A kind of lignin-based phenolic resin adhesive and its synthesis method

Abstract

The present invention relates to a lignin-based phenolic resin adhesive and a synthesis method thereof, comprising: (1) adding lignin to an acid solution, heating to 80-120°C, adding a ketone reagent for reaction, and obtaining modified lignin; (2) modifying the lignin in step (1), adding phenol, controlling the temperature to 60-80°C, adjusting the pH to 10-12, adding a formaldehyde solution and an alkali in three batches, stopping the reaction until the viscosity reaches 120-250 mPa·s, cooling, and obtaining a lignin-based phenolic resin adhesive. The present invention destroys the lignin structure in the presence of an acid, and then adding a ketone reagent to avoid the formation of macromolecular lignin, and finally obtaining a high-performance and environmentally friendly phenolic resin adhesive.

Description

Technical Field

[0001] The invention belongs to the field of polymer material preparation, and particularly relates to a lignin-based phenolic resin adhesive and a synthesis method thereof. Background Art

[0002] Phenolic resin adhesive is a water-soluble or alcohol-soluble resin formed by phenols and aldehydes under the action of a catalyst. It is one of the main types of adhesives widely used in the field of wood processing. Phenolic resin adhesives are mainly used to produce outdoor-grade plywood such as concrete formwork and car body panels. At present, lignin-phenol-formaldehyde adhesives have been put into feasible production, which can reduce the pollution of waste liquid from the papermaking industry and cellulosic ethanol industry, reduce the use of phenol, and reduce the cost of phenolic resin adhesives. However, lignin itself has a complex structure, a large molecular weight, and few active sites. It will degrade and condense during the reaction, and the molecular structure will change, which limits the process preparation conditions of lignin phenolic resin adhesives and high-performance applications.

[0003] CN201610162479.8 discloses a demethylated lignin-containing phenolic resin adhesive and a preparation method thereof, belonging to the field of material technology. Phenol, sodium hydroxide, water and formaldehyde solution are added to a container, heated to 60°C, stirred to make the system evenly dispersed, then the temperature is raised to 90°C, the reaction is kept warm for 1.5 hours, then the demethylated lignin is added, and the reaction is continued for 2 hours, the material is cooled and discharged, and the demethylated lignin-based phenolic resin adhesive is obtained. Compared with the unmodified lignin-based phenolic resin adhesive, the free formaldehyde content is reduced from 0.65% to 0.22%, the free phenol content is reduced from 1.37% to 0.82%, and the adhesive strength is increased from 0.97MPa to 2.11MPa. The method uses N,N-dimethylformamide and iodocyclohexane to react at 145°C for 7 hours to prepare demethylated lignin. The process operation is complicated, the lignin recovery is difficult, the energy consumption is large and the cost is high.

[0004] CN201711497797.0 discloses a method for preparing a hydroxymethylated modified lignin phenolic resin adhesive, which comprises the following steps: a first step, adding the first batch of formaldehyde F1, lignin L and the first batch of alkali solution into a reactor, and reacting at 75-95°C for 30-120min; a second step, adding phenol P to the reaction solution of the first step, and controlling the reaction temperature to 75-95°C by dripping the second batch of alkali solution, and reacting for 40-70min; a third step, cooling the reaction solution of the second step to 65- 75℃, add the second batch of formaldehyde F2, and control the reaction temperature to 75-95℃ by dropping the third batch of alkali solution for 40-70min; fourth step, cool the reaction solution of the third step to 65-75℃, add the third batch of formaldehyde F3, and control the reaction temperature to 70-80℃ by dropping the fourth batch of alkali solution for 40-70min; fifth step, add urea U, maintain the reaction at 70-85℃, adjust the pH value to 12.0-13.0, measure the viscosity at 50-1500mPa.s, and cool the material. Since the phenolic resin adhesive is hydroxymethylated to the benzene ring during the preparation process, the modification reaction in advance does not increase the active sites, and the effect is not obvious.

[0005] CN201210557028.6 provides a method for preparing a lignin phenolic resin prepolymer, comprising the following steps: mixing a lignin compound, a phenolic compound and an acidic catalyst, heating to 180-350°C for reaction, and obtaining a mixed reaction liquid; mixing the mixed reaction liquid with formaldehyde, and obtaining a lignin phenolic resin prepolymer after polycondensation reaction. With a phenolic compound as a solvent, the double bonds and ether bonds on the molecular chain of the lignin compound are destroyed by an acidic environment provided by an acidic catalyst under high temperature conditions of 180-350°C, thereby reducing the molecular weight of the lignin compound; at the same time, the phenol molecule is connected to the hydroxymethyl active group of the lignin, thereby increasing the chemical reaction activity of the lignin molecule, thereby increasing the reaction activity of the lignin phenolic resin prepolymer, so that the obtained lignin phenolic resin has good fluidity and heat resistance, and high strength. However, under the condition of an acidic catalyst, the ether bond structure of the lignin is destroyed to produce highly active carbon cations, which are easily condensed with other positions in the lignin structure; after being connected to the phenol molecule, the active sites of the phenol will be occupied, increasing the consumption of phenol. Summary of the invention

[0006] In view of the shortcomings of the prior art, the present invention provides a lignin-based phenolic resin adhesive and a synthesis method thereof. The present invention destroys the lignin structure in the presence of an acid, then adds a ketone reagent to avoid the formation of macromolecular lignin, and finally obtains a high-performance and environmentally friendly phenolic resin adhesive.

[0007] The method for synthesizing the lignin-based phenolic resin adhesive provided by the present invention specifically comprises the following steps:

[0008] (1) Add lignin to an acid solution, mix well, heat to 80-120°C, add a ketone reagent to react, and obtain modified lignin;

[0009] (2) Add phenol to the modified lignin prepared in step (1), control the temperature to 60-80°C, adjust the pH to 10-12, add formaldehyde solution and alkali in three batches, stop the reaction when the viscosity reaches 120-250 mPa·s, cool and obtain a lignin-based phenolic resin adhesive.

[0010] In the present invention, the lignin in step (1) is at least one of alkali lignin, enzymatic lignin, etc.

[0011] In the present invention, the mass fraction of the acid solution in step (1) is 20%-40%. The acid is preferably an inorganic acid, specifically at least one of sulfuric acid, hydrochloric acid, nitric acid, etc., preferably sulfuric acid.

[0012] In the present invention, the solid-to-liquid ratio of the lignin to the acid solution in step (1) is 1:5-10, measured in g / mL.

[0013] In the present invention, the ketone reagent in step (1) is a ketone reagent having a carbon number of not less than 4, preferably a carbon number of 4-6, and specifically can be one of butanone, cyclohexanone, methyl ethyl ketone, methyl isobutyl ketone, etc.

[0014] In the present invention, the ketone reagent in step (1) is added according to a solid-liquid ratio of lignin to ketone reagent of 1:0.1-1, measured in g / mL.

[0015] In the present invention, after the ketone reagent is added in step (1), the reaction is carried out for 1.5-4 hours.

[0016] In the present invention, the phenol in step (2) is added in a mass ratio of lignin to phenol of 1:1-4.

[0017] In the present invention, the base in step (2) is an inorganic base, specifically at least one of sodium hydroxide, potassium hydroxide, calcium hydroxide and the like.

[0018] In the present invention, the mass fraction of the formaldehyde solution in step (2) is 30%-40%.

[0019] In the present invention, the formaldehyde solution is added in step (2) in three batches. The first batch is added at a molar ratio of formaldehyde to phenol of 1-1.4:1, the second batch is the same as the first batch, and the third batch is added at a molar ratio of formaldehyde to phenol of 0.2-0.5:1.

[0020] In the present invention, after the formaldehyde solution is added for the first time in step (2), the reaction is carried out at a temperature of 80-100°C for 40-70 minutes; after the formaldehyde solution is added for the second time, the reaction is carried out at a temperature of 80-100°C for 40-70 minutes; after the formaldehyde solution is added for the third time, the reaction is carried out at 60-80°C until the solution viscosity reaches 120-250 mPa·s, then the reaction is stopped and the temperature is cooled.

[0021] The lignin-based phenolic resin adhesive of the present invention is prepared by the above-mentioned method of the present invention. In the prepared phenolic resin adhesive, the molecular weight of lignin is less than 2300, the mass content of lignin is 4%-16%, the content of ketone reagent is 0.5%-10%, the content of free formaldehyde is less than 0.4%, and the content of free phenol is less than 0.1%.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] (1) In view of the problems that lignin itself has a complex structure, a large molecular weight, and few active sites, it will degrade and condense during the reaction, and its molecular structure will change. The present invention first destroys the lignin structure in the presence of an acid, degrades the lignin molecular structure, breaks ether bonds such as α-O-4 and β-O-4, and reduces the steric hindrance effect of the lignin space structure. At this time, a ketone reagent is added at a certain temperature. On the one hand, it can prevent the α-C produced by degradation from condensing with other positions in the lignin structure, which helps to obtain a smaller lignin structure; at the same time, it increases the active sites of the reaction between lignin and formaldehyde, and finally obtains a high-performance, environmentally friendly phenolic resin adhesive with a low lignin molecular weight and low free formaldehyde and free phenol contents.

[0024] (2) Compared with phenolic compounds such as phenol and resorcinol and acid catalysts to modify lignin, the ketone reagents used in the present invention have less steric hindrance in the synthesis of phenolic resins, fewer active sites for reaction with formaldehyde, no waste of formaldehyde, and a relatively low reaction temperature.

[0025] (3) The method of the present invention is simple to operate and avoids complex process conditions such as high temperature and high pressure. DETAILED DESCRIPTION

[0026] The synthesis method and effect of the lignin-based phenolic resin adhesive of the present invention are described in detail below in conjunction with the examples. The examples are implemented based on the technical solution of the present invention, and provide detailed implementation methods and specific operation processes, but the protection scope of the present invention is not limited to the following examples.

[0027] The experimental methods in the following examples, unless otherwise specified, are all conventional methods in the art. The experimental materials used in the following examples, unless otherwise specified, were purchased from conventional biochemical reagent stores.

[0028] In the embodiments of the present invention, the free formaldehyde and free phenol indicators are measured according to GB / T 14074-2006 "Test methods for wood adhesives and resins", the bonding strength is tested by using a CMT4304 microcomputer-controlled electronic universal testing machine of Meters Industrial Systems Co., Ltd. according to GB / T 9846.3-2004, the formaldehyde emission indicator is tested according to the dryer method of GB / T 17657-2003 "Test methods for physical and chemical properties of wood-based panels and veneered wood-based panels", and the lignin molecular weight is measured by gel permeation chromatography of Malvern Panalytical.

[0029] Example 1

[0030] (1) Add 30 g of alkali lignin to 240 mL of 30% sulfuric acid solution, mix evenly, and heat to 110 °C. Add 15 mL of methyl isobutyl ketone and react for 3 h before separating the modified lignin.

[0031] (2) Add 70g of phenol to the modified lignin in step (1), control the temperature at 70°C, add sodium hydroxide to adjust the pH to 11.5, stir and mix, and add formaldehyde solution and alkali in three batches. After adding 73g of formaldehyde solution (mass fraction 37%) for the first time, add sodium hydroxide to adjust the pH value of the solution to 11.5, and react at 90°C for 60min; after adding 73g of formaldehyde solution for the second time, add sodium hydroxide to adjust the pH value of the solution to 11.5, and react at 90°C for 60min; after adding 24g of formaldehyde solution for the third time, add a small amount of sodium hydroxide to adjust the pH value of the solution to 11.5, control the temperature at 70°C, stir until the solution viscosity reaches 150mPa·s, then stop the reaction, cool and cool, and obtain a lignin-based phenolic resin adhesive. The properties of the obtained phenolic resin adhesive are shown in Table 1.

[0032] Example 2

[0033] (1) Add 30 g of alkali lignin to 150 mL of 20% sulfuric acid solution, mix evenly, and heat to 80 °C. Add 3 ml of methyl isobutyl ketone and react for 1.5 h to separate the modified lignin.

[0034] (2) Add 30g of phenol to the modified lignin in step (1), control the temperature at 60°C, add sodium hydroxide to adjust the pH to 11, stir and mix, and add formaldehyde solution and alkali in three batches. After adding 31g of formaldehyde solution for the first time, add sodium hydroxide to adjust the pH value of the solution to 11, and react at 80°C for 40min; after adding 31g of formaldehyde solution for the second time, add sodium hydroxide to adjust the pH value of the solution to 11, and react at 80°C for 40min; after adding 10.4g of formaldehyde solution for the third time, add a small amount of sodium hydroxide to adjust the pH value of the solution to 11, control the temperature at 60°C, stir until the solution viscosity reaches 150mPa·s, then stop the reaction, and cool to obtain a lignin-based phenolic resin adhesive. The properties of the obtained phenolic resin adhesive are shown in Table 1.

[0035] Example 3

[0036] (1) Add 30 g of alkali lignin to 300 mL of 40% sulfuric acid solution, mix evenly, and heat to 120 °C. Add 30 mL of methyl isobutyl ketone and react for 4 h to obtain modified lignin.

[0037] (2) Add 120g of phenol to the modified lignin in step (1), control the temperature at 80°C, add sodium hydroxide to adjust the pH to 12, stir and mix, and add formaldehyde solution and alkali in three batches. After adding 145g of formaldehyde solution for the first time, add sodium hydroxide to adjust the pH value of the solution to 12, and react at 80°C for 70min; after adding 145g of formaldehyde solution for the second time, add sodium hydroxide to adjust the pH value of the solution to 12, and react at 80°C for 70min; after adding 51.7g of formaldehyde solution for the third time, add a small amount of sodium hydroxide to adjust the pH value of the solution to 12, control the temperature at 80°C, stir until the solution viscosity reaches 150mPa·s, then stop the reaction, cool and cool down to obtain a lignin-based phenolic resin adhesive. The properties of the obtained phenolic resin adhesive are shown in Table 1.

[0038] Example 4

[0039] The synthesis process is the same as that of Example 1, except that the lignin used in step (1) is enzymatically hydrolyzed lignin. The properties of the prepared phenolic resin adhesive are shown in Table 1.

[0040] Example 5

[0041] The synthesis process is the same as that of Example 1, except that the ketone reagent used in step (1) is methyl ethyl ketone. The properties of the prepared phenolic resin adhesive are shown in Table 1.

[0042] Example 6

[0043] The synthesis process is the same as that of Example 1, except that the ketone reagent used in step (1) is butanone. The properties of the prepared phenolic resin adhesive are shown in Table 1.

[0044] Example 7

[0045] The synthesis process is the same as that of Example 1, except that the ketone reagent used in step (1) is cyclohexanone. The properties of the prepared phenolic resin adhesive are shown in Table 1.

[0046] Comparative Example 1

[0047] The synthesis process is the same as that of Example 1, except that sodium hydroxide is used instead of sulfuric acid in step (1). The properties of the prepared phenolic resin adhesive are shown in Table 1.

[0048] Comparative Example 2

[0049] The synthesis process is the same as that of Example 1. The difference is that no ketone reagent is added in step (1). The properties of the prepared phenolic resin adhesive are shown in Table 1.

[0050] Comparative Example 3

[0051] The synthesis process is the same as that of Example 1. The difference is that in step (1), lignin is added to the acid solution, mixed and heated to 180° C. The properties of the prepared phenolic resin adhesive are shown in Table 1.

[0052] Comparative Example 4

[0053] The synthesis process is the same as that of Example 1. The difference is that formaldehyde is used instead of ketone reagent in step (1). The properties of the prepared phenolic resin adhesive are shown in Table 1.

[0054] Comparative Example 5

[0055] The synthesis process is the same as that of Example 1. The difference is that the ketone reagent used in step (1) is acetone. The properties of the prepared phenolic resin adhesive are shown in Table 1.

[0056] Comparative Example 6

[0057] The synthesis process is the same as in Example 1, except that in step (2), phenol and formaldehyde are added in batches. The properties of the prepared phenolic resin adhesive are shown in Table 1.

[0058] Comparative Example 7

[0059] The synthesis process is the same as that of Example 1, except that phenol is used in step (1) instead of the ketone reagent. The properties of the prepared phenolic resin adhesive are shown in Table 1.

[0060] Table 1 Test results of adhesives prepared in Examples and Comparative Examples

[0061]

[0062] It can be seen from Table 1 that the adhesive prepared by the method of the present invention has better comprehensive performance.

Claims

1. A method for synthesizing a lignin-based phenolic resin adhesive, characterized in that The following steps are involved: (1) adding lignin to an acid solution, wherein the mass fraction of the acid solution is 20%-40%, and the solid-liquid ratio of lignin to the acid solution is 1:5-10, measured in g / mL; heating to 80-120° C., adding a ketone reagent for reaction, wherein the ketone reagent is added according to the solid-liquid ratio of lignin to the ketone reagent of 1:0.1-1, measured in g / mL; obtaining modified lignin; (2) adding phenol to the modified lignin of step (1), controlling the temperature at 60-80° C., adjusting the pH at 10-12, adding formaldehyde solution and alkali in three batches, stopping the reaction when the viscosity reaches 120-250 mPa·s, cooling, and obtaining a lignin-based phenolic resin adhesive; the ketone reagent is at least one of cyclohexanone, methyl ethyl ketone, and methyl isobutyl ketone.

2. The method according to claim 1, characterized in that: The lignin in step (1) is at least one of alkali lignin and enzymatic lignin.

3. The method according to claim 1, characterized in that: The acid in step (1) is an inorganic acid.

4. The method according to claim 3, characterized in that: The inorganic acid in step (1) is at least one of sulfuric acid, hydrochloric acid and nitric acid.

5. The method according to claim 4, characterized in that: The inorganic acid in step (1) is sulfuric acid.

6. The method according to claim 1, characterized in that: After adding the ketone reagent in step (1), the reaction is carried out for 1.5-4.0 hours.

7. The method according to claim 1, characterized in that: The phenol in step (2) is added in a mass ratio of lignin to phenol of 1:1-4.

8. The method according to claim 1, characterized in that: The base in step (2) is an inorganic base.

9. The method according to claim 8, characterized in that: The alkali in step (2) is at least one of sodium hydroxide, potassium hydroxide and calcium hydroxide.

10. The method according to claim 1, characterized in that: The mass fraction of the formaldehyde solution in step (2) is 30%-40%.

11. The method according to claim 1 or 10, characterized in that: In step (2), formaldehyde solution is added in three batches. The first batch is added at a molar ratio of formaldehyde to phenol of 1-1.4:1, the second batch is the same as the first batch, and the third batch is added at a molar ratio of formaldehyde to phenol of 0.2-0.5:

1.

12. The method according to claim 1, characterized in that: In step (2), after the formaldehyde solution is added for the first time, the reaction is carried out at a temperature of 80-100° C. for 40-70 minutes; after the formaldehyde solution is added for the second time, the reaction is carried out at a temperature of 80-100° C. for 40-70 minutes; after the formaldehyde solution is added for the third time, the reaction is carried out at 60-80° C. until the solution viscosity reaches 120-250 mPa·s, and then the reaction is stopped.

13. A lignin-based phenolic resin adhesive, characterized in that The adhesive is prepared by the method described in any one of claims 1 to 12.

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