Preparation method and application of lignin modified urea-formaldehyde resin

Abstract

The invention discloses a preparation method and application of lignin modified urea-formaldehyde resin, and belongs to the technical field of urea-formaldehyde resin adhesives, the preparation method comprises the following steps: (1) preparing aldehyde group modified lignin; the preparation method comprises the following steps: reacting lignin with 2-chloro-1, 1-dimethoxyethane under the action of alkali, and adding strong acid into a reaction system after the reaction is finished, so as to prepare aldehyde modified lignin; (2) preparing lignin-based modified urea-formaldehyde resin; and mixing the aldehyde group modified lignin prepared in the step (1) with urea and formaldehyde to prepare the lignin-based modified urea-formaldehyde resin. According to the preparation method, the degradable biological raw material lignin is subjected to derivatization to introduce aldehyde groups, then the lignin is added into a urea-formaldehyde resin synthesis system, and due to the existence of the aldehyde groups in the lignin, the lignin can partially replace formaldehyde to be subjected to a polymerization reaction with urea, so that the lignin-based modified urea-formaldehyde resin is prepared; the adhesion can be improved while the formaldehyde emission can be reduced.

Description

Technical Field

[0001] The invention relates to the technical field of urea-formaldehyde resin adhesives, and in particular to a preparation method of a lignin-modified urea-formaldehyde resin and application thereof. Background Art

[0002] Urea-formaldehyde resin has many advantages such as abundant raw material sources, low cost, fast curing, good operating performance, high bonding strength, simple manufacturing and excellent comprehensive performance. Therefore, it is widely used in various home improvement fields, such as wood adhesives, wallpaper adhesives and other home improvement industries.

[0003] However, traditional urea-formaldehyde resin is prepared by polymerization of urea and formaldehyde. After the synthesis, there is still a certain amount of unreacted formaldehyde. These free formaldehydes will be slowly released with the processed wood products over a long period of time, posing great health and safety risks to consumers. At the same time, it also makes the urea-formaldehyde resin adhesive not very water-resistant and very brittle after curing, greatly reducing its adhesion performance. Summary of the invention

[0004] The present invention aims to solve the defects of high residual free formaldehyde and low adhesion performance in existing urea-formaldehyde resin adhesives, and provides a preparation method of lignin-modified urea-formaldehyde resin and application thereof.

[0005] To achieve the above object, the technical solution of the present invention is:

[0006] First, the present invention provides a method for preparing a lignin-modified urea-formaldehyde resin, which comprises the following steps:

[0007] (1) Preparation of aldehyde-modified lignin;

[0008] Lignin is reacted with 2-chloro-1,1-dimethoxyethane under the action of a base to obtain a derivative lignin containing an acetal structure, and then the acetal structure in the derivative lignin is converted into an aldehyde group to prepare an aldehyde-modified lignin. The reaction process is shown in formula (1):

[0009]

[0010] (2) Preparation of lignin-based modified urea-formaldehyde resin;

[0011] The aldehyde-modified lignin prepared in step (1) is mixed with urea and formaldehyde to prepare a lignin-modified urea-formaldehyde resin, and the reaction process is shown in formula (2):

[0012]

[0013] In one embodiment, in step (1), lignin is reacted with 2-chloro-1,1-dimethoxyethane under the action of a base, and after the reaction, the base is filtered out, and a strong acid is added to the reaction system to hydrolyze the acetal structure into an aldehyde group.

[0014] In one embodiment, step (2) includes:

[0015] Sodium hydroxide is added to the formaldehyde solution, and then the aldehyde-modified lignin prepared in step (1) is added to the system and reacted with urea for 30 to 45 minutes, and then formic acid solution is added to react for 30 minutes, and sodium hydroxide solution and urea are added again. After the reaction is complete, a lignin-modified urea-formaldehyde resin is prepared.

[0016] In one embodiment, step (1) comprises:

[0017] An organic base is added to lignin to prepare a solution, and then an inorganic base and 2-chloro-1,1-dimethoxyethane are added to the solution.

[0018] In one embodiment, the molar ratio of the 2-chloro-1,1-dimethoxyethane to the lignin is 1:6-9.

[0019] In one embodiment, the organic base is an amide organic base.

[0020] In one embodiment, the amide organic base is one of N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc) or N-methylpyrrolidine (NMP).

[0021] In one embodiment, the inorganic base is one of potassium carbonate, sodium carbonate or lithium carbonate.

[0022] In one embodiment, the molar ratio of the inorganic base to the lignin is 1:15-20.

[0023] In one embodiment, the strong acid is one of hydrochloric acid, sulfuric acid or methanesulfonic acid.

[0024] Secondly, the present invention also provides an application of a lignin-modified urea-formaldehyde resin, wherein the urea-formaldehyde resin prepared by any of the above-mentioned methods for preparing a lignin-modified urea-formaldehyde resin is used as an adhesive.

[0025] The present invention introduces aldehyde groups by derivatizing degradable biological raw material lignin, and then adds it into the synthesis system of urea-formaldehyde resin. Due to the presence of aldehyde groups in lignin, formaldehyde can be partially replaced to undergo polymerization reaction with urea to prepare lignin-based modified urea-formaldehyde resin. The introduction of aldehyde-based lignin can effectively reduce the usage of formaldehyde, and thus can effectively reduce the residual amount and release amount of formaldehyde in urea-formaldehyde resin. At the same time, due to the introduction of aldehyde-based lignin, not only aldehyde groups are contained, but also aromatic groups and hydroxyls are contained, thereby containing Pi-Pi stacking conjugation effect and hydrogen bond effect, etc., effectively strengthening the adhesion performance of lignin-based modified urea-formaldehyde resin adhesive.

[0026] In order to make the above features and advantages of the invention more obvious and easy to understand, embodiments are given below and described in detail with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is the infrared absorption spectrum of the aldehyde-modified lignin prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0028] In order to make the purpose and technical solution of the embodiment of the present invention clearer, the technical solution of the embodiment of the present invention will be clearly and completely described below in conjunction with the drawings of the embodiment of the present invention. Obviously, the described embodiment is a part of the embodiment of the present invention, not all of the embodiments. Based on the described embodiment 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.

[0029] The present invention provides a method for preparing a lignin-modified urea-formaldehyde resin, which comprises the following steps:

[0030] (1) Preparation of aldehyde-modified lignin;

[0031] An amide solution is added to lignin to prepare a 0.01-0.05 mol / L solution, and then an inorganic base of 15-20 times the molar number of the raw material is added to the solution, and 2-chloro-1,1-dimethoxyethane of 6-9 times the molar number of the raw material is added dropwise. After the addition is completed, the reaction system is heated to 80-100° C., and heated and stirred for 12-18 hours to complete the reaction to obtain a substituted intermediate.

[0032] After the reaction is complete, the reaction system is cooled to room temperature, and the excess inorganic base solid is filtered out. The substituted intermediate in the filtrate does not need to be further purified. The filtrate is directly and slowly added dropwise to an excess of strong acid, and the reaction solution is raised to 50-60°C, heated and stirred for 6-10 hours to hydrolyze the acetal structure of the substituted intermediate into aldehyde. After the reaction is completed, the temperature is cooled to room temperature, and the reaction solution is added to 10L of water. At this time, the aldehyde-based lignin generated is a brown-black precipitate. The system is filtered, and the solid is washed with water for multiple times to prepare the target product of aldehyde-modified lignin with a yield of 82-88%.

[0033] The reaction process is shown in formula (1):

[0034]

[0035] (2) Preparation of lignin-based modified urea-formaldehyde resin;

[0036] Add 3-5 mol / L sodium hydroxide to 1000 mmol formaldehyde solution (37%) to adjust the pH of the solution to 7.8-8.2. Then add 600 mmol urea and the aldehyde lignin (1%-5% of the mass fraction of urea) prepared in step (1), raise the temperature of the reaction system to 90°C and stir for 30-45 minutes, then add formic acid solution (40%) to adjust the pH of the reaction system to 4.6-5.0, keep the reaction system at 90°C and continue to stir for 30 minutes, and after it becomes an emulsion, cool to room temperature. Use 3-5 mol / L sodium hydroxide again to adjust the pH of the reaction system to 7.8-8.2, then add 410 mmol urea, raise the temperature to 65-70°C and continue to react for 25-35 minutes, and cool to room temperature after the reaction is complete to prepare a lignin-based modified urea-formaldehyde resin.

[0037] The reaction process is shown in formula (2):

[0038]

[0039] The present invention will be further described below with reference to specific embodiments.

[0040] Example 1

[0041] Weigh 100g of lignin and add N,N-dimethylformamide (DMF) solution to prepare a 0.03mol / L solution, then add 18 times the molar number of the raw material inorganic base to the solution, and add 7 times the molar number of the raw material 2-chloro-1,1-dimethoxyethane dropwise. After the addition is complete, raise the reaction system to 90°C, heat and stir for 15h to complete the reaction, and obtain a substituted intermediate.

[0042] After the reaction is complete, the reaction system is cooled to room temperature, and the excess inorganic base solid is filtered out. The substituted intermediate in the filtrate does not need to be further purified. The filtrate is directly and slowly added dropwise to an excess of strong acid. The reaction solution is raised to 55°C and heated with stirring for 8 hours to hydrolyze the acetal structure of the substituted intermediate into aldehyde. After the reaction is completed, the temperature is cooled to room temperature and the reaction solution is added to 10L of water. At this time, the generated aldehyde lignin is a brown-black precipitate. The system is filtered and the solid is washed with water several times to prepare the target product of aldehyde-modified lignin. The aldehyde-modified lignin is subjected to infrared testing, and its infrared absorption spectrum is as follows Figure 1 shown.

[0043] 4 mol / L sodium hydroxide was added to 1000 mmol formaldehyde solution (37%) to adjust the pH of the solution to 8.0. Then 600 mmol urea and 1% aldehyde-modified lignin were added, the reaction system was heated to 90°C and stirred for 40 minutes, then formic acid solution (40%) was added to adjust the pH of the reaction system to 4.8, the reaction system was kept stirring at 90°C for 30 minutes, and after it became an emulsion, it was cooled to room temperature. 4 mol / L sodium hydroxide was used again to adjust the pH of the reaction system to 8.0, and then 410 mmol urea was added, the temperature was raised to 68°C and the reaction was continued for 30 minutes, and after the reaction was complete, it was cooled to room temperature to prepare a lignin-based modified urea-formaldehyde resin.

[0044] Example 2

[0045] The difference between this embodiment and embodiment 1 is that the addition amount of aldehyde-modified lignin is 3% of the mass fraction of urea.

[0046] Example 3

[0047] The difference between this embodiment and embodiment 1 is that the addition amount of aldehyde-modified lignin is 5% of the mass fraction of urea.

[0048] Comparative Example 1

[0049] This comparative example is a blank comparative example. Compared with Example 1, the difference is that only formaldehyde and urea are used to prepare urea-formaldehyde resin.

[0050] Comparative Example 2

[0051] The difference between this comparative example and Example 1 is that unmodified lignin is reacted with formaldehyde and urea to prepare urea-formaldehyde resin.

[0052] The urea-formaldehyde resins prepared in Example 1, Example 2, Example 3, Comparative Example 1 and Comparative Example 2 were tested for performance, and the test results of the performance are shown in Table 1:

[0053] Table 1 Urea-formaldehyde resin performance test results

[0054]

[0055] It can be seen from the above table that compared with traditional urea-formaldehyde resin (Comparative Example 1) and directly using lignin to modify urea-formaldehyde resin (Comparative Example 2), the lignin-based modified urea-formaldehyde resin (Examples 1 to 3) prepared by the lignin-modified urea-formaldehyde resin preparation method provided by the present invention has greatly reduced formaldehyde emission, improved bonding strength and viscosity, and shortened curing time.

[0056] In summary, the present invention introduces aldehyde groups by derivatizing degradable biological raw material lignin, and then adds it to the synthesis system of urea-formaldehyde resin. Due to the presence of aldehyde groups in lignin, formaldehyde can be partially replaced by polymerization reaction with urea to prepare lignin-based modified urea-formaldehyde resin. The introduction of aldehyde-based lignin can effectively reduce the usage of formaldehyde, so the residual amount and release amount of formaldehyde in urea-formaldehyde resin can be effectively reduced. At the same time, due to the introduction of aldehyde-based lignin, not only aldehyde groups are contained, but also aromatic groups and hydroxyls are contained, so as to contain Pi-Pi stacking conjugation effect and hydrogen bond effect, etc., effectively strengthening the adhesion performance of lignin-based modified urea-formaldehyde resin adhesive.

[0057] Although the present invention has been disclosed as above by way of embodiments, it is not intended to limit the present invention. Any person having ordinary knowledge in the technical field may make some changes and modifications without departing from the spirit and scope of the present invention. Therefore, the protection scope of the present invention shall be determined by the scope of the attached patent application.

Claims

1. A method for preparing a lignin-modified urea-formaldehyde resin, characterized in that: The steps include: (1) Preparation of aldehyde-modified lignin; The lignin is reacted with 2-chloro-1,1-dimethoxyethane under the action of a base to obtain a derivative lignin containing an acetal structure, and then the acetal structure in the derivative lignin is converted into an aldehyde group to prepare an aldehyde-modified lignin; (2) Preparation of lignin-based modified urea-formaldehyde resin; The aldehyde-modified lignin prepared in step (1) is mixed with urea and formaldehyde to prepare a lignin-modified urea-formaldehyde resin.

2. The method for preparing the lignin-modified urea-formaldehyde resin according to claim 1, characterized in that: In the step (1), lignin is reacted with 2-chloro-1,1-dimethoxyethane under the action of a base, and after the reaction is completed, the base is filtered out, and a strong acid is added to the reaction system to hydrolyze the acetal structure into an aldehyde group.

3. The method for preparing the lignin-modified urea-formaldehyde resin according to claim 1, characterized in that: Step (2) comprises: adding sodium hydroxide to the formaldehyde solution, then adding the aldehyde-modified lignin prepared in step (1) to the system and reacting with urea for 30 to 45 minutes, then adding formic acid solution to react for 30 minutes, then adding sodium hydroxide solution and urea again, and preparing lignin-modified urea-formaldehyde resin after the reaction is complete.

4. The method for preparing the lignin-modified urea-formaldehyde resin according to claim 1, characterized in that: An organic base is added to lignin to prepare a solution, and then an inorganic base and 2-chloro-1,1-dimethoxyethane are added to the solution.

5. The method for preparing the lignin-modified urea-formaldehyde resin according to claim 4, characterized in that: The organic base is an amide organic base.

6. The method for preparing the lignin-modified urea-formaldehyde resin according to claim 5, characterized in that: The amide organic base is one of N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc) or N-methylpyrrolidine (NMP).

7. The method for preparing the lignin-modified urea-formaldehyde resin according to claim 3, characterized in that: The inorganic base is one of potassium carbonate, sodium carbonate or lithium carbonate.

8. The method for preparing the lignin-modified urea-formaldehyde resin according to claim 7, characterized in that: The molar ratio of the inorganic alkali to the lignin is 1:15-20.

9. The method for preparing the lignin-modified urea-formaldehyde resin according to claim 1, characterized in that: The strong acid is one of hydrochloric acid, sulfuric acid or methanesulfonic acid.

10. An application of lignin modified urea-formaldehyde resin, characterized in that: The urea-formaldehyde resin prepared by the method for preparing the lignin-modified urea-formaldehyde resin according to any one of claims 1 to 9 is used as an adhesive.

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