Environment-friendly starch type solid gum and preparation method thereof

Abstract

The invention relates to the technical field of adhesives, and discloses environment-friendly starch type solid gum and a preparation method thereof.The environment-friendly starch type solid gum is composed of, by weight, 50-65 parts of modified starch sodium with the carboxypropyl substitution degree being 0.25-0.45; 8 to 18 parts of chitosan with a degree of deacetylation of 85 to 95% and a molecular weight of 80000 to 150000 Da; 0.5 to 1.2 parts of a monovalent salt ion strength regulator; 8-15 parts of a glycerin plasticizer; 0.2 to 1.5 parts of a composite antibacterial agent; 15 to 25 parts of deionized water; by selecting modified starch sodium with a specific substitution degree and chitosan with a high deacetylation degree, matching with a composite antibacterial agent and a nano-zinc oxide modification technology and combining with optimized preparation steps, the core properties such as initial adhesion strength, peel strength, thermal aging stability and rewetting adhesion force of the product are obviously improved, the coating and drying time is shorter, and the product has a good application prospect. The bonding requirements of high strength and weather resistance are met.

Description

Technical Field

[0001] The invention relates to the technical field of adhesives, in particular to an environmentally friendly starch-type solid glue and a preparation method thereof. Background Art

[0002] Traditional solid adhesives, primarily made from polyvinyl alcohol, polyacrylate, or thermoplastic resins, possess considerable mechanical strength and adhesive properties. However, these raw materials are often derived from petrochemicals, making them difficult to degrade, and some contain volatile organic compounds (VOCs), posing potential hazards to the environment and human health. In recent years, natural polymers such as starch have become a hot topic in solid adhesive research due to their renewable and biodegradable properties. However, currently available environmentally friendly starch adhesives often suffer from the following issues: insufficient bonding strength, especially on non-paper surfaces; susceptibility to moisture absorption, cracking, or oil-water separation during storage; and poor film-forming and aging resistance. Summary of the Invention

[0003] In view of the shortcomings of the existing technology, the present invention provides an environmentally friendly starch-based solid glue and a preparation method thereof, which solves the technical problems of low performance and poor stability of traditional starch-based adhesives.

[0004] To achieve the above object, the present invention provides the following technical solution: an environmentally friendly starch-based solid glue, comprising the following components in parts by weight: Modified sodium starch with a carboxypropyl substitution degree of 0.25-0.45: 50-65 parts (made by reacting corn starch with sodium acryloyloxypropane sulfonate); Chitosan with a degree of deacetylation of 85-95% and a molecular weight of 80,000-150,000 Da: 8-18 parts; Monovalent salt ionic strength regulator: 0.5-1.2 parts (selected from NaCl); Glycerol plasticizer: 8-15 parts; Composite antibacterial agent: 0.2-1.5 parts; Deionized water: 15-25 parts.

[0005] Preferably, the preparation steps of the modified sodium starch include: Step (1) 100 parts of corn starch and 100 parts of deionized water were mixed and stirred at room temperature and 200 rpm for 30 minutes; Step (2) adding 10% NaOH solution dropwise to adjust the pH to 11-12; Step (3) adding 8-10 parts of sodium acryloyloxypropane sulfonate and keeping the temperature in a water bath at 55°C; Step (4) adding 0.5 parts of potassium persulfate at a rate of 0.1 g / min and reacting for 60 min; Step (5) After cooling, neutralize with hydrochloric acid to pH 7.0, filter, and vacuum dry at 60°C; The modified sodium starch obtained by grinding through a 200-mesh sieve in step (6) has a gelatinization temperature of ≤65°C.

[0006] Preferably, the surface of the nano zinc oxide is modified with a silane coupling agent KH-550, and the amount of the modifier added is 1.5-2.0% of the mass of the nano zinc oxide.

[0007] Preferably, the composite antibacterial agent is a compound system of potassium sorbate and nano zinc oxide, with a mass ratio of 1:1-1:1.5, and a particle size of the nano zinc oxide is 30-50 nm.

[0008] A method for preparing an environmentally friendly starch-based solid glue comprises the following steps: Step a: Starch gelatinization: Modified sodium starch was added to deionized water and mechanically stirred at 400 rpm in a 70°C water bath for 40 min until the slurry transmittance was >90% (λ=600 nm); Step b: Plasticizing system construction: add glycerol and monovalent salt, maintain the temperature at 65°C, and continue stirring for 10 minutes; Step c: gradient incorporation of chitosan; Step d: Antibacterial enhancement: adding composite antibacterial agent and ultrasonic dispersion (40kHz, 10min); Step e: vacuum concentration: transfer to a vacuum evaporator and concentrate at 60°C and -0.08 MPa to a water content of 20±2%; Step f: Molding and aging: inject the concentrated colloid into a polytetrafluoroethylene mold, extrude it into strips under a pressure of 5 MPa, and let it stand at 25° C. in the dark for 24 hours.

[0009] Preferably, the chitosan presol in step (3) needs to be prepared and used immediately, and the storage time after preparation is ≤2h, and the concentration of the acetic acid solution is controlled at 0.48-0.52%.

[0010] Preferably, the moisture content in step (5) is controlled by real-time monitoring: when the moisture content drops to 22%, the vacuum degree is adjusted to -0.05 MPa, and the concentration is terminated when the moisture content reaches 20%.

[0011] Preferably, the mold in step (6) has a micro-tapered structure, a demoulding slope ≥ 5°, and an inner wall roughness Ra ≤ 0.2 μm.

[0012] Preferably, the chitosan gradient incorporation in step c specifically comprises the following steps: Step c1: dissolving chitosan in 0.5% acetic acid solution to prepare a 3 wt% presol; Step c2: Control the system temperature to ≤50°C and add the presol at a rate of 0.5 mL / min; After the addition in step c3 was completed, the mixture was stirred at 500 rpm for 20 min.

[0013] Compared with the existing technology, the present invention provides an environmentally friendly starch-based solid glue and a preparation method thereof, which has the following beneficial effects: by selecting modified starch sodium with a specific degree of substitution and high deacetylation degree chitosan, combined with composite antibacterial agents and nano-zinc oxide modification technology, and combining optimized preparation steps, the product has significantly improved core properties such as initial adhesion strength, peel strength, thermal aging stability, and rewetting adhesion, and the coating drying time is shorter, meeting the requirements of high-strength and weather-resistant bonding.

[0014] Using naturally degradable starch and chitosan as the main raw materials, the use of petrochemical-based adhesives is reduced, thus lowering environmental pollution. The use of composite antimicrobial agents avoids the toxicity risk of traditional preservatives, and the product can be naturally decomposed after disposal, which is in line with the concept of sustainable development.

[0015] Innovative preparation processes, such as precise control of starch gelatinization, gradient incorporation of chitosan, and real-time monitoring of moisture during vacuum concentration, ensure stable product quality, effectively avoid problems such as colloid agglomeration and uneven dispersion, improve production efficiency and yield, and provide a reliable solution for industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is a TEM image of the microstructure of the product prepared in Example 1 of the present invention.

[0017] Figure 2 The figure is a bar chart showing the test results of the initial adhesion strength of the embodiments of the present invention and the comparative examples. DETAILED DESCRIPTION

[0018] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0019] Figure 1 Figure a in the middle represents chitosan aggregates (scale bar 5 μm), which were obtained by the following method: Sample preparation: Chitosan solution (0.5% w / v) was diluted and centrifuged to remove acetic acid, then resuspended and dropped onto a carbon-coated copper grid and allowed to dry naturally. TEM instrument model: JEOL JEM-2100, accelerating voltage: 120 kV, magnification: 10,000x-15,000x, imaging mode: bright field, sample staining: unstained (natural contrast) or lightly negatively stained with 1% phosphotungstic acid; Figure 1 b is the colloidal nanofiber network of the present invention (scale 500 nm), which is obtained by the following method: Sample preparation: The concentrated colloidal mixture was diluted 100-fold by freezing → dispersed by ultrasonication for 10 min → added dropwise to a carbon film grid → dried at room temperature. TEM instrument model: FEITecnai G2 Spirit, accelerating voltage: 120–200 kV (200 kV is recommended for nanoscale observation), magnification: 50,000x-80,000x, imaging mode: Bright-field, sample staining: no staining or very low concentration uranyl acetate staining for contrast enhancement (optional).

[0020] Initial adhesion strength test: refer to GB / T4852-2002 "Test method for initial adhesion of pressure-sensitive adhesive tapes (rolling ball method)", and combine with the relevant requirements for initial adhesion test in GB / T2790-1995 "Test method for 180° peel strength of adhesives - Flexible materials to rigid materials".

[0021] Peel strength test: The test is conducted in accordance with GB / T2790-1995 "Adhesive 180° Peel Strength Test Method - Flexible Material to Rigid Material" to ensure that the test conditions are consistent with the standard requirements.

[0022] Coating drying time test: Refer to the drying time test method in QB / T2859-2007 "Solid Glue", and make appropriate adjustments based on the actual application scenario.

[0023] Thermal aging stability test: According to the relevant provisions of thermal aging test in GB / T13936-1992 "Determination of tensile shear strength of bonds between vulcanized rubber and metal", the strength retention rate is tested after aging at 80°C for 24 hours.

[0024] Rewetting Adhesion Test: There is currently no national standard. This test method is formulated with reference to common industry methods and in combination with product characteristics to ensure that the test results can accurately reflect the adhesive performance of the product after rewetting.

[0025] Initial adhesion strength test Test equipment: initial adhesion tester (rolling ball method), steel ball (diameter 1 / 32 inch to 1 inch, in line with standard requirements), test platform (level and smooth).

[0026] Sample preparation: evenly coat the solid glue on a standard paper with a size of 25 mm × 100 mm, with a coating thickness of 0.1 mm and a coating area of ​​25 mm × 50 mm, and place it in an environment with a temperature of 23 ± 2 ° C and a relative humidity of 50 ± 5% for 24 hours.

[0027] Test steps: Fix the prepared sample on the test platform with the adhesive surface facing up and kept horizontal. Select a steel ball of appropriate diameter and allow it to roll freely down the inclined track, stopping after rolling over the adhesive surface. Record the maximum distance the steel ball rolls on the adhesive surface. Test each sample 5 times and take the average value. Determine the sample's initial adhesion strength grade according to the rating standards in GB / T4852-2002 and convert it into N / cm 2 unit.

[0028] Peel strength test Testing equipment: electronic universal material testing machine, fixture (suitable for paper and rigid materials), standard steel plate (size 100mm×25mm×2mm).

[0029] Sample preparation: Apply solid glue evenly on standard paper of size 25mm×150mm, with a coating thickness of 0.1mm and a coating area of ​​25mm×100mm. Immediately laminate the coated paper onto a standard steel plate, using a 2kg roller to roll back and forth on the laminated surface three times to ensure a tight fit. Place the paper in an environment with a temperature of 23±2℃ and a relative humidity of 50±5% for 24 hours.

[0030] Test Procedure: Mount the prepared sample in the fixture of an electronic universal testing machine, aligning the paper with the steel plate at a 180° angle. Stretch the sample at a rate of 100 mm / min, recording the maximum tensile force. Test each sample five times, taking the average value, and calculate the peel strength (in N / cm) according to the formula in GB / T 2790-1995.

[0031] Coating drying time test Test equipment: constant temperature and humidity chamber, stopwatch, standard coating rod.

[0032] Test Procedure: At a temperature of 23±2°C and a relative humidity of 50±5%, apply solid adhesive evenly to a standard paper sheet measuring 100mm x 100mm using a standard coating rod to a coating thickness of 0.2mm. Immediately after coating, begin timing. Gently touch the adhesive surface with a clean finger every 30 seconds until the finger is free of adhesive. Record the time. Test each sample three times, and take the average value (in minutes).

[0033] Thermal aging stability test Testing equipment: high temperature aging chamber, electronic universal material testing machine.

[0034] Sample preparation: Prepare samples according to the peel strength test method. Prepare two groups of each sample, one group as the test sample before aging, and the other group as the test sample after aging.

[0035] Test steps: Place the aged test sample in a high-temperature aging chamber and age at 80°C for 24 hours. Remove and place in an environment with a temperature of 23±2°C and a relative humidity of 50±5% for 2 hours to allow it to return to room temperature. Test the peel strength of the sample before and after aging using the peel strength test method. Calculate the strength retention rate after thermal aging using the formula: Strength retention rate (%) = (peel strength after aging / peel strength before aging) × 100%. Test each sample five times and calculate the average value.

[0036] Rewetting Adhesion Test Testing equipment: electronic universal material testing machine, constant temperature water bath, standard paper.

[0037] Sample preparation: evenly apply the solid glue on a standard paper with a size of 25mm×100mm, with a coating thickness of 0.1mm and a coating area of ​​25mm×50mm. Place it in an environment with a temperature of 23±2℃ and a relative humidity of 50±5% for 24 hours to allow it to dry completely.

[0038] Test steps: Place the prepared sample adhesive side up on a constant temperature water bath and evenly spray distilled water with a sprayer to fully wet the adhesive surface. Immediately cover the wet adhesive surface with another piece of standard paper and use a 2kg roller to roll back and forth on the bonding surface three times to ensure a tight bond. Place the sample in an environment with a temperature of 23±2°C and a relative humidity of 50±5% for 1 hour. Test the peel strength after rewetting according to the peel strength test method. Each sample is tested 5 times and the average value is calculated in N / cm. 2 .

[0039] Modified sodium starch preparation equipment Agitator: Models such as JJ-1 precision power-boosting electric agitator have a speed range of 0-2000rpm, which can meet the stirring requirement of 200rpm when mixing corn starch and deionized water to ensure uniform mixing.

[0040] pH meter: Such as Leici PHS-3C precision pH meter, with a measurement accuracy of ±0.01pH, used to accurately adjust the pH of the reaction system to 11-12.

[0041] Constant temperature water bath: Model HH-S4 digital display constant temperature water bath, temperature control accuracy ±0.5℃, can stably maintain a reaction temperature of 55℃.

[0042] Vacuum drying oven: DZF-6050 vacuum drying oven, temperature control range is room temperature + 5℃-250℃, vacuum degree can reach -0.1MPa, meeting the vacuum drying requirements of 60℃.

[0043] Pulverizer: FW100 high-speed universal pulverizer, which can pulverize the dried product until it passes through a 200-mesh sieve.

[0044] Solid glue preparation equipment Water bath stirring pot: DF-101S heat-collecting constant temperature magnetic stirrer, which can achieve 70℃ water bath and 400rpm mechanical stirring to meet the starch gelatinization conditions.

[0045] Vacuum evaporator: RE-52AA rotary evaporator, operating temperature range room temperature -99 ° C, vacuum degree can reach 0.098 MPa, used for vacuum concentration operations at 60 ° C and -0.08 MPa.

[0046] Mould: Customized polytetrafluoroethylene mould with micro-taper structure, demoulding slope ≥5°, inner wall roughness Ra≤0.2μm, made of custom-made polytetrafluoroethylene rod through precision machining.

[0047] Pressure molding machine: Models such as YH-400T hydraulic press, with a maximum pressure of 5MPa, are used to extrude concentrated colloids into shape.

[0048] Ultrasonic disperser: KQ-500DE CNC ultrasonic cleaner, frequency 40kHz, used for ultrasonic dispersion of composite antibacterial agents.

[0049] Example 1 An environmentally friendly starch-based solid glue and its preparation method, comprising 50 parts of modified sodium starch with a carboxypropyl substitution degree of 0.25, prepared by reacting corn starch with sodium acryloxypropane sulfonate according to a specific process. It is also combined with 8 parts of chitosan with a deacetylation degree of 85% and a molecular weight in the range of 80,000-150,000 Da, 0.5 parts of NaCl as a monovalent salt ion strength regulator, and 8 parts of glycerol as a plasticizer. It is also combined with 0.2 parts of a composite antibacterial agent, wherein the mass ratio of potassium sorbate to nano-zinc oxide is 1:1, the nano-zinc oxide particle size is between 30-50 nm and is modified with a silane coupling agent KH-550, and the amount of modifier added is 1.5-2.0% of the mass of the nano-zinc oxide. Finally, 25 parts of deionized water are added.

[0050] Starch gelatinization: Add corresponding parts of modified sodium starch into deionized water and stir mechanically at 400 rpm in a 70°C water bath for 40 min until the slurry transmittance is greater than 90% (λ=600 nm).

[0051] Plasticizing system construction: Add corresponding parts of glycerol and NaCl, maintain the temperature at 65°C, and continue stirring for 10 minutes.

[0052] Chitosan gradient incorporation: Dissolve the corresponding amount of chitosan in 0.5% acetic acid solution to prepare a 3wt% presol; control the system temperature to ≤50°C and add the presol at a rate of 0.5mL / min; stir at 500rpm for 20min after the addition is completed.

[0053] Antibacterial enhancement: Add corresponding parts of composite antibacterial agent and perform ultrasonic dispersion (40kHz, 10min). The nano zinc oxide in comparative example 4 is not modified, and the rest of the operations are the same as those in the embodiment.

[0054] Vacuum concentration: Transfer the mixed liquid to a vacuum evaporator and concentrate at 60°C and -0.08 MPa. When the moisture content drops to 22%, adjust the vacuum degree to -0.05 MPa and stop the concentration when the moisture content reaches 20%.

[0055] Molding and aging: Inject the concentrated colloid into a polytetrafluoroethylene mold with a micro-tapered structure (demolding slope ≥5°, inner wall roughness Ra ≤0.2μm), extrude it into strips under a pressure of 5MPa, and let it stand at 25℃ in the dark for 24h.

[0056] Example 2 An environmentally friendly starch-based solid glue and a preparation method thereof. The environmentally friendly starch-based solid glue is mainly composed of 65 parts of modified sodium starch with a carboxypropyl substitution degree of 0.45. It is also combined with 18 parts of chitosan with a deacetylation degree of 95% and a molecular weight of 80,000-150,000 Da, 1.2 parts of NaCl, and 15 parts of glycerol plasticizer. A composite antibacterial agent is added in an amount of 1.5 parts, wherein the mass ratio of potassium sorbate to nano-zinc oxide is 1:1.5. In addition, 15 parts of deionized water are added. The other steps are the same as those in Example 1.

[0057] Example 3 An environmentally friendly starch-based solid glue and a preparation method thereof. The environmentally friendly starch-based solid glue comprises 57 parts of modified sodium starch with a carboxypropyl substitution degree of 0.35, 13 parts of chitosan with a deacetylation degree of 90% and an appropriate molecular weight, 0.85 parts of NaCl, 11.5 parts of glycerol plasticizer, 0.85 parts of a composite antibacterial agent, wherein the mass ratio of potassium sorbate to nano-zinc oxide is 1:1.25, and 20 parts of deionized water are added. The other steps are the same as those in Example 1.

[0058] Example 4 An environmentally friendly starch-based solid glue and a preparation method thereof. The environmentally friendly starch-based solid glue comprises 52 parts of modified sodium starch with a carboxypropyl substitution degree of 0.28, 10 parts of chitosan with a deacetylation degree of 87%, 0.6 parts of NaCl, 9 parts of glycerol, 0.3 parts of a composite antibacterial agent (potassium sorbate and nano-zinc oxide in a mass ratio of 1:1.1), and 23 parts of deionized water. Other steps are the same as those in Example 1.

[0059] Example 5 An environmentally friendly starch-based solid glue and a preparation method thereof. The environmentally friendly starch-based solid glue comprises 62 parts of modified sodium starch with a carboxypropyl substitution degree of 0.42, 16 parts of chitosan with a deacetylation degree of 93%, 1.0 part of NaCl, 13 parts of glycerol, 1.2 parts of a composite antibacterial agent (potassium sorbate and nano-zinc oxide in a mass ratio of 1:1.4) and 17 parts of deionized water. Other steps are the same as those in Example 1.

[0060] Comparative Example 1 The solid glue was prepared using 57 parts corn starch (without modified sodium starch), 13 parts chitosan with a 90% deacetylation degree and a molecular weight of 80,000-150,000 Da, 0.85 parts NaCl, 11.5 parts glycerol as a plasticizer, 0.85 parts of a composite antimicrobial agent (potassium sorbate to nano-zinc oxide in a mass ratio of 1:1.25), and 20 parts of deionized water. Unlike the example above, the starch was not modified. Other steps were the same as in Example 1.

[0061] Comparative Example 2 The solid gelatin contained 57 parts of modified sodium starch glycolate with a carboxypropyl substitution degree of 0.35, 13 parts of chitosan with a deacetylation degree of 75%, 0.85 parts of NaCl, 11.5 parts of glycerol, 0.85 parts of a composite antimicrobial agent (potassium sorbate and nano-zinc oxide in a mass ratio of 1:1.25), and 20 parts of deionized water. This comparative example primarily varied the deacetylation degree of the chitosan; the remaining steps were the same as in Example 1.

[0062] Comparative Example 3 The solid glue is composed of 57 parts of modified sodium starch with a carboxypropyl substitution degree of 0.35, 13 parts of chitosan with a deacetylation degree of 90%, 0.85 parts of NaCl, 11.5 parts of glycerol and 20 parts of deionized water, without adding a composite antibacterial agent. The other steps are the same as those in Example 1.

[0063] Comparative Example 4 The solid gelatin comprises 57 parts of modified sodium starch with a carboxypropyl substitution degree of 0.35, 13 parts of chitosan with a deacetylation degree of 90%, 0.85 parts of NaCl, 11.5 parts of glycerol, 0.85 parts of a composite antibacterial agent (a mass ratio of potassium sorbate to nano-zinc oxide of 1:1.25) and 20 parts of deionized water, wherein the nano-zinc oxide is not modified with a silane coupling agent KH-550. Other steps are the same as those in Example 1.

[0064] Comparative Example 5 The solid gelatin formulation was the same as that of Example 3, consisting of 57 parts of modified sodium starch glycolate with a degree of carboxypropyl substitution of 0.35, 13 parts of chitosan with a degree of deacetylation of 90%, 0.85 parts of NaCl, 11.5 parts of glycerol, 0.85 parts of a composite antimicrobial agent (potassium sorbate to nano-zinc oxide in a mass ratio of 1:1.25), and 20 parts of deionized water. However, the preparation process employed a conventional concentration method, without vacuum and moisture monitoring. Other steps were the same as those of Example 1.

[0065] Comparative Example 6: Common starch solid glue on the market was selected, and the specific ingredients are shown in Table 1.

[0066] Table 1 Composition of Comparative Example 6 The physical properties of the products of the examples and comparative examples were tested, including the initial adhesion strength (N / cm 2 ), peel strength (N / cm), coating drying time (min), thermal aging stability (80℃, strength retention after 24h) and rewetting adhesion (N / cm 2 ), the specific test results are shown in Table 2 and Table 3, Figure 2 .

[0067] Table 2 Test results of initial adhesion strength, peel strength and coating drying time Initial adhesion strength (N / cm2) Peel strength (N / cm) Coating drying time (min) Example 1 12.8 8.5 14 Example 2 15.2 9.8 11 Example 3 14.1 9.1 12 Example 4 13.2 8.7 13 Example 5 14.8 9.4 12 Comparative Example 1 8.7 5.5 19 Comparative Example 2 10.6 7.2 17 Comparative Example 3 11.8 7.8 15 Comparative Example 4 12.3 8.1 14 Comparative Example 5 12.5 8.3 15 Comparative Example 6 7.5 4.8 22 Table 3 Test results of thermal aging stability and rewetting adhesion Heat aging stability (80℃, strength retention after 24h) Rewetting adhesion (N / cm2) Example 1 0.89 10.6 Example 2 0.93 12.5 Example 3 0.91 11.6 Example 4 0.9 11 Example 5 0.92 12 Comparative Example 1 0.72 6.8 Comparative Example 2 0.82 8.5 Comparative Example 3 0.86 9.2 Comparative Example 4 0.87 9.8 Comparative Example 5 0.88 9.6 Comparative Example 6 0.68 5.5 Comparing the test data of the Examples with that of Comparative Example 1 (which used corn starch directly instead of modified sodium starch), Examples 1 to 5 all showed superior initial adhesion and peel strength to the comparative example. This demonstrates that the modified sodium starch with carboxypropyl groups, introduced through the reaction of corn starch with sodium acryloxypropane sulfonate, increases the polarity and reactivity of the starch molecules, enhancing their interaction with the adherend surface and significantly improving the initial adhesion and peel strength of the solid adhesive. Furthermore, the modified sodium starch's lower gelatinization temperature (≤65°C) facilitates the formation of a more uniform colloid during the subsequent preparation process, ensuring product performance.

[0068] In Comparative Example 2, the chitosan deacetylation degree is 75%, and its initial adhesive strength is 10.6N / cm 2 , the peel strength is 7.2N / cm, which is lower than 14.1N / cm of Example 3 (chitosan deacetylation degree 90%). 2 The chitosan with a deacetylation degree of 85-95% in the present invention has a high amino content, which can form more hydrogen bonds and ionic bonds with other components such as modified sodium starch, thereby strengthening the cross-linking structure within the colloid. This not only increases the bonding strength, but also improves the toughness and stability of the colloid, resulting in better thermal aging stability and rewetting adhesion of the solid glue.

[0069] Comparative Example 3, which did not include a composite antimicrobial agent, exhibited lower thermal aging stability than Example 3. The present invention utilizes a composite antimicrobial agent formulated with potassium sorbate and nano-zinc oxide. Potassium sorbate can destroy microbial cell membranes and inhibit enzyme activity. The synergistic effect of the two broadens the antimicrobial spectrum and prolongs the antimicrobial duration, effectively preventing the solid colloid from deteriorating due to microbial action during storage and use, thereby ensuring the product's thermal aging stability and long-term performance. Furthermore, the reasonable mass ratio and nano-zinc oxide particle size ensure uniform dispersion and high efficacy of the antimicrobial agent in the colloid.

[0070] The nano-zinc oxide in Comparative Example 4, which was not modified with the silane coupling agent KH-550, had a lower initial adhesion strength than that of Example 3. The modified nano-zinc oxide, with its surface grafted with organic groups, improved its dispersibility in the colloid, preventing agglomeration and enabling better interaction with other components, enhancing the overall performance of the colloid. This not only increased bonding strength but also had a positive impact on thermal aging stability and rewetting adhesion.

[0071] Strict control of starch gelatinization conditions (70°C water bath, 400 rpm mechanical stirring for 40 minutes, until the slurry transmittance exceeds 90%) ensures that the modified sodium starch fully absorbs water and expands, forming a uniform and stable colloid, laying a good foundation for the addition and mixing of subsequent components. When constructing the plasticizing system, glycerol and monovalent salt are added at 65°C and stirred for 10 minutes to allow the glycerol to fully penetrate the starch molecules, reducing intermolecular forces and improving the flexibility and plasticity of the colloid. Test data shows that the coating drying time of the examples is significantly shorter than that of some comparative examples, and the overall colloid performance is superior.

[0072] A chitosan gradient incorporation method was used. Chitosan was first dissolved in 0.5% acetic acid solution to form a 3wt% presol. The chitosan was then added dropwise at a low temperature (≤50°C) and a slow rate (0.5mL / min) with stirring. This prevented chitosan from clumping, ensuring its uniform dispersion in the colloid and allowing it to fully react with other components to form a stable network structure. The comparative example did not adopt this method, resulting in uneven chitosan dispersion and affecting colloid performance. For example, the bonding strength of Comparative Example 2 was lower than that of Example 3.

[0073] During the vacuum concentration process, the moisture content is monitored in real time, and the vacuum level is adjusted according to moisture changes. This allows precise control of the moisture content, avoiding the adverse effects of excessive or insufficient moisture on the colloid's properties and ensuring the colloid has the appropriate consistency and hardness. During molding and maturation, the polytetrafluoroethylene mold's slightly tapered structure and low roughness ensure the colloid's molding quality. Standing at 25°C in the dark for 24 hours further stabilizes the colloid structure, improving the product's mechanical properties and appearance. Compared to Example 5, the embodiment exhibits significant advantages in all performance indicators.

[0074] In summary, the present invention significantly improves the initial adhesion strength, peel strength, coating drying time, thermal aging stability and rewetting adhesion of the environmentally friendly starch-based solid glue through the rational selection and precise ratio of specific ingredients, as well as the optimization and improvement of the preparation steps. Compared with the starch solid glue purchased on the market, it shows obvious advantages in all aspects of performance.

[0075] The above are only specific embodiments of the present invention, but the technical features of the present invention are not limited thereto. Any simple changes, equivalent substitutions, or modifications based on the present invention to solve substantially the same technical problems and achieve substantially the same technical effects are all included in the scope of protection of the present invention.

Claims

1. An environmentally friendly starch-based solid glue, characterized by: It is composed of the following components in parts by weight: 50-65 parts of modified sodium starch with a degree of carboxypropyl substitution of 0.25-0.45, prepared by reacting corn starch with sodium acryloyloxypropane sulfonate; Chitosan with a degree of deacetylation of 85-95% and a molecular weight of 80,000-150,000 Da: 8-18 parts; Monovalent salt ionic strength regulator: 0.5-1.2 parts, selected from NaCl; Glycerol plasticizer: 8-15 parts; Composite antibacterial agent: 0.2-1.5 parts; Deionized water: 15-25 parts.

2. The environmentally friendly starch-based solid glue according to claim 1, characterized in that: The preparation steps of the modified starch sodium include: Step (1) 100 parts of corn starch and 100 parts of deionized water were mixed and stirred at room temperature and 200 rpm for 30 minutes; Step (2) adding 10% NaOH solution dropwise to adjust the pH to 11-12; Step (3) adding 8-10 parts of sodium acryloyloxypropane sulfonate and keeping the temperature in a water bath at 55°C; Step (4) adding 0.5 parts of potassium persulfate at a rate of 0.1 g / min and reacting for 60 min; Step (5) After cooling, neutralize with hydrochloric acid to pH 7.0, filter, and vacuum dry at 60°C; The modified sodium starch obtained by grinding through a 200-mesh sieve in step (6) has a gelatinization temperature of ≤65°C.

3. The environmentally friendly starch-based solid glue according to claim 1, characterized in that: The surface of the nano zinc oxide is modified by a silane coupling agent KH-550, and the amount of the modifier added is 1.5-2.0% of the mass of the nano zinc oxide.

4. The environmentally friendly starch-based solid glue according to claim 1, characterized in that: The composite antibacterial agent is a compound system of potassium sorbate and nano zinc oxide, the mass ratio of the two is 1:1-1:1.5, and the particle size of the nano zinc oxide is 30-50nm.

5. A method for preparing the environmentally friendly starch-based solid glue according to any one of claims 1 to 4, characterized in that: The following steps are involved: Step a: Starch gelatinization: Modified sodium starch was added to deionized water and mechanically stirred at 400 rpm in a 70°C water bath for 40 minutes until the slurry transmittance was greater than 90%; Step b: Plasticizing system construction: add glycerol and monovalent salt, maintain the temperature at 65°C, and continue stirring for 10 minutes; Step c: gradient incorporation of chitosan; Step d: Antibacterial enhancement: adding a composite antibacterial agent and ultrasonically dispersing; Step e: vacuum concentration: transfer to a vacuum evaporator and concentrate at 60°C and -0.08 MPa to a water content of 20±2%; Step f: Molding and aging: inject the concentrated colloid into a polytetrafluoroethylene mold, extrude it into strips under a pressure of 5 MPa, and let it stand at 25° C. in the dark for 24 hours.

6. The method for preparing the starch-based solid glue according to claim 5, wherein: The chitosan presol in step (3) needs to be prepared and used immediately, and the storage time after preparation is ≤2h, and the concentration of the acetic acid solution is controlled at 0.48-0.52%.

7. The method for preparing the starch-based solid glue according to claim 5, wherein: The moisture content in step (5) is controlled by real-time monitoring: when the moisture content drops to 22%, the vacuum degree is adjusted to -0.05 MPa, and the concentration is terminated when the moisture content reaches 20%.

8. The method for preparing the starch-based solid glue according to claim 5, wherein: The mold in step (6) has a micro-tapered structure, a demoulding slope ≥5°, and an inner wall roughness Ra ≤0.2μm.

9. The method for preparing the starch-based solid glue according to claim 5, wherein: The chitosan gradient incorporation in step c specifically comprises the following steps: Step c1: dissolving chitosan in 0.5% acetic acid solution to prepare a 3 wt% presol; Step c2: Control the system temperature to ≤50°C and add the presol at a rate of 0.5 mL / min; After the addition in step c3 was completed, the mixture was stirred at 500 rpm for 20 min.

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