Multifunctional soybean protein adhesive and preparation method thereof

Abstract

The invention discloses a multifunctional soybean protein adhesive and a preparation method thereof, and belongs to the technical field of bio-based adhesives. According to the method, a halloysite nanotube is subjected to acid etching to expand a tube cavity of the halloysite nanotube, and then an epoxy group is grafted and introduced by a silane coupling agent, so that the loading capacity and interfacial compatibility of the carrier are improved. Then, loading different functional agents into the tube cavity of the halloysite nanotube to prepare a functional carrier; and finally, compounding the functional carriers according to a ratio, and adding the compounded functional carriers into the soybean protein-based adhesive to prepare different functional soybean protein adhesives. The adhesive not only has improved bonding strength, but also has better mildew-proof and flame-retardant effects. The mechanical, mildew-proof and flame-retardant properties of the adhesive are synergistically improved.

Description

Technical Field

[0001] The present invention relates to the technical field of bio-based adhesives, and in particular to a multifunctional soybean protein adhesive and a preparation method thereof. Background Art

[0002] The wood-based panel industry has long relied on formaldehyde-based resin adhesives, but the formaldehyde they release is classified as a Class I carcinogen, and the raw materials rely on non-renewable petrochemical resources. Soy protein (SPI), a candidate for green adhesives, suffers from poor water resistance, insufficient mechanical properties, and susceptibility to mildew. Research on modifying SPI adhesives has primarily focused on physical crosslinking, chemical modification, and nanocomposites. However, when traditional functional agents are directly added to the SPI matrix, phase separation occurs easily due to the lack of chemical bonding between the functional agent molecules and the SPI, resulting in an uneven adhesive layer structure. Excessive addition can also disrupt the interactions between the SPI molecular chains, weakening the bond strength.

[0003] Halloysite nanotubes (HNTs) have shown potential in drug delivery and nanoenhancement due to their unique hollow structure, high specific surface area, and excellent biocompatibility. However, natural HNTs have a small lumen volume, few surface active sites, and unmodified nanotubes tend to aggregate in adhesives, making it difficult to achieve high loading rates and interfacial synergy.

[0004] Based on this background, the present invention proposes a synergistic "carrier-interface-functionality" modification strategy: using HNTs modified by acid etching and silane coupling agent grafting as carriers, loaded with specific functional agents (such as carvacrol (CAR) and tricresyl phosphate (TCP)), to construct an adhesive system with multifunctional properties such as mildew resistance, flame retardancy, and fragrance release. The nanoconfinement effect of HNTs enables controlled release of functional molecules, while the epoxy groups of the silane coupling agent form a covalent crosslinking network with SPI molecules, aiming to simultaneously enhance the mechanical properties and functional durability of the adhesive. This research provides new insights into the multifunctional design of SPI adhesives and lays a technical foundation for the industrial application of green adhesives for wood-based panels. Summary of the Invention

[0005] The purpose of the present invention is to provide a soy protein (SPI) adhesive with good bonding strength, water resistance, mildew resistance and flame retardancy and a preparation method thereof, so as to effectively improve the performance defects of traditional bio-based adhesives and realize their multifunctionality.

[0006] To achieve the above object, the present invention adopts the following technical solutions: In a first aspect, the present invention provides a modified halloysite nanotube and a preparation method thereof, comprising the following steps: (1) Acid etching modification: HNTs were mixed with a 4 mol / L hydrochloric acid solution and reacted in an 80°C water bath with magnetic stirring for 8 hours. After the reaction, the solid material was separated by centrifugation at 5000 rpm for 5 minutes. The solid product was washed with deionized water until neutral and dried in a vacuum at 80°C for 12 hours. (2) Silane coupling agent grafting: The acid-etched modified HNTs obtained in step (1) were dispersed in a mixture of ethanol and deionized water with a volume ratio of 4:1 and ultrasonically treated for 30 minutes. Silane coupling agent KH560 (γ-glycidyloxypropyltrimethoxysilane) was added and refluxed at 100°C for 20 hours under magnetic stirring. The product was washed with ethanol to remove the residual coupling agent and dried in a vacuum at 90°C for 12 hours.

[0007] In a second aspect, the present invention provides a method for preparing functionalized halloysite nanotubes, comprising the following steps: (1) Preparation of HNTs-CAR: The acid-etched and silanized HNTs were mixed with CAR at a mass-to-volume ratio of 1:10 (g / mL) and subjected to ice-bath ultrasonic treatment for 30 minutes. This was followed by a vacuum-normal pressure cycle (vacuum degree 0.1 MPa, maintained for 30 minutes, then returned to normal pressure, repeated twice). The mixture was centrifuged at 5000 rpm for 5 minutes to separate the solid phase, washed with ethanol to remove surface adsorbents, and finally freeze-dried in a vacuum for 12 hours.

[0008] (2) Preparation of HNTs-TCP: The acid-etched and silanized HNTs were mixed with TCP at a mass-to-volume ratio of 1:10 (g / mL) and subjected to ice-bath ultrasonic treatment for 30 minutes. This was followed by a vacuum-normal pressure cycle (vacuum degree 0.1 MPa, maintained for 30 minutes, then returned to normal pressure, repeated twice). The mixture was centrifuged at 5000 rpm for 5 minutes to separate the solid phase, washed with ethanol to remove surface adsorbents, and dried at 100°C for 12 hours.

[0009] *(Note: HNTs-CAR and HNTs-TCP are usually mixed in a mass ratio of 1:1)* In a third aspect, the present invention provides a method for preparing a halloysite nanotube-modified multifunctional soybean protein adhesive, comprising the following steps: Soy protein isolate (SPI) and deionized water were mixed in a mass ratio of 1:9 and stirred at 500 rpm at room temperature for 30 minutes to form an SPI adhesive. HNTs-CAR and HNTs-TCP were compounded in a mass ratio of 1:1 and added to the SPI adhesive (the total amount of compounded functionalized HNTs was 1 wt% to 4 wt% of the SPI adhesive mass). Stirring was continued for 30 minutes until uniformly dispersed, thus preparing a multifunctional SPI adhesive.

[0010] In a fourth aspect, the present invention provides application of the soybean protein adhesive in the field of artificial board processing.

[0011] The beneficial effects of the present invention are: (1) Significantly improved bonding performance and water resistance: HNTs were modified by acid etching and expansion and silane coupling agent grafting to optimize the interfacial crosslinking between HNTs and SPI, significantly improving the bonding strength of the adhesive while effectively reducing water absorption. This solves the key problem of low strength and poor water resistance of traditional bio-based adhesives. The data from the examples show that the maximum dry / wet bonding strengths reached 3.11 MPa and 1.24 MPa, respectively, which are approximately 59.5% and 79.7% higher than the unmodified adhesive (control group, dry / wet strength 1.95 MPa / 0.69 MPa).

[0012] (2) Integration of long-term mildew resistance and high-efficiency flame retardancy: HNTs-loaded CAR achieves long-term mildew resistance by destroying the integrity of microbial cell membranes (the mildew resistance period in the embodiment exceeds 30 days, while the control group becomes moldy on the second day); HNTs-loaded trimethylol phosphate (TCP) interrupts the combustion chain reaction through the gas-phase free radical capture mechanism, giving the adhesive long-lasting flame retardancy (microcalorimetry test shows that the peak heat release rate of the embodiment is about 44.3% lower than that of the control group). The combination of the two functionalized HNTs overcomes the limitations of single functional modification and achieves synergistic enhancement.

[0013] (3) Enhanced environmental friendliness: Using renewable SPI as the matrix to replace formaldehyde-based adhesives fundamentally eliminates the risk of releasing carcinogens such as formaldehyde.

[0014] (4) Controlled release of functional molecules and economic efficiency: The nano-confinement effect of HNTs is used to achieve controlled release of functional molecules, extending the effective period of the function. At the same time, the use of natural mineral HNTs as functional agent carriers reduces the cost of raw materials. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 The anti-mildew performance of soy protein adhesive in different implementation cases: uncured (left) and cured (right). DETAILED DESCRIPTION

[0015] The present invention is further described in detail below with reference to the embodiments, but the protection scope of the present invention is not limited to the embodiments. Example 1

[0016] 1. Raw materials (by mass): soy protein isolate (SPI) 10 g, deionized water 90 g, HNTs-CAR 0.5 g, HNTs-TCP 0.5 g.

[0017] Synthesis of functionalized halloysite nanotubes: (1) Acid etching modification: 12.5 g of HNTs were mixed with 200 ml of 4 mol / L hydrochloric acid and reacted in an 80°C water bath with magnetic stirring for 8 hours. After the reaction, the solid material was separated by centrifugation at 5000 rpm for 5 minutes. The product was washed with deionized water until neutral and dried in a vacuum at 80°C for 12 hours. (2) Silane coupling agent grafting: 6 g of acid-etched HNTs were dispersed in 200 ml of a mixture of ethanol and deionized water (volume ratio 4:1) and ultrasonically treated for 30 min. 16 ml of silane coupling agent KH560 was added and the mixture was refluxed at 100°C for 20 h under magnetic stirring. The residual coupling agent was removed by washing with ethanol and then dried in a vacuum at 90°C for 12 h.

[0018] (3) Loading of functional agent: HNTs-CAR: The product from step (2) was mixed with CAR at a mass-to-volume ratio of 1:10 (g / mL). The mixture was ultrasonically treated in an ice bath for 30 minutes. The mixture was then subjected to a vacuum-to-normal pressure cycle with a vacuum of -0.1 MPa maintained for 30 minutes before returning to normal pressure. This cycle was repeated twice. The mixture was centrifuged at 5000 rpm for 5 minutes to separate the solid phase. The solid phase was then washed with ethanol to remove surface adsorbents and freeze-dried in a vacuum for 12 hours.

[0019] HNTs-TCP: The product from step (2) was mixed with TCP at a mass-to-volume ratio of 1:10 (g / mL). The mixture was ultrasonically treated in an ice bath for 30 minutes. The mixture was then subjected to a vacuum-to-normal pressure cycle, maintained at -0.1 MPa for 30 minutes, and then returned to normal pressure. This cycle was repeated twice. The solid phase was separated by centrifugation at 5000 rpm for 5 minutes. The solid phase was washed with ethanol to remove surface adsorbents and dried at 100°C for 12 hours.

[0020] 2. Adhesive Preparation: Mix 10 g of SPI with 90 g of deionized water and stir at room temperature for 30 minutes. Add the prepared HNTs-CAR (0.5 g) and HNTs-TCP (0.5 g) and continue stirring for 30 minutes until uniformly dispersed to prepare a multifunctional SPI adhesive (the total amount of functionalized HNTs added is 1 wt%). Example 2

[0021] The preparation method was the same as that in Example 1, except that the raw material amounts were: 10 g SPI, 90 g deionized water, 1.0 g HNTs-CAR, and 1.0 g HNTs-TCP (the total amount of functionalized HNTs added was 2 wt%). Example 3

[0022] The preparation method was the same as that in Example 1, except for the amounts of raw materials: 10 g SPI, 90 g deionized water, 1.5 g HNTs-CAR, and 1.5 g HNTs-TCP (the total amount of functionalized HNTs added was 3 wt%). Example 4

[0023] The preparation method was the same as that in Example 1, except for the amounts of raw materials: SPI 10 g, deionized water 90 g, HNTs-CAR 2.0 g, HNTs-TCP 2.0 g (total addition amount of functionalized HNTs 4 wt %).

[0024] Example 5 Control group The preparation method is the same as that of Example 1, except that HNTs-CAR and HNTs-TCP are not added. Performance test methods and data 1. Bonding strength test According to the testing requirements for Class II plywood in Section 4.17 of GB / T 17657-2022, "Test Methods for Physical and Chemical Properties of Wood-Based Panels and Faced Wood-Based Panels," plywood specimens measuring 25 mm × 100 mm were prepared. Grooves were cut along the core thickness, with the groove depth not exceeding two-thirds of the core thickness. Half of the specimen was placed in a constant-temperature water bath at 63±2°C for 3 hours, then removed and allowed to stand at room temperature for 10 minutes to allow thermal equilibrium. Dry and wet bond strength measurements were performed on six parallel sets of specimens using a universal mechanical testing machine.

[0025] The detected performance indicators are shown in Table 1.

[0026] Table 1 Dry and wet bonding strength data of HNTs-CAR / TCP modified SPI adhesive Test Group Dry bonding strength (MPa) Wet bond strength (MPa) Example 1 2.47 0.93 Example 2 2.76 1.11 Example 3 3.11 1.24 Example 4 2.50 1.08 control group 1.95 0.69 (2) Anti-mildew test 15 g of adhesive sample was placed in a culture dish, which was placed in a constant temperature and humidity chamber at 28 ± 2°C and 80 ± 2% relative humidity. 2 ml of deionized water was added to the adhesive to simulate a high humidity environment. The moldy state was observed and recorded daily. Figure 1 As shown (the control group showed mildew on the second day, while the samples in each example showed no obvious mildew during the observation period (>30 days)).

[0027] (3) Flame retardancy test The flame retardancy of the SPI adhesive was determined using a microcalorimeter. The sample was heated at a rate of 1°C / min over a temperature range of 120-700°C to measure heat release parameters. The test results are shown in Table 2.

[0028] Table 2 Micro-combustion calorimetry data of HNTs-CAR / TCP modified SPI adhesive Test items Peak heat release rate (W / g) Total heat release rate (kJ / g) Peak temperature (℃) control group 430.3 43.9 318.8 Example 3 239.7 40.6 348.4 The halloysite nanotube-modified multifunctional soy protein adhesive provided by this invention utilizes carvacrol (CAR) and tricresyl phosphate (TCP) functional agents synergistically loaded onto a HNT carrier modified by acid etching and silane coupling. This successful preparation demonstrates high bond strength, excellent water resistance, long-lasting mildew resistance (>30 days), high flame retardancy (peak heat release rate reduced by approximately 44.3%), and environmental friendliness. Its performance significantly outperforms that of unmodified SPI adhesives, meeting the high strength, durability, safety, and environmental requirements of the wood-based panel industry. It provides an effective, green alternative to traditional formaldehyde-based adhesives.

Claims

1. A multifunctional soybean protein adhesive and a preparation method thereof, characterized in that: The following steps are involved: 10 g of soy protein isolate (SPI) and 90 g of deionized water were placed in a 250 mL beaker and mechanically stirred at 500 rpm at 25±1°C for 30 min. During the stirring process, different mass fractions of surface-modified halloysite nanotubes loaded with functional agents were added. Stirring was continued for 30 min until uniform dispersion was achieved to prepare the modified soy protein adhesive.

2. The preparation method according to claim 1, wherein: The preparation method of the surface-modified halloysite nanotubes comprises the following steps: (1) acid etching: treating halloysite nanotubes (HNTs) with hydrochloric acid, heating in a water bath and magnetically stirring, centrifuging to separate solid matter, washing and drying; (2) silane coupling agent grafting: dispersing the acid-etched modified HNTs obtained in step (1) in an ethanol-water mixture, adding a silane coupling agent after ultrasonic treatment, and performing a reflux reaction under magnetic stirring. After the reaction is completed, washing with ethanol and vacuum drying are performed.

3. The preparation method according to claim 1, wherein: The preparation method of surface-modified halloysite nanotubes loaded with functional agents comprises the following steps: mixing the surface-modified halloysite nanotubes with the corresponding liquid of the functional agent, ultrasonically treating the nanotubes in an ice bath, performing a vacuum suction cycle, centrifuging and separating the solid phase, washing, and then drying; wherein the functional agent is loaded into the lumen of the halloysite nanotubes by a vacuum negative pressure method.

4. The preparation method according to claim 1 or 3, characterized in that: The functional agent loaded in the HNTs lumen is carvacrol or tricresyl phosphate.

5. The preparation method according to claim 1, wherein: The addition amount of the surface-modified HNTs loaded with the functional agent is 1 wt% to 4 wt% of the mass of the SPI adhesive.

6. The preparation method according to claim 2, wherein: The concentration of hydrochloric acid used in the acid etching in step (1) is 4 mol / L; the silane coupling agent in step (2) is 3-glycidyloxypropyltrimethoxysilane.

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