Bio-based adhesive and preparation method thereof

Abstract

The invention provides a bio-based adhesive and a preparation method thereof. Inspired by a spider thread structure, biomass adhesive interface enhancement based on a tannic acid adhesion group is combined with construction of a differential phase separation structure by biomass-induced polylipoic acid depolymerization, and a brand new strategy of adhesion-cohesion synergistic enhancement of the adhesive strength of the adhesive is realized. According to the invention, tannic acid and carboxymethyl chitosan are introduced into a lipoic acid-based adhesive, so that the purpose of synergistically enhancing the bonding performance of the adhesive through adhesion-cohesion is achieved, and the defects of weak cohesion, low bonding strength, poor water resistance, poor moisture resistance and the like of the conventional biomass adhesive are overcome. Benefited from a new strategy of adhesion-cohesion synergistic enhancement, the biomass adhesive has good adhesive strength in various environments and materials. In addition, the biomass adhesive also has the characteristics of biological safety, antibacterial and mildew-proof properties and recoverability, so that the product has wider application and potential compared with the previous product, and has a good application prospect.

Description

Technical Field

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

[0002] Adhesives are closely related to our daily lives. Since ancient times, people have used natural biomass, such as plants and animals, to make adhesives. In modern times, with the development of the chemical industry, petroleum-based adhesives have replaced bio-based adhesives due to their high bond strength, durability, and low raw material costs.

[0003] However, petroleum-based adhesives emit large amounts of toxic substances during production and use and are difficult to degrade, posing a serious threat to human life and environmental safety. With growing awareness of environmental protection and health, green and safe bio-based adhesives have rekindled research interest among scholars both domestically and internationally. Biomass adhesives, such as protein, starch, soy protein, and lignin, have been extensively studied. However, common drawbacks of bio-based adhesives include low bond strength, poor water and moisture resistance, poor environmental adaptability, susceptibility to mold, and non-recyclability, which significantly hinder their commercial use. Currently, the market and consumers are in urgent need of green biomass adhesives with high bond strength, excellent durability, and strong environmental adaptability.

[0004] Lipoic acid is a naturally occurring small molecule found widely in plants and animals. Thanks to its five-membered disulfide ring and terminal hydroxyl group, polylipoic acid (PLA) produced through ring-opening polymerization exhibits adhesive properties. Driven by the urgent need to develop "green" adhesives, the natural, renewable, and unique molecular structure and physicochemical properties of biomass-derived lipoic acid have shown great application value, particularly in the field of adhesive materials. This has led to extensive research into lipoic acid-based biomass adhesives.

[0005] The prior art discloses a method for preparing a supramolecular polymer based on cyclodextrin / lipoic acid, comprising: adding a cyclodextrin derivative and lipoic acid to water, adding a base containing an amino group, heating and stirring, and forming a viscous supramolecular polymer. However, the polymer has poor cohesion, a long reaction heating time, and high energy consumption. The prior art also discloses a hot-melt injectable adhesive, its preparation method, and its use, which utilizes a mixture of α-lipoic acid, N-alkyl lipoamide, and tris(2-carbonylethyl)phosphine hydrochloride or citric acid, followed by hot melting and cooling to form the adhesive. However, this method is cumbersome, requires high laboratory instrumentation, and involves toxic chemical reagents, which poses a biosafety risk and is not conducive to industrial production.

[0006] In summary, the lipoic acid-based adhesives disclosed in the prior art, prepared using lipoic acid as a matrix, have the following drawbacks: Firstly, although they are bio-based adhesives, their biosafety remains questionable due to the unavoidable use of chemical reagents during their preparation; secondly, these lipoic acid-based adhesives have low mechanical strength and a mismatch between adhesion and cohesion, resulting in a lack of adhesive strength compared to other biomass adhesives, and their preparation process is cumbersome.

[0007] Based on the defects of current lipoic acid-based adhesives, it is necessary to improve this. Summary of the Invention

[0008] In order to solve the defects in the prior art, the present invention provides a bio-based adhesive and a preparation method thereof.

[0009] In a first aspect, the present invention provides a bio-based adhesive comprising the following raw materials in parts by weight:

[0010] 10-20 parts of lipoic acid, 0.1-1 part of biomass providing adhesion groups, and 0.1-1 part of biomass containing carboxymethyl groups.

[0011] Preferably, the biomass providing the adhesion groups includes at least one of tannic acid, lignin, and dopamine;

[0012] The carboxymethyl-containing biomass includes at least one of carboxymethyl chitosan, carboxymethyl cellulose, carboxymethyl starch, carboxymethyl-β-cyclodextrin, and carboxymethyl cysteine.

[0013] Preferably, the following raw materials are included in parts by weight:

[0014] 10-20 parts of lipoic acid, 0.1-1 part of tannic acid, and 0.1-1 part of carboxymethyl chitosan.

[0015] Preferably, the following raw materials are included in parts by weight:

[0016] 10 parts of lipoic acid, 0.2-0.5 parts of tannic acid, and 0.2-0.4 parts of carboxymethyl chitosan.

[0017] In a second aspect, the present invention further provides a method for preparing the bio-based adhesive, comprising the following steps:

[0018] heating lipoic acid to obtain polylipoic acid;

[0019] Biomass providing adhesive groups is added to polylipoic acid, and after stirring, biomass containing carboxymethyl groups is added, and stirring is continued to obtain a bio-based adhesive.

[0020] Preferably, the method comprises the following steps:

[0021] Heating lipoic acid at 150-160° C. for 20-30 min to obtain polylipoic acid;

[0022] Biomass providing adhesion groups is added to polylipoic acid, and the mixture is stirred at 150-160° C. for 20-30 minutes. Then, biomass containing carboxymethyl groups is added, and the mixture is stirred for 10-20 minutes to obtain a bio-based adhesive.

[0023] Preferably, the biomass providing the adhesion group is tannic acid;

[0024] The carboxymethyl-containing biomass is carboxymethyl chitosan;

[0025] The preparation method of the bio-based adhesive comprises the following steps:

[0026] Heating lipoic acid at 150-160° C. for 20-30 min to obtain polylipoic acid;

[0027] Tannic acid was added to polylipoic acid, and the mixture was stirred at 150-160° C. for 20-30 minutes. Carboxymethyl chitosan was then added, and the mixture was stirred for 10-20 minutes to obtain a bio-based adhesive.

[0028] Preferably, lipoic acid is heated at 150° C. for 30 min to obtain polylipoic acid;

[0029] Tannic acid was added to polylipoic acid, and the mixture was stirred at 150° C. for 20 min. Then, carboxymethyl chitosan was added and the mixture was stirred for 10 min to obtain a bio-based adhesive.

[0030] The bio-based adhesive and its preparation method of the present invention have the following effects compared with the prior art:

[0031] 1. The preparation method of the bio-based adhesive of the present invention combines the interface enhancement of the biomass adhesive based on tannic acid adhesion groups with the construction of a differential phase separation structure by biomass-induced polylipoic acid depolymerization to achieve a new strategy of adhesion-cohesion synergistic enhancement of the adhesive. The mechanism of this strategy is as follows: (1) In response to the shortcoming of weak interfacial adhesion of biomass adhesives, the present invention adopts a biomass adhesive interface enhancement strategy based on tannic acid adhesion groups. Tannic acid is added. After cross-linking with polylipoic acid in the system through hydrogen bonding, the tannic acid increases the adhesion groups inside the adhesive, thereby enhancing the interfacial adhesion of the adhesive; (2) The above-mentioned lipoic acid-tannic acid adhesive system has the shortcoming of weak cohesion (which is also a shortcoming that most biomass adhesives urgently need to solve). To address this shortcoming, the present invention adopts a strategy of constructing a differential phase separation structure by biomass-induced polylipoic acid depolymerization. Carboxymethyl polysaccharide was further added to the system. The stronger hydrogen bond donor - carboxymethyl on the carboxymethyl polysaccharide destroyed the hydrogen bond between polylipoic acid and tannic acid, inducing polylipoic acid to depolymerize and form a differential phase separation structure, thereby enhancing the cohesion of the adhesive and achieving adhesion-cohesion synergistic enhancement of the adhesive's bonding performance.

[0032] 2. The present invention uses lipoic acid as the matrix, which has a disulfide five-membered ring and a terminal hydroxyl group. The polylipoic acid liquid obtained by ring-opening polymerization has excellent flow and adhesion properties, and can form a tighter mechanical interlocking structure with the interface of the object, which is beneficial to improving the adhesion of the adhesive.

[0033] 3. The bio-based adhesive prepared by the present invention has good fluidity and is easy to apply. It can be evenly applied on various substrates (glass, ceramics, metal, wood, plastic) and in various environments (air, water, seawater) and has high bonding strength.

[0034] 4. The bio-based adhesive prepared by the present invention has a large number of adhesion groups (phenolic hydroxyl groups of tannic acid and terminal hydroxyl groups of lipoic acid), which enables the adhesive to form a large number of hydrogen bonds with the surfaces of various substances, overcoming the shortcomings of biomass adhesives in terms of poor water and moisture resistance, and giving the adhesive the advantages of water and moisture resistance.

[0035] 5. The bio-based adhesive prepared by the present invention contains antibacterial biomass such as lipoic acid and tannic acid. The synergistic enhancement of the antibacterial effect of the two makes the adhesive have the advantages of hindering bacterial reproduction and being antibacterial and mildew-proof. It overcomes the shortcomings of biomass adhesives such as short service life and easy mildew, and achieves the purpose of long-term use of biomass adhesives.

[0036] 6. The bio-based adhesive prepared by the present invention is composed of biomass such as lipoic acid, tannic acid, and carboxymethyl polysaccharide, all of which are biosafe. Therefore, the prepared adhesive is harmless to organisms and the natural environment and has good biosafety.

[0037] 7. The bio-based adhesive prepared by this invention has a rich internal structure of dynamic covalent bonds (disulfide bonds) and non-covalent bonds (hydrogen bonds). Lipoic acid and polylipoic acid have reversible disulfide bonds, and lipoic acid, tannic acid, and carboxymethyl polysaccharides are cross-linked via hydrogen bonds. By simply heating the used adhesive, it can be melted and reused again. This overcomes the drawback of most biomass adhesives, making it recyclable and reusable multiple times.

[0038] 8. The preparation method of the bio-based adhesive prepared by the present invention is simple and can be prepared by simple heating. There are no strict requirements on production conditions and it is expected to achieve large-scale production. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] To more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. Those skilled in the art can also derive other drawings based on these drawings without inventive effort.

[0040] Figure 1 The synthetic route and mechanism diagram of the bio-based adhesive of the present invention;

[0041] Figure 2 The infrared spectra of the bio-based adhesives prepared in Example 6 and Comparative Examples 1-2 are shown;

[0042] Figure 3 Macroscopic property diagrams, adhesion failure diagrams, and adhesion failure descriptions of the adhesives of Example 6 and Comparative Examples 1 to 5;

[0043] Figure 4 is the XRD spectra of lipoic acid (LA) powder, the adhesives prepared in Comparative Examples 1 to 3 and Example 6;

[0044] Figure 5 1H NMR spectra of the bio-based adhesive (i.e., polylipoic acid) and lipoic acid (LA) powder in Comparative Example 1;

[0045] Figure 6 1H NMR spectra of the adhesives and lipoic acid (LA) powder prepared in Comparative Examples 1 to 3 and Example 6;

[0046] Figure 7 is a graph showing the molar ratio of la to pla in the adhesives prepared in Comparative Examples 1 to 3 and Example 6;

[0047] Figure 8 This is the SEM image of the adhesive prepared in Example 6;

[0048] Figure 9 is an AFM image of the adhesive prepared in Example 6;

[0049] Figure 10 The graph shows the shear strength of the adhesive prepared in Example 1 on glass as a function of time (0.5 h to 150 d) when tested in air;

[0050] Figure 11 Graph showing the change in shear strength of the adhesive prepared in Example 1 on glass over time (0.5 h to 30 d) during underwater testing;

[0051] Figure 12 This is a comparison chart of the shear strength of the adhesive prepared in Example 1 on different substrates in air, underwater, and seawater;

[0052] Figure 13 This is a diagram of the recycling mechanism of the adhesive prepared in Example 1;

[0053] Figure 14 This is a graph showing the change in bonding strength of the adhesive prepared in Example 1 after five cycles of use on glass;

[0054] Figures 15-16 This is a biosafety experiment of the adhesive prepared in Example 1;

[0055] Figure 17 Schematic diagram of adhesive shear strength test.

[0056] Figure 18 Schematic diagram of adhesive failure and cohesive failure. DETAILED DESCRIPTION

[0057] To facilitate understanding of the present invention, the present invention will be described more fully below in conjunction with the specific embodiments. Preferred embodiments of the present invention are provided in the specific embodiments. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to provide a more thorough and comprehensive understanding of the disclosure of the present invention.

[0058] The order of description of the following embodiments is not intended to limit the preferred order of the embodiments. In addition, in the description of this application, the term "including" means "including but not limited to". Various embodiments of the present invention may be presented in the form of a range; it should be understood that the description in the form of a range is merely for convenience and brevity and should not be understood as a rigid limitation on the scope of the invention; therefore, it should be considered that the range description has specifically disclosed all possible sub-ranges and single numerical values ​​within the range. For example, the range description from 1 to 6 should be considered to have specifically disclosed sub-ranges, such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., as well as single numbers within the range, such as 1, 2, 3, 4, 5 and 6, regardless of the range. In addition, whenever a numerical range is indicated herein, it is meant to include any cited number (fractional or integer) within the indicated range.

[0059] The present invention provides a bio-based adhesive comprising the following raw materials in parts by weight:

[0060] 10-20 parts of lipoic acid, 0.1-1 part of biomass providing adhesion groups, and 0.1-1 part of biomass containing carboxymethyl groups.

[0061] In some embodiments, the biomass providing the adhesion groups includes at least one of tannic acid, lignin, and dopamine;

[0062] The carboxymethyl-containing biomass includes at least one of carboxymethyl chitosan, carboxymethyl cellulose, carboxymethyl starch, carboxymethyl-β-cyclodextrin, and carboxymethyl cysteine.

[0063] The bio-based adhesive of the present invention includes lipoic acid, biomass providing adhesion groups, and biomass containing carboxymethyl groups. The bonding strength of the adhesive is determined by both adhesion and cohesion. Adhesion is the adhesion property between the adhesive and the interface of the object; cohesion is determined by the mechanical strength of the adhesive. How to enhance the bonding strength of the adhesive by synergistically enhancing the adhesion-cohesion balance strategy is a difficulty faced by lipoic acid-based bioadhesives.

[0064] The biomimetic concept inspired by the biological world provides a multi-dimensional research approach for the innovative development of adhesive technology, one of which is spider silk. Spider silk used to capture prey can be simply divided into two parts: one is the capture glue used to adhere prey, composed of glycoproteins and rich in adhesive groups, which is used to stick to prey; the other is the load-bearing silk, whose interior is composed of a differential phase separation structure composed of β-layer nanocrystals, which gives the spider silk excellent mechanical properties. Together, they form a capture silk with excellent adhesion and mechanical strength. Inspired by spider capture silk, if biomass with adhesive groups and a differential phase separation structure that enhances cohesion can be simultaneously introduced into lipoic acid-based adhesives, the goal of synergistic enhancement of adhesion and cohesion can be achieved.

[0065] Biomasses that provide adhesive groups, such as tannic acid, are rich in phenolic hydroxyl groups, which can form strong interfacial adhesion with surfaces through hydrogen bonding. However, tannic acid inhibits the depolymerization of polylipoic acid through non-covalent bonding with polylipoic acid (PLA), weakening the adhesive's cohesion and resulting in an imbalanced state between strong adhesion and weak cohesion. To enhance adhesive cohesion, strong hydrogen bond donors are added to the adhesive system to disrupt the hydrogen bonds between tannic acid and polylipoic acid, promoting the depolymerization of polylipoic acid and forming a crystalline phase separation structure within the adhesive. This differential phase separation structure, composed of anti-spider silk β-layer nanocrystals, can enhance the adhesive's cohesion. Biomasses containing carboxymethyl groups, such as carboxymethyl chitosan, are obtained by treating chitosan. The carboxymethyl groups on their molecular chains disrupt the hydrogen bonds between tannic acid and polylipoic acid within the system, promoting the depolymerization of polylipoic acid and forming a differential phase separation structure, thereby enhancing adhesive cohesion.

[0066] The present invention is based on the following principles: (1) To enhance the interfacial adhesion of the adhesive, the present invention adopts a biomass adhesive interface enhancement strategy based on adhesion groups such as tannic acid. First, tannic acid is introduced into the polylipoic acid system to increase the interfacial adhesion of the adhesive. (2) The lipoic acid-tannic acid adhesive system has the disadvantage of weak cohesion. To address this disadvantage, the present invention adopts a biomass-induced depolymerization of polylipoic acid to construct a differential phase separation structure. Carboxymethyl-containing biomass, such as carboxymethyl chitosan, is further added to the system to promote the depolymerization of polylipoic acid to form a differential phase separation structure, thereby enhancing the cohesion of the adhesive and achieving the purpose of synergistic enhancement of the adhesive's bonding performance through adhesion and cohesion.

[0067] The bio-based adhesive of this invention exhibits excellent bonding properties and can be used on a variety of substrates and in a variety of environments. Furthermore, thanks to the dynamic covalent and non-covalent bonds within the adhesive, it is recyclable and can be reused multiple times. It is also biosafe and antibacterial and mildew-resistant.

[0068] Compared to existing technologies, the bio-based adhesive of the present invention achieves a dry bond strength of 5.1 MPa on glass and an underwater bond strength of over 1.5 MPa, both with long-lasting adhesion. Environmentally friendly, the preparation process of the bio-based adhesive of the present invention does not involve the use of toxic chemicals, resulting in excellent biosafety. Furthermore, the adhesive is recyclable, which helps reduce costs, pollution, and carbon emissions. Industrially, the preparation method of the present invention is simple, has a short reaction time, and does not involve tedious precursor modification, so the raw materials are commercially available, facilitating commercial production. Currently, there are no technical solutions for preparing lipoic acid-based adhesives using lipoic acid, tannic acid, and carboxymethyl polysaccharides. Nor are there technical solutions for combining the biomass adhesive interface enhancement strategy based on tannic acid adhesion groups with the strategy of constructing a differential phase separation structure through biomass-induced depolymerization of polylipoic acid to enhance adhesive properties through a synergistic adhesion-cohesion enhancement strategy.

[0069] In some embodiments, the bio-based adhesive comprises the following raw materials in parts by weight:

[0070] 10-20 parts of lipoic acid, 0.1-1 part of tannic acid, and 0.1-1 part of carboxymethyl chitosan.

[0071] In some embodiments, the following raw materials are included in parts by weight:

[0072] 10 parts of lipoic acid, 0.2-0.5 parts of tannic acid, and 0.2-0.4 parts of carboxymethyl chitosan.

[0073] In some embodiments, the following raw materials are included in parts by weight:

[0074] 10 parts of lipoic acid, 0.3-0.5 parts of tannic acid, and 0.2-0.4 parts of carboxymethyl chitosan.

[0075] Inspired by the structure of spider silk, this invention combines the interfacial enhancement of biomass adhesives based on tannic acid adhesion groups with the construction of a differential phase separation structure through biomass-induced depolymerization of polylipoic acid, achieving a novel strategy for synergistic adhesion-cohesion enhancement of adhesive bond strength. By introducing tannic acid and carboxymethyl chitosan into a lipoic acid-based adhesive, this synergistic adhesion-cohesion enhancement of adhesive properties is achieved. This overcomes the shortcomings of previous biomass adhesives, such as weak cohesion, low bond strength, and poor water and moisture resistance, resulting in a biomass-based adhesive with excellent performance. Thanks to this novel adhesion-cohesion synergistic enhancement strategy, this biomass adhesive exhibits excellent bond strength in a variety of environments and materials. Furthermore, this biomass adhesive is biosafe, antibacterial, and recyclable, making it more versatile and promising compared to previous products, with promising application prospects.

[0076] Based on the same inventive concept, the present invention also provides a method for preparing the above-mentioned bio-based adhesive, comprising the following steps:

[0077] S1, heating lipoic acid to obtain polylipoic acid;

[0078] S2. Add biomass that provides adhesion groups to polylipoic acid, stir, then add biomass containing carboxymethyl groups, continue stirring, and obtain a bio-based adhesive.

[0079] In some embodiments, a method for preparing a bio-based adhesive comprises the following steps:

[0080] S1. heating lipoic acid at 150-160° C. for 20-30 min to obtain polylipoic acid;

[0081] S2. Add biomass providing adhesion groups to polylipoic acid, continue stirring at 150-160° C. for 20-30 minutes, then add biomass containing carboxymethyl groups, continue stirring for 10-20 minutes to obtain a bio-based adhesive.

[0082] In some embodiments, the biomass providing the adhesion group is tannic acid;

[0083] The biomass containing carboxymethyl groups is carboxymethyl chitosan;

[0084] The preparation method of the bio-based adhesive comprises the following steps:

[0085] S1. heating lipoic acid at 150-160° C. for 20-30 min to obtain polylipoic acid;

[0086] S2. Maintaining the temperature of S1 (i.e., all reactions are carried out at 150-160° C.), adding tannic acid to polylipoic acid, stirring for 20-30 minutes, then adding carboxymethyl chitosan, and continuing stirring for 10-20 minutes to obtain a bio-based adhesive.

[0087] Specifically, Figure 1 The synthetic route and mechanism diagram of the bio-based adhesive of the present invention.

[0088] like Figure 1 As shown, the present invention prepares a bio-based adhesive by a solvent-free one-pot polymerization method; first, lipoic acid (LA) powder is ring-opening polymerized at high temperature to form a polylipoic acid adhesive (Comparative Example 1). When it is cooled, the polylipoic acid depolymerizes. When the lipoic acid monomers produced after depolymerization are sufficient, lipoic acid crystals are generated, which produces a strong cohesive effect, but its interfacial adhesion effect is weak;

[0089] Subsequently, in order to imitate the strong adhesion effect brought by spider silk glycoprotein, tannic acid (TA) was added until it was completely dissolved to obtain lipoic acid / tannic acid adhesive (Comparative Example 2). The phenolic hydroxyl groups in tannic acid can provide abundant adhesion sites, thereby significantly enhancing the interfacial adhesion performance of the adhesive. However, tannic acid forms hydrogen bonds with polylipoic acid, inhibiting the depolymerization of polylipoic acid. When it is cooled, the depolymerization of polylipoic acid is inhibited, and the amount of lipoic acid monomers generated is insufficient to form lipoic acid crystals, resulting in a decrease in adhesive cohesion. Although the introduction of tannic acid increases the interfacial adhesion of the adhesive, the disappearance of lipoic acid crystals causes the adhesive cohesion to decrease, which in turn reduces the bonding strength.

[0090] Finally, in order to increase the cohesive force of the adhesive, the β-layer phase separation structure of spider silk is imitated. Carboxymethyl chitosan (CMCS) is introduced until it is completely dissolved to obtain lipoic acid / tannic acid / carboxymethyl chitosan adhesive (Example 1). The introduction of carboxymethyl chitosan will compete for hydrogen bonding to destroy the network crosslinking between polylipoic acid and tannic acid. After cooling, it will induce polylipoic acid to depolymerize and generate a large amount of lipoic acid monomers, forming lipoic acid crystals, and then forming a differential phase separation structure to enhance the cohesive force of the adhesive. In this way, the interfacial adhesion of the adhesive can be increased by tannic acid, and the cohesive force of the adhesive can be enhanced by internal lipoic acid crystals, realizing the adhesion-cohesion synergistic enhancement of spider silk-like structures, and preparing adhesives with high bonding strength.

[0091] The preparation method of the bio-based adhesive of the present invention combines the interface enhancement of the biomass adhesive based on tannic acid adhesion groups with the construction of a differential phase separation structure by biomass-induced polylipoic acid depolymerization, thereby realizing a new strategy of synergistically enhancing the adhesive by adhesion and cohesion. The mechanism of this strategy is as follows: (1) To address the shortcoming of weak interfacial adhesion of biomass adhesives, the present invention adopts a biomass adhesive interface enhancement strategy based on tannic acid adhesion groups. Tannic acid is added, and after cross-linking with polylipoic acid in the system through hydrogen bonding, the tannic acid increases the adhesion groups inside the adhesive, thereby enhancing the interfacial adhesion of the adhesive; (2) The above-mentioned lipoic acid-tannic acid adhesive system has the shortcoming of weak cohesion (which is also a shortcoming that most biomass adhesives urgently need to solve). To address this shortcoming, the present invention adopts a strategy of constructing a differential phase separation structure by biomass-induced polylipoic acid depolymerization. Carboxymethyl polysaccharide was further added to the system. The stronger hydrogen bond donor - carboxymethyl on the carboxymethyl polysaccharide destroyed the hydrogen bond between polylipoic acid and tannic acid, inducing polylipoic acid to depolymerize and form a differential phase separation structure, thereby enhancing the cohesion of the adhesive and achieving adhesion-cohesion synergistic enhancement of the adhesive's bonding performance.

[0092] The present invention uses lipoic acid as a matrix, which has a disulfide five-membered ring and a terminal hydroxyl group. The polylipoic acid liquid obtained by ring-opening polymerization has excellent flow and adhesion properties, can form a tighter mechanical interlocking structure with the interface of the object, and is conducive to improving the adhesion of the adhesive.

[0093] The bio-based adhesive prepared by the present invention has good fluidity and is easy to apply. It can be evenly applied on various substrates (glass, ceramics, metal, wood, plastic) and in various environments (air, water, seawater) and has high bonding strength.

[0094] The bio-based adhesive prepared by the present invention has a large number of adhesion groups (phenolic hydroxyl groups of tannic acid and terminal hydroxyl groups of lipoic acid), which enables the adhesive to form a large number of hydrogen bonds with the surfaces of various substances, overcoming the shortcomings of biomass adhesives in terms of poor water and moisture resistance, and giving the adhesive the advantages of water and moisture resistance.

[0095] The bio-based adhesive prepared by the present invention contains antibacterial biomass such as lipoic acid and tannic acid. The synergistic enhancement of the antibacterial effect of the two enables the adhesive to have the advantages of hindering bacterial reproduction and being antibacterial and mildew-proof. It overcomes the shortcomings of biomass adhesives such as short service life and easy mildew, and achieves the purpose of long-term use of biomass adhesives.

[0096] The bio-based adhesive prepared by the present invention is composed of biomass such as lipoic acid, tannic acid, and carboxymethyl polysaccharide, all of which are biosafe. Therefore, the prepared adhesive is harmless to organisms and the natural environment and has good biosafety.

[0097] The bio-based adhesive prepared by this invention has a rich internal structure of dynamic covalent bonds (disulfide bonds) and non-covalent bonds (hydrogen bonds); lipoic acid and polylipoic acid have reversible disulfide bonds; and lipoic acid, tannic acid, and carboxymethyl polysaccharides are cross-linked via hydrogen bonds. By simply heating the used adhesive, it can be melted again for a second use. This overcomes the drawback of most biomass adhesives, making it recyclable and reusable multiple times.

[0098] The preparation method of the bio-based adhesive prepared by the present invention is simple, can be prepared by simple heating, has no strict requirements on production conditions, and is expected to achieve large-scale production.

[0099] The following further illustrates the bio-based adhesive and its preparation method of the present invention with reference to specific examples. This section further illustrates the present invention with reference to specific examples, but should not be construed as limiting the present invention. Unless otherwise specified, the techniques employed in the examples are conventional techniques known to those skilled in the art. Unless otherwise specified, the reagents, methods, and equipment employed in the present invention are conventional in the art.

[0100] In the following examples, lipoic acid (C8H 14 O2S2), tannic acid (C 76 H 52 O 46 ) and carboxymethyl chitosan (C804727, Cas No.: 83512-85-0) were purchased from MacLean Reagent.

[0101] In the following examples, the shear strength in air was tested as follows: the bio-based adhesives prepared in different examples and comparative examples were drawn up with a syringe and then applied to a substrate (e.g., glass) using the syringe to form an adhesion area. The adhesion area was then quickly covered with another substrate (e.g., glass). The adhesive was allowed to stand at room temperature (25°C) for 24 hours before a shear test was performed. The adhesive was then pulled apart using a tensile testing machine, and the maximum force required was recorded. The shear strength was then calculated by dividing the force by the overlapping area of ​​the two pieces of glass (1 cm × 0.5 cm). The calculation formula is as follows:

[0102]

[0103] The test method for underwater shear strength is the same as above, except that the substrate is placed underwater for different periods of time, and then taken out of the water for testing when the shear strength is tested using a tensile testing machine (for example, to test the underwater shear strength for 0.5h, the bonded substrate is placed underwater for 0.5h and then taken out for testing); the test diagram is shown in the figure below. Figure 17 shown.

[0104] In the following examples and comparative examples, where the shear strength does not specify the time, the shear strength data are after 24 hours of storage.

[0105] Example 1

[0106] This embodiment provides a bio-based adhesive, including the following raw materials:

[0107] 10g lipoic acid, 0.4g tannic acid, 0.3g carboxymethyl chitosan.

[0108] The preparation method of the above-mentioned bio-based adhesive comprises the following steps:

[0109] S1. Place 10 g of lipoic acid in a beaker and heat at 150° C. for 30 min to obtain polylipoic acid;

[0110] S2. At 150° C., 0.4 g of tannic acid was added to polylipoic acid and stirred for 20 min. Finally, 0.3 g of carboxymethyl chitosan was added and the mixture was stirred for 10 min to obtain a bio-based adhesive.

[0111] Example 2

[0112] This embodiment provides a bio-based adhesive, including the following raw materials:

[0113] 10g lipoic acid, 0.3g tannic acid, 0.3g carboxymethyl chitosan.

[0114] The preparation method of the above-mentioned bio-based adhesive comprises the following steps:

[0115] S1. Place 10 g of lipoic acid in a beaker and heat at 150° C. for 30 min to obtain polylipoic acid;

[0116] S2. At 150° C., 0.3 g of tannic acid was added to polylipoic acid and stirred for 20 min. Finally, 0.3 g of carboxymethyl chitosan was added and the mixture was stirred for 10 min to obtain a bio-based adhesive.

[0117] Example 3

[0118] This embodiment provides a bio-based adhesive, including the following raw materials:

[0119] 10g lipoic acid, 0.5g tannic acid, 0.3g carboxymethyl chitosan.

[0120] The preparation method of the above-mentioned bio-based adhesive comprises the following steps:

[0121] S1. Place 10 g of lipoic acid in a beaker and heat at 150° C. for 30 min to obtain polylipoic acid;

[0122] S2. At 150° C., 0.5 g of tannic acid was added to polylipoic acid and stirred for 20 min. Finally, 0.3 g of carboxymethyl chitosan was added and the mixture was stirred for 10 min to obtain a bio-based adhesive.

[0123] Example 4

[0124] This embodiment provides a bio-based adhesive, including the following raw materials:

[0125] 10g lipoic acid, 0.4g tannic acid, 0.2g carboxymethyl chitosan.

[0126] The preparation method of the above-mentioned bio-based adhesive comprises the following steps:

[0127] S1. Place 10 g of lipoic acid in a beaker and heat at 150° C. for 30 min to obtain polylipoic acid;

[0128] S2. At 150° C., 0.4 g of tannic acid was added to polylipoic acid and stirred for 20 min. Finally, 0.2 g of carboxymethyl chitosan was added and the mixture was stirred for 10 min to obtain a bio-based adhesive.

[0129] Example 5

[0130] This embodiment provides a bio-based adhesive, including the following raw materials:

[0131] 10g lipoic acid, 0.4g tannic acid, 0.4g carboxymethyl chitosan.

[0132] The preparation method of the above-mentioned bio-based adhesive comprises the following steps:

[0133] S1. Place 10 g of lipoic acid in a beaker and heat at 150° C. for 30 min to obtain polylipoic acid;

[0134] S2. At 150° C., 0.4 g of tannic acid was added to polylipoic acid and stirred for 20 min. Finally, 0.4 g of carboxymethyl chitosan was added and the mixture was stirred for 10 min to obtain a bio-based adhesive.

[0135] Example 6

[0136] This embodiment provides a bio-based adhesive, including the following raw materials:

[0137] 10g lipoic acid, 0.2g tannic acid, 0.2g carboxymethyl chitosan.

[0138] The preparation method of the above-mentioned bio-based adhesive comprises the following steps:

[0139] S1. Place 10 g of lipoic acid in a beaker and heat at 150° C. for 30 min to obtain polylipoic acid;

[0140] S2. At 150° C., 0.2 g of tannic acid was added to polylipoic acid and stirred for 20 min. Finally, 0.2 g of carboxymethyl chitosan was added and the mixture was stirred for 10 min to obtain a bio-based adhesive.

[0141] Comparative Example 1

[0142] This comparative example provides a method for preparing a bio-based adhesive, comprising the following steps:

[0143] S1. Place 10 g of lipoic acid in a beaker and heat at 150° C. for 30 min to obtain a bio-based adhesive.

[0144] Comparative Example 2

[0145] This comparative example provides a method for preparing a bio-based adhesive, comprising the following steps:

[0146] S1. Place 10 g of lipoic acid in a beaker and heat at 150° C. for 30 min to obtain polylipoic acid;

[0147] S2. Add 0.2 g of tannic acid to polylipoic acid at 150° C. and stir for 20 min to obtain a bio-based adhesive.

[0148] Comparative Example 3

[0149] This comparative example provides a method for preparing a bio-based adhesive, comprising the following steps:

[0150] S1. Place 10 g of lipoic acid in a beaker and heat at 150° C. for 30 min to obtain polylipoic acid;

[0151] S2. At 150° C., 0.2 g of tannic acid was added to polylipoic acid and stirred for 20 min. Finally, 0.2 g of chitosan was added and the stirring was continued for 10 min to obtain a bio-based adhesive.

[0152] Comparative Example 4

[0153] This comparative example provides a method for preparing a bio-based adhesive, comprising the following steps:

[0154] S1. Place 10 g of lipoic acid in a beaker and heat at 150° C. for 30 min to obtain polylipoic acid;

[0155] S2. Add 0.2 g of carboxymethyl chitosan to polylipoic acid at 150° C. and stir for 10 min to obtain a bio-based adhesive.

[0156] Comparative Example 5

[0157] This comparative example provides a method for preparing a bio-based adhesive, comprising the following steps:

[0158] S1. Place 10 g of lipoic acid in a beaker and heat at 150° C. for 30 min to obtain polylipoic acid;

[0159] S2. Add 0.2 g of chitosan to polylipoic acid at 150° C. and stir for 10 min to obtain a bio-based adhesive.

[0160] Performance Testing

[0161] The shear strength of the bio-based adhesives prepared in Examples 1 to 6 and Comparative Examples 1 to 5 was tested according to the above method (in air, with the substrate being glass), as shown in Table 1 below.

[0162] Table 1 - Adhesion strength of bio-based adhesives prepared in Examples 1 to 6 and Comparative Examples 1 to 5

[0163] Example Shear strength (MPa) Comparative Example Shear strength (MPa) Example 1 5.09 Comparative Example 1 1.4 Example 2 3.95 Comparative Example 2 0.45 Example 3 4.05 Comparative Example 3 1.15 Example 4 4.5 Comparative Example 4 1.22 Example 5 4.16 Comparative Example 5 0.57 Example 6 3.3

[0164] As can be seen from Table 1, by comparing Example 6 with Comparative Examples 1 to 5, it can be seen that the shear strength of the adhesive is greatly improved only when tannic acid and carboxymethyl chitosan are added simultaneously; this is because tannic acid can increase the number of adhesive groups in the adhesive and increase interfacial adhesion, but will weaken the cohesion of the adhesive; only after the addition of carboxymethyl chitosan can the depolymerization of polylipoic acid be promoted, forming a phase separation structure within the adhesive, thereby enhancing the cohesion of the adhesive and achieving the effect of synergistic enhancement of cohesion and adhesion.

[0165] By comparing Examples 1 to 5, it can be found that the optimal ratio of the adhesive obtained by orthogonal test is 10 parts of lipoic acid, 0.4 parts of tannic acid, and 0.3 parts of carboxymethyl chitosan.

[0166] Figure 2 This is the infrared spectra of the bio-based adhesives prepared in Example 6 and Comparative Examples 1-2.

[0167] Figure 2 There is no new peak in the ions, indicating that no new functional groups are generated; the C=O band energy of the adhesives prepared in Comparative Examples 1-2 and Example 6 is 1687 cm -1 、1688cm -1 and 1690cm -1 , indicating that only non-covalent bonds (hydrogen bonds) exist inside the adhesive.

[0168] Figure 3 The following are macroscopic property diagrams, adhesion failure diagrams, and adhesion failure explanations for the adhesives of Example 6 and Comparative Examples 1-5. Comparative Examples 1 and 2 show that the addition of tannic acid softens the lipoic acid adhesive from hard to soft, and the adhesion failure type changes from adhesive failure to cohesive failure. Simultaneously, the shear strength decreases from 1.4 MPa to 0.45 MPa. This indicates that while the addition of tannic acid increases the adhesive groups within the adhesive, it weakens the adhesive's cohesion, resulting in a decrease in bond strength. Comparative Example 5 and Example 6, in which chitosan and carboxymethyl chitosan were added, respectively, exhibit macroscopic properties of soft and hard, respectively, and adhesion failure types of cohesive failure and adhesive failure, respectively. The corresponding shear strengths are 0.57 MPa and 3.3 MPa, respectively. This indicates that compared to chitosan, carboxymethyl chitosan significantly enhances the cohesion of the lipoic acid-tannic acid adhesive, and that the combination with tannic acid enhances the adhesive's adhesion, thereby increasing its bond strength. In order to eliminate the influence of chitosan and carboxymethyl chitosan on the interfacial adhesion of the adhesive, it can be seen from Comparative Examples 3 and 4 that the macroscopic properties of the adhesives without adding tannic acid and only adding chitosan and carboxymethyl chitosan are hard, the adhesion failure type is adhesion failure, and the shear strengths are 1.15 MPa and 1.22 MPa, respectively; this indicates that the addition of chitosan and carboxymethyl chitosan does not increase the interfacial adhesion of the adhesive.

[0169] Figure 4The XRD spectra of lipoic acid (LA) powder, the adhesives prepared in Comparative Examples 1 to 3 and Example 6.

[0170] Depend on Figure 4 The analysis showed that comparative examples 2 and 3 were amorphous structures; the adhesives of comparative example 1 and example 6 had the same crystallization peak as the lipoic acid powder, indicating that the adhesives of comparative example 1 and example 6 contained lipoic acid crystals; Figure 3 , which shows that the cohesive strength of the adhesive is determined by the lipoic acid crystals inside the adhesive. When the adhesive contains a large amount of lipoic acid crystals, a differential phase separation structure will be formed inside the adhesive, which greatly enhances the cohesive strength of the adhesive.

[0171] Figure 5 This is the hydrogen nuclear magnetic resonance spectrum of the bio-based adhesive (i.e., polylipoic acid) and lipoic acid (LA) powder in Comparative Example 1.

[0172] Figure 5 The purpose of this is to compare the H NMR spectra of the lipoic acid powder with that of Comparative Example 1. This is because the different peak positions of the hydrogen at the b-position of the lipoic acid monomer (Ia) and the hydrogen at the b' position of the polylipoic acid (ploy-Ia) on the H NMR spectrum, as well as the corresponding peak area ratio, can be used to determine the content and molar ratio of lipoic acid monomer (Ia) to polylipoic acid (ploy-Ia) in the adhesive. Lipoic acid powder contains only lipoic acid monomer (Ia), which can be used as a baseline for comparison. Specifically, lipoic acid powder contains only lipoic acid monomer (Ia). When heated, it polymerizes to form polylipoic acid (ploy-Ia). However, polylipoic acid (ploy-Ia) is unstable and regenerates lipoic acid monomer (Ia) upon cooling. When the number of lipoic acid monomers (Ia) produced by depolymerization is sufficient, these lipoic acid monomers (Ia) aggregate and arrange in an orderly manner to form lipoic acid crystals. Lipoic acid crystals enhance the cohesion of the adhesive, which is desirable for the present invention. In order to characterize the quantitative ratio of lipoic acid monomer (la) to polylipoic acid (ploy-la) in the adhesive, the molar ratio la / pla of lipoic acid monomer (la) to polylipoic acid (ploy-la) in the adhesive can be determined by the difference in the peak positions of hydrogen at the b position of lipoic acid monomer (la) and hydrogen at the b' position of polylipoic acid (ploy-la) on the nuclear magnetic resonance hydrogen spectrum and the corresponding peak area ratio (e.g. Figure 6 Generally speaking, a larger la / pla value indicates more lipoic acid monomers (la) in the adhesive, more lipoic acid crystals are formed, and stronger adhesive cohesion.

[0173] Figure 6 1H NMR spectra of the adhesives and lipoic acid (LA) powder prepared in Comparative Examples 1 to 3 and Example 6;

[0174] Figure 7Graph showing the molar ratio of la to pla in the adhesives prepared in Comparative Examples 1 to 3 and Example 6. Figure 7 yes Figure 6 The peak area ratio of the hydrogen at the b' position of lipoic acid monomer (Ia) to the hydrogen at the b' position of polylipoic acid (ploy-Ia) in each adhesive is the specific value of the molar ratio of lipoic acid monomer (Ia) to polylipoic acid (ploy-Ia). The absence of lipoic acid powder serves as a baseline to help determine the molar ratio of lipoic acid monomer (Ia) to polylipoic acid (ploy-Ia) in Comparative Examples 1-3 and Example 6.

[0175] la (lipoic acid monomer, when there are enough lipoic acid monomers in the adhesive, they will aggregate to form crystals), pla (polylipoic acid, obtained by polymerizing lipoic acid monomers after heating, after cooling, part of the pla will depolymerize and regenerate la monomers), la / pla (the molar ratio of lipoic acid monomer to polylipoic acid in the adhesive, la / pla, the larger the la / pla value, the more la monomers in the adhesive, the more lipoic acid crystals formed, and the stronger the cohesion of the adhesive).

[0176] from Figure 5 It can be seen that lipoic acid (la) monomers are polymerized by heating and ring-opening to obtain pla (polylipoic acid), and pla will generate la after depolymerization; the molar ratio of la to pla inside the adhesive can be obtained by nuclear magnetic resonance hydrogen spectrum. When the number of la monomers inside the adhesive is large enough, the la molecules are arranged in order, and a lipoic acid crystalline differential phase separation structure will be generated inside the adhesive. Figure 3 、 4 ,analyze Figures 6-7 It can be concluded that the adhesive of Comparative Example 2 has an amorphous structure and weakened cohesion because tannic acid prevents the depolymerization of polylipoic acid (PLA) through hydrogen bonding, and there are few La monomers in the adhesive, which are insufficient to form crystals; Comparative Example 3 and Example 6 show that compared with chitosan, carboxymethyl chitosan has a strong hydrogen bond donor - carboxymethyl, which can better destroy the hydrogen bonding between tannic acid and polylipoic acid and better promote the depolymerization of polylipoic acid (PLA), so the adhesive of Example 6 has the best bonding strength.

[0177] Figure 8 This is the SEM image of the adhesive prepared in Example 6.

[0178] Figure 9 This is the AFM image of the adhesive prepared in Example 6.

[0179] from Figure 8 It can be seen that obvious lipoic acid crystal particles are generated in the adhesive prepared in Example 6; Figure 9This indicates that the modulus of the crystallized particles on the adhesive prepared in Example 6 is significantly different from the modulus of the surrounding adhesive, indicating that a differential phase separation structure of soft and hard phases is formed after the adhesive crystallizes.

[0180] Figure 10 The shear strength of the adhesive prepared in Example 1 on glass was tested in air according to the above method and the shear strength changes with time (0.5h to 150d).

[0181] Figure 11 The graph shows the change of shear strength of the adhesive prepared in Example 1 on glass over time (0.5h to 30d) in underwater testing according to the above method.

[0182] Figure 10 This shows that the adhesive prepared in Example 1 has good durability and the bonding effect will not be significantly reduced even after half a year. Figure 11 This demonstrates that the adhesive prepared in Example 1 can generate excellent shear strength with the surface through strong hydrogen bonding, even when underwater, and maintains this strength for over 30 days. This is because underwater, water molecules gradually disrupt the hydrogen bonds between the adhesive and the glass, causing the shear strength to decrease. However, as water molecules gradually penetrate the interface, the resistance increases, and the shear strength decreases. Even after 30 days underwater, the shear strength still exceeds 0.1 MPa.

[0183] Figure 12 According to the above method, the adhesive prepared in Example 1 was tested on different substrates (quartz, ceramic, PTEF (polytetrafluoroethylene), PC (polycarbonate), PET (polyethylene terephthalate), PMMA (polymethyl methacrylate), PVC (polyvinyl chloride), aluminum, copper, iron, zinc, wood, etc.) in air, underwater, and seawater for shear strength comparison. Figure 12 shown.

[0184] from Figure 12 As can be seen from the figure, adhesives can generate good shear strength on various substrate surfaces and in various environments through hydrogen bonding and hydrophobic interactions. The adhesive exhibits the highest shear strengths on ceramics and quartz, at 7.3 MPa and 5.8 MPa, respectively. This is because ceramics and quartz are composed of oxides, whose surfaces can form a strong bond with the adhesive through numerous hydrogen bonds.

[0185] The shear strength between adhesive and metal is about 3MPa, because the carboxyl and hydroxyl groups in the adhesive can form coordination bonds with the metal atoms on the metal surface.

[0186] The shear strength between the adhesive and the plastic is approximately 2.8 MPa. Because plastics are hydrophobic and some plastic surfaces have a small amount of hydrogen bond acceptor carbonyl oxygen (C=O), the adhesive can form a good bond with the plastic surface through hydrogen bonding and strong hydrophobic interaction.

[0187] The shear strength between the adhesive and wood is only 1.5 MPa. Although the abundant hydroxyl groups on the wood surface can form strong hydrogen bonds with the adhesive, the numerous micropores on the wood surface absorb the liquid adhesive, resulting in a low shear strength between the adhesive and the wood.

[0188] Figure 13 This is a diagram of the recycling mechanism of the adhesive prepared in Example 1. Specifically, the used adhesive is scraped off to recover the adhesive powder, which is then placed in a beaker and heated at 150°C to obtain a recyclable adhesive.

[0189] Figure 14 This is a graph showing the shear strength change of the adhesive prepared in Example 1 after five cycles of use on glass.

[0190] Figure 13 This indicates that the adhesive prepared in Example 1 contains a large number of disulfide bonds (SS) and hydrogen bonds with dynamic reversible properties, and the used adhesive can be reused by heating and melting. Figure 14 This shows that the adhesive prepared in Example 1 has excellent recycling performance. After five cycles of use, the shear strength still maintains the shear strength of the initial use and is not affected by the number of recycling times.

[0191] Figures 15-16 This is a biosafety experiment of the adhesive prepared in Example 1. Figure 15 A small hole was poked through a plastic bottle filled with malachite green dye solution to simulate an emergency underwater leak of hazardous materials. Next, the adhesive from Example 1 was extruded onto a PET substrate to quickly and urgently seal the leak. As can be seen, the adhesive quickly and securely sealed the leak within 30 seconds. The bottle was then placed in a zebrafish aquarium for biosafety testing. Figure 16 It can be seen that within seven days, the survival rate of zebrafish was 100%, indicating that no leakage of harmful substances occurred and the adhesive also had good biosafety.

[0192] Figure 17 Schematic diagram of adhesive shear strength testing. The prepared adhesive was applied to different substrates using a syringe and tested after curing. Dry shear strength was tested by curing in air, while underwater shear strength was tested by curing underwater.

[0193] According to the above method, the adhesive in Example 1 was applied to the glass to form an adhesion area, and then another piece of glass was quickly used to cover the adhesion area. The glass was placed at room temperature (25°C) for 24 hours. After curing for 24 hours, a 73 kg weight was hung under the glass. The adhesive was stable and did not damage, further demonstrating that the adhesive prepared by the present invention has excellent shear strength.

[0194] Figure 18 Schematic diagram of adhesive failure and cohesive failure.

[0195] Adhesion failure occurs when the interfacial bonding strength (adhesion) between the adhesive and the substrate is lower than the adhesive's own cohesive strength. Failure occurs at the adhesive-substrate interface, manifesting as separation between the adhesive and substrate, with no adhesive residue remaining on the substrate surface.

[0196] Cohesive failure occurs when the adhesive's internal cohesion is lower than the interfacial bonding (adhesion) between the adhesive and the substrate being bonded. Failure occurs within the adhesive layer, primarily manifesting as damage to the adhesive itself and residual adhesive on the substrate surface.

[0197] It can be understood that the various technical features of the above-described embodiments can be combined arbitrarily. In order to make the description concise, not all possible combinations of the various technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0198] The above are merely preferred embodiments of the present application and only specifically describe the technical principles of the present application. These descriptions are intended only to explain the principles of the present application and should not be construed in any way as limiting the scope of protection of the present application. Based on the explanations herein, any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present application, as well as other specific implementations of the present application that can be conceived by those skilled in the art without inventive effort, shall be included within the scope of protection of the present application.

Claims

1. A bio-based adhesive, characterized in that: It includes the following raw materials in parts by weight: 10-20 parts of lipoic acid, 0.1-1 part of biomass providing adhesion groups, and 0.1-1 part of biomass containing carboxymethyl groups.

2. The bio-based adhesive according to claim 1, wherein The biomass providing the adhesion group includes at least one of tannic acid, lignin, and dopamine; The carboxymethyl-containing biomass includes at least one of carboxymethyl chitosan, carboxymethyl cellulose, carboxymethyl starch, carboxymethyl-β-cyclodextrin, and carboxymethyl cysteine.

3. The bio-based adhesive according to claim 1, wherein It includes the following raw materials in parts by weight: 10-20 parts of lipoic acid, 0.1-1 part of tannic acid, and 0.1-1 part of carboxymethyl chitosan.

4. The bio-based adhesive according to claim 1, wherein It includes the following raw materials in parts by weight: 10 parts of lipoic acid, 0.2-0.5 parts of tannic acid, and 0.2-0.4 parts of carboxymethyl chitosan.

5. A method for preparing a bio-based adhesive according to any one of claims 1 to 4, characterized in that: The following steps are involved: heating lipoic acid to obtain polylipoic acid; Biomass providing adhesive groups is added to polylipoic acid, and after stirring, biomass containing carboxymethyl groups is added, and stirring is continued to obtain a bio-based adhesive.

6. The method for preparing a bio-based adhesive according to claim 5, wherein: The following steps are involved: Heating lipoic acid at 150-160° C. for 20-30 min to obtain polylipoic acid; Biomass providing adhesion groups is added to polylipoic acid, and the mixture is stirred at 150-160° C. for 20-30 minutes. Then, biomass containing carboxymethyl groups is added, and the mixture is stirred for 10-20 minutes to obtain a bio-based adhesive.

7. The method for preparing a bio-based adhesive according to claim 6, wherein: The biomass providing the adhesion group is tannic acid; The carboxymethyl-containing biomass is carboxymethyl chitosan; The preparation method of the bio-based adhesive comprises the following steps: Heating lipoic acid at 150-160° C. for 20-30 min to obtain polylipoic acid; Tannic acid was added to polylipoic acid, and the mixture was stirred at 150-160° C. for 20-30 minutes. Carboxymethyl chitosan was then added, and the mixture was stirred for 10-20 minutes to obtain a bio-based adhesive.

8. The method for preparing a bio-based adhesive according to claim 7, wherein: Heating lipoic acid at 150°C for 30 min yields polylipoic acid; Tannic acid was added to polylipoic acid, and the mixture was stirred at 150° C. for 20 min. Then, carboxymethyl chitosan was added and the mixture was stirred for 10 min to obtain a bio-based adhesive.

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