A bio-based adhesive and its preparation method and application

Abstract

The present invention provides a bio-based adhesive and a preparation method and application thereof. The bio-based adhesive of the present invention includes caffeic acid, glyoxal, water, sodium hydroxide, poly-4,4'-diphenylmethane diisocyanate thickener, defoamer, and preservative. The bio-based formaldehyde-free adhesive of the present invention uses caffeic acid and glyoxal as a matrix, adds glyoxal to the phenolic ring of caffeic acid to form cresol, and then forms a prepolymer by connecting the phenolic ring to grow the chain to form an adhesive. Sodium hydroxide is used as an alkaline catalyst to improve the adhesion strength through the poly-4,4'-diphenylmethane diisocyanate thickener. The adhesive of the present invention uses bio-based raw materials, can replace the role of petroleum-based in the production of phenolic resin, is a safe and environmentally friendly bio-based formaldehyde-free adhesive, and has a large development prospect.

Description

Technical Field

[0001] The present invention belongs to the technical field of adhesives, and in particular relates to a bio-based adhesive and a preparation method and application thereof. Background Art

[0002] The wood products industry widely uses aldehyde adhesives (phenolic, urea-formaldehyde, melamine resin adhesives) in the manufacturing process. Among them, phenolic resin adhesives are the most widely used due to their high bonding strength, good water resistance, and good heat resistance. As we all know, phenolic resin is synthesized from formaldehyde and phenol. Phenol and its vapor are harmful to human eyes, skin, respiratory tract, central nervous system and heart. Formaldehyde is listed as a genotoxic carcinogen by the World Health Organization. At the same time, people's growing concern for environmental protection, the continuous rise in phenol prices, and people's desire to reduce dependence on crude oil have prompted people to use more green and renewable alternatives to partially replace phenol and formaldehyde in production.

[0003] The prior art discloses a method for preparing a lignin-based biomass formaldehyde-free adhesive, which uses lignin and phenol to replace acetaldehyde and phenol to synthesize a bio-based formaldehyde-free adhesive, and the prepared lignin-based biomass formaldehyde-free adhesive has good mechanical properties. However, lignin has high steric hindrance, complex structure, and a small number of active groups, which limits its reactivity in adhesive production. It is often necessary to increase the content of active groups or introduce new active groups through active modification methods, and such a preparation process is relatively time-consuming and labor-intensive.

[0004] Based on the defects of current phenolic resin adhesives, it is necessary to improve them. Summary of the invention

[0005] In view of this, the present invention proposes a bio-based adhesive and a preparation method and application thereof to solve the technical problems existing in the prior art.

[0006] In a first aspect, the present invention provides a bio-based adhesive comprising the following raw materials in parts by weight: 0.1 to 20 parts of glyoxal, 0.5-2 parts of a catalyst, 40 to 50 parts of caffeic acid, 80 to 100 parts of water, 1 to 10 parts of a thickener, 0.2 to 0.5 parts of a preservative, and 0.2 to 0.5 parts of a defoaming agent.

[0007] Preferably, in the bio-based adhesive, the thickener is poly-4,4'-diphenylmethane diisocyanate.

[0008] Preferably, in the bio-based adhesive, the preservative is methyl benzimidazole-5-carboxylate.

[0009] Preferably, in the bio-based adhesive, the defoaming agent includes at least one of polydimethylsiloxane and diethyl ethanol.

[0010] Preferably, in the bio-based adhesive, the catalyst is sodium hydroxide.

[0011] In a second aspect, the present invention also provides a method for preparing the bio-based adhesive, comprising the following steps:

[0012] Caffeic acid is added to water, a catalyst is added to adjust the pH to 8-9, glyoxal is added, and the mixture is stirred at 60-100° C. to react, and a thickener, a preservative and a defoaming agent are finally added, and the mixture is stirred continuously to obtain a bio-based adhesive.

[0013] Preferably, the method for preparing the bio-based adhesive comprises adding caffeic acid to water, adding a catalyst to adjust the pH to 8-9, adding glyoxal, stirring and reacting at 60-100° C. for 0.5-2 hours, and finally adding a thickener, a preservative and a defoaming agent, and continuing to stir to obtain the bio-based adhesive.

[0014] Preferably, the method for preparing the bio-based adhesive comprises adding caffeic acid to water, adding a catalyst to adjust the pH to 8-9, adding glyoxal, stirring and reacting at 60-100° C., and finally adding a thickener, a preservative and a defoaming agent, and continuing stirring for 0.5-1h to obtain the bio-based adhesive.

[0015] In a third aspect, the present invention further provides an application of the bio-based adhesive or the bio-based adhesive prepared by the preparation method in wood processing and artificial boards.

[0016] The preparation method of a bio-based adhesive of the present invention has the following beneficial effects compared with the prior art:

[0017] The preparation method of the bio-based adhesive of the present invention replaces phenol and acetaldehyde petroleum-based adhesive with caffeic acid and ethylene glycol bio-based adhesive to prepare formaldehyde-free adhesive; cresol is formed by adding glyoxal to the phenol ring of caffeic acid, and then the phenol ring is connected to form a prepolymer to grow the chain to form an adhesive; by adding poly-4,4'-diphenylmethane diisocyanate thickener, the adhesion strength can be improved on the basis of the obtained bio-based adhesive, and the bio-based adhesive obtained by this preparation method is safe and environmentally friendly, has a wide source of raw materials, and has good development prospects; the traditional phenolic resin adhesive has a high content of free phenol and formaldehyde, which endangers human life safety, and the toxicity of the bio-based adhesive of the present invention is greatly reduced; the raw materials used in the present invention are bio-based, have a wide source, and are relatively more affordable, reducing dependence on phenol and formaldehyde petroleum-based adhesives, and responding to the national policy of reducing carbon emissions; the main solvent used in the preparation process of the bio-based phenolic resin is water, reducing organic reagents as solvents, and advocating the concept of green environmental protection. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0019] Figure 1 It is the bonding strength of the bio-based adhesive obtained in Examples 1 to 8 of the present invention and Comparative Example 1. DETAILED DESCRIPTION

[0020] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in combination with the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0021] It should be noted that the order of description of the following embodiments is not intended to limit the preferred order of the embodiments. In addition, in the description of the present application, the term "including" means "including but not limited to". Various embodiments of the present invention may be in the form of a range; it should be understood that the description in the form of a range is only for convenience and brevity, and should not be understood as a rigid limitation on the scope of the present invention; therefore, it should be considered that the range description has specifically disclosed all possible sub-ranges and single numerical values ​​within the range. For example, it should be considered that the range description from 1 to 6 has specifically disclosed sub-ranges, such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., as well as single numbers within the numbered range, such as 1, 2, 3, 4, 5 and 6, which applies regardless of the range. In addition, whenever a numerical range is indicated in this article, it is meant to include any cited numbers (fractions or integers) within the indicated range.

[0022] The invention provides a bio-based adhesive, comprising the following raw materials in parts by weight: 0.1 to 20 parts of glyoxal, 0.5 to 2 parts of a catalyst, 40 to 50 parts of caffeic acid, 80 to 100 parts of water, 1 to 10 parts of a thickener, 0.2 to 0.5 parts of a preservative, and 0.2 to 0.5 parts of a defoaming agent.

[0023] In some embodiments, the thickener is poly-4,4'-diphenylmethane diisocyanate, ie, a polymer of 4,4'-diphenylmethane diisocyanate, 4,4'-diphenylmethane diisocyanate is also known as diphenylmethane-4,4'-diisocyanate, diphenylmethane diisocyanate, MDI, and the like.

[0024] In some embodiments, the preservative is methyl benzimidazole-5-carboxylate (also known as methyl benzimidazole-5-carboxylate).

[0025] In some embodiments, the defoaming agent includes at least one of polydimethylsiloxane and diethyl ethanol.

[0026] In some embodiments, the catalyst is sodium hydroxide.

[0027] The bio-based adhesive of the present invention comprises glyoxal, a catalyst, caffeic acid, water, a thickener, a preservative and a defoaming agent; wherein caffeic acid is widely present in coffee beans, olives, citrus, apples, propolis and the like, and is a plant polyphenol with a wide source and low price. Its basic structural unit is similar to phenol, and can replace the role of phenol in the synthesis of phenolic resin; glyoxal shows a toxicity significantly lower than that of formaldehyde, and there are multiple ways to produce glyoxal from bio-based raw materials or intermediates (including sugar, ethanol and ethylene glycol); therefore, glyoxal, as a non-volatile, biodegradable and low-cost raw material, has been proven to be a suitable substitute for formaldehyde; therefore, the present invention completely replaces petroleum-based phenol and formaldehyde by caffeic acid and glyoxal (bio-based bisphenol), and develops a safe and environmentally friendly bio-based formaldehyde-free wood adhesive; at the same time, compared with the prior art of using lignin to synthesize bio-based formaldehyde-free adhesives, the caffeic acid used in the present invention has small steric hindrance and many active groups, and can effectively and quickly prepare safe and environmentally friendly bio-based formaldehyde-free adhesives.

[0028] The bio-based adhesive of the present invention uses caffeic acid and glyoxal as a matrix, adds glyoxal to the phenolic ring of caffeic acid to form cresol, and then forms a prepolymer by connecting the phenolic ring to grow the chain to form an adhesive. Sodium hydroxide is used as an alkaline catalyst, and the adhesion strength is improved by a poly-4,4'-diphenylmethane diisocyanate thickener. The adhesive of the present invention uses bio-based raw materials, can replace the role of petroleum-based in the production of phenolic resin, is a safe and environmentally friendly bio-based formaldehyde-free adhesive, and has great development prospects.

[0029] Based on the same inventive concept, the present invention also provides a method for preparing the above-mentioned bio-based adhesive, comprising the following steps:

[0030] Caffeic acid is added to water, a catalyst is added to adjust the pH to 8-9, glyoxal is added, and the mixture is stirred at 60-100° C. to react, and a thickener, a preservative and a defoaming agent are finally added, and the mixture is stirred continuously to obtain a bio-based adhesive.

[0031] In some embodiments, caffeic acid is added to water, a catalyst is added to adjust the pH to 8-9, glyoxal is added, and the mixture is stirred at 60-100° C. for 0.5-2 h. Finally, a thickener, a preservative and a defoaming agent are added, and stirring is continued to obtain a bio-based adhesive.

[0032] Specifically, in the above embodiment, since the catalyst is sodium hydroxide, the sodium hydroxide can play the role of both a catalyst and a pH regulator.

[0033] In some embodiments, caffeic acid is added to water, a catalyst is added to adjust the pH to 8-9, glyoxal is added, and the mixture is stirred at 60-100° C. to react, and finally a thickener, a preservative and a defoaming agent are added, and stirring is continued for 0.5-1 h to obtain a bio-based adhesive.

[0034] The preparation method of the bio-based adhesive of the present invention prepares a formaldehyde-free adhesive by replacing phenol and acetaldehyde petroleum-based with caffeic acid and ethylene glycol bio-based; cresol is formed by adding glyoxal to the phenol ring of caffeic acid, and then the phenol ring is connected to form a prepolymer to grow the chain to form the adhesive; and the adhesion strength can be improved on the basis of the obtained bio-based adhesive by adding a poly-4,4'-diphenylmethane diisocyanate thickener. The bio-based adhesive obtained by this preparation method is safe and environmentally friendly, has a wide source of raw materials, and has a good development prospect.

[0035] The preparation method of the bio-based adhesive of the present invention has the following advantages:

[0036] Traditional phenolic resin adhesives have high contents of free phenol and formaldehyde, which endanger human life safety. The bio-based adhesive of the present invention has greatly reduced toxicity; the raw materials used in the present invention are bio-based, which are widely available and relatively more affordable, reducing dependence on petroleum-based phenol and formaldehyde, and responding to the national policy of reducing carbon emissions; the main solvent used in the preparation process of bio-based phenolic resin is water, reducing organic reagents as solvents, and advocating the concept of green environmental protection.

[0037] Specifically, the preparation principle of the present invention is:

[0038] (1) Glyoxal is added to the phenolic ring of caffeic acid to form cresol:

[0039]

[0040] (2) Connecting phenol rings to form prepolymers to grow chains to form adhesives:

[0041]

[0042] Based on the same inventive concept, the present invention also provides an application of the above-mentioned bio-based adhesive or the bio-based adhesive prepared by the above-mentioned preparation method in wood processing and artificial boards.

[0043] The following further illustrates the preparation method of the bio-based adhesive of the present application with specific examples. This section further illustrates the content of the present invention in conjunction with specific examples, but should not be construed as limiting the present invention. Unless otherwise specified, the technical means used in the examples are conventional means known to those skilled in the art. Unless otherwise specified, the reagents, methods and equipment used in the present invention are conventional reagents, methods and equipment in the art.

[0044] Example 1

[0045] The embodiment of the present application provides a bio-based adhesive, including: 5 g of glyoxal, 1 g of a catalyst, 50 g of caffeic acid, 100 mL of water, 5 g of a thickener, 0.3 g of a preservative, and 0.3 g of a defoaming agent;

[0046] Wherein, the thickener is poly-4,4'-diphenylmethane diisocyanate;

[0047] The preservative is methyl benzimidazole-5-carboxylate;

[0048] The defoaming agent is polydimethylsiloxane;

[0049] The catalyst is sodium hydroxide.

[0050] The preparation method of the above-mentioned bio-based adhesive comprises the following steps:

[0051] At room temperature, take 50g of caffeic acid, add 100mL of deionized water, add 1g of sodium hydroxide catalyst (the solution is alkaline at this time), add 5g of glyoxal, and then stir at a water bath temperature of 80°C for 1h. Finally, add 5g of thickener, 0.3g of preservative and 0.3g of defoamer, and continue stirring for 0.5h to obtain a bio-based adhesive.

[0052] Example 2

[0053] The embodiment of the present application provides a bio-based adhesive, including: 10 g of glyoxal, 1 g of a catalyst, 50 g of caffeic acid, 100 mL of water, 5 g of a thickener, 0.3 g of a preservative, and 0.3 g of a defoaming agent;

[0054] Wherein, the thickener is poly-4,4'-diphenylmethane diisocyanate;

[0055] The preservative is methyl benzimidazole-5-carboxylate;

[0056] The defoaming agent is polydimethylsiloxane;

[0057] The catalyst is sodium hydroxide.

[0058] The preparation method of the above-mentioned bio-based adhesive comprises the following steps:

[0059] At room temperature, take 50g of caffeic acid, add 100mL of deionized water, add 1g of sodium hydroxide catalyst (the solution is alkaline at this time), then add 10g of glyoxal, and then stir at a water bath temperature of 80°C for 1h, finally add 5g of thickener, 0.3g of preservative and 0.3g of defoamer, and continue stirring for 0.5h to obtain a bio-based adhesive.

[0060] Example 3

[0061] The embodiment of the present application provides a bio-based adhesive, including: 15 g of glyoxal, 1 g of a catalyst, 50 g of caffeic acid, 100 mL of water, 5 g of a thickener, 0.3 g of a preservative, and 0.3 g of a defoaming agent;

[0062] Wherein, the thickener is poly-4,4'-diphenylmethane diisocyanate;

[0063] The preservative is methyl benzimidazole-5-carboxylate;

[0064] The defoaming agent is polydimethylsiloxane;

[0065] The catalyst is sodium hydroxide.

[0066] The preparation method of the above-mentioned bio-based adhesive comprises the following steps:

[0067] At room temperature, take 50g of caffeic acid, add 100mL of deionized water, add 1g of sodium hydroxide catalyst (the solution is alkaline at this time), then add 15g of glyoxal, and then stir at a water bath temperature of 80°C for 1h, finally add 5g of thickener, 0.3g of preservative and 0.3g of defoamer, and continue stirring for 0.5h to obtain a bio-based adhesive.

[0068] Example 4

[0069] The embodiment of the present application provides a bio-based adhesive, including: 20 g of glyoxal, 1 g of a catalyst, 50 g of caffeic acid, 100 mL of water, 5 g of a thickener, 0.3 g of a preservative, and 0.3 g of a defoaming agent;

[0070] Wherein, the thickener is poly-4,4'-diphenylmethane diisocyanate;

[0071] The preservative is methyl benzimidazole-5-carboxylate;

[0072] The defoaming agent is polydimethylsiloxane;

[0073] The catalyst is sodium hydroxide.

[0074] The preparation method of the above-mentioned bio-based adhesive comprises the following steps:

[0075] At room temperature, take 50g of caffeic acid, add 100mL of deionized water, add 1g of sodium hydroxide catalyst (the solution is alkaline at this time), add 20g of glyoxal, and then stir at a water bath temperature of 80°C for 1h. Finally, add 5g of thickener, 0.3g of preservative and 0.3g of defoamer, and continue stirring for 0.5h to obtain a bio-based adhesive.

[0076] Example 5

[0077] The embodiment of the present application provides a bio-based adhesive, including: 20 g of glyoxal, 1 g of a catalyst, 50 g of caffeic acid, 100 mL of water, 1 g of a thickener, 0.3 g of a preservative, and 0.3 g of a defoaming agent;

[0078] Wherein, the thickener is poly-4,4'-diphenylmethane diisocyanate;

[0079] The preservative is methyl benzimidazole-5-carboxylate;

[0080] The defoaming agent is polydimethylsiloxane;

[0081] The catalyst is sodium hydroxide.

[0082] The preparation method of the above-mentioned bio-based adhesive comprises the following steps:

[0083] At room temperature, take 50g of caffeic acid, add 100mL of deionized water, add 1g of sodium hydroxide catalyst (the solution is alkaline at this time), add 20g of glyoxal, and then stir at a water bath temperature of 80°C for 1h. Finally, add 1g of thickener, 0.3g of preservative and 0.3g of defoamer, and continue stirring for 0.5h to obtain a bio-based adhesive.

[0084] Example 6

[0085] The embodiment of the present application provides a bio-based adhesive, including: 20 g of glyoxal, 1 g of a catalyst, 50 g of caffeic acid, 100 mL of water, 3 g of a thickener, 0.3 g of a preservative, and 0.3 g of a defoaming agent;

[0086] Wherein, the thickener is poly-4,4'-diphenylmethane diisocyanate;

[0087] The preservative is methyl benzimidazole-5-carboxylate;

[0088] The defoaming agent is polydimethylsiloxane;

[0089] The catalyst is sodium hydroxide.

[0090] The preparation method of the above-mentioned bio-based adhesive comprises the following steps:

[0091] At room temperature, take 50g of caffeic acid, add 100mL of deionized water, add 1g of sodium hydroxide catalyst (the solution is alkaline at this time), add 20g of glyoxal, and then stir at a water bath temperature of 80°C for 1h. Finally, add 3g of thickener, 0.3g of preservative and 0.3g of defoamer, and continue stirring for 0.5h to obtain a bio-based adhesive.

[0092] Example 7

[0093] The embodiment of the present application provides a bio-based adhesive, including: 20 g of glyoxal, 1 g of a catalyst, 50 g of caffeic acid, 100 mL of water, 7 g of a thickener, 0.3 g of a preservative, and 0.3 g of a defoaming agent;

[0094] Wherein, the thickener is poly-4,4'-diphenylmethane diisocyanate;

[0095] The preservative is methyl benzimidazole-5-carboxylate;

[0096] The defoaming agent is polydimethylsiloxane;

[0097] The catalyst is sodium hydroxide.

[0098] The preparation method of the above-mentioned bio-based adhesive comprises the following steps:

[0099] At room temperature, take 50g of caffeic acid, add 100mL of deionized water, add 1g of sodium hydroxide catalyst (the solution is alkaline at this time), add 20g of glyoxal, and then stir at a water bath temperature of 80°C for 1h. Finally, add 7g of thickener, 0.3g of preservative and 0.3g of defoamer, and continue stirring for 0.5h to obtain a bio-based adhesive.

[0100] Example 8

[0101] The embodiment of the present application provides a bio-based adhesive, including: 20 g of glyoxal, 1 g of a catalyst, 50 g of caffeic acid, 100 mL of water, 10 g of a thickener, 0.3 g of a preservative, and 0.3 g of a defoaming agent;

[0102] Wherein, the thickener is poly-4,4'-diphenylmethane diisocyanate;

[0103] The preservative is methyl benzimidazole-5-carboxylate;

[0104] The defoaming agent is polydimethylsiloxane;

[0105] The catalyst is sodium hydroxide.

[0106] The preparation method of the above-mentioned bio-based adhesive comprises the following steps:

[0107] At room temperature, take 50g of caffeic acid, add 100mL of deionized water, add 1g of sodium hydroxide catalyst (the solution is alkaline at this time), add 20g of glyoxal, and then stir at a water bath temperature of 80°C for 1h. Finally, add 10g of thickener, 0.3g of preservative and 0.3g of defoamer, and continue stirring for 0.5h to obtain a bio-based adhesive.

[0108] Comparative Example 1

[0109] The embodiment of the present application provides a bio-based adhesive, including: 20 g of glyoxal, 50 g of caffeic acid, 100 mL of water, 5 g of thickener, 0.3 g of preservative, and 0.3 g of defoaming agent;

[0110] Wherein, the thickener is poly-4,4'-diphenylmethane diisocyanate;

[0111] The preservative is methyl benzimidazole-5-carboxylate;

[0112] The defoaming agent is polydimethylsiloxane.

[0113] The preparation method of the above-mentioned bio-based adhesive comprises the following steps:

[0114] At room temperature, take 50g of caffeic acid, add 100mL of deionized water, then add 20g of glyoxal, and then stir at 80°C in a water bath for 1h. Finally, add 5g of thickener, 0.3g of preservative and 0.3g of defoamer, and continue stirring for 0.5h to obtain a bio-based adhesive.

[0115] Mechanical properties test

[0116] The bio-based adhesives prepared in Examples 1 to 8 and Comparative Example 1 were poured into a polytetrafluoroethylene rectangular mold and dried at 80°C to form a film. A universal tester was used to perform a tensile test on the prepared adhesive at room temperature to detect the tensile strength and elongation at break of the samples. The sample size was 60×10 mm (length×width), the initial test distance between the two fixtures was 20 mm, and the sample was tested at a loading speed of 5 mm / min. The test results are shown in Table 1.

[0117] Table 1 - Mechanical properties of bio-based adhesives obtained from different examples

[0118]

[0119]

[0120] As can be seen from Table 1, in Examples 1 to 4, the addition of glyoxal is beneficial to enhancing the tensile strength and elongation at break of the bio-based adhesive; in Examples 5 to 8, the addition of thickener has less effect on the tensile strength and elongation at break than glyoxal. Compared with Comparative Example 1, the above Examples 1 to 8 have better tensile strength and elongation at break, which indicates that sodium hydroxide plays a role in adjusting the pH of the solution and as a catalyst, greatly affecting the addition reaction of aldehydes and phenol rings and the formation of hydroxymethylphenol.

[0121] Tensile shear strength test

[0122] Take 1mL of the bio-based adhesive prepared in Examples 1 to 8 and Comparative Example 1 and evenly apply it on 304 stainless steel, plastic, and wood, respectively, control the thickness of the adhesive layer to be 0.2mm, take out the same substrate on the other side (i.e., 304 stainless steel, plastic, and wood) and fix it with it, and the overlap size is 25mm×25mm to obtain a bonding sample. The bonding sample is placed in an oven at 80 degrees Celsius for drying. After drying, cool at room temperature, use a tensile machine to perform a shear strength test, and the tensile rate is 5mm / min to obtain the shear strength. The results are shown in Table 2.

[0123] Table 2- Shear strength of bio-based adhesives obtained from different examples

[0124]

[0125]

[0126] As can be seen from Table 2, all bio-based adhesives have greater shear strength on wood, and the bio-based adhesives in Examples 1-8 have better shear strength than the bio-based adhesive in Example 1.

[0127] Bonding strength performance test

[0128] According to the provisions of Class II plywood in the Chinese national standard "Ordinary Plywood" (GB / T9846-2015), the plywood prepared with the bio-based adhesive obtained in Examples 1 to 8 and Comparative Example 1 was tested for bonding strength. Nine test specimens (average value) were sawn from each three-layer plywood, with a size of 100×25mm and a bonding area of ​​25×25mm. 2 , the test results are as follows Figure 1 As shown, Figure 1 The unit of bonding strength is Kpa.

[0129] from Figure 1It can be seen that as the amount of glyoxal in Examples 1-4 increases, more bio-based adhesives are generated, and their bonding strength increases accordingly. The increase in the amount of thickener in Examples 5-8 is beneficial to the adhesion performance of the bio-based phenolic resin, so their bonding strengths are proportional. The bonding strengths of Examples 1-8 are all stronger than those of Comparative Example 1, which is attributed to the fact that no sodium hydroxide is added as a catalyst and to adjust the pH in Comparative Example 1, so the content of the bio-based phenolic resin obtained is small, and its bonding strength is low.

[0130] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing a bio-based adhesive, characterized in that: The bio-based adhesive comprises the following raw materials in parts by weight: 0.1 to 20 parts of glyoxal, 0.5 to 2 parts of a catalyst, 40 to 50 parts of caffeic acid, 80 to 100 parts of water, 1 to 10 parts of a thickener, 0.2 to 0.5 parts of a preservative, and 0.2 to 0.5 parts of a defoaming agent; The thickener is poly-4,4'-diphenylmethane diisocyanate; The preservative is methyl benzimidazole-5-carboxylate; The defoaming agent includes at least one of polydimethylsiloxane and diethyl ethanol; The catalyst is sodium hydroxide; The method for preparing the bio-based adhesive comprises the following steps: Caffeic acid is added to water, a catalyst is added to adjust the pH to 8-9, glyoxal is added, and the mixture is stirred at 60-100° C. to react, and a thickener, a preservative and a defoaming agent are finally added, and the mixture is stirred continuously to obtain a bio-based adhesive.

2. The method for preparing a bio-based adhesive according to claim 1, characterized in that: Caffeic acid is added to water, and then a catalyst is added to adjust the pH to 8-9, and then glyoxal is added, and the reaction is stirred at 60-100°C for 0.5-2h, and finally a thickener, a preservative and a defoaming agent are added, and stirring is continued to obtain a bio-based adhesive.

3. The method for preparing a bio-based adhesive according to claim 1, characterized in that: Caffeic acid is added to water, and then a catalyst is added to adjust the pH to 8-9, and then glyoxal is added, and the mixture is stirred and reacted at 60-100°C. Finally, a thickener, a preservative and a defoaming agent are added, and stirring is continued for 0.5-1h to obtain a bio-based adhesive.

4. Use of a bio-based adhesive prepared by the preparation method according to any one of claims 1 to 3 in wood processing and artificial boards.

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