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

Abstract

The application discloses a graft copolymerization modified high-water-retention formaldehyde-free adhesive and a preparation method and application thereof, and belongs to the technical field of adhesive preparation. The adhesive is composed of the following components: deionized water, plant protein meal powder, cationic polyamide polyamine epichlorohydrin resin and anionic moisturizing factor. The anionic moisturizing factor is prepared from the following components: deionized water, an initiator, acrylamide, itaconic acid, chitosan, hydrochloric acid, N,N'-methylene bisacrylamide, 1-ethyl-(3-dimethylaminopropyl) carbonyldiimidazole hydrochloride and N-hydroxy succinimide. In the graft copolymerization reaction of acrylamide, itaconic acid and chitosan, the negatively charged moisturizing factor is formed in situ, and is used in combination with the positively charged polyamide polyamine resin. The water-retention performance of the plant protein adhesive is significantly improved, and the mechanical strength characteristics are simultaneously enhanced.

Description

Technical Field

[0001] This invention relates to the field of adhesive preparation technology, and in particular to a graft copolymer modified high water-retaining formaldehyde-free adhesive, its preparation method, and its application. Background Technology

[0002] Based on the "green building materials" development strategy, the research and development of low-formaldehyde, environmentally friendly plant protein-based adhesives is of great significance for promoting technological innovation in the engineered wood products industry. Soybean meal, as a byproduct of soybean oil processing, has advantages such as good processability, low cost, renewability, and abundant resources, making it a preferred raw material for preparing formaldehyde-free adhesives. In plant protein adhesive systems, water acts as a plasticizer, inserting into protein molecules, reducing intermolecular forces, improving molecular chain mobility, and lowering the glass transition temperature. However, existing plant protein adhesives generally suffer from insufficient water retention, leading to excessively high adhesive viscosity, decreased mechanical properties, and impaired processing performance. This increases the defect rate and usage costs during production, hindering their widespread application in the engineered wood products sector.

[0003] The water retention properties of plant protein adhesives can be improved by adding traditional small-molecule moisturizing agents used in building materials and soil water retention applications, including glycerol, amides, zwitterions, and metal chlorides, as shown in CN110054785A and CN110128678A. However, these small-molecule water-retaining agents are susceptible to migration and failure due to chemical effects (compatibility) and kinetic effects (diffusion, penetration), significantly reducing the adhesive's water-resistant bonding strength and coating performance. For example, water-retaining plant protein adhesives with added sulfobetaine methacrylate and LiCl exhibit significantly reduced wet shear strength due to the excessive presence of hydrophilic groups. When modifying plant protein adhesives with water retention using inorganic components to construct organic-inorganic hybrid systems, the rigid structures formed by the inorganic components reduce the adhesive's fluidity, hindering application during the production of engineered wood products and leading to uneven dispersion, stress concentration in the adhesive layer, and subsequent tool wear and saw breakage during sawing. Furthermore, this significantly increases the cost of the adhesive. Summary of the Invention

[0004] To address the problems existing in the prior art, this invention provides a graft copolymerized high water-retaining formaldehyde-free adhesive, its preparation method, and its application. This invention employs a free radical polymerization-dynamic electrostatic gel complexation strategy to graft copolymerize acrylamide, itaconic acid, and chitosan, during which a negatively charged moisturizing factor is formed in situ. This moisturizing factor, when combined with a positively charged polyamide polyamine resin, not only significantly improves the water-retaining properties of the plant protein adhesive but also simultaneously enhances its mechanical strength properties.

[0005] To solve the above-mentioned technical problems, the present invention provides the following technical solution:

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

[0007] 100 parts deionized water;

[0008] 90 parts of plant protein meal powder;

[0009] 48 parts of cationic polyamide polyamine epichlorohydrin resin;

[0010] Anionic moisturizing factor 84-108 parts;

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

[0012] 113 portions of deionized water;

[0013] Two parts of initiator;

[0014] Acrylamide 10-50 parts;

[0015] Itaconic acid 6 parts;

[0016] 1 part chitosan;

[0017] 0.6 parts hydrochloric acid;

[0018] Crosslinking agent 0.5 parts;

[0019] 5 parts of 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride;

[0020] 1.5 parts of N-hydroxysuccinimide.

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

[0022] 113 portions of deionized water;

[0023] Two parts of initiator;

[0024] 30 parts acrylamide;

[0025] Itaconic acid 6 parts;

[0026] 1 part chitosan;

[0027] 0.6 parts hydrochloric acid;

[0028] Crosslinking agent 0.5 parts;

[0029] 5 parts of 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride;

[0030] 1.5 parts of N-hydroxysuccinimide.

[0031] Furthermore, the plant protein meal powder has a protein content of 45% and a particle size of 100-250 mesh; it can be soybean protein meal powder, camellia oil meal powder, peanut meal powder, etc., and 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; and the hydrochloric acid is an aqueous solution of hydrochloric acid with a concentration of 37% and analytical grade.

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

[0034] 1) Weigh out the following raw materials according to their weight: deionized water, initiator, acrylamide, itaconic acid, chitosan, hydrochloric acid, and crosslinking agent.

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

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

[0037] 4) Dissolve itaconic acid in the solution from step 3), heat the reaction system to 25-30℃ and maintain it for 0.5h to obtain acrylamide-itaconic acid reaction solution;

[0038] 5) Add the chitosan hydrochloric acid solution to the acrylamide-itaconic acid reaction solution to obtain the chitosan-acrylamide-itaconic acid reaction solution;

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

[0040] 7) Under nitrogen protection, gradually increase the reaction temperature to 55℃ and maintain the temperature for 2 hours;

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

[0042] 9) Anionic moisturizing factor was obtained after reacting at room temperature (25℃) for 6-24 hours.

[0043] On the other hand, the present invention also provides a method for preparing the above-mentioned graft copolymer modified high water-retaining formaldehyde-free adhesive, comprising:

[0044] (1) Preparation of anionic moisturizing factors;

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

[0046] (3) Under continuous stirring, the anionic moisturizing factor was slowly added to deionized water to prepare an aqueous solution of the anionic moisturizing factor.

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

[0048] (5) Under continuous stirring, the solid plant protein meal powder is slowly added to the mixed aqueous solution containing anions and cations obtained in step (4) and stirred 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] Furthermore, the present invention also provides an application of the above-mentioned graft copolymer modified high water-retaining formaldehyde-free adhesive as an adhesive for engineered wood products.

[0051] Graft copolymerization introduces hydrophilic functional groups and forms a three-dimensional network structure, which is an effective way to improve the water retention performance of adhesives. Graft copolymerization can achieve directional regulation of material properties by introducing functional side chains while maintaining the basic properties of the main chain. This method not only provides flexibility in structural design but also significantly improves the interfacial properties and processing performance of materials. Moisturizing factors formed by graft copolymerization of double bonds with carboxyl, hydroxyl, and amino segments exhibit excellent water retention performance. This method can construct a dual system of dynamic networks based on intermolecular forces and static networks formed by covalent bonds, enabling effective binding of water molecules and thus solving the migration and failure problems 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 plant protein adhesives. This precise energy dissipation system helps improve the water retention and bonding performance of plant protein adhesives.

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

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

[0054] (2) A method of synthesizing a flexible skeleton structure as a moisturizing factor by in-situ polymerization gel method. The moisturizing factor has high reactivity and rich water-retaining functional groups. It is introduced into plant protein adhesive to construct a hard-soft skeleton structure and form a dense cross-linked network, thereby effectively improving the water retention performance of the adhesive.

[0055] The water retention and bonding properties of the adhesive are enhanced by constructing a multi-layered chemical cross-linking network. The dynamic hydrogen bonding and electrostatic interactions in the system improve the overall tensile properties, while the formation of the rigid-soft framework effectively disperses and dissipates concentrated stress, giving this plant protein-based adhesive excellent mechanical properties.

[0056] (3) Experimental verification shows that the three-layer plywood prepared using the process of this invention has significant cost advantages and water retention effect, effectively solving the technical problem of easy dehydration of plant protein. The modified plant protein adhesive has a wet bonding strength of over 0.7 MPa after 24 hours, which meets the requirements of the national Class II plywood standard, and the performance is significantly improved.

[0057] (4) As an environmentally friendly adhesive for plywood, the product of this invention does not contain formaldehyde or other volatile organic compounds, effectively solving the problem of indoor air pollution caused by traditional plywood. Attached Figure Description

[0058] Figure 1 Macroscopic morphology images of the adhesive layers after curing and storage for 24 hours for the adhesive (modified low-temperature soybean meal water-retaining adhesive) prepared in Example 1 of the present invention and the adhesive (unmodified low-temperature soybean meal water-retaining adhesive) prepared in Comparative Example 1. Detailed Implementation

[0059] To make the technical problems, technical solutions and advantages of the present invention clearer, a detailed description will be given below in conjunction with the accompanying drawings and specific embodiments.

[0060] Unless otherwise specified, all materials and reagents used in this invention are commercially available. Specifically, the plant protein meal powders used below have a protein content of 45% (mass percentage). These plant protein meal powders include soybean protein meal powder, camellia oil meal powder, peanut meal powder, etc., with a preferred particle size range of 100-250 mesh, and not exceeding 250 mesh. Soybean protein meal powder has a protein content of 45% and a particle size of 100-250 mesh; camellia oil meal powder has a protein content of 40% and a particle size of 100-200 mesh; peanut meal powder has a protein content of 45% and a particle size of 100-250 mesh. The cationic polyamide polyamine epichlorohydrin resin was purchased from Shandong Tiancheng Chemical Co., Ltd. as a wet strength agent. The hydrochloric acid was an aqueous solution with a concentration of 37%, analytical grade.

[0061] This invention provides a graft copolymer modified high water-retaining formaldehyde-free adhesive and its preparation method, with specific embodiments as follows.

[0062] Example 1

[0063] A method for preparing a graft copolymer-modified high water-retaining formaldehyde-free adhesive, the amounts of each substance are shown in Table 1; including:

[0064] (1) Preparation of anionic moisturizing factors;

[0065] (2) Weigh out the 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, the anionic moisturizing factor is slowly added to deionized water to prepare an aqueous solution of anionic moisturizing factor;

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

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

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

[0070] The preparation method of the above-mentioned anionic moisturizing factor, and the content of each component are shown in Table 2, including:

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

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

[0073] 3) Add ammonium persulfate as 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 at that temperature for 0.5 h;

[0075] 5) After the solution system has stabilized, 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 nitrogen protection, gradually increase the temperature of the reaction system from 30℃ to 55℃ and maintain the temperature for 2 hours.

[0078] 8) Add 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride and N-hydroxysuccinimide sequentially, allowing them to dissolve completely;

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

[0080] Example 2

[0081] A method for preparing a graft copolymer-modified high water-retaining formaldehyde-free adhesive, the amounts of each substance are shown in Table 1; including:

[0082] (1) Preparation of anionic moisturizing factors;

[0083] (2) Weigh out the 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 continuous stirring, the anionic moisturizing factor is slowly added to deionized water to prepare an aqueous solution of anionic moisturizing factor;

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

[0086] (5) Under continuous stirring, the soybean protein meal powder solid is slowly added to the mixed aqueous solution containing anions and cations obtained in step (4) and stirred until homogeneous.

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

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

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

[0090] 2) Dissolve acrylamide in deionized water to obtain an acrylamide aqueous solution; dissolve chitosan in hydrochloric acid aqueous solution to obtain a chitosan hydrochloric acid 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 resulting solution to 30°C, and keep it at that temperature for 0.5 h;

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

[0094] 6) Add N,N′-methylenebisacrylamide to the resulting mixed solution and dissolve it completely;

[0095] 7) Under nitrogen protection, gradually increase the temperature of the reaction system from 30℃ to 55℃ and keep it at that temperature for 2 hours;

[0096] 8) Add 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride and N-hydroxysuccinimide sequentially, allowing them to dissolve completely;

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

[0098] Example 3

[0099] A method for preparing a graft copolymer-modified high water-retaining formaldehyde-free adhesive, the amounts of each substance are shown in Table 1; including:

[0100] (1) Preparation of anionic moisturizing factors;

[0101] (2) Weigh out the 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 continuous stirring, the anionic moisturizing factor is slowly added to deionized water to prepare an aqueous solution of anionic moisturizing factor;

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

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

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

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

[0107] 1) Weigh the raw materials according to the mass fractions;

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

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

[0110] 4) Dissolve itaconic acid in the acrylamide aqueous solution, heat the resulting solution to 25°C, and keep it at that temperature for 1 hour;

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

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

[0113] 7) Under nitrogen protection, gradually increase the temperature of the reaction system from 25℃ to 55℃ and keep it at that temperature for 2 hours;

[0114] 8) Add 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride and N-hydroxysuccinimide sequentially, allowing them to dissolve completely;

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

[0116] Example 4

[0117] A method for preparing a graft copolymer-modified high water-retaining formaldehyde-free adhesive, the amounts of each substance are shown in Table 1; including:

[0118] (1) Preparation of anionic moisturizing factors;

[0119] (2) Weigh out the 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 continuous stirring, the anionic moisturizing factor is slowly added to deionized water to prepare an aqueous solution of anionic moisturizing factor;

[0121] (4) Under continuous stirring, the cationic polyamide polyamine epichlorohydrin resin is gradually added to the anionic moisturizing factor aqueous solution obtained in step (3);

[0122] (5) Under continuous stirring, the soybean protein meal powder solid is slowly added to the mixed aqueous solution containing anions and cations obtained in step (4) and stirred until homogeneous.

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

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

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

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

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

[0128] 4) Dissolve itaconic acid in the acrylamide aqueous solution, heat the resulting solution to 25°C, and keep it at that temperature for 1 hour;

[0129] 5) After the solution system has stabilized, add the chitosan acidic solution to the acrylamide-itaconic acid mixed solution;

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

[0131] 7) Under nitrogen protection, gradually increase the temperature of the reaction system from 25℃ to 55℃ and keep it at that temperature for 2 hours;

[0132] 8) Add 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride and N-hydroxysuccinimide sequentially, allowing them to dissolve completely;

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

[0134] Example 5

[0135] A method for preparing a graft copolymer-modified high water-retaining formaldehyde-free adhesive, the amounts of each substance are shown in Table 1; including:

[0136] (1) Preparation of anionic moisturizing factors;

[0137] (2) Weigh out the 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, the anionic moisturizing factor is slowly added to deionized water to prepare an aqueous solution of anionic moisturizing factor;

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

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

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

[0142] The preparation method of the above-mentioned anionic moisturizing factor, and the content of each component are shown in Table 2, including:

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

[0144] 2) Dissolve acrylamide in deionized water to obtain an acrylamide aqueous solution; dissolve chitosan in hydrochloric acid aqueous solution to obtain a chitosan hydrochloric acid 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 resulting solution to 25°C, and keep it at that temperature for 1.5 hours;

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

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

[0149] 7) Under nitrogen protection, gradually increase the temperature of the reaction system from 25℃ to 55℃ and keep it at that temperature for 2 hours;

[0150] 8) Add 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride and N-hydroxysuccinimide sequentially, allowing them to dissolve completely;

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

[0152] Example 6

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

[0154] Example 7

[0155] In this embodiment, peanut meal powder was selected as the plant protein 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 space limitations, only Example 3 is used as an example to construct a comparative case as follows.

[0161] Comparative Example 1

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

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

[0164] (1) Mix soybean protein meal powder with deionized water and stir initially with a stirring rod until a homogeneous system is formed;

[0165] (2) Mechanically stir the above homogeneous system at a speed of 1000 rpm for 10 min.

[0166] Comparative Example 2

[0167] In the preparation of this comparative moisturizing factor, 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] In the preparation of this comparative moisturizing factor, 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] In the preparation of this comparative moisturizing factor, 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 of this comparative moisturizing factor, itaconic acid was replaced with an equal mass of acrylic acid, and the other conditions were the same as in Example 3.

[0174] Comparative Example 6

[0175] In this comparative example, the moisturizing factor was replaced with hyperbranched polyester, which was prepared by the following method: Trimethylolpropane (TMP) and 2,2-dimethylolpropionic acid (DMPA) were added to a four-necked flask at a molar ratio of 1:21. Under nitrogen protection, the temperature was gradually raised to 140°C. After the temperature stabilized, 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 another 3 hours. The reaction was then stopped and cooled to 50°C. Acetone was added to dissolve the product, and the hyperbranched polyester was obtained by precipitation with hexane.

[0176] The remaining conditions are the same as in Example 3.

[0177] Comparative Example 7

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

[0179] Comparative Example 8

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

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

[0186] 10 g of adhesive sample was placed in a petri dish and exposed to outdoor conditions. The residual mass rate was recorded after 24 hours. The results are shown in Table 1 and 2. Figure 1 The adhesive was applied to a 200 mm × 200 mm veneer at a density of 180 g / m², and the warping deformation of the veneer was observed and evaluated. The results are shown in Table 3-4.

[0187] The adhesives prepared according to the embodiments 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 prepared using poplar veneers with a thickness of 1.6 ± 0.1 mm and a moisture content of 8% to 15%, with the veneers assembled with the grain direction perpendicular to each other in adjacent layers. Adhesive was applied to the core layer surface at a 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 an open-air environment 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 in the embodiments and comparative examples of the present invention were tested using the following methods:

[0190] According to GB / T 9846-2015 "Ordinary Plywood" standard, the bonding strength of the prepared three-layer plywood was tested. The dry shear strength of the samples was determined using a universal testing machine with the beam moving at a speed of 10 mm / min. Before the wet shear strength test, the samples were immersed in water at 63℃ for 3 hours, and then cooled at room temperature (23±2℃) for 10 minutes before testing. All tests were repeated 6 times, and the strength value was calculated as the arithmetic mean of the valid test results. The final data are expressed as mean ± standard error. Detailed test results are shown in Table 3-4.

[0191] Table 3

[0192]

[0193] like Figure 1 These are macroscopic morphology images of the adhesive layers after curing and storage for 24 hours for the adhesives prepared in Example 1 and Comparative Example 1 of this invention; Figure 1 It can be seen that the adhesive prepared in Comparative Example 1 cracked after being stored for 24 hours, while the adhesive prepared in Example 5 of the present invention achieved a water retention rate of 52% after 24 hours.

[0194] Table 1 shows that the viscosity of the plant protein adhesive developed in this invention increases with the amount of anionic moisturizing factor. When the amount of anionic moisturizing factor is 120 parts (Comparative Example 7), although other properties are good, the high viscosity makes it difficult to disperse the adhesive evenly during application, leading to construction difficulties. The 24-hour water retention performance of the adhesive prepared in this invention also increases with the amount of anionic moisturizing factor, but the problem of construction difficulties exists when the amount is large. The veneer warpage angle gradually decreases with the increase of anionic moisturizing factor, and then tends to stabilize; moreover, the adhesive prepared in this invention has high dry and wet shear strength.

[0195] Table 4

[0196]

[0197] As shown in Table 4, Comparative Example 1, containing only plant protein meal and deionized water, exhibits significantly insufficient water retention. When the plant protein adhesive of Comparative Example 1 is applied to the veneer surface, moisture readily and rapidly penetrates into the wood substrate, severely reducing the water resistance of the final plywood and consequently causing the bonding strength to fail to meet usage requirements. Comparative Examples 2-3, by omitting chitosan or itaconic acid reactions during the preparation of the anionic moisture-retaining factor, resulted in a 1-2 times increase in veneer warpage angle, and a significant decrease in both dry and wet shear strength and wet adhesive performance after 24 hours. Comparative Examples 4-5, by omitting itaconic acid or replacing itaconic acid with acrylic acid, also yielded adhesives with poor performance. Comparative Examples 6-10 also exhibited some performance issues. The cationic PAE utilized in this invention, if replaced with a nonionic polyamide polyamine resin, would reduce the shear strength of the adhesive and lead to a decrease in 24-hour water retention. Replacing it with cationic polyacrylamide resin will excessively increase viscosity, reduce dry and wet shear strength, and slightly improve moisture retention.

[0198] This invention provides a moisturizing factor for plant protein adhesives and its preparation method, using acrylamide, itaconic acid, and chitosan as graft copolymer monomers. This moisturizing factor-modified high-water-retention, formaldehyde-free adhesive is applied to engineered wood products. This enhanced water retention capacity stems from a free radical polymerization-dynamic electrostatic gel complexation reinforcement system constructed from anionic moisturizing factor, cationic polyamide polyamine epichlorohydrin resin, and plant protein. 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. This effectively anchors water molecules in the adhesive and inhibits water molecule penetration into the veneer substrate. The resulting dense cross-linked network significantly improves the water retention performance of the adhesive.

[0199] In summary, this invention enhances the water retention and bonding performance of plant protein adhesives by constructing a multi-layered chemical bond cross-linking network. The dynamic hydrogen bonds and electrostatic interactions within the system improve overall tensile properties, and the formed rigid-soft framework disperses and dissipates concentrated stress, mitigating performance failure issues during storage and endowing plant protein-based adhesives with excellent mechanical properties. This provides a new technical solution for the application of plant protein adhesives in the field of engineered wood products.

[0200] The above description represents the preferred embodiments of the present invention. For those skilled in the art, any improvements and modifications made without departing from the principles described herein should also be considered within the scope of protection of the present invention.

Claims

1. A graft copolymer-modified high water-retaining formaldehyde-free adhesive, characterized in that, Composed of the following components in parts by weight: 100 parts deionized water; 90 parts of plant protein meal powder; 48 parts of cationic polyamide polyamine epichlorohydrin resin; Anionic moisturizing factor 84–108 parts; The anionic moisturizing factor is prepared from the following components in parts by weight: 113 portions of deionized water; Two parts of initiator; Acrylamide 10–50 parts; Itaconic acid 6 parts; 1 part chitosan; 0.6 parts hydrochloric acid; Crosslinking agent 0.5 parts; 5 parts of 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride; 1.5 parts of N-hydroxysuccinimide; The anionic moisturizing factor was prepared by the following method: 1) Weigh out the following raw materials according to their weight: deionized water, initiator, acrylamide, itaconic acid, chitosan, hydrochloric acid, and crosslinking agent. 2) Dissolve acrylamide in deionized water to obtain an acrylamide aqueous solution; add chitosan to hydrochloric acid to obtain a chitosan hydrochloric acid solution; 3) Add an initiator to the acrylamide aqueous solution; 4) Dissolve itaconic acid in the solution from step 3), heat the reaction system to 25–30°C and maintain the temperature for 0.5–1.5 h to obtain an acrylamide-itaconic acid reaction solution; 5) Add the chitosan hydrochloric acid solution to the acrylamide-itaconic acid reaction solution to obtain the chitosan-acrylamide-itaconic acid reaction solution; 6) Add a crosslinking agent to the chitosan-acrylamide-itaconic acid reaction solution and dissolve it; 7) Under nitrogen protection, gradually increase the reaction temperature to 55℃ and maintain the temperature for 2 hours; 8) Dissolve 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride and N-hydroxysuccinimide in the chitosan-acrylamide-itaconic acid reaction solution from step 7); 9) After the above reaction is completed, the anionic moisturizing factor is obtained after reacting at room temperature for 6–24 hours.

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

3. The graft copolymer-modified high water-retaining formaldehyde-free adhesive according to claim 1 or 2, characterized in that, The plant protein meal has a protein content of 45% and a particle size of 100–250 mesh.

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

5. The graft copolymer-modified high water-retaining 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 an aqueous solution of hydrochloric acid with a concentration of 37%.

6. A method for preparing the graft copolymer modified high water-retaining formaldehyde-free adhesive according to any one of claims 1-5, characterized in that, include: (1) Preparation of anionic moisturizing factors; (2) Weigh out deionized water, plant protein meal powder, anionic moisturizing factor and cationic polyamide polyamine epichlorohydrin resin; (3) Under continuous stirring, the anionic moisturizing factor was slowly added to deionized water to prepare an aqueous solution of the anionic moisturizing factor. (4) Under continuous stirring, the cationic polyamide polyamine epichlorohydrin resin is gradually added to the anionic moisturizing factor aqueous solution in step (3); (5) Under continuous stirring, the solid plant protein meal powder is slowly added to the mixed aqueous solution containing anions and cations obtained in step (4) and stirred until homogeneous.

7. The preparation method according to claim 6, characterized in that, In steps (3)–(5), the stirring speed is 900–1200 rpm and the time is 30–40 min.

8. The application of the graft copolymer modified high water-retaining formaldehyde-free adhesive according to any one of claims 1–5 as an adhesive for engineered wood products.

Images