Urea-formaldehyde resin modifier and modified urea-formaldehyde resin wood adhesive

Abstract

The invention relates to a urea-formaldehyde resin modifier and a modified urea-formaldehyde resin wood adhesive. Modified rGO is polymerized with vinyl acetate, methyl methacrylate, sodium vinylsulfonate, acrylic acid and alanine; the preparation method comprises the following steps: taking methoxypolyethylene glycol, epoxy chloropropane and aminoethyl chitosan as monomers to react to obtain polyether grafted chitosan; dissolving the polyether grafted chitosan in water, then adding into a polymerization system, and discharging to obtain a urea-formaldehyde resin modifier; and mixing the urea-formaldehyde resin modifier and the urea-formaldehyde resin adhesive according to the weight ratio of (5-15): (95-85) to obtain the modified urea-formaldehyde resin wood adhesive. The urea-formaldehyde resin wood adhesive has the beneficial effects that after the urea-formaldehyde resin modifier is added, the formaldehyde emission of the old national standard E1-grade urea-formaldehyde resin wood adhesive is less than 0.1 mg / L and reaches the new national standard E1-grade standard; the water resistance is enhanced, and the requirements of class-II water-resistant plywood are met.

Description

Technical Field

[0001] The invention relates to the field of wood adhesives, in particular to a urea-formaldehyde resin modifier and a modified urea-formaldehyde resin wood adhesive. Background Art

[0002] Wood is an indispensable material in our living and office environments, used in wardrobes, cabinets, wood floors, desks, and more. Due to production costs, in addition to using logs, plywood, composite boards, particleboard, fiberboard, and other materials are increasingly used. All of these materials require adhesives. Currently, urea-formaldehyde and phenol-formaldehyde resins are still the main wood adhesives. Urea-formaldehyde resins offer significant advantages such as fast curing speed and low manufacturing cost, making them widely used. However, they suffer from issues such as susceptibility to hydrolysis and high formaldehyde emissions. Phenolic resins are second only to urea-formaldehyde resins in terms of usage and offer excellent water and weather resistance, but their cost is higher and their curing speed is lower. Research has shown that adding phenol to the urea-formaldehyde resin preparation process can effectively reduce free formaldehyde, but the large-scale use of phenol increases costs. Furthermore, while free formaldehyde is effectively reduced, the resulting free phenols still pose significant environmental risks.

[0003] Existing board adhesives usually use formaldehyde, which is harmful to the human body and the environment, as a raw material during production. The boards produced also contain residual formaldehyde, which will cause great harm to the health of manufacturers and users over time. Therefore, it is very necessary to modify urea-formaldehyde resin to reduce its formaldehyde emission. Chinese invention patent CN103540282B provides a urea-formaldehyde resin wood adhesive modifier, which can effectively reduce formaldehyde emission by 20% after being added to the adhesive and coated on the fiberboard. However, the modifier is directly mixed by multiple components. Although the performance of E2-grade urea-formaldehyde resin adhesive has been improved, the mixing effect is not as good as that of a single component. The durability of the hot-pressed board produced is not as good as that of the board produced by the original E2-grade adhesive, and the formaldehyde emission is still high, which does not meet the new national standard E1-grade standard. Summary of the Invention

[0004] In view of the deficiencies in the prior art, the present invention proposes a To achieve the above object, the present invention provides the following technical solutions: A urea-formaldehyde resin modifier is prepared by the following method: 1) rGO was first treated with KH570 and then amination was performed to obtain modified rGO, which was placed in a reactor. Vinyl acetate, methyl methacrylate, sodium vinyl sulfonate, acrylic acid, alanine, potassium persulfate, benzoyl peroxide, and ethyl acetate were added to the reactor. The mixture was stirred thoroughly and reacted. After the reaction was completed, the mixture was cooled to room temperature. 2) First, polyethylene glycol monomethyl ether and epichlorohydrin undergo a chlorine substitution reaction to obtain polyethylene glycol grafted with epoxy propane; in a reaction kettle, aminoethyl chitosan and polyethylene glycol grafted with epoxy propane are added, and the epoxy alkane undergoes ring-opening under alkaline conditions to obtain polyether grafted chitosan; 3) Dissolve the polyether grafted chitosan in water and then add it to the system in step 1). While stirring, heat up to 40 °C. After stirring and mixing evenly, cool down and discharge to obtain the product.

[0005] Furthermore, the specific modification process of the modified rGO in step 1) is as follows: S1. Add graphene oxide rGO to an ethanol aqueous solution, ultrasonically disperse it evenly, heat up to 40 °C, add KH570, stir overnight, and cool to room temperature; S2. Add ethylenediamine ten times the amount of graphene oxide rGO to the above reaction system, mix evenly, adjust the pH to 9 - 10 with ammonia water, then transfer it to a high-pressure reaction kettle and react at 180 - 200 °C for 8 - 12 h; S3. After cooling, centrifuge and separate, and dry to obtain.

[0006] Furthermore, the weight ratio of each component in step 1) is: modified rGO 1 - 5%, vinyl acetate 20 - 40%, methyl methacrylate 15 - 30%, sodium vinyl sulfonate 5 - 10%, acrylic acid 10 - 15%, alanine 2 - 6%, potassium persulfate 1 - 2%, benzoyl peroxide 1 - 2%, and the balance is ethyl acetate.

[0007] Furthermore, the reaction conditions in step 1) are: react at 70 - 80 °C for 2 - 4 h.

[0008] Furthermore, the specific preparation process of step 2) is as follows: S1. Add polyethylene glycol monomethyl ether and epichlorohydrin to a reaction kettle, heat up to 120 °C and react for 2 - 5 h to obtain polyethylene glycol grafted with epoxy propane; S2. Dissolve aminoethyl chitosan in water and transfer it to a reaction kettle. Dropwise add polyethylene glycol grafted with epoxy propane with a mass four times that of aminoethyl chitosan, adjust the pH of the system to 8 - 9, heat up to 80 °C, stir and react for 8 h. After the reaction is completed, remove the water and dry to obtain.

[0009] Furthermore, the molecular weight of the polyethylene glycol monomethyl ether is 2000 - 4000, and its molar ratio to epichlorohydrin is 1:10 - 20.

[0010] Furthermore, the mass fraction of the polyether grafted chitosan in water is 30 - 40%, and the mass ratio of the polyether grafted chitosan to the system in step 1) is 0.3 - 0.5:1.

[0011] The present invention further provides a modified urea-formaldehyde resin, which comprises the urea-formaldehyde resin modifier and the urea-formaldehyde resin adhesive as described above, and the weight ratio is 5-15:95-85.

[0012] Compared with the prior art, the beneficial effects of the present invention are as follows: after adding the urea-formaldehyde resin modifier, the formaldehyde release amount of the old national standard E1-level urea-formaldehyde resin wood adhesive is <0.1 mg / L, meeting the new national standard E1-level standard; the water resistance is enhanced, meeting the requirements of type II water-resistant plywood. Specific Embodiments

[0013] The technical solutions of the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0014] In addition, the technical features involved in different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0015] Example 1: A urea-formaldehyde resin modifier is prepared by the following method: 1) First, prepare modified rGO S1. Add graphene oxide rGO to the ethanol aqueous solution, ultrasonically disperse it evenly, heat it to 40 °C, add KH570, stir overnight, and cool it to room temperature; S2. Add ethylenediamine ten times the amount of graphene oxide rGO to the above reaction system, mix it evenly, adjust the pH to 9-10 with ammonia water, and then transfer it to a high-pressure reaction kettle, and react at 180-200 °C for 8-12 h; S3. After cooling, centrifuge and separate, and dry to obtain modified rGO; Then, place 5 parts of the obtained modified rGO in a reaction kettle, add 20 parts of vinyl acetate, 30 parts of methyl methacrylate, 8 parts of sodium vinyl sulfonate, 12 parts of acrylic acid, 2 parts of alanine, 1 part of potassium persulfate, 2 parts of benzoyl peroxide, and 25 parts of ethyl acetate to the reaction kettle. After stirring evenly, react at 70-80 °C for 2-4 h, and cool to room temperature after the reaction is completed.

[0016] 2) Add polyethylene glycol monomethyl ether with a molecular weight of 2000 and epichlorohydrin to the reaction kettle in a molar ratio of 1:10, heat it to 120 °C and react for 2-5 h to obtain polyethylene glycol grafted epoxy propane; dissolve aminoethyl chitosan in water and transfer it to the reaction kettle, dropwise add 4 times the mass of polyethylene glycol grafted epoxy propane to it, adjust the pH of the system to 8-9, heat it to 80 °C, stir and react for 8 h, remove the water after the reaction is completed, and dry to obtain polyether grafted chitosan.

[0017] 3) Dissolve 3 parts of polyether-grafted chitosan in 10 parts of water, then add it to the system in step 1), heat it to 40 °C while stirring, cool it down after stirring and mixing evenly, and discharge to obtain the product, denoted as sample 1.

[0018] Example 2: A urea-formaldehyde resin modifier is prepared by the following method: 1) First, prepare modified rGO S1. Add graphene oxide rGO to an ethanol aqueous solution, ultrasonically disperse it evenly, heat it to 40 °C, add KH570, stir overnight, and cool it to room temperature; S2. Add ethylenediamine in an amount ten times that of graphene oxide rGO to the above reaction system, mix it evenly, adjust the pH to 9 - 10 with ammonia water, then transfer it to a high-pressure reactor, and react at 180 - 200 °C for 8 - 12 h; S3. After cooling, centrifuge and separate, and dry to obtain modified rGO; Then place 3 parts of the obtained modified rGO in a reaction kettle, add 30 parts of vinyl acetate, 17 parts of methyl methacrylate, 5 parts of sodium vinyl sulfonate, 10 parts of acrylic acid, 5 parts of alanine, 1 part of potassium persulfate, 2 parts of benzoyl peroxide, and 27 parts of ethyl acetate to the reaction kettle, stir evenly, and react at 70 - 80 °C for 2 - 4 h. After the reaction is completed, cool it to room temperature.

[0019] 2) Add polyethylene glycol monomethyl ether with a molecular weight of 2000 and epichlorohydrin to a reaction kettle in a molar ratio of 1:10, heat it to 120 °C and react for 2 - 5 h to obtain polyethylene glycol-grafted propylene oxide; dissolve aminoethyl chitosan in water and transfer it to the reaction kettle, dropwise add 4 times the mass of polyethylene glycol-grafted propylene oxide to it, adjust the pH of the system to 8 - 9, heat it to 80 °C, stir and react for 8 h, remove water after the reaction is completed, and dry to obtain polyether-grafted chitosan.

[0020] 3) Dissolve 4 parts of polyether-grafted chitosan in 10 parts of water, then add it to the system in step 1), heat it to 40 °C while stirring, cool it down after stirring and mixing evenly, and discharge to obtain the product, denoted as sample 2.

[0021] Example 3: A urea-formaldehyde resin modifier is prepared by the following method: 1) First, prepare modified rGO S1. Add graphene oxide rGO to an ethanol aqueous solution, ultrasonically disperse it evenly, heat it to 40 °C, add KH570, stir overnight, and cool it to room temperature; S2. Add ethylenediamine in an amount ten times that of reduced graphene oxide (rGO) to the above reaction system, mix evenly, add ammonia water to adjust the pH to 9 - 10, then transfer it to a high-pressure reactor and react at 180 - 200 °C for 8 - 12 h; S3. After cooling, perform centrifugal separation and drying to obtain modified rGO; Then place 3 parts of the obtained modified rGO in a reaction kettle, add 40 parts of vinyl acetate, 15 parts of methyl methacrylate, 5 parts of sodium vinyl sulfonate, 10 parts of acrylic acid, 2 parts of alanine, 1 part of potassium persulfate, 2 parts of benzoyl peroxide, and 25 parts of ethyl acetate to the reaction kettle. After stirring evenly, react at 70 - 80 °C for 2 - 4 h. After the reaction is completed, cool to room temperature.

[0022] 2) Add polyethylene glycol monomethyl ether with a molecular weight of 2000 and epichlorohydrin to the reaction kettle in a molar ratio of 1:10, heat up to 120 °C and react for 2 - 5 h to obtain polyethylene glycol grafted propylene oxide; dissolve aminoethyl chitosan in water and transfer it to the reaction kettle, dropwise add 4 times the mass of polyethylene glycol grafted propylene oxide to it, adjust the pH of the system to 8 - 9, heat up to 80 °C, stir and react for 8 h. After the reaction is completed, remove the water and dry to obtain polyether grafted chitosan.

[0023] 3) Dissolve 4 parts of polyether grafted chitosan in 10 parts of water, then add it to 10 parts of the system in step 1). While stirring, heat up to 40 °C, stir and mix evenly, then cool down and discharge to obtain the product, denoted as sample 3.

[0024] Example 4: The preparation of aminoethyl chitosan refers to International Journal of Biological Macromolecules, 2012, 50(4): 918 - 924. In actual production, to save costs, hydroxyethyl chitosan can be directly purchased for replacement. A urea - formaldehyde resin modifier, the preparation process is the same as that in Example 1, except that aminoethyl chitosan is replaced by hydroxyethyl chitosan. Denote it as sample 4.

[0025] Application Example 1: Weigh 5 parts of sample 1 and 95 parts of urea - formaldehyde resin (Zhengzhou Xinke Chemical Products Co., Ltd.), stir and mix evenly, add 0.5% ammonium chloride curing agent, and coat it on the substrate board at a single - side coating amount of 150 g / m 2 Then stick a veneer board with a thickness of 2 mm and hot - press it into shape.

[0026] Application Example 2: Weigh 10 parts of sample 1 and 90 parts of urea - formaldehyde resin, stir and mix evenly, add 0.5% ammonium chloride curing agent, and coat it on the substrate board at a single - side coating amount of 150 g / m 2Coated on the substrate board, and then a veneer board with a thickness of 2 mm is pasted and hot-pressed into shape.

[0027] Application Example 3: Weigh 10 parts of Sample 2 and 90 parts of urea-formaldehyde resin, stir and mix evenly, add 0.5% ammonium chloride curing agent, and coat it on the substrate board at a rate of 150 g / m² on one side 2 Coated on the substrate board, and then a veneer board with a thickness of 2 mm is pasted and hot-pressed into shape.

[0028] Application Example 4: Weigh 10 parts of Sample 3 and 90 parts of urea-formaldehyde resin, stir and mix evenly, add 0.5% ammonium chloride curing agent, and coat it on the substrate board at a rate of 150 g / m² on one side 2 Coated on the substrate board, and then a veneer board with a thickness of 2 mm is pasted and hot-pressed into shape.

[0029] Application Example 5: Weigh 10 parts of Sample 4 and 90 parts of urea-formaldehyde resin, stir and mix evenly, add 0.5% ammonium chloride curing agent, and coat it on the fiber board at a rate of 150 g / m² on one side 2 Coated on the fiber board, and then an oak board with a thickness of 2 mm is pasted and hot-pressed into shape.

[0030] Using the purchased urea-formaldehyde resin to prepare plywood as a control example.

[0031] Take some samples of the wood adhesives obtained by stirring and mixing in Application Examples 1 - 5, and test the basic properties of the adhesives such as free formaldehyde, solid content, viscosity, etc. according to the national standard GB / T 14074-2017. The results are shown in Table 1.

[0032] Table 1 Test the basic properties of the prepared plywood such as formaldehyde release amount, bonding strength, and water resistance according to GBT9846—2015. The results are shown in Table 2.

[0033] Table 2 It can be seen from Table 1 that adding the modifier prepared in this application to the existing urea-formaldehyde resin can effectively reduce the amount of free formaldehyde, and does not affect its storage stability after mixing, has a small impact on viscosity, and can be used normally. When it is used to prepare plywood, it can effectively reduce the formaldehyde release amount of the glued board. The control example meets the old national standard E1 grade standard. However, the E1 grade formaldehyde release amount stipulated in the current national standard GB / T 39600-2021 has been reduced to 0.124 mg / L, and this board cannot be used for interior decoration boards. But after modification, adding a small amount of modifier to the existing urea-formaldehyde resin can make the prepared plywood meet the current national standard, and at the same time, its water resistance is improved, meeting the requirements of Class II water-resistant plywood.

[0034] The dispersibility and reactivity of the modified rGO are improved, and it can be in-situ polymerized with functional monomers such as vinyl acetate to form an interpenetrating network structure with polyether-grafted chitosan. When it is added to urea-formaldehyde resin, it has good compatibility, high storage stability, and a high absorption rate of free formaldehyde by functional groups; aminoethyl chitosan has a higher ability to capture formaldehyde than hydroxyethyl chitosan, but its preparation cost is also higher. To save costs, hydroxyethyl chitosan can be selected for preparation. Referring to Application Example 5, its formaldehyde release amount also meets the E1 standard.

[0035] Although the embodiments of the present invention have been disclosed above, it is not limited to the applications listed in the specification and embodiments. It can be fully applied to various fields suitable for the present invention. For those familiar with the field, additional modifications can be easily made. Therefore, without departing from the general concept defined by the claims and the equivalent scope, the present invention is not limited to specific details.

Claims

1. A urea-formaldehyde resin modifier, characterized in that, It is prepared by the following method: 1) First, treat rGO with KH570, then amino-functionalize it. Place the modified rGO in a reaction kettle, add vinyl acetate, methyl methacrylate, sodium vinyl sulfonate, acrylic acid, alanine, potassium persulfate, benzoyl peroxide and ethyl acetate to the reaction kettle. After stirring evenly, react. After the reaction is completed, cool to room temperature; 2) First, carry out a chlorine substitution reaction between methoxypolyethylene glycol and epichlorohydrin to obtain polyethylene glycol grafted epoxy propane; add aminoethyl chitosan and polyethylene glycol grafted epoxy propane to the reaction kettle, and open the epoxy ring under alkaline conditions to obtain polyether grafted chitosan; 3) Dissolve the polyether grafted chitosan in water and then add it to the system of step 1). While stirring, heat up to 40 °C, stir and mix evenly, then cool down and discharge to obtain the product.

2. The urea formaldehyde resin modifier according to claim 1, characterized in that, The specific modification process of the modified rGO in step 1) is as follows: S1. Add graphene oxide rGO to an ethanol aqueous solution, disperse it evenly by ultrasonic wave, heat up to 40 °C, add KH570, stir overnight, and cool to room temperature; S2. Add ethylenediamine in an amount ten times that of graphene oxide rGO to the above reaction system, mix evenly, adjust the pH to 9-10 with ammonia water, then transfer it to a high-pressure reaction kettle and react at 180-200 °C for 8-12 h; S3. After cooling, centrifuge and separate, and dry to obtain.

3. The urea-formaldehyde resin modifier according to claim 1, characterized in that The weight ratio of each component in step 1) is: modified rGO 1-5%, vinyl acetate 20-40%, methyl methacrylate 15-30%, sodium vinyl sulfonate 5-10%, acrylic acid 10-15%, alanine 2-6%, potassium persulfate 1-2% and benzoyl peroxide 1-2%, and the balance is ethyl acetate.

4. The urea-formaldehyde resin modifier according to claim 1, wherein The reaction conditions in step 1) are: react at 70-80 °C for 2-4 h.

5. The urea-formaldehyde resin modifier according to claim 1, characterized in that, The specific preparation process of step 2) is as follows: S1. Add methoxypolyethylene glycol and epichlorohydrin to the reaction kettle, heat up to 120 °C and react for 2-5 h to obtain polyethylene glycol grafted epoxy propane; S2. Dissolve aminoethyl chitosan in water and transfer it to the reaction kettle. Dropwise add polyethylene glycol grafted epoxy propane with a mass four times that of aminoethyl chitosan, adjust the pH of the system to 8-9, heat up to 80 °C, stir and react for 8 h. After the reaction is completed, remove the moisture and dry to obtain.

6. The urea-formaldehyde resin modifier according to claim 5, characterized in that, The molecular weight of the methoxypolyethylene glycol is 2000-4000, and its molar ratio to epichlorohydrin is 1:10-20.

7. The urea-formaldehyde resin modifier according to claim 1, characterized in that, The mass fraction of the polyether grafted chitosan in water is 30-40%, and the mass ratio of the polyether grafted chitosan to the system of step 1) is 0.3-0.5:

1.

8. A modified urea-formaldehyde resin, characterized in that, It includes the urea-formaldehyde resin modifier and the urea-formaldehyde resin adhesive described in claims 1-7, and the weight ratio is 5-15:95-85.

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