Modified urea-formaldehyde resin with low free formaldehyde content and preparation method of modified urea-formaldehyde resin

Abstract

The invention relates to modified urea-formaldehyde resin with low free formaldehyde content and a preparation method of the modified urea-formaldehyde resin. The urea-formaldehyde resin is prepared by acid-alkali two-step polymerization, replacement of part of urea with sodium lignin sulfonate, blocking feeding, introduction of biomass filler and the like. The invention has the following beneficial effects: sodium lignin sulfonate is adopted to replace part of urea, benzene rings and sodium sulfonate are introduced, water resistance is enhanced, formaldehyde crosslinking is promoted, the reaction degree of urea and formaldehyde is improved, and the content of free formaldehyde in the system is reduced; amino groups in the polyether grafted chitosan react with free formaldehyde, so that the amount of free formaldehyde in the resin is reduced, the capability of capturing free formaldehyde is greatly improved through the polyether grafted and modified chitosan, and the net capturing effect is stronger; grafting modified rGO and chitosan grafted and modified by long-chain polyether form an interpenetrating network structure, so that the toughness of an adhesive layer is improved, the situation that the plywood is unglued after being aged for a long time is avoided, and the water resistance is improved; the adhesive is suitable for bonding artificial boards such as plywood, shaving boards and fiberboards.

Description

Technical Field

[0001] The invention relates to the field of wood adhesives, in particular to a modified urea-formaldehyde resin with low free formaldehyde content and a preparation method thereof. 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 often use formaldehyde, a raw material that is harmful to humans and the environment, as a raw material. The resulting boards also contain residual formaldehyde, which can cause significant health hazards to both manufacturers and users over time. Therefore, it is crucial to develop a urea-formaldehyde resin with low formaldehyde emissions, high strength, and relatively high water and weather resistance to control production costs. Summary of the Invention

[0004] In view of the shortcomings of the prior art, the present invention provides a method for preparing a modified urea-formaldehyde resin with low free formaldehyde.

[0005] To achieve the above object, the present invention provides the following technical solutions: A method for preparing a modified urea-formaldehyde resin with low free formaldehyde content comprises the following steps: S1. Add 100 parts by weight of 37% formaldehyde solution to the reactor, adjust the pH to 8-8.5, add 28-35 parts by weight of urea, and heat to 70-80°C for 30 minutes; S2. Add 12-16 parts of sodium lignin sulfonate to the reactor, cool to 60°C, adjust the pH to 4.8-5.5, and react for 30-60 minutes; S3, add 20-25 parts by weight of urea three times, add 7-10 parts by weight of polyether grafted chitosan after the second addition of urea, adjust the pH to neutral after all the urea is added, and keep the reaction warm for 30 minutes; S4, dispersing the grafted modified rGO in water, adding it to the reactor and stirring evenly, and vacuum dehydrating it to a solid content of 60-65%; The polyether grafted chitosan is obtained by firstly reacting polyethylene glycol monomethyl ether with epichlorohydrin to obtain polyethylene glycol grafted propylene oxide; and then reacting with hydroxyethyl chitosan to obtain the obtained polyether grafted chitosan by ring opening of alkylene oxide under alkaline conditions. The graft-modified rGO is prepared as follows: rGO is first treated with KH570, and then amination is performed to obtain the modified rGO, which is placed in a reactor. Vinyl acetate, methyl methacrylate, sodium vinyl sulfonate, acrylic acid, alanine, potassium persulfate, benzoyl peroxide, and ethyl acetate are added to the reactor, and the mixture is stirred thoroughly and reacted. After the reaction is completed, the mixture is cooled to room temperature, the solvent is removed, and the mixture is dried.

[0006] Furthermore, the specific preparation process of the polyether grafted chitosan is as follows: S1. Add polyethylene glycol monomethyl ether and epichlorohydrin into a reactor, heat to 120°C and react for 2-5 hours to obtain polyethylene glycol grafted propylene oxide; S2. Dissolve hydroxyethyl chitosan in water and transfer it to a reactor. Add 4 times the mass of polyethylene glycol grafted propylene oxide dropwise therein, adjust the pH of the system to 8-9, raise the temperature to 80°C, stir and react for 8 hours. After the reaction is complete, remove water and dry to obtain the product.

[0007] Furthermore, the molecular weight of the polyethylene glycol monomethyl ether is 2000-4000, and the molar ratio of the polyethylene glycol monomethyl ether to epichlorohydrin is 1:10-20.

[0008] Furthermore, the preparation process of the grafted modified rGO is as follows: S1. Add graphene oxide rGO to ethanol aqueous solution, disperse evenly by ultrasonication, heat to 40°C, add KH570, stir overnight, and cool to room temperature; S2. Add ten times the amount of ethylenediamine as that of graphene oxide rGO to the above reaction system and mix evenly. Add ammonia water to adjust the pH to 9-10. Then transfer to a high-pressure reactor, react at 180-200° C. for 8-12 hours, cool, centrifuge, and dry to obtain modified rGO. S3. The obtained modified rGO is placed in a reactor, and vinyl acetate, methyl methacrylate, sodium vinyl sulfonate, acrylic acid, alanine, potassium persulfate, benzoyl peroxide and ethyl acetate are added to the reactor. The mixture is stirred thoroughly and reacted. After the reaction is completed, the mixture is cooled to room temperature, the solvent is removed and dried.

[0009] Furthermore, the weight ratios of the components are: 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 ethyl acetate.

[0010] Furthermore, the amount of the graft-modified rGO is 4 to 8 parts.

[0011] The present invention further provides a modified urea-formaldehyde resin with low free formaldehyde content obtained by the above-mentioned preparation method.

[0012] Compared with the prior art, the present invention has the following beneficial effects: urea-formaldehyde resin is prepared in this case through acid-base two-step polymerization, using sodium lignin sulfonate to replace part of the urea, sealing the feed, and introducing biomass fillers. Sodium lignin sulfonate introduces benzene rings and sodium sulfonate, enhancing water resistance, promoting formaldehyde cross-linking, increasing the degree of reaction between urea and formaldehyde, and reducing the free formaldehyde content in the system; the amino groups in the polyether-grafted chitosan react with free formaldehyde, reducing the amount of free formaldehyde in the resin, and the chitosan modified by polyether grafting greatly enhances its ability to capture free formaldehyde, resulting in a stronger netting effect; the modified rGO has improved dispersibility and reactivity, and can be in situ polymerized with functional monomers such as vinyl acetate to form grafted modified rGO, which forms an interpenetrating network structure with the chitosan modified by long-chain polyether grafting, improving the toughness of the adhesive layer, preventing the debonding of plywood after long-term aging, and simultaneously improving water resistance. The urea-formaldehyde resin wood adhesive prepared by the invention is suitable for bonding artificial boards such as plywood, particleboard, fiberboard, etc. DETAILED DESCRIPTION

[0013] The following will clearly and completely describe the technical solutions of the present invention in conjunction with the embodiments. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection 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: A modified urea-formaldehyde resin with low free formaldehyde S1. Add 100 parts by weight of 37% formaldehyde solution to the reactor, adjust the pH to 8-8.5, add 28-35 parts by weight of urea, and heat to 70-80°C for 30 minutes; S2. Add 12-16 parts of sodium lignin sulfonate to the reactor, cool to 60°C, adjust the pH to 4.8-5.5, and react for 30-60 min; S3, add 20-25 parts by weight of urea three times, add 7-10 parts by weight of polyether grafted chitosan after the second addition of urea, adjust the pH to neutral after all the urea is added, and keep the reaction warm for 30 minutes; S4, dispersing the grafted modified rGO in water, adding it to the reactor and stirring evenly, and vacuum dehydrating it to a solid content of 60-65%; The specific preparation process of the polyether grafted chitosan is as follows: S1. Add polyethylene glycol monomethyl ether and epichlorohydrin into a reactor, heat to 120°C and react for 2-5 hours to obtain polyethylene glycol grafted propylene oxide; S2. Dissolve hydroxyethyl chitosan in water and transfer it to a reactor. Add 4 times the mass of polyethylene glycol grafted propylene oxide dropwise therein, adjust the pH of the system to 8-9, raise the temperature to 80°C, stir and react for 8 hours. After the reaction is complete, remove water and dry to obtain the product.

[0016] The preparation process of the grafted modified rGO is as follows: S1. Add graphene oxide rGO to ethanol aqueous solution, disperse evenly by ultrasonication, heat to 40°C, add KH570, stir overnight, and cool to room temperature; S2. Add ten times the amount of ethylenediamine as that of graphene oxide rGO to the above reaction system and mix well. Add ammonia water to adjust the pH to 9-10. Then transfer to a high-pressure reactor and react at 180-200°C for 8-12 hours. S3, cooling, centrifuging, and drying to obtain modified rGO; Then, 5 parts of the obtained modified rGO were placed in a reactor, and 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 were added to the reactor. After being fully stirred, the mixture was reacted at 70-80°C for 2-4 hours. After the reaction was completed, the mixture was cooled to room temperature.

[0017] Example 1: S1. Add 100 parts by weight of 37% formaldehyde solution to the reactor, adjust the pH to 8, add 33 parts by weight of urea, and heat to 80° C. for 30 minutes; S2. Add 12 parts of sodium lignin sulfonate to the reactor, cool to 60°C, adjust the pH to 4.8, and react for 30 minutes; S3, add 20 parts by weight of urea three times, add 7 parts by weight of polyether grafted chitosan after the second addition of urea, adjust the pH to neutral after all the urea is added, and keep the reaction warm for 30 minutes; S4. Disperse 4 parts of grafted modified rGO in water, add it into the reactor, stir evenly, and vacuum dehydrate to a solid content of 60%.

[0018] Free formaldehyde ≤0.01%, no abnormality after standing at 25℃ for 45 days.

[0019] Example 2: S1. Add 100 parts by weight of 37% formaldehyde solution to the reactor, adjust the pH to 8, add 30 parts by weight of urea, and heat to 75° C. for 30 minutes; S2. Add 14 parts of sodium lignin sulfonate to the reactor, cool to 60°C, adjust the pH to 4.8, and react for 30-60 minutes; S3, adding 21 parts by weight of urea in three times, adding 8 parts by weight of polyether grafted chitosan after the second addition of urea, adjusting the pH to neutral after all the urea is added, and keeping the reaction warm for 30 minutes; S4. Disperse 6 parts of grafted modified rGO in water, add it into the reactor, stir evenly, and vacuum dehydrate to a solid content of 60%.

[0020] Free formaldehyde ≤0.01%, no abnormality after standing at 25℃ for 45 days.

[0021] Example 3: S1. Add 100 parts by weight of 37% formaldehyde solution to the reactor, adjust the pH to 8, add 28 parts by weight of urea, and heat to 75° C. for 30 minutes; S2. Add 16 parts of sodium lignin sulfonate to the reactor, cool to 60°C, adjust the pH to 5, and react for 30 min; S3, adding 22 parts by weight of urea in three times, adding 10 parts by weight of polyether grafted chitosan after the second addition of urea, adjusting the pH to neutral after all the urea is added, and keeping the reaction warm for 30 minutes; S4. Disperse 8 parts of grafted modified rGO in water, add it into the reactor, stir evenly, and vacuum dehydrate to a solid content of 60%.

[0022] Free formaldehyde ≤0.01%, no abnormality after standing at 25℃ for 45 days.

[0023] Comparative Example 1: S1. Add 100 parts by weight of 37% formaldehyde solution to the reactor, adjust the pH to 8, add 28 parts by weight of urea, and heat to 75° C. for 30 minutes; S2. Add 16 parts of sodium lignin sulfonate to the reactor, cool to 60°C, adjust the pH to 5, and react for 30 min; S3, add 22 parts by weight of urea in three times, adjust the pH to neutral after all the urea is added, and keep the reaction warm for 30 minutes; S4. Disperse 8 parts of grafted modified rGO in water, add it into the reactor, stir evenly, and vacuum dehydrate to a solid content of 60%.

[0024] Free formaldehyde ≤0.5%, precipitation occurs after standing at 25℃ for 25 days.

[0025] Comparative Example 2: S1. Add 100 parts by weight of 37% formaldehyde solution to the reactor, adjust the pH to 8, add 28 parts by weight of urea, and heat to 75° C. for 30 minutes; S2. Add 16 parts of sodium lignin sulfonate to the reactor, cool to 60°C, adjust the pH to 5, and react for 30 min; S3. Add 22 parts by weight of urea in three times, add 10 parts by weight of polyether grafted chitosan after the second addition of urea, adjust the pH to neutral after all the urea is added, keep the reaction warm for 30 minutes, vacuum dehydrate to a solid content of 60%, and discharge.

[0026] Free formaldehyde ≤0.1%, no abnormality after standing at 25℃ for 45 days.

[0027] Comparative Example 3: S1. Add 100 parts by weight of 37% formaldehyde solution to the reactor, adjust the pH to 8, add 28 parts by weight of urea, and heat to 75° C. for 30 minutes; S2. Add 16 parts of sodium lignin sulfonate to the reactor, cool to 60°C, adjust the pH to 5, and react for 30 min; S3, adding 22 parts by weight of urea in three times, adding 10 parts by weight of chitosan after the second addition of urea, adjusting the pH to neutral after all the urea is added, and keeping the reaction warm for 30 minutes; S4. Disperse 8 parts of rGO in water, add it into the reactor, stir evenly, and vacuum dehydrate to a solid content of 60%.

[0028] Free formaldehyde ≤0.5%, precipitation occurs after standing at 25℃ for 35 days.

[0029] application: 1 wt% ammonium chloride curing agent was added to the urea-formaldehyde resins prepared in Examples 1-3 and Comparative Examples 1-3 to prepare three-layer poplar plywood. The poplar board had a thickness of 3 mm and a width of 30 × 30 cm. The double-sided 300 g / m 2 Apply it to the board, then attach boards on both sides and hot press it at 1.5MPa and 105℃.

[0030] Table 1 It can be seen from the table that the formaldehyde emission of the plywood made from the urea-formaldehyde resin of the present invention is less than 0.11, reaching the E1 level. The wet bonding strength is reduced, but can still meet the construction requirements and conform to the requirements of GB / T9846-2015 for Class II water-resistant plywood.

[0031] Although the embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the description and implementation methods. They can be fully applied to various fields suitable for the present invention. For those familiar with the art, additional modifications can be easily implemented. Therefore, without departing from the general concept defined by the claims and the scope of equivalents, the present invention is not limited to specific details.

Claims

1. A method for preparing a modified urea-formaldehyde resin with low free formaldehyde content, characterized in that: The steps include: S1. Add 100 parts by weight of 37% formaldehyde solution to the reactor, adjust the pH to 8-8.5, add 28-35 parts by weight of urea, and heat to 70-80°C for 30 minutes; S2. Add 12-16 parts of sodium lignin sulfonate to the reactor, cool to 60°C, adjust the pH to 4.8-5.5, and react for 30-60 minutes; S3, add 20-25 parts by weight of urea three times, add 7-10 parts by weight of polyether grafted chitosan after the second addition of urea, adjust the pH to neutral after all the urea is added, and keep the reaction warm for 30 minutes; S4, dispersing the grafted modified rGO in water, adding it to the reactor and stirring evenly, and vacuum dehydrating it to a solid content of 60-65%; The polyether grafted chitosan is obtained by firstly reacting polyethylene glycol monomethyl ether with epichlorohydrin to obtain polyethylene glycol grafted propylene oxide; and then reacting with hydroxyethyl chitosan to obtain the obtained polyether grafted chitosan by ring opening of alkylene oxide under alkaline conditions. The graft-modified rGO is prepared as follows: rGO is first treated with KH570, and then amination is performed to obtain the modified rGO, which is placed in a reactor. Vinyl acetate, methyl methacrylate, sodium vinyl sulfonate, acrylic acid, alanine, potassium persulfate, benzoyl peroxide, and ethyl acetate are added to the reactor, and the mixture is stirred thoroughly and reacted. After the reaction is completed, the mixture is cooled to room temperature, the solvent is removed, and the mixture is dried.

2. The method for preparing a modified urea-formaldehyde resin with low free formaldehyde content according to claim 1, wherein The specific preparation process of the polyether grafted chitosan is as follows: S1. Add polyethylene glycol monomethyl ether and epichlorohydrin into a reactor, heat to 120°C and react for 2-5 hours to obtain polyethylene glycol grafted propylene oxide; S2. Dissolve hydroxyethyl chitosan in water and transfer it to a reactor. Add 4 times the mass of polyethylene glycol grafted propylene oxide dropwise therein, adjust the pH of the system to 8-9, raise the temperature to 80°C, stir and react for 8 hours. After the reaction is complete, remove water and dry to obtain the product.

3. The method for preparing a modified urea-formaldehyde resin with low free formaldehyde content according to claim 2, wherein: The molecular weight of the polyethylene glycol monomethyl ether is 2000-4000, and the molar ratio of the polyethylene glycol monomethyl ether to epichlorohydrin is 1:10-20.

4. The method for preparing a modified urea-formaldehyde resin with low free formaldehyde content according to claim 1, wherein The preparation process of the grafted modified rGO is as follows: S1. Add graphene oxide rGO to ethanol aqueous solution, disperse evenly by ultrasonication, heat to 40°C, add KH570, stir overnight, and cool to room temperature; S2. Add ten times the amount of ethylenediamine as that of graphene oxide rGO to the above reaction system and mix evenly. Add ammonia water to adjust the pH to 9-10. Then transfer to a high-pressure reactor, react at 180-200° C. for 8-12 hours, cool, centrifuge, and dry to obtain modified rGO. S3. The obtained modified rGO is placed in a reactor, and vinyl acetate, methyl methacrylate, sodium vinyl sulfonate, acrylic acid, alanine, potassium persulfate, benzoyl peroxide and ethyl acetate are added to the reactor. The mixture is stirred thoroughly and reacted. After the reaction is completed, the mixture is cooled to room temperature, the solvent is removed and dried.

5. The method for preparing a modified urea-formaldehyde resin with low free formaldehyde content according to claim 4, wherein: The weight ratios of the components are: 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 ethyl acetate.

6. The method for preparing a modified urea-formaldehyde resin with low free formaldehyde content according to claim 1, wherein: The amount of the grafted modified rGO is 4 to 8 parts.

7. A modified urea-formaldehyde resin with low free formaldehyde content obtained by the preparation method according to any one of claims 1 to 6.

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