Manufacturing method of soybean protein glue for plates

Abstract

The invention relates to the technical field of soybean protein glue, in particular to a manufacturing method of soybean protein glue for plates, which comprises the following steps: S1, adding a certain amount of diethylenetriamine into a reaction container, mixing, slowly heating to 80-90 DEG C, adding binary acid, and reacting at constant temperature for 0.5-0.7 hour; s2, adding sulfuric acid and boric acid, heating to 14-150 DEG C, keeping the temperature for 3-3.5 hours, then continuously heating to 170-190 DEG C, and keeping the temperature for 2 hours to complete polycondensation reaction after no water is discharged, so as to form polyamide polyamine; s3, preparing a modified PAE wet strength agent; s4, a modified PAE wet strength agent and a reinforcing agent are added into the soybean meal powder, mechanical stirring is carried out for 3-5 min, and the soybean protein glue is obtained.The soybean protein adhesive is modified, synergistic reinforcing and toughening of a plant fiber based multiphase composite system on soybean protein are achieved, meanwhile, lignin epoxy polymer takes a lignin macromolecular unit as a main body structure, and the lignin epoxy polymer can be used for preparing the soybean protein adhesive. The modified soybean protein adhesive with a water-resistant cross-linked structure can be formed through reaction with soybean protein molecules.

Description

Technical Field

[0001] The present invention relates to the technical field of soybean protein glue manufacturing, and particularly relates to a method for manufacturing a soybean protein glue for plates. Background Art

[0002] PAE resin is a widely used wet strength agent. In the papermaking process, mainly through the self-crosslinking of PAE resin, a hydrophobic network structure is formed on the fiber surface to improve the wet strength of the paper; while in the modified soybean protein adhesive, a co-crosslinking effect generated by the chemical reaction between PAE and soybean meal forms a crosslinked network structure, thereby endowing the adhesive with excellent bonding strength and water resistance of the bond. Due to the different action mechanisms of the above two, directly using PAE resin for papermaking as a crosslinking modifier for soybean protein-based adhesives is not the optimal choice. Although PAE resin has been proven to be usable as a modifier for soybean protein-based wood adhesives, the modified adhesives still have problems such as low bonding strength, poor water resistance, and easy mildew, which limit the application range of soybean protein-based wood adhesives and make them only applicable to the production of indoor artificial boards. Defatted soybean meal powder is a by-product generated during the process of extracting edible oil from soybeans, containing about 38 - 52% soybean protein and 40 - 45% carbohydrates. Among them, the protein plays a major role in bonding. Due to the relatively low protein content in soybean meal powder, conventional modification treatments cannot significantly improve the bonding performance of soybean meal adhesives, and the method of enhancing modification with a crosslinking agent can help improve its water resistance. Summary of the Invention

[0003] The present invention aims to provide a method for manufacturing a soybean protein glue for plates. The present invention uses a silane coupling agent to functionalize and modify flax fibers and a crosslinking agent to modify the soybean protein adhesive, achieving the synergistic strengthening and toughening of soybean protein by a plant fiber-based multiphase composite system. At the same time, lignin epoxy polymer has a main structure of lignin macromolecular units and contains a large number of active epoxy groups, which can react with soybean protein molecules to form a modified soybean protein adhesive with a water-resistant crosslinked structure.

[0004] The above technical object of the present invention is achieved through the following technical solutions: A method for manufacturing a soybean protein glue for plates, including the following preparation steps:

[0005] S1: Add a certain amount of diethylenetriamine to a reaction vessel, mix well, and slowly heat up to 80 - 90 °C, then add a dibasic acid and react at a constant temperature for 0.5 - 0.7 h;

[0006] S2: Add sulfuric acid and boric acid, heat up to 140 - 150 °C, keep warm for 3 - 3.5 h, then continue to heat up to 170 - 190 °C. After no water is discharged, keep warm for 2 h to complete the polycondensation reaction and form polyamide polyamine;

[0007] S3: Dilute the polyamide polyamine obtained in step S2 with water to 25%, then gradually add dropwise the modified epoxy polymer. After the addition is completed, raise the temperature to 50 - 60 °C and maintain for 30 min. Then raise the temperature again to 60 - 65 °C. After reaching the specified viscosity, lower the temperature to 40 - 50 °C, add the modifier and continue the reaction for 2 - 3 h, and then add dilute acid to terminate the reaction to obtain the modified PAE wet strength agent.

[0008] S4: Add the modified PAE wet strength agent and the reinforcing agent to the soybean meal powder and mechanically stir for 3 - 5 min to obtain the soybean protein glue.

[0009] As a further setting of the present invention, the preparation steps of the modified epoxy polymer are as follows: Add lignin to the sodium hydroxide aqueous solution. After the lignin is completely dissolved, directly raise the temperature to 50 - 60 °C, and gradually add dropwise ethylene glycol diglycidyl ether. After the addition is completed, keep the temperature for reaction for 3 - 4 h, and then lower the temperature to obtain the modified epoxy polymer.

[0010] As a further setting of the present invention, the concentration of the sodium hydroxide aqueous solution is 1 - 1.5 wt%.

[0011] As a further setting of the present invention, the mass fraction ratio of the sodium hydroxide aqueous solution, lignin and ethylene glycol diglycidyl ether is 10:1:5 - 8.

[0012] As a further setting of the present invention, the reinforcing agent is prepared by grafting an amide compound onto the surface of calcium carbonate nanoparticles using a coupling agent to enhance the crosslinking between the modified calcium carbonate nanoparticles and soybean protein.

[0013] As a further setting of the present invention, the specific preparation method of the reinforcing agent is as follows: (1) Mix a calcium chloride solution with a concentration of 0.1 mol / L and ramie fibers in a closed container, react at 100 °C for 30 - 40 min, cool and filter, remove the filtrate, and then add a sodium carbonate solution with a concentration of 0.1 mol / L and continue to react at 100 °C for 30 - 40 min, cool, filter and wash to obtain the modified fibers; the volume ratio of the calcium chloride solution to the sodium carbonate solution is 1:1; (2) Dissolve N - cyclohexyl - 2 - benzothiazole sulfenamide and a silane coupling agent in absolute ethanol, reflux and stir at 90 °C under nitrogen for 3 h, then add the modified fibers and continue to stir for 12 h and then cool, and filter, wash and dry the obtained suspension to obtain the modified calcium carbonate nanoparticles.

[0014] As a further setting of the present invention, the mass ratio of N - cyclohexyl - 2 - benzothiazole sulfenamide, the silane coupling agent to the modified fibers is 1 - 1.2:1:40.

[0015] As a further setting of the present invention, the dilute acid includes one or more of sulfuric acid, hydrochloric acid, formic acid, oxalic acid, and citric acid.

[0016] As a further setting of the present invention, the molar ratio of diethylenetriamine to dibasic acid is 3:4 - 4.5.

[0017] As a further setting of the present invention, in step S1, the dibasic acid is a mixture of adipic acid and maleic acid, and their molar mass ratio is 1:0.2 - 0.5.

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0019] 1. The synthesis principle of the modified epoxy polymer is to graft lignin with epoxy compounds by the ring-opening and ring-closing reaction of epoxy groups between phenolic hydroxyl groups in lignin and epichlorohydrin under the action of an alkaline catalyst. The lignin epoxy polymer has a main structure of lignin macromolecular units and contains a large number of active epoxy groups, which can react with soy protein molecules to form a modified soy protein adhesive with a water-resistant cross-linked structure. The epoxy group is a three-membered ring composed of two carbon atoms and one oxygen atom, and has two reactive active sites: an oxygen atom with a higher electron cloud density and a carbon atom with a lower electron cloud density. When an electrophilic reagent approaches, it will attack the oxygen atom, and when a nucleophilic reagent approaches, it will attack the carbon atom, and a rapid reaction will occur, causing the cleavage of the C-O bond and the ring-opening of the epoxy group. The phenolic hydroxyl group in lignin becomes phenolate under alkaline conditions and undergoes a ring-opening addition reaction with the epoxy group of ethylene glycol diglycidyl ether to form a modified epoxy polymer.

[0020] 2. The present invention uses a silane coupling agent to functionalize and modify ramie fibers and a cross-linking agent to modify the soy protein adhesive, realizing the synergistic enhancement and toughening of soy protein by a plant fiber-based multiphase composite system. Using ramie fibers as the main reinforcing phase, calcium carbonate nanoparticles are in-situ grown on the ramie fibers to increase the surface roughness of the fibers. A silane coupling agent is used to graft N-cyclohexyl-2-benzothiazole sulfenamide onto the surface of calcium carbonate nanoparticles to promote the cross-linking reaction between the cross-linking agent, the surface-roughened fibers, and the soy protein matrix.

[0021] 3. In the present invention, the introduction of an appropriate amount of ramie fibers will effectively hinder the propagation of microcracks. The fibers can bear part of the stress, resulting in an increase in the gluing strength. Due to the presence of N-cyclohexyl-2-benzothiazole sulfenamide on the rough structure of the ramie fibers, the cross-linking reaction of the system is accelerated, endowing a higher interfacial binding force. When an external force acts, the shear force between the fiber and matrix interface transfers the external load from the matrix to the fiber and also prevents the further propagation of cracks, so that the adhesive obtains better bonding performance.

[0022] 4. The calcium carbonate nanoparticles are uniformly distributed on the fiber surface, forming a micro-nano convex structure on the surface of the hemp fiber, which produces an excellent mechanical meshing effect with the matrix. When the adhesive is subjected to an external force, the protrusions on the fiber surface can dissipate energy and prevent the rapid propagation of cracks. Secondly, introducing N-cyclohexyl-2-benzothiazole sulfenamide and silane coupling agent into the modified fiber can enhance its chemical reaction activity, improve the interfacial compatibility with the matrix, make it more difficult to pull out the fiber, and thus improve the gluing performance of the adhesive. Detailed implementation mode

[0023] The technical solutions in the embodiments will be described clearly and completely below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts belong to the scope of protection of the present invention.

[0024] Example 1, a method for making a soybean protein glue for plates, including the following preparation steps:

[0025] S1: Add 30 mL of diethylenetriamine to the reaction vessel, mix well, and slowly heat up to 80 - 90 °C, then add 40 g of dibasic acid, and react at a constant temperature for 0.5 - 0.7 h;

[0026] S2: Add 1 g of boric acid, heat up to 140 - 150 °C, keep warm for 3 - 3.5 h, then continue to heat up to 170 - 190 °C. After no water is discharged, keep warm for 2 h to complete the polycondensation reaction and form polyamide polyamine;

[0027] S3: Take 10 g of polyamide polyamine and dilute it with water to a mass concentration of 25%, then gradually add 8 g of epichlorohydrin dropwise. After the dropwise addition is completed, heat up to 50 - 60 °C, keep for 30 min, then heat up to 60 - 65 °C again. After reaching the specified viscosity, cool down to 40 - 50 °C, add a modifier and continue to react for 2 - 3 h, then add dilute acid to terminate the reaction to obtain a wet strength agent;

[0028] S4: Add 80 g of wet strength agent to 200 g of soybean meal powder, and mechanically stir for 3 - 5 min to obtain soybean protein glue.

[0029] Example 2, a method for making a soybean protein glue for plates, including the following preparation steps:

[0030] S1: Add 30 mL of diethylenetriamine to the reaction vessel, mix well, and slowly heat up to 80 - 90 °C, then add 40 g of dibasic acid, and react at a constant temperature for 0.5 - 0.7 h;

[0031] S2: Add 1 g of boric acid, heat up to 14 - 150 °C, keep warm for 3 - 3.5 h, then continue to heat up to 170 - 190 °C. After no water is discharged, keep warm for 2 h to complete the polycondensation reaction to form polyamide polyamine;

[0032] S3: Take 10 g of polyamide polyamine and dilute it with water to a mass concentration of 25%. Then gradually add 8 g of modified epoxy polymer dropwise. After the addition is completed, heat up to 50 - 60 °C and keep it for 30 min. Then heat up to 60 - 65 °C again. After reaching the specified viscosity, cool down to 40 - 50 °C, add the modifier and continue to react for 2 - 3 h, then add diluted acid to terminate the reaction to obtain the modified wet strength agent;

[0033] S4: Add 80 g of modified wet strength agent to 200 g of soybean meal powder and stir mechanically for 3 - 5 min to obtain soybean protein glue.

[0034] Example 3, A method for making soybean protein glue for plates, including the following preparation steps:

[0035] S1: Add 30 mL of diethylenetriamine to the reaction vessel, mix and slowly heat up to 80 - 90 °C, then add 40 g of dibasic acid and react at a constant temperature for 0.5 - 0.7 h;

[0036] S2: Add 1 g of boric acid, heat up to 14 - 150 °C, keep warm for 3 - 3.5 h, then continue to heat up to 170 - 190 °C. After no water is discharged, keep warm for 2 h to complete the polycondensation reaction to form polyamide polyamine;

[0037] S3: Take 10 g of polyamide polyamine and dilute it with water to a mass concentration of 25%. Then gradually add 8 g of epichlorohydrin dropwise. After the addition is completed, heat up to 50 - 60 °C and keep it for 30 min. Then heat up to 60 - 65 °C again. After reaching the specified viscosity, cool down to 40 - 50 °C, add the modifier and continue to react for 2 - 3 h, then add diluted acid to terminate the reaction to obtain the modified wet strength agent;

[0038] S4: Add 80 g of modified wet strength agent and 15 g of enhancer to 200 g of soybean meal powder and stir mechanically for 3 - 5 min to obtain soybean protein glue.

[0039] Example 4, A method for making soybean protein glue for plates, including the following preparation steps:

[0040] S1: Add 30 mL of diethylenetriamine to the reaction vessel, mix and slowly heat up to 80 - 90 °C, then add 40 g of dibasic acid and react at a constant temperature for 0.5 - 0.7 h;

[0041] S2: Add 1 g of boric acid, heat up to 14 - 150 °C, keep warm for 3 - 3.5 h, then continue to heat up to 170 - 190 °C. After no water is discharged, keep warm for 2 h to complete the polycondensation reaction to form polyamide polyamine;

[0042] S3: Take 10 g of polyamide polyamine, dilute it with water to a mass concentration of 25%, then gradually add 8 g of modified epoxy polymer dropwise. After the addition is completed, heat up to 50 - 60 °C and hold for 30 min. Then heat up to 60 - 65 °C again. After reaching the specified viscosity, cool down to 40 - 50 °C, add a modifier and continue to react for 2 - 3 h, then add dilute acid to terminate the reaction to obtain a modified wet strength agent;

[0043] S4: Add 80 g of the modified wet strength agent and 15 g of a reinforcing agent to 200 g of soybean meal powder, and mechanically stir for 3 - 5 min to obtain a soybean protein glue.

[0044] Perform performance analysis on the soybean protein glue obtained in Examples 1 - 4 to obtain Table 1

[0045] Example 1 Example 2 Example 3 Example 4 Viscosity / Pa·s 256 3451 4215 5047 Solid content / % 29.57 36.43 35.25 39.84

[0046] When the viscosity of the adhesive is very high, it is not conducive to the coating and penetration of the soybean protein adhesive, thereby affecting the bonding strength of the plywood; when the viscosity of the adhesive is very low, it is difficult to evenly coat on the veneer, and at the same time, the adhesive easily penetrates too much into the interior of the wood veneer, causing lack of glue and making it difficult to play a bonding role between the wood boards. The viscosity of the protein glue prepared in Example 4 is appropriate, making it have good coatability in practical applications. During the use of the adhesive, the solid content of the adhesive needs to exceed 35% to obtain good bonding performance. It can be seen that after adding the modified epoxy polymer and the reinforcing agent, its solid content is 39.84%, making the bonding ability between the adhesive and the wood board stronger.

[0047] Apply the soybean protein glue obtained in Examples 1 - 4 to plywood. The process parameters of the plywood are as follows: the single-sided glue content is 180 g / m2. The hot pressing temperature, time and pressure are 130 °C, 7 min and 1.3 MPa respectively. Place the prepared plywood at room temperature for 24 h to balance, and measure its bonding strength (the measurement of the shear strength of the glue layer is carried out with reference to the measurement method of Class II plywood in the national standard GB / T 17657 - 2013 "Test Methods for Physical and Chemical Properties of Wood-based Panels and Decorative Wood-based Panels") to obtain Table 2.

[0048] Table 1 Data table of performance test of plywood prepared using Examples 1 - 4 respectively

[0049] Example 1 Example 2 Example 3 Example 4 Gluing strength / MPa 0.5 0.86 0.89 1.25 Moisture absorption rate / % 20.15 12.36 10.54 9.2

[0050] As can be seen from Table 2, in Examples 3 and 4, a modified epoxy polymer was added. The active epoxy groups contained in the modified epoxy polymer formed a soy protein adhesive system with a three-dimensional network structure through cross-linking reactions with soy protein molecular groups. The cross-linking reactions introduced lignin macromolecules with rigid rings into the structure of the soy protein adhesive, and the formed three-dimensional cross-linked network structure prevented the erosion and penetration of moisture, thus improving its water resistance.

Claims

1. A method for preparing soybean protein glue for plate materials, characterized in that: The method comprises the following preparation steps: S1: Add a certain amount of diethylenetriamine into the reaction container, mix and slowly heat to 80-90°C, then add dibasic acid and react at constant temperature for 0.5-0.7h; S2: Add sulfuric acid and boric acid, raise the temperature to 14-150°C, keep it warm for 3-3.5 hours, then continue to raise the temperature to 170-190°C, and keep it warm for 2 hours after no water is discharged to complete the polycondensation reaction and form polyamide polyamine; S3: diluting the polyamide polyamine obtained in step S2 with water to 25%, then gradually adding the modified epoxy polymer dropwise, heating to 50-60° C. after the addition is completed, maintaining for 30 minutes, heating again to 60-65° C., and after reaching a specified viscosity, cooling to 40-50° C., adding a modifier and continuing the reaction for 2-3 hours, and then adding a dilute acid to terminate the reaction to obtain a modified wet strength agent; S4: Add modified wet strength agent and reinforcing agent to soybean meal powder, and stir mechanically for 3-5 minutes to obtain soybean protein glue.

2. The method for preparing soybean protein glue for plate material according to claim 1, characterized in that: The preparation steps of the modified epoxy polymer are as follows: adding lignin to a sodium hydroxide aqueous solution, heating to 50-60° C. after the lignin is completely dissolved, adding ethylene glycol diglycidyl ether dropwise, keeping the temperature for reaction for 3-4 hours after the addition is completed, and cooling to obtain the modified epoxy polymer.

3. The method for preparing soybean protein glue for plate material according to claim 1, characterized in that: The concentration of the sodium hydroxide aqueous solution is 1-1.5 wt %.

4. The method for preparing soybean protein glue for plate material according to claim 3, characterized in that: The mass fraction ratio of the sodium hydroxide aqueous solution, lignin and ethylene glycol diglycidyl ether is 10:1::5-8.

5. The method for preparing soybean protein glue for plate material according to claim 1, characterized in that: The reinforcing agent adopts a coupling agent to graft the amide compound onto the surface of the calcium carbonate nanoparticles, so as to enhance the cross-linking property between the modified calcium carbonate nanoparticles and the soybean protein.

6. The method for preparing soybean protein glue for plate material according to claim 1, characterized in that: The specific preparation method of the reinforcing agent is as follows: (1) mixing a calcium chloride solution with a concentration of 0.1 mol / L with hemp fiber in a closed container, reacting at 100° C. for 30-40 minutes, cooling and filtering, removing the filtrate, and then adding a sodium carbonate solution with a concentration of 0.1 mol / L, continuing to react at 100° C. for 30-40 minutes, cooling, filtering, and washing to obtain modified fiber; The volume ratio of calcium chloride solution to sodium carbonate solution is 1:1; (2) N-cyclohexyl-2-benzothiazole sulfonamide and silane coupling agent are dissolved in anhydrous ethanol, refluxed and stirred at 90°C for 3 hours under nitrogen, and then the modified fiber is added and stirred for 12 hours and then cooled. The obtained suspension is filtered, washed and dried to obtain modified calcium carbonate nanoparticles.

7. The method for preparing soybean protein glue for plate material according to claim 1, characterized in that: The mass ratio of the N-cyclohexyl-2-benzothiazole sulfoxide amide, the silane coupling agent and the modified fiber is 1-1.2:1:

40.

8. The method for preparing soybean protein glue for plate material according to claim 1, characterized in that: The diluent acid includes one or more of sulfuric acid, hydrochloric acid, formic acid, oxalic acid, and citric acid.

9. The method for preparing soybean protein glue for plate material according to claim 1, characterized in that: The molar ratio of diethylenetriamine to dibasic acid is 3:4-4.

5.

10. The method for preparing soybean protein glue for plate material according to claim 1, characterized in that: The dibasic acid in step S1 is a mixture of adipic acid and maleic acid, and the molar mass ratio thereof is 1:0.2-0.5.