A method for modifying phenol-formaldehyde resins with lignin and tannin and the resulting products

Abstract

The application discloses a method for modifying phenolic resin by lignin and tannin and a product obtained by the method, and comprises the following steps: mixing partially molten phenol and an acidic catalyst, then adding lignin powder in batches to perform lignin phenolation reaction, and forming phenolated lignin; performing precondensation of the remaining molten phenol and a tannin water solution to form a tannin-phenol oligomer water solution; uniformly mixing the tannin-phenol oligomer water solution, the acidic catalyst and the phenolated lignin, slowly adding an aqueous formaldehyde solution, and performing phenolic aldehyde condensation reaction by heating; and after the reaction is completed, post-treatment is performed to obtain modified phenolic resin. By introducing biomass lignin and tannin, the application can reduce free phenol and free aldehyde, effectively reduce harm to human body and environmental pollution in the synthesis process, and greatly improve processing performance and mechanical properties of the glue.

Description

Technical Field

[0001] This invention relates to a method for synthesizing phenolic resin, specifically a simple, green, and sustainable method for modifying phenolic resin using biomass lignin and tannins, and also relates to the modified phenolic resin obtained according to this method, belonging to the field of biomaterial preparation technology. Background Technology

[0002] Thermoplastic phenolic resin is prepared by polycondensation of phenol and formaldehyde compounds under an acidic catalyst. Currently, both phenol and formaldehyde are derived from petroleum and possess a certain degree of toxicity. In the long run, it is imperative to find green, non-toxic, and renewable resources to replace petroleum-based raw materials.

[0003] Lignin is an abundant biomass resource with a complex three-dimensional network structure composed of guaiacol (G), p-hydroxyl (H), and syringyl (S) groups, containing numerous functional groups such as phenolic hydroxyl, alcoholic hydroxyl, methoxy, and carboxyl groups. In recent years, lignin has attracted significant attention from researchers as a raw material for phenolic resins, replacing phenol. However, the presence of numerous methoxy groups in the lignin molecule increases steric hindrance, affecting its activity and significantly limiting its industrial application. To improve the reactivity and rubber compatibility of lignin, physical or chemical modifications are generally employed, including ball milling, demethylation, phenolization, and sulfonation. Modified lignin exhibits significantly improved reactivity and can be widely applied in various fields. However, in actual production, excessively high lignin substitution rates can significantly degrade the mechanical properties of the resin. Therefore, to further improve the overall performance of the resin, it is still necessary to explore the possibility of using other renewable biomass resources as phenol substitutes. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a method for modifying phenolic resin using lignin and tannin. This method first involves phenolic modification of lignin, then pre-condensation of tannin with phenol, and finally reaction with formaldehyde to prepare thermoplastic phenolic resin. This method reduces the amount of phenol used, improves the utilization rate of tannin, and results in a phenolic resin with low free phenol and free aldehyde content and excellent mechanical properties.

[0005] The specific technical solution of this invention is as follows: A method for modifying phenolic resin using lignin and tannin, the method comprising the following steps: (1) Partially molten phenol, lignin powder and acid catalyst are stirred and mixed to carry out lignin phenolization reaction to form phenolized lignin; (2) Add the remaining molten phenol to the tannin aqueous solution, adjust the pH to weakly alkaline, and then heat to 70-75℃ to carry out a pre-condensation reaction to form an aqueous solution of tannin-phenol oligomers; (3) Add the aqueous solution of tannin-phenol oligomer and acidic catalyst to the product obtained in step (1), mix them evenly, then add the aqueous solution of formaldehyde dropwise to the mixture, and heat to carry out the phenol-formaldehyde condensation reaction. (4) The reaction solution is post-treated to obtain modified phenolic resin.

[0006] Furthermore, in step (1), the lignin used in this invention can be various types of lignin, such as hardwood lignin, softwood lignin, etc., preferably softwood lignin, which includes pine lignin, spruce lignin, cypress wood lignin and other commercially available lignins.

[0007] Furthermore, in step (1), the mass ratio of lignin to phenol in step (1) is 1:1.1 to 1.9, for example 1:1.1, 1:1.3, 1:1.5, 1:1.7, 1:1.9, preferably 1:1.7.

[0008] Furthermore, in step (1), the acidic catalyst is any one or a combination of several acids selected from hydrochloric acid, sulfuric acid, oxalic acid and p-toluenesulfonic acid.

[0009] Furthermore, in step (1), the amount of acidic catalyst used is 6-10% of the lignin content.

[0010] Furthermore, in step (1), the temperature of the lignin phenolation reaction is 80-120℃, for example 80℃, 90℃, 100℃, 110℃, 120℃, preferably 90℃; the phenolation reaction time is 1~4h, for example 1h, 2h, 3h, 4h, preferably 2h.

[0011] Furthermore, in step (1), the phenolation reaction is preferably carried out under stirring at a speed of 250 rpm to 400 rpm.

[0012] Furthermore, in step (2), the tannin is catechin.

[0013] Furthermore, in step (2), the mass ratio of the tannin to the phenol in step (2) is 1:0.5-2, for example 1:0.5, 1:1, 1:1.5, 1:2, preferably 1:1.

[0014] Furthermore, in step (2), the mass fraction of the tannin aqueous solution is 10% to 60%, for example 10%, 20%, 30%, 40%, 50%, 60%, preferably 40% to 50%.

[0015] Furthermore, in step (2), the pH of the system is adjusted to a weakly alkaline state using an alkali, where weakly alkaline means a pH of 8-9. The alkali can be an aqueous solution of sodium hydroxide, etc.

[0016] Furthermore, in step (2), the pre-condensation reaction takes 30-60 min.

[0017] Furthermore, the mass ratio of phenol in step (1) to phenol in step (2) is 1.5-1.8:1.

[0018] Furthermore, in step (3), the acidic catalyst is any one or a combination of several acids selected from hydrochloric acid, sulfuric acid, oxalic acid, and p-toluenesulfonic acid. The mass ratio of the acidic catalyst to the formaldehyde aqueous solution is 1:2 to 6, for example, 1:2, 1:3, 1:4, 1:5, 1:6, preferably 1:4.

[0019] Furthermore, in step (3), the concentration of the formaldehyde aqueous solution is 30-37.5 wt%.

[0020] Furthermore, in step (3), the molar ratio of the total phenolic compounds to formaldehyde is 1:0.6~1, for example 1:0.6, 1:0.7, 1:0.8, 1:0.9, 1:1.0, preferably 1:0.7~0.8. The total phenolic compounds are the sum of phenol, lignin and tannin.

[0021] Furthermore, in step (3), the formaldehyde aqueous solution is added at a temperature of 80~100℃, for example, 80℃, 85℃, 90℃, 95℃, 100℃, preferably 90℃. The addition time is 0.5~2.5h, for example, 0.5h, 1h, 1.5h, 2h, 2.5h, preferably 2h.

[0022] Furthermore, in step (3), after the formaldehyde aqueous solution is added, the temperature is raised to carry out the phenol-formaldehyde condensation reaction. The phenol-formaldehyde condensation reaction is carried out under reflux, and the temperature of the phenol-formaldehyde condensation reaction is 90~120℃, for example 90℃, 100℃, 110℃, 120℃, preferably 110℃. The reaction time of the phenol-formaldehyde condensation reaction is 2~5h, for example 2h, 3h, 4h, 5h, preferably 3h.

[0023] Furthermore, in step (4), the post-treatment process is as follows: after the reaction is completed, the temperature is raised to about 150℃ for atmospheric distillation to initially remove a large amount of free water and some free monomers for 1-2 hours; then, vacuum distillation is carried out to remove residual free phenol / formaldehyde at a pressure of -0.07 MPa to -0.098 MPa for 2-3 hours; finally, qualified modified phenolic resin is obtained.

[0024] Furthermore, the modified phenolic resin obtained by the method of the present invention has a low free phenol content, which enables the rubber compound to have better mechanical and vulcanization properties. Therefore, the modified phenolic resin obtained by this method is also within the scope of protection of the present invention.

[0025] Compared with the prior art, the present invention has the following advantages: 1. Tannins are a class of water-soluble tannin compounds widely found in plants. Under acidic or alkaline conditions, they can react with formaldehyde in aqueous solution, a reaction widely considered a type of aldol condensation reaction, including hydroxymethylation, condensation, and polymerization. This invention innovatively introduces tannins into the preparation of phenolic resins, utilizing their unique molecular structure of tannin hydroxyl groups to undergo a condensation reaction with formaldehyde, thereby forming a novel thermoplastic phenolic resin with a linear structure.

[0026] 2. This invention designs a pre-condensation step for tannins and phenols. Under controllable and mild conditions, tannins and phenols undergo preliminary covalent bond "combination" to generate some stable dimers or oligomers. This avoids the risk of precipitation or excessive self-polymerization that may occur when tannins directly enter a strong acid environment, and improves their utilization rate and compatibility with the system.

[0027] 3. Lignin and tannin are both renewable biomass resources with wide availability, reducing the use of fossil-based raw materials and contributing to green and sustainable development. Furthermore, the use of lignin and tannin can effectively reduce harm to the human body during resin preparation and also lower free phenol content.

[0028] 4. The modified phenolic resin obtained by this invention has excellent properties and can be used to prepare rubber composites. The rubber composites obtained by modifying the phenolic resin with lignin and tannins in this invention have better vulcanization properties and mechanical properties, which can greatly improve the application performance of the rubber compound. The tensile strength and elongation at break of the rubber compound are significantly improved. Detailed Implementation

[0029] The present invention will be further described below with reference to embodiments, but the following embodiments are merely exemplary and do not limit its content.

[0030] Unless otherwise specified, all concentrations below are mass percentages.

[0031] In the following examples and comparative examples, the lignin used was commercially available pine lignin.

[0032] In the following examples and comparative examples, the softening point of the modified phenolic resin was determined using the ring and ball method, the free phenol content of the modified phenolic resin was determined using liquid chromatography, and the free formaldehyde content was determined using chemical titration. The molecular weight and distribution of lignin were determined using gel permeation chromatography (GPC) to obtain the number average molecular weight (Mn); the molar amount of lignin was calculated by dividing the mass by the number average molecular weight.

[0033] Example 1 1. Preheat a 500mL four-necked flask to 80℃ in an oil bath. Add 50g of molten phenol, 30g of lignin, and 3g of p-toluenesulfonic acid to the flask. Start stirring at 300rpm and heat to 90℃. Maintain the temperature for 2 hours to carry out the phenolization reaction and obtain phenolized lignin. At the same time, add 30g of molten phenol and 75g of 40% catechin aqueous solution to another flask. Add an appropriate amount of sodium hydroxide to adjust the pH to 8. Heat to 70-75℃ and maintain the temperature for 30 minutes to form an aqueous solution of tannin-phenol oligomers.

[0034] 2. Add the tannin-phenol oligomer aqueous solution and 15g of p-toluenesulfonic acid to the phenolic lignin, then heat to 90℃ and slowly add 60g of 37.5% formaldehyde aqueous solution (total phenol to aldehyde molar ratio of 1:0.78) dropwise over 2 hours. After the addition is complete, heat to 110℃ and carry out the phenol-formaldehyde condensation reaction under reflux for 3 hours.

[0035] 3. After the reaction is complete, the temperature is raised to 150℃, and the mixture is first distilled at atmospheric pressure for 1.5 hours, and then distilled under reduced pressure for 2 hours. The vacuum pressure is maintained at -0.07 MPa to -0.098 MPa to obtain modified phenolic resin. The softening point of the product is 98.5℃, the free phenol content is 0.41%, and the free formaldehyde content is 0.078%.

[0036] Example 2 1. Preheat a 500mL four-necked flask to 80℃ in an oil bath. Add 40g of molten phenol, 30g of lignin, and 2g of oxalic acid to the flask. Start stirring at 300rpm and heat to 80℃. Maintain the temperature for 2 hours to carry out the phenolization reaction. At the same time, add 30g of molten phenol and 100g of 40% catechin aqueous solution to another flask. Heat to 70-75℃ and maintain the temperature for 30 minutes to form an aqueous solution of tannin-phenol oligomers.

[0037] 2. Add the tannin-phenol oligomer aqueous solution and 15g of oxalic acid to the phenolic lignin, then heat to 80℃ and slowly add 60g of 37.5% formaldehyde aqueous solution (total phenol to aldehyde molar ratio of 1:0.85) dropwise over 2 hours. After the addition is complete, heat to 100℃ and carry out the phenol-formaldehyde condensation reaction under reflux for 3 hours.

[0038] 3. After the reaction is complete, the temperature is raised to 150℃, and the mixture is first distilled under normal pressure for 1.5 hours, and then distilled under reduced pressure for 2 hours. The vacuum pressure is maintained at -0.07 MPa to -0.098 MPa to obtain modified phenolic resin. The softening point of the product is 102.5℃, the free phenol content is 0.86%, and the free formaldehyde content is 0.092%.

[0039] Example 3 1. Preheat a 500mL four-necked flask to 80℃ in an oil bath. Add 55g of molten phenol, 30g of lignin, and 3g of p-toluenesulfonic acid to the flask. Start stirring at 300rpm and heat to 100℃. Maintain the temperature for 2 hours to carry out the phenolization reaction. At the same time, add 30g of molten phenol and 70g of 50% catechin aqueous solution to another flask. Add an appropriate amount of sodium hydroxide to adjust the pH to 8. Heat to 70-75℃ and maintain the temperature for 30 minutes to form an aqueous solution of tannin-phenol oligomers.

[0040] 2. Add the tannin-phenol oligomer aqueous solution and 15g of p-toluenesulfonic acid to the phenolic lignin, then heat to 100℃ and slowly add 60g of 37.5% formaldehyde aqueous solution (total phenol to aldehyde molar ratio of 1:0.73) dropwise over 2 hours. After the addition is complete, heat to 120℃ and carry out the phenol-formaldehyde condensation reaction under reflux for 3 hours.

[0041] 3. After the reaction is complete, the temperature is raised to 150℃, and the mixture is first distilled at atmospheric pressure for 1.5 hours, and then distilled under reduced pressure for 2 hours. The vacuum pressure is maintained at -0.07 MPa to -0.098 MPa to obtain modified phenolic resin. The softening point of the product is 95.6℃, the free phenol content is 1.15%, and the free formaldehyde content is 0.065%.

[0042] Comparative Example 1 Modified phenolic resin was prepared according to the method in Example 1, except that tannin and phenol were not pre-condensed. After the phenolization reaction was completed, 30g of molten phenol, 75g of a 40% (w / w) catechin aqueous solution, and 15g of p-toluenesulfonic acid were directly added to the phenolized lignin. Then, 60g of a 37.5% formaldehyde aqueous solution (total phenol to aldehyde molar ratio of 1:0.78) was uniformly added dropwise over 2 hours. After the addition was complete, the temperature was raised to 110°C, and the phenolic condensation reaction was carried out under reflux for 3 hours. The resulting product had a softening point of 92.4°C, a free phenol content of 1.18%, and a free formaldehyde content of 0.125%.

[0043] Comparative Example 2 Modified phenolic resin was prepared according to the method in Example 1, except that: after the phenolation reaction was completed, tannin was not added, and 40g of molten phenol and 15g of p-toluenesulfonic acid were directly added to the phenolized lignin. Then, the temperature was raised to 90°C and 60g of a 37.5% formaldehyde aqueous solution (total phenol to aldehyde molar ratio of 1:0.78) was slowly added dropwise over 2 hours. After the addition was complete, the temperature was raised to 110°C, and the phenolic condensation reaction was carried out under reflux for 3 hours. The resulting product had a softening point of 91.7°C, a free phenol content of 1.51%, and a free formaldehyde content of 0.135%.

[0044] Performance verification 1. Instruments used XK-160 Internal Mixer: High-speed Rail Testing Instruments Co., Ltd.; MDR2000 Closed Mold Vulcanizing Tester: Alpha Technology Co., Ltd., USA; MV2000 Mooney Viscosity Tester: Alpha Technologies, USA; AGS Universal Tensile Testing Machine: Shimadzu Testing Instruments Testing Machine; TH200 Hardness Tester: Jiangsu Mingzhu Testing Machinery Co., Ltd. GT-7017-NW High Temperature Aging Chamber: High-speed Rail Testing Instruments Co., Ltd.

[0045] 2. Rubber compound preparation The rubber-steel wire bonding evaluation formula contains the following components: 100 parts natural rubber, 55 parts carbon black, 0.8 parts cobalt borylate, 1.5 parts antioxidant 4020, 1 part antioxidant RD, 8 parts zinc oxide, 3.5 parts HMMM, 5 parts insoluble sulfur, 1.2 parts accelerator DZ, and 1.5 parts modified phenolic resin, wherein the modified phenolic resin is the modified phenolic resin prepared in each example and comparative example.

[0046] The preparation method of the rubber compound is as follows: First stage of mixing: Natural rubber, carbon black, cobalt borate, antioxidant, zinc oxide and modified phenolic resin are added to the internal mixer according to the weight ratio. The mixture is pressed and mixed for 60 seconds, then lifted for 10 seconds. This process is repeated 3 times. The rubber is discharged and sheeted from the open mill to obtain the first stage of masterbatch.

[0047] Two-stage mixing: The first-stage masterbatch rubber, HMMM, accelerator DZ, and insoluble sulfur are added to the open mill according to the weight ratio. The temperature is controlled at 70℃-80℃. The mixture is turned 4 times on the open mill with a roller cutter and rolled 7 times. The open mill cutter cuts off the sheet to obtain the second-stage final rubber.

[0048] 3. Testing Methods Scorch performance test: The test was conducted in accordance with GB / T 1233-2008.

[0049] Vulcanization performance test: The rubber compound was tested in accordance with GB / T 16584-1996.

[0050] Mechanical performance testing: The tests were conducted in accordance with GB / T 528-2009.

[0051] Hardness test of vulcanized rubber: The test shall be conducted in accordance with GB / T 531.1-2008.

[0052] 4. Experimental Results The performance analysis results of each rubber compound are shown in Table 1 below: Table 1. Data table of application performance analysis results for each rubber compound As can be seen from the above performance test data, compared with Comparative Example 1, Examples 1-3 showed significantly improved scorch time, vulcanization rate, and crosslinking density, and tensile strength and elongation at break before and after aging were all increased by more than 4%. Compared with Comparative Example 2, Examples 1-3 showed an approximately 10% increase in scorch time, an approximately 17% increase in vulcanization rate, an approximately 5% increase in crosslinking density, and tensile strength, stress at a given elongation, and elongation at break before and after aging were all increased by more than 10%.

Claims

1. A method for modifying phenolic resin using lignin and tannin, characterized in that: Includes the following steps: (1) Partially molten phenol, lignin powder and acidic catalyst are stirred and mixed to carry out lignin phenolization reaction to form phenolized lignin; (2) Add the remaining molten phenol to the tannin aqueous solution, adjust the pH to weakly alkaline, and then heat to 70-75℃ to carry out a pre-condensation reaction to form an aqueous solution of tannin-phenol oligomers; (3) Add the aqueous solution of tannin-phenol oligomer and acidic catalyst to the product obtained in step (1), mix them evenly, then add the aqueous solution of formaldehyde dropwise to the mixture, and heat to carry out the phenol-formaldehyde condensation reaction. (4) The reaction solution is post-treated to obtain modified phenolic resin.

2. The method according to claim 1, characterized in that: In step (1), the lignin is hardwood lignin or softwood lignin, preferably softwood lignin.

3. The method according to claim 1, characterized in that: In step (1), the mass ratio of lignin to phenol in step (1) is 1:1.1~1.9; Preferably, in step (2), the mass ratio of tannin to phenol in step (2) is 1:0.5-2; Preferably, the mass ratio of phenol in step (1) to phenol in step (2) is 1.5-1.8:

1.

4. The method according to any one of claims 1-3, characterized in that: In step (1), the acidic catalyst is at least one of hydrochloric acid, sulfuric acid, oxalic acid and p-toluenesulfonic acid; Preferably, in step (1), the amount of acidic catalyst used is 6-10% of the lignin content; Preferably, in step (1), the temperature of the phenolation reaction is 80-120℃ and the reaction time is 1-4h.

5. The method according to any one of claims 1-3, characterized in that: In step (2), the tannin is catechin; preferably, the mass fraction of the tannin aqueous solution is 10%~60%.

6. The method according to any one of claims 1-3, characterized in that: In step (2), adjust the pH to 8-9; Preferably, the pre-condensation reaction time is 30-60 min.

7. The method according to any one of claims 1-3, characterized in that: In step (3), the molar ratio of total phenolic compounds to formaldehyde is 1:0.6~1, and the total phenolic compounds are the sum of phenol, lignin and tannin; preferably, the concentration of the formaldehyde aqueous solution is 30-37.5wt%.

8. The method according to any one of claims 1-3, characterized in that: In step (3), the formaldehyde aqueous solution is added at a temperature of 80~100℃ and for a time of 0.5~2.5h. Preferably, in step (3), the temperature of the phenolic condensation reaction is 90~120℃ and the reaction time is 2~5h.

9. The method according to any one of claims 1-3, characterized in that: In step (3), the acidic catalyst is any one or a combination of several acids selected from hydrochloric acid, sulfuric acid, oxalic acid and p-toluenesulfonic acid; preferably, in step (3), the mass ratio of the acidic catalyst to the formaldehyde aqueous solution is 1:2~6.

10. The modified phenolic resin prepared according to any one of claims 1-9.

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