adding graphene quantum dots; wherein the graphene quantum dots account for 5% of the total mass of the functionalized deep eutectic solvent.

[0007] Preferably, the bamboo powder is pretreated by bleaching with hydrogen peroxide solution, and the pretreated bamboo powder is mixed with the functionalized deep eutectic solvent at a mass ratio of 1:4-6, and the particle size of the bamboo powder is 60-120 mesh.

[0008] Preferably, sodium alginate is added during the mixing stage of bamboo powder and functionalized deep eutectic solvent, with the added amount being 2% to 3% of the mass of the bamboo powder.

[0009] Preferably, nano-titanium dioxide is added in the composite additive adding step of preparing the adhesive, and the added amount is 1% to 2% of the mass of the pretreated bamboo powder; cellulose nano-whiskers are also added in the composite additive adding stage, and the added amount is 0.8% to 1.2% of the mass of the pretreated bamboo powder.

[0010] Preferably, the addition amount of the bio-based plasticizer is 1% to 1.5% of the mass of the pretreated bamboo powder, and the bio-based plasticizer is specifically triethyl citrate.

[0011] Preferably, ethanol is added in the co-processing step in an amount of 10% to 15% of the volume of the mixed solution; water is used to adjust the solid content of the adhesive to 35% to 60%.

[0012] Preferably, it is suitable for bonding including but not limited to artificial boards, bamboo fiber composite materials or bamboo-wood laminates, wherein the artificial boards include poplar and eucalyptus.

[0013] The preparation method of the green deep eutectic solvent-driven bamboo powder adhesive comprises the green deep eutectic solvent-driven bamboo powder adhesive as described above, and the steps are as follows: S1: Preparation of functionalized deep eutectic solvents Accurately weigh the quaternary ammonium salt and the dibasic aliphatic carboxylic acid, and add them to a reaction vessel equipped with a stirring device and a temperature control system according to a molar ratio of 1:1-2. At the same time, add graphene quantum dots accounting for 5% of the total mass of the quaternary ammonium salt and the dibasic aliphatic carboxylic acid to the container. Place the reaction vessel in a constant temperature water bath at 60°C, turn on the stirring device, and stir continuously at a speed of 200-300 r / min for 2 hours until a uniform and transparent functionalized deep eutectic solvent is formed, and set aside. S2: Pretreatment of bamboo powder Select high-quality bamboo and crush it into bamboo powder of appropriate particle size using a grinder. Place the bamboo powder in a 3% hydrogen peroxide solution with a mass ratio of bamboo powder to hydrogen peroxide solution controlled at 1:10-1:15 to ensure that the bamboo powder is completely immersed. Soak at room temperature for 3 hours and then bleach it to remove impurities and some pigments in the bamboo powder, thereby improving the purity and reactivity of the bamboo powder. After soaking, rinse the bamboo powder repeatedly with deionized water until the washing water is neutral. Then, transfer the washed bamboo powder to an oven and dry it at 80°C to constant weight for later use. S3: Mixed reaction of bamboo powder and functionalized deep eutectic solvent The pretreated bamboo powder and the previously prepared functionalized deep eutectic solvent were added to a reactor at a bamboo powder to functionalized deep eutectic solvent mass ratio of 1:4-6. At the same time, sodium alginate (2% to 3% by mass of the bamboo powder) was added to the reactor. The heating and stirring functions of the reactor were turned on, the reaction temperature was controlled at 110°C, the stirring speed was set to 150-250 rpm, and stirring was continued for 5 hours to allow the bamboo powder and the functionalized deep eutectic solvent to fully mix and react, thereby obtaining a uniform mixed solution. S4: Collaborative Processing The mixed solution obtained in S3 is transferred to an ultrasonic reaction device, and ethanol accounting for 0% to 15% of the volume of the mixed solution is added. The ultrasonic equipment is turned on and the ultrasonic frequency is set to 40 kHz. The ultrasonic treatment is carried out for 30 minutes. After the ultrasonic treatment is completed, the mixed solution is quickly transferred to a high-speed centrifuge and centrifuged at a speed of 11000 rpm for 12 minutes to separate the mixed solution into layers. The lower layer of precipitate is collected to obtain the pretreated bamboo powder; S5: Addition of composite additives and preparation of adhesives The pretreated bamboo powder collected in S4 and water are added to a reaction vessel equipped with a stirring and temperature control device. The solid content of the system is controlled at 35% to 60% by adjusting the amount of water added. Then, 1% to 2% of the mass of the pretreated bamboo powder is added to the vessel, 0.8% to 1.2% of cellulose nanowhiskers, and 1% to 1.5% of a bio-based plasticizer are added to the vessel in sequence. The stirring device is turned on and the mixture is stirred uniformly at a speed of 100 to 200 r / min. The temperature of the reaction vessel is then raised to 50° C. and the mixture is reacted at a constant temperature for 2 hours to allow the various components to fully fuse and react, thereby finally preparing a bamboo powder adhesive driven by a green deep eutectic solvent. S6: Recovery of Functionalized Deep Eutectic Solvents The upper layer liquid after centrifugation in step S4 is transferred to a distillation flask of a rotary evaporator, the temperature of the rotary evaporator is set to 55°C, the vacuum degree is ≤0.08 MPa, the rotary evaporator is turned on, and a rotary evaporation operation is performed under these conditions to separate the solvent in the upper layer liquid from the functionalized deep eutectic solvent. The recovered functionalized deep eutectic solvent can be reused in step S3, thereby realizing resource recycling and reducing production costs.

[0014] The beneficial effects of the present invention are as follows: the functionalized low eutectic solvent in the adhesive of the present invention can induce in-situ carboxylation of bamboo powder, thereby enhancing the bonding force between bamboo powder and other materials; at the same time, the synergistic effect of additives such as sodium alginate, nano-titanium dioxide, and cellulose nanowhiskers further enhances the cohesive strength and bonding strength of the adhesive, making it suitable for bonding a variety of materials such as artificial boards, bamboo fiber composites, or bamboo-wood laminates, with strong bonding, overcoming the defect of poor water resistance of traditional biomass adhesives. Through a special raw material formula and preparation process, the adhesive can still maintain good bonding performance in humid environments, effectively broadening its application scenarios. The added nano-titanium dioxide gives the adhesive antibacterial properties, making it suitable for fields with high requirements for sanitary conditions; the introduction of graphene quantum dots gives the adhesive certain conductive properties, which can be used in special scenarios such as conductive bonding of electronic devices; The cost of bamboo powder is lower than that of biomass raw materials such as soy protein and tannin, significantly reducing the production cost of adhesives. At the same time, DES's closed-loop recycling technology reduces solvent procurement costs and improves resource utilization. Furthermore, this adhesive is suitable for the production of a variety of products, promoting the high-value utilization of bamboo processing waste, reducing companies' raw material procurement costs, improving production efficiency, and promoting the green upgrade of the wood-based panel industry, with good economic benefits and market competitiveness. The innovative use of DES in bamboo powder modification has realized the integrated process of "solvent activation-self-adhesion-closed loop circulation", breaking through the traditional technical path of biomass adhesives relying on chemical cross-linking agents and complex chemical modifications, and providing a new paradigm for the high-value utilization of biomass. This technological innovation not only solves the industry problem of the difficulty in synergistic optimization of "performance-environmental protection-cost" of biomass adhesives, but also provides an efficient technical solution for the resource utilization of bamboo processing waste and the sustainable development of the wood-based panel industry, which has important industry demonstration significance and promotion value. DETAILED DESCRIPTION

[0015] The present invention will be further described below with reference to the embodiments.

[0016] The present invention provides an embodiment: a bamboo powder adhesive driven by a green deep eutectic solvent, which includes the following components, by mass percentage: 40% to 50% of a functionalized deep eutectic solvent, 20% to 30% of bamboo powder, 0.4% to 0.9% of sodium alginate, 0.2% to 0.6% of nano-titanium dioxide, 0.16% to 0.36% of cellulose nanowhiskers, 0.2% to 0.45% of a bio-based plasticizer, and ethanol and water.

[0017] The functionalized deep eutectic solvent is prepared by mixing a quaternary ammonium salt and a dibasic aliphatic carboxylic acid in a molar ratio of 1:1-2, and adding graphene quantum dots; wherein the graphene quantum dots account for 5% of the total mass of the functionalized deep eutectic solvent.

[0018] The bamboo powder is pretreated by bleaching with a hydrogen peroxide solution, and the pretreated bamboo powder is mixed with a functionalized low eutectic solvent in a mass ratio of 1:4-6 for reaction, and the particle size of the bamboo powder is 60-120 meshes.

[0019] Sodium alginate is added during the mixing stage of bamboo powder and functionalized low eutectic solvent, and the added amount is 2% to 3% of the mass of bamboo powder.

[0020] Nano-titanium dioxide is added in the composite additive adding step of preparing the adhesive, and the added amount is 1% to 2% of the mass of the pretreated bamboo powder; cellulose nano-whiskers are also added in the composite additive adding stage, and the added amount is 0.8% to 1.2% of the mass of the pretreated bamboo powder.

[0021] The added amount of the bio-based plasticizer is 1% to 1.5% of the mass of the pre-treated bamboo powder, and the bio-based plasticizer is specifically triethyl citrate.

[0022] Ethanol is added in the co-processing step, and the amount added is 10% to 15% of the volume of the mixed liquid; water is used to adjust the solid content of the adhesive to 35% to 60%.

[0023] The invention is applicable to the bonding of, but not limited to, artificial boards, bamboo fiber composite materials or bamboo-wood laminated materials, wherein the artificial boards include poplar and eucalyptus.

[0024] The preparation method of the green deep eutectic solvent-driven bamboo powder adhesive comprises the green deep eutectic solvent-driven bamboo powder adhesive as described above, and the steps are as follows: S1: Preparation of functionalized deep eutectic solvents Accurately weigh the quaternary ammonium salt and the dibasic aliphatic carboxylic acid, and add them to a reaction vessel equipped with a stirring device and a temperature control system according to a molar ratio of 1:1-2. At the same time, add graphene quantum dots accounting for 5% of the total mass of the quaternary ammonium salt and the dibasic aliphatic carboxylic acid to the container. Place the reaction vessel in a constant temperature water bath at 60°C, turn on the stirring device, and stir continuously at a speed of 200-300 r / min for 2 hours until a uniform and transparent functionalized deep eutectic solvent is formed, and set aside. S2: Pretreatment of bamboo powder Select high-quality bamboo and crush it into bamboo powder of appropriate particle size using a grinder. Place the bamboo powder in a 3% hydrogen peroxide solution with a mass ratio of bamboo powder to hydrogen peroxide solution controlled at 1:10-1:15 to ensure that the bamboo powder is completely immersed. Soak at room temperature for 3 hours and then bleach it to remove impurities and some pigments in the bamboo powder, thereby improving the purity and reactivity of the bamboo powder. After soaking, rinse the bamboo powder repeatedly with deionized water until the washing water is neutral. Then, transfer the washed bamboo powder to an oven and dry it at 80°C to constant weight for later use. S3: Mixed reaction of bamboo powder and functionalized deep eutectic solvent The pretreated bamboo powder and the previously prepared functionalized deep eutectic solvent were added to a reactor at a bamboo powder to functionalized deep eutectic solvent mass ratio of 1:4-6. At the same time, sodium alginate (2% to 3% by mass of the bamboo powder) was added to the reactor. The heating and stirring functions of the reactor were turned on, the reaction temperature was controlled at 110°C, the stirring speed was set to 150-250 rpm, and stirring was continued for 5 hours to allow the bamboo powder and the functionalized deep eutectic solvent to fully mix and react, thereby obtaining a uniform mixed solution. S4: Collaborative Processing The mixed solution obtained in S3 is transferred to an ultrasonic reaction device, and ethanol accounting for 0% to 15% of the volume of the mixed solution is added. The ultrasonic equipment is turned on and the ultrasonic frequency is set to 40 kHz. The ultrasonic treatment is carried out for 30 minutes. After the ultrasonic treatment is completed, the mixed solution is quickly transferred to a high-speed centrifuge and centrifuged at a speed of 11000 rpm for 12 minutes to separate the mixed solution into layers. The lower layer of precipitate is collected to obtain the pretreated bamboo powder; S5: Addition of composite additives and preparation of adhesives The pretreated bamboo powder collected in S4 and water are added to a reaction vessel equipped with a stirring and temperature control device. The solid content of the system is controlled at 35% to 60% by adjusting the amount of water added. Then, 1% to 2% of the mass of the pretreated bamboo powder is added to the vessel, 0.8% to 1.2% of cellulose nanowhiskers, and 1% to 1.5% of a bio-based plasticizer are added to the vessel in sequence. The stirring device is turned on and the mixture is stirred uniformly at a speed of 100 to 200 r / min. The temperature of the reaction vessel is then raised to 50° C. and the mixture is reacted at a constant temperature for 2 hours to allow the various components to fully fuse and react, thereby finally preparing a bamboo powder adhesive driven by a green deep eutectic solvent. S6: Recovery of Functionalized Deep Eutectic Solvents The upper layer liquid after centrifugation in step S4 is transferred to a distillation flask of a rotary evaporator, the temperature of the rotary evaporator is set to 55°C, the vacuum degree is ≤0.08 MPa, the rotary evaporator is turned on, and a rotary evaporation operation is performed under these conditions to separate the solvent in the upper layer liquid from the functionalized deep eutectic solvent. The recovered functionalized deep eutectic solvent can be reused in step S3, thereby realizing resource recycling and reducing production costs.

[0025] Example 1 The present invention provides an embodiment: a method for preparing a bamboo powder adhesive driven by a green deep eutectic solvent, the steps of which are as follows: Step 1: Weigh the raw materials, specifically 14.0 g of choline chloride and 9.0 g of oxalic acid, in a molar ratio of choline chloride to oxalic acid of 1:1. At the same time, prepare bamboo powder with a particle size of 80 mesh, place the bamboo powder in a 3% hydrogen peroxide solution with a mass ratio of bamboo powder to hydrogen peroxide solution of 1:12, and soak at room temperature for 3 hours for bleaching pretreatment. After the soaking, rinse the bamboo powder repeatedly with deionized water until the washing water is neutral, and then transfer the bamboo powder to an 80°C oven to dry to constant weight for later use; Step 2: Add the weighed choline chloride and oxalic acid to a reaction vessel equipped with a stirring device and a temperature control system, and stir at 100°C until a uniform and transparent functionalized low eutectic solvent is formed. Add the pretreated bamboo powder and the functionalized low eutectic solvent to the reactor in a mass ratio of 1:5, turn on the heating and stirring function of the reactor, control the temperature to 100°C, and stir at a speed of 200r / min. Stir continuously for 4 hours to obtain an activated bamboo powder mixture. Add deionized water of equal mass to the functionalized low eutectic solvent to the mixture. After stirring for 30 minutes, transfer the mixture to a high-speed centrifuge and centrifuge at 12000rpm to collect the lower precipitate to obtain activated bamboo powder. Mix the activated bamboo powder and deionized water in a mass ratio of 1:1.5, adjust the solid content to 38%, and prepare a bamboo powder adhesive. Apply the adhesive to the plywood surface at a coating amount of 140 g / m², and then heat at 200°C and 1.2 MPa. The mixture was hot pressed for 7 minutes under the same conditions to form plywood, and the upper liquid after centrifugation was transferred to a rotary evaporator and the functionalized deep eutectic solvent was recovered by rotary evaporation at 80°C. The prepared plywood was subjected to a shear strength test, and according to the GB / T17657-2013 standard, the average shear strength was measured to be 1.8 MPa; a water resistance test was conducted, and the plywood was immersed in 63°C hot water for 3 hours. After being taken out and dried, it was observed that there was no cracking or falling off of the glue layer, and the shear strength retention rate was 85%.

[0026] Example 2 The present invention provides an embodiment: a method for preparing a bamboo powder adhesive driven by a green deep eutectic solvent, the steps of which are as follows: Step 1: The raw materials and bamboo powder pretreatment process are the same as in Example 1; Step 2: When preparing the activated bamboo powder mixture, the bamboo powder and the functionalized deep eutectic solvent are mixed in a mass ratio of 1:5, and the stirring time is extended to 6 hours at 100° C. The remaining steps are exactly the same as in Example 1, namely, the subsequent steps of adding water and stirring, centrifugal separation, mixing with water to adjust the solid content, coating with glue and hot pressing, and recovering the functionalized deep eutectic solvent are performed in sequence; After testing, the average shear strength of the prepared plywood was 2.1 MPa; in the water resistance test, after soaking in 63°C hot water for 3 hours, the shear strength retention rate was 90%. Compared with Example 1, the extended stirring time made the adhesive activate the bamboo powder more fully, thereby improving the bonding performance and water resistance of the plywood.

[0027] Example 3 The present invention provides an embodiment: a method for preparing a bamboo powder adhesive driven by a green deep eutectic solvent, the steps of which are as follows: Step 1: The raw materials and bamboo powder pretreatment process are the same as in Example 1; Step 2: First, an activated bamboo powder mixture was prepared according to the method of Example 1, and the mixture was centrifuged and the functionalized deep eutectic solvent was recovered by rotary evaporation. The recovered functionalized deep eutectic solvent was then remixed with bamboo powder in a mass ratio of 1:5 and stirred at 100° C. for 4 hours. Subsequent steps, such as adding water, stirring, centrifuging, and adjusting the solid content with water to 38%, applying glue and hot pressing with a glue amount of 40 g / m², and hot pressing at 200° C. and 1.2 MPa for 7 minutes, were all consistent with Example 1. The test results show that the average shear strength of the plywood is 1.7 MPa, and the shear strength retention rate is 83% after immersion in 63°C hot water for 3 hours, indicating that the reuse of the recycled functionalized low eutectic solvent has little effect on the performance of the adhesive, verifying the feasibility of the closed-loop recycling technology of functionalized low eutectic solvents.

[0028] Comparative Example 1 The present invention provides a comparative example: a method for preparing a bamboo powder adhesive driven by a green deep eutectic solvent, the steps of which are as follows: Step 1: The raw materials and bamboo powder pretreatment process are the same as in Example 1; Step 2: When preparing the activated bamboo powder mixture, the bamboo powder and the functionalized deep eutectic solvent were mixed in a mass ratio of 1:5, and the stirring time was shortened to 1 hour at 100°C. The remaining steps were the same as in Example 1, including the subsequent addition of water and stirring, centrifugation, mixing with water to adjust the solid content to 38%, glue coating and hot pressing, and functionalized deep eutectic solvent recovery. The glue coating amount was 140 g / m², and hot pressing was performed at 200°C and 1.2 MPa for 7 minutes. The average shear strength of the plywood produced was only 1.2 MPa. After soaking in 63°C hot water for 3 hours, the glue layer showed obvious cracking and falling off, and the shear strength retention rate was only 50%, indicating that the short stirring time led to insufficient activation of the bamboo powder, seriously affecting the bonding and water resistance of the adhesive.

[0029] Comparative Example 2 The present invention provides a comparative example: a method for preparing a bamboo powder adhesive driven by a green deep eutectic solvent, the steps of which are as follows: Step 1: The raw materials and bamboo powder pretreatment process are the same as in Example 1; Step 2: Bamboo powder and a functionalized deep eutectic solvent were mixed in a mass ratio of 1:5. After stirring at 100°C for 4 hours, water (equivalent in mass to the functionalized deep eutectic solvent) was added and stirred for 30 minutes. The mixture was then applied directly to the plywood surface as an adhesive at a coating weight of 140 g / m² without centrifugation. The plywood was then hot-pressed at 200°C and 1.2 MPa for 7 minutes. After testing, the average shear strength of the plywood was 1.5 MPa. After soaking in 63°C hot water for 3 hours, the shear strength retention rate was 70%. Since the functionalized low eutectic solvent was not separated, the residual functionalized low eutectic solvent in the adhesive affected the curing effect of the adhesive layer, resulting in performance lower than that of the embodiment.

[0030] Comparative Example 3 The present invention provides a comparative example: a method for preparing a bamboo powder adhesive driven by a green deep eutectic solvent, the steps of which are as follows: Step 1: Accurately weigh 14.0 g of choline chloride and 6.0 g of urea in a molar ratio of 1:1. The bamboo powder pretreatment process is the same as in Example 1; Step 2: Add choline chloride and urea to a reaction vessel and stir at 100° C. to form a functionalized deep eutectic solvent. Subsequently, bamboo powder and the functionalized deep eutectic solvent are mixed in a mass ratio of 1:5 and stirred at 100° C. for 4 hours. Then, water is added and stirred, centrifuged, mixed with water to adjust the solid content to 38%, and the solid content is adjusted to 38%. The glue is applied and hot pressed, and the functionalized deep eutectic solvent is recovered. The glue application amount is 140 g / m², and hot pressed at 200° C. and 1.2 MPa for 7 minutes. The steps are the same as in Example 1. The average shear strength of the prepared plywood was 1.3 MPa. After soaking in 63°C hot water for 3 hours, the shear strength retention rate was 60%, indicating that replacing the hydrogen bond donor with non-acid urea could not effectively induce in-situ carboxylation of bamboo powder, significantly reducing the performance of the adhesive.

[0031] Comparative Example 4 The present invention provides a comparative example: a method for preparing a bamboo powder adhesive driven by a green deep eutectic solvent, the steps of which are as follows: Step 1: The raw materials and bamboo powder pretreatment process are the same as in Example 1; Step 2: Bamboo powder and DES were mixed in a mass ratio of 1:5 and stirred at 40°C for 4 hours. The remaining preparation steps, such as adding water and stirring, centrifugal separation, and adjusting the solid content by mixing with water to 38%, glue coating and hot pressing, and functionalized deep eutectic solvent recovery, were consistent with Example 1. The glue coating amount was 140 g / m², and hot pressing was performed at 200°C and 1.2 MPa for 7 minutes. The average shear strength of plywood is 1.1 MPa. After soaking in 63°C hot water for 3 hours, the adhesive layer fell off over a large area, and the shear strength retention rate was only 45%. The low activation treatment temperature caused insufficient reaction between the functionalized low eutectic solvent and bamboo powder, resulting in a significant decrease in adhesive performance.

[0032] Comparative Example 5 The present invention provides a comparative example: a method for preparing a bamboo powder adhesive driven by a green deep eutectic solvent, the steps of which are as follows: Step 1: The raw materials and bamboo powder pretreatment process are the same as in Example 1; Step 2: To prepare the adhesive, activated bamboo powder and water were mixed at a mass ratio of 0.5:1, and the solid content was adjusted to 28%. The remaining preparation steps, including the mixing reaction of bamboo powder and functionalized deep eutectic solvent, the addition of water and stirring, centrifugal separation, adhesive application and hot pressing, and recovery of the functionalized deep eutectic solvent, were the same as in Example 1. The adhesive application amount was 140 g / m², and hot pressing was performed at 200°C and 1.2 MPa for 7 minutes. The test showed that the average shear strength of plywood was 1.4 MPa. After soaking in 63°C hot water for 3 hours, the shear strength retention rate was 72%. Reducing the proportion of activated bamboo powder reduced the effective ingredients in the adhesive, thus affecting its bonding and water resistance. The specific test results are shown in Table 1:

[0033] Note: “---” means no data.

[0034] As shown in Table 1, the plywood prepared by the method of the present invention has good water resistance. In comparison, it is found that the plywood prepared by the bamboo powder adhesive activated by the functionalized low eutectic solvent recovered for the first time has obvious advantages.

Claims

1. Bamboo powder adhesive driven by green deep eutectic solvent, characterized in that: Calculated by mass percentage, the composition includes: 40% to 50% of a functionalized low eutectic solvent, 20% to 30% of bamboo powder, 0.4% to 0.9% of sodium alginate, 0.2% to 0.6% of nano-titanium dioxide, 0.16% to 0.36% of cellulose nanowhiskers, 0.2% to 0.45% of a bio-based plasticizer, and ethanol and water.

2. The green deep eutectic solvent-driven bamboo powder adhesive according to claim 1, characterized in that: The functionalized deep eutectic solvent is prepared by mixing a quaternary ammonium salt and a dibasic aliphatic carboxylic acid in a molar ratio of 1:1-2, and adding graphene quantum dots; wherein the graphene quantum dots account for 5% of the total mass of the functionalized deep eutectic solvent.

3. The green deep eutectic solvent-driven bamboo powder adhesive according to claim 1, characterized in that: The bamboo powder is pretreated by bleaching with a hydrogen peroxide solution, and the pretreated bamboo powder is mixed with a functionalized low eutectic solvent in a mass ratio of 1:4-6 for reaction, and the particle size of the bamboo powder is 60-120 meshes.

4. The green deep eutectic solvent-driven bamboo powder adhesive according to claim 1, characterized in that: Sodium alginate is added during the mixing stage of bamboo powder and functionalized low eutectic solvent, and the added amount is 2% to 3% of the mass of bamboo powder.

5. The green deep eutectic solvent-driven bamboo powder adhesive according to claim 1, characterized in that: Nano-titanium dioxide is added in the composite additive adding step of preparing the adhesive, and the added amount is 1% to 2% of the mass of the pretreated bamboo powder; cellulose nano-whiskers are also added in the composite additive adding stage, and the added amount is 0.8% to 1.2% of the mass of the pretreated bamboo powder.

6. The green deep eutectic solvent-driven bamboo powder adhesive according to claim 1, characterized in that: The added amount of the bio-based plasticizer is 1% to 1.5% of the mass of the pre-treated bamboo powder, and the bio-based plasticizer is specifically triethyl citrate.

7. The green deep eutectic solvent-driven bamboo powder adhesive according to claim 1, characterized in that: Ethanol is added in the co-processing step, and the amount added is 10% to 15% of the volume of the mixed liquid; water is used to adjust the solid content of the adhesive to 35% to 60%.

8. The green deep eutectic solvent-driven bamboo powder adhesive according to claim 1, characterized in that: The invention is applicable to the bonding of, but not limited to, artificial boards, bamboo fiber composite materials or bamboo-wood laminated materials, wherein the artificial boards include poplar and eucalyptus.

9. A method for preparing a bamboo powder adhesive driven by a green deep eutectic solvent, characterized in that The method comprises the green deep eutectic solvent-driven bamboo powder adhesive according to claims 1-8, wherein the steps are as follows: S1: Preparation of functionalized deep eutectic solvents Accurately weigh the quaternary ammonium salt and the dibasic aliphatic carboxylic acid, and add them to a reaction vessel equipped with a stirring device and a temperature control system according to a molar ratio of 1:1-2. At the same time, add graphene quantum dots accounting for 5% of the total mass of the quaternary ammonium salt and the dibasic aliphatic carboxylic acid to the container. Place the reaction vessel in a constant temperature water bath at 60°C, turn on the stirring device, and stir continuously at a speed of 200-300 r / min for 2 hours until a uniform and transparent functionalized deep eutectic solvent is formed, and set aside. S2: Pretreatment of bamboo powder Select high-quality bamboo and crush it into bamboo powder of appropriate particle size using a grinder. Place the bamboo powder in a 3% hydrogen peroxide solution with a mass ratio of bamboo powder to hydrogen peroxide solution controlled at 1:10-1:15 to ensure that the bamboo powder is completely immersed. Soak at room temperature for 3 hours and then bleach it to remove impurities and some pigments in the bamboo powder, thereby improving the purity and reactivity of the bamboo powder. After soaking, rinse the bamboo powder repeatedly with deionized water until the washing water is neutral. Then, transfer the washed bamboo powder to an oven and dry it at 80°C to constant weight for later use. S3: Mixed reaction of bamboo powder and functionalized deep eutectic solvent The pretreated bamboo powder and the previously prepared functionalized deep eutectic solvent were added to a reactor at a bamboo powder to functionalized deep eutectic solvent mass ratio of 1:4-6. At the same time, sodium alginate (2% to 3% by mass of the bamboo powder) was added to the reactor. The heating and stirring functions of the reactor were turned on, the reaction temperature was controlled at 110°C, the stirring speed was set to 150-250 rpm, and stirring was continued for 5 hours to allow the bamboo powder and the functionalized deep eutectic solvent to fully mix and react, thereby obtaining a uniform mixed solution. S4: Collaborative Processing The mixed solution obtained in S3 is transferred to an ultrasonic reaction device, and ethanol accounting for 0% to 15% of the volume of the mixed solution is added. The ultrasonic equipment is turned on and the ultrasonic frequency is set to 40 kHz. The ultrasonic treatment is carried out for 30 minutes. After the ultrasonic treatment is completed, the mixed solution is quickly transferred to a high-speed centrifuge and centrifuged at a speed of 11000 rpm for 12 minutes to separate the mixed solution into layers. The lower layer of precipitate is collected to obtain the pretreated bamboo powder; S5: Addition of composite additives and preparation of adhesives The pretreated bamboo powder collected in S4 and water are added to a reaction vessel equipped with a stirring and temperature control device. The solid content of the system is controlled at 35% to 60% by adjusting the amount of water added. Then, 1% to 2% of the mass of the pretreated bamboo powder is added to the vessel, 0.8% to 1.2% of cellulose nanowhiskers, and 1% to 1.5% of a bio-based plasticizer are added to the vessel in sequence. The stirring device is turned on and the mixture is stirred uniformly at a speed of 100 to 200 r / min. The temperature of the reaction vessel is then raised to 50° C. and the mixture is reacted at a constant temperature for 2 hours to allow the various components to fully fuse and react, thereby finally preparing a bamboo powder adhesive driven by a green deep eutectic solvent. S6: Recovery of Functionalized Deep Eutectic Solvents The upper layer liquid after centrifugation in step S4 is transferred to a distillation flask of a rotary evaporator, the temperature of the rotary evaporator is set to 55°C, the vacuum degree is ≤0.08 MPa, the rotary evaporator is turned on, and a rotary evaporation operation is performed under these conditions to separate the solvent in the upper layer liquid from the functionalized deep eutectic solvent. The recovered functionalized deep eutectic solvent can be reused in step S3, thereby realizing resource recycling and reducing production costs.

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