Lignin-based strong adhesive prepared from DES pretreated biomass as well as preparation method and application of lignin-based strong adhesive

Abstract

The invention discloses a lignin-based strong adhesive prepared from DES pretreated biomass and a preparation method and application thereof.The preparation method comprises the following steps that L-malic acid and beta-cyclodextrin are mixed, heated and stirred till uniform and transparent liquid is formed, and a eutectic solvent system is obtained; mixing biomass with the eutectic solvent system prepared in the step (1), heating and stirring; adding an acetone aqueous solution for quenching reaction, performing vacuum filtration, and collecting filtrate to obtain lignin and DES mixed liquid; and heating and stirring the obtained lignin and DES mixed liquid until the mixed liquid is thick to obtain the lignin-based adhesive. Compared with the existing lignin-based adhesive, the adhesive prepared by the method does not release formaldehyde and is green and environment-friendly. And the material has the advantages of extremely strong mechanical property, wide temperature adaptability, capability of being used for various materials, solvent corrosion resistance and the like. The method can be widely applied to the fields of furniture manufacturing, aerospace and the like.

Description

Technical Field

[0001] The present invention relates to the field of biomass adhesives, and particularly to a lignin-based strong adhesive prepared from DES-pretreated biomass, its preparation method and application. Background Art

[0002] An adhesive is a substance used to bond two or more materials together. Its main function is to bond the surfaces of materials together through physical or chemical forces and has a wide range of applications in aerospace and various other fields. The current adhesive market is mainly occupied by petroleum-derived products, which has led to increasing concerns about environmental sustainability. Lignin is considered a sustainable material and has potential applications to replace existing petroleum-derived polymers. In recent years, lignin adhesives have received great attention due to their environmentally friendly and non-toxic properties. To obtain these biological products, it is necessary to effectively separate cellulose, hemicellulose, and lignin through pretreatment, which is of great significance in the biorefinery process.

[0003] Currently, two main strategies for manufacturing lignin-based thermosetting materials as wood adhesives have been reported. A common strategy is to perform additional chemical modifications on lignin, such as hydroxymethylation, phenolation, demethylation, and depolymerization, which are necessary to improve the reactivity of lignin. Unfortunately, these processes are both troublesome and energy-consuming. Another strategy is to directly add unmodified lignin into commercial resins, such as phenolic resins, to prepare lignin-phenol-formaldehyde resin adhesives using biorefinery technology lignin. However, compared with adhesives without lignin, the higher the amount of lignin added to the resin, the lower the bonding strength of the wood-based panels. In addition, adding lignin to phenolic resins cannot completely prevent the release of formaldehyde. While preparing adhesives by pretreatment with natural deep eutectic solvents has a simple process, does not require the addition of extra solvents, has good bonding performance, and is environmentally friendly without formaldehyde release, which exactly solves the disadvantages of traditional adhesives.

[0004] Deep eutectic solvents (DES) are a new type of functional liquid composed of a hydrogen bond donor and a hydrogen bond acceptor. Through the formation of strong hydrogen bond interactions, their melting points are lower than those of any of their components. Due to their low surface tension, DES can well wet the substrate surface, providing a better contact area, thereby enhancing the bonding strength. In wood, lignin acts as a filling and bonding substance and can physically and chemically bond and strengthen the cellulose fibers in the wood cell wall, increasing the bonding strength of the wood and its resistance to microbial erosion, making the lignified plants stand upright without decay. Therefore, combining the two to prepare lignin-based adhesives not only has good bonding strength but also can be widely applied in various fields.

[0005] However, in the prior art, a large amount of substances such as cellulose and hemicellulose still remain in the waste residue after processing biological materials, such as bagasse. How to make full use of the lignocellulose in the waste residue by using a more effective method for pretreating biomass is a technical problem to be solved in the prior art. Summary of the Invention

[0006] The primary object of the present invention is to overcome the disadvantages and deficiencies of the prior art and provide a preparation method of a lignin-based strong binder prepared by DES pretreatment of biomass.

[0007] The second object of the present invention is to provide a lignin-based strong binder obtained by the above preparation method.

[0008] The third object of the present invention is to provide the application of the above lignin-based strong binder.

[0009] The object of the present invention is achieved by the following technical solutions: A preparation method of a lignin-based binder, comprising the following steps: (1) Mix L-malic acid and β-cyclodextrin, and heat and stir until a uniform transparent liquid is formed to obtain a deep eutectic solvent system; (2) Mix biomass with the deep eutectic solvent system prepared in step (1), and heat and stir; (3) Add an aqueous acetone solution to quench the reaction, and perform vacuum filtration to collect the filtrate to obtain a mixed liquid of lignin and DES; (4) Heat and stir the obtained mixed liquid of lignin and DES until it becomes viscous to obtain a lignin-based binder.

[0010] Further, the molar ratio of L-malic acid to β-cyclodextrin in step (1) is: (30-50):1; more preferably 40:1.

[0011] Further, the heating in step (1) is at 110-140°C, more preferably 120°C.

[0012] Further, the biomass in step (2) includes plant residues; more preferably bagasse.

[0013] Further, the conditions for heating and stirring in step (2) are: the temperature is 110-140°C, and heating and stirring are carried out for 2-5 h; more preferably: the temperature is 120°C, and heating and stirring are carried out for 3 h.

[0014] Further, the volume percentage concentration of the aqueous acetone solution in step (3) is 20%-80%; more preferably 50%.

[0015] Further, the temperature of the heating and stirring in step (4) is 100-110°C; more preferably 105°C.

[0016] A lignin-based binder is prepared by the above preparation method.

[0017] The application of the above lignin-based binder in a bonding material.

[0018] Further, the material is a wood material.

[0019] Further, the curing temperature of the lignin-based binder when bonding the material is 150-180°C; more preferably 170°C.

[0020] Further, the curing time of the lignin-based binder when bonding the material is 3-24 h; more preferably 12 h.

[0021] The present invention has the following advantages and effects compared with the prior art: (1) Compared with other binders, the lignin-based binder prepared by the present invention has no formaldehyde release, is green and environmentally friendly, and contributes to the realization of the dual-carbon goal.

[0022] (2) Compared with other lignin-based binders, the present invention combines DES to directly prepare a lignin-based binder (3) Compared with other lignin-based binders, the present invention overcomes the disadvantage of poor water resistance of traditional lignin-based binders.

[0023] (4) The method for preparing the lignin-based binder by this pretreatment helps to form a macromolecular cross-linked network. It has excellent tensile strength (5.14 MPa), can be used in extreme environments (-196°C), has no formaldehyde release, is applicable to multiple materials, and has broad prospects for application in aerospace. Description of the Drawings

[0024] Figure 1 It is a schematic process flow diagram for preparing the lignin-based binder of the present invention.

[0025] Figure 2 It is a result diagram of the cellulose retention rate, hemicellulose removal rate, and lignin removal rate of the cellulose-rich residue obtained as a by-product.

[0026] Figure 3 It is a two-dimensional NMR diagram of the prepared lignin-based binder.

[0027] Figure 4 It is a mechanical strength diagram of different pretreatment times and temperatures.

[0028] Figure 5 It is a mechanical strength diagram of different curing times and temperatures.

[0029] Figure 6 It is the result diagram showing that the adhesives of the present invention are applicable to different acidic and alkaline conditions.

[0030] Figure 7 It is the result diagram of the tensile strength of the glued wooden strip samples in Example 5. Detailed implementation manners

[0031] The present invention will be further described in detail below in conjunction with examples and the accompanying drawings, but the implementation manners of the present invention are not limited thereto.

[0032] The bagasse selected in the example is 100-mesh bagasse after being simply processed by a pulverizer. This bagasse contains 40.29% cellulose, 30.03% hemicellulose and 11.85% lignin, and the content of aryl ether bonds in the lignin is 69.23%.

[0033] Example 1 A preparation method of a lignin-based adhesive, comprising the following steps: (1) Mix β-cyclodextrin and L-malic acid in a molar ratio of 1:40, and heat in an oil bath at 120 °C until a uniform and transparent liquid is formed to obtain a deep eutectic solvent system.

[0034] (2) Mix 3 g of bagasse with the deep eutectic solvent system prepared in step (1) in a pressure-resistant bottle, and then transfer it to an oil bath at 120 °C for oil bath heating and stirring for 3 h.

[0035] (3) Transfer 50 mL of 50% (v / v) acetone aqueous solution to the mixture to quench the reaction. Subsequently, vacuum filter the mixture through a Buchner funnel, collect the filter residue as cellulose-rich filter residue, and collect the filtrate to obtain a liquid rich in lignin and DES.

[0036] (4) Heat (105 °C) and stir (400 r / min) the liquid prepared in step (3) in a constant-temperature magnetic stirrer until it becomes viscous to obtain a lignin-based adhesive.

[0037] The schematic diagram of the lignin-based adhesive is as Figure 1 shown.

[0038] Performance test: 1) The three-component content of the cellulose-rich residue The contents of hemicellulose, cellulose, and lignin in cellulose-rich residues were analyzed using a two-step sulfuric acid hydrolysis method and determined using high-performance liquid chromatography (HPLC, Shimadzu LC-2030CLT Plus, JPN). The masses of cellulose and hemicellulose in the original BP (bagasse) and cellulose-rich residues were calculated based on the concentrations of monomeric sugars in the hydrolysis products. The results are as Figure 2 shown. This method successfully fractionated bagasse, with cellulose retention rate, hemicellulose removal rate, and lignin removal rate reaching 82.59%, 56.15%, and 77.06% respectively.

[0039] 2) 2D-HSQC spectrum of lignin in lignin-based adhesives The results are as Figure 3 shown, and the β-O-4 bond was converted to Hibbert ketone (HK).

[0040] Example 2 According to the method of Example 1, the temperature and heating and stirring time in step (2) were adjusted to prepare 8 groups of lignin-based adhesives. The conditions for each group are shown in Table 1.

[0041] Table 1 .

[0042] The 8 groups of prepared lignin-based adhesives were applied to a wooden strip sample. The size of the applied adhesive was 0.7 * 20 mm, the application amount of the adhesive was 0.5 mg. After application, the two wooden strip samples were bonded together, and the curing temperature after bonding was 170 °C and the curing time was 12 h. For the dry strength test, the specimens were tested directly without any treatment. For the wet strength test, the specimens were pre-soaked in water at 63 °C for 3 hours and then air-dried at room temperature for 10 minutes before the test.

[0043] The tensile strength of the bonded wooden strip samples was tested using a universal material testing machine (UTM5504) at a testing speed of 2 mm / min. During the test, each sample was cut into a size of 100 × 20 mm 2 and a thickness of approximately 3 mm.

[0044] Tensile strength calculation formula: The tensile strength results of the wooden strip samples applied with 8 groups of lignin-based adhesives obtained under different pretreatment conditions are as Figure 4 shown.

[0045] Example 3 The lignin-based binder was prepared according to the method of Example 1, and the prepared lignin-based binder was applied to a wooden strip sample. The size of the applied binder was 0.7 * 20 mm, and the application amount of the binder was 0.5 mg. After application, the two wooden strip samples were bonded together, and a series of experimental groups were set for the curing temperature and curing time after bonding to test the tensile strength of the wooden strip samples with different curing temperatures and curing times after applying the lignin-based binder. The specific conditions are shown in Table 2. For the dry strength test, the specimens were tested directly without any treatment. For the wet strength test, the specimens were pre-soaked in water at 63 °C for 3 hours and then air-dried at room temperature for 10 minutes before the test.

[0046] Table 2 。

[0047] The tensile strength of the wooden strip samples was tested using a universal material testing machine (UTM5504) at a testing speed of 2 mm / min. During the test, each sample was cut into a size of 100 × 20 mm 2 and a thickness of about 3 mm.

[0048] Tensile strength calculation formula: The tensile strength results of the wooden strip samples with different curing temperatures and curing times after applying the lignin-based binder are as Figure 5 shown.

[0049] Example 4 The lignin-based binder was prepared according to the method of Example 1, and the prepared lignin-based binder was applied to a wooden strip sample. The size of the applied binder was 0.7 * 20 mm, and the application amount of the binder was 0.5 mg. After application, the two wooden strip samples were bonded together, and the curing temperature after bonding was 170 °C and the curing time was 12 h. For the dry strength test, the specimens were tested directly without any treatment. In this example, only the wet strength was tested. After the cured wooden strip samples were soaked in solvents with different acid-base properties for 24 h, they were air-dried at room temperature for 10 minutes before the test, and the tensile strength of the samples was measured.

[0050] The tensile strength of the wooden strip samples was tested using a universal material testing machine (UTM5504) at a testing speed of 2 mm / min. During the test, each sample was cut into a size of 100 × 20 mm 2 and a thickness of about 3 mm.

[0051] Tensile strength calculation formula: The tensile strength results of the wooden strip samples applied with the lignin-based binder in environments with different acid-base properties are as Figure 6 shown.

[0052] Example 5 Compared with Example 1, the difference lies in that "the molar ratio of β-cyclodextrin to L-malic acid is 1:40" in step (5) is replaced by "the molar ratio of malic acid: choline chloride: aluminum chloride is 1:2:0.01".

[0053] Performance test: 1) Tensile strength test Apply the prepared lignin-based adhesive to a wooden strip sample. The size of the applied adhesive is 0.7 * 20 mm, the application amount of the adhesive is 0.5 mg. After application, bond the two wooden strip samples together. The curing temperature after bonding is 170 °C and the curing time is 12 h.

[0054] In this example, only the wet strength is tested. The specimen is pre-soaked in water at 63 °C for 3 hours and then air-dried at room temperature for 10 minutes before the test.

[0055] Use a universal material testing machine (UTM5504) to test the tensile strength of the wooden strip sample. The test speed is 2 mm / min. When testing, cut each sample into a size of 100×20 mm 2 and a thickness of about 3 mm.

[0056] Tensile strength calculation formula: The results are as Figure 7 shown, and the tensile strength of the wooden strip is 1.67 MPa.

[0057] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications made without departing from the spirit and principle of the present invention shall be equivalent replacement methods and are all included in the protection scope of the present invention.

Claims

1. A method for preparing a lignin-based adhesive, characterized in that: The following steps are involved: (1) mixing L-malic acid and β-cyclodextrin, heating and stirring until a uniform transparent liquid is formed to obtain a deep eutectic solvent system; (2) mixing the biomass with the low eutectic solvent system prepared in step (1), heating and stirring; (3) adding an acetone aqueous solution to quench the reaction, vacuum filtering, and collecting the filtrate to obtain a mixed liquid of lignin and DES; (4) The obtained mixed liquid of lignin and DES is heated and stirred until it becomes viscous to obtain a lignin-based adhesive.

2. The preparation method according to claim 1, characterized in that: The molar ratio of L-malic acid to β-cyclodextrin in step (1) is (30-50):1; The heating in step (1) is 110-140°C.

3. The preparation method according to claim 2, characterized in that: The molar ratio of L-malic acid to β-cyclodextrin in step (1) is 40:1; The heating in step (1) is 120°C.

4. The preparation method according to claim 1, characterized in that: The biomass in step (2) includes plant residues; The heating and stirring conditions in step (2) are: temperature of 110-140° C., heating and stirring for 2-5 hours.

5. The preparation method according to claim 4, characterized in that: The biomass in step (2) includes sugarcane bagasse; The heating and stirring conditions in step (2) are: temperature of 120° C., heating and stirring for 3 h.

6. The preparation method according to claim 1, characterized in that: The volume percentage concentration of the acetone aqueous solution in step (3) is 20% to 80%.

7. The preparation method according to claim 1, characterized in that: The temperature of the heating and stirring in step (4) is 100-110°C.

8. A lignin-based adhesive, characterized in that It is prepared by the preparation method according to any one of claims 1 to 7.

9. Use of the lignin-based adhesive according to claim 8 in adhesive materials.

10. The use according to claim 9, characterized in that: The wood material of the material; The curing temperature of the lignin-based adhesive when bonding the material is 150-180°C; The curing time of the lignin-based adhesive when bonding the material is 3 to 24 hours.

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