Preparation Method and Application of a Bamboo and Wood-Based Bio-Epoxy Adhesive

Abstract

The present invention discloses a preparation method and application of a bamboo-wood-based bio-epoxy adhesive. After crushing and grinding bamboo / wood raw materials, the obtained powder is mixed with polyol and water and left standing, and then the micro-nanoization of bamboo powder and wood powder is achieved through mechanical grinding; then it is mixed with an epoxide, polybasic acid / anhydride and a solvent, and the bamboo-wood-based bio-epoxy adhesive is prepared through stirring reaction. The present invention utilizes rich bamboo and wood resources and innovatively develops a brand-new adhesive, which has excellent bonding strength, water resistance, heat resistance and good environmental friendliness, and can be directly applied to fields where curing and bonding are achieved through hot pressing, such as the preparation of plywood, fiberboard, particleboard, bamboo-wood composite board, etc., to address the environmental and health problems of traditional petroleum-based adhesives, and at the same time overcome the deficiencies of existing bio-based adhesives in terms of bonding performance.

Description

Technical Field

[0001] The present invention belongs to the field of adhesives, and particularly relates to a preparation method and application of a bamboo / wood-based bio-epoxy adhesive. Background Art

[0002] With the increasing global emphasis on environmental protection and sustainable development, adhesives are facing the pressure of transformation. Traditional adhesives, such as petroleum-based phenolic resins and urea-formaldehyde resins, although widely used due to their good bonding performance and low cost, the harmful substances released during their production and use, such as formaldehyde, pose a major threat to the environment and human health; and in addition to the negative impact on the environment, these products rely on non-renewable resources, exacerbating resource depletion and environmental degradation.

[0003] In the existing market, the demand for high-efficiency and environmentally friendly adhesives has increased sharply, especially in the manufacture of plywood, fiberboard, particleboard, and bamboo-wood composite materials. However, existing bio-based adhesive products often struggle to find a balance between environmental performance and industrial application performance. The market urgently needs an adhesive that can meet environmental protection standards and provide excellent bonding performance.

[0004] In recent years, epoxy soybean oil-based adhesives, as an alternative, have received extensive attention for using renewable soybean oil as a raw material. However, although such adhesives have significant advantages in environmental friendliness, in practical applications, these adhesives often cannot compare with traditional petroleum-based adhesives in terms of key properties such as bonding strength, water resistance, and heat resistance, especially the performance stability problem in high humidity or high temperature environments, which limits their application in key fields such as outdoor furniture and building materials. On the other hand, bamboo and wood resources, as a rapidly renewable biomass resource, are widely distributed in our country. The abundance of these resources provides opportunities for the development of new bio-based adhesives, but also brings challenges. The chemical composition and structural characteristics of bamboo and wood make it difficult to achieve ideal bonding effects in traditional adhesive formulations. At the same time, the technical and cost issues that may arise during the processing and transformation of bamboo and wood raw materials also become factors restricting their wider application.

[0005] In view of this, the present invention provides a novel bamboo / wood-based bio-epoxy adhesive, its preparation method and application. The present invention makes full use of the natural advantages of bamboo and wood resources, and optimizes the overall performance of the adhesive by compounding them with epoxy compounds, thus solving the limitations of traditional bio-based adhesives in terms of bonding strength, water resistance and heat resistance. At the same time, the preparation method of the present invention simplifies the production process and reduces the cost, making it more feasible for industrial-scale production. Therefore, the bamboo / wood-based bio-epoxy adhesive of the present invention not only meets the market demand for high-performance and environmentally friendly adhesives, but also opens up a new way for the efficient utilization of widely distributed bamboo and wood resources globally, promoting the sustainable development of the wood processing industry. Summary of the Invention

[0006] To solve the deficiencies of the prior art, the present invention provides a preparation method and application of a bamboo / wood-based bio-epoxy adhesive.

[0007] To achieve the above object, the present invention adopts the following technical solutions:

[0008] A preparation method of a bamboo / wood-based bio-epoxy adhesive, which comprises the following steps:

[0009] (1) Crushing and grinding bamboo / wood raw materials;

[0010] (2) Mixing the powder obtained in step (1) with polyol and water and standing to obtain a dispersion;

[0011] (3) Mechanically grinding the dispersion obtained in step (2) to achieve the micro-nanoization of bamboo powder or wood powder;

[0012] (4) Mixing the product ground in step (3) with an epoxy compound, a polybasic acid / anhydride and a solvent, and stirring and reacting to obtain the bamboo / wood-based bio-epoxy adhesive.

[0013] Further, the particle size of the powder obtained after grinding in step (1) is 50-400 mesh, preferably 100-400 mesh, more preferably 200-400 mesh, and most preferably 300-400 mesh.

[0014] Further, the polyol in step (2) is one or more of ethylene glycol, propylene glycol, glycerol, polyethylene glycol, polypropylene glycol, polyglycerol, pentaerythritol.

[0015] Further, the mass of the polyol added in step (2) is 1%-200% of the mass of the powder used, preferably 5%-100%, more preferably 10%-50%, and most preferably 10%-30%.

[0016] Further, the amount of water added in step (2) is 10% - 500% of the mass of the powder used, preferably 50% - 300%, more preferably 50% - 200%, and most preferably 50% - 100%. The actual amount of water added should be adjusted according to the type of bamboo / wood powder and the mass of ethanol added to ensure complete wetting of the powder.

[0017] Further, the temperature for standing in step (2) is 0 - 100°C, preferably 20 - 100°C, more preferably 50 - 80°C; the time is 1 - 4 h.

[0018] Further, the grinding time in step (3) depends on the grinding process adopted, and the particle size of the ground product should be below 1200 nm, preferably below 1000 nm, more preferably below 800 nm. Taking a colloid mill as an example, the grinding time is 5 - 180 min, preferably 10 - 150 min, more preferably 20 - 100 min, and most preferably 20 - 50 min.

[0019] Further, the epoxide in step (4) is one or more of epoxy vegetable oil and glycidyl ether.

[0020] Further, the addition amount of the epoxide in step (4) is 0.01% - 100% of the mass of the ground product used, preferably 5% - 100%, more preferably 10% - 100%, more preferably 10% - 80%, and most preferably 20% - 60%.

[0021] Further, the polybasic acid in step (4) is one or more of oxalic acid, citric acid, malic acid, lactic acid, tartaric acid, maleic acid, fumaric acid, and phthalic acid, and the acid anhydride is one or more of maleic anhydride, bismaleic anhydride, and pyromellitic dianhydride.

[0022] Further, the addition amount of the polybasic acid / acid anhydride in step (4) is 1% - 100% of the mass of the ground product used, preferably 10% - 100%, more preferably 20% - 100%, and most preferably 30% - 100%.

[0023] Further, the solvent in step (4) is one or more of water, 1,4 - dioxane, 4 - methylbutyrolactone, 2 - methyltetrahydrofuran, methanol, ethanol, propanol, butanol, acetone, and butanone.

[0024] Further, the addition amount of the solvent in step (4) is 0% - 300% of the mass of the ground product used, preferably 0% - 100%, more preferably 0 - 50%, and most preferably 0 - 20%.

[0025] Further, the temperature of the stirring reaction in step (4) is 30 - 180°C, preferably 50 - 180°C, more preferably 70 - 180°C, still more preferably 70 - 150°C, and most preferably 70 - 120°C; the time is 5 - 60 min.

[0026] The prepared bamboo - wood - based bio - epoxy adhesive can be directly used in the field of curing and bonding through hot - pressing without further reaction or addition of other active ingredients. For example, it can be used in the production of original wood boards, artificial boards or particle boards. The application method is to spray the bamboo - wood - based bio - epoxy adhesive on the surface of the wood and perform hot - pressing cross - linking at 100 - 200°C to bond the wood. Among them, the added polyols and polyacids / anhydrides can react with lignin during hot - pressing to form ester bonds or ether bonds, strengthening the bonding effect, so there is no need to remove them.

[0027] Further, the temperature of the hot - pressing cross - linking is 100 - 220°C, preferably 110 - 200°C, more preferably 120 - 200°C, and most preferably 150 - 190°C. In actual application, the hot - pressing temperature can be adjusted according to actual requirements (such as board thickness, moisture content, etc.).

[0028] Further, the pressure of the hot - pressing cross - linking is 0.4 - 3 Mpa, preferably 0.5 - 2.5 Mpa, more preferably 0.7 - 2.0 Mpa.

[0029] Meanwhile, the prepared bamboo - wood - based bio - epoxy adhesive can also be applied after adding thickeners and dispersants.

[0030] Further, the thickeners include carboxymethyl cellulose, starch, flour, protein, etc.; the addition of thickeners is beneficial to the uniform application of the adhesive.

[0031] Further, the dispersants are mainly surfactants, such as sodium dodecylbenzenesulfonate, sodium lignosulfonate, etc. The addition of dispersants can disperse solid lignin more evenly in solvents such as water.

[0032] The beneficial effects of the present invention compared with the prior art are:

[0033] (1)The present invention provides a method for preparing a fully bio - based adhesive. This method micronizes bamboo powder or wood powder through mechanical treatment and then blends it with an epoxy compound to obtain a fully bio - based adhesive with high adhesiveness. It simplifies the synthesis process of traditional adhesives and reduces the use of harmful chemicals. Different from existing patents that require multiple steps to extract lignin from wood powder to make adhesives, which involve the use of a large amount of solvents, modifiers, and multiple separation and purification operations, the present invention makes full use of cellulose and hemicellulose in bamboo / wood. By micronization, it improves their reactivity and dispersibility, and uses them as the support or filler structure after adhesion to help improve the viscosity, adhesiveness, and thermodynamic stability of the adhesive. It realizes the full utilization of biomass, reduces waste generation and emissions.

[0034] (2)In the present invention, the amounts of dispersant, modifier, and solvent used are less. Different from existing patents that use chemical methods to modify lignin and prevent the self - polymerization of degraded lignin units under acidic conditions, which require the use of modifiers and solvents such as formaldehyde, paraformaldehyde, and acetone, the present invention innovatively uses the method of mechanochemistry. By micronizing biomass particles, it fully exposes the active groups of lignin, cellulose, and hemicellulose contained therein, greatly increases their specific surface area, and effectively enhances the reactivity. The process of the present invention is simple, reduces the complexity and operating cost of producing lignin - based adhesives, effectively improves the process economy, is more suitable for large - scale applications, and is a more green and sustainable process.

[0035] (3)The bamboo - wood - based bio - epoxy adhesive obtained by the present invention has good physical and chemical stability, and its paste form is easy to store and transport.

[0036] (4)The present invention completely avoids the use of aldehyde - based chemicals. A small amount of auxiliaries required in the process can select environmentally friendly and non - toxic chemicals to achieve aldehyde - free throughout the process, meeting the requirements of environmental friendliness and green chemistry.

[0037] (5)The bamboo - wood - based bio - epoxy adhesive produced by the present invention has a large bonding strength and solves the problem of poor water resistance of current bio - based adhesives. Detailed implementation mode

[0038] A method for preparing a bamboo - wood - based bio - epoxy adhesive, which comprises the following steps:

[0039] (1)Crush and grind the bamboo / wood raw material to a particle size of 50 - 400 mesh;

[0040] (2)Mix the powder obtained in step (1) with 1% - 200% of polyol and 10% - 500% of water based on its mass, and let it stand at 0 - 100 °C for 1 - 4 h to fully wet the powder and obtain a dispersion;

[0041] (3) Add the dispersion obtained in step (2) into a colloid mill, high-pressure homogenizer or high-speed shear mixer for mechanical grinding. The particle size of the ground product should be below 1200 nm to achieve the micro-nanoization of bamboo or wood powder;

[0042] (4) Mix the product ground in step (3) with 0.01%-100% of its mass of epoxide, 1%-100% of polybasic acid / acid anhydride and 0%-300% of solvent, and stir and react at 30-180 °C for 5-60 min to obtain the bamboo-wood-based bio-epoxy adhesive.

[0043] Among them, the polyol in step (2) is one or more of ethylene glycol, propylene glycol, glycerol, polyethylene glycol, polypropylene glycol, polyglycerol, and pentaerythritol.

[0044] The epoxide in step (4) is one or more of epoxy vegetable oil and glycidyl ether. The polybasic acid is one or more of oxalic acid, citric acid, malic acid, lactic acid, tartaric acid, maleic acid, fumaric acid, and phthalic acid, and the acid anhydride is one or more of maleic anhydride, bismaleic anhydride, and pyromellitic dianhydride. The solvent is one or more of water, 1,4-dioxane, 4-methylbutyrolactone, 2-methyltetrahydrofuran, methanol, ethanol, propanol, butanol, acetone, and butanone.

[0045] To make the content of the present invention easier to understand, the technical solutions of the present invention will be further described below in conjunction with specific embodiments, but the present invention is not limited thereto.

[0046] Example 1

[0047] (1) Crush 100 g of dried bamboo powder raw material to about 200 meshes using a pulverizer.

[0048] (2) Mix the powder obtained in step (1) with 40 g of ethylene glycol and 150 g of water, and let it stand at room temperature for 2 h to obtain a dispersion.

[0049] (3) Add the dispersion obtained in step (2) into a colloid mill and grind for 20 min to make the average particle size of the obtained product below 1000 nm;

[0050] (4) Take 100 g of the ground product obtained in step (3), mix it with 50 g of epoxy soybean oil and 50 g of citric acid, and stir and react at 70 °C for 10 min for use as an adhesive.

[0051] Example 2

[0052] Replace 40 g of ethylene glycol in step (2) with 20 g of ethylene glycol, and the other operations are the same as in Example 1.

[0053] Example 3

[0054] Replace 40 g of ethylene glycol in step (2) with 60 g of ethylene glycol, and perform other operations in the same manner as in Example 1.

[0055] Example 4

[0056] Replace 40 g of ethylene glycol in step (2) with 40 g of polyethylene glycol (molecular weight 2000), and perform other operations in the same manner as in Example 1.

[0057] Example 5

[0058] Replace the treatment for 20 min in the colloid mill in step (3) with 7 cycles of high-pressure homogenizer treatment, and perform other operations in the same manner as in Example 1.

[0059] Example 6

[0060] Replace the treatment for 20 min in the colloid mill in step (3) with 10 min of colloid mill treatment, and perform other operations in the same manner as in Example 1.

[0061] Example 7

[0062] Replace the treatment for 20 min in the colloid mill in step (3) with 30 min of colloid mill treatment, and perform other operations in the same manner as in Example 1.

[0063] Example 8

[0064] Replace 50 g of citric acid in step (4) with 30 g of citric acid, and perform other operations in the same manner as in Example 1.

[0065] Example 9

[0066] Replace 50 g of citric acid in step (4) with 70 g of citric acid, and perform other operations in the same manner as in Example 1.

[0067] Example 10

[0068] Replace 50 g of citric acid in step (4) with 50 g of phthalic acid, and perform other operations in the same manner as in Example 1.

[0069] Example 11

[0070] Replace 50 g of citric acid in step (4) with 50 g of maleic anhydride, and perform other operations in the same manner as in Example 1.

[0071] Example 12

[0072] Replace 50 g of epoxidized soybean oil in step (4) with 30 g of epoxidized soybean oil, and perform other operations in the same manner as in Example 1.

[0073] Example 13

[0074] Replace 50 g of epoxidized soybean oil in step (4) with 70 g of epoxidized soybean oil, and perform other operations in the same manner as in Example 1.

[0075] Example 14

[0076] Replace 100 g of bamboo powder in step (1) with 100 g of Chinese fir powder (about 200 mesh, water content 5%), and perform other operations as in Example 1.

[0077] Example 15

[0078] Replace 100 g of bamboo powder in step (1) with 100 g of masson pine bark powder (about 100 mesh, water content 8%), and perform other operations as in Example 1.

[0079] Example 16

[0080] Replace 150 g of water in step (2) with 100 g of water, and perform other operations as in Example 1.

[0081] Example 17

[0082] Replace 150 g of water in step (2) with 200 g of water, and perform other operations as in Example 1.

[0083] Example 18

[0084] Add 20 g more methanol in step (4), and perform other operations as in Example 1.

[0085] Comparative Example 1

[0086] Replace 40 g of ethylene glycol in step (2) with 40 g of water, and perform other operations as in Example 1.

[0087] Comparative Example 2

[0088] Change the colloid mill treatment for 20 min in step (3) to stirring for 20 min, and perform other operations as in Example 1.

[0089] Comparative Example 3

[0090] Replace 50 g of citric acid in step (4) with 50 g of phosphoric acid, and perform other operations as in Example 1.

[0091] The adhesives prepared in the examples and comparative examples were made into plywood according to the following method to test their bonding performance.

[0092] The plywood manufacturing and strength testing were carried out according to the provisions in Subsection 4.17 of GB / T 17657-2022 "Test Methods for Physical and Chemical Properties of Wood-Based Panels and Decorative Wood-Based Panels", and the specific preparation steps are as follows:

[0093] (1) Select fast-growing poplar veneers to prepare three-layer plywood. The moisture content of the veneers is 10%-12%, and the length, width, and thickness of the veneers are 145 mm, 110 mm, and 1.5 mm respectively. Use the prepared adhesive to apply glue to the middle veneer. The glue application method is double-sided glue application, and the single-sided glue application amount is 100 g / m2 。

[0094] (2) Adhere an unsized veneer on each of the upper and lower sides of the sized veneer, making the fiber directions of adjacent veneers perpendicular to each other. Place the assembled three-layer plywood on the heating plate of a hot press. The hot pressing temperature is 180 °C, the hot pressing pressure is 2 MPa, and the hot pressing time is 5 minutes.

[0095] The obtained plywood was tested according to the standard of GB / T 9846-2015 "General Plywood", and the results are shown in Table 1.

[0096] Table 1 Gluing Strength of Bamboo / Wood Flour Adhesive

[0097]

[0098] It can be seen from Examples 1-4 and Comparative Example 1 that the addition of polyols is very important for the gluing performance of the adhesive, and crosslinking performance cannot be generated without the action of polyols. Ethylene glycol is an excellent dispersant, which can effectively improve the gluing performance of the adhesive. This is because the penetration of ethylene glycol into lignocellulosic biomass can cause chemical changes, such as delignification of lignin, swelling of cellulose and hemicellulose, hydrolysis of hemicellulose, change of lignin structure, and formation of solvent-biomass complexes.

[0099] It can be seen from Examples 5-7 and Comparative Example 2 that mechanical treatment using a colloid mill or a high-pressure homogenizer can effectively improve the crosslinking performance. This may be due to the realization of powder nano-microization through mechanical treatment (after detection, the average particle sizes of the products after grinding in Examples 5-7 and Comparative Example 2 are 213 nm, 412 nm, 334 nm, and 15644 nm respectively), which increases the specific surface area of the particles and exposes more active sites, thus being effective.

[0100] It can be seen from Examples 1, 8-11 and Comparative Example 3 that the addition of polyacids / anhydrides is also necessary for improving the gluing performance. The addition of polyacids / anhydrides is beneficial to the formation of a crosslinking network of nanocellulose lignin particles, thereby improving the bonding strength. Comparing Examples 1, 8, and 9, it can be seen that increasing the dosage of polyacids / anhydrides is beneficial to improving the crosslinking strength. Comparing Examples 1, 10, and 11, it can be seen that compared with an equal amount of citric acid and maleic anhydride, phthalic acid can provide higher bonding and tensile strength due to its stronger molecular rigidity.

[0101] Examples 12 - 13 can prove that epoxidized soybean oil can help form a cross - linked network, thus improving the bonding strength. Examples 14 - 15 can prove that this method can provide excellent cross - linking performance for adhesives prepared from bamboo / wood flour from various sources. Examples 16 - 17 illustrate that an appropriate water content in the system can help improve the gluing performance of the resulting adhesive. Example 18 shows that adding a small amount of methanol can help form a cross - linked network and improve the adhesive strength.

[0102] The above plywood gluing strength experiments prove that the adhesive produced by the method for preparing the bamboo - wood - based bio - epoxy adhesive provided by the present invention has good adhesive performance and can achieve a bonding strength far greater than 0.7 Mpa of the national standard.

[0103] The above are only the preferred embodiments of the present invention. All equivalent changes and modifications made according to the scope of the patent application of the present invention shall fall within the scope covered by the present invention.

Claims

1. A preparation method of a bamboo and wood-based bio-epoxy adhesive, characterized in that, It includes the following steps: (1) Crush and grind the bamboo / wood raw materials; (2) Mix the powder obtained in step (1) with polyol and water and let it stand to obtain a dispersion; (3) Mechanically grind the dispersion obtained in step (2) to achieve the micro-nanoization of bamboo powder or wood powder; (4) Mix the product ground in step (3) with an epoxide, polybasic acid / anhydride and a solvent, and obtain the bamboo-wood-based bio-epoxy adhesive through stirring reaction; In step (2), the amount of polyol added is 5%-100% of the mass of the powder used, and the amount of water added is 50%-300% of the mass of the powder used; The particle size of the product after mechanical grinding in step (3) is below 1200 nm; In step (4), the addition amount of the epoxide used is 10%-80% of the mass of the ground product used, the addition amount of the polybasic acid / anhydride used is 20%-100% of the mass of the ground product used, and the addition amount of the solvent used is 0%-300% of the mass of the ground product used.

2. The preparation method of the bamboo and wood-based bio-epoxy adhesive according to claim 1, characterized in that: The particle size of the powder obtained after grinding in step (1) is 50-400 mesh.

3. The preparation method of the bamboo and wood-based bio-epoxy adhesive according to claim 1, wherein: The polyol is one or more of ethylene glycol, propylene glycol, glycerol, polyethylene glycol, polypropylene glycol, polyglycerol, pentaerythritol.

4. The preparation method of the bamboo and wood-based bio-epoxy adhesive according to claim 1, characterized in that: In step (2), the temperature for standing is 0-100 °C and the time is 1-4 h.

5. The preparation method of the bamboo and wood-based bio-epoxy adhesive according to claim 1, wherein: The epoxide is one or more of epoxy vegetable oil, glycidyl ether; The polybasic acid is one or more of oxalic acid, citric acid, malic acid, lactic acid, tartaric acid, maleic acid, fumaric acid, phthalic acid, and the anhydride is one or more of maleic anhydride, bismaleic anhydride, pyromellitic dianhydride; The solvent is one or more of water, 1,4-dioxane, 4-methylbutyrolactone, 2-methyltetrahydrofuran, methanol, ethanol, propanol, butanol, acetone, butanone.

6. The preparation method of the bamboo and wood-based bio-epoxy adhesive according to claim 1, characterized in that: In step (4), the temperature of the stirring reaction is 30-180 °C and the time is 5-60 min.

7. Use of the bamboo and wood-based bio-epoxy adhesive prepared by the method according to any one of claims 1 to 6 in the production of original wood boards, wood-based panels or particle boards, characterized in that, Its application method is to spray the bamboo-wood-based bio-epoxy adhesive on the surface of wood and conduct hot pressing cross-linking at 100-200 °C to play the role of bonding wood.

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