Method for measuring hydroxyl value content in phenolic resin

Abstract

The invention provides a method for determining the hydroxyl value content in phenolic resin, and belongs to the technical field of chemical detection. The determination method comprises the following steps: 1) dissolving a sample to be determined to obtain a solution of the sample to be determined; 2) mixing acetic anhydride and a composite acylation catalyst with the solution of the product to be detected, and carrying out acylation reaction; (3) 5-10 minutes before the acylation reaction is finished, adding n-butyl alcohol, after the acylation reaction is finished, adding n-butyl alcohol and an indicator, titrating by adopting a sodium hydroxide standard solution under a stirring condition until the solution is pink and does not fade for 15 seconds, namely a titration end point, and recording the volume of the sodium hydroxide standard solution consumed for titration as V1; and 4) calculating the content of the hydroxyl value in the phenolic resin. The determination method provided by the invention can determine the content of the hydroxyl value in the phenolic resin, and is accurate, efficient, simple and convenient in detection and good in repeatability.

Description

Technical Field

[0001] The invention belongs to the technical field of chemical detection, and in particular relates to a method for determining the hydroxyl value content in a phenolic resin. Background Art

[0002] Phenolic resin has excellent heat resistance, mechanical properties and chemical stability, and is widely used in electronic packaging materials, aerospace coatings, high-performance composite materials and other fields. As an important parameter of phenolic resin, hydroxyl value is closely related to the curing reaction activity, crosslinking density and performance of the final product. Accurate determination of the hydroxyl value of phenolic resin is extremely critical for its quality control, product development and formulation design.

[0003] Traditional methods for measuring hydroxyl value mainly include phthalic anhydride-pyridine method, infrared spectroscopy and acetic anhydride-pyridine method. However, phenolic resin has a complex structure and there are multiple active groups in the molecule. The traditional acetic anhydride method for measuring hydroxyl value has some limitations when applied to phenolic resin. For example, side reactions are prone to occur during the acetic anhydride acylation reaction, resulting in inaccurate measurement results. At the same time, the traditional method is not fine enough for the control of reaction conditions, such as the temperature, time, emulsification of hydrolysis and catalyst dosage of the acylation reaction are not optimized, so that the repeatability and accuracy of the measurement are poor, and pyridine is volatile and toxic, and long-term contact affects health. In addition, during the titration process, there is also a certain subjectivity in the selection of indicators and the end point judgment, which is easy to introduce errors. CN101430308B discloses a pyridine-free esterification reagent for measuring the hydroxyl value of polyols by anhydride method, but the experimental steps of this method are complicated, and the data parallelism is not good, which cannot meet market demand. Summary of the invention

[0004] The invention provides a method for determining the hydroxyl value content in a phenolic resin. The determination method provided by the invention can determine the hydroxyl value content in the phenolic resin, and the detection is accurate, efficient, simple and has good repeatability.

[0005] In order to achieve the above object, the present invention provides a method for determining the hydroxyl value content in a phenolic resin, comprising the following steps:

[0006] 1) dissolving the sample to be tested to obtain a test solution;

[0007] 2) mixing acetic anhydride, a composite acylation catalyst and a solution of the sample to be tested to carry out an acylation reaction;

[0008] The composite acylation catalyst is a mixture of p-toluenesulfonic acid and N,N-dimethylaniline, and the molar ratio of p-toluenesulfonic acid to N,N-dimethylaniline is 1:1 to 1:2;

[0009] 3) 5 to 10 minutes before the end of the acylation reaction, add n-butanol. After the acylation reaction is completed, add n-butanol and an indicator, and titrate with a sodium hydroxide standard solution under stirring until the solution turns pink and remains pink for 15 seconds, which is the titration end point. Record the volume of the sodium hydroxide standard solution consumed in the titration, which is recorded as V1;

[0010] 4) Calculate the content of hydroxyl value in phenolic resin, the specific formula is:

[0011] IOH=(V1*c*56.10) / m

[0012] in:

[0013] IOH: hydroxyl value content in phenolic resin, in mg / g;

[0014] V1: The volume of sodium hydroxide standard titration solution consumed by the sample, in mL;

[0015] c: concentration of sodium hydroxide standard titration solution, in mol / L;

[0016] m: mass of the sample, in g;

[0017] 56.10: Relative molecular mass of potassium hydroxide.

[0018] Preferably, a blank test is performed using a phenolic resin containing no hydroxyl value, and the specific operation is the same as steps 1) to 3) in the above scheme. After the titration is completed, the volume of the sodium hydroxide standard solution consumed in the titration is recorded as V0;

[0019] Combined with the blank test, the hydroxyl value content in the phenolic resin is calculated. The specific formula is:

[0020] IOH=[(V0-V1)*c*56.10] / m

[0021] Where: V0: the volume of sodium hydroxide standard titration solution consumed by the blank sample, in mL.

[0022] Preferably, step 1) further comprises drying the sample to be tested before dissolving the sample to be tested; the drying method is vacuum drying; the vacuum drying temperature is 80-100° C., and the vacuum drying time is 1-2 hours.

[0023] Preferably, in step 1), acetone is used to dissolve the sample to be tested; the mass volume ratio of the sample to be tested to acetone is 1-2 g:10-25 mL.

[0024] Preferably, in step 2), the volume mass ratio of acetic anhydride to phenolic resin is 2.5-10 mL:1 g.

[0025] Preferably, inert gas is used for protection during the acylation reaction in step 2); the temperature during the acylation reaction is 100-150° C. and the time is 1-3 hours.

[0026] Preferably, in step 3), the ratio of the volume of n-butanol added 5 to 10 minutes before the end of the acylation reaction to the mass of the sample to be tested is 15 to 10 mL: 1 to 2 g; and the ratio of the volume of n-butanol added after the end of the acylation reaction to the mass of the sample to be tested is 10 to 50 mL: 1 to 2 g.

[0027] Preferably, the concentration of the sodium hydroxide standard solution in step 3) is 0.5-2.0 mol / L.

[0028] Preferably, the indicator in step 3) is a mixed solution of pyridine, methanol and starch; based on 100 parts, the mass ratio of pyridine, methanol and starch is 1-9:90:9-1.

[0029] Preferably, in step 3), during the titration process, a potentiometric titrator is used to assist in determining the titration endpoint.

[0030] Compared with the prior art, the advantages and positive effects of the present invention are:

[0031] The method for determining the hydroxyl value content in phenolic resin provided by the present invention uses acetic anhydride to react specifically with the hydroxyl group in the phenolic resin, has high selectivity for acetylation of the hydroxyl group, is less interfered by other functional groups, can accurately determine the hydroxyl value in the phenolic resin, and provides a reliable basis for evaluating its performance and quality. Moreover, acetic anhydride is relatively stable in chemical properties, is not easy to decompose and deteriorate at room temperature and pressure, is easy to store and use, and can maintain the effectiveness of the reagent for a long time, reducing the risk of inaccurate test results due to reagent problems. At the same time, a mixture of p-toluenesulfonic acid and N, N-dimethylaniline is used as a composite acylation catalyst, p-toluenesulfonic acid catalyzes, promotes the reaction of hydroxyl groups with the acylating agent, and accelerates the reaction rate; N, N-dimethylaniline is a neutralizer, which can neutralize the acid produced by the reaction to prevent the hydroxyl value from being inaccurately measured due to the presence of acidic substances in the sample, and the two work together to ensure the accuracy of the measurement results.

[0032] The determination method provided by the present invention has relatively simple experimental steps, does not require complicated instruments and equipment and cumbersome sample pretreatment processes, is easy to master and operate, can be carried out in general laboratories, and has high test efficiency.

[0033] The determination method provided by the present invention is not only suitable for the determination of the hydroxyl values ​​of different types of phenolic resins, but can also be used for quality control in the production process of phenolic resins and evaluation of product performance, etc. It has a wide range of applications and also plays an important guiding role in studying the synthesis process of phenolic resins, optimizing reaction conditions, etc. DETAILED DESCRIPTION

[0034] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments 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.

[0035] The present invention provides a method for determining the hydroxyl value content in a phenolic resin, comprising the following steps:

[0036] 1) dissolving the sample to be tested to obtain a test solution;

[0037] 2) mixing acetic anhydride, a composite acylation catalyst and a solution of the sample to be tested to carry out an acylation reaction;

[0038] The composite acylation catalyst is a mixture of p-toluenesulfonic acid and N,N-dimethylaniline, and the molar ratio of p-toluenesulfonic acid to N,N-dimethylaniline is 1:1 to 1:2;

[0039] 3) 5 to 10 minutes before the end of the acylation reaction, add n-butanol. After the acylation reaction is completed, add n-butanol and an indicator, and titrate with a sodium hydroxide standard solution under stirring until the solution turns pink and remains pink for 15 seconds, which is the titration end point. Record the volume of the sodium hydroxide standard solution consumed in the titration, which is recorded as V1;

[0040] 4) Calculate the content of hydroxyl value in phenolic resin, the specific formula is:

[0041] IOH=(V1*c*56.10) / m

[0042] in:

[0043] IOH: hydroxyl value content in phenolic resin, in mg / g;

[0044] V1: The volume of sodium hydroxide standard titration solution consumed by the sample, in mL;

[0045] c: concentration of sodium hydroxide standard titration solution, in mol / L;

[0046] m: mass of the sample, in g;

[0047] 56.10: Relative molecular mass of potassium hydroxide.

[0048] The present invention dissolves the sample to be tested to obtain a solution of the sample to be tested. In the present invention, the sample to be tested is preferably dried before being dissolved. In the present invention, the drying method is preferably vacuum drying; the temperature of the vacuum drying is preferably 80 to 100°C, and the time of the vacuum drying is preferably 1 to 2 hours. The present invention can remove moisture and volatile solvents in the sample by drying the sample to be tested. In the present invention, acetone is preferably used to dissolve the sample to be tested; the mass volume ratio of the sample to be tested to acetone is preferably 1 to 2g:10 to 25mL.

[0049] After obtaining the solution of the product to be tested, the present invention mixes acetic anhydride, a composite acylation catalyst and the solution of the product to be tested to carry out an acylation reaction; the composite acylation catalyst is a mixture of p-toluenesulfonic acid and N,N-dimethylaniline, and the molar ratio of p-toluenesulfonic acid to N,N-dimethylaniline is 1:1-1:2. In the present invention, the addition amount of the composite acylation catalyst is preferably 0.1%-10% of the mass of the phenolic resin. In the present invention, the volume mass ratio of the acetic anhydride to the phenolic resin is preferably 2.5-10mL:1g. In the present invention, acetic anhydride is used for the acylation reaction, and the chemical properties of acetic anhydride are relatively stable, and it is not easy to decompose and deteriorate at room temperature and pressure, which is convenient for storage and use, and can maintain the effectiveness of the reagent for a long time, reducing the risk of inaccurate test results due to reagent problems. At the same time, acetic anhydride can react specifically with the hydroxyl group in the phenolic resin, has high acetylation selectivity for the hydroxyl group, is less interfered by other functional groups, and can accurately determine the hydroxyl value in the phenolic resin, providing a reliable basis for evaluating its performance and quality. In the present invention, an inert gas is preferably used for protection during the acylation reaction; the temperature during the acylation reaction is preferably 100-150°C, and the time is preferably 1-3 hours. In the present invention, the reaction is carried out under the protection of an inert gas to prevent moisture and impurities in the air from interfering with the reaction. The present invention adds a composite acylation catalyst, wherein p-toluenesulfonic acid acts as a catalyst to promote the reaction of the hydroxyl group with the acylating agent and accelerate the reaction rate; N,N-dimethylaniline is a neutralizer that can neutralize the acid produced by the reaction to prevent the hydroxyl value from being inaccurately measured due to the presence of acidic substances in the sample, and the two work together to ensure the accuracy of the measurement results.

[0050] After the acylation reaction, the present invention adds n-butanol 5 to 10 minutes before the end of the acylation reaction. After the acylation reaction is completed, n-butanol and an indicator are added, and titration is performed with a sodium hydroxide standard solution under stirring until the solution turns pink and remains unfaded for 15 seconds, which is the titration end point. The volume of the sodium hydroxide standard solution consumed in the titration is recorded and recorded as V1. In the present invention, the volume ratio of n-butanol added 5 to 10 minutes before the end of the acylation reaction to the mass ratio of the sample to be tested is preferably 15 to 10 mL: 1 to 2 g; the volume ratio of n-butanol added after the acylation reaction is completed to the mass ratio of the sample to be tested is preferably 10 to 50 mL: 1 to 2 g. In the present invention, the addition of n-butanol can prevent the occurrence of hydrolysis and emulsification reaction. In the present invention, the concentration of the sodium hydroxide standard solution is preferably 0.5 to 2 mol / L. In the present invention, the indicator is preferably a mixed solution of pyridine, methanol and starch; based on 100 parts, the mass ratio of pyridine, methanol and starch is preferably 1 to 9: 90: 9 to 1. In the present invention, during the titration process, a potentiometric titrator is preferably used to assist in determining the titration endpoint. In the present invention, during the titration process, a potentiometric titrator is used to assist in determining the titration endpoint, which can improve the accuracy of endpoint determination.

[0051] In the present invention, in order to further improve the accuracy of detection, it is preferred to use a phenolic resin without hydroxyl value for a blank test. The specific operation is the same as steps 1) to 3) in the above scheme. After the titration is completed, the volume of the sodium hydroxide standard solution consumed in the titration is recorded and recorded as V0.

[0052] Combined with the blank test, the hydroxyl value content in the phenolic resin is calculated. The specific formula is:

[0053] IOH=[(V0-V1)*c*56.10] / m

[0054] Where: V0: the volume of sodium hydroxide standard titration solution consumed by the blank sample, in mL.

[0055] In order to further illustrate the present invention, the technical solutions provided by the present invention are described in detail below in conjunction with embodiments, but they should not be construed as limiting the protection scope of the present invention.

[0056] Example 1

[0057] The phenolic resin sample (the hydroxyl value in the phenolic resin sample is 88) was placed in a vacuum drying oven at 80°C for 2h to remove moisture and volatile solvents in the sample, and then placed in a drying container. Weigh 1g (1g here is a rough value, only for the convenience of weighing acetone, acetic anhydride and composite acylation catalyst, the actual accurate measurement value is shown in Table 1) and place the dried sample in a reaction conical flask, and add 10mL of acetone to completely dissolve the sample. Use a pipette to accurately transfer 10mL of acetic anhydride and 0.5mL of a composite acylation catalyst solution with a mass concentration of 1% (the molar ratio of p-toluenesulfonic acid and N,N-dimethylaniline in the composite acylation catalyst solution is 1:1). Moisten the condenser joint with pyridine, connect the condenser to the conical flask, shake the material in the flask to make it lower than the oil bath surface, and carry out acylation reaction in a 100°C oil bath. After heating for 10 minutes, shake the reaction conical flask evenly and continue heating for 1 hour. During the reaction, use nitrogen for protection to prevent moisture and impurities in the air from interfering with the reaction.

[0058] 5 minutes before the end of the acylation reaction, add 10 mL of n-butanol into the conical flask through a condenser and shake well. After the acylation reaction is completed, cool the reaction conical flask and its materials to room temperature, add 10 mL of n-butanol, remove the condenser, rinse the ground glass joint with water, add 3 drops of indicator into the reaction conical flask (the indicator is a mixed indicator prepared with pyridine: methanol: starch, and the mass ratio of pyridine, methanol and starch is 1:18:1), and titrate with 1.0 mol / L sodium hydroxide standard titration solution under stirring. The solution turns pink and remains pink for 15 seconds without fading, which is the end point. The volume is recorded as V1.

[0059] Example 2

[0060] The phenolic resin sample (the hydroxyl value content of the phenolic resin sample is 88) was placed in a vacuum drying oven at 80°C for 1 hour to remove the moisture and volatile solvent in the sample, and then placed in a drying container. Weigh 1g of the dried sample and place it in a reaction conical flask, and add 5mL of acetone to completely dissolve the sample. Use a pipette to accurately transfer 5mL of acetic anhydride and 0.3mL of a composite acylation catalyst solution with a mass concentration of 1% (the molar ratio of p-toluenesulfonic acid and N,N-dimethylaniline in the composite acylation catalyst solution is 1:2). Wet the condenser joint with pyridine, connect the condenser to the conical flask, shake the material in the flask, and the material in the flask is below the oil bath surface. Acylation reaction is carried out in an oil bath at 150°C. After heating for 10 minutes, shake the reaction conical flask evenly and continue to heat for 1 hour. During the reaction, nitrogen is used for protection to prevent moisture and impurities in the air from interfering with the reaction.

[0061] 10 minutes before the end of the acylation reaction, add 10 mL of n-butanol into the conical flask through a condenser and shake well. After the acylation reaction is completed, cool the reaction conical flask and its materials to room temperature, add 10 mL of n-butanol, remove the condenser, rinse the ground glass joint with water, add 3 drops of indicator into the reaction conical flask (the indicator is a mixed indicator prepared with pyridine: methanol: starch, and the mass ratio of pyridine, methanol and starch is 1:18:1), and titrate with 1.0 mol / L sodium hydroxide standard titration solution under stirring. The solution turns pink and remains pink for 15 seconds without fading, which is the end point. The volume is recorded as V1.

[0062] Example 3

[0063] The phenolic resin sample (the hydroxyl value content of the phenolic resin sample is 88) was placed in a vacuum drying oven at 80°C for 1 hour to remove the moisture and volatile solvent in the sample, and then placed in a drying container. Weigh 1g of the dried sample and place it in a reaction conical flask, and add 15mL of acetone to dissolve the sample completely. Use a pipette to accurately transfer 5mL of acetic anhydride and 1.0mL of the composite acylation catalyst solution (the molar ratio of p-toluenesulfonic acid and N,N-dimethylaniline in the composite acylation catalyst solution is 1:1). Wet the condenser joint with pyridine, and connect the condenser to the conical flask, shake the material in the flask, and the material in the flask is lower than the oil bath surface. The acylation reaction is carried out in an oil bath at 100°C. After heating for 10 minutes, shake the reaction conical flask evenly and continue to heat for 1 hour. During the reaction, nitrogen is used for protection to prevent moisture and impurities in the air from interfering with the reaction.

[0064] 5 minutes before the end of the acylation reaction, add 10 mL of n-butanol into the conical flask through a condenser and shake well. After the acylation reaction is completed, cool the reaction conical flask and its materials to room temperature, add 10 mL of n-butanol, remove the condenser, rinse the ground glass joint with water, add 3 drops of indicator into the reaction conical flask (the indicator is a mixed indicator prepared with pyridine: methanol: starch, and the mass ratio of pyridine, methanol and starch is 1:18:1), and titrate with 1.0 mol / L sodium hydroxide standard titration solution under stirring. The solution turns pink and remains pink for 15 seconds without fading, which is the end point. The volume is recorded as V1.

[0065] Comparative Example 1

[0066] The difference from Example 1 is that p-toluenesulfonic acid is not added, and other operations are the same as those in Example 1. The specific operations are as follows:

[0067] The phenolic resin sample (the hydroxyl value of the phenolic resin sample is 88) was placed in a vacuum drying oven at 80°C for 2 hours to remove moisture and volatile solvents in the sample, and then placed in a drying container. Weigh 1g of the dried sample and place it in a reaction conical flask, and add 10mL of acetone to completely dissolve the sample. Use a pipette to accurately transfer 10mL of acetic anhydride and 0.5mL of a 1% N,N-dimethylaniline solution. Wet the condenser joint with pyridine, and connect the condenser to the conical flask. Shake the material in the flask so that the material in the flask is below the oil bath surface. Acylation reaction is carried out in an oil bath at 100°C. After heating for 10 minutes, shake the reaction conical flask evenly and continue to heat for 1 hour. During the reaction, nitrogen is used for protection to prevent moisture and impurities in the air from interfering with the reaction.

[0068] 5 minutes before the end of the acylation reaction, add 10 mL of n-butanol into the conical flask through a condenser and shake well. After the acylation reaction is completed, cool the reaction conical flask and its materials to room temperature, add 10 mL of n-butanol, remove the condenser, rinse the ground glass joint with water, add 3 drops of indicator into the reaction conical flask (the indicator is a mixed indicator prepared with pyridine, methanol and starch, and the mass ratio of pyridine, methanol and starch is 1:18:1), and titrate with 1.0 mol / L sodium hydroxide standard titration solution under stirring. The solution turns pink and remains pink for 15 seconds without fading, which is the end point. The volume is recorded as V1.

[0069] Comparative Example 2

[0070] The difference from Example 1 is that N,N-dimethylaniline is not added, and the other operations are the same as those in Example 1. The specific operations are as follows:

[0071] Place the phenolic resin sample (the hydroxyl value content in the phenolic resin sample is 88) in a vacuum drying oven at 80°C for 2 hours to remove moisture and volatile solvents in the sample, and then place it in a drying container. Weigh 1g of the dried sample and place it in a reaction conical flask, and add 10mL of acetone to completely dissolve the sample. Use a pipette to accurately transfer 10mL of acetic anhydride and 0.5mL of 1% p-toluenesulfonic acid. Moisten the condenser joint with pyridine, and connect the condenser to the conical flask. Shake the material in the flask so that the material in the flask is lower than the oil bath surface. Perform the acylation reaction in an oil bath at 100°C. After heating for 10 minutes, shake the reaction conical flask evenly and continue heating for 1 hour. During the reaction, use nitrogen for protection to prevent moisture and impurities in the air from interfering with the reaction.

[0072] 5 minutes before the end of the acylation reaction, add 10 mL of n-butanol into the conical flask through a condenser and shake well. After the acylation reaction is completed, cool the reaction conical flask and its materials to room temperature, add 10 mL of n-butanol, remove the condenser, rinse the ground glass joint with water, add 3 drops of indicator into the reaction conical flask (the indicator is a mixed indicator prepared with pyridine: methanol: starch, and the mass ratio of pyridine, methanol and starch is 1:18:1), and titrate with 1.0 mol / L sodium hydroxide standard titration solution under stirring. The solution turns pink and remains pink for 15 seconds without fading, which is the end point. The volume is recorded as V1.

[0073] Comparative Example 3

[0074] The difference from Example 1 is that deionized water is used instead of n-butanol. The other operations are the same as those in Example 1. The specific operations are as follows:

[0075] The phenolic resin sample (the hydroxyl value content of the phenolic resin sample is 88) was placed in a vacuum drying oven at 80°C for 2h to remove the moisture and volatile solvent in the sample, and then placed in a drying container. Weigh 1g of the dried sample and place it in a reaction conical flask, and add 10mL of acetone to dissolve the sample completely. Use a pipette to accurately transfer 10mL of acetic anhydride and 0.5mL of a composite acylation catalyst solution with a mass concentration of 1% (the molar ratio of p-toluenesulfonic acid and N,N-dimethylaniline in the composite acylation catalyst solution is 1:1). Wet the condenser joint with pyridine, connect the condenser to the conical flask, shake the material in the flask, and the material in the flask is lower than the oil bath surface. The acylation reaction is carried out in an oil bath at 100°C. After heating for 10min, shake the reaction conical flask evenly and continue to heat for 1h. During the reaction, nitrogen is used for protection to prevent moisture and impurities in the air from interfering with the reaction.

[0076] 5 minutes before the end of the acylation reaction, add 10 mL of deionized water into the conical flask through the condenser and shake well. After the acylation reaction is completed, cool the reaction conical flask and its materials to room temperature, add 10 mL of deionized water, remove the condenser, rinse the ground glass joint with water, add 3 drops of indicator into the reaction conical flask (the indicator is a mixed indicator prepared with pyridine: methanol: starch, and the mass ratio of pyridine, methanol and starch is 1:18:1), and titrate with 1.0 mol / L sodium hydroxide standard titration solution under stirring. The solution turns pink and remains pink for 15 seconds without fading, which is the end point. The volume is recorded as V1.

[0077] Blank control:

[0078] Place the phenolic resin sample (phenolic resin sample does not contain hydroxyl value) in a vacuum drying oven at 80℃ for 2h to remove moisture and volatile solvents in the sample, and then place it in a drying container. Weigh 1g of the dried sample and place it in a reaction conical flask, add 10mL of acetone to dissolve the sample completely. Use a pipette to accurately transfer 10mL of acetic anhydride and 0.5mL of the composite acylation catalyst solution (the molar ratio of p-toluenesulfonic acid and N,N-dimethylaniline in the composite acylation catalyst solution is 1:1). Wet the condenser joint with pyridine, connect the condenser to the conical flask, shake the material in the flask, the material in the flask is lower than the oil bath surface, and perform the acylation reaction in a 100℃ oil bath. After heating for 10min, shake the reaction conical flask evenly and continue to heat for 1h. During the reaction, nitrogen is used for protection to prevent moisture and impurities in the air from interfering with the reaction.

[0079] 5 minutes before the end of the acylation reaction, add 10 mL of n-butanol into the conical flask through a condenser and shake well. After the acylation reaction is completed, cool the reaction conical flask and its materials to room temperature, add 10 mL of n-butanol, remove the condenser, rinse the ground glass joint with water, add 3 drops of indicator into the reaction conical flask (the indicator is a mixed indicator prepared with pyridine: methanol: starch, and the mass ratio of pyridine, methanol and starch is 1:18:1), and titrate with a standard sodium hydroxide solution. When the solution is titrated with a 1.0 mol / L sodium hydroxide standard titration solution under stirring and turns pink, and the color does not fade for 15 seconds, it is the end point, and the volume is recorded as V0.

[0080] Note: Each embodiment and comparative example was tested twice, and the actual weighed sample mass is shown in Table 1. The sample mass is recorded as 1 g in each embodiment and comparative example only for the convenience of weighing the amount of acetone, acetic anhydride and composite acylation catalyst.

[0081] The hydroxyl value content of the phenolic resin in the examples and comparative examples is specifically shown in Table 1.

[0082] Table 1

[0083]

[0084] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for determining the hydroxyl value content in a phenolic resin, characterized in that: The steps include: 1) dissolving the sample to be tested to obtain a test solution; 2) mixing acetic anhydride, a composite acylation catalyst and a solution of the sample to be tested to carry out an acylation reaction; The composite acylation catalyst is a mixture of p-toluenesulfonic acid and N,N-dimethylaniline, and the molar ratio of p-toluenesulfonic acid to N,N-dimethylaniline is 1:1 to 1:2; 3) 5 to 10 minutes before the end of the acylation reaction, add n-butanol. After the acylation reaction is completed, add n-butanol and an indicator, and titrate with a sodium hydroxide standard solution under stirring until the solution turns pink and remains pink for 15 seconds, which is the titration end point. Record the volume of the sodium hydroxide standard solution consumed in the titration, which is recorded as V1; 4) Calculate the content of hydroxyl value in phenolic resin, the specific formula is: IOH=(V1*c*56.10) / m in: IOH: hydroxyl value content in phenolic resin, in mg / g; V1: The volume of sodium hydroxide standard titration solution consumed by the sample, in mL; c: concentration of sodium hydroxide standard titration solution, in mol / L; m: mass of the sample, in g; 56.10: Relative molecular mass of potassium hydroxide.

2. The method according to claim 1, characterized in that: The method further comprises performing a blank test using a phenolic resin having no hydroxyl value, wherein the specific operations are the same as steps 1) to 3) in claim 1, and after the titration is completed, recording the volume of the sodium hydroxide standard solution consumed in the titration, which is recorded as V0; Combined with the blank test, the hydroxyl value content in the phenolic resin is calculated. The specific formula is: IOH=[(V0-V1)*c*56.10] / m Where: V0: the volume of sodium hydroxide standard titration solution consumed by the blank sample, in mL.

3. The method according to claim 1, characterized in that Step 1) also includes drying the sample to be tested before dissolving it; the drying method is vacuum drying; the vacuum drying temperature is 80-100° C., and the vacuum drying time is 1-2 hours.

4. The method according to claim 1, characterized in that: In step 1), acetone is used to dissolve the sample to be tested; the mass volume ratio of the sample to be tested to acetone is 1-2 g:10-25 mL.

5. The method according to claim 1, characterized in that In step 2), the volume mass ratio of acetic anhydride to phenolic resin is 2.5-10 mL:1 g.

6. The method according to claim 1, characterized in that In the step 2), an inert gas is used for protection during the acylation reaction; the temperature of the acylation reaction is 100-150° C. and the time is 1-3 hours.

7. The method according to claim 1, characterized in that In step 3), the volume ratio of n-butanol added 5 to 10 minutes before the end of the acylation reaction to the mass ratio of the sample to be tested is 15 to 10 mL: 1 to 2 g; the volume ratio of n-butanol added after the end of the acylation reaction to the mass ratio of the sample to be tested is 10 to 50 mL: 1 to 2 g.

8. The method according to claim 1, characterized in that: The concentration of the sodium hydroxide standard solution in step 3) is 0.5-2.0 mol / L.

9. The method according to claim 1, characterized in that: In step 3), the indicator is a mixed solution of pyridine, methanol and starch; based on 100 parts, the mass ratio of pyridine, methanol and starch is 1-9:90:9-1.

10. The method according to claim 1, characterized in that In step 3), during the titration process, a potentiometric titrator is used to assist in determining the titration endpoint.

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