Modified starch-based water-based adhesive as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of adhesive materials, and particularly relates to a modified starch-based water-based adhesive as well as a preparation method and application thereof. According to the adhesive, oxidized corn starch is taken as a base material, hydrophobic and weather-resistant modification is realized by introducing a fluorine-silicon-containing functional monomer, and hydroxypropyl quaternized chitosan is compounded to endow antibacterial property and a film-forming enhancement effect; a borax cross-linked polyol system is supplemented to improve the cohesive strength, and a plasticizer, a thickening agent and an emulsifier are matched to optimize the rheological property and wettability. The preparation process comprises the steps of starch gelatinization, fluorosilicone urea grafting, chitosan derivative compounding, auxiliary agent blending and the like, and the process is mild, environment-friendly and non-toxic. The obtained water-based adhesive has the characteristics of strong initial adhesion, good water resistance, moderate flexibility, excellent biocompatibility and the like, and is especially suitable for adhesion and manufacturing of ball products such as basketballs, footballs and the like.

Description

Technical Field

[0001] This invention belongs to the field of adhesive materials technology, specifically relating to a modified starch-based water-based adhesive, its preparation method, and its application. Background Technology

[0002] Starch, as a readily available, inexpensive, and biodegradable natural polymer, has long been a focus of attention in the preparation of environmentally friendly water-based adhesives. Traditional water-based starch adhesives use water as the dispersion medium, offering significant advantages such as being non-toxic and releasing no volatile organic compounds, aligning with the current important directions of green chemistry and sustainable development. However, natural starch molecules possess a large number of hydrophilic hydroxyl groups, resulting in adhesives prepared directly from starch exhibiting extremely poor water resistance after drying. When exposed to humid environments or direct contact with water, the adhesive strength drops sharply or even completely disappears, severely limiting its application in applications requiring a certain level of durability. Furthermore, starch adhesive films are brittle and lack flexibility, easily cracking under repeated bending or impact; their adhesive strength, especially initial tack and final bond strength, still lags behind many synthetic polymer adhesives. These inherent defects limit the application of traditional starch-based adhesives to temporary bonding or low-value-added products with low performance requirements, making it difficult to meet the needs of industrial manufacturing, especially in applications with stringent requirements for comprehensive material performance.

[0003] Specifically, in the manufacturing of sporting goods, especially in the production of ball products such as basketballs, footballs, and volleyballs, the performance requirements for adhesives are extremely stringent. These adhesives are needed to bond different materials such as the inner bladder, lining, and outer skin. The finished ball needs to withstand cyclic stress, severe impacts, and friction generated by inflation and deflation pressure over long periods. Therefore, an ideal adhesive must not only possess high initial adhesive strength but also excellent water resistance to withstand the effects of athletes' sweat and humid environments, outstanding flexibility and fatigue resistance to accommodate ball deformation, and good anti-mildew properties to ensure hygiene and safety during long-term storage and use. Existing petroleum-based synthetic adhesives, such as some solvent-based polyurethanes, while having acceptable performance, pose risks of environmental pollution and health hazards. Ordinary water-based starch adhesives or simply modified products, due to the aforementioned fundamental problems such as poor water resistance, high brittleness, and insufficient strength, are completely unable to meet the requirements of such high-end dynamic applications. Although researchers have tried to modify starch by means such as oxidation, esterification, and etherification, or to physically mix other resins into the formulation, these improvements often only focus on improving one aspect of performance. It is difficult to achieve a synergistic improvement and balance of key indicators such as strength, water resistance, flexibility and durability, and sometimes the environmental characteristics are sacrificed.

[0004] To overcome the application bottlenecks caused by the insufficient performance of starch-based adhesives, it is urgent to develop innovative modification strategies from the molecular design level. The purpose of this invention is to deeply and synergistically chemically modify starch by introducing two newly designed functional compounds. One compound can firmly introduce hydrophobic segments with extremely low surface energy into the starch molecular network through stable chemical bonds, thereby fundamentally and significantly improving the water and moisture resistance of the adhesive film. The other compound simultaneously provides efficient cross-linking ability and inherent antibacterial and antifungal functions, constructing a strong and stable three-dimensional network structure between starch molecules, significantly enhancing the overall mechanical strength, flexibility, and durability of the adhesive. Through the synergistic effect of these two compounds, it is expected that while retaining the environmentally friendly nature of starch adhesives, their comprehensive performance will reach or even surpass the level of traditional synthetic adhesives, thus providing a truly green, efficient, and reliable bonding solution for the manufacture of high-performance sports balls such as basketballs, footballs, and volleyballs. Summary of the Invention

[0005] In view of the shortcomings of the prior art, the purpose of this invention is to provide a modified starch-based water-based adhesive, its preparation method and application.

[0006] In a first aspect, the present invention provides a method for preparing a modified starch-based waterborne adhesive, comprising the steps of: S1. By weight, add 180-220 parts of deionized water to the reactor, stir, and heat to 48-52℃; add 80-120 parts of oxidized corn starch, stir, and obtain a suspension; heat the suspension to 68-72℃ to gelatinize, cool to 58-62℃, adjust the pH to 4-5 while stirring, and add 8-12 parts of N-(perfluorohexylethyl)-N'-(3-triethoxysilylpropyl)urea dropwise to react and obtain the reaction mixture; S2. Cool the reaction mixture to 38-42℃, add 13-17 parts of hydroxypropyl quaternized chitosan, and simultaneously add 1.2-1.7 parts of borax. Adjust the pH to 5-7 and continue stirring the reaction. After the reaction is complete, cool to room temperature, and then add 18-22 parts of a mixture of glycerol and sorbitol, 2-4 parts of sodium carboxymethyl cellulose, and 0.2-0.4 parts of sodium dodecyl sulfate in sequence. Stir at room temperature and filter.

[0007] In this invention, the overall construction of the modified starch-based waterborne adhesive incorporates multiple synergistic reaction mechanisms. First, oxidized corn starch is thermally gelatinized to form a homogeneous colloid, exposing a large number of hydroxyl groups. Under weakly acidic conditions, the triethoxysilyl groups in the fluorosilane monomer undergo partial hydrolysis to generate silanol, which then condenses and dehydrates with the starch hydroxyl groups, forming stable Si-OC covalent bonds, achieving chemical grafting of hydrophobic functional groups. Subsequently, hydroxypropyl quaternized chitosan is introduced by cooling. Its epoxy groups undergo a slow ring-opening reaction with the remaining hydroxyl groups of starch under near-neutral conditions, forming a cross-linked network. Simultaneously, borax, within this pH range, forms a dynamically reversible borate ester cross-linked network with subsequently added polyols such as glycerol and sorbitol, endowing the colloid with shear-thinning and self-healing properties. Sodium carboxymethyl cellulose acts as a thickening and stabilizing agent to improve storage stability, while sodium dodecyl sulfate improves wetting and spreading properties. The resulting adhesive system integrates the biodegradability of starch, the weather resistance and hydrophobicity of perfluorinated chains, the antibacterial adhesion of quaternary ammonium salts, and the mechanical reinforcement effect of borate ester / epoxy crosslinking. It has excellent overall performance and is particularly suitable for the manufacturing of ball products where there are stringent requirements for flexibility, resistance to damp heat, and environmental protection.

[0008] According to a preferred embodiment of the present invention, in step S1, the time for gelatinizing the suspension at 68-72°C is 30-60 minutes.

[0009] According to a preferred embodiment of the present invention, in step S2, the stirring reaction is carried out for 2-4 hours.

[0010] According to a preferred embodiment of the present invention, the preparation method of N-(perfluorohexylethyl)-N'-(3-triethoxysilylpropyl)urea includes: A1, under dry nitrogen protection, adding 50-70 parts of 1H,1H,2H,2H-perfluorohexylethylamine and 400-489 parts of anhydrous tetrahydrofuran to a three-necked flask, stirring, and adding 50-55 parts of N,N'-carbonyldiimidazole at room temperature, stirring the reaction at room temperature to obtain a reaction mixture; A2, dissolving 60-80 parts of 3-aminopropyltriethoxysilane in anhydrous tetrahydrofuran, adding it dropwise to the reaction mixture, and after the addition is complete, heating to 58-62°C and continuing to stir the reaction; after the reaction is complete, filtering to obtain a filtrate, and rotary evaporating the filtrate under reduced pressure to obtain a crude product; purifying the crude product by silica gel column chromatography, collecting the target component, and rotary evaporating.

[0011] In this invention, the synthesis of N-(perfluorohexylethyl)-N'-(3-triethoxysilylpropyl)urea is based on the mechanism of carbonyl diimidazole activating the amine group to form an asymmetric urea bond. First, under an inert atmosphere, 1H,1H,2H,2H-perfluorohexylethylamine reacts with carbonyl diimidazole at room temperature. The primary amino group nucleophilically attacks the carbonyl carbon, releasing one molecule of imidazole to generate a highly reactive perfluoroalkyl acyl imidazole intermediate. This intermediate exhibits good electrophilicity. Subsequently, under temperature-controlled conditions, it is slowly added dropwise to 3-aminopropyltriethoxysilane. The primary amino group in 3-aminopropyltriethoxysilane acts as a nucleophile, attacking the carbonyl carbon of the acyl imidazole, resulting in a nucleophilic substitution reaction. This again releases the imidazole byproduct, ultimately constructing the asymmetric urea structure. This route avoids the use of highly toxic phosgene or isocyanates. By stepwise feeding and time control, it effectively suppresses the formation of symmetrical urea byproducts. The resulting target molecule has a long-chain perfluoroalkyl group at one end, which endows the material with excellent hydrophobic, oil-resistant and low surface energy properties. The other end is a hydrolyzable triethoxysilyl group, which can be gradually hydrolyzed into silanol in a weakly acidic water environment, and further undergoes a condensation reaction with the hydroxyl groups in starch molecules to achieve organic-inorganic hybrid grafting, thereby significantly improving the water resistance and interfacial adhesion of the adhesive.

[0012] According to a preferred embodiment of the present invention, in step A1, the stirring reaction time at room temperature is 2-4 hours.

[0013] According to a preferred embodiment of the present invention, in step A2, the stirring reaction is continued for 5-10 hours.

[0014] According to a preferred embodiment of the present invention, the preparation method of the hydroxypropyl quaternized chitosan includes: dispersing 80-120 parts of chitosan in a mixed solvent of 800-1200 parts of isopropanol and 200-300 parts of deionized water; adjusting the pH to 4.5-5.5 with acetic acid solution; adjusting the pH to 8.5-9.0 with sodium hydroxide solution; adding 150-220 parts of an aqueous solution of 2,3-epoxypropyltrimethylammonium chloride; heating to 60-65°C to react and obtain a reaction mixture; filtering the reaction mixture to obtain a precipitate; washing the precipitate with ethanol; and vacuum drying to obtain hydroxypropyl quaternized chitosan.

[0015] In this invention, the preparation of hydroxypropyl quaternized chitosan employs a one-step functionalization strategy. Using natural chitosan as the backbone, chitosan is dispersed in a water-alcohol mixed solvent. The pH is adjusted to 4.5-5.5 with a 5% (w / w) acetic acid solution to ensure complete dissolution of the chitosan. Then, the pH is adjusted to 10-12 with sodium hydroxide solution to deprotonate the amino groups on the glucosamine units, enhancing their nucleophilicity. Subsequently, 2,3-epoxypropyltrimethylammonium chloride is added. This molecule possesses both an epoxy ring and a quaternary ammonium salt structure. The free amino groups of chitosan nucleophilically attack the less sterically hindered carbon atoms of the epoxy ring, initiating a ring-opening reaction to form CN bonds and hydroxyl groups, while simultaneously anchoring the trimethyl quaternary ammonium group to the chitosan backbone. This process not only imparts a permanent positive charge to the product, giving it broad-spectrum antibacterial properties and strong adsorption capacity to negatively charged substrates (such as cellulose and leather), but also allows the hydroxyl groups retained in the product to form a dynamic borate ester crosslinking network with polyols, boric acid, or starch hydroxyl groups during subsequent adhesive formulation. This results in a three-dimensional network structure that significantly enhances the cohesive strength, flexibility, and durability of the adhesive film. This modification method is efficient and environmentally friendly, avoiding the yield loss and toxicity risks associated with multi-step synthesis.

[0016] According to a preferred embodiment of the present invention, the reaction time is 7-8 hours after heating to 60-65°C.

[0017] In a second aspect, the present invention provides a modified starch-based waterborne adhesive prepared according to the method for preparing the modified starch-based waterborne adhesive.

[0018] A third aspect of the present invention provides the application of the modified starch-based water-based adhesive in ball products.

[0019] Compared with the prior art, the present invention has the following beneficial effects: (1) The modified starch-based waterborne adhesive provided by this invention, through the preparation method and the synergistic effect of the two key modified compounds, achieves a fundamental innovation and comprehensive improvement in the performance of natural starch adhesives, enabling its comprehensive performance to fully meet the stringent requirements of high-end ball manufacturing. Its technical effect is first reflected in the breakthrough improvement of core physicochemical properties. This adhesive completely overcomes the fatal defect of poor water resistance of traditional starch adhesives. Due to the stable covalent bonding of fluorinated alkyl chains and silane groups on the starch molecular chain, after curing, it can form a durable and dense hydrophobic protective layer at the bonding interface and the adhesive film body, effectively blocking the wetting and erosion of water molecules, so that the product can still maintain excellent bonding integrity in humid environments or even short-term water immersion conditions. Meanwhile, by introducing reactive hydroxyl and silane groups, a high-density three-dimensional chemical cross-linking network is constructed between starch molecules and between starch and the substrate. This not only endows the film with tensile and shear strengths far exceeding those of ordinary starch adhesives, but also significantly improves its flexibility and resistance to deformation, making the adhesive layer less prone to brittleness or fatigue failure when subjected to repeated dynamic stress, thus achieving an ideal balance between high strength and high flexibility.

[0020] (2) The superior technical effect of this invention stems from the precise design and functional complementarity of two innovative modified compounds. The molecular structure of the N-(perfluorohexylethyl)-N'-(3-triethoxysilylpropyl)urea integrates a perfluoroalkyl chain with extremely low surface energy, a urea bond structure that can form strong hydrogen bonds, and a highly reactive silane group. The introduction of the perfluoroalkyl chain is like putting a "raincoat" on the film, providing excellent hydrophobic, oleophobic, and antifouling properties; the silane group can condense with the hydroxyl groups of starch and form strong siloxane chemical bonds with the polar groups on the surface of spherical substrates (such as rubber, leather, and synthetic leather) during curing, thus achieving water resistance enhancement and adhesion improvement throughout the entire process from the film body to the interface bonding. The hydroxypropyl quaternized chitosan compound cleverly integrates the antibacterial properties of natural chitosan, the strong antibacterial properties of the quaternary ammonium salt group, and the efficient crosslinking ability of the epoxy group. During the preparation and curing process of the adhesive, its hydroxyl groups form a dynamic borate ester crosslinking network with the hydroxyl and carboxyl groups of starch and the residual silanol groups of fluorinated silane urea, forming a dense interpenetrating network that greatly enhances the cohesive strength and durability of the adhesive layer. At the same time, the quaternary ammonium salt cations it carries can act on the microbial cell membrane for a long time, giving the adhesive its inherent and lasting anti-mold and antibacterial ability, fundamentally solving the problem of easy mold and spoilage of starch products, and ensuring the hygiene and safety of sports equipment.

[0021] (3) The performance improvements achieved at the molecular level by this invention result in unparalleled practical advantages when applied to ball products. When this adhesive is used in key processes such as bonding the inner bladder and splicing the outer skin sheets of balls such as basketballs, footballs, and volleyballs, the resulting finished balls exhibit comprehensive performance improvements. Its bonding interface is firm and reliable with extremely high peel strength, sufficient to withstand prolonged and severe impacts and friction; its resistance to sweat and humid environments is outstanding, ensuring lifespan and reliability in diverse usage scenarios; its adhesive layer is flexible and elastic, able to withstand repeated inflation and deflation of the ball and high-intensity impacts without cracking or delamination; the dynamic borate ester crosslinking network formed by hydroxyl groups and borax gives it excellent fatigue resistance. In addition, the entire product system uses water as the dispersion medium, and there is no odor or release of toxic volatiles during production and use, possessing both high performance and high environmental friendliness. Detailed Implementation

[0022] To facilitate understanding of the present invention, the following embodiments are provided. Those skilled in the art should understand that these embodiments are merely illustrative and should not be construed as limiting the scope of the invention.

[0023] Preparation Example 1 This embodiment provides a method for preparing 1H,1H,2H,2H-perfluorohexylethylamine, the steps of which include: In a 250 mL dry three-necked flask equipped with a magnetic stirrer and a reflux condenser, 30.0 g of 1H,1H,2H,2H-perfluorohexylethanol and 120 mL of anhydrous dichloromethane (dried with anhydrous sodium sulfate) were added, and the mixture was cooled to 0 °C in an ice-water bath. While stirring, 12.1 mL of triethylamine and 6.5 mL of methanesulfonyl chloride (purity ≥98%) were added sequentially, controlling the reaction temperature to not exceed 10 °C. After the addition was complete, the ice bath was removed, and the mixture was allowed to rise to room temperature and the reaction was continued with stirring for 4 h. After the reaction was complete, the mixture was washed sequentially with 50 mL of 5% hydrochloric acid solution, 50 mL of saturated sodium bicarbonate solution, and 50 mL of saturated sodium chloride solution. The organic phase was dried with 20 g of anhydrous sodium sulfate for 30 min. The mixture was filtered, and the solvent was removed by rotary evaporation under reduced pressure to obtain a pale yellow oily substance, 1H,1H,2H,2H-perfluorohexylethyl methanesulfonate, which can be used directly in the next step. The crude methanesulfonate was dissolved in 150 mL of anhydrous N,N-dimethylformamide, and 9.1 g of sodium azide (purity ≥98%) was added. The mixture was heated to 60 °C and stirred for 12 h. After cooling to room temperature, the reaction solution was slowly poured into 500 mL of ice water and extracted three times with 200 mL of ethyl acetate. The organic phases were combined and washed successively with 100 mL of water and 100 mL of saturated brine. The mixture was dried over 20 g of anhydrous sodium sulfate. After filtration, the mixture was concentrated under reduced pressure to obtain the crude product 1H,1H,2H,2H-perfluorohexylethyl azide. The crude azide was dissolved in a mixed solvent of 100 mL tetrahydrofuran and 100 mL water, and 30 g of triphenylphosphine (purity ≥99%) was added. The mixture was heated to 50 °C and stirred for 8 h. After the reaction was completed, most of the solvent was removed by rotary evaporation under reduced pressure. The residue was dissolved in 80 mL of diethyl ether, and the triphenylphosphine oxide precipitate was removed by filtration. The ether filtrate was washed with 50 mL of 5% hydrochloric acid aqueous solution, and the aqueous phase was separated. The pH of the aqueous phase was adjusted to be greater than 10 with 10% sodium hydroxide solution, and then extracted twice with 80 mL of dichloromethane. The organic phases were combined, dried over anhydrous sodium sulfate, filtered, and distilled under reduced pressure. The fraction collected at 82–86 °C / 10 mmHg was used to obtain 1H,1H,2H,2H-perfluorohexylethylamine.

[0024] Example 1 This embodiment provides a method for preparing a modified starch-based waterborne adhesive, the steps of which include: Preparation of compound N-(perfluorohexylethyl)-N'-(3-triethoxysilylpropyl)urea: Under a dry nitrogen atmosphere, 60.0 g of 1H,1H,2H,2H-perfluorohexylethylamine and 450 g of anhydrous tetrahydrofuran were added to a three-necked round-bottom flask equipped with a magnetic stirrer, thermometer, constant-pressure dropping funnel, and reflux condenser. Stirring was initiated to completely dissolve the amine. At room temperature (25°C), 52.0 g of N,N'-carbonyldiimidazole was added to the constant-pressure dropping funnel and dissolved in 100 mL of anhydrous tetrahydrofuran. With continuous stirring, the N,N'-carbonyldiimidazole solution was slowly added dropwise to the reaction flask over 30 minutes, controlling the dropping rate to maintain the reaction system temperature below 30°C. After the addition was complete, the reaction system was kept at 25°C and stirred vigorously for 3 hours. During this time, the disappearance of the starting amine was monitored by thin-layer chromatography, yielding a reaction mixture of the perfluoroalkylformate imidazole ester intermediate. Subsequently, 70.0 g of 3-aminopropyltriethoxysilane was dissolved in 100 mL of anhydrous tetrahydrofuran and transferred to another clean constant-pressure dropping funnel. This amine solution was slowly added dropwise to the above reaction mixture containing the active ester intermediate under stirring, with the addition time controlled at 1 hour, during which the temperature of the reaction solution was maintained below 30°C. After the addition was complete, the reaction system was heated to 60°C and refluxed at this temperature for 8 hours. After the reaction was completed, the reaction solution was cooled to room temperature, and a white solid precipitated. This solid was filtered through a Buchner funnel and the filter cake was washed twice with 50 mL of anhydrous tetrahydrofuran. The filtrate and washings were combined. The solvent was removed from the filtrate by rotary evaporation under reduced pressure in a 40°C water bath, yielding a pale yellow viscous crude product. Purification was performed by column chromatography using 300-mesh silica gel. The column dimensions were 5 cm in diameter x 40 cm in height, and the eluent was a mixture of petroleum ether and ethyl acetate at a volume ratio of 10:1. The target fraction was collected and the eluent was removed again by rotary evaporation at 40°C to obtain N-(perfluorohexylethyl)-N'-(3-triethoxysilylpropyl)urea.

[0025] Preparation of the compound hydroxypropyl quaternized chitosan: In a three-necked flask equipped with a mechanical stirrer, thermometer, and pH meter, 100.0 g of chitosan powder with a degree of deacetylation of 95% was added. Then, 250 mL of deionized water and 1000 mL of isopropanol were added, and stirring was started. The mixture was dispersed at room temperature for 30 minutes to form a homogeneous suspension. While continuously stirring, the pH was first adjusted to 4.5 with a 5% acetic acid solution to ensure complete dissolution of the chitosan. Then, a 10% sodium hydroxide aqueous solution was slowly added dropwise through a dropping funnel to precisely adjust the pH to 8.7. Next, 185.0 g of a 70% aqueous solution of 2,3-epoxypropyltrimethylammonium chloride was added to the flask. The reaction system was heated to 62°C and stirred continuously at this temperature for 8 hours, maintaining the pH at 11 by adding small amounts of sodium hydroxide solution. After the reaction was complete, the reaction mixture was cooled to room temperature and stirring was stopped, resulting in the precipitation of a large amount of solid. The solid filter cake was collected by suction filtration through a Buchner funnel. The filter cake was washed three times with 200 mL of an ethanol / water mixture with a volume ratio of 80:20. The washed solid was transferred to a vacuum drying oven and dried at 40 °C for 12 hours to constant weight to obtain hydroxypropyl quaternized chitosan.

[0026] Preparation of modified starch-based waterborne adhesives: In a four-necked glass reactor equipped with an anchor-type stirrer, thermometer, pH meter, and condenser, 200.0 g of deionized water was added. Stirring was started at 200 rpm, and the water bath was heated to 50°C. While maintaining stirring, 100.0 g of oxidized corn starch (aldehyde content 0.8 mmol / g) was slowly added. After the addition was complete, the stirring speed was increased to 300 rpm, and the water bath temperature was raised to 70°C. Gelatinization was carried out under these conditions for 45 minutes to obtain a translucent, viscous starch paste. Subsequently, the water bath temperature was lowered to 60°C, and the stirring speed was adjusted back to 200 rpm. The pH of the starch paste was adjusted to 4.5 using a 10% (w / w) dilute acetic acid aqueous solution. 10.0 g of N-(perfluorohexylethyl)-N'-(3-triethoxysilylpropyl)urea was slowly added dropwise to the reactor over 30 minutes using a constant-pressure dropping funnel. After the addition was complete, the temperature was maintained at 60°C, and the reaction was continued with stirring for 4 hours to obtain a hydrophobically modified starch reaction mixture. Then, the water bath temperature was lowered to 40°C. 15.0 g of hydroxypropyl quaternized chitosan and 1.5 g of borax pre-dissolved in 20 mL of deionized water were added to the reactor. The pH of the reaction mixture was adjusted to 6.0 with a 5% sodium hydroxide aqueous solution. The reaction was continued with stirring at 40°C for 3 hours. After the reaction was complete, the water bath was removed, and the adhesive system was allowed to cool naturally to 25°C (room temperature). 20.0 g of a plasticizer pre-mixed with glycerol and sorbitol in a 1:1 mass ratio, 3.0 g of sodium carboxymethyl cellulose (viscosity grade 1500 mPa·s), and 0.3 g of sodium dodecyl sulfate were added sequentially to the reactor. The stirring speed was increased to 500 rpm, and stirring was continued at 25°C for 1 hour to ensure uniform dispersion of all additives. Finally, the adhesive solution was filtered through a 100-mesh nylon sieve to remove any trace amounts of gel or impurities, thus obtaining the modified starch-based water-based adhesive. The 1H,1H,2H,2H-perfluorohexylethylamine described in this example is the substance obtained in Preparation Example 1.

[0027] Example 2 The difference between this embodiment and Example 1 is that the compound N-(perfluorohexylethyl)-N'-(3-triethoxysilylpropyl)urea was prepared: Under a dry nitrogen atmosphere, 55.0 g of 1H,1H,2H,2H-perfluorohexylethylamine and 400 g of anhydrous tetrahydrofuran were added to a three-necked round-bottom flask equipped with a magnetic stirrer, thermometer, constant-pressure dropping funnel, and reflux condenser. Stirring was initiated to completely dissolve the amine. At room temperature (25°C), 51.0 g of N,N'-carbonyldiimidazole was added to the constant-pressure dropping funnel and dissolved in 100 mL of anhydrous tetrahydrofuran. With continuous stirring, the N,N'-carbonyldiimidazole solution was slowly added dropwise to the reaction flask over 30 minutes, controlling the dropping rate to maintain the reaction system temperature below 30°C. After the addition was complete, the reaction system was kept at 25°C and stirred vigorously for 2.5 hours to obtain a reaction mixture of the perfluoroalkyl formazan imidazole ester intermediate. Subsequently, 65.0 g of 3-aminopropyltriethoxysilane was dissolved in 100 mL of anhydrous tetrahydrofuran and transferred to a constant-pressure dropping funnel. This amine solution was slowly added dropwise to the above reaction mixture with stirring, controlling the addition time to be 1 hour. After the addition was complete, the reaction system was heated to 59 °C and refluxed at this temperature for 7 hours with stirring. After the reaction was complete, the reaction solution was cooled to room temperature and filtered. The filtrate was evaporated by removing the solvent in a rotary evaporator under reduced pressure in a 40 °C water bath to obtain the crude product. Purification was performed using silica gel column chromatography with a mixture of petroleum ether and ethyl acetate as the eluent (volume ratio 10:1). The target fraction was collected, and the solvent was removed by rotary evaporation to obtain N-(perfluorohexylethyl)-N'-(3-triethoxysilylpropyl)urea.

[0028] Preparation of the compound hydroxypropyl quaternized chitosan: In a three-necked flask equipped with a mechanical stirrer, thermometer, and pH meter, 90.0 g of chitosan powder with a degree of deacetylation of 95% was added. Then, 220 mL of deionized water and 900 mL of isopropanol were added, and stirring was started to disperse the mixture. While continuously stirring, the pH was first adjusted to 5 with a 5% acetic acid solution to ensure complete dissolution of the chitosan; then, a 10% sodium hydroxide aqueous solution was added dropwise to adjust the pH to 8.5. Next, 170.0 g of an aqueous solution of 2,3-epoxypropyltrimethylammonium chloride (70% by mass) was added to the flask. The reaction system was heated to 60°C and stirred continuously at this temperature for 7 hours, maintaining a stable pH throughout. After the reaction was complete, the reaction mixture was cooled to room temperature and filtered, collecting the solid filter cake. The filter cake was washed three times with an 80:20 ethanol / water mixture. The washed solid was dried to constant weight in a vacuum drying oven at 40°C to obtain hydroxypropyl quaternized chitosan.

[0029] Preparation of modified starch-based waterborne adhesives: In a four-necked glass reactor equipped with a stirrer, thermometer, pH meter, and condenser, 190.0 g of deionized water was added. Stirring was started at 200 rpm, and the water bath was heated to 49°C. While stirring, 85.0 g of oxidized corn starch was slowly added. After the addition was complete, the stirring speed was increased, and the water bath temperature was raised to 69°C, allowing gelatinization for 35 minutes. Subsequently, the water bath temperature was lowered to 59°C, and the stirring speed was returned to normal. The pH of the starch paste was adjusted to 4.2 using dilute acetic acid. 9.0 g of N-(perfluorohexylethyl)-N'-(3-triethoxysilylpropyl)urea was slowly added dropwise to the reactor using a dropping funnel. After the addition was complete, the temperature was maintained at 59°C, and the reaction was continued with stirring for 3.5 hours. Afterward, the water bath temperature was lowered to 39°C. 14.0 g of hydroxypropyl quaternized chitosan and a solution of 1.3 g of borax pre-dissolved in 20 mL of deionized water were added to the reactor. The pH of the reaction mixture was adjusted to 5.5 using an aqueous sodium hydroxide solution. The reaction mixture was stirred at 39°C for 2.5 hours. After the reaction was complete, it was cooled to 25°C. 19.0 g of a 1:1 mixture of glycerol and sorbitol, 2.5 g of sodium carboxymethyl cellulose, and 0.25 g of sodium dodecyl sulfate were added sequentially to the reaction vessel. The stirring speed was increased, and stirring was continued at 25°C for 1 hour. Finally, the adhesive solution was filtered through a 100-mesh nylon sieve to obtain the modified starch-based aqueous adhesive. The 1H,1H,2H,2H-perfluorohexylethylamine described in this example is the substance obtained in Preparation Example 1.

[0030] Example 3 The difference between this embodiment and Example 1 is that the compound N-(perfluorohexylethyl)-N'-(3-triethoxysilylpropyl)urea was prepared: Under a dry nitrogen atmosphere, 65.0 g of 1H,1H,2H,2H-perfluorohexylethylamine and 489 g of anhydrous tetrahydrofuran were added to a three-necked round-bottom flask equipped with a magnetic stirrer, thermometer, constant-pressure dropping funnel, and reflux condenser. Stirring was initiated until the amine was completely dissolved. At room temperature (25°C), 53.0 g of N,N'-carbonyldiimidazole was added to the constant-pressure dropping funnel and dissolved in 100 mL of anhydrous tetrahydrofuran. The solution was slowly added dropwise to the reaction flask over 30 minutes with continuous stirring. After the addition was complete, the reaction system was kept at 25°C and stirred vigorously for 3.5 hours. Subsequently, 75.0 g of 3-aminopropyltriethoxysilane was dissolved in 100 mL of anhydrous tetrahydrofuran and added dropwise to the above reaction mixture over a period of 1 hour. After the addition was complete, the reaction system was heated to 61°C and refluxed at this temperature for 9 hours. After the reaction was completed, the reaction solution was cooled to room temperature and filtered. The filtrate was concentrated by rotary evaporation to obtain the crude product. Purification was performed using silica gel column chromatography with a mixed solvent of petroleum ether and ethyl acetate in a volume ratio of 10:1. The target fraction was collected, and the solvent was removed by rotary evaporation to obtain N-(perfluorohexylethyl)-N'-(3-triethoxysilylpropyl)urea.

[0031] Preparation of the compound hydroxypropyl quaternized chitosan: In a three-necked flask equipped with a mechanical stirrer, thermometer, and pH meter, 110.0 g of chitosan powder with a degree of deacetylation of 95% was added. Then, 280 mL of deionized water and 1100 mL of isopropanol were added, and stirring was started to disperse the mixture. The pH was first adjusted to 5.5 with a 5% acetic acid solution to ensure complete dissolution of the chitosan; then, a 10% sodium hydroxide aqueous solution was added dropwise to adjust the pH to 9.0. Next, 200.0 g of an aqueous solution of 2,3-epoxypropyltrimethylammonium chloride (70% by mass) was added. The reaction system was heated to 65°C and stirred continuously at this temperature for 8 hours. After the reaction was complete, the mixture was cooled, filtered, and the solid was washed with an ethanol / water mixture. The solid was dried to constant weight in a vacuum drying oven at 40°C to obtain hydroxypropyl quaternized chitosan.

[0032] Preparation of modified starch-based waterborne adhesives: In a four-necked glass reactor equipped with a stirrer, thermometer, pH meter, and condenser, 210.0 g of deionized water was added. Stirring was started and the mixture was heated to 51°C. 115.0 g of oxidized corn starch was added. The temperature was raised to 71°C, and gelatinization was carried out for 55 minutes. The temperature was then lowered to 61°C, and the pH was adjusted to 4.8 with dilute acetic acid. 11.0 g of the prepared N-(perfluorohexylethyl)-N'-(3-triethoxysilylpropyl)urea was added dropwise. The reaction was maintained at 61°C for 4.5 hours. The temperature was then lowered to 41°C. 16.0 g of the prepared hydroxypropyl quaternized chitosan and 1.6 g of borax aqueous solution were added. The pH was adjusted to 6.5. The reaction was carried out at 41°C for 3.5 hours. The mixture was cooled to 25°C. A 1:1 mixture of 21.0 g of glycerol and sorbitol, 3.5 g of sodium carboxymethyl cellulose, and 0.35 g of sodium dodecyl sulfate were added sequentially. Stir at high speed for 1 hour. Filter through a 100-mesh sieve to obtain the modified starch-based water-based adhesive. The 1H,1H,2H,2H-perfluorohexylethylamine described in this example is the substance obtained in Preparation Example 1.

[0033] Comparative Example 1 The difference between this comparative example and Example 1 is that 200.0 g of deionized water was added to a four-necked glass reactor equipped with a stirrer. Stirring was started and the mixture was heated to 50°C. 100.0 g of oxidized corn starch was slowly added. The temperature was raised to 70°C, and gelatinization was carried out for 45 minutes. The reaction mixture was then cooled to 25°C. A 1:1 mixture of 20.0 g of glycerol and sorbitol, 3.0 g of sodium carboxymethyl cellulose, and 0.3 g of sodium dodecyl sulfate were added sequentially to the reactor. The mixture was stirred at high speed at 25°C for 1 hour. Finally, the adhesive solution was filtered through a 100-mesh nylon sieve to obtain the starch-based adhesive of Comparative Example 1. This adhesive was prepared without the use of N-(perfluorohexylethyl)-N'-(3-triethoxysilylpropyl)urea and hydroxypropyl quaternized chitosan.

[0034] Comparative Example 2 The difference between this comparative example and Example 1 is that 200.0 g of deionized water was added to a four-necked glass reactor equipped with a stirrer, thermometer, pH meter, and condenser. Stirring was started and the mixture was heated to 50°C. 100.0 g of oxidized corn starch was added. The temperature was raised to 70°C and gelatinized for 45 minutes. The temperature was then lowered to 60°C, and the pH was adjusted to 4.5 with dilute acetic acid. 10.0 g of 3-aminopropyltriethoxysilane was added dropwise. The reaction was maintained at 60°C for 4 hours. The temperature was then lowered to 40°C. 1.5 g of borax aqueous solution was added, and the pH was adjusted to 6.0. The reaction was maintained at 40°C for 3 hours. The mixture was cooled to 25°C. A 1:1 mixture of 20.0 g of glycerol and sorbitol, 3.0 g of sodium carboxymethyl cellulose, and 0.3 g of sodium dodecyl sulfate were added sequentially. After high-speed stirring for 1 hour, the mixture was filtered to obtain the adhesive of Comparative Example 2. The adhesive was modified using only 3-aminopropyltriethoxysilane, without the use of N-(perfluorohexylethyl)-N'-(3-triethoxysilylpropyl)urea and hydroxypropyl quaternized chitosan.

[0035] Comparative Example 3 The difference between this comparative example and Example 1 is that chitosan hydrochloride was prepared first: 10.0 g of chitosan powder was added to 200.0 g of a 1% hydrochloric acid aqueous solution and stirred until completely dissolved. This solution was then added dropwise to 1000 mL of acetone with stirring to precipitate the mixture. The solid was collected by filtration, washed three times with ethanol, and dried under vacuum at 40°C to obtain chitosan hydrochloride. The adhesive was then prepared: 200.0 g of deionized water was added to a four-necked glass reactor equipped with a stirrer, thermometer, pH meter, and condenser. Stirring was started and the temperature was raised to 50°C. 100.0 g of oxidized corn starch was added. The temperature was raised to 70°C and gelatinized for 45 minutes. The temperature was then lowered to 60°C, and the pH was adjusted to 4.5 with dilute acetic acid. 10.0 g of 3-aminopropyltriethoxysilane was added dropwise. The reaction was maintained at 60°C for 4 hours. The temperature was then lowered to 40°C. Add 10.0 g of the previously prepared chitosan hydrochloride and 1.5 g of borax aqueous solution, and adjust the pH to 6.0. React at 40°C for 3 hours. Cool to 25°C. Add 20.0 g of a 1:1 mixture of glycerol and sorbitol, 3.0 g of sodium carboxymethyl cellulose, and 0.3 g of sodium dodecyl sulfate sequentially. After stirring at high speed for 1 hour, filter to obtain the adhesive of Comparative Example 3. This adhesive uses 3-aminopropyltriethoxysilane and chitosan hydrochloride, but does not use N-(perfluorohexylethyl)-N'-(3-triethoxysilylpropyl)urea and hydroxypropyl quaternized chitosan.

[0036] According to relevant national and industry standards, the performance of the modified starch-based waterborne adhesives provided in the above embodiments and comparative examples was tested, and the test methods are as follows: The adhesive performance testing method is as follows: For the bond strength test, each adhesive sample was tested at 150 g / m². 2 The coating was evenly applied to the surface of the standard soccer ball synthetic leather and rubber inner bladder substrate. After drying for 5 minutes at 25℃ and 50% relative humidity, the substrate was bonded together and placed in a hot press to cure at 0.3MPa pressure and 80℃ for 30 minutes. Then, it was placed in a standard environment (23℃, 50%RH) for 24 hours to prepare a 25mm wide T-shaped peel test specimen. The peel strength was tested using a universal testing machine at a tensile speed of 300mm / min. The result was the arithmetic mean of 5 valid specimens, and the unit was N / mm. For the water resistance test, the above-mentioned bonded sample was completely immersed in a constant temperature water bath at 40℃. After soaking for 48 hours, it was taken out and excess water on the surface was absorbed with filter paper. The wet peel strength test was completed within 10 minutes after removal. The strength retention rate was calculated by the formula (wet peel strength / initial dry peel strength) × 100%. For flexibility and durability testing, a dedicated sphere fatigue testing machine was used. The bonded complete sphere was fixed in the cavity, and periodic inflation and deflation cycles were performed at a frequency of 1Hz within a pressure range of 0.6 bar to 0.8 bar. The experiment was conducted continuously, and after every 10,000 cycles, the test was paused and the sphere bonding seams were inspected. The number of cycles taken when any bonding seam showed visible cracking or delamination was recorded as the inflation and deflation fatigue life, in units of 10,000 cycles. For the mildew resistance test, each adhesive was cast into a homogeneous film with a thickness of 2 mm, and 50 mm × 50 mm samples were cut. The surface was sprayed with a concentration of 1 × 10⁻⁶. 6 A spore suspension of mixed Aspergillus niger and Penicillium spores / mL was placed in a petri dish and continuously cultured for 28 days in a constant temperature and humidity chamber at 28℃ and 95% relative humidity. Every 7 days, the spores were taken out and observed under a microscope to observe the growth of fungal hyphae on the surface. The spores were graded according to the following standards: Grade 0: no fungal growth on the surface; Grade 1: the area of ​​fungal growth is less than 10%; Grade 2: the area is between 10% and 30%; Grade 3: the area is between 30% and 60%; Grade 4: the area is more than 60%.

[0037] The performance test data above are shown in Table 1.

[0038] Table 1 Performance Test Results

[0039] As can be seen from the above, Examples 1-3 comprehensively and synergistically solve the technical problems of insufficient bonding strength, poor water resistance, low flexibility and easy cracking, and easy mold growth of existing starch-based water-based adhesives compared with Comparative Examples 1-3.

[0040] Specifically, the embodiment contains both N-(perfluorohexylethyl)-N'-(3-triethoxysilylpropyl)urea and hydroxypropyl quaternized chitosan, and its initial peel strength reaches more than 8.3 N / mm, far exceeding the 4.2 N / mm of the unmodified comparative example 1. This is due to the combined effect of the interfacial adhesion enhanced by the fluorosilane urea and the three-dimensional cross-linked network constructed by the chitosan quaternary ammonium salt.

[0041] In addressing the critical deficiency of water resistance, the strength retention rates of the examples after water immersion were all above 91%, while the retention rates of Comparative Examples 1, 2, and 3 were only 35.7%, 47.5%, and 54.7%, respectively. The fundamental reason for this is that Comparative Example 1 completely lacks hydrophobic components, Comparative Example 2 uses only ordinary silane, which cannot provide a durable hydrophobic barrier, and the chitosan hydrochloride in Comparative Example 3 is even hydrophilic. Only the chemically bonded perfluoroalkyl chains in the examples can endow the film with excellent water resistance properties.

[0042] In terms of flexibility and dynamic durability, the inflation and deflation fatigue life of the embodiment exceeded 100,000 cycles, while that of Comparative Examples 1, 2, and 3 was only 3,000, 25,000, and 38,000 cycles, respectively. The huge difference proves that ordinary silanes (Comparative Example 2) or simple physical mixtures of chitosan salts (Comparative Example 3) cannot form the dynamic borate ester crosslinking network formed by hydroxyl groups and silanol groups as in the embodiment. This network endows the adhesive layer with excellent high toughness and fatigue resistance.

[0043] Finally, regarding mold resistance, the examples achieved the highest level of mold resistance of 28 days (Level 0) thanks to the inherent quaternary ammonium salt antibacterial groups in hydroxypropyl quaternized chitosan. In contrast, Comparative Example 1 suffered severe mold growth (Level 4) due to its rich content of nutrients. Comparative Examples 2 and 3, due to the lack of effective antibacterial components or the use of chitosan hydrochloride with certain antibacterial properties, had mold resistance levels of only Level 3 and Level 2, respectively.

[0044] In summary, each comparative example has significant shortcomings in various performance aspects due to the lack of one or two core modifying compounds of the present invention. However, Examples 1-3 achieve a unified performance of high strength, high water resistance, high flexibility and long-lasting mildew resistance through the synergistic effect of two compounds, completely overcoming the limitations of the prior art.

Claims

1. A method for preparing a modified starch-based waterborne adhesive, characterized in that the steps include... include: S1. By weight, add 180-220 parts of deionized water to the reactor, stir, and heat to 48-52℃; add 80-120 parts of oxidized corn starch, stir, and obtain a suspension; heat the suspension to 68-72℃ to gelatinize, cool to 58-62℃, adjust the pH to 4-5 while stirring, and add 8-12 parts of N-(perfluorohexylethyl)-N'-(3-triethoxysilylpropyl)urea dropwise to react and obtain the reaction mixture; S2. Cool the reaction mixture to 38-42℃, add 13-17 parts of hydroxypropyl quaternized chitosan, and simultaneously add 1.2-1.7 parts of borax. Adjust the pH to 5-7 and continue stirring the reaction. After the reaction is complete, cool to room temperature, and then add 18-22 parts of a mixture of glycerol and sorbitol, 2-4 parts of sodium carboxymethyl cellulose, and 0.2-0.4 parts of sodium dodecyl sulfate in sequence. Stir at room temperature and filter.

2. The method for preparing the modified starch-based waterborne adhesive according to claim 1, characterized in that, In step S1, the suspension is heated to 68-72℃ and gelatinized for 30-60 minutes.

3. The method for preparing the modified starch-based waterborne adhesive according to claim 1, characterized in that, In step S2, the reaction is continuously stirred for 2-4 hours.

4. The method for preparing the modified starch-based waterborne adhesive according to claim 1, characterized in that, The preparation method of the N-(perfluorohexylethyl)-N'-(3-triethoxysilylpropyl)urea includes: A1. By weight, under dry nitrogen protection, add 50-70 parts of 1H,1H,2H,2H-perfluorohexylethylamine and 400-489 parts of anhydrous tetrahydrofuran to a three-necked flask, stir, add 50-55 parts of N,N'-carbonyldiimidazole at room temperature, stir the reaction at room temperature to obtain the reaction mixture. A2. Dissolve 60-80 parts of 3-aminopropyltriethoxysilane in anhydrous tetrahydrofuran and add it dropwise to the reaction mixture. After the addition is complete, heat to 58-62℃ and continue stirring the reaction. After the reaction is complete, filter to obtain the filtrate. Evaporate the filtrate under reduced pressure to obtain the crude product. Purify the crude product by silica gel column chromatography, collect the target component, and rotary evaporate it.

5. The method for preparing the modified starch-based waterborne adhesive according to claim 4, characterized in that, In step A1, the reaction is stirred at room temperature for 2-4 hours.

6. The method for preparing the modified starch-based waterborne adhesive according to claim 4, characterized in that, In step A2, the stirring reaction should continue for 5-10 hours.

7. The method for preparing the modified starch-based waterborne adhesive according to claim 1, characterized in that, The preparation method of the hydroxypropyl quaternized chitosan includes: dispersing 80-120 parts by weight of chitosan in a mixed solvent of 800-1200 parts isopropanol and 200-300 parts deionized water; adjusting the pH to 4.5-5.5 with acetic acid solution; adjusting the pH to 8.5-9.0 with sodium hydroxide solution; adding 150-220 parts of an aqueous solution of 2,3-epoxypropyltrimethylammonium chloride; heating to 60-65℃ to react and obtain a reaction mixture; filtering the reaction mixture to obtain a precipitate; washing the precipitate with ethanol; and vacuum drying to obtain hydroxypropyl quaternized chitosan.

8. The method for preparing the modified starch-based waterborne adhesive according to claim 7, characterized in that, The reaction time is 7-8 hours after the temperature is raised to 60-65℃.

9. A modified starch-based water-based adhesive, characterized in that, The modified starch-based waterborne adhesive is prepared according to any one of claims 1-8.

10. An application of the modified starch-based waterborne adhesive according to claim 9, characterized in that, Application of the modified starch-based water-based adhesive in ball products.

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