A multi-component synergistic adhesive based on waxy cassava starch / gelatin / citric acid, its preparation method and application

Abstract

This invention belongs to the field of adhesive technology, and discloses a multi-component synergistic adhesive based on waxy cassava starch / gelatin / citric acid, its preparation method, and its application. The adhesive includes a main component and water, wherein the mass fraction of the main component is 25%. The main component includes waxy cassava starch (WCS), gelatin, citric acid (CA), and glycerol, with a mass ratio of waxy cassava starch:gelatin:citric acid of 75-25:25-75:20-80. The adhesive of this invention has extremely high storage stability, showing no obvious stratification or precipitation after being placed at 25°C for one month, solving the industry problem of short shelf life of traditional biomass adhesives, and facilitating industrial production and long-distance transportation. The bonding performance of the adhesive of this invention to cardboard, wood, steel, and glass plates stems from the synergistic effect of physical-mechanical interlocking and intermolecular hydrogen bonding.

Description

Technical Field

[0001] This invention belongs to the field of adhesive technology, and in particular to a multi-component synergistic adhesive based on waxy cassava starch / gelatin / citric acid, its preparation method and application. Background Technology

[0002] With increasingly stringent environmental regulations and growing public awareness of environmental protection, the development of environmentally friendly adhesives has become an inevitable trend in the industry. Biomass adhesives, due to their renewable, biodegradable, non-toxic, and harmless raw materials, show broad application prospects in packaging, wood processing, and home decoration. Starch-based adhesives are among the most researched and widely used. However, traditional starch adhesives suffer from low solids content, slow drying speed, poor water resistance, poor storage stability, and insufficient bonding strength, limiting their application in high-performance applications.

[0003] Gelatin, as a natural protein, possesses excellent film-forming and adhesive properties. Its abundant amino and carboxyl groups on its molecular chain can form hydrogen bonds or electrostatic interactions with various substrates. Citric acid, as an inexpensive and readily available multifunctional organic acid, can not only regulate the pH of the system, but its multiple carboxyl groups can also act as "bridging molecules" to participate in the formation of cross-linked networks, enhancing interfacial bonding. However, there are currently few reports on the combined use of starch, gelatin, and citric acid, and on their systematic study of the multi-component adhesive mechanism on different substrates (such as cardboard, wood, metal, and glass).

[0004] Furthermore, existing biomass adhesives generally suffer from poor storage stability, often exhibiting stratification, precipitation, or mold growth within a short period (e.g., a few days), severely impacting their industrial application and shelf life. Therefore, developing a biomass adhesive with excellent storage stability, strong adhesive properties, and universal adhesion to various substrates is of significant practical importance.

[0005] In summary, existing starch-based adhesives still have the following shortcomings in practical applications: 1. Poor storage stability and short shelf life Traditional starch adhesives are prone to retrogradation during storage, manifesting as stratification, sedimentation, or a significant increase in viscosity. They typically only last a few days to a week at room temperature before showing obvious deterioration. This problem hinders the industrial-scale mass production and long-distance transportation of these adhesives, severely limiting their marketability as commodities. Even with chemical modification or the addition of preservatives, low-temperature storage is often necessary, increasing costs and energy consumption.

[0006] Second, it has weak adhesion to high-energy surface substrates such as metals and glass.

[0007] Traditional starch adhesives rely primarily on mechanical penetration and interlocking with porous substrates (such as paper and wood). The polar groups, primarily hydroxyl groups, in their molecular structure exhibit weak interactions with surfaces like metal oxides and glass silanol groups, making it difficult to form strong interfacial bonds. Therefore, existing starch adhesives exhibit extremely low peel strength, or even complete inability to bond to smooth, high-energy surfaces such as steel plates and glass. This limits their application in scenarios requiring cross-material bonding, such as packaging (e.g., exposed metal at the seal of a box) and home decoration.

[0008] Third, it is difficult to balance adhesive strength and film flexibility.

[0009] Existing starch adhesives typically form brittle and hard films with insufficient cohesive strength, making them prone to brittle fracture under bending or impact. To improve strength, chemical crosslinking agents (such as aldehydes) or synthetic resins are often introduced. However, these methods often further reduce the film's flexibility and may lead to environmental problems such as formaldehyde release. Without adding chemical crosslinking agents, existing products struggle to simultaneously achieve high adhesive strength and good flexibility, failing to meet the requirements of paper tapes in practical applications such as bending and wrapping irregularly shaped objects. Summary of the Invention

[0010] The purpose of this invention is to overcome the shortcomings of the prior art and provide a multi-component synergistic adhesive based on waxy cassava starch / gelatin / citric acid, its preparation method, and its application.

[0011] The technical solution adopted by this invention to solve its technical problem is: A multi-component synergistic adhesive based on waxy tapioca starch / gelatin / citric acid, the adhesive comprising a main component and water, wherein the main component has a mass fraction of 25%; The main components include waxy tapioca starch (WCS), gelatin, citric acid (CA), and glycerin, with a mass ratio of waxy tapioca starch: gelatin: citric acid of 75-25: 25-75: 20-80.

[0012] Furthermore, in the preparation of the adhesive, gelatin is added in the form of an aqueous solution with a mass concentration of 30 wt%, citric acid is added in the form of an aqueous solution, and glycerol accounts for 20% of the total dry basis mass.

[0013] The preparation method of the multi-component synergistic adhesive as described above includes the following steps: (1) Disperse waxy cassava starch in deionized water and stir to make it evenly dispersed to obtain starch dispersion; (2) Weigh out gelatin and prepare an aqueous solution with a mass concentration of 30 wt%. Stir and dissolve the gelatin at 50°C for 15 min to obtain a gelatin solution. (3) Weigh out citric acid, add deionized water and stir to dissolve, to obtain citric acid solution; (4) The gelatin solution and the citric acid solution are added sequentially to the starch dispersion in step (1), and the mixture is stirred at 90°C for 20 min. (5) Add 20% of the total dry weight of glycerol to the mixture in step (4), continue stirring for 15 min, and cool to obtain the adhesive.

[0014] Furthermore, the stirring speed in steps (1) to (5) is 200-600 rpm.

[0015] Furthermore, the mass concentration of the starch dispersion in step (1) is 20±2%.

[0016] Furthermore, the mass concentration of the citric acid solution in step (3) is 40±2%.

[0017] The application of the multi-component synergistic adhesives described above in substrate bonding and / or paper tape preparation.

[0018] Furthermore, the application involves applying the adhesive to the surface of a substrate and achieving bonding after drying.

[0019] Furthermore, the substrate includes kraft paper, wood board, steel plate, and glass plate.

[0020] Furthermore, in preparing the paper tape, the adhesive is coated onto the surface of kraft paper at a coating amount of 40-50 g / m². 2 After drying, it is made into a wet-type paper tape.

[0021] The advantages and positive effects of this invention are as follows: 1. The adhesive described in this invention has extremely high storage stability. It shows no obvious stratification or precipitation after being placed at 25°C for one month, solving the industry problem of short shelf life of traditional biomass adhesives and facilitating industrial production and long-distance transportation. The bonding performance of the adhesive to cardboard, wood, steel and glass plates is due to the synergistic effect of physical-mechanical interlocking and intermolecular hydrogen bonding.

[0022] 2. The adhesive of this invention has a moderate viscosity (~1000 mPa·s), which can effectively penetrate into the fiber gaps of porous substrates such as cardboard and wood panels. After curing, it forms mechanical anchor points, creating physical interlocking. Simultaneously, the active groups in the adhesive—hydroxyl groups of starch, amino and carboxyl groups of gelatin, and carboxyl groups of citric acid—form intermolecular hydrogen bonds with polar functional groups on the substrate surface (such as hydroxyl groups of cellulose, metal oxides, and silanol groups of glass), enhancing interfacial bonding. Within the adhesive layer, a uniform network is formed through hydrogen bond cross-linking between starch and gelatin, providing sufficient cohesive strength. Citric acid not only regulates the viscosity in the system but also acts as a multifunctional small molecule to enhance the interfacial hydrogen bond density.

[0023] 3. The paper tape coated with the adhesive of this invention exhibits excellent adhesion to various substrates. For cellulose substrates rich in hydroxyl groups (paper, wood), hydrogen bonding is dominant; for high-energy surfaces such as steel plates and glass, the coordination of carboxyl groups with metal oxides and the hydrogen bonding with silanol groups contribute to the adhesive strength. All raw materials are bio-based or naturally derived, non-toxic, and release no formaldehyde. The production process involves no complex chemical reactions, making it safe and environmentally friendly.

[0024] 4. This invention utilizes the chemical and physical synergistic effects between high-branched waxy cassava starch, gelatin, and citric acid to construct a stable network structure, resulting in an adhesive that not only has excellent storage stability (does not separate after one month) but also exhibits superior adhesion to various substrates such as cardboard, wood, steel, and glass.

[0025] 5. Comparison with relevant publicly available literature in the prior art.

[0026] The prior art discloses "a bio-based adhesive based on cassava starch, waste gelatin capsules and citric acid and its preparation method", the specific contents of which are as follows: (1) Raw material preparation: Prepare cassava starch (ordinary, branched content not limited), waste pharmaceutical capsule gelatin (containing 2.91% TiO2 impurities) and citric acid (purity 99.5%).

[0027] (2) Mixing and dispersing: Mix starch, gelatin and citric acid in a certain proportion, add water and disperse, with a total solid content of 20% w / w. The amount of citric acid used is 20%, 40% or 80% w / w of the polymer blend.

[0028] (3) Heat treatment: The mixed dispersion is heated in a 90°C water bath for 20 minutes to gelatinize the starch and dissolve the gelatin. At the same time, citric acid induces cross-linking and hydrolysis of starch and gelatin.

[0029] (4) Molding: After the reaction is cooled, a liquid adhesive (pH 1–4, viscosity 90–158 mPa·s) is obtained; or the liquid adhesive is dried into a film to obtain a pressure-sensitive adhesive film (CA-80 formulation).

[0030] The present invention will now be compared and analyzed item by item with those of the present invention to clarify the inventiveness of the present invention: (1) The core contribution of the comparative literature is that high concentration of citric acid (80%) can destroy the gel network of gelatin, causing the system to change from a gel state to a viscoelastic concentrated solution, which forms a permanently viscous pressure-sensitive adhesive film after drying. The technical path is "destroy cross-linking – obtain viscosity".

[0031] The technical concept of this invention is the opposite: through the synergistic effect of waxy cassava starch, gelatin, citric acid, and glycerin, a highly cross-linked and locked glassy network is constructed, ensuring non-stickiness when dry; it reversibly dissociates when wet, activating adhesion; and it re-crosslinks after the moisture evaporates, achieving high-strength adhesion. This is a "reversible switch" design, completely different from the "permanent adhesion" path of pressure-sensitive adhesives.

[0032] (2) This invention differs from the prior art not only in the selection of raw materials and the composition of the formulation, but also in the product form, adhesive activation mechanism, and component action mechanism: This invention pertains to water-based (rewetting) adhesives, which use water as a "switch" for adhesion; they are non-adhesive when dry, adhesive when wet, and cured when dry. In contrast, the literature pertains to pressure-sensitive adhesives, which are permanently tacky after drying and rely on pressure to trigger bonding. The molecular design logics of the two are opposite: this invention constructs a reversible hydrogen bond-locked network, while the comparative literature constructs a permanent viscoelastic network; the comparative literature does not reveal or imply the technical concept of water-soluble adhesives, nor does it involve the balancing and regulating role of glycerol between "dry non-sticky" and "water-activated".

[0033] (3) This invention explicitly uses waxy cassava starch (highly branched structure), emphasizing its superior resistance to retrogradation and storage stability in adhesives. The aforementioned published literature uses ordinary cassava starch, does not limit the branched content, and does not address the special advantages of highly branched starch.

[0034] (4) In this invention, 20% glycerol (by dry basis mass) is added at a fixed amount. Glycerol acts as a plasticizer and participates in synergistic thickening. The above-mentioned published literature does not use any added glycerol, and the system contains no plasticizer components.

[0035] (5) This invention clearly demonstrates that the material does not separate after being stored at 25°C for one month, thus solving the industry pain point of short shelf life for biomass adhesives. The aforementioned published literature only mentions no regeneration within one week and does not provide long-term stability data.

[0036] (6) The present invention systematically tested the peel strength of steel plates and glass plates (both reaching 4.64 N / cm or higher), and clearly quantified the multi-substrate bonding performance. Although the above-mentioned published literature involves metals and glass, it is presented qualitatively or in different units, and no comparable peel strength data is given. Attached Figure Description

[0037] Figure 1 This is an infrared characterization image of the sample in this invention. Detailed Implementation

[0038] The present invention will be further described below with reference to the embodiments. The following embodiments are descriptive and not limiting, and should not be used to limit the scope of protection of the present invention.

[0039] The various experimental operations involved in the specific embodiments are all conventional techniques in the field. For parts not specifically annotated in this document, those skilled in the art can refer to various commonly used reference books, scientific and technological documents or related instructions and manuals prior to the filing date of this invention to carry out the operations.

[0040] A multi-component synergistic adhesive based on waxy tapioca starch / gelatin / citric acid, the adhesive comprising a main component and water, wherein the main component has a mass fraction of 25%; The main components include waxy tapioca starch (WCS), gelatin, citric acid (CA), and glycerin, with a mass ratio of waxy tapioca starch: gelatin: citric acid of 75-25: 25-75: 20-80.

[0041] Furthermore, in the preparation of the adhesive, gelatin is added in the form of an aqueous solution with a mass concentration of 30 wt%, citric acid is added in the form of an aqueous solution, and glycerol accounts for 20% of the total dry basis mass.

[0042] The preparation method of the multi-component synergistic adhesive as described above includes the following steps: (1) Disperse waxy cassava starch in deionized water and stir to make it evenly dispersed to obtain starch dispersion; (2) Weigh out gelatin and prepare an aqueous solution with a mass concentration of 30 wt%. Stir and dissolve the gelatin at 50°C for 15 min to obtain a gelatin solution. (3) Weigh out citric acid, add deionized water and stir to dissolve, to obtain citric acid solution; (4) The gelatin solution and the citric acid solution are added sequentially to the starch dispersion in step (1), and the mixture is stirred at 90°C for 20 min. (5) Add 20% of the total dry weight of glycerol to the mixture in step (4), continue stirring for 15 min, and cool to obtain the adhesive.

[0043] Furthermore, the stirring speed in steps (1) to (5) is 200-600 rpm.

[0044] Furthermore, the mass concentration of the starch dispersion in step (1) is 20±2%.

[0045] Furthermore, the mass concentration of the citric acid solution in step (3) is 40±2%.

[0046] The application of the multi-component synergistic adhesives described above in substrate bonding and / or paper tape preparation.

[0047] Furthermore, the application involves applying the adhesive to the surface of a substrate and achieving bonding after drying.

[0048] Furthermore, the substrate includes kraft paper, wood board, steel plate, and glass plate.

[0049] Furthermore, in preparing the paper tape, the adhesive is coated onto the surface of kraft paper at a coating amount of 40-50 g / m². 2 After drying, it is made into a wet-type paper tape.

[0050] Specifically, the relevant preparation and testing methods are as follows: Example 1 A multi-component synergistic adhesive based on waxy cassava starch / gelatin / citric acid is prepared as follows: (1) Disperse 13.4 g of waxy cassava starch in 50 g of deionized water and stir at room temperature (300 rpm) to make it evenly dispersed to obtain starch dispersion; (2) Weigh 4.46 g of gelatin, add 10 g of deionized water, and stir to dissolve in a 50°C water bath for 15 min to obtain a gelatin solution of about 30 wt%; (3) Weigh 7.14 g of citric acid, add 10 g of deionized water to dissolve it, and obtain a citric acid solution; (4) Add the gelatin solution from step (2) and the citric acid solution from step (3) to the starch dispersion from step (1) in sequence, heat to 90°C, and stir for 20 min. (5) Add 5 g of glycerol to the mixture in step (4), add 5 g of deionized water and continue stirring for 15 min. Cool to room temperature to obtain an adhesive with a viscosity of 825 mPa·s.

[0051] Example 2 A multi-component synergistic adhesive based on waxy cassava starch / gelatin / citric acid is prepared as follows: (1) Disperse 10.42 g of waxy cassava starch in 40 g of deionized water and stir at room temperature (300 rpm) to make it evenly dispersed to obtain starch dispersion; (2) Weigh 10.42 g of gelatin, add 24 g of deionized water, and stir to dissolve in a 50°C water bath for 15 min to obtain a gelatin solution of about 30 wt%. (3) Weigh 4.17 g of citric acid, add 10 g of deionized water to dissolve it, and obtain a citric acid solution; (4) Add the gelatin solution from step (2) and the citric acid solution from step (3) to the starch dispersion from step (1) in sequence, heat to 90°C, and stir for 20 min. (5) Add 5 g of glycerol to the mixture in step (4), add 1 g of deionized water and continue stirring for 15 min. Cool to room temperature to obtain an adhesive with a viscosity of 2400 mPa·s.

[0052] Example 3 A multi-component synergistic adhesive based on waxy cassava starch / gelatin / citric acid is prepared as follows: (1) Disperse 5.95 g of waxy cassava starch in 30 g of deionized water and stir at room temperature (300 rpm) to make it evenly dispersed to obtain starch dispersion; (2) Weigh 11.9 g of gelatin, add 28 g of deionized water, and stir to dissolve in a 50°C water bath for 15 min to obtain a gelatin solution of about 30 wt%. (3) Weigh 7.14 g of citric acid, add 10 g of deionized water to dissolve it, and obtain a citric acid solution; (4) Add the gelatin solution from step (2) and the citric acid solution from step (3) to the starch dispersion from step (1) in sequence, heat to 90°C, and stir for 20 min. (5) Add 5 g of glycerol to the mixture in step (4), add 7 g of deionized water and continue stirring for 15 min. Cool to room temperature to obtain an adhesive with a viscosity of 1320 mPa·s.

[0053] Example 4 A multi-component synergistic adhesive based on waxy cassava starch / gelatin / citric acid is prepared as follows: (1) Disperse 4.46 g of waxy cassava starch in 25 g of deionized water and stir at room temperature (300 rpm) to make it evenly dispersed to obtain starch dispersion; (2) Weigh 13.4 g of gelatin, add 31 g of deionized water, and stir to dissolve in a 50°C water bath for 15 min to obtain a gelatin solution of about 30 wt%. (3) Weigh 7.14 g of citric acid, add 10 g of deionized water to dissolve it, and obtain a citric acid solution; (4) Add the gelatin solution from step (2) and the citric acid solution from step (3) to the starch dispersion from step (1) in sequence, heat to 90°C, and stir for 20 min. (5) Add 5 g of glycerol to the mixture in step (4), add 9 g of deionized water and continue stirring for 15 min. Cool to room temperature to obtain an adhesive with a viscosity of 1460 mPa·s.

[0054] Example 5 A multi-component synergistic adhesive based on waxy cassava starch / gelatin / citric acid is prepared as follows: (1) Disperse 8.33 g of waxy cassava starch in 38 g of deionized water and stir at room temperature (300 rpm) to make it evenly dispersed to obtain starch dispersion; (2) Weigh 8.33 g of gelatin, add 19 g of deionized water, and stir to dissolve in a 50°C water bath for 15 min to obtain a gelatin solution of about 30 wt%; (3) Weigh 8.33 g of citric acid, add 15 g of deionized water to dissolve it, and obtain a citric acid solution; (4) Add the gelatin solution from step (2) and the citric acid solution from step (3) to the starch dispersion from step (1) in sequence, heat to 90°C, and stir for 20 min. (5) Add 5 g of glycerol to the mixture in step (4), add 3 g of deionized water and continue stirring for 15 min. Cool to room temperature to obtain an adhesive with a viscosity of 980 mPa·s.

[0055] Example 6 A multi-component synergistic adhesive based on waxy cassava starch / gelatin / citric acid is prepared as follows: (1) Disperse 6.94 g of waxy cassava starch in 41 g of deionized water and stir at room temperature (300 rpm) to make it evenly dispersed to obtain starch dispersion; (2) Weigh 6.94 g of gelatin, add 16 g of deionized water, and stir to dissolve in a 50°C water bath for 15 min to obtain a gelatin solution of about 30 wt%. (3) Weigh 11.11 g of citric acid, add 15 g of deionized water to dissolve it, and obtain a citric acid solution; (4) Add the gelatin solution from step (2) and the citric acid solution from step (3) to the starch dispersion from step (1) in sequence, heat to 90°C, and stir for 20 min. (5) Add 5 g of glycerol to the mixture in step (4), add 3 g of deionized water and continue stirring for 15 min. Cool to room temperature to obtain an adhesive with a viscosity of 250 mPa·s.

[0056] Example 7 A multi-component synergistic adhesive based on waxy cassava starch / gelatin / citric acid is prepared as follows: (1) Disperse 10.42 g of waxy cassava starch in 45 g of deionized water and stir at room temperature (300 rpm) to make it evenly dispersed to obtain starch dispersion; (2) Weigh 5.21 g of gelatin, add 12 g of deionized water, and stir to dissolve in a 50°C water bath for 15 min to obtain a gelatin solution of about 30 wt%; (3) Weigh 9.38 g of citric acid, add 15 g of deionized water to dissolve it, and obtain a citric acid solution; (4) Add the gelatin solution from step (2) and the citric acid solution from step (3) to the starch dispersion from step (1) in sequence, heat to 90°C, and stir for 20 min. (5) Add 5 g of glycerol to the mixture in step (4), add 3 g of deionized water and continue stirring for 15 min. Cool to room temperature to obtain an adhesive with a viscosity of 300 mPa·s.

[0057] Comparative Example 1 A multi-component synergistic adhesive based on waxy cassava starch / citric acid was prepared. To verify the necessity of gelatin, a control sample without gelatin was included. Maintaining a total solids content of 25%, and keeping the amounts of waxy cassava starch and citric acid constant, the preparation method is as follows: (1) Disperse 8.33 g of waxy cassava starch in 38 g of deionized water and stir at room temperature (300 rpm) to make it evenly dispersed (300 rpm) to obtain starch dispersion; (2) Weigh 8.33 g of citric acid, add 10 g of deionized water to dissolve it, and obtain a citric acid solution; (3) Add the citric acid solution from step (2) to the starch dispersion from step (1), heat to 90°C, and stir for 20 min. (4) Add 5 g of glycerol to the mixture in step (3), add 3 g of water and continue stirring for 15 min. Cool to room temperature to obtain an adhesive with a viscosity of 600 mPa·s.

[0058] Comparative Example 2 A multi-component synergistic adhesive based on waxy cassava starch / gelatin / citric acid, maintaining a total solids content of 25%, with the starch to gelatin ratio set as 1:1 in Example 5 and the amount of citric acid reduced, is prepared as follows: (1) Disperse 8.33 g of waxy cassava starch in 36 g of deionized water and stir at room temperature (300 rpm) to make it evenly dispersed to obtain starch dispersion; (2) Weigh 8.33 g of gelatin, add 19 g of deionized water, and stir to dissolve in a 50°C water bath for 15 min to obtain a gelatin solution of about 30 wt%; (3) Weigh 2.27 g of citric acid, add 3 g of deionized water to dissolve it, and obtain a citric acid solution; (4) Add the gelatin solution from step (2) and the citric acid solution from step (3) to the starch dispersion from step (1) in sequence, heat to 90°C, and stir for 20 min. (5) Add 5 g of glycerol to the mixture in step (4), continue stirring for 15 min, cool to room temperature, and obtain an adhesive with a viscosity of 3800 mPa·s.

[0059] Comparative Example 3 To verify the necessity of citric acid, a control sample without citric acid was prepared. The amounts of starch and gelatin were kept constant, but because starch gelatinization is difficult without citric acid, the solid content needed to be reduced to ensure operability. The preparation method is as follows: (1) Disperse 8.33 g of waxy cassava starch in 90 g of deionized water and stir at room temperature (300 rpm) to make it evenly dispersed to obtain starch dispersion; (2) Weigh 8.33 g of gelatin, add 19 g of deionized water, and stir to dissolve in a 50°C water bath for 15 min to obtain a gelatin solution of about 30 wt%; (3) Add the gelatin solution from step (2) to the starch dispersion from step (1), heat to 90°C, and stir for 20 min. (4) Add 5 g of glycerol and 7.6 g of deionized water to the mixture in step (3), continue stirring for 15 min, the solid content is about 12.5%, cool to room temperature, and obtain an adhesive with a viscosity of 3470 mPa·s.

[0060] Comparative Example 4 A multi-component synergistic adhesive based on corn starch / gelatin / citric acid is prepared as follows: (1) Disperse 8.33 g of corn starch in 38 g of deionized water and stir at room temperature (300 rpm) to make it evenly dispersed to obtain starch dispersion; (2) Weigh 8.33 g of gelatin, add 19 g of deionized water, and stir to dissolve in a 50°C water bath for 15 min to obtain a gelatin solution of about 30 wt%; (3) Weigh 8.33 g of citric acid, add 15 g of deionized water to dissolve it, and obtain a citric acid solution; (4) Add the gelatin solution from step (2) and the citric acid solution from step (3) to the starch dispersion from step (1) in sequence, heat to 90°C, and stir for 20 min. (5) Add 5 g of glycerol to the mixture in step (4), add 3 g of deionized water and continue stirring for 15 min. Cool to room temperature to obtain an adhesive with a viscosity of 765 mPa·s.

[0061] Performance Experiment Paper tapes were prepared by coating kraft paper with adhesive in the examples and comparative examples, wherein the adhesive coating was 50 g / m². 2 A paper tape with a width of 48 mm and a length of 60 mm was obtained, and its adhesive performance was tested after drying. The storage stability of the adhesive solution was also tested (observed after standing at 25℃).

[0062] Its performance is shown in Table 1.

[0063] Table 1 Performance Comparison Table

[0064] The measurement of initial tack of the tape is based on GB / T 4852-2002; the measurement of peel strength of the tape is based on GB / T2790-1995.

[0065] A comparison of the data in Table 1 shows that: 1. Comparative Example 1 (without gelatin) showed poor adhesion to both steel and glass plates; Comparative Example 3 (without citric acid) showed no adhesion to either steel or glass plates, with an initial tack of only #3. This demonstrates that gelatin and citric acid are key components that impart adhesion to metal / glass.

[0066] 2. Comparing the results of adhesives with different proportions of starch, gelatin and citric acid in Examples 1-6, it can be seen that Example 5 (starch:gelatin:citric acid ≈ 1:1:1) has the best overall performance, with an initial tack of 13# and a peel strength of over 7 N / cm on four substrates: paper, wood, steel and glass.

[0067] 3. Comparing the results of Examples 2 and 3, it can be seen that citric acid plays a dual role in this system: on the one hand, it moderately degrades starch molecular chains through acidic hydrolysis, reducing viscosity (980 mPa·s in Example 2, 3470 mPa·s in Comparative Example 3 without citric acid), thus improving permeability; on the other hand, its polycarboxyl groups act as bridging molecules, forming hydrogen bond networks with starch and gelatin, enhancing cohesive strength and interfacial bonding with the substrate. Insufficient citric acid (Comparative Example 2) results in incomplete hydrolysis, insufficient cross-linking, high viscosity, and poor stability; complete absence (Comparative Example 3) leads to phase separation, maximum viscosity, and the worst adhesion (no adhesion to steel plates and glass). An appropriate amount of citric acid (Examples 2) achieves moderate viscosity, excellent stability (>30 days), and high adhesion.

[0068] 4. Example 5: Viscosity of 980 mPa·s can effectively penetrate the porous substrate to form physical interlocking and form a sufficient adhesive layer on the surface. Example 6: Excessive citric acid leads to excessively low viscosity (250 mPa·s), resulting in decreased adhesive performance. Comparative Example 2: Excessively high viscosity (3800 mPa·s) affects penetration and results in poor adhesive effect.

[0069] 5. Comparative Example 4: The waxy cassava starch in Example 5 was replaced with ordinary corn starch, while the rest of the formulation and preparation steps were exactly the same as in Example 5. The results showed that the initial tack of Comparative Example 4 decreased from 13# to 9#, and the peel strength to cardboard, wood, steel, and glass decreased from 7.13, 7.53, 7.11, and 7.33 N / cm to 5.34, 5.68, 4.72, and 4.43 N / cm, respectively, a significant decrease (25%~38%). Although Comparative Example 4 maintained storage stability for >30 days, all adhesive properties were far lower than in Example 5. This is because ordinary corn starch contains approximately 25% amylose, which is prone to crystallization retrogradation during drying, disrupting the uniformity of the ternary network structure formed with gelatin and citric acid. This weakens the synergistic effect between starch and gelatin in the wet state, resulting in a significant decrease in adhesive performance. Waxy tapioca starch is almost entirely amylopectin (>97%), and its highly branched structure provides abundant hydrogen bond sites, enabling it to form a denser and more uniform physical cross-linking network with gelatin and citric acid, thereby achieving higher initial tack and peel strength.

[0070] Figure 1 Infrared characterization was performed on the films of Example 5 (optimal sample), Comparative Example 3 (without citric acid), and Comparative Example 4 (corn starch replacement). The results showed that the OH peak of Example 5 was located at the lowest wavenumber (3294 cm⁻¹). -1 ), Comparison ratio 3, redshift 11cm -1 Comparison ratio 4, redshift 8 cm -1 And 1714 / 1543 cm -1 The carboxyl peak is the strongest, at 1202 cm⁻¹. -1 The peaks are clear, indicating the formation of the densest hydrogen-bonded cross-linked network. Comparative Example 3, lacking citric acid, has no characteristic carboxyl peak, and the OH peak shows a blue shift, indicating weak hydrogen bonding. Comparative Example 4, although containing citric acid, suffers from a blue shift of the OH peak and a weakened carboxyl peak due to the introduction of ordinary corn starch, resulting in a lower 1202 cm⁻¹ peak. -1 The blue shift and decreased intensity of the peak indicate that starch retrogradation disrupts the network uniformity. The infrared data are in high agreement with the adhesion performance in Table 1 (Example 5 is the best, Comparative Example 3 is the worst, and Comparative Example 4 is in the middle).

[0071] Meanwhile, by comparing Example 5, Comparative Example 2 and Comparative Example 4, it can be seen that the waxy cassava starch and the starch:gelatin:citric acid in a mass ratio of 1:1:1 have a synergistic effect, which can synergistically improve the relevant properties of the prepared multi-component synergistic adhesive.

[0072] Meanwhile, by comparing Example 5, Comparative Example 1 and Comparative Example 4, it can be seen that the waxy cassava starch dispersion and gelatin solution in this invention have a synergistic effect, which can synergistically improve the relevant properties of the prepared multi-component synergistic adhesive.

[0073] This invention has the following advantages over the closest prior art: Significantly superior adhesive performance: The peel strength (>7 N / cm) of this invention on cardboard and glass substrates is significantly better than the adhesive strength (approximately 0.39 N / mm) of the comparative technology. 2 This demonstrates the technical advantages of the starch-gelatin-citric acid three-component synergistic system of the present invention.

[0074] The testing method is closer to practical applications: This invention uses a 180° peel test to directly simulate the use scenario of paper tape; the comparison technology uses the T-peel test, which is a laboratory evaluation method.

[0075] Wider range of applicable substrates: This invention covers four substrates: cardboard, wood, steel, and glass, while the comparative technology only involves cardboard and glass.

[0076] The product form is more clearly defined: This patent is for a wet-type paper tape (non-adhesive when dry, adhesive when wet), while the comparative technology is for pressure-sensitive adhesive (permanent adhesion), and the two belong to different technical branches.

[0077] Although embodiments of the invention have been disclosed for illustrative purposes, those skilled in the art will understand that various substitutions, variations, and modifications are possible without departing from the spirit and scope of the invention and the appended claims. Therefore, the scope of the invention is not limited to the contents disclosed in the embodiments.

Claims

1. A multi-component synergistic adhesive based on waxy cassava starch / gelatin / citric acid, characterized in that: The adhesive comprises a main component and water, wherein the main component has a mass fraction of 25%. The main components include waxy tapioca starch (WCS), gelatin, citric acid (CA), and glycerin, with a mass ratio of waxy tapioca starch: gelatin: citric acid of 75-25: 25-75: 20-80.

2. The multi-component synergistic adhesive according to claim 1, characterized in that: In the preparation of the adhesive, gelatin is added in the form of a 30 wt% aqueous solution, citric acid is added in the form of an aqueous solution, and glycerol accounts for 20% of the total dry basis mass.

3. The method for preparing the multi-component synergistic adhesive as described in claim 1 or 2, characterized in that: Includes the following steps: (1) Disperse waxy cassava starch in deionized water and stir to make it evenly dispersed to obtain starch dispersion; (2) Weigh out gelatin and prepare an aqueous solution with a mass concentration of 30 wt%. Stir and dissolve the gelatin at 50°C for 15 min to obtain a gelatin solution. (3) Weigh out citric acid, add deionized water and stir to dissolve, to obtain citric acid solution; (4) The gelatin solution and the citric acid solution are added sequentially to the starch dispersion in step (1), and the mixture is stirred at 90°C for 20 min. (5) Add 20% of the total dry weight of glycerol to the mixture in step (4), continue stirring for 15 min, and cool to obtain the adhesive.

4. The preparation method according to claim 3, characterized in that: The stirring speed in steps (1) to (5) is 200-600 rpm.

5. The preparation method according to claim 3, characterized in that: The mass concentration of the starch dispersion in step (1) is 20±2%.

6. The preparation method according to any one of claims 3 to 5, characterized in that: The mass concentration of the citric acid solution in step (3) is 40±2%.

7. The application of the multi-component synergistic adhesive as described in claim 1 or 2 in substrate bonding and / or paper tape preparation.

8. The application according to claim 7, characterized in that: The application involves applying the adhesive to the surface of a substrate, which then dries to achieve bonding.

9. The application according to claim 7, characterized in that: The substrates include kraft paper, wood panels, steel plates, and glass plates.

10. The application according to claim 7, characterized in that: When preparing paper tape, the adhesive is coated onto the surface of kraft paper at a coating amount of 40-50 g / m². 2 After drying, it is made into a wet-type paper tape.

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