A fully bio-based adhesive and its preparation method and application

Abstract

The present invention discloses a fully bio-based adhesive and its preparation method and application, which are particularly suitable for the wood products manufacturing industry. This technology solves the problem of toxic gas release during the production and application of traditional adhesives and provides an alternative solution for the increasing scarcity of fossil resources. Utilizing China's rich bamboo and wood resources, the present invention uses natural lignin and cellulose as raw materials and converts them into high-performance adhesives through a series of innovative steps. First, bamboo powder or wood powder is mixed with a dispersant and water to achieve sufficient swelling and loosening of the raw materials; secondly, through mechanical treatment such as a colloid mill or a high-pressure homogenizer, the raw materials are micronized to obtain a smooth paste; finally, this paste is mixed with a modifier and a solvent, and a stirring reaction is carried out under specific conditions to prepare the adhesive. The dispersant and the modifier do not need to be removed from the adhesive because they react with lignin during the hot pressing process to form stable chemical bonds, improving the bonding effect.

Description

Technical Field

[0001] The present invention relates to the field of adhesives, and particularly to a fully bio-based adhesive and its preparation method and application. Background Art

[0002] An adhesive is a polymer material that can connect two or more homogeneous or heterogeneous materials into one body through interfacial adhesion and cohesion, etc., and has wide applications in various fields of the national economy such as construction, packaging, electronics, medical and health, and light textile industries. As an important material second only to wood in the wood-based panel industry, wood adhesives determine the grade and quality of wood-based panels and are also key materials essential for the development of the wood-based panel industry. At present, the adhesives in China's wood-based panel industry are mainly dominated by "three aldehyde adhesives" (urea formaldehyde resin, phenolic resin, melamine formaldehyde resin). Although these traditional adhesives have advantages such as easy sizing, fast drying speed, high bonding strength, and strong water resistance, toxic and harmful gases such as formaldehyde and phenols can be released during their production and use, posing a great threat to human health; their raw materials mainly come from fossil resources. With the increasing scarcity of petroleum resources, the raw material prices of synthetic resin adhesives are rising steadily and their sustainability is challenged.

[0003] China is rich in bamboo and wood resources, and these natural materials contain a large amount of lignin and cellulose. As a natural adhesive, lignin not only plays a role in bonding cellulose in plants, enhancing the structural stability of plants, but its stable aromatic ring structure can also improve the resistance of plants to external attacks; the cellulose structure contains (semi) acetal groups, which can be converted into aldehyde substances through acid hydrolysis and dehydration.

[0004] The development of environmentally friendly adhesives using biomass materials helps to effectively replace fossil-based raw materials and promote the "dual carbon goals". The existing use of bio-based materials to develop adhesives mainly replaces one of phenol and formaldehyde, but this still cannot completely get rid of dependence on petroleum-based raw materials. For example, the patent with patent document number CN108587538A discloses a method for preparing phenolic resin adhesives by using lignin to replace phenol and formaldehyde to react, and the patent with patent document number CN107337774A discloses a method for preparing adhesives by using hemicellulose to produce furfural to replace formaldehyde and phenol to react. Due to the low reactivity of aldehyde raw materials and phenol raw materials, the prepared adhesives often fail to meet the requirements of use. The use of unilateral biomass raw materials and bilateral biomass raw materials that are difficult to replace 100% has not completely overcome the problem of toxic and harmful gas release. The development of all-biomass-based adhesives often has complex processes and requires a large amount of solvents and additives to activate lignin. Although green raw materials are used, the cumbersome processing technology reduces the economy and environmental protection of the process. For example, patent document number CN111100581A discloses a method for preparing a fully bio-based adhesive using demethylated nano-lignin and oxidized nano-cellulose, and patent document number CN114736652A discloses a method for extracting lignin from wood biomass and using the lignin as a wood adhesive.

[0005] Existing technologies cannot yet realize the direct development of adhesives from biomass materials. Developing a simplified process for directly synthesizing adhesives from lignin-rich biomass can significantly reduce production costs and reduce environmental impact. By simplifying the process design, reducing the use of chemical modification steps and harmful solvents, it can not only improve the ecological efficiency of adhesive production, which is consistent with the goal of global sustainable development, but also provide a new direction for the high-value utilization of agricultural and forestry wastes. Summary of the invention

[0006] The technical task of the invention is to solve the problems that the existing technology cannot directly prepare adhesives from natural raw materials, the lignin and cellulose all-biobased cross-linking agents have poor reactivity with other substances, the cross-linking properties are low, and the glued boards have low recycling value, and to provide a preparation method for preparing all-biobased adhesives using bamboo / wood powder.

[0007] Another object of the present invention is to provide a fully bio-based adhesive prepared by the above preparation method.

[0008] Another object of the present invention is to provide the use of the above-mentioned all-biobased adhesive as an adhesive for the production of raw wood boards or artificial boards.

[0009] The present invention includes a method for preparing a fully bio-based adhesive, and the technical solution is implemented in the following manner, including the following specific steps:

[0010] Mix bamboo powder or wood powder, a dispersant, and water, and let it stand for 0.1 - 3 h. The dispersant is one or more of 1,4 - dioxane, 1,4 - epoxybutane, dimethyl sulfoxide, pyridine, formamide, dichloroethane, 4 - methyl - butyrolactone, tetrahydrofuran, 2 - methyltetrahydrofuran, methanol, ethanol, ethylene glycol, propylene glycol, glycerol, polyethylene glycol, polypropylene glycol, and polyglycerol. The synergistic effect of the dispersant and the solvent can fully swell the bamboo powder / wood powder, break various intermolecular forces, make the fibers loose, and at the same time make the powder easier to disperse in the solvent.

[0011] Add the raw material dispersion liquid obtained in step (1) to a colloid mill or a high - pressure homogenizer for mechanical treatment for a period of time to achieve the micro - nanoization of bamboo powder or wood powder. The treated product is a smooth paste.

[0012] Mix the smooth paste obtained in step (2), a modifier, and a solvent, and stir and react at 30 - 180 °C for 5 - 60 min to be used as an adhesive. The modifier is one or more of formic acid, acetic acid, oxalic acid, citric acid, malic acid, lactic acid, tartaric acid, maleic acid, fumaric acid, phthalic acid, maleic anhydride, and bismaleic anhydride.

[0013] Furthermore, apply the adhesive obtained in step (3) evenly on the surface of the wood and hot - press and cure it cross - linked at a certain temperature. The dispersant added in step (1) and the modifier added in step (3) 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. This all - lignin - based adhesive can be directly used in the fields that achieve curing and bonding through hot - pressing without further reaction or adding other active ingredients. These applications are not limited to the preparation of plywood, fiberboard, particleboard, bamboo - wood composite board, etc.; in actual applications, the hot - pressing temperature can be adjusted according to actual needs (such as the thickness of the board, moisture, etc.). The hot - press curing and cross - linking temperature is 100 - 220 °C, preferably 110 - 200 °C, more preferably 120 - 180 °C, and even more preferably 130 - 170 °C. The hot - press curing and cross - linking pressure is 0.4 - 3 Mpa, preferably 0.5 - 2.5 Mpa, more preferably 0.7 - 2.0 Mpa.

[0014] Furthermore, the addition amount of water in step (1) is 0.5 - 5 times the mass of the bamboo powder / wood powder, preferably 0.5 - 3 times, more preferably 0.5 - 2 times, and even more preferably 0.5 - 1 times.

[0015] Furthermore, the addition amount of the dispersant in step (1) is 0.01 - 1.5 times the mass of the bamboo powder / wood powder, preferably 0.1 - 1 times, more preferably 0.1 - 0.5 times, and even more preferably 0.1 - 0.3 times.

[0016] Further, the grinding time in step (2) is 0.01 - 2 h, preferably 0.1 - 1 h, more preferably 0.1 - 0.5 h.

[0017] Further, the solvent in step (3) is one or more of water, 1,4 - dioxane, 4 - methylbutyrolactone, 2 - methyltetrahydrofuran, methanol, ethanol, propanol, butanol, acetone, and butanone.

[0018] Further, the addition amount of the solvent in step (3) is 0 - 3 times the mass of the paste obtained in step (2), preferably 0 - 1 times, more preferably 0 - 0.5 times, and even more preferably 0 - 0.2 times; for a batch reactor, in actual application, it needs to be adjusted according to the water addition amount in step (1).

[0019] Further, the addition amount of the modifier in step (3) is 0.01 - 1 times the mass of the paste obtained in step (2), preferably 0.1 - 0.5 times, more preferably 0.1 - 0.3 times.

[0020] Further, a thickener and a dispersant can also be added to the adhesive obtained in step (3). The addition of the thickener is beneficial to the uniform application of the adhesive, and thickeners that can achieve this effect include carboxymethyl cellulose, starch, flour, protein, etc.; the addition of the dispersant can disperse solid lignin more evenly in solvents such as water, and the dispersants that can achieve this effect are mainly surfactants, such as sodium dodecylbenzenesulfonate and sodium lignosulfonate.

[0021] The beneficial effects of the present invention compared with the prior art are as follows:

[0022] China is rich in bamboo / forest resources. This invention patent proposes a green, environmentally friendly, and efficient high - value - added utilization method, and at the same time can effectively replace petrochemical - based adhesives. The mechanical force method proposed in this invention to directly micro / nano - size bamboo / wood powder rich in lignin can effectively improve its reaction activity and adhesion performance. The production process is simple and has good environmental and economic benefits, and has the following beneficial effects:

[0023] (1) The present invention provides a method for preparing a fully bio-based adhesive. This method micronizes bamboo powder or wood powder through mechanical and chemical treatments to obtain a fully bio-based adhesive with high adhesiveness. This method simplifies the synthesis process of traditional adhesives and reduces the use of harmful chemicals. Different from existing patents that extract lignin from wood powder through multiple steps and then use it as an adhesive, which requires a large amount of solvents, modifiers, and multiple separation and purification operations, the present invention fully utilizes cellulose and hemicellulose in bamboo / wood, improves their reactivity and dispersibility through micronization, and uses them as the support or filler structure after adhesion, which helps to improve the viscosity, adhesiveness, and thermodynamic stability of the adhesive, realizes the full utilization of biomass, and reduces waste generation and emissions.

[0024] (2) The present invention uses less dispersant, modifier, and solvent. Different from existing patents that modify lignin by chemical methods to 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 patent innovatively uses the method of mechanochemistry. By micronizing biomass particles, the active groups of lignin, cellulose, and hemicellulose are fully exposed, the specific surface area is greatly increased, and the reactivity is effectively enhanced. The process 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.

[0025] (3) The paste obtained in step (2) has good physical and chemical stability and is easy to store and transport. Steps (2) and (3) can be carried out separately, and the modifier is compounded before use, which can effectively prevent denaturation and inactivation and avoid the use of other stabilizers at the same time.

[0026] (4) The present invention completely avoids the use of aldehyde chemicals. The small amount of auxiliaries used in the process can select environmentally friendly and non-toxic chemicals to achieve formaldehyde-free throughout the process, which is environmentally friendly and meets the requirements of green chemistry. Specific Embodiments

[0027] The present invention will be further illustrated by the following examples, but it is not limited to the present invention. The specific experimental conditions and methods not specified in the following examples are usually conventional means well-known to those skilled in the art.

[0028] Example 1

[0029] 1. Mix 100 g of bamboo powder (about 200 mesh, water content 17%), 20 g of ethylene glycol, and 100 g of water, and let it stand for 2 h.

[0030] 2. Add the raw material dispersion obtained in step (1) to a colloid mill and grind for 20 min to obtain 200 g of grinding product.

[0031] 3. Stir and react the 200 g of ground product obtained in step (2) with 40 g of citric acid at 70 °C for 20 min, and use it as an adhesive.

[0032] Example 2

[0033] Except that 20 g of ethylene glycol in step (1) is replaced with 10 g of ethylene glycol, other steps are the same as those in Example 1.

[0034] Example 3

[0035] Except that 20 g of ethylene glycol in step (1) is replaced with 30 g of ethylene glycol, other steps are the same as those in Example 1.

[0036] Example 4

[0037] Except that 20 g of ethylene glycol in step (1) is replaced with 50 g of ethylene glycol, other steps are the same as those in Example 1.

[0038] Example 5

[0039] Except that 20 g of ethylene glycol in step (1) is replaced with 70 g of ethylene glycol, other steps are the same as those in Example 1.

[0040] Example 6

[0041] Except that 20 g of ethylene glycol in step (1) is replaced with 20 g of polyethylene glycol (molecular weight 2000), other steps are the same as those in Example 1.

[0042] Example 7

[0043] Except that 20 g of ethylene glycol in step (1) is replaced with 20 g of formamide, other steps are the same as those in Example 1.

[0044] Example 8

[0045] Except that 20 g of ethylene glycol in step (1) is replaced with 20 g of tetrahydrofuran, other steps are the same as those in Example 1.

[0046] Example 9

[0047] Except that 20 g of ethylene glycol in step (1) is replaced with 20 g of glycerol, other steps are the same as those in Example 1.

[0048] Example 10

[0049] Except that the colloid mill treatment for 20 minutes in step (2) is replaced with 7 cycles of high-pressure homogenizer treatment, other steps are the same as those in Example 1.

[0050] Example 11

[0051] Except that the colloid mill treatment for 20 minutes in step (2) is replaced with a colloid mill treatment for 10 minutes, other steps are the same as those in Example 1.

[0052] Example 12

[0053] Except that the colloid mill treatment in step (2) is changed from 20 minutes to 30 minutes, other steps are the same as those in Example 1.

[0054] Example 13

[0055] Except that the colloid mill treatment in step (2) is changed from 20 minutes to 60 minutes, other steps are the same as those in Example 1.

[0056] Example 14

[0057] Except that 40 g of citric acid in step (3) is changed to 20 g of citric acid, other steps are the same as those in Example 1.

[0058] Example 15

[0059] Except that 40 g of citric acid in step (3) is changed to 80 g of citric acid, other steps are the same as those in Example 1.

[0060] Example 16

[0061] Except that 40 g of citric acid in step (3) is changed to 40 g of phthalic acid, other steps are the same as those in Example 1.

[0062] Example 17

[0063] Except that 40 g of citric acid in step (3) is changed to 40 g of maleic anhydride, other steps are the same as those in Example 1.

[0064] Example 18

[0065] Except that 100 g of bamboo powder in step (1) is changed to 100 g of Chinese fir powder (about 200 mesh, water content 5%), other steps are the same as those in Example 1.

[0066] Example 19

[0067] Except that 100 g of bamboo powder in step (1) is changed to 100 g of masson pine bark powder (about 100 mesh, water content 8%), other steps are the same as those in Example 1.

[0068] Example 20

[0069] Except that 100 g of water in step (1) is changed to 50 g of water, other steps are the same as those in Example 1.

[0070] Example 21

[0071] Except that 100 g of water in step (1) is changed to 200 g of water, other steps are the same as those in Example 1.

[0072] Example 22

[0073] Except that 100 g of water is replaced with 400 g of water in step (1), other steps are the same as those in Example 1.

[0074] Comparative Example 1

[0075] Except that 20 g of ethylene glycol is replaced with 20 g of distilled water in step (1), other steps are the same as those in Example 1.

[0076] Comparative Example 2

[0077] Except that the colloid mill treatment for 20 min in step (2) is changed to stirring for 20 min, other steps are the same as those in Example 1.

[0078] Comparative Example 3

[0079] Except that 40 g of citric acid is replaced with 10 g of phosphoric acid in step (3), other steps are the same as those in Example 1.

[0080] Experimental Example:

[0081] Prepare the bamboo / wood flour all-bio-based adhesive according to the methods described in Examples 1 to 17 and Comparative Examples 1 to 3, and then conduct the detection according to the following method. The detection results are shown in Table 1.

[0082] Performance evaluation of three-ply plywood with biomass-based adhesive:

[0083] Test the bonding performance of the plywood by pressing with the biomass-based adhesive. The plywood manufacturing and strength tests are carried out according to the provisions in Section 4.17 of GB / T 17657-2022 "Test Methods for Physical and Chemical Properties of Wood-Based Panels and Decorative Wood-Based Panels". The specific preparation steps are as follows:

[0084] (1) Select fast-growing poplar veneers to prepare three-ply 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. Apply the lignin adhesive prepared in step (2) to the middle veneer, and the application method is double-sided application. The single-sided application amount is 100 g / m 2 .

[0085] (2) Adhere an uncoated veneer on each side of the coated veneer, so that the fiber directions of adjacent veneers are perpendicular to each other. Place the assembled three-ply plywood on the heating plate of the hot press. The hot pressing temperature is 180 °C, the hot pressing pressure is 2 MPa, and the hot pressing time is 5 minutes.

[0086] Test the bonding strength of the final adhesive with different particle sizes of nanoparticles according to the standard of GB / T 9846-2015 "General Plywood". The bonding strengths in different application environments are shown in Table 1.

[0087] Table 1 Bonding strength table of bamboo / wood flour adhesive

[0088]

[0089] It can be seen from Examples 1-9 and Comparative Example 1 that the addition of a dispersant is very important for the bonding performance of the all-bio-based adhesive. Without the action of the dispersant, the crosslinking performance cannot be generated. Ethylene glycol is an excellent dispersant, which can effectively improve the bonding 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 in lignin structure, and formation of solvent-biomass complexes. It can be seen from Examples 10-13 and Comparative Example 2 that treating bamboo / wood powder with a colloid mill or a high-pressure homogenizer can achieve powder nano-microization, increase the specific surface area of the particles, expose more active sites, and effectively improve the crosslinking performance. It can be seen from Examples 14-17 and Comparative Example 3 that the addition of a modifier in step (3) is also necessary for improving the viscose performance. The addition of the modifier is beneficial to the formation of a crosslinked network of nano-cellulose lignin particles, thereby improving the bonding strength. Citric acid is an excellent modifier. Examples 18-19 can prove the formation of a crosslinked network, thereby improving the bonding strength. Citric acid is an excellent modifier. Examples 18-19 can prove that this patent is applicable to bamboo / wood powder from various sources and can provide excellent crosslinking performance. Examples 20-22 show that reducing the water content of the system can help improve the bonding performance of the generated adhesive. The plywood strength experiment proves that the adhesive produced by the all-bio-based adhesive preparation method provided by this patent has good adhesive performance and can achieve a bonding strength far greater than 0.7 Mpa of the national standard.

[0090] The descriptions and explanations of the above examples can enable those skilled in the art to understand and implement the present invention. However, the present invention will not be limited to these examples. The inventive principles disclosed herein can be implemented in other examples without departing from the spirit or scope of the present invention. Modifications to these examples should be obvious to those skilled in the art and will still be within the protection scope of this patent.

Claims

1. A method for preparing a fully bio-based adhesive, characterized in that: The following steps are involved: (1) Mix bamboo powder or wood powder, dispersant and water and let stand for 0.1-3h; (2) adding the raw material dispersion obtained in step (1) to a colloid mill or a high-pressure homogenizer for mechanical treatment to achieve micronization of bamboo powder or wood powder. The finished product after treatment is a smooth paste. The treatment time of the colloid mill is 0.1-2h; (3) mixing the smooth paste obtained in step (2), a modifier and a solvent, stirring and reacting at 30-180° C. for 5-60 min, and using the mixture as an adhesive; The dispersant in step (1) is one or more of 1,4-dioxane, 1,4-butylene oxide, dimethyl sulfoxide, pyridine, formamide, ethylene dichloride, 4-methylbutyrolactone, tetrahydrofuran, 2-methyltetrahydrofuran, methanol, ethanol, ethylene glycol, propylene glycol, glycerol, polyethylene glycol, polypropylene glycol, and polyglycerol; The amount of the dispersant added in step (1) is 0.1-1.5 times the mass of the bamboo powder / wood powder; The modifier in step (3) is one or more of formic acid, acetic acid, oxalic acid, citric acid, malic acid, lactic acid, tartaric acid, maleic acid, fumaric acid, phthalic acid, maleic anhydride, and bismaleic anhydride; The bamboo powder or wood powder is used as a support or filler structure after gluing, and the nanocellulose lignin particles of the bamboo powder or wood powder form a cross-linked network.

2. The method for preparing a fully bio-based adhesive according to claim 1, characterized in that: The amount of water added in step (1) is 0.5-5 times the mass of bamboo powder / wood powder.

3. The method for preparing a fully bio-based adhesive according to claim 1, characterized in that: The solvent described in step (3) is one or more of water, 1,4-dioxane, 4-methylbutyrolactone, 2-methyltetrahydrofuran, methanol, ethanol, propanol, butanol, acetone and butanone.

4. The method for preparing a fully bio-based adhesive according to claim 1, characterized in that: The amount of solvent added in step (3) is 0-3 times the mass of the paste obtained in step (2).

5. The method for preparing a fully bio-based adhesive according to claim 1, characterized in that: The amount of the modifier added in step (3) is 0.01-1 times the mass of the paste obtained in step (2).

6. The method for preparing a fully bio-based adhesive according to claim 1, characterized in that: Step (3) further includes a thickener, which includes one or more of carboxymethyl cellulose, starch, flour, and protein.

7. An adhesive prepared by the method according to any one of claims 1 to 6.

8. Use of the adhesive according to claim 7 in the production of log wood, artificial board or particle board, characterized in that: The adhesive is applied to the wood surface and cross-linked by heat pressing at 100-200 degrees Celsius to bond the wood.

Images