Use of a corn protein formed into a coagulum or coagulum suspension by liquid-liquid phase separation in a bio-based glue or coating

Abstract

This invention discloses the application of corn protein coagulants or suspensions formed through liquid-liquid phase separation in bio-based adhesives or coatings. The preparation includes: dissolving corn gliadin or crude corn protein powder in a 70-90% v / v ethanol aqueous solution, removing impurities, adjusting the ethanol concentration to 40-60% v / v with water, and inducing phase separation to obtain coagulants; or directly adding corn gliadin to a 40-60% v / v ethanol aqueous solution and stirring to form coagulants. The resulting product is used as a bio-based adhesive for bonding sheet or paper-based materials, or as a coating to impart water / oil barrier properties to paper-based materials. This invention utilizes corn protein coagulants to achieve excellent adhesive performance and water resistance without crosslinking agents. The product is completely biodegradable, providing a green solution for replacing traditional plastic coatings and solving sheet bonding problems.

Description

Technical Field

[0001] This invention belongs to the technical field of bio-based materials and high-value utilization of food industry by-products, and specifically relates to the application of corn protein in bio-based adhesives or coatings through liquid-liquid phase separation to form coagulants or coagulant suspensions. Background Technology

[0002] In widely used everyday products, such as the waterproof coating on paper cups, the tape and waterproof labels on cardboard boxes, and the adhesive layers on engineered wood products, a thin film layer is usually attached to the surface of the substrate for bonding or barrier purposes. These thin films are usually made of fossil-based polymer materials, and although they account for only a small portion of the total plastic production, their environmental impact is enormous. Recent research (Nature Sustainability, 2026, 9(3), 340-342) points out that the glue and coatings attached to recyclable natural substrates are key bottlenecks hindering the full life cycle recycling of products. These fossil-based thin films are neither biodegradable like paper and wood substrates, nor are they easy to strip and recycle in traditional pulping systems. In addition, they generate microplastic pollution after aging and disposal, and some of these materials continue to release volatile organic compounds such as formaldehyde during use, posing significant ecological and health risks.

[0003] Developing bio-based adhesives and coatings has always been a challenge for the industry. The key lies in balancing the feasibility of natural degradation and recycling, performance characteristics (such as adhesive strength and water resistance), and compatibility with existing industrial production lines. In the coating field, widely used bioplastics such as polylactic acid (PLA) require specific industrial composting facilities for degradation, making them difficult to degrade in the natural environment and effectively separate from conventional paper pulp systems. Currently, adhesives developed based on agricultural byproducts such as lignin, soybean protein, or starch generally have poor water resistance and insufficient adhesive strength, often requiring the use of fossil-based resins or crosslinking agents, thus reintroducing the risk of microplastic and volatile organic compound (VOC) pollution. Furthermore, the rheological properties and surface wetting capabilities of many novel bio-based adhesives and coating materials are incompatible with traditional sizing and coating equipment, resulting in excessively high costs for process switching and equipment modification, thus hindering the large-scale commercialization of bio-based adhesives and coating materials.

[0004] Crude corn gluten meal is a byproduct of starch processing and bioethanol fermentation. It is produced in large quantities, with a protein content typically between 50-70% w / w, and is currently mostly used as low-value-added animal feed. Its main protein component is zein, which requires purification through alcohol extraction, solvent separation, and drying. Zein meal typically has a protein content of 80-99% w / w, but production volumes are small. Due to its natural, non-toxic, highly biocompatible, and inherently hydrophobic properties, zein has attracted considerable attention in the field of bio-based adhesives and coatings. A common method is to completely dissolve it in high-concentration ethanol to prepare a homogeneous solution. However, due to limited solubility, the effective solid content of the homogeneous solution is low, resulting in insufficient adhesive strength and difficulty in forming dense, high-barrier films. Furthermore, existing applications almost entirely rely on refined zein, and its high cost severely restricts its large-scale commercialization. Summary of the Invention

[0005] Purpose of the invention: This invention aims to provide an application of corn protein in bio-based adhesives or coatings through liquid-liquid phase separation to form coagulants or coagulant suspensions, thereby improving the adhesive strength of the adhesive and the barrier properties of the film. This solves the problems in the prior art where corn gliadin is used in adhesives or coatings, resulting in insufficient adhesive strength of the adhesive and difficulty in forming a dense, high-barrier film.

[0006] Technical solution: The application of the corn protein formed by liquid-liquid phase separation to form coagulants or coagulant suspensions in bio-based adhesives according to the present invention.

[0007] Preferably, the agglomerate or agglomerate suspension is used directly as an adhesive.

[0008] Preferably, the bio-based adhesive is used for bonding engineered wood products, wood processing materials, or paper-based packaging materials.

[0009] The bonding method is as follows: the agglomerate or its suspension is applied to the surface of the substrate by scraping or spraying, and after bonding, it is pressed under a pressure of 1-3 MPa for 5-15 minutes, and then placed in an oven at 40-80℃ to dry for more than 12-24 hours to cure it.

[0010] The application of the corn protein condensate formed by liquid-liquid phase separation described in this invention in bio-based coatings.

[0011] Preferably, the aggregate is used directly as a bio-based coating.

[0012] Preferably, the bio-based coating is used for surface treatment of paper-based materials to provide water and / or oil barrier properties.

[0013] The surface treatment method is as follows: the agglomerate is applied to the surface of the substrate by scraping, and then naturally dried and cured at room temperature.

[0014] Preferably, the preparation method of the coagulant or coagulant suspension is a solvent displacement method or a direct solvent method;

[0015] The solvent replacement method is as follows: dissolve corn gliadin powder in a 70%-90% v / v ethanol aqueous solution. After complete dissolution, slowly add water to adjust the ethanol concentration of the system to 40%-60% v / v, induce liquid-liquid phase separation, form a protein aggregate suspension, and separate the aggregate.

[0016] The direct solvent method involves directly adding zein powder to a 40%-60% v / v ethanol aqueous solution, stirring and mixing thoroughly to directly induce the protein to enter a liquid-liquid phase separation state, forming a protein aggregate suspension, and then separating the aggregate.

[0017] The concentration of zein powder in the coagulant suspension (40-60% v / v ethanol aqueous solution) is 0.5-15% w / v. The adhesive strength of the coagulant suspension initially increases and then tends to stabilize with increasing zein powder content.

[0018] The protein content of the zein is 80-99% w / w.

[0019] Preferably, the preparation method of the coagulant or coagulant suspension is a solvent replacement method, wherein the solvent replacement method is as follows: crude corn gluten powder is added to a 70%-90% v / v ethanol aqueous solution, stirred and mixed thoroughly, and after the protein is fully dissolved, insoluble solids are removed, and water is slowly added to adjust the ethanol concentration of the system to 40%-60% v / v, inducing liquid-liquid phase separation to form a protein coagulant suspension, and the coagulant is obtained by separation; the concentration of crude corn gluten powder in the initial 70-90% v / v ethanol aqueous solution is 8-35% w / v.

[0020] Preferably, the crude corn gluten meal has a protein content of 50-70% w / w.

[0021] Preferably, the pH of the system in the method for preparing the coagulant or coagulant suspension is 5 to 10. More preferably, the pH is 5 to 8.

[0022] Mechanism of Invention: Liquid-Liquid Phase Separation (LLPS) is a widely studied physical phenomenon in colloid chemistry, referring to the process by which a homogeneous polymer solution spontaneously forms two coexisting liquid phases under specific conditions: one is a polymer-rich coacervate phase, and the other is a low-concentration dilute phase. The polymer content of the coacervate phase can typically reach 10-50% w / w, while exhibiting extremely low liquid-liquid interfacial tension (on the order of approximately 100 µN / m). The coacervate maintains a high solids content while also possessing good flowability. This invention utilizes corn protein to form coacervates through liquid-liquid phase separation for use as an adhesive to bond wood or paper-based materials. It has been found that this achieves efficient wetting and spreading on rough or porous solid substrate surfaces, exhibiting high-strength adhesion. Directly using the coacervate suspension as an adhesive not only eliminates the separation step but also allows for a wider range of adhesive application processes (such as spraying). Furthermore, based on the efficient wetting and spreading ability of the agglomerates on rough or porous solid substrate surfaces, they were further applied to bio-coatings. It was found that the agglomerates can form dense films, significantly improving the substrate's barrier properties against water and oil.

[0023] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: (1) The corn protein coagulant prepared by liquid-liquid phase separation maintains fluidity while maintaining high local solid content, and can be adapted to existing scraping and spraying processes, avoiding the problems of difficult coating at high concentrations and insufficient bonding strength and barrier performance at low concentrations of traditional plant protein adhesives and coating materials; (2) The coagulant can wet and penetrate the surface of rough wood or porous paper, and form a tight structure and continuous dense film after curing, significantly improving the bonding strength and coating barrier performance, giving the material excellent water resistance, and without the need for external crosslinking agents; (3) The bonding strength of the corn protein coagulant reaches about 13 MPa; (4) When the pH of the corn protein coagulant suspension is 5 and the corn gliadin concentration reaches 8-10% w / v, the bonding strength of the suspension is comparable to that of the separated coagulant, about 13 MPa; (5) When the crude corn protein powder concentration in the initial extract reaches 24-35% w / v and the pH of the coagulant suspension is 6, the bonding strength of the obtained suspension is about 9 MPa. MPa; (6) This invention can use either corn gliadin or inexpensive crude corn gluten powder to achieve high-value utilization of industrial by-products; (7) The entire process uses only ethanol and water as solvents, without the addition of toxic substances such as formaldehyde. The product is natural and completely biodegradable, solving the formaldehyde release problem of artificial boards from the source and providing a safe, environmentally friendly, and sustainable solution for replacing plastic coatings (such as polyethylene and polylactic acid). Attached Figure Description

[0024] Figure 1This is a process flow diagram of the adhesive and coating preparation method of the present invention;

[0025] Figure 2 The diagrams show the phase diagram and microstructure of zein in an ethanol-water solvent system; (a) Phase diagram of zein as a function of ethanol concentration (% v / v) and pH value. Different symbols and regions in the diagram represent different states of the protein: region b (triangle) represents the precipitation region, region c (solid dot and shaded area) represents the aggregate region (i.e., LLPS region), and region d (hexagon) represents the solution region; (bd) Microscopic images of zein at pH 7 and 1% w / v solid content at different ethanol concentrations show solid precipitation, aggregate droplets, and homogeneous solution diagrams, respectively.

[0026] Figure 3 The graph shows the yield of corn protein aggregates as a function of pH (mean ± standard deviation, n = 3).

[0027] Figure 4 The diagram shows the macroscopic morphology, flowability, and adhesive properties of corn protein aggregates; (a) Macroscopic state diagram of corn gliadin solution after LLPS and standing for a period of time, with the upper layer being the dilution phase and the lower layer being the aggregate phase; (b) Diagram showing the flow behavior of the liquid in the aggregate phase; (c) Demonstration diagram of the adhesion of the aggregate as glue on the wood surface.

[0028] Figure 5 Schematic diagrams of the adhesive application and coating process for aggregates: (a) a blade coating process based on the aggregate phase; (b) a spray coating process based on the aggregate suspension.

[0029] Figure 6 The images show scanning electron microscope (SEM) images of the interface between corn protein coagulant adhesive and wood substrate: (a) a cross-sectional view of two wood boards bonded together by the coagulant adhesive of the present invention; and (b) a view of the coagulant adhesive of the present invention coated on the surface of porous wood.

[0030] Figure 7 The following are diagrams showing the adhesive strength test results of corn protein aggregates: (a) Schematic diagram of overlap shear test; (b) Effect of ethanol concentration on adhesive strength (mean ± standard deviation, n ≥ 10), where the corn gliadin concentration is fixed at 10% w / v and pH = 5.

[0031] Figure 8 The following graphs show the effect of zein concentration on the adhesion strength of the coagulated suspension and its comparison with the coagulated phase: (a) Effect of different protein concentrations in the suspension on adhesion strength; (b) Adhesion strength of the coagulated phase, with ethanol concentration maintained at 50% v / v and pH = 5. Data are expressed as mean ± standard deviation (n ≥ 8).

[0032] Figure 9 The graph shows the effect of initial crude corn gluten meal concentration on the adhesion strength of the coagulant suspension. The ethanol concentration was kept at 50% v / v and the pH was 6. The data are expressed as mean ± standard deviation (n ≥ 4).

[0033] Figure 10 A comparison graph showing the bonding strength of corn protein coagulant glue (coagulant phase, pH 5) with fossil-based and other bio-based glues; the numbers in the text on the horizontal axis correspond to the references.

[0034] Figure 11 The following graphs are used to evaluate the water resistance of corn protein aggregate adhesive: (a) Schematic diagram of the bonded area immersed in water; (b) Graph of the change in bond strength with immersion time (mean ± standard deviation, n ≥ 9).

[0035] Figure 12 This image illustrates application scenarios of corn protein aggregates as coating materials and adhesives.

[0036] Figure 13 Comparison of SEM morphology at the interface between the corn protein aggregate coating and the uncoated substrate;

[0037] Figure 14 A comparative illustration of the surface waterproofing and oil-repellent properties of corn protein aggregate coating and uncoated substrates;

[0038] Figure 15 A comparison of water absorption (a) and oil absorption (b) over time for corn protein coagulant coated and uncoated substrates and various commercial coatings (polyethylene, polylactic acid, silicone oil) (mean ± standard deviation, n = 3).

[0039] Figure 16 Thermogravimetric analysis (TGA) curve of dry corn protein aggregate;

[0040] Figure 17 A comparison of the soil burial degradation performance of corn protein coagulant coated paper and polyethylene coated paper. Detailed Implementation

[0041] The technical solution of the present invention will be further described below with reference to the embodiments.

[0042] Example 1: Determining the formation conditions of maize protein aggregates by constructing a phase diagram

[0043] This embodiment uses zein as raw material to study the effects of ethanol concentration and pH on protein solubility, constructs its phase diagram under different solvent environments, and determines the formation conditions of aggregates. First, the concentration of zein was fixed at 1% w / v. 1 g of zein powder was completely dissolved in a predetermined volume of 80% v / v ethanol aqueous solution. Then, deionized water was slowly added to adjust the system to the target ethanol concentration gradient (0, 10, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, and 80% v / v), with the total volume of each sample fixed at 100 mL. For each ethanol gradient, the pH value was adjusted stepwise from 5 to 12 using 2 M HCl or NaOH solution, and the dissolution state and phase behavior were observed under a microscope. The results are as follows: Figure 2 As shown.

[0044] Depend on Figure 2 It was found that under high ethanol concentrations, the protein completely dissolved into a homogeneous solution. As the ethanol concentration decreased to 30-65%, especially in the 40-60% range, the system underwent LLPS (Liquid-Liquid Polysaccharide Synthesis) and produced a large number of agglomerated droplets. Further reduction in ethanol concentration induced the protein to transform into a solid precipitate. Therefore, the optimal ethanol-water concentration for the formation of agglomerated corn protein solutions was confirmed to be 40-60%. In addition, pH value had a significant impact on protein solubility. Under all ethanol concentration gradients, the protein was completely dissolved when pH > 11; while within the LLPS range, when the pH increased above 10, the agglomerated substances gradually disappeared and the solution transformed into a homogeneous one.

[0045] Example 2: Effect of pH on coagulant yield

[0046] This embodiment aims to investigate the effect of pH on the yield of corn gluten aggregates and determine the optimal pH range. First, 250 mg of corn gliadin powder was added, and the volume was adjusted to 25 mL with 50% v / v ethanol aqueous solution. The pH of the system was then adjusted to 3, 4, 5, 6, 7, 8, 9, and 10, respectively. The samples were then centrifuged at 6,500 g for 45 minutes at 20°C. The supernatant was discarded, and the bottom aggregate phase was collected. The aggregate was freeze-dried to obtain the dry weight, and the aggregate yield was calculated as a percentage of the dry weight to the initial protein mass (250 mg). The results are as follows: Figure 3 As shown.

[0047] Depend on Figure 3 It can be seen that the coagulant yield is greater than 40% in the pH range of 5 to 8, and the effect is best at pH 6. Therefore, the preferred pH range is determined to be 5 to 8.

[0048] Example 3: Preparation of aggregates and their macroscopic and microscopic structural characterization at the wood interface

[0049] First, zein powder was dissolved in an 80% v / v ethanol aqueous solution and stirred until completely dissolved. Then, under continuous stirring, deionized water was slowly added dropwise to the solution to reduce the ethanol concentration to 50% v / v, inducing LLPS formation. The final protein concentration in the system was controlled at 2% w / v. The resulting coagulated suspension was centrifuged at 6,500 g for 15 minutes at 20°C. After centrifugation, the upper diluted phase was discarded, and the bottom protein-rich coagulated phase was collected. Figure 4 a). The resulting condensate phase exhibits macroscopically homogeneous, viscous fluid characteristics, demonstrating liquid flowability, and can be used as a bio-based adhesive or coating material. Figure 4 b). For example Figure 5 As shown, the agglomerate suspension and the separated agglomerate phase can be applied to the substrate surface by spraying and scraping, respectively.

[0050] When the collected corn protein aggregate phase is directly applied to wood substrate bonding, the aggregate can be evenly coated onto the surface of the wood veneer, and two wood veneers can be manually glued together. Before drying and curing, attempts to separate the wood veneers reveal obvious stringing in the aggregate. Figure 4 c), demonstrating its excellent adhesion and wetting and spreading ability on wood surfaces. The corn protein aggregate adhesive was applied to a wood substrate (either by laminating two pieces of wood or by directly applying the adhesive to the wood surface), and then dried in a 60°C oven for 24 hours. Further microscopic observation of the bonding interface using SEM revealed that, thanks to the extremely low interfacial tension of the aggregate, the adhesive effectively penetrated and filled the pores on the wood surface. Figure 6 After curing, the proteins that have penetrated into the pores form a stable interlocking structure, which can improve the bonding strength of the interface.

[0051] Example 4: Testing and comparison of the adhesive properties of corn protein coagulants or coagulant suspensions as adhesives

[0052] This embodiment aims to test the adhesive properties of corn protein aggregate adhesive and compare it with a variety of commercially available fossil-based adhesives and other bio-based adhesives reported in the literature.

[0053] This embodiment includes three sets of experiments, and the preparation method is as described in Example 3. The first set studied the effect of ethanol concentration (30, 40, 50, 60, 70, 80% v / v) on adhesive strength, fixing the zein concentration at 10% w / v and the pH at 5, directly using the solution or suspension as adhesive. The second set studied the effect of zein concentration (0.5, 1, 4, 8, 10, 12, 15% w / v) on adhesive strength, fixing the ethanol concentration at 50% v / v and the pH at 5, directly using the suspension, and comparing the adhesive strength with that of the aggregate phase obtained after centrifugation (20℃, 6,500 g, 45 minutes). The third set studied the effect of different initial crude corn gluten powder concentrations (8, 9.6, 11.2, 16, 24, 30, 35% w / v) extracted in an 80% v / v ethanol aqueous solution on adhesive strength. The specific steps are as follows: First, the crude corn gluten powder of each concentration was extracted in an 80% v / v ethanol aqueous solution... The mixture was stirred in a v / v ethanol aqueous solution for 3 hours, with the pH controlled at 10 to enhance protein solubility. Subsequently, it was centrifuged (20°C, 6,500 g, 10 minutes) to remove insoluble solids. Water was added to the supernatant to bring the ethanol concentration to 50% v / v, and the pH was adjusted to 6 to obtain a coagulated suspension. The coagulated phase was then coated using a blade coating process. Figure 5 a), while the coagulant suspension is applied using a spray coating process ( Figure 5 b).

[0054] Commercially available maple veneer with dimensions of 60×5×2 mm was used as the bonding substrate in the experiment, with the overlap area controlled at approximately 5×(4-6) mm. To simulate actual industrial production, the bonded samples were pressed together under a pressure of 3 MPa for 10 minutes, and then dried in a 60℃ oven for more than 24 hours to ensure that the solvent evaporated fully and the adhesive layer was completely cured.

[0055] like Figure 7 As shown in Figure a, the adhesion performance was tested using a texture analyzer (TMS-Pro) for lap shear testing. During the test, both ends of the wood chip were clamped and subjected to unidirectional tension at a constant speed of 2 mm / min. The maximum failure load and displacement curves were recorded, and the bond strength (MPa) was calculated by dividing the maximum tensile force by the actual bonded area.

[0056] The results of the first group of tests ( Figure 7(b) indicates that ethanol concentration has a significant impact on adhesive strength, with higher adhesive strength observed in the 40-60% v / v range. When the ethanol concentration is above 60% v / v, the system is in a transitional phase between a homogeneous solution and a coagulant phase, with limited protein molecule aggregation and a low coagulant yield. However, when the ethanol concentration is below 40% v / v, especially below 30% v / v, the increased water content enhances the hydrophobic interactions between protein molecules, causing the originally fluid liquid coagulant to transform into a solid precipitate. Tests revealed that this physical state transition leads to a loss of interfacial wettability and spreading ability, thus losing the adhesive properties required for its application as a glue. Therefore, the presence of coagulants can significantly improve adhesive strength, and the preferred ethanol concentration in the corn protein coagulant suspension is 40-60% v / v.

[0057] The results of the second group of tests ( Figure 8 The results showed that the concentration of zein significantly affected the adhesion strength. As the zein concentration increased, the adhesion strength gradually increased because the amount of coagulants in the suspension increased with increasing zein concentration. When the concentration reached 8% w / v, the adhesion strength of the suspension was approximately 12 MPa, comparable to the separated coagulants (approximately 13 MPa). When the concentration reached 10% w / v, the adhesion strength of the suspension was 14 MPa, slightly higher than the adhesion strength of the pure coagulants. This may be due to batch-to-batch variations and is within the normal range of fluctuation. Further increasing the zein concentration did not increase the adhesion strength of the suspension further; it remained essentially comparable to the adhesion strength of the pure coagulants.

[0058] The results of the third group of tests ( Figure 9 The results showed that the initial concentration of crude corn gluten meal had a significant effect on the adhesive strength in the 80% v / v ethanol extract. The adhesive strength gradually increased with increasing crude corn gluten meal concentration, reaching approximately 9 MPa when the concentration reached 24–35% w / v. Further increases in crude corn gluten meal concentration did not significantly increase the adhesive strength.

[0059] When using crude corn gluten meal as a raw material, the resulting coagulated suspension exhibits slightly lower adhesive strength than that of alcohol-soluble corn gluten. This is primarily because, at high protein concentrations, the solubility of crude corn gluten meal in an 80% v / v ethanol aqueous solution has an upper limit. When the concentration exceeds 35% w / v, the system becomes very viscous, making it difficult for more protein to dissolve. The actual protein concentration of the coagulated suspension obtained after removing insoluble solids and diluting the supernatant with water may be lower than the concentration required to achieve the desired effect when using alcohol-soluble corn gluten as a starting material, thus resulting in an adhesive strength slightly lower than the optimal value.

[0060] To further verify the market competitiveness of the present invention, the adhesive strength of the corn protein coagulant adhesive (coagulant phase, pH 5) prepared in this embodiment was compared with that of other mainstream adhesives. Figure 10 Except for the data from this invention, all other comparative data in the figure are taken from published literature in relevant fields. The comparison objects cover mainstream fossil-based adhesives (urea-formaldehyde resin, phenolic resin, polyvinyl alcohol adhesive, polyurethane adhesive, cyanoacrylate, epoxy resin) and various bio-based adhesives (hide glue, soybean glue, starch glue, lignin glue, corn protein-tannic acid composite adhesive). The results show that the corn protein coagulant adhesive prepared by this invention has significantly better adhesive strength than existing bio-based adhesives and surpasses most commonly used commercial fossil-based synthetic adhesives. This fully demonstrates that the method described in this invention overcomes the problem of insufficient adhesive ability of bio-based adhesives and has the potential to replace high-carbon-footprint petrochemical adhesive products in terms of adhesive performance.

[0061] Figure 10 The sources of the comparative data are as follows:

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[10] Feng S, Yuan Z, Leitch M, et al. Adhesives formulated from barkbio-crude and phenol formaldehyde resole[J]. Industrial crops and products, 2015, 76: 258-268.

[0072] Example 5: Evaluation of the water resistance of corn protein coagulant adhesive

[0073] Referring to Example 3, maple bonded samples were prepared using a corn protein aggregate phase at pH 5. To evaluate the residual strength of the adhesive layer in a humid environment, the bonded and cured samples were completely immersed in deionized water (e.g., ...). Figure 11 As shown in Figure a), the samples were immersed in water for preset time intervals (0, 1, 8, 16, 24, 32, and 48 hours). After the set immersion time was reached, the samples were removed from the water and immediately placed in an oven at 60°C to dry for at least 24 hours. After the samples were completely dry, the residual adhesive strength of each group of samples was measured using a texture analyzer according to the tensile testing procedure described in Example 4.

[0074] Experimental results are as follows Figure 11 As shown in b, the average bonding strength of the control group (0 h) without water immersion was about 15 MPa. After 48 hours of continuous water immersion and drying, the residual bonding strength of the sample remained at about 12 MPa, which is more than 80% of the initial strength.

[0075] This embodiment demonstrates that the corn protein aggregate adhesive possesses excellent water resistance, attributed to the strong hydrophobicity of corn gliadin itself and the dense protein network structure formed by LLPS, which effectively prevents the destructive penetration of moisture into the bonding interface. This water resistance makes it valuable for applications in outdoor furniture, high-humidity packaging environments, and other fields, overcoming the performance bottleneck of traditional bio-based adhesives (such as soybean glue and starch glue) that are prone to failure when exposed to water.

[0076] Example 6: Application of corn protein aggregates as a coating in coated paper

[0077] This embodiment demonstrates the application of corn protein aggregates as a high-performance barrier coating on paper-based materials. A bio-based coating was constructed on the paper surface using a blade coating process, and its macroscopic application effects and microscopic morphology were evaluated.

[0078] Using the corn protein aggregate phase collected by centrifugation in Example 3 as the coating material, the preparation steps are as follows: The paper base material to be treated is fixed on a flat substrate of the coating machine. The temperature of the coating head (scraper) is set to 40°C to further increase the fluidity of the aggregate. The aggregate is placed in front of the scraper, and the scraping speed is set to 200 mm / min. The gap between the scraper and the substrate is set between 0 and 200 μm according to the target coating thickness. After the scraping is completed, the coated paper is placed at room temperature to dry naturally, allowing the solvent to fully evaporate and the protein molecules to solidify into a film.

[0079] The dried coated paper has a light yellow surface with a reflective luster, macroscopically indicating that a uniform and continuous thin film has formed on its surface. Figure 12 Compared to uncoated paper, coated paper has a lower surface roughness and a smoother feel. In an application demonstration, the coated paper was processed into a baking paper mold and bonded with the cohesive adhesive described in this invention, making it suitable for baking cakes and other foods.

[0080] The surface microstructure of the coated paper was observed using SEM, such as... Figure 13 As shown, the SEM images clearly reveal the boundary between the coated and uncoated areas. The uncoated area exhibits the inherent porous fibrous network structure of the paper substrate, while the fibrous structure of the coated area is completely covered, replaced by a dense, flat protein film. This microscopic demonstration proves that corn protein aggregates can wet, spread, and fill the pores between fibers on the paper surface. This dense physical barrier endows the coating material with excellent barrier properties.

[0081] Example 7: Evaluation and comparison of water and oil resistance properties of corn protein aggregate coated paper

[0082] This embodiment evaluates the barrier properties of corn protein coagulant coated paper against moisture and oil through macroscopic permeation experiments and quantitative absorption tests, and compares it with commercially available polyethylene, polylactic acid and silicone oil coated papers.

[0083] Sample preparation and testing methods: Brown parchment paper was selected as the test substrate. A corn protein aggregate coating with a thickness of about 10 μm was applied to one side of the paper according to the method described in Example 6.

[0084] In macroscopic tolerance test ( Figure 14 In this process, coated and uncoated paper are folded into paper templates for designated areas to hold the test liquid.

[0085] Water resistance test: Add an equal amount of deionized water to the mold and let it stand for 30 minutes. The results showed that the water exhibited low wettability on the surface of the coated paper. After the water was poured off, only a few wet spots were visible on the surface of the coated paper, while the uncoated paper was completely soaked in water.

[0086] Oil resistance test: An equal amount of soybean oil was added to the mold, and after standing for 5 minutes, the penetration on the back of the paper was observed. The results showed that large areas of oil-soaked patches appeared on the back of the uncoated paper, while only tiny oil penetration points were observed on the back of the coated paper, confirming the effective barrier of the dense coating to oil flow.

[0087] In the quantitative absorption performance comparison test, to accurately evaluate the barrier efficiency, this embodiment measured the changes in water absorption rate and oil absorption rate over time (1, 3, 5, 10, and 20 minutes). 100 μL of deionized water or 100 μL of sunflower seed oil was used as the test medium. The water / oil absorption rate (%) was calculated as "(mass of absorbed liquid / total liquid volume) × 100%". During the water absorption rate test, the influence of natural water evaporation on the experimental results was corrected by weighing a control group. The experimental results are as follows: Figure 15 As shown:

[0088] Comparison of water absorption rates ( Figure 15 a): During the 1-20 minute test period, the water absorption rate of uncoated paper rapidly increased to over 11%. In contrast, the water absorption rate of corn protein coagulant coated paper was significantly reduced (below 6% at 20 minutes), and its waterproof performance was comparable to that of silicone-coated paper and polylactic acid-coated paper.

[0089] Comparison of oil absorption rates ( Figure 15 b): Uncoated paper exhibits a strong affinity for sunflower seed oil, with an oil absorption rate exceeding 25% after 20 minutes. In contrast, corn protein coagulant coated paper demonstrates good oil resistance, with the oil absorption rate curve remaining at a low level (approximately 7% after 20 minutes). Its oil barrier performance is superior to uncoated paper but slightly weaker than coated papers such as polyethylene and polylactic acid.

[0090] This embodiment demonstrates that the corn protein coagulant coating prepared by the present invention can provide excellent water and oil resistance barriers for paper-based materials, achieving a barrier level similar to that of some commercially available synthetic polymer coatings. This provides a new high-performance bio-based coating option for disposable catering packaging, baking paper molds, and high-fat food packaging.

[0091] Example 8: Thermal stability assessment of zein gliadin aggregate materials

[0092] This embodiment uses thermogravimetric analysis (TGA) to evaluate the mass loss of a coating material prepared from corn protein aggregates during the heating process, in order to define the thermal stability window of the material.

[0093] First, using the coating process described in Example 6, the prepared corn protein aggregate was uniformly coated onto a smooth plastic (PET) film surface. After it was completely dried at room temperature, it was peeled off from the PET substrate to obtain a dry film sample for thermal analysis testing.

[0094] The sample was tested using a thermogravimetric analyzer (TGA 550). Approximately 10 mg of dried sample was placed in a platinum crucible and heated from room temperature (approximately 20 °C) to 600 °C at a constant heating rate of 20 °C / min under nitrogen protection (flow rate of 25 mL / min). The mass percentage of the sample as a function of temperature was continuously recorded.

[0095] Thermogravimetric analysis curve ( Figure 16 The results show that the thermal degradation process of corn protein coagulated membranes can be clearly divided into three stages: the first stage (20-260℃) is characterized by small mass loss, mainly due to the evaporation of a small amount of bound water and residual solvent within the membrane; the second stage (260-390℃) is a zone of intense thermal decomposition, where the mass fraction of the sample decreases significantly due to the thermal degradation of protein molecules, the release of volatile components, and the breakdown of macromolecules into smaller molecules; the third stage (390-600℃) is a zone of slow thermal decomposition, where the degradation rate slows down significantly and the residue gradually tends towards a carbonized state.

[0096] Experimental results show that the corn protein aggregate material prepared by this invention only begins to undergo significant thermal degradation when the temperature exceeds 260℃. This thermal stability means that the material can meet the needs of most application scenarios, including everyday food baking and hot pressing processes in the manufacture of artificial boards.

[0097] Example 9: Degradation performance test of corn protein aggregate coated paper

[0098] This embodiment evaluates the biodegradability of corn protein coagulant coated paper through a soil burial experiment in a home environment, and compares it with traditional polyethylene coated paper.

[0099] At the beginning of the experiment (day 0), corn protein coagulant coated paper strips obtained in Example 6 of this invention were prepared, as well as paper strips of the same specifications cut from commercially available polyethylene coated paper cups. Figure 17 The experiment was divided into two groups:

[0100] Control group: Both types of paper strips were stored in a dry environment at room temperature;

[0101] Test group: The two types of paper strips were partially buried in outdoor garden soil to simulate the degradation process under natural conditions.

[0102] On the 8th day after burial, the paper strips were carefully removed from the soil and their morphology was compared with that of the control group.

[0103] The observation results show that:

[0104] Control group: Both polyethylene coated paper and corn protein coagulant coated paper stored at room temperature remained in good condition.

[0105] Test group: Although traditional polyethylene-coated paper strips were contaminated with soil, their overall structure and shape remained intact, showing no signs of degradation. In contrast, the corn protein conglomerate-coated paper strips prepared in this invention exhibited significant degradation. Except for the marked areas exposed to air (above the burial line), most of the paper strips buried in the soil had disintegrated, with fragments so fine that they were difficult to discern with the naked eye.

[0106] This embodiment demonstrates that the corn protein coagulant coating prepared by this invention has significant biodegradability. In a natural soil environment, this material can undergo significant degradation within approximately one week, effectively solving the environmental accumulation and microplastic pollution problems caused by traditional plastic-coated paper.

Claims

1. The application of corn protein in bio-based adhesives via liquid-liquid phase separation to form aggregates or aggregate suspensions.

2. In the application according to claim 1, the coagulant or coagulant suspension is used directly as an adhesive.

3. The application according to claim 1 or 2, wherein the bio-based adhesive is used for bonding engineered wood products, wood processing materials, or paper-based packaging materials.

4. Application of a corn protein aggregate formed by liquid-liquid phase separation in bio-based coatings.

5. In the application according to claim 4, the aggregate is used directly as a bio-based coating.

6. The application according to claim 4 or 5, wherein the bio-based coating is used for surface treatment of paper-based materials to provide water and / or oil barrier properties.

7. In the application according to claim 1, 2, 4 or 5, the preparation method of the coagulant or coagulant suspension is a solvent displacement method or a direct solvent method; The solvent replacement method is as follows: dissolve corn gliadin powder in a 70%-90% v / v ethanol aqueous solution. After complete dissolution, slowly add water to adjust the ethanol concentration of the system to 40%-60% v / v, induce liquid-liquid phase separation, form a protein aggregate suspension, and separate the aggregate. The direct solvent method involves directly adding zein powder to a 40%-60% v / v ethanol aqueous solution, stirring and mixing thoroughly to directly induce the protein to enter a liquid-liquid phase separation state, forming a protein aggregate suspension, and then separating the aggregate. The concentration of zein powder in the coagulant suspension is 0.5-15% w / v.

8. In the application according to claim 1, 2, 4 or 5, the method for preparing the coagulant or coagulant suspension is a solvent displacement method; The solvent replacement method is as follows: crude corn gluten powder is added to a 70%-90% v / v ethanol aqueous solution, stirred and mixed thoroughly, and after the protein is fully dissolved, insoluble solids are removed. Water is slowly added to adjust the ethanol concentration of the system to 40-60% v / v, inducing liquid-liquid phase separation to form a protein aggregate suspension, and the aggregate is separated. The concentration of crude corn gluten powder in the initial 70-90% v / v ethanol aqueous solution is 8-35% w / v.

9. In the application according to claim 7 or 8, the pH of the system in the method for preparing the coagulant or coagulant suspension is 5 to 10.

10. The application according to claim 9, wherein the pH is 5 to 8.

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