Graft copolymerization modified high-water-retention formaldehyde-free adhesive as well as preparation method and application thereof

Abstract

The invention discloses a graft copolymerization modified high-water-retention formaldehyde-free adhesive as well as a preparation method and application thereof, and belongs to the technical field of adhesive preparation. The adhesive is prepared from the following components: deionized water, vegetable protein meal powder, cationic polyamide polyamine epichlorohydrin resin and an anionic moisturizing factor, wherein the anionic moisturizing factor is prepared from the following components: deionized water, an initiator, acrylamide, itaconic acid, chitosan, hydrochloric acid, N, N '-methylenebisacrylamide, 1-ethyl-(3-dimethylaminopropyl) carbodiimide hydrochloride and N-hydroxy succinimide. According to the invention, acrylamide, itaconic acid and chitosan are subjected to a graft copolymerization reaction, a moisturizing factor with negative charges is formed in situ in the process, and the moisturizing factor is compounded with polyamide polyamine resin with positive charges for use, so that not only can the water retention capacity of the plant protein adhesive be remarkably improved, but also the mechanical strength characteristic of the plant protein adhesive can be synchronously enhanced.

Description

Technical Field

[0001] The present invention relates to the technical field of adhesive preparation, and particularly relates to a graft copolymerization modified high water-retaining formaldehyde-free adhesive, a preparation method thereof, and an application thereof. Background Art

[0002] Based on the "green building materials" development strategy, the research and development of low-formaldehyde environmental protection plant protein-based adhesives is of great significance for promoting technological innovation in the wood-based panel industry. As a by-product of soybean oil processing, soybean meal has the advantages of good processability, low cost, renewable and rich resources, and is an excellent raw material for preparing formaldehyde-free adhesives. In the plant protein adhesive system, water, as a plasticizer, can be inserted between protein molecules, reducing the intermolecular force, improving the molecular chain mobility, and lowering the glass transition temperature. However, the plant protein adhesives developed by the existing technologies generally have the defect of insufficient water retention, resulting in too high viscosity of the adhesive, decline in mechanical properties, and impaired processing performance, increasing the defective rate and use cost in the production process, and restricting its popularization and application in the wood-based panel field.

[0003] By adding traditional small molecule humectants used in building materials and soil water retention applications, including glycerol, amides, zwitterions, and metal chlorides, the water retention performance of plant protein adhesives can be improved, such as in CN110054785A and CN110128678A. However, these small molecule water retention agents will migrate and fail due to the influence of chemical effects (compatibility) and kinetic effects (diffusion, osmosis), greatly reducing the water-resistant bonding strength and coating performance of the adhesive. For example, in the water-retaining plant protein adhesive by adding sulfobetaine methacrylate and LiCl, due to the existence of too many hydrophilic groups, the wet shear strength of the obtained formulation is significantly reduced; when using inorganic components to construct an organic-inorganic hybrid system for water retention modification of plant protein adhesives, the hard structure formed by the inorganic components in the system reduces the fluidity of the adhesive, which is not conducive to the sizing operation in the production process of wood-based panels, and there is easily a phenomenon of uneven dispersion, resulting in stress concentration in the adhesive layer and easy tool wear and saw jumping problems during the subsequent sawing process. In addition, the cost of the adhesive is significantly increased. Summary of the Invention

[0004] In order to solve the problems existing in the prior art, the present invention provides a graft copolymerization modified high water-retaining formaldehyde-free adhesive, a preparation method thereof, and an application thereof; the present invention adopts a free radical polymerization-dynamic electrostatic gel complexation strategy to carry out a graft copolymerization reaction of acrylamide, itaconic acid, and chitosan, and in this process, a negatively charged water retention factor is formed in situ; the water retention factor is used in combination with a positively charged polyamide polyamine resin, which can not only significantly improve the water retention performance of the plant protein adhesive, but also simultaneously enhance its mechanical strength characteristics.

[0005] To solve the above technical problems, the present invention provides the following technical solutions:

[0006] On the one hand, the present invention provides a graft copolymerization modified high water retention formaldehyde-free adhesive, which is composed of the following components in parts by weight:

[0007] Deionized water: 100 parts

[0008] Plant protein meal powder: 90 parts

[0009] Cationic polyamide polyamine epichlorohydrin resin: 48 parts

[0010] Anionic moisturizing factor: 84 - 108 parts

[0011] The anionic moisturizing factor is prepared from the following components in parts by weight:

[0012] Deionized water: 113 parts

[0013] Initiator: 2 parts

[0014] Acrylamide: 10 - 50 parts

[0015] Itaconic acid: 6 parts

[0016] Chitosan: 1 part

[0017] Hydrochloric acid: 0.6 part

[0018] Crosslinking agent: 0.5 part

[0019] 1-Ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride: 5 parts

[0020] N-Hydroxysuccinimide: 1.5 parts

[0021] Preferably, the anionic moisturizing factor is prepared from the following components in parts by weight:

[0022] Deionized water: 113 parts

[0023] Initiator: 2 parts

[0024] Acrylamide: 30 parts

[0025] Itaconic acid: 6 parts

[0026] Chitosan: 1 part

[0027] Hydrochloric acid: 0.6 part

[0028] Crosslinking agent: 0.5 part

[0029] 1-Ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride: 5 parts

[0030] 1.5 parts of N-hydroxysuccinimide.

[0031] Furthermore, the protein content of the plant protein meal powder is 45%, and the particle size is 100 - 250 mesh; it can include soybean protein meal powder, camellia oleifera meal powder, peanut meal powder, etc. The cationic polyamide polyamine epichlorohydrin resin is a commercially available product with a solid content of 12.5%.

[0032] Preferably, the initiator is ammonium persulfate, potassium persulfate or sodium persulfate; the crosslinking agent is N,N'-methylenebisacrylamide, ethylene glycol diacrylate or triethylene glycol diacrylate; the hydrochloric acid is an aqueous hydrochloric acid solution with a concentration of 37% and is of analytical purity.

[0033] Furthermore, the anionic moisturizing factor is prepared by the following method:

[0034] 1) Weigh deionized water, initiator, acrylamide, itaconic acid, chitosan, hydrochloric acid, and crosslinking agent according to the weights of each raw material.

[0035] 2) Dissolve acrylamide in deionized water to obtain an acrylamide aqueous solution; add chitosan to hydrochloric acid to obtain a chitosan hydrochloride solution.

[0036] 3) Add the initiator to the acrylamide aqueous solution.

[0037] 4) Dissolve itaconic acid in the solution of step 3), raise the reaction temperature to 25 - 30 °C and maintain it for 0.5 h to obtain an acrylamide-itaconic acid reaction solution.

[0038] 5) Add the chitosan hydrochloride solution to the acrylamide-itaconic acid reaction solution to obtain a chitosan-acrylamide-itaconic acid reaction solution.

[0039] 6) Add the crosslinking agent to the chitosan-acrylamide-itaconic acid reaction solution and dissolve it.

[0040] 7) Under the protection of nitrogen, gradually raise the reaction temperature to 55 °C and keep it warm for 2 h.

[0041] 8) Dissolve 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride and N-hydroxysuccinimide in the chitosan-acrylamide-itaconic acid reaction solution of step 7).

[0042] 9) React at room temperature (25 °C) for 6 - 24 h to obtain the anionic moisturizing factor.

[0043] On the other hand, the present invention also provides a preparation method of the graft copolymerization modified high water-retaining formaldehyde-free adhesive, including:

[0044] (1) Prepare the anionic moisturizing factor.

[0045] (2) Weigh deionized water, plant protein meal powder, anionic moisturizing factor, and cationic polyamide polyamine epichlorohydrin resin;

[0046] (3) Under continuous stirring conditions, slowly add the anionic moisturizing factor to deionized water to obtain an anionic moisturizing factor aqueous solution;

[0047] (4) Under continuous stirring conditions, gradually add the cationic polyamide polyamine epichlorohydrin resin to the anionic moisturizing factor aqueous solution in step (3);

[0048] (5) Under continuous stirring conditions, slowly add the solid plant protein meal powder to the mixed aqueous solution containing anions and cations obtained in step (4), and stir until homogeneous. The solid content of the modified plant protein adhesive is controlled within the range of 30 - 40 wt%.

[0049] Preferably, in steps (3) - (5), the stirring speed is 900 - 1200 rpm and the time is 30 min.

[0050] On the other hand, the present invention also provides an application of the above graft copolymerization modified high water - retaining formaldehyde - free adhesive as an artificial board adhesive.

[0051] The hydrophilic functional groups introduced by graft copolymerization modification and the formed three - dimensional network structure are effective ways to improve the water - retaining performance of the adhesive. Graft copolymerization can, while maintaining the basic properties of the main chain, achieve directional regulation of material properties by introducing functional side chains. This method not only provides flexibility in structural design but also can significantly improve the interfacial properties and processing performance of materials. The moisturizing factor formed by graft copolymerization of double bonds with carboxyl, hydroxyl, and amino segments exhibits excellent water - retaining performance. This method can construct a dual system of a dynamic network based on intermolecular forces and a static network formed by covalent bonds, which can effectively bind water molecules, thus solving the problems of migration and failure of traditional water - retaining agents. The rich interfacial interactions formed by this method contribute to the formation of a dense cross - linked network, enhancing the cohesive strength and interfacial adhesion performance of the plant protein adhesive. This precise energy dissipation system helps to improve the water - retaining and bonding performance of the plant protein adhesive.

[0052] Compared with the prior art, the present invention has the following beneficial effects:

[0053] (1) An anionic moisturizing factor, a cationic polyamide polyamine epichlorohydrin resin, and plant protein are innovatively used to construct a free radical polymerization-dynamic electrostatic gel complexation enhancement system. This system utilizes the negatively charged carboxylate groups in plant protein and the positively charged nitrogen heterocycles in the polyamide polyamine resin to construct a dynamic electrostatic gel complexation network, achieving effective anchoring of water molecules. Through the synergistic effect of the two modifiers, the water retention effect of the plant protein adhesive is significantly improved.

[0054] (2) A method for synthesizing a flexible skeleton structure as a moisturizing factor by in-situ polymerization gel method. This moisturizing factor has high reactivity and abundant water retention functional groups. Introducing it into the plant protein adhesive to construct a hard-soft skeleton structure and form a dense crosslinked network, thereby effectively improving the water retention performance of the adhesive.

[0055] The water retention and adhesive bonding performance of the adhesive are enhanced by constructing a multi-bond crosslinked network. The dynamic hydrogen bonds and electrostatic interactions in the system improve the overall tensile performance. At the same time, the formation of the hard-soft framework can effectively disperse and consume concentrated stress, endowing the plant protein-based adhesive with excellent mechanical properties.

[0056] (3) It has been experimentally verified that the three-layer plywood prepared by the process of the present invention has significant cost advantages and water retention effects, effectively solving the technical problem of easy dehydration of plant protein. The wet bonding strength of the modified plant protein adhesive exceeds 0.7 MPa after 24 hours, meeting the requirements of the national Class II plywood standard, and the performance has been significantly improved.

[0057] (4) As an environmentally friendly adhesive for plywood, the product of the present invention does not contain organic volatiles such as formaldehyde, effectively solving the problem of indoor air pollution caused by traditional plywood. Description of the Drawings

[0058] Figure 1 It is a macroscopic morphology diagram of the adhesive layer after 24-hour storage after curing of the adhesive (modified low-temperature soybean meal water retention adhesive) prepared in Example 1 of the present invention and the adhesive (unmodified low-temperature soybean meal water retention adhesive) prepared in Comparative Example 1. Detailed Embodiments

[0059] To make the technical problems, technical solutions, and advantages to be solved by the present invention clearer, the following will be described in detail with reference to the drawings and specific embodiments.

[0060] In the present invention, materials and reagents used without special instructions can be obtained commercially. Among them, the protein content of the following plant protein meal powder is 45% (mass percentage). The plant protein meal powder includes soybean protein meal powder, camellia oleifera meal powder, peanut meal powder, etc. The preferred particle size range is 100 - 250 mesh, and it is not more than 250 mesh. The protein content of soybean protein meal powder (soybean meal) is 45%, and the particle size is 100 - 250 mesh. The protein content of camellia oleifera meal powder is 40%, and the particle size is 100 - 200 mesh. The protein content of peanut meal powder is 45%, and the particle size is 100 - 250 mesh. The cationic polyamide polyamine epichlorohydrin resin is purchased from Shandong Tiancheng Chemical Co., Ltd. as a wet strength agent. Hydrochloric acid is an aqueous solution of hydrochloric acid with a concentration of 37% and is of analytical grade.

[0061] The present invention provides a graft copolymerization modified high water retention formaldehyde-free adhesive and its preparation method. The specific embodiments are as follows.

[0062] Example 1

[0063] A preparation method of a graft copolymerization modified high water retention formaldehyde-free adhesive, the amounts of each substance are shown in Table 1; it includes:

[0064] (1) Prepare an anionic moisturizing factor;

[0065] (2) Weigh deionized water, soybean protein meal powder, anionic moisturizing factor, and cationic polyamide polyamine epichlorohydrin resin according to the weight parts of each raw material;

[0066] (3) Under continuous stirring, slowly add the anionic moisturizing factor to deionized water to obtain an anionic moisturizing factor aqueous solution;

[0067] (4) Under continuous stirring, gradually add the cationic polyamide polyamine epichlorohydrin resin to the anionic moisturizing factor aqueous solution obtained in step (3);

[0068] (5) Under continuous stirring, slowly add the solid soybean protein meal powder to the mixed aqueous solution containing anions and cations obtained in step (4), and stir until homogeneous.

[0069] In the above preparation process of the modified protein adhesive, mechanical stirring is used for mixing, wherein the stirring speed is controlled at 900 rpm, the reaction temperature is 25 °C, and the stirring duration is 30 min.

[0070] The above preparation method of the anionic moisturizing factor, the contents of each component are shown in Table 2, and it includes:

[0071] 1) Weigh the raw materials according to the mass parts;

[0072] 2) Dissolve acrylamide in deionized water to obtain an acrylamide aqueous solution; dissolve chitosan in hydrochloric acid to obtain a chitosan hydrochloride solution;

[0073] 3) Add ammonium persulfate, an initiator, to the acrylamide aqueous solution;

[0074] 4) Dissolve itaconic acid in the acrylamide aqueous solution, heat the resulting solution to 30 °C, and keep it warm for 0.5 h;

[0075] 5) After the solution system is stable, add the chitosan acidic solution to the acrylamide-itaconic acid mixed solution;

[0076] 6) Add N,N'-methylenebisacrylamide to the resulting mixed solution and dissolve it completely;

[0077] 7) Under the condition of nitrogen protection, gradually raise the temperature of the reaction system from 30 °C to 55 °C and keep it warm for reaction for 2 h;

[0078] 8) Add 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride and N-hydroxysuccinimide in sequence and dissolve them fully;

[0079] 9) React at room temperature (25 °C) for 12 h to obtain the target product CA1I.

[0080] Example 2

[0081] A preparation method of a graft copolymerization modified high water-retaining formaldehyde-free adhesive, the dosage of each substance is shown in Table 1; it includes:

[0082] (1) Prepare an anionic moisturizing factor;

[0083] (2) Weigh deionized water, soybean protein meal powder, anionic moisturizing factor and cationic polyamide polyamine epichlorohydrin resin according to the weight parts of each raw material;

[0084] (3) Under the condition of continuous stirring, slowly add the anionic moisturizing factor to deionized water to prepare an anionic moisturizing factor aqueous solution;

[0085] (4) Under the condition of continuous stirring, gradually add the cationic polyamide polyamine epichlorohydrin resin to the anionic moisturizing factor aqueous solution obtained in step (3);

[0086] (5) Under the condition of continuous stirring, slowly add the solid soybean protein meal powder to the aqueous solution containing anions and cations obtained in step (4) and stir until homogeneous.

[0087] In the above preparation process of the modified protein adhesive, mechanical stirring is used for mixing, wherein the stirring speed is controlled at 1000 rpm, the reaction temperature is 25 °C, and the stirring duration is 30 min.

[0088] The preparation method of the above-mentioned anionic moisturizing factor, the content of each component is shown in Table 2, including:

[0089] 1) Weigh the raw materials according to parts by mass;

[0090] 2) Dissolve acrylamide in deionized water to obtain an acrylamide aqueous solution; dissolve chitosan in hydrochloric acid aqueous solution to obtain a chitosan hydrochloride solution;

[0091] 3) Add ammonium persulfate as an initiator to the acrylamide aqueous solution;

[0092] 4) Dissolve itaconic acid in the acrylamide aqueous solution, heat the obtained solution to 30 °C, and keep it warm for 0.5 h;

[0093] 5) After the solution system is stable, add the chitosan acidic solution to the acrylamide-itaconic acid mixed solution;

[0094] 6) Add N,N'-methylenebisacrylamide to the obtained mixed solution to make it completely dissolve;

[0095] 7) Under the condition of nitrogen protection, gradually raise the temperature of the reaction system from 30 °C to 55 °C, and keep it warm for 2 h;

[0096] 8) Add 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride and N-hydroxysuccinimide in sequence to make them fully dissolve;

[0097] 9) React at room temperature (25 °C) for 12 h to obtain the target product CA2I.

[0098] Example 3

[0099] A preparation method of a graft copolymerization modified high water-retaining formaldehyde-free adhesive, the dosage of each substance is shown in Table 1; including:

[0100] (1) Prepare an anionic moisturizing factor;

[0101] (2) Weigh deionized water, soybean protein meal powder, anionic moisturizing factor and cationic polyamide polyamine epichlorohydrin resin according to the weight parts of each raw material;

[0102] (3) Under the condition of continuous stirring, slowly add the anionic moisturizing factor to deionized water to prepare an anionic moisturizing factor aqueous solution;

[0103] (4) Under the condition of continuous stirring, gradually add the cationic polyamide polyamine epichlorohydrin resin to the anionic moisturizing factor aqueous solution obtained in step (3);

[0104] (5) Under continuous stirring conditions, slowly add the solid soybean protein meal powder to the mixed aqueous solution containing anions and cations obtained in step (4), and stir until homogeneous.

[0105] In the above preparation process of the modified protein adhesive, mechanical stirring is used for mixing, where the stirring speed is controlled at 1000 rpm, the reaction temperature is 25 °C, and the stirring duration is 40 min.

[0106] The preparation method of the above-mentioned anionic moisturizing factor, the content of each component is shown in Table 2, including:

[0107] 1) Weigh the raw materials by mass parts;

[0108] 2) Dissolve acrylamide in deionized water to obtain an acrylamide aqueous solution; dissolve chitosan in hydrochloric acid aqueous solution to obtain a chitosan hydrochloride solution;

[0109] 3) Add the initiator ammonium persulfate to the acrylamide aqueous solution;

[0110] 4) Dissolve itaconic acid in the acrylamide aqueous solution, heat the obtained solution to 25 °C, and keep it warm for 1 h;

[0111] 5) After the solution system is stable, add the chitosan acidic solution to the acrylamide-itaconic acid mixed solution;

[0112] 6) Add N,N′-methylenebisacrylamide to the obtained mixed solution and dissolve it completely;

[0113] 7) Under the condition of nitrogen protection, gradually raise the temperature of the reaction system from 25 °C to 55 °C, and keep it warm for 2 h;

[0114] 8) Add 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride and N-hydroxysuccinimide in sequence and dissolve them fully;

[0115] 9) React at room temperature (25 °C) for 12 h to obtain the target product CA3I.

[0116] Example 4

[0117] A preparation method of a graft copolymerization modified high water-retaining formaldehyde-free adhesive, the dosage of each substance is shown in Table 1; including:

[0118] (1) Prepare an anionic moisturizing factor;

[0119] (2) Weigh deionized water, soybean protein meal powder, anionic moisturizing factor and cationic polyamide polyamine epichlorohydrin resin according to the weight parts of each raw material;

[0120] (3) Under the condition of continuous stirring, slowly add the anionic moisturizing factor into deionized water to obtain an aqueous solution of the anionic moisturizing factor;

[0121] (4) Under the condition of continuous stirring, gradually add the cationic polyamide polyamine epichlorohydrin resin into the aqueous solution of the anionic moisturizing factor obtained in step (3);

[0122] (5) Under the condition of continuous stirring, slowly add the solid soybean protein meal powder into the aqueous solution containing mixed anions and cations obtained in step (4), and stir until homogeneous.

[0123] In the preparation process of the above modified protein adhesive, mechanical stirring is used for mixing, wherein the stirring speed is controlled at 1100 rpm, the reaction temperature is 25 °C, and the stirring duration is 40 min.

[0124] The preparation method of the above anionic moisturizing factor, the content of each component is shown in Table 2, including:

[0125] 1) Weigh the raw materials according to the mass parts;

[0126] 2) Dissolve acrylamide in deionized water to obtain an aqueous solution of acrylamide; dissolve chitosan in hydrochloric acid aqueous solution to obtain a hydrochloric acid solution of chitosan;

[0127] 3) Add the initiator ammonium persulfate to the aqueous solution of acrylamide;

[0128] 4) Dissolve itaconic acid in the aqueous solution of acrylamide, heat the obtained solution to 25 °C, and keep it warm for 1 h;

[0129] 5) After the solution system is stable, add the acidic solution of chitosan into the acrylamide-itaconic acid mixed solution;

[0130] 6) Add N,N′-methylenebisacrylamide to the obtained mixed solution to make it completely dissolve;

[0131] 7) Under the condition of nitrogen protection, gradually raise the temperature of the reaction system from 25 °C to 55 °C, and keep it warm for 2 h;

[0132] 8) Add 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride and N-hydroxysuccinimide in sequence to make them fully dissolve;

[0133] 9) React at room temperature (25 °C) for 12 h to obtain the target product CA4I.

[0134] Example 5

[0135] A preparation method of a graft copolymerization modified high water retention formaldehyde-free adhesive, the dosage of each substance is shown in Table 1; including:

[0136] (1) Prepare an anionic moisturizing factor;

[0137] (2) Weigh deionized water, soybean protein meal powder, anionic moisturizing factor, and cationic polyamide polyamine epichlorohydrin resin according to the weight parts of each raw material;

[0138] (3) Under continuous stirring, slowly add the anionic moisturizing factor to deionized water to obtain an anionic moisturizing factor aqueous solution;

[0139] (4) Under continuous stirring, gradually add the cationic polyamide polyamine epichlorohydrin resin to the anionic moisturizing factor aqueous solution obtained in step (3);

[0140] (5) Under continuous stirring, slowly add the solid soybean protein meal powder to the mixed aqueous solution containing anions and cations obtained in step (4), and stir until homogeneous.

[0141] In the above preparation process of the modified protein adhesive, mechanical stirring is used for mixing, where the stirring speed is controlled at 1200 rpm, the reaction temperature is 25 °C, and the stirring duration is 30 min.

[0142] For the above preparation method of the anionic moisturizing factor, the content of each component is shown in Table 2, including:

[0143] 1) Weigh the raw materials according to the mass parts;

[0144] 2) Dissolve acrylamide in deionized water to obtain an acrylamide aqueous solution; dissolve chitosan in hydrochloric acid aqueous solution to obtain a chitosan hydrochloride solution;

[0145] 3) Add ammonium persulfate as an initiator to the acrylamide aqueous solution;

[0146] 4) Dissolve itaconic acid in the acrylamide aqueous solution, heat the obtained solution to 25 °C, and keep it warm for 1.5 h;

[0147] 5) After the solution system is stable, add the chitosan acidic solution to the acrylamide-itaconic acid mixed solution;

[0148] 6) Add N,N'-methylenebisacrylamide to the obtained mixed solution and dissolve it completely;

[0149] 7) Under nitrogen protection, gradually raise the temperature of the reaction system from 25 °C to 55 °C and keep it warm for 2 h;

[0150] 8) Add 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride and N-hydroxysuccinimide in sequence and dissolve them fully;

[0151] 9) React at room temperature (25 °C) for 12 h to obtain the target product CA5I.

[0152] Example 6

[0153] In this example, the plant protein meal powder was selected as camellia seed meal powder, and the other conditions were the same as in Example 3.

[0154] Example 7

[0155] In this example, the plant protein meal powder was selected as peanut meal powder, and the other conditions were the same as in Example 3.

[0156] Table 1

[0157]

[0158] Table 2

[0159]

[0160] To further illustrate the beneficial effects of the present invention, due to limited space, only Example 3 was taken as an example to construct the following comparative examples.

[0161] Comparative Example 1

[0162] A plant protein adhesive was composed of 35 parts of deionized water and 15 parts of soybean protein meal powder;

[0163] The specific preparation method of the above plant protein adhesive was as follows:

[0164] (1) Mix the soybean protein meal powder with deionized water, and use a stirring rod to perform preliminary stirring until a homogeneous system is formed;

[0165] (2) Perform mechanical stirring on the above homogeneous system, set the stirring speed to 1000 rpm, and continuously stir for 10 min.

[0166] Comparative Example 2

[0167] During the preparation process of the moisturizing factor in this comparative example, chitosan, hydrochloric acid, 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride, and N-hydroxysuccinimide were replaced with an equal mass of deionized water, and the other conditions were the same as in Example 3.

[0168] Comparative Example 3

[0169] During the preparation process of the moisturizing factor in this comparative example, itaconic acid, chitosan, hydrochloric acid, 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride, and N-hydroxysuccinimide were replaced with an equal mass of deionized water, and the other conditions were the same as in Example 3.

[0170] Comparative Example 4

[0171] During the preparation process of the moisturizing factor in this comparative example, itaconic acid was replaced with an equal mass of deionized water, and the other conditions were the same as in Example 3.

[0172] Comparative Example 5

[0173] In the preparation process of the moisturizing factor in this comparative example, itaconic acid was replaced with an equal mass of acrylic acid, and the other conditions were the same as those in Example 3.

[0174] Comparative Example 6

[0175] In this comparative example, the moisturizing factor was replaced with hyperbranched polyester, and the above hyperbranched polyester was prepared by the following method: Trimethylolpropane (TMP) and 2,2-dimethylolpropionic acid (DMPA) were added to a four-necked flask in a molar ratio of 1:21, and the temperature was gradually raised to 140 °C under the protection of nitrogen. When the temperature was stable, an appropriate amount of p-TSA catalyst was added. After reacting at a constant temperature for three hours, the reaction was continued under reduced pressure for 3 h, the reaction was stopped and cooled to 50 °C, and acetone was added for dissolution, and the hyperbranched polyester was obtained by precipitation with hexane.

[0176] The other conditions were the same as those in Example 3.

[0177] Comparative Example 7

[0178] In this comparative example, the dosage of the anionic moisturizing factor was 120 parts, and the other conditions were the same as those in Example 3.

[0179] Comparative Example 8

[0180] In this comparative example, the dosage of the anionic moisturizing factor was 70 parts, and the other conditions were the same as those in Example 3.

[0181] Comparative Example 9

[0182] In this comparative example, the cationic polyamide polyamine epichlorohydrin resin was replaced with an equal mass of polyamide resin, and the other conditions were the same as those in Example 3.

[0183] Comparative Example 10

[0184] In this comparative example, the cationic polyamide polyamine epichlorohydrin resin was replaced with an equal mass of cationic polyacrylamide resin, and the other conditions were the same as those in Example 3.

[0185] The properties of the adhesives prepared in the above examples and comparative examples were tested, and the specific test methods were as follows:

[0186] Put 10 g of the adhesive sample into a petri dish, expose it to outdoor environmental conditions, and record the mass residue rate after 24 h. The results are shown in Table 1 and Figure 1 . The adhesive was applied to a veneer with a density of 180 g / m² at a size of 200 mm × 200 mm, and the warping deformation of the veneer was observed and evaluated. The results are shown in Table 3-4.

[0187] The adhesives prepared in the examples and comparative examples of the present invention were used to prepare three-layer plywood according to the following method:

[0188] Three - layer plywood samples were made using poplar veneers with a thickness of 1.6 ± 0.1 mm and a water content of 8% to 15%. The veneers were assembled with grain directions perpendicular to each other in adjacent layers. An adhesive was applied to the surface of the core layer with a coating density of 180 - 240 g / m². The assembled plywood was hot - pressed at 1 MPa and 120 °C for 350 seconds. After hot - pressing, the plywood was placed in the open air at 25 °C and 60% RH for 24 hours and then cut into standard samples of 25 mm × 100 mm × 4.5 mm.

[0189] The mechanical properties of the adhesives of the examples and comparative examples of the present invention were tested according to the following method:

[0190] According to the standard of GB / T 9846 - 2015 "General Plywood", the bonding strength of the prepared three - layer plywood was tested. A universal testing machine was used to determine the dry shear strength of the samples, and the cross - beam moving speed was set at 10 mm / min; before the wet shear strength test, the samples were soaked in water at 63 °C for 3 h, and then cooled at room temperature (23 ± 2 °C) for 10 min before testing. All tests were repeated 6 times, and the strength values were calculated as the arithmetic mean of the valid test results. The final data was expressed in the form of mean ± standard error. The specific test results are shown in Table 3 - 4.

[0191] Table 3

[0192]

[0193] As Figure 1 is the macroscopic morphology diagram of the adhesive layer after curing and 24 - hour storage of the adhesive prepared in Example 1 of the present invention and the adhesive prepared in Comparative Example 1; from Figure 1 it can be seen that after 24 h of storage, the cured adhesive prepared in Comparative Example 1 has cracked, while the water retention rate of the adhesive prepared in Example 5 of the present invention reaches 52%.

[0194] As can be seen from Table 1, the viscosity of the plant - protein adhesive developed in the present invention increases with the increase in the dosage of the anionic moisturizing factor; when the dosage of the anionic moisturizing factor is 120 parts (Comparative Example 7), although the other properties are good, due to its high viscosity, it is not easy to disperse the adhesive evenly during the specific use process, and the construction is difficult. The 24 - hour water retention performance of the adhesive prepared in the present invention also increases with the increase in the dosage of the anionic moisturizing factor, but there is also a problem of difficult construction when the dosage is large. The warping angle of the veneer decreases gradually and then tends to be stable with the increase in the dosage of the anionic moisturizing factor; and the adhesive prepared in the present invention has high dry and wet shear strengths.

[0195] Table 4

[0196]

[0197] As can be seen from Table 4, Comparative Example 1 contains only two components, namely plant protein meal powder and deionized water, and its water retention performance is significantly insufficient. When the plant protein adhesive of Comparative Example 1 is coated on the surface of the veneer, water is easily permeated into the interior of the wood substrate quickly, resulting in a serious reduction in the water resistance of the finally prepared plywood, and further leading to the failure of the bonding strength to meet the usage requirements. In the preparation process of the anionic moisturizing factors in Comparative Examples 2-3, the relevant reactions of chitosan or itaconic acid are omitted, and the warping angle of the veneer of the prepared adhesive is increased by 1-2 times, and both the dry-wet shear strength and the wet adhesive performance after 24 hours are greatly reduced; in Comparative Examples 4-5, itaconic acid is omitted or replaced by acrylic acid, and the performance of the obtained adhesive is also poor; in Comparative Examples 6-10, there are also problems with some poor performances. If the cationic PAE used in the present invention is replaced by a non-ionic polyamide polyamine resin, the shear strength of the adhesive will be reduced and the water retention performance after 24 hours will decrease. If it is replaced by a cationic polyacrylamide resin, the viscosity will be excessively increased, the dry-wet shear strength will be reduced, and the moisturizing performance will be slightly improved.

[0198] The present invention uses acrylamide, itaconic acid and chitosan as graft copolymerization monomers, and provides a moisturizing factor for plant protein adhesives and a preparation method thereof. The high water retention formaldehyde-free adhesive modified by this moisturizing factor is applied to wood-based panels. This enhanced water retention ability stems from the fact that the anionic moisturizing factor, cationic polyamide polyamine epichlorohydrin resin and plant protein construct a free radical polymerization-dynamic electrostatic gel complex enhancement system. The anionic moisturizing factor forms a dynamic electrostatic gel complex structure with the carboxylate anions in the plant protein and the positively charged nitrogen heterocycles in the polyamide polyamine resin, effectively anchoring the water molecules in the adhesive and effectively inhibiting the penetration of water molecules into the veneer substrate. The formed dense cross-linked network significantly improves the water retention performance of the adhesive.

[0199] In summary, the present invention enhances the water retention and bonding performance of plant protein adhesives by constructing a variety of chemical bond cross-linked networks. The dynamic hydrogen bonds and electrostatic interactions in the system can improve the overall tensile performance. The formed hard-soft framework can disperse and consume concentrated stress, improve the performance failure problem during the storage of plant protein adhesives, and endow the plant protein-based adhesives with excellent mechanical properties. It provides a new technical solution for the application of plant protein adhesives in the field of wood-based panels.

[0200] The above is the preferred embodiment of the present invention. For those of ordinary skill in the art, without departing from the principle described in the present invention, making several improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A graft copolymer modified high water retention formaldehyde-free adhesive, characterized in that: It is composed of the following components in parts by weight: 100 parts of deionized water; 90 portions of vegetable protein meal powder; 48 parts of cationic polyamide polyamine epichlorohydrin resin; Anion moisturizing factor 84-108 parts; The anionic moisturizing factor is prepared from the following components in parts by weight: Deionized water 113 parts; 2 parts of initiator; 10-50 parts of acrylamide; Itaconic acid 6 parts; Chitosan 1 part; 0.6 parts of hydrochloric acid; 0.5 part of cross-linking agent; 5 parts of 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride; 1.5 parts of N-hydroxysuccinimide.

2. The graft copolymer modified high water retention formaldehyde-free adhesive according to claim 1, characterized in that: The anionic moisturizing factor is prepared from the following components in parts by weight: Deionized water 113 parts; 2 parts of initiator; 30 parts of acrylamide; Itaconic acid 6 parts; Chitosan 1 part; 0.6 parts of hydrochloric acid; 0.5 part of cross-linking agent; 5 parts of 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride; 1.5 parts of N-hydroxysuccinimide.

3. The graft copolymer modified high water retention formaldehyde-free adhesive according to claim 1 or 2, characterized in that: The vegetable protein meal powder has a protein content of 45% and a particle size of 100-250 meshes.

4. The graft copolymer modified high water retention formaldehyde-free adhesive according to claim 3, characterized in that: The solid content of the cationic polyamide polyamine epichlorohydrin resin is 12.5%.

5. The graft copolymer modified high water retention formaldehyde-free adhesive according to claim 4, characterized in that: The initiator is ammonium persulfate, potassium persulfate or sodium persulfate; the crosslinking agent is N,N′-methylenebisacrylamide, ethylene glycol diacrylate or triethylene glycol diacrylate; and the hydrochloric acid is a hydrochloric acid aqueous solution with a concentration of 37%.

6. The graft copolymer modified high water retention formaldehyde-free adhesive according to claim 5, characterized in that: The anionic moisturizing factor is prepared by the following method: 1) Weigh deionized water, initiator, acrylamide, itaconic acid, chitosan, hydrochloric acid and cross-linking agent according to the weight of each raw material; 2) dissolving acrylamide in deionized water to obtain an acrylamide aqueous solution; adding chitosan to hydrochloric acid to obtain a chitosan hydrochloric acid solution; 3) Adding an initiator to the aqueous solution of acrylamide; 4) dissolving itaconic acid in the solution of step 3), heating the reaction system to 25-30° C. and maintaining the temperature for 0.5-1.5 h to obtain an acrylamide-itaconic acid reaction solution; 5) adding the chitosan hydrochloric acid solution to the acrylamide-itaconic acid reaction solution to obtain a chitosan-acrylamide-itaconic acid reaction solution; 6) adding a cross-linking agent to the chitosan-acrylamide-itaconic acid reaction solution and dissolving the cross-linking agent; 7) Under nitrogen protection, gradually increase the reaction temperature to 55°C and keep it for 2 hours; 8) dissolving 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride and N-hydroxysuccinimide in the chitosan-acrylamide-itaconic acid reaction solution of step 7); 9) After the above reaction is completed, the anionic moisturizing factor is obtained after reacting at room temperature for 6-24 hours.

7. The method for preparing the graft copolymerization modified high water-retention formaldehyde-free adhesive according to any one of claims 1 to 6, characterized in that: include: (1) preparing anionic moisturizing factor; (2) Weigh deionized water, vegetable protein meal powder, anionic moisturizing factor and cationic polyamide polyamine epichlorohydrin resin; (3) Under continuous stirring, the anionic moisturizing factor is slowly added into deionized water to prepare an anionic moisturizing factor aqueous solution; (4) under continuous stirring, gradually adding the cationic polyamide polyamine epichlorohydrin resin into the anionic moisturizing factor aqueous solution of step (3); (5) Under continuous stirring, slowly add the solid vegetable protein meal powder to the anion- and cation-containing mixed aqueous solution obtained in step (4), and stir until the mixture becomes homogeneous.

8. The preparation method according to claim 7, characterized in that: In the steps (3) to (5), the stirring speed is 900-1200 rpm and the stirring time is 30-40 min.

9. Use of the graft copolymer modified high water retention formaldehyde-free adhesive according to any one of claims 1 to 6 as an adhesive for artificial boards.

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