Urea-formaldehyde resin adhesive based on biologically modified bamboo powder and preparation method thereof

Abstract

The application belongs to the technical field of adhesives, and particularly relates to a urea-formaldehyde resin adhesive based on biologically modified bamboo powder and a preparation method thereof, the preparation method comprising the following steps: S1. splitting a male sweet dragon bamboo into bamboo pieces, removing the nodes, and then placing the bamboo pieces in a container, adding an emulsifier to immerse the bamboo pieces, stirring, drying, crushing with a crusher, and sieving to obtain male sweet dragon bamboo powder; S2. mixing the male sweet dragon bamboo powder obtained in step S1 with water, ultrasonic dispersion to obtain a bamboo powder solution, adding a biological enzyme, constant-temperature enzymolysis to obtain a modified bamboo powder solution; and S3. adding formaldehyde, urea, a crosslinking aid, and a toughening agent to the modified bamboo powder solution obtained in step S2 to react to obtain a urea-formaldehyde resin adhesive. The application improves the crosslinking reaction capacity of the bamboo powder and the urea-formaldehyde resin molecules by enzymolysis of the biomass macromolecules in the bamboo powder, enhances the performance of the urea-formaldehyde resin adhesive, reduces the content of free formaldehyde, and thus prepares an environmentally friendly urea-formaldehyde resin adhesive with excellent performance.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of adhesives, and particularly relates to a urea-formaldehyde resin adhesive based on biologically modified bamboo powder and a preparation method thereof. BACKGROUND

[0002] In today's society, with the acceleration of industrialization and the continuous improvement of people's environmental awareness, higher requirements are put forward for the performance and environmental protection of adhesives. As a traditional synthetic resin adhesive, urea-formaldehyde resin adhesive has a wide application in the fields of wood processing, building, furniture manufacturing, etc. due to its low price and other reasons, and occupies an important position in many industries.

[0003] However, traditional urea-formaldehyde resin adhesives have some problems to be solved. On the one hand, urea-formaldehyde resin adhesives release a large amount of free formaldehyde during production, use and later use. Formaldehyde is a harmful gas that is extremely harmful to human health. Long-term exposure may cause respiratory diseases, allergic reactions, and even cancer, which limits the use of urea-formaldehyde resin adhesives in fields such as indoor decoration and furniture manufacturing that have high requirements for environmental performance. On the other hand, urea-formaldehyde resin adhesives have poor water resistance. In humid environments or water immersion conditions, the bonding strength will decrease significantly, which limits their application in some scenarios that require long-term water resistance, such as outdoor building materials bonding and wood bonding in shipbuilding.

[0004] In order to solve the above problems, common modification methods include adding formaldehyde capture agents, changing synthesis process conditions, and introducing nanomaterials. However, these methods have certain limitations. Under this research background, biologically modified technology has gradually attracted attention. Enzymes have the advantages of high efficiency, specificity and environmental friendliness, and can catalyze chemical reactions under mild conditions. In recent years, enzymes have attracted attention in the field of material modification. The application of enzymes to the modification of urea-formaldehyde resin adhesives is expected to improve their overall performance.

[0005] Chinese patent CN 19119928 A discloses a soy protein modified high-performance environmentally friendly urea-formaldehyde resin adhesive and a preparation method thereof. The adhesive comprises a modified soy protein solution, a polyformaldehyde component and a urea component, wherein the modified soy protein solution is obtained by enzymatic hydrolysis and ultrasonic treatment. The adhesive of this invention reduces the content of free formaldehyde, but lacks the addition of reasonable additives, which is not conducive to improving the overall performance of the adhesive.

[0006] Therefore, there is an urgent need for a urea-formaldehyde resin adhesive based on biologically modified bamboo powder, which not only reduces the content of free formaldehyde in the adhesive, but also improves the overall performance of the adhesive. SUMMARY

[0007] In view of the existing technical problems, the present application aims to provide a urea-formaldehyde resin adhesive based on biological enzyme modification and a preparation method thereof.The present application improves the cross-linking reaction ability of bamboo powder and urea-formaldehyde resin molecules by enzymatically degrading the biomass macromolecules in the bamboo powder, enhances the bonding performance of the urea-formaldehyde resin adhesive, and reduces the content of free formaldehyde, thereby preparing an environmentally friendly urea-formaldehyde resin adhesive with excellent performance.

[0008] In order to achieve the above-mentioned purpose, the technical scheme adopted by the present application is as follows:

[0009] The present application provides a preparation method of a urea-formaldehyde resin adhesive based on biological enzyme modification, comprising the following steps:

[0010] S1. Split the Dendrocalamus latiflorus into bamboo pieces and remove the nodes, then place them in a container, immerse the bamboo pieces in an emulsifier, stir, take out and dry, crush with a pulverizer and sieve to obtain Dendrocalamus latiflorus powder;

[0011] S2. Mix the Dendrocalamus latiflorus powder obtained in step S1 with water, ultrasonically disperse to obtain a bamboo powder solution, add biological enzymes, and perform constant-temperature enzymatic hydrolysis to obtain a modified bamboo powder solution;

[0012] S3. Add formaldehyde, urea, a cross-linking aid and a toughening agent to the modified bamboo powder solution obtained in step S2 to react, and obtain a urea-formaldehyde resin adhesive.

[0013] The reaction mechanism and action of the present application are as follows:

[0014] 1. In the preparation of the urea-formaldehyde resin adhesive, the present application adds the cross-linking aid 2-imidazolidone twice. The cross-linking structure of the urea-formaldehyde resin itself is relatively limited. After adding 2-imidazolidone, it can chemically react with the active groups in the resin. Not only can it undergo Mannich reaction with the carbonyl group in formaldehyde and the amino group to generate stable Mannich base without side effects, thereby removing the content of free formaldehyde and making the urea-formaldehyde resin adhesive meet the requirements of low-aldehyde environmentally friendly products, but also can control the cross-linking degree of the urea-formaldehyde resin, improve the curing rate, and improve the water resistance of the urea-formaldehyde resin adhesive.

[0015] 2. The present application mainly considers using a modified bamboo powder solution to replace part of the synthetic raw materials urea and formaldehyde of the urea-formaldehyde resin. Bamboo powder is a cheap and abundant biomass material. The applicant selects a specific Dendrocalamus latiflorus to make bamboo powder, and further modifies it with a specific biological enzyme to obtain a modified bamboo powder solution.

[0016] In one aspect, the biological enzyme (protease, laccase, cellulase) can depolymerize the protein macromolecules, cellulose macromolecules and lignin in the Dendrocalamus latiflorus powder, which not only reduces the molecular weight of the biomass macromolecules, but also exposes more active groups such as amino, hydroxyl and other active groups in the main chain and side chain, thereby generating more reactive active points, so as to realize copolymerization with formaldehyde and reaction intermediates such as hydroxymethyl and aminomethylene groups in the urea-formaldehyde resin synthesis process, and significantly improve the performance of the adhesive.

[0017] On the other hand, after the bamboo powder is treated by the biological enzyme, the chemical structure and physical form on the surface of the bamboo powder are changed, the compatibility with the urea-formaldehyde resin is better, and the bamboo powder can be uniformly dispersed in the urea-formaldehyde resin system, thereby avoiding the performance decline caused by phase separation.

[0018] In some embodiments, the emulsifier in step S1 is a combination of water, Tween 80 and sodium dodecyl sulfate.

[0019] Preferably, the mass ratio of the water, Tween 80 and sodium dodecyl sulfate is 100:1:(1-2).

[0020] In some embodiments, the temperature of the enzymolysis in step S2 is 40-50℃, the pH value of the enzymolysis is 4.5-5.5, and the time of the enzymolysis is 4-6h.

[0021] In some embodiments, the biological enzyme in step S2 is a combination of cellulase, laccase and protease.

[0022] In some embodiments, the mass ratio of the cellulase, laccase and protease is (3-4):(1.2-1.8):1.

[0023] Further preferably, the laccase is white rot fungus laccase and / or Aspergillus laccase; and the protease is papain.

[0024] In some embodiments, the mass concentration of the bamboo powder solution in step S2 is 5-10%, and the addition amount of the biological enzyme is 0.2-0.5% of the mass of the bamboo powder solution.

[0025] In some embodiments, the molar ratio of the formaldehyde and urea in step S3 is 1:(0.9-1.1).

[0026] In some embodiments, the crosslinking aid in step S3 is 2-imidazolidone.

[0027] Preferably, the amount of the crosslinking aid is 1.8-2.2% of the total mass of the formaldehyde and urea.

[0028] Further preferably, the amount of the crosslinking aid is 2% of the total mass of the formaldehyde and urea.

[0029] In some embodiments, the toughening agent in step S3 is polyvinyl alcohol.

[0030] Preferably, the amount of polyvinyl alcohol is 0.9-1.1% of the mass of urea.

[0031] Further preferably, the amount of polyvinyl alcohol is 1% of the mass of urea.

[0032] In some embodiments, the specific steps of step S3 are as follows:

[0033] S31. Add formaldehyde to the bamboo powder modified solution obtained in step S2, adjust the pH value to 8.0-8.5 by adding an aqueous NaOH solution, add the first portion of urea, and increase the temperature to 75-80℃ for addition reaction to obtain a first reaction liquid;

[0034] S32. Adjust the pH value of the first reaction liquid to 3.5-5.5 by adding an aqueous formic acid solution, increase the temperature to 85-90℃ for polycondensation reaction, then add the second portion of urea, the first portion of crosslinking aid, and the toughening agent for reaction to obtain a second reaction liquid;

[0035] S33. Adjust the temperature of the second reaction liquid to 75-80℃, adjust the pH value to 7.0-8.0 by adding an aqueous NaOH solution, add the third portion of urea, and add the second portion of crosslinking aid for reaction, and then cool to 30-40℃ for glue discharge to obtain the urea-formaldehyde resin adhesive.

[0036] In some embodiments, the mass ratio of the first portion of urea, the second portion of urea, and the third portion of urea is (3.5-4.5) : 1 : (1.5-2).

[0037] Another aspect of the present application provides a urea-formaldehyde resin adhesive obtained by the preparation method.

[0038] Compared with the prior art, the present application has the following advantages:

[0039] 1. The present application improves the crosslinking reaction ability of bamboo powder and urea-formaldehyde resin molecules by enzymatically decomposing biomass macromolecules in the bamboo powder, enhances the bonding performance of the urea-formaldehyde resin adhesive, and reduces the content of free formaldehyde, thereby preparing an environmentally friendly urea-formaldehyde resin adhesive with excellent performance.

[0040] 2. The present application adds the crosslinking aid 2-imidazolidone twice in the preparation of the urea-formaldehyde resin adhesive, which can not only react with the active groups of the resin to remove free formaldehyde and make the adhesive environmentally friendly, but also control the crosslinking degree, improve the curing rate, and enhance the water resistance.

[0041] 3. The bamboo powder modified solution added in the present application replaces part of the synthetic raw materials urea and formaldehyde. After the male sweet dragon bamboo powder is modified by specific biological enzymes, the biomass macromolecules are depolymerized, and the exposed active groups will react with urea-formaldehyde resin, thereby improving the performance of the adhesive. DETAILED DESCRIPTION

[0042] The present application will be described below in conjunction with specific embodiments. It should be noted that the following examples are examples of the present application and are only used to illustrate the present application, but not to limit the present application. Other combinations and various modifications within the concept of the present application can be made without departing from the spirit or scope of the present application.

[0043] According to the ratio and preparation method of each raw material specified in the following examples, each urea-formaldehyde resin adhesive is prepared.

[0044] In order to facilitate the implementation of the present application by those skilled in the art, the manufacturers of some raw materials of the examples and comparative examples are described as follows:

[0045] Polyvinyl alcohol: purchased from Nantong Changchen Chemical Co., Ltd., product number HH8120EXXSVK;

[0046] Cellulase and papain: purchased from Hebei Jiuyu Biological Technology Co., Ltd., with an activity of 100000 U / g;

[0047] White rot fungus laccase: purchased from Qingdao Longchuan Biological Technology Co., Ltd., with an activity of 12000 U / g;

[0048] Formaldehyde: 37% formaldehyde solution; urea: purity 98%;

[0049] Other raw materials are not specially mentioned and can be purchased from the market.

[0050] Example 1

[0051] A preparation method of a urea-formaldehyde resin adhesive based on biological enzyme modification, comprising the following preparation steps:

[0052] S1. Mix distilled water, Tween 80 and sodium dodecyl sulfate in a mass ratio of 100:1:1.5, stir uniformly to obtain an emulsifier; split the male sweet dragon bamboo into bamboo pieces and remove the nodes, then place them in a container, immerse the bamboo pieces in the emulsifier for 12 h, stir every 2 h, take out and dry at 80℃ to constant weight, then crush with a crusher to pass through a 200 mesh sieve to obtain male sweet dragon bamboo powder;

[0053] S2. Mixing 250 g of the male sweet bamboo powder obtained in step S1 with 3250 mL of water, and ultrasonic dispersing for 5 min to obtain a bamboo powder solution, adding 12.25 g of a biological enzyme, and constant-temperature enzymolysis, wherein the enzymolysis temperature is 45℃, the enzymolysis pH value is 5, and the enzymolysis time is 5 h, and the bamboo powder solution is constantly stirred during the enzymolysis to obtain a modified bamboo powder solution; wherein the biological enzyme is a composition of cellulase, white rot fungus laccase and papain with a mass ratio of 3.5:1.5:1;

[0054] S3. Adding 300 g of formaldehyde, 226 g of urea, 17.8 g of 2-imidazolidone and 5.9 g of polyvinyl alcohol to the 2000 mL of the modified bamboo powder solution obtained in step S2 to react to obtain a urea-formaldehyde resin adhesive;

[0055] The specific steps of step S3 are as follows:

[0056] S31. Adding 300 g of formaldehyde to the 2000 mL of the modified bamboo powder solution obtained in step S2, adding 100 g / L of NaOH aqueous solution to adjust the pH value to 8.5, adding the first portion of urea, and increasing the temperature to 80℃ for 1 h of addition reaction to obtain a first reaction liquid;

[0057] S32. Adding formic acid aqueous solution (10%) to the first reaction liquid to adjust the pH value to 4.5, increasing the temperature to 90℃ for 1.5 h of polycondensation reaction, then adding the second portion of urea, 11.8 g of 2-imidazolidone, and 5.9 g of polyvinyl alcohol for 0.5 h of reaction to obtain a second reaction liquid;

[0058] S33. Adjusting the temperature of the second reaction liquid to 80℃, and adding 100 g / L of NaOH aqueous solution to adjust the pH value to 8.0, adding the third portion of urea, and adding 6 g of 2-imidazolidone for 1 h of reaction, and then cooling to 35℃ to release the glue, to obtain the urea-formaldehyde resin adhesive; wherein the mass ratio of the first portion of urea, the second portion of urea and the third portion of urea is 4:1:1.75.

[0059] Example 2

[0060] A preparation method of a urea-formaldehyde resin adhesive based on biological enzyme modification, comprising the following preparation steps:

[0061] S1. Mixing distilled water, Tween 80 and sodium dodecyl sulfate according to a mass ratio of 100:1:1 to obtain an emulsifier; splitting male sweet bamboo into bamboo pieces, removing the nodes, and placing the bamboo pieces in a container; immersing the bamboo pieces in the emulsifier for 12 h, stirring every 2 h, taking out, drying at 80℃ until the weight is constant, crushing with a crusher to pass through a 200 mesh sieve to obtain male sweet bamboo powder;

[0062] S2. Mixing 250 g of the male sweet bamboo powder obtained in step S1 with 4750 mL of water, and ultrasonic dispersing for 5 min to obtain a bamboo powder solution, adding 10 g of a biological enzyme, and constant-temperature enzymolysis, wherein the enzymolysis temperature is 40℃, the enzymolysis pH value is 4.5, and the enzymolysis time is 6 h, and the bamboo powder solution is constantly stirred during the enzymolysis to obtain a modified bamboo powder solution; wherein the biological enzyme is a composition of cellulase, white rot fungus laccase and papain with a mass ratio of 3:1.2:1;

[0063] S3. Adding 300 g of formaldehyde, 204 g of urea, 16.8 g of 2-imidazolidone and 5.4 g of polyvinyl alcohol to the 1850 mL of the modified bamboo powder solution obtained in step S2 to react to obtain a urea-formaldehyde resin adhesive;

[0064] The specific steps of step S3 are as follows:

[0065] S31. Adding 300 g of formaldehyde to the 1850 mL of the modified bamboo powder solution obtained in step S2, adding 100 g / L of NaOH aqueous solution to adjust the pH value to 8.0, adding the first portion of urea, and increasing the temperature to 75℃ for 1 h of addition reaction to obtain a first reaction liquid;

[0066] S32. Adding formic acid aqueous solution (10%) to the first reaction liquid to adjust the pH value to 5.5, increasing the temperature to 85℃ for 1.5 h of polycondensation reaction, then adding the second portion of urea, 11.2 g of 2-imidazolidone, and 5.4 g of polyvinyl alcohol for 0.5 h of reaction to obtain a second reaction liquid;

[0067] S33. Adjusting the temperature of the second reaction liquid to 75℃, adding 100 g / L of NaOH aqueous solution to adjust the pH value to 7.0, adding the third portion of urea, and adding 5.6 g of 2-imidazolidone for 1 h of reaction, and then cooling to 30℃ to release the glue, thereby obtaining the urea-formaldehyde resin adhesive; wherein the mass ratio of the first portion of urea, the second portion of urea and the third portion of urea is 4.5:1:1.5.

[0068] Example 3

[0069] A preparation method of a urea-formaldehyde resin adhesive based on biological enzyme modification, comprising the following preparation steps:

[0070] S1. Mixing distilled water, Tween 80 and sodium dodecyl sulfate according to a mass ratio of 100:1:2 to obtain an emulsifier; splitting male sweet bamboo into bamboo pieces, removing the nodes, and placing the bamboo pieces in a container; adding the emulsifier to immerse the bamboo pieces for 12 h, stirring every 2 h, taking out, drying at 80℃ until the weight is constant, crushing with a crusher to pass through a 200 mesh sieve to obtain male sweet bamboo powder;

[0071] S2. Mix 250 g of the male sweet bamboo powder obtained in step S1 and 2250 mL of water, and ultrasonically disperse for 5 min to obtain a bamboo powder solution, then add 12.5 g of a biological enzyme, and perform constant-temperature enzymolysis at a temperature of 50℃, a pH value of 5.5, and for a time of 4 h, with constant stirring during the enzymolysis, to obtain a modified bamboo powder solution; wherein the biological enzyme is a combination of cellulase, white rot fungus laccase, and papain at a mass ratio of 4:1.8:1.

[0072] S3. Add 300 g of formaldehyde, 249 g of urea, 19.2 g of 2-imidazolidone, and 6.6 g of polyvinyl alcohol to the 2250 mL of the modified bamboo powder solution obtained in step S2 to perform a reaction, to obtain a urea-formaldehyde resin adhesive.

[0073] The specific steps of step S3 are as follows:

[0074] S31. Add 300 g of formaldehyde to the 2250 mL of the modified bamboo powder solution obtained in step S2, add 100 g / L of an NaOH aqueous solution to adjust the pH value to 8.5, add a first portion of urea, heat to 80℃, and perform an addition reaction for 1 h to obtain a first reaction liquid.

[0075] S32. Add a formic acid aqueous solution (10%) to the first reaction liquid to adjust the pH value to 4.5, heat to 90℃, and perform a condensation reaction for 1.5 h, then add a second portion of urea, 12.8 g of 2-imidazolidone, and 6.6 g of polyvinyl alcohol to perform a reaction for 0.5 h to obtain a second reaction liquid.

[0076] S33. Adjust the temperature of the second reaction liquid to 80℃, add 100 g / L of an NaOH aqueous solution to adjust the pH value to 8.0, add a third portion of urea, and add 6.4 g of 2-imidazolidone to perform a reaction for 1 h, and then cool to 35℃ to release the glue, to obtain the urea-formaldehyde resin adhesive; wherein the mass ratio of the first portion of urea, the second portion of urea, and the third portion of urea is 3.5:1:2.

[0077] Example 4

[0078] A preparation method of a urea-formaldehyde resin adhesive based on biological enzyme modification, and the specific implementation manner is the same as that of example 1, except that the mass ratio of cellulase, white rot fungus laccase, and papain in the biological enzyme in step S2 is 2:1.5:1.

[0079] Example 5

[0080] A preparation method of a urea-formaldehyde resin adhesive based on biological enzyme modification, and the specific implementation manner is the same as that of example 1, except that the biological enzyme in step S2 is a combination of cellulase and white rot fungus laccase, and the mass ratio of the two is 3.5:1.5.

[0081] Example 6

[0082] A preparation method of urea-formaldehyde resin adhesive based on biological enzyme modification, the specific implementation is the same as example 1, the difference is that the biological enzyme in step S2 is a combination of cellulase and papain, and the mass ratio of the two is 3.5:1.

[0083] Example 7

[0084] A preparation method of urea-formaldehyde resin adhesive based on biological enzyme modification, the specific implementation is the same as example 1, the difference is that the biological enzyme in step S2 is a combination of cellulase and papain, and the mass ratio of the two is 3.5:1.

[0085] Example 8

[0086] A preparation method of urea-formaldehyde resin adhesive based on biological enzyme modification, the specific implementation is the same as example 1, the difference is that the biological enzyme in step S2 is a combination of cellulase and papain, and the mass ratio of the two is 3.5:1.

[0087] Example 9

[0088] A preparation method of urea-formaldehyde resin adhesive based on biological enzyme modification, the specific implementation is the same as example 1, the difference is that the mass ratio of the first portion of urea, the second portion of urea and the third portion of urea is 3:1:1.5.

[0089] Effect evaluation:

[0090] The urea-formaldehyde resin adhesives prepared in the above examples 1-9 were tested and analyzed, and the specific results are shown in Tables 1-2.

[0091] Performance test:

[0092] (1) According to the standard GB / T 14732-2017, the performance tests of solid content, viscosity and free formaldehyde content were carried out.

[0093] Table 1

[0094] No. Solids content / % Viscosity / mPa-s Free formaldehyde content / % Example 1 54.5 145 0.015 Example 2 55.0 150 0.016 Example 3 54.0 148 0.018 Example 4 54.5 148 0.020 Example 5 54.0 146 0.026 Example 6 54.5 149 0.028 Example 7 54.0 146 0.035 Example 8 54.0 147 0.056 Example 9 54.5 150 0.035

[0095] From the results in Table 1, it can be seen that the urea-formaldehyde resin adhesives prepared in examples 1-3 have low free formaldehyde content, which improves the environmental friendliness of the adhesives.

[0096] Compared with example 1, example 4 changes the mass ratio of cellulase, laccase and protease in the biological enzyme, examples 5-6 change the composition of the biological enzyme, and example 7 changes the mass ratio of the added biological enzyme to the bamboo powder solution. The change of the type, ratio and proportion of the biological enzyme in the system will affect the crosslinking density of the urea-formaldehyde resin, resulting in an increase in formaldehyde release.

[0097] Example 8 changes the type of crosslinking coagent compared to Example 1. Although melamine can also react with formaldehyde to reduce the free formaldehyde content, its reaction efficiency is relatively low compared to 2-imidazolidone, and it is prone to insufficient reaction, resulting in a relatively high formaldehyde release.

[0098] Example 9 changes the mass ratio of the first portion of urea, the second portion of urea, and the third portion of urea compared to Example 1. Formaldehyde may not be consumed in time and sufficiently in the reaction, increasing the amount of free formaldehyde in the system.

[0099] (2) The fiberboards obtained by pressing the adhesive of Examples 1-3 and the urea-formaldehyde resin adhesive prepared by the conventional method in the same way were compared with the urea-formaldehyde resin adhesive prepared by the conventional method as the control group. The thickness of the fiberboard was 12 mm, and the density was 780 kg / m 3 The performance tests of formaldehyde release, internal bond strength, and 24h water absorption thickness expansion rate of the fiberboard were carried out according to the method specified in the standard GB / T17657 2022, wherein:

[0100] The steps for preparing the urea-formaldehyde resin adhesive by the conventional method are as follows:

[0101] S1. Adjust the pH value of 300g formaldehyde to 8.5 by adding 100g / L NaOH aqueous solution, add the first portion of urea, heat to 80℃, and add 1h to obtain the first reaction liquid;

[0102] S2. Adjust the pH value of the first reaction liquid to 4.5 by adding formic acid aqueous solution (10%), heat to 90℃, and condense for 1.5h, then add the second portion of urea, 11.8g 2-imidazolidone, and 5.9g polyvinyl alcohol, and react for 0.5h to obtain the second reaction liquid;

[0103] S3. Adjust the temperature of the second reaction liquid to 80℃, adjust the pH value to 8.0 by adding 100g / L NaOH aqueous solution, add the third portion of urea, and add 6g 2-imidazolidone and react for 1h, then cool to 35℃ and glue, to obtain the urea-formaldehyde resin adhesive; wherein the total amount of urea is 590g, and the mass ratio of the first portion of urea, the second portion of urea, and the third portion of urea is 4:1:1.75.

[0104] Table 2

[0105] No. Formaldehyde release mg / 100g Internal bond strength MPa 24h water absorption thickness expansion rate % Example 1 2.7 1.30 6.8 Example 2 2.9 1.25 6.5 Example 3 3.0 1.35 6.4 Control group 4.5 0.95 8.2

[0106] As can be seen from the results in Table 2, the adhesive performance and waterproof performance of the urea-formaldehyde resin adhesives prepared in Examples 1-3 are excellent, and the formaldehyde release is low.

[0107] The above merely describes preferred embodiments of the present application, and is not intended to limit the present application in any form. Although the present application is disclosed as above with preferred embodiments, it is not intended to limit the present application. Any person skilled in the art, without departing from the scope of the technical scheme of the present application, can make some changes or modifications to the disclosed technical content, which are equivalent to equivalent embodiments. Any simple modification, equivalent change and modification made to the above embodiments according to the technical essence of the present application, without departing from the technical scheme content of the present application, are still within the scope of the technical scheme.

Claims

1. A method for preparing a urea-formaldehyde resin adhesive based on bio-enzyme modified bamboo powder, characterized in that ,comprising the following steps: S1. Splitting the Dendrocalamopsis oldhami into bamboo pieces and removing the nodes, then placing them in a container, adding an emulsifier to immerse the bamboo pieces, stirring, taking them out and drying, crushing them with a crusher and sieving to obtain Dendrocalamopsis oldhami powder; S2. Mixing the Dendrocalamopsis oldhami powder obtained in step S1 with water, ultrasonic dispersion to obtain a bamboo powder solution, adding a biological enzyme, constant temperature enzymolysis to obtain a modified bamboo powder solution; S3. Adding formaldehyde, urea, a crosslinking aid and a toughening agent to the modified bamboo powder solution obtained in step S2 to react to obtain a urea-formaldehyde resin adhesive; The biological enzyme in step S2 is a combination of cellulase, laccase and protease; The specific steps of step S3 are as follows: S31. Adding formaldehyde to the modified bamboo powder solution obtained in step S2, adding NaOH aqueous solution to adjust the pH value to 8.0-8.5, adding the first portion of urea, heating to 75-80℃, and addition reaction to obtain a first reaction liquid; S32. Adding formic acid aqueous solution to the first reaction liquid to adjust the pH value to 3.5-5.5, heating to 85-90℃, and polycondensation reaction, then adding the second portion of urea, the first portion of crosslinking aid, and adding the toughening agent to react to obtain a second reaction liquid; S33. Adjusting the temperature of the second reaction liquid to 75-80℃, and adding NaOH aqueous solution to adjust the pH value to 7.0-8.0, adding the third portion of urea, and adding the second portion of crosslinking aid to react, cooling to 30-40℃, and then glue is discharged to obtain the urea-formaldehyde resin adhesive; The crosslinking aid in step S3 is 2-imidazolidone.

2. The preparation method of the urea-formaldehyde resin adhesive based on the bio-enzyme modified bamboo powder according to claim 1, characterized in that The temperature of the enzymolysis in step S2 is 40-50℃, the pH value of the enzymolysis is 4.5-5.5, and the time of the enzymolysis is 4-6h.

3. The method according to claim 1, characterized in that The mass ratio of the cellulase, laccase and protease is (3-4):(1.2-1.8):

1.

4. The preparation method of the urea-formaldehyde resin adhesive based on the bio-enzyme modified bamboo powder according to claim 1, characterized in that The mass concentration of the bamboo powder solution in step S2 is 5-10%, and the addition amount of the biological enzyme is 0.2-0.5% of the mass of the bamboo powder solution.

5. The method according to claim 1, characterized in that The molar ratio of the formaldehyde and urea in step S3 is 1:(0.9-1.1).

6. The method for preparing a urea-formaldehyde resin adhesive based on biologically modified bamboo powder according to claim 1, characterized in that The mass ratio of the first portion of urea, the second portion of urea and the third portion of urea is (3.5-4.5):1:(1.5-2).

7. A urea-formaldehyde resin adhesive prepared by the preparation method of any one of claims 1-6.