Preparation method and application of reed fiber reinforced starch boiling water-resistant adhesive based on hyperbranched strategy
By hyperbranching reed fiber and starch, a cross-linked network structure adhesive is formed, which solves the problems of poor water resistance and weather resistance of starch-based adhesives, and achieves high wet strength and wide application capability.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-12-05
- Publication Date
- 2026-03-13
AI Technical Summary
Traditional starch-based adhesives have poor water and weather resistance, failing to meet Class I plywood standards, and their application is limited by cellulose substrates.
Hyperbranching strategy was adopted to modify reed fiber and starch. Reed fiber was oxidized with sodium periodate and reacted with diethylenetriamine and urea to synthesize hyperbranched polyamide, and hyperbranched modified starch was prepared to form a cross-linked network structure adhesive.
It improves the wet strength and boiling water resistance of the adhesive, exceeding the Class I plywood standard, and expands its bonding capabilities to a variety of substrates such as metal, glass, and leather.
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Abstract
Description
Technical Field
[0001] This invention relates to a method for preparing a reed fiber-reinforced starch boiling water resistant adhesive based on a hyperbranching strategy and its application, specifically for various substrates such as wood, metal, glass, and leather, belonging to the field of adhesive technology. Background Technology
[0002] In the traditional production and use of plywood, adhesives based on petroleum-based raw materials, such as urea-formaldehyde resin and phenolic resin, are mainly used. These adhesives generate volatile toxic substances during synthesis and application; long-term exposure may lead to respiratory diseases and increase the risk of cancer. Formaldehyde, in particular, was classified as a Group 1 carcinogen by the World Health Organization as early as 2006, and the rising price of oil in recent years has also significantly increased the cost of adhesives. Therefore, the development of green and environmentally friendly bio-based adhesives using biomass materials has attracted considerable attention.
[0003] Among numerous biomass adhesives, starch has attracted much attention due to its low cost, high yield, and the fact that its molecular chain is rich in hydroxyl groups, enabling it to bond with woody substrates via hydrogen bonds and achieve environmentally friendly adhesion. However, it is precisely because of its rich polyhydroxyl structure that starch is too hydrophilic, resulting in extremely poor water resistance for this type of adhesive. After soaking in 60°C hot water for 2 hours, the bond strength decreases by more than 80%, which greatly limits the application of starch-based adhesives.
[0004] To overcome the aforementioned shortcomings of starch adhesives, researchers have focused on chemically modifying starch to improve the bonding performance of starch-based adhesives. For example, methods such as oxidative modification, cross-linking modification, and grafting modification are used to promote the formation of a denser macromolecular network structure between starch molecules, thereby preventing water molecule penetration and improving bonding performance. However, according to the national standard (GB / T 9846-2015), most current starch-based adhesives are limited to bonding materials containing cellulose substrates, and the plywood produced only meets the standards for Class II plywood. Furthermore, this type of plywood cannot be used outdoors, lacks boiling water resistance and weather resistance, and fails to meet the standards for Class I plywood. Summary of the Invention
[0005] To overcome the defects in the performance of existing starch-based adhesives and the limitations of modification technologies, this invention provides a method for preparing a reed fiber-reinforced starch-based adhesive resistant to boiling water based on a hyperbranching strategy and its application. By constructing a hyperbranched crosslinked network to enhance the starch-based adhesive system, the problems of low bonding strength, poor water resistance, and poor weather resistance of starch adhesives are solved.
[0006] Fiber reinforcement is a potential and reliable method to improve the bonding strength of adhesives. Renewable reed fiber is inexpensive, readily available, lightweight, has high mechanical strength, and is biodegradable, making it an ideal green reinforcing filler. However, a large amount of reed fiber is discarded or incinerated every year, which not only wastes resources but also causes serious environmental pollution. Therefore, actively promoting the research and application of reeds can not only reduce environmental pollution but also achieve efficient utilization of reed resources, which has significant economic value. To improve the bonding strength and water resistance of starch-based adhesives, this invention selects reed fiber as the reinforcement and proposes a hyperbranching strategy to hyperbranch both the reed fiber and starch. First, reed fiber is oxidized using sodium periodate as an oxidant to produce oxidized reed fiber. Using diethylenetriamine and urea as monomers, hyperbranched polyamide is synthesized through a deamination reaction, and then reacted with aldehyde groups on the surface of oxidized reed fiber through a Schiff base reaction to hyperbranch the reed fiber. Secondly, a carboxyl-terminated hyperbranched polymer was synthesized using citric acid and glycerol triglycidyl ether as raw materials. This product was then used to functionalize and modify starch, preparing hyperbranched modified starch. Finally, the hyperbranched modified starch was combined with hyperbranched modified reed fiber to prepare a reed fiber-reinforced starch-based adhesive for boiling water resistance. This adhesive exhibits a wet strength higher than the bonding strength index for Class I plywood specified in GB / T 9846-2015, and demonstrates excellent boiling water resistance and aging resistance. Furthermore, this adhesive overcomes the limitations of traditional starch-based adhesives that are restricted to cellulose substrates, enabling effective bonding to various substrates such as metals, glass, and leather, thus broadening the application range of starch-based adhesives.
[0007] To achieve the above objectives, the present invention is mainly implemented through the following technical solutions: The first claim of this invention is for a method of preparing hyperbranched modified fibers. This preparation method specifically includes the following steps: (1) Place the reed fiber in a sodium hydroxide solution and stir continuously at 95°C for 4 hours. Then wash it with deionized water until neutral and dry it in a forced-air drying oven at 80°C for 12 hours to obtain alkali-treated reed fiber (ARF). (2) Alkali-treated reed fibers were uniformly dispersed in deionized water at a bath ratio of 1:70, and the pH was adjusted to 4.5 with acetate buffer to obtain a reed fiber dispersion. The reed fiber dispersion was then stirred and heated to 60°C, and sodium periodate was added. The reed fibers were then continuously stirred for 6 hours under light-protected conditions to oxidize them. Finally, the oxidized reed fibers were washed three times with deionized water to obtain pure oxidized reed fiber (ORF). (3) Diethylenetriamine and urea were mixed in a 1:1 molar ratio in a three-necked flask and stirred at 120°C for 2 hours. Then the mixture was cooled to room temperature to obtain hyperbranched polyamide (HP). (4) Dissolve the hyperbranched polyamide obtained in step (3) in deionized water to prepare a hyperbranched polyamide solution of a certain concentration and adjust the pH to 9. Then add the oxidized reed fiber from step (2) to the hyperbranched polyamide solution, stir until uniform to obtain a mixed solution, heat the mixed solution to 60°C, stir continuously for 15 min, wash three times with deionized water, and dry in an oven at 50°C for 24 h to obtain hyperbranched modified fiber (HOF).
[0008] Furthermore, in step (1), the mass of reed fiber is 3% of the mass of sodium hydroxide solution, and the concentration of sodium hydroxide solution is 5wt%; in step (2), the mass of sodium periodate is 30% of the dry weight of reed fiber; in step (4), the concentration of hyperbranched polyamide solution is 20g / L; and the content of oxidized reed fiber is 5% of the mass of hyperbranched polyamide solution.
[0009] This invention also claims protection for a method for preparing a reed fiber-reinforced starch-based boiling water resistant adhesive based on a hyperbranching strategy. The method specifically includes the following steps: Citric acid was dissolved in deionized water to prepare a 40 wt% citric acid solution, which was then placed in a three-necked flask and heated to 140 °C. Glycerol triglycidyl ether was then slowly added dropwise to the citric acid solution, with the molar ratio of citric acid solution to glycerol triglycidyl ether solution controlled at 2:1. After reacting for 1 hour, the mixture was cooled to room temperature to obtain a carboxyl-terminated hyperbranched polymer (CHP). b. In a three-necked flask, prepare a 20 wt% starch solution. After stirring evenly, add the carboxyl-terminated hyperbranched polymer prepared in step a. Then, add the hyperbranched modified fiber to the starch solution, adjust the pH to 6 with a 10 wt% sodium hydroxide solution, and heat to 95°C. Continue the reaction for 1 hour to obtain the adhesive (CHSt-HOF). The amount of carboxyl-terminated hyperbranched polymer used accounts for 50% of the starch mass. The amount of hyperbranched modified fiber added is 0.5%-2.0% of the starch mass.
[0010] The adhesive prepared by the method of the present invention is a starch-based adhesive.
[0011] The present invention also requests the application of the adhesive prepared by the above preparation method in bonding wood, metal, glass and leather.
[0012] In practical applications, when the adhesive is used to bond wood, the concentration should be 180-200 g / m³. 2The prepared adhesive was uniformly applied to one side of the wood, covering an area of 25×25 mm. The wood was then hot-pressed at 180℃ for 5 minutes at a pressure of 1 MPa to obtain plywood. The dry strength of the plywood was tested using an electronic universal testing machine at a tensile speed of 10.0 mm / min. The wet strength of the plywood was determined according to the Chinese national standard (GB / T9846-2015). The plywood sample was immersed in boiling water (93±3℃) for 3 hours, then dried at room temperature for 10 minutes, and tested under the same conditions.
[0013] When used for bonding metals, glass, and leather, use 180-200 g / m 2 The prepared adhesive was applied to a coating area of 25×12.5mm, and the metal, glass and leather to be bonded were uniformly pressed at a pressure of 1MPa to obtain metal samples, glass samples and leather samples. After the samples were completely cured, the bonding strength of the bonded substrate was tested using an electronic universal testing machine at a tensile speed of 10.0mm / min.
[0014] The advantages of this invention compared to the prior art are: This invention, based on a hyperbranching strategy, synthesized carboxyl-terminated hyperbranched polymers and hyperbranched polyamides, and modified starch and reed fibers respectively to prepare adhesives with cross-linked network structures. Compared with existing technologies, this invention has the following significant advantages: This invention is based on a hyperbranching strategy. CHP is prepared by the condensation reaction of citric acid and glycerol triglycidyl ether, and then used to functionalize starch to obtain hyperbranched modified starch. At the same time, HP is prepared by the deamination condensation reaction of diethylenetriamine and urea, which is used for surface modification of reed fiber to obtain HOF. Then, HOF is used to reinforce the hyperbranched modified starch to prepare an adhesive with both three-dimensional crosslinking network and fiber reinforcement effect.
[0015] By utilizing the abundant terminal groups in hyperbranched polymers, starch and reed fibers are hyperbranched and modified. The abundant amino and carboxyl groups at the ends of these two hyperbranched polymers improve the interfacial compatibility between reed fibers and starch matrix through multiple bonding, thus solving the problems of low adhesive strength and poor water resistance.
[0016] Plywood bonded using the adhesive prepared in this invention exhibits a maximum wet strength of 1.45 MPa after immersion in water at 93°C for 3 hours, exceeding the 0.7 MPa requirement for Class I plywood in GB / T 9846-2015 by 107.14%. Furthermore, the bonded plywood also demonstrates excellent aging resistance.
[0017] The adhesive prepared by this invention has good bonding effect on metals, glass and leather, which greatly expands the application field of starch adhesives.
[0018] The raw materials used in this invention are all non-toxic and environmentally friendly, and the main agent is biomass material. This not only realizes the recycling and reuse of reeds, but also provides new ideas and methods for the research and development of starch adhesives. Attached Figure Description
[0019] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.
[0020] Figure 1 The following are the spectral diagrams for structural analysis. (a) The infrared spectrum of citric acid and CHP in Example 1; (b) The infrared spectrum of CHP in Example 1. 13 (c) The figure shows the infrared spectra of urea and HP in Example 1; (d) The figure shows the infrared spectra of HP in Example 1. 13 (e) The figure shows the infrared spectra of RF, ORF and HOF in Example 1; (f) The figure shows the infrared spectra of St, CHSt and CHSt-HOF adhesives in Example 2.
[0021] Figure 2 Figure 1 shows the microstructure of the unmodified reed fiber in Comparative Example 2; Figure 2 shows the microstructure of the hyperbranched modified reed fiber in Example 1; Figure 3 shows the cross-section of the CHSt-RF adhesive in Comparative Example 2; and Figure 4 shows the microstructure of the CHSt-HOF adhesive in Example 2. 1.0% Adhesive cross-section.
[0022] Figure 3 The water contact angles are those of the different adhesives used in Examples 1-4 and Comparative Examples 1-2.
[0023] Figure 4 CHSt-HOF after UV aging treatment in Example 2 1.0% The bonding strength of the adhesive. Detailed Implementation
[0024] The present invention is described in detail below through specific embodiments, but this does not limit the scope of protection of the present invention. Unless otherwise specified, the experimental methods used in the present invention are all conventional methods, and the experimental equipment, materials, reagents, etc. used can all be obtained commercially.
[0025] This invention provides a method for preparing a boiling-water resistant starch adhesive reinforced with reed fiber based on a hyperbranching strategy. The method primarily addresses the poor bonding strength, water resistance, and weather resistance of traditional starch adhesives through hyperbranching. Hyperbranched polyamide is synthesized from diethylenetriamine and urea to modify oxidized reed fiber, resulting in hyperbranched reed fiber. Then, a carboxyl-terminated hyperbranched polymer is prepared using citric acid and glycerol triglycidyl ether to hyperbranch the starch. Finally, the two hyperbranched modified products are synergistically combined to obtain a boiling-water resistant starch adhesive. The hyperbranched structure enhances interfacial compatibility through multiple bonds, enabling plywood to achieve a wet strength of 1.45 MPa after immersion in 93°C hot water for 3 hours, meeting the Class I standard of GB / T 9846-2015 and representing an improvement of 107.14%. Furthermore, this adhesive can be used on various substrates such as metal, glass, and leather, overcoming the limitation of traditional starch adhesives that can only be used on lignocellulose substrates.
[0026] Example 1: A method for preparing a reed fiber reinforced adhesive based on a hyperbranching strategy.
[0027] S1. Preparation of HOF: Hyperbranching modification of reed fiber, including the following steps: (1) Place 3wt% reed fiber in a 5wt% sodium hydroxide solution and stir continuously at 95℃ for 4h. Then wash with deionized water until neutral and dry in an 80℃ drying oven for 12h to obtain ARF for later use.
[0028] (2) Disperse the ARF obtained in step (1) uniformly into deionized water at a bath ratio of 1:70, and adjust the pH to 4.5 with acetate buffer to obtain a reed fiber dispersion. Then, heat the reed fiber dispersion to 60°C with stirring, and add 30% sodium periodate (relative to the dry weight of the reed fiber). Then, under light-protected conditions, continue stirring for 6 hours to oxidize the reed fiber in the reed fiber dispersion. Finally, wash the oxidized reed fiber three times with deionized water to obtain a relatively pure ORF for later use.
[0029] (3) Mix diethylenetriamine and urea in a 1:1 molar ratio in a three-necked flask, stir at 120°C for 2 hours, and then cool to room temperature to obtain HP.
[0030] (4) Dissolve the HP obtained in step (3) in deionized water to prepare an HP solution with a concentration of 20 g / L, and adjust the pH to 9. Then add 1 g of ORF from step (2) to the HP solution, stir until homogeneous to obtain a mixed solution, and heat the mixed solution to 60°C for 15 min. After washing three times with deionized water, dry in an oven at 50°C for 24 h to obtain HOF.
[0031] S2. Preparation of adhesive: The preparation of hyperbranched modified reed fiber reinforced adhesive includes the following steps: A citric acid solution was prepared by dissolving citric acid in deionized water to a concentration of 40 wt%. This citric acid solution was placed in a three-necked flask and heated to 140 °C. Glycerol triglycidyl ether was then slowly added dropwise to the citric acid solution, maintaining a molar ratio of citric acid solution to glycerol triglycidyl ether solution of 2:1. The reaction was continued for 1 hour, then cooled to room temperature to obtain CHP.
[0032] In a 250ml three-necked flask, 10g of starch was dissolved in 40ml of deionized water and stirred until homogeneous. CHP was then added to obtain a mixed solution. A certain amount of HOF was then added to this mixed solution, and the pH was adjusted to 6 with 10wt% sodium hydroxide solution. The mixture was then heated to 95℃ and reacted for 1 hour to obtain the binder CHT-HOF. 0.5% .
[0033] In step b, the amount of CHP used accounts for 50% of the starch mass.
[0034] In step b, the amount of HOF added is 0.5% of the starch mass.
[0035] In practical applications, when bonding wood with adhesive, a hot press is used at a temperature of 180℃ for 5 minutes and a pressure of 1 MPa to obtain plywood.
[0036] The prepared plywood was soaked in water at 93±3℃ for 3 hours, then dried at room temperature for 10 minutes before its wet strength was tested. The results are shown in Table 1.
[0037] Example 2: A method for preparing a reed fiber reinforced adhesive based on a hyperbranching strategy.
[0038] S1. Preparation of HOF: Hyperbranching modification of reed fiber, including the following steps: (1) Place 3wt% reed fiber in a 5wt% sodium hydroxide solution and stir continuously at 95℃ for 4h. Then wash with deionized water until neutral and dry in an 80℃ drying oven for 12h to obtain ARF for later use.
[0039] (2) Disperse the ARF from step (1) uniformly into deionized water at a bath ratio of 1:70, and adjust the pH to 4.5 with acetate buffer to obtain a reed fiber dispersion. Then, heat the reed fiber dispersion to 60°C with stirring, and add 30% sodium periodate (relative to the dry weight of unmodified reed fiber). Then, under light-protected conditions, continue stirring for 6 hours to oxidize the reed fiber. Finally, wash the oxidized reed fiber three times with deionized water to obtain a relatively pure ORF for later use.
[0040] (3) Mix diethylenetriamine and urea in a 1:1 molar ratio in a three-necked flask, stir at 120°C for 2 hours, and then cool to room temperature to obtain HP.
[0041] (4) Dissolve the HP obtained in step (3) in deionized water to prepare an HP solution with a concentration of 20 g / L, and adjust the pH to 9. Then add 1 g of ORF from step (2) to the HP solution, stir until homogeneous to obtain a mixed solution, and heat the mixed solution to 60°C for 15 min. After washing three times with deionized water, dry in an oven at 50°C for 24 h to obtain HOF.
[0042] S2. Preparation of adhesive: The preparation of hyperbranched modified reed fiber reinforced adhesive includes the following steps: A citric acid solution was prepared by dissolving citric acid in deionized water to a concentration of 40 wt%. This citric acid solution was placed in a three-necked flask and heated to 140 °C. Glycerol triglycidyl ether was then slowly added dropwise to the citric acid solution, maintaining a molar ratio of citric acid solution to glycerol triglycidyl ether solution of 2:1. The reaction was continued for 1 hour, then cooled to room temperature to obtain CHP.
[0043] In a 250ml three-necked flask, 10g of starch was dissolved in 40ml of deionized water and stirred until homogeneous. CHP was then added to obtain a mixed solution. A certain amount of HOF was then added to this mixed solution, and the pH was adjusted to 6 with 10wt% sodium hydroxide solution. The mixture was then heated to 95℃ and reacted for 1 hour to obtain the binder CHT-HOF. 0.5% .
[0044] In step b, the amount of CHP used accounts for 50% of the starch mass.
[0045] In step b, the amount of HOF added is 1.0% of the starch mass.
[0046] In practical applications, when bonding wood with adhesive, a hot press is used at a temperature of 180℃ for 5 minutes and a pressure of 1 MPa to obtain plywood.
[0047] The prepared plywood was soaked in water at 93±3℃ for 3 hours, then dried at room temperature for 10 minutes before its wet strength was tested. The results are shown in Table 1.
[0048] When used for bonding metals, glass, and leather, use 180-200 g / m 2 The prepared adhesive was applied to a surface area of 25 × 12.5 mm, and uniform pressure was applied to the metal, glass, and leather to be bonded. After the samples were fully cured, the bond strength of the bonded substrates was tested using an electronic universal testing machine at a tensile speed of 10.0 mm / min. The results are shown in Table 2.
[0049] Example 3: A method for preparing a reed fiber reinforced adhesive based on a hyperbranching strategy.
[0050] S1. Preparation of HOF: Hyperbranching modification of reed fiber, including the following steps: (1) Place 3wt% reed fiber in a 5wt% sodium hydroxide solution and stir continuously at 95℃ for 4h. Then wash with deionized water until neutral and dry in an 80℃ drying oven for 12h to obtain ARF for later use.
[0051] (2) Disperse the ARF from step (1) uniformly into deionized water at a bath ratio of 1:70, and adjust the pH to 4.5 with acetate buffer to obtain a reed fiber dispersion. Then, heat the reed fiber dispersion to 60°C with stirring, and add 30% sodium periodate (relative to the dry weight of the unmodified reed fiber). Then, under light-protected conditions, continue stirring for 6 hours to oxidize the reed fiber. Finally, wash the oxidized reed fiber three times with deionized water to obtain a relatively pure ORF for later use.
[0052] (3) Mix diethylenetriamine and urea in a 1:1 molar ratio in a three-necked flask, stir at 120°C for 2 hours, and then cool to room temperature to obtain HP.
[0053] (4) Dissolve the HP obtained in step (3) in deionized water to prepare an HP solution with a concentration of 20 g / L, and adjust the pH to 9. Then add 1 g of ORF from step (2) to the HP solution, stir until homogeneous to obtain a mixed solution, and heat the mixed solution to 60°C for 15 min. After washing three times with deionized water, dry in an oven at 50°C for 24 h to obtain HOF.
[0054] S2. Preparation of adhesive: The preparation of hyperbranched modified reed fiber reinforced adhesive includes the following steps: A citric acid solution was prepared by dissolving citric acid in deionized water to a concentration of 40 wt%. This citric acid solution was placed in a three-necked flask and heated to 140 °C. Glycerol triglycidyl ether was then slowly added dropwise to the citric acid solution, maintaining a molar ratio of citric acid solution to glycerol triglycidyl ether solution of 2:1. The reaction was continued for 1 hour, then cooled to room temperature to obtain CHP.
[0055] In a 250ml three-necked flask, 10g of starch was dissolved in 40ml of deionized water and stirred until homogeneous. CHP was then added to obtain a mixed solution. A certain amount of HOF was then added to this mixed solution, and the pH was adjusted to 6 with 10wt% sodium hydroxide solution. The mixture was then heated to 95℃ and reacted for 1 hour to obtain the binder CHT-HOF. 1.5% .
[0056] In step b, the amount of CHP used accounts for 50% of the starch mass.
[0057] In step b, the amount of HOF added is 1.5% of the starch mass.
[0058] In practical applications, when bonding wood with adhesive, a hot press is used at a temperature of 180℃ for 5 minutes and a pressure of 1 MPa to obtain plywood.
[0059] The prepared plywood was soaked in water at 93±3℃ for 3 hours, then dried at room temperature for 10 minutes before its wet strength was tested. The results are shown in Table 1.
[0060] Example 4: A method for preparing a reed fiber reinforced adhesive based on a hyperbranching strategy.
[0061] S1. Preparation of HOF: Hyperbranching modification of reed fiber, including the following steps: (1) Place 3wt% reed fiber in a 5wt% sodium hydroxide solution and stir continuously at 95℃ for 4h. Then wash with deionized water until neutral and dry in an 80℃ drying oven for 12h to obtain ARF for later use.
[0062] (2) Disperse the ARF from step (1) uniformly into deionized water at a bath ratio of 1:70, and adjust the pH to 4.5 with acetate buffer to obtain a reed fiber dispersion. Then, heat the reed fiber dispersion to 60°C with stirring, and add 30% sodium periodate (relative to the dry weight of the unmodified reed fiber). Then, under light-protected conditions, continue stirring for 6 hours to oxidize the reed fiber. Finally, wash the oxidized reed fiber three times with deionized water to obtain a relatively pure ORF for later use.
[0063] (3) Mix diethylenetriamine and urea in a 1:1 molar ratio in a three-necked flask, stir at 120°C for 2 hours, and then cool to room temperature to obtain HP.
[0064] (4) Dissolve the HP obtained in step (3) in deionized water to prepare an HP solution with a concentration of 20 g / L, and adjust the pH to 9. Then add 1 g of ORF from step (2) to the HP solution, stir until homogeneous to obtain a mixed solution, and heat the mixed solution to 60°C for 15 min. After washing three times with deionized water, dry in an oven at 50°C for 24 h to obtain HOF.
[0065] S2. Preparation of adhesive: The preparation of hyperbranched modified reed fiber reinforced adhesive includes the following steps: A citric acid solution was prepared by dissolving citric acid in deionized water to a concentration of 40 wt%. This citric acid solution was placed in a three-necked flask and heated to 140 °C. Glycerol triglycidyl ether was then slowly added dropwise to the citric acid solution, maintaining a molar ratio of citric acid solution to glycerol triglycidyl ether solution of 2:1. The reaction was continued for 1 hour, then cooled to room temperature to obtain CHP.
[0066] In a 250ml three-necked flask, 10g of starch was dissolved in 40ml of deionized water and stirred until homogeneous. CHP was then added to obtain a mixed solution. A certain amount of HOF was then added to this mixed solution, and the pH was adjusted to 6 with 10wt% sodium hydroxide solution. The mixture was then heated to 95℃ and reacted for 1 hour to obtain the binder CHT-HOF. 2.0% .
[0067] In step b, the amount of CHP used accounts for 50% of the starch mass.
[0068] In step b, the amount of HOF added is 2.0% of the starch mass.
[0069] In practical applications, when bonding wood with adhesive, a hot press is used at a temperature of 180℃ for 5 minutes and a pressure of 1 MPa to obtain plywood.
[0070] The prepared plywood was soaked in water at 93±3℃ for 3 hours, then dried at room temperature for 10 minutes before its wet strength was tested. The results are shown in Table 1.
[0071] Comparative Example 1: Preparation of hyperbranched modified starch adhesive: This comparative study primarily investigated the performance of hyperbranched modified starch adhesives without the addition of reed fiber.
[0072] S1. Citric acid was dissolved in deionized water to prepare a 40 wt% citric acid solution. The citric acid solution was placed in a three-necked flask and heated to 140 °C. Then, glycerol triglycidyl ether (nCA / nGTE=2 / 1) was slowly added dropwise to the citric acid solution. After reacting for 1 hour, the mixture was cooled to room temperature to obtain CHP.
[0073] S2. In a 250ml three-necked flask, dissolve 10g of starch in 40ml of deionized water, stir well, add CHP, adjust the pH to 6 with 10wt% sodium hydroxide solution, and heat to 95℃. Continue the reaction for 1h to obtain the starch binder CHSt.
[0074] In step S2, the amount of CHP used accounts for 50% of the starch mass.
[0075] In practical applications, when starch adhesive is used to bond wood, a hot press is used with a temperature of 180℃, a pressing time of 5 minutes, and a pressing pressure of 1MPa to obtain plywood.
[0076] The prepared plywood was soaked in water at 93±3℃ for 3 hours, then dried at room temperature for 10 minutes before its wet strength was tested. The results are shown in Table 1.
[0077] Comparative Example 2: Preparation of reed fiber reinforced starch binder: This comparative study investigated the effect of introducing unmodified reed fiber on the performance of hyperbranched starch adhesives.
[0078] S1. Citric acid was dissolved in deionized water to prepare a 40 wt% citric acid solution. This citric acid solution was placed in a three-necked flask and heated to 140°C. Then, glycerol triglycidyl ether was slowly added dropwise to the citric acid solution, controlling the molar ratio of citric acid solution to glycerol triglycidyl ether solution to be 2:1. After reacting for 1 hour, the mixture was cooled to room temperature to obtain CHP.
[0079] S2. In a 250ml three-necked flask, dissolve 10g of starch in 40ml of deionized water, stir well, and then add CHP to obtain a mixed solution. Then add a certain amount of reed fiber to the mixed solution, adjust the pH to 6 with 10wt% sodium hydroxide solution, and heat to 95℃. Continue the reaction for 1 hour to obtain the adhesive CHT-RF.
[0080] In step S2, the amount of CHP used accounts for 50% of the starch mass.
[0081] In step S2, the amount of reed fiber added is 1.0% of the starch mass.
[0082] In practical applications, when bonding wood with adhesive, a hot press is used at a temperature of 180℃ for 5 minutes and a pressure of 1 MPa to obtain plywood.
[0083] The prepared plywood was soaked in water at 93±3℃ for 3 hours, then dried at room temperature for 10 minutes before its wet strength was tested. The results are shown in Table 1.
[0084] Table 1. Test results of the adhesives prepared in the examples and comparative examples after application. Table 2 Test results of adhesion strength to other substrates in Example 2 As shown in Table 1, all plywoods exhibited resistance to boiling water, with wet bond strengths exceeding 0.7 MPa, meeting the requirements for Class I plywood in GB / T 9846-2015, representing a maximum improvement of 107.14%. The excellent bonding performance is primarily due to two factors: firstly, the wood surface contains numerous micropores, facilitating adhesive penetration and forming "glue nails" after curing; secondly, the CHP terminals contain abundant carboxyl groups, which not only form hydrogen bonds with the macromolecular skeleton of starch but also undergo esterification reactions with active groups in starch. This dense cross-linked network structure enhances the cohesive force of the CHP adhesive, effectively preventing water molecule intrusion. Simultaneously, the active carboxyl groups also form chemical bonds at the adhesive-wood interface through esterification, reducing hydrophilic groups while increasing the adhesive's bonding strength. Furthermore, strong hydrogen bonds are formed between the hydroxyl groups at the adhesive-wood interface. Ultimately, the synergistic effect of the hydrogen bond network, chemical bonding, and mechanical interlocking enhances the adhesive's bonding strength.
[0085] As shown in the comparative examples, the introduction of fibers further enhances the bonding strength. This is because the polyhydroxyl properties of cellulose fibers and the polar matrix of starch exhibit good interfacial compatibility, thereby improving the cohesive force of the adhesive. Furthermore, as shown in Example 2, when the HOF content is 1.0%, CHSt-HOF… 1.0%The plywood bonded with the adhesive exhibited an optimal wet strength of 1.45 MPa after immersion in water at 93°C for 3 hours. Furthermore, the water contact angle reached a maximum of 96.2°, indicating strong water resistance. This is because the hyperbranched modification of reed fibers and starch resulted in a higher content of amino and carboxyl groups, enhancing the compatibility between the fibers and the starch matrix. Under external force, stress can be effectively transferred through the fibers, reducing stress concentration and thus enhancing the overall energy dissipation capacity of the adhesive layer. Moreover, the good interaction between the reed fibers and the starch matrix reduces the moisture content of the adhesive, resulting in a higher solids content. At a HOF content of 1.0%, CHSt-HOF… 1.0% The adhesive has a solid content of 52.91%. However, when the HOF content is too high, the various interactions will increase the viscosity of the system, which not only reduces the effective collision between reactive groups, but also makes it difficult for the adhesive to penetrate into the gaps in the wood, resulting in poor bonding and lower bond strength.
[0086] This invention synthesizes hyperbranched fibers and hyperbranched starch based on hyperbranching modification technology. The three-dimensional network structure and abundant terminal groups of the hyperbranched polymer have a breakthrough effect in adhesive development. The high-density active groups not only form a dense three-dimensional network structure with starch, resisting water molecule invasion, but also increase the cohesive strength of the adhesive, thereby increasing its bonding strength. Furthermore, due to the polyhydroxyl nature of plant fibers, they can form strong hydrogen bonds and chain entanglements with starch molecular chains, further enhancing the cohesive force of the adhesive. When applied to plywood, the wet strength is increased by 107.14% compared to the Class I standard in GB / T 9846-2015.
[0087] Furthermore, as shown in Table 2, CHSt-HOF 1.0% The adhesive has bonding properties to metals, glass, and leather. CHSt-HOF is one such adhesive. 1.0% The adhesive exhibits optimal adhesion to metals, with a bond strength of 1.68 MPa. This is attributed to the interfacial bonding between the hydroxyl and carboxyl functional groups in the adhesive structure and the hydroxyl groups on the metal oxide layer via hydrogen bonding. Furthermore, the carboxylate ions form coordination bonds with the metal surface, further enhancing the interfacial adhesion between the adhesive and the metal. Simultaneously, the liquid adhesive penetrates into the micropores of the metal surface during curing, forming a mechanically interlocking structure and enhancing the physical anchoring effect. Therefore, through the synergistic effect of hydrogen bonding, coordination, and physical anchoring, this adhesive demonstrates excellent adhesion to metals. In addition, CHSt-HOF… 1.0% The adhesive also effectively bonds leather and glass, with bond strengths of 0.77 MPa and 1.05 MPa, respectively. This is mainly due to the silanol groups on the glass surface and the abundant amino and carboxyl groups on the leather, which react with CHSt-HOF.1.0% The hydroxyl and carboxyl groups in the adhesive macromolecular chain can form a hydrogen bond network, which is the main driving force for adhesion. Additionally, for leather, the carboxyl groups in the adhesive can form amide bonds with the amino groups on the leather, thereby increasing the bonding strength through chemical bonding. In summary, CHSt-HOF... 1.0% The adhesive exhibits good adhesion to a variety of substrates. It overcomes the limitation of traditional starch adhesives to cellulose substrates, thus broadening the application range of starch adhesives.
[0088] The embodiments described above are merely preferred embodiments of the present invention, and not all feasible embodiments of the present invention. Any obvious modifications made by those skilled in the art without departing from the principles and spirit of the present invention should be considered to be included within the scope of protection of the claims of the present invention.
Claims
1. A method for preparing hyperbranched modified fibers, characterized in that, Specifically, the following steps are included: (1) Place 3wt% reed fiber in a 5wt% sodium hydroxide solution and stir continuously at 95℃ for 4h. Then wash with deionized water until neutral and dry in an 80℃ drying oven for 12h to obtain alkali-treated reed fiber ARF for later use. (2) Disperse ARF evenly in deionized water at a bath ratio of 1:70, and adjust the pH to 4.5 with acetate buffer to obtain a reed fiber dispersion. Then, heat the reed dispersion to 60°C and add sodium periodate. Then, under light-protected conditions, stir continuously for 6 hours to oxidize the reed fiber. Finally, wash the oxidized reed fiber three times with deionized water to obtain pure oxidized reed fiber (ORF). (3) Diethylenetriamine and urea were mixed in a 1:1 molar ratio in a three-necked flask and stirred at 120°C for 2 hours. The mixture was then cooled to room temperature to obtain hyperbranched polyamide HP. (4) Dissolve the HP obtained in step (3) in deionized water to prepare an HP solution of a certain concentration and adjust the pH to 9; then add the ORF in step (2) to the HP solution, stir until uniform to obtain a mixed solution, heat the mixed solution to 60°C, stir continuously for 15 min, wash three times with deionized water, and dry in an oven at 50°C for 24 h to obtain hyperbranched modified fiber HOF.
2. The method for preparing hyperbranched modified fibers as described in claim 1, characterized in that, In step (1), the mass of reed fiber is 3% of the mass of sodium hydroxide solution; the concentration of sodium hydroxide solution is 5 wt%.
3. The method for preparing hyperbranched modified fibers as described in claim 1, characterized in that, In step (2), the mass of sodium periodate is 30% of the dry weight of unmodified reed fiber.
4. The method for preparing hyperbranched modified fibers as described in claim 1, characterized in that, In step (4), the concentration of the HP solution is 20 g / L; the amount of ORF added is 5% of the mass of the HP solution.
5. A method for preparing a reed fiber-reinforced starch-based boiling water resistant adhesive based on a hyperbranching strategy, characterized in that, Specifically, the following steps are included: a) Citric acid was dissolved in deionized water to prepare a 40 wt% citric acid solution, which was then placed in a three-necked flask and heated to 140 °C. Glycerol triglycidyl ether was then slowly added dropwise to the citric acid solution, with the molar ratio of citric acid solution to glycerol triglycidyl ether solution controlled at 2:
1. After reacting for 1 hour, the mixture was cooled to room temperature to obtain the carboxyl-terminated hyperbranched polymer CHP. b. In a three-necked flask, prepare a 20 wt% starch solution, stir evenly, and then add the CHP prepared in step a; then add the HOF prepared by the method of preparing hyperbranched modified fiber according to any one of claims 1-4 to the starch solution, adjust the pH to 6 with 10 wt% sodium hydroxide solution, and heat to 95°C, and continue the reaction for 1 hour to obtain the adhesive.
6. The method for preparing the starch-based adhesive as described in claim 5, characterized in that, CHP is used at a rate of 50% of the starch mass.
7. The method for preparing the starch-based adhesive as described in claim 5, characterized in that, The amount of HOF fiber added is 0.5%-2.0% of the starch mass.
8. The application of the adhesive prepared by the method of starch-based adhesive as described in claim 5 in bonding wood, metal, glass and leather.
9. The application as claimed in claim 8, characterized in that, When the adhesive is used to bond wood, use 180-200g / m 2 The prepared adhesive was uniformly applied to one side of the wood, with a coating area of 25×25mm. The wood was then hot-pressed using a hot press at a temperature of 180℃ for 5 minutes and a pressure of 1MPa to obtain plywood.
10. The application as claimed in claim 8, characterized in that, When adhesives are used for bonding metals, glass, and leather, the concentration should be 180-200 g / m³. 2 The prepared adhesive was applied to a coating area of 25×12.5mm, and the metal, glass and leather to be bonded were uniformly pressed at a pressure of 1MPa. After complete curing, metal, glass and leather samples were obtained.