Single-component chitosan adhesive as well as preparation method and application thereof
By employing a two-step dehydration process using a temperature gradient of a single-component chitosan acetic acid solution, the water resistance problem of chitosan adhesives in humid environments has been solved, enabling the application of high-strength bonding and environmentally friendly adhesives, and expanding the applicability of substrates, including difficult-to-bond materials such as glass.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- SOUTHWEST FORESTRY UNIVERSITY
- Filing Date
- 2026-04-01
- Publication Date
- 2026-05-19
AI Technical Summary
Existing chitosan adhesives are prone to swelling and failure in humid environments, making it difficult to meet water resistance requirements. Furthermore, traditional chemical crosslinking agents present problems such as complexity, toxicity, and high energy consumption. There is a lack of environmentally friendly adhesive solutions that are all-biomass and formaldehyde-free.
Using a single-component chitosan acetic acid solution, a two-step dehydration process with temperature gradient is used to first form a gel-state nascent film. Then, during hot pressing, the molecular chains rearrange to build a physically dense network, achieving efficient adhesion.
This invention achieves high-strength bonding of a single-component chitosan adhesive in humid environments, avoids the use of chemical crosslinking agents, reduces energy consumption, expands the applicability of substrates, including difficult-to-bond materials such as glass, and meets environmental protection requirements.
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Figure CN122060428A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of adhesive technology, specifically to a one-component chitosan adhesive, its preparation method, and its application. Background Technology
[0002] Wood adhesives are a core technological element of the engineered wood products industry. For a long time, the industry has heavily relied on petroleum-based formaldehyde resins such as urea-formaldehyde (UF), phenol-formaldehyde (PF), and melamine-formaldehyde (MF). While these resins offer advantages such as low cost, fast curing, and high bonding strength, they continuously release formaldehyde, a carcinogen, during production and use, posing a significant threat to human health. With increasingly stringent global requirements for environmental protection and low-carbon production, the development of all-biomass, zero-formaldehyde, and performance-comparable to petroleum-based resins green adhesives is an urgent need for the industry's transformation and upgrading. Chitosan, as an abundant natural polysaccharide, possesses excellent biocompatibility, film-forming properties, and active functional groups. However, in the development of chitosan adhesives, existing mainstream technical approaches (such as modification through the addition of glutaraldehyde, isocyanates, or epoxy crosslinking agents) generally suffer from significant technical drawbacks: On the one hand, traditional thinking holds that chitosan's own hydrogen bond network is highly susceptible to swelling or even hydrolysis in humid environments due to the intervention of water molecules, leading to the perception that single-component systems typically exhibit only slight adhesiveness, making it difficult to meet the water resistance requirements of structured bonding; on the other hand, while the introduction of chemical crosslinking agents improves strength, it also brings a series of significant side effects, including system complexity, short curing time, cytotoxicity caused by crosslinking agent residues, and high energy consumption during preparation. Currently, the industry lacks a solution that can completely eliminate chemical cross-linking agents and achieve adhesive breakthroughs solely through the evolution of chitosan's own physical structure. Therefore, there is a need to develop an environmentally friendly, safe adhesive with excellent bonding performance and simple composition. Summary of the Invention
[0003] The purpose of this invention is to overcome the technical limitations of biomass adhesives that rely excessively on chemical crosslinking, and to provide a single-component chitosan adhesive that achieves super water-resistant bonding by using a temperature gradient "two-step dehydration" formulation, as well as its preparation and application method. The technical solution of this invention is implemented as follows: This invention provides a one-component chitosan adhesive, which is composed of a single-component chitosan-acetic acid solution. By weight, its components are as follows: water: 82-90 parts; acetic acid: 5-10 parts; chitosan powder: 5-8 parts. The adhesive has a viscosity range of 4500-6500 mPa·s at 25°C and a pH value of 4.0-5.5. As a further improvement of the present invention, the degree of deacetylation of the chitosan powder is ≥85%, and the molecular weight is 30-50kDa. This invention further protects a method for preparing the above-mentioned single-component chitosan adhesive, comprising the following steps: (1) Preparation of acetic acid aqueous solution: Add acetic acid to water according to the proportion and stir until the mixture is uniform; (2) Dissolving chitosan: Slowly add chitosan powder to the above aqueous acetic acid solution and stir until the powder is completely dissolved to obtain a homogeneous viscous liquid; (3) Degassing: The obtained liquid is placed in a vacuum environment to degas, thus obtaining a single-component chitosan adhesive. As a further improvement of the present invention, the stirring speed in step (1) is 500-800 rpm and the time is 5-10 min; the stirring temperature in step (2) is 25-40℃ and the time is 5-8 h; the degassing time in step (3) is 1-3 h. This invention further protects the application of the above-mentioned single-component chitosan adhesive in the bonding of sheet materials. As a further improvement of the present invention, the board material is a wood board, bamboo board, and / or glass board. As a further improvement to the present invention, the application method is as follows: S1. Applying adhesive: Apply the adhesive evenly to the surface of the wood, bamboo or glass substrate; S2. Pre-drying: Through graded dehydration control, the adhesive layer forms a gel-like primary film layer containing 10%-15% residual solvent; S3. Densification: Choose one of the following two curing methods, a or b: a. Hot pressing curing: The assembled substrate is fed into a hot press to press and build a physically dense network; b. Room temperature curing: Pressing is performed at room temperature while maintaining the pressure of the substrate after assembly. As a further improvement of the present invention, the amount of adhesive applied to one side in step S1 is 160-200 g / m². As a further improvement of the present invention, the pre-drying conditions in step S2 are at least one of the following two: a. air-drying at 25°C for 3-6 hours; b. drying in circulating hot air at 40-65°C for 5-15 minutes. As a further improvement of the present invention, in step S3, during hot pressing curing, the pressing temperature is 120-160℃, the pressure is 1.0-1.5MPa, and the time is 5-10min; during room temperature curing, the pressing pressure is 0.1-0.5MPa, and the pressing time is ≥48h. This invention is based on the following core scientific logic: Chitosan, after being protonated in anhydrous acetic acid solution, forms a high molecular electrolyte with excellent film-forming potential. During the bonding process, this invention utilizes the "glue nail" mechanical locking effect formed by chitosan's penetration into the shallow surface of wood-based substrates (wood, bamboo) during film formation, and the strong hydrogen bonding coupling between amino / hydroxyl groups and silanol groups (Si-OH) on the glass surface. Combined with the high cohesive strength of the adhesive film after thermal densification, efficient bonding is achieved. This invention differs fundamentally from traditional adhesives (whose typical process is: adhesive preparation → adhesive application → hot pressing of preforms) in its application process. This invention employs a controlled "pre-drying-hot pressing" process. Figure 1 By introducing the key physical evolution step of "pre-drying film formation," a staged dehydration process was artificially constructed: (1) Pre-drying (stage one of graded dehydration): After sizing, most of the free water is removed by precisely controlling the temperature and time, so that the sizing layer changes from a liquid state to a gel-state nascent film containing 10%-15% residual solvent. At this time, the residual solvent acts as an internal plasticizer, which significantly reduces the energy barrier of chitosan molecular chain segment movement, laying the physical basis for molecular chain rearrangement during subsequent hot pressing. (2) Densification (stage two of graded dehydration): During the subsequent hot pressing process, as the bound water is further discharged, the chitosan segments driven by heat undergo large-scale rearrangement and interpenetrate and entangle with each other, achieving a highly regular and compact stack through hydrogen bonding. This invention offers the following advantages: Addressing the bottleneck of insufficient adhesiveness in single-component chitosan raw materials, this invention proposes a novel approach to achieve a "two-step dehydration" adhesive breakthrough through physical temperature control. First, a gentle gradient pre-drying process induces the chitosan to transform from a solution state to a "nascent gel film," initially establishing a physical adsorption and anchoring foundation at the substrate interface. Subsequently, the high-temperature field of the hot-pressing process drives large-scale rearrangement of molecular chains and achieves thermal densification, thereby constructing a super-strong water-resistant physical barrier under single-component conditions. This solution not only supports efficient hot-pressing processes but also achieves adhesive bonding under room-temperature cold-pressing conditions (although the strength is slightly lower than with hot pressing), providing a completely new and green alternative paradigm for the physical strengthening of biomass adhesives. 1. Advantages of single-component simplicity: Completely eliminates chemical crosslinking agents, avoids multi-component ratios and complex chemical reaction processes, and has extremely strong production applicability; there is no need to consider the pot life after adding curing agents, the single-component solution is stable for long-term storage, and the sizing process can be seamlessly integrated with existing automated production lines. 2. Breakthrough in physical curing path: For the first time, a two-step physical process of "graded dehydration-thermal densification" was systematically elucidated and utilized to achieve an extremely high shear strength of 11.53 MPa for single-component chitosan adhesive. 3. Universality of substrates: In addition to conventional wood and bamboo, it also has excellent adhesion (3.42MPa) to non-polar interfaces such as glass that are extremely difficult to bond, which greatly expands the application boundaries of biomass adhesives. 4. Low-energy dual-temperature-range curing: Supports industrial high-temperature rapid curing at 120-160℃ (5min), and also supports room temperature cold pressing curing at 25℃, which significantly reduces the carbon footprint in the production process. 5. Clean throughout the entire life cycle: The raw materials are derived from aquatic waste such as shrimp and crab shells, and the solvent is bio-derived acetic acid, truly realizing a closed-loop environmental protection that "comes from nature and goes back to nature". Attached Figure Description To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. Figure 1 : Schematic diagram of the densification film formation mechanism induced by the "controlled pre-drying-hot pressing" process of this invention. Figure 2 A one-component chitosan adhesive was prepared according to the parameters in Example 1, applied to a glass plate, and then characterized by TGA curves after a controlled pre-drying process. The TGA revealed a stepwise dehydration process in which free water and bound water molecules were released with increasing temperature. Figure 3 XRD diffraction patterns of the single-component chitosan adhesive prepared according to the parameters in Example 2 and heated at three different temperatures. As the hot-pressing temperature increases, the (020) crystal plane diffraction peak at 20.29°C is significantly enhanced, indicating that the physical crystal domains are well-developed and tend to become denser. Figure 4 The solid-state NMR carbon spectra of the single-component chitosan adhesive prepared according to the parameters in Example 2 and the chitosan powder after heating at four different temperatures were obtained. Comparing the carbon signals under different temperature treatments, almost no acetylation chemical reaction occurred in the range of 25-180℃, and the chitosan remained unchanged, indicating that the increase in adhesive strength was entirely due to physical densification. Figure 5 DMA curves of Examples 1 and 2 and Comparative Example 6. DMA revealed a significant jump in the modulus of the adhesive layer in the range of 30-192°C, marking the final construction of the physically dense network. Detailed Implementation The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Example 1 This invention discloses a single-component chitosan adhesive based on a physical film-forming-thermal densification mechanism. The adhesive is a single-component polymeric electrolyte, and a two-layer overlapping board is made from 2mm thick bamboo veneer. A schematic diagram of the densification film-forming mechanism induced by the controlled pre-drying-hot pressing process of this invention is shown below. Figure 1 . The preparation and use method of the single-component chitosan adhesive of the present invention includes the following steps: (1) Preparation: Add 10g of anhydrous acetic acid to 84g of deionized water and stir for 10min to mix evenly. Then slowly add 6g of chitosan powder and stir continuously at 30℃ for 6h until completely dissolved. The adhesive is obtained by vacuum degassing for 2h. (2) Applying adhesive: Apply chitosan adhesive evenly to the area to be glued on the bamboo veneer at a rate of 160g / m² and let it stand for 5 minutes. (3) Controlled pre-drying: Place in a 50℃ oven for 5 minutes to pre-treat the adhesive layer so that the residual solvent content is about 12%. (4) Hot pressing curing: The assembled veneer is placed in a hot pressing environment at 160℃ and 1.0MPa for 5 minutes to obtain the overlapping veneer. Figure 2 Following the parameters in Example 1, a one-component chitosan adhesive was prepared and applied to a glass plate. After a controlled pre-drying process, the TGA curves were characterized. The TGA revealed a stepwise dehydration process in which free and bound water molecules were released with increasing temperature. Figure 2 The TG curves demonstrate the kinetic characteristics of this stepwise dehydration: the chitosan membrane experiences a mass loss of approximately 14.45% within the temperature range of 30-150℃ (on top of the loss of most of the solvent water), corresponding to the stepwise removal of adsorbed and bound water. The symmetrical peak of the DTG curve at 99.4℃ marks the core region of this physical transformation. Bonding strength of the boards: The physical and mechanical properties of the boards were tested according to the national standard GB / T17657-2022 "Test Methods for Physical and Chemical Properties of Wood-based Panels and Decorative Wood-based Panels", using the mechanical strength test standard for Class II water-resistant plywood. The specific results are as follows: dry shear strength 11.53 MPa (wood breakage rate 90%), wet shear strength after boiling in water at 100±2℃ for 3 hours 4.26 MPa, which meets and exceeds the national standard (≥0.7 MPa). Example 2 The present invention discloses a single-component chitosan adhesive based on a physical film-forming and thermal densification mechanism. The adhesive is a single-component polymeric electrolyte and is made of three-layer plywood using black walnut veneer with a thickness of 2 mm. The preparation and use method of the single-component chitosan adhesive of the present invention includes the following steps: (1) Preparation: Add 8g of anhydrous acetic acid to 85g of deionized water and stir for 10min to mix evenly. Then slowly add 7g of chitosan powder and stir continuously at 35℃ for 5h until completely dissolved. The adhesive is obtained by vacuum degassing for 2h. (2) Applying adhesive: Apply chitosan adhesive evenly to the area to be glued on the bamboo veneer surface at a rate of 170g / m² and let it stand for 5 minutes. (3) Controlled pre-drying: Place in a 48°C oven for 7 minutes to pre-treat the adhesive layer so that the residual solvent content is about 13%. (4) Hot pressing curing: After the veneer is assembled, it is placed in a hot pressing environment at 150℃ and 1.2MPa for 6 minutes to obtain plywood. Figure 3 XRD diffraction patterns of the single-component chitosan adhesive prepared according to the parameters in Example 2 and heated at three different temperatures. As the hot-pressing temperature increases, the (020) crystal plane diffraction peak at 20.29°C is significantly enhanced, indicating that the physical crystal domains are well-developed and tend to become denser. Figure 3 The XRD results further confirmed the physical evolution path of "close stacking": when the drying temperature reached 120°C, due to solvent evaporation and molecular chain rearrangement, the three characteristic weak peaks (11.29°, 18.10°, 22.3°) resulting from the combined action of acetic acid and chitosan disappeared, while the 7.51° peak representing water molecules was significantly weakened; at the same time, a broad β-type orthorhombic peak belonging to the intrinsic (020) crystal plane of chitosan appeared near 20.29°. This proves from the perspective of microscopic crystal development that chitosan molecules transform from an amorphous state to a semi-crystalline state during thermal motion, achieving physical densification of the structure. The above physical enhancement logic is in Figure 4 This was essentially confirmed in solid-state NMR carbon spectra. Figure 4A single-component chitosan adhesive was prepared according to the parameters in Example 2, and solid-state NMR carbon spectra of the samples and chitosan powder were obtained after heating at four different temperatures. Comparing the carbon signals at different temperatures, almost no acetylation reaction occurred in the 25-180℃ range, and the chitosan remained unchanged, indicating that the increased adhesive strength originated entirely from physical densification. After temperature changes from 25-180℃, the characteristic peaks of the sugar rings of protonated chitosan—C1 (100ppm), C2 (split into 58ppm and 61ppm), C5 (84ppm), and C3 / C4 (75ppm)—did not undergo any substantial shift or disappearance, proving that the main component always maintained the intrinsic structure of chitosan. In particular, from 25-180℃, the signal intensity of acetate carbonyl (180ppm) remained consistently higher than that of acetyl carbonyl (174ppm), indicating that in this critical bonding window, the protonation effect of chitosan was much stronger than the acetylation reaction. The stability of the chitosan glycocycle backbone and the extremely low degree of acetylation reaction jointly demonstrate that physical rearrangement rather than chemical cross-linking is the main reason for the super strong adhesive effect. Bonding strength of the boards: The physical and mechanical properties of the boards were tested according to the national standard GB / T17657-2022 "Test Methods for Physical and Chemical Properties of Wood-based Panels and Decorative Wood-based Panels", using the mechanical strength test standard for Class II water-resistant plywood. The specific results are as follows: dry shear strength 5.31 MPa (wood breakage rate 90%), wet shear strength after boiling in water at 100±2℃ for 3 hours 1.87 MPa, which meets and exceeds the national standard (≥0.7 MPa). Example 3 The present invention discloses a single-component chitosan adhesive based on a physical film-forming and thermal densification mechanism. The adhesive is a single-component polymeric electrolyte and is made of three-layer plywood using black walnut veneer with a thickness of 2 mm. The preparation and use method of the single-component chitosan adhesive of the present invention includes the following steps: (1) Preparation: Add 9g of anhydrous acetic acid to 85g of deionized water and stir for 10min to mix evenly. Then slowly add 6g of chitosan powder and stir continuously at 30℃ for 8h until completely dissolved. The adhesive is obtained by vacuum degassing for 2h. (2) Applying adhesive: Apply chitosan adhesive evenly to the area to be glued on the bamboo veneer surface at a rate of 180g / m² and let it stand for 5 minutes. (3) Controlled pre-drying: Place at room temperature of 25°C and let it air dry naturally for 3 hours to make the adhesive layer contain about 15% residual solvent. (4) Cold pressing and curing: After the veneer is assembled, it is placed in an environment with a temperature of 25℃ and a pressure of 0.1MPa for 72 hours to press and obtain plywood. Bonding strength of the boards: The physical and mechanical properties of the boards were tested according to the national standard GB / T17657-2022 "Test Methods for Physical and Chemical Properties of Wood-based Panels and Decorative Wood-based Panels", using the mechanical strength test standard for Class II water-resistant plywood. The specific results are as follows: dry shear strength 2.83 MPa (wood breakage rate 20%), wet shear strength after soaking in cold water at 20±3℃ for 24 hours 0.79 MPa, which meets and exceeds the national standard (≥0.7 MPa). Example 4 The present invention discloses a single-component chitosan adhesive based on a physical film-forming and thermal densification mechanism. The adhesive is a single-component polymeric electrolyte and is made of a two-layer overlapping board using bamboo veneer with a thickness of 2 mm. The preparation and use method of the single-component chitosan adhesive of the present invention includes the following steps: (1) Preparation: Add 8g of anhydrous acetic acid to 84g of deionized water and stir for 10min to mix evenly. Then slowly add 8g of chitosan powder and stir continuously at 35℃ for 8h until completely dissolved. The adhesive is obtained by vacuum degassing for 2h. (2) Applying adhesive: Apply chitosan adhesive evenly to the area to be glued on the bamboo veneer at a rate of 160g / m² and let it stand for 5 minutes. (3) Controlled pre-drying: Place at room temperature of 25°C and let it air dry naturally for 5 hours to make the adhesive layer contain about 14% residual solvent. (4) Cold pressing and curing: The assembled veneer is placed in an environment with a temperature of 25℃ and a pressure of 0.3MPa for 96 hours to obtain plywood. Bonding strength of the boards: The physical and mechanical properties of the boards were tested according to the national standard GB / T17657-2022 "Test Methods for Physical and Chemical Properties of Wood-based Panels and Decorative Wood-based Panels", using the mechanical strength test standard for Class II water-resistant plywood. The specific results are as follows: dry shear strength 5.21 MPa (100% wood breakage rate), wet shear strength after soaking in cold water at 20±3℃ for 24 hours 1.17 MPa, which meets and exceeds the national standard (≥0.7 MPa). Example 5 The present invention discloses a single-component chitosan adhesive based on a physical film-forming and thermal densification mechanism. The adhesive is a single-component polymer electrolyte and a two-layer overlapping plate is made of 10mm thick plexiglass. The preparation and use method of the single-component chitosan adhesive of the present invention includes the following steps: (1) Preparation: Add 10g of anhydrous acetic acid to 82g of deionized water and stir for 10min to mix evenly. Then slowly add 8g of chitosan powder and stir continuously at 40℃ for 8h until completely dissolved. The adhesive is obtained by vacuum degassing for 2h. (2) Applying adhesive: Apply chitosan adhesive evenly to the area to be glued on the bamboo veneer surface at a rate of 180g / m² and let it stand for 5 minutes. (3) Controlled pre-drying: Place in a 60℃ oven for 5 minutes to pre-treat the adhesive layer so that the residual solvent content is about 11%. (4) Hot pressing curing: The assembled veneer is placed in a hot pressing environment at 160℃ and 1.0MPa for 10 minutes to obtain the overlapping veneer. The adhesive strength of the board is as follows: dry shear strength 3.42 MPa, wet shear strength 0.91 MPa after soaking in cold water at 20±3℃ for 24 hours. Comparative Example 1 Compared to the patent "An Environmentally Friendly Tannin-Chitosan-Based Adhesive" (Patent No.: CN201910803059.7), which is based on the principle of chemical condensation and requires the introduction of external curing agents such as glutaraldehyde or glyoxal to construct a covalent cross-linked network, the significant differences between this invention and that patent are: First, improved environmental performance, as this invention completely abandons aldehyde curing agents, avoiding potential chemical toxicity; second, a revolutionary curing mechanism, where the patent relies on chemical grafting, while this invention utilizes "controlled hierarchical dehydration" to induce molecular chain rearrangement to achieve physical densification, with the highest measured wet shear strength consistently above 4.26 MPa, far exceeding the performance of its Class II boards; finally, extreme simplification of the system, as this invention is a single-component solution, eliminating the need to consider the failure risks of multi-component distribution errors and short pot life. Comparative Example 2 Compared to the patent "A Multi-level Crosslinked Formaldehyde-free Adhesive with a Three-dimensional Network Structure and Its Preparation Method" (Patent No.: CN202510716897.6), which employs extremely complex chemical pretreatment involving phytic acid modification, citric acid / chitosan gradient crosslinking, and tannic acid network curing, the significant differences between this invention and that patent are: First, the restructuring of the production process. The patent involves multi-level grafting and prolonged heating reactions, while this invention uses a simple one-step dissolution method, significantly improving production efficiency. Second, the advancement of the technological logic. The patent relies on multi-level chemical bonding, while this invention achieves a leap from a chemical field to a physical field by controlling the development of the (020) crystal face through a purely physical field (temperature gradient). Finally, the energy efficiency advantage is evident. This invention avoids complex intermediate synthesis, significantly reducing industrialization costs and energy efficiency. Comparative Example 3 Compared to the patent "A Bio-based Adhesive and Its Preparation Method" (Patent No.: CN202211474110.2), which requires the introduction of glyoxal as a core crosslinking agent on the basis of starch and chitosan to form a network structure through chemical grafting, the significant differences between this invention and that patent are: First, the curing path is optimized. The patent belongs to traditional covalent crosslinking, while this invention explores the modulus transition characteristics of chitosan molecular chains within a specific temperature window (120-160℃), relying on the physical densification of the three-dimensional hydrogen bond network to form a film; Second, the water resistance is significantly improved. The patent system's performance is limited under boiling water immersion, while the physical barrier constructed by this invention can still maintain extremely high mechanical strength after boiling in water for 3 hours; Finally, the process stability of the single component avoids the problem of uncontrollable system viscosity caused by the addition of crosslinking agents. Comparative Example 4 Compared to the patent "An Aqueous Chitosan / Citrate Supramolecular Adhesive and Its Preparation Method and Application" (Patent No.: CN202310984517.8), which emphasizes supramolecular self-assembly and the formation of an ionic cross-linked network through high-concentration citric acid and chitosan, the significant differences between this invention and that patent are: First, the fundamental difference in bonding strength; the patent focuses on ionic bonding, while this invention utilizes low-concentration acetic acid as a temporary solvent, with the core being the physical evolution during hot pressing and the forced removal of bound water; second, a leap in substrate compatibility; this invention not only targets wood and bamboo but also successfully solves the bonding problem of extremely difficult-to-bond interfaces such as glass; and finally, the stability of the physical structure; this invention, through the construction of dense crystalline domains, provides more durable resistance to humid heat than traditional supramolecular networks. Comparative Example 5 Compared to the patent "Preparation Method and Application of Biomass Environmentally Friendly Adhesive Based on Longan Shell" (Patent No.: CN202511449792.5), which focuses on chemical modification of agricultural waste fillers such as alkalization and acetylation, the principle of this invention belongs to traditional filler reinforcement. The significant differences between this invention and that patent are: First, a revolutionary modification logic: the patent modifies fillers through wet chemical reactions, while this invention delves into the physical structural evolution of chitosan's main molecular chains under controlled drying-hot pressing curing; second, a qualitative leap in clean production: this invention eliminates the need for chemical pretreatment processes that generate large amounts of wastewater, such as alkalization, achieving a clean lifecycle from raw materials to the process; finally, an advanced microscopic bonding method: this invention forms a continuous and dense "glue nail" effect and physical film layer on the substrate surface, significantly improving mechanical strength compared to traditional filler systems. Comparative Example 6 The single-component chitosan adhesive of this invention uses a traditional glue preparation → glue application → hot pressing process, and employs a 2mm thick black walnut veneer to produce a three-layer plywood. The process includes the following steps: (1) Preparation: Add 8g of anhydrous acetic acid to 85g of deionized water and stir for 10min to mix evenly. Then slowly add 7g of chitosan powder and stir continuously at 35℃ for 5h until completely dissolved. The adhesive is obtained by vacuum degassing for 2h. (2) Applying adhesive: Apply chitosan adhesive evenly to the area to be glued on the bamboo veneer surface at a rate of 180g / m² and let it stand for 5 minutes. (3) Hot pressing curing: The assembled veneer is placed in a hot pressing environment at 150℃ and 1.0MPa for 10 minutes to obtain the overlapping veneer. The three-dimensional high-density hydrogen bond network formed after chitosan stacking and solidification has extremely high mechanical strength and can effectively block water molecules from penetrating into the adhesive interface. Figure 5 DMA curves of Examples 1 and 2 and Comparative Example 6. DMA revealed a significant jump in the modulus of the adhesive layer in the range of 30-192°C, marking the final construction of the physically dense network. Figure 5 The DMA curves provided mechanical confirmation: physical densification led to an exponential jump in the modulus of the adhesive layer within the 125-192℃ range. Experimental data showed that at 30℃, the initial storage moduli of black walnut and bamboo were 137MPa and 57.8MPa, respectively, while the storage modulus of bamboo lap joints increased to 1539MPa at 177℃, and to 2923MPa at 192℃ for black walnut lap joints. The three-layer plywood prepared in this comparative example could not be bonded. This example used the same glue preparation and application process as Example 2, but the lack of a pre-drying step resulted in extremely weak adhesion, thus demonstrating the key innovation and effectiveness of the two-step dehydration process of this patent. Based on the embodiments and comparative examples of the present invention, the following conclusions are drawn: The single-component chitosan adhesive disclosed in this invention, based on a physical film-forming-thermal densification mechanism, successfully constructs a physical curing system that relies on graded dehydration to promote film densification. By deeply utilizing the molecular chain rearrangement characteristics induced by controlled pre-drying and hot pressing, the industry problem of biomass adhesives relying on toxic chemical crosslinking agents to achieve water resistance is solved. The adhesive prepared by this method is green, formaldehyde-free, and exhibits a significant improvement in wet strength, with an extremely simple process, providing a competitive technical solution for the low-carbon transformation of my country's forestry board industry and the development of glass-wood composite materials. This solution has broad application prospects in the future fields of high-end solid wood, bamboo structural materials, and special composite adhesives. The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.
Claims
1. A one-component chitosan adhesive, characterized in that, The adhesive is composed of a single-component chitosan acetic acid solution, and its components are as follows by weight: water: 82-90 parts; acetic acid: 5-10 parts; chitosan powder: 5-8 parts. The adhesive has a viscosity range of 4500-6500 mPa·s at 25°C and a pH value of 4.0-5.
5.
2. The single-component chitosan adhesive according to claim 1, characterized in that, The chitosan powder has a degree of deacetylation ≥85% and a molecular weight of 30-50 kDa.
3. A method for preparing a single-component chitosan adhesive as described in claim 1 or 2, characterized in that, Includes the following steps: (1) Preparation of acetic acid aqueous solution: Add acetic acid to water according to the proportion and stir until the mixture is uniform; (2) Dissolving chitosan: Slowly add chitosan powder to the above aqueous acetic acid solution and stir until the powder is completely dissolved to obtain a homogeneous viscous liquid; (3) Degassing: The obtained liquid is placed in a vacuum environment to degas, thus obtaining a single-component chitosan adhesive.
4. The preparation method according to claim 3, characterized in that, The stirring speed in step (1) is 500-800 rpm and the stirring time is 5-10 min; the stirring temperature in step (2) is 25-40℃ and the stirring time is 5-8 h; the degassing time in step (3) is 1-3 h.
5. The application of a single-component chitosan adhesive as described in claim 1 or 2 in the bonding of sheet materials.
6. The application according to claim 5, characterized in that, The material is wood, bamboo, and / or glass.
7. The application according to claim 6, characterized in that, The application method is as follows: S1. Applying adhesive: Apply the adhesive evenly to the surface of the wood, bamboo or glass substrate; S2. Pre-drying: Through graded dehydration control, the adhesive layer forms a gel-like primary film layer containing 10%-15% residual solvent; S3. Densification: Choose one of the following two curing methods, a or b: Hot pressing curing: The assembled substrate is fed into a hot press to press and build a physically dense network; Room temperature curing: Pressing is performed at room temperature while maintaining the pressure of the assembled substrate.
8. The application according to claim 7, characterized in that, In step S1, the amount of adhesive applied to one side is 160-200 g / m².
9. The application according to claim 7, characterized in that, The pre-drying conditions described in step S2 are at least one of the following two: a. air-drying at 25°C for 3-6 hours; b. drying in circulating hot air at 40-65°C for 5-15 minutes.
10. The application according to claim 7, characterized in that, In step S3, during hot pressing curing, the pressing temperature is 120-160℃, the pressure is 1.0-1.5MPa, and the time is 5-10min; during room temperature curing, the pressing pressure is 0.1-0.5MPa, and the pressing time is ≥48h.