I. Preface

Acid value refers to the mass number of KOH or NaOH consumed by the acid component in each gram of the sample. The acid value of resin is one of the important indicators of resin. Generally speaking, the higher the acid value, the stronger the adhesion to metal substrates, the better the wetting and dispersion of pigments, and the higher the crosslinking degree and speed of baking varnish.

This method uses ethanol as the solvent to dissolve the sample and titrates it with a standard potassium hydroxide solution. After determining the endpoint by the color of the indicator, an endpoint titration plan is formulated. It replaces the traditional manual titration, is stable and fast, improves safety, and reduces the contact between people and reagents.

Ii. Instruments and Reagents

2.1 Instruments

JH-T6 fully automatic potentiometric titrator, PH composite electrode, analytical balance, etc

2.2. Reagents

Sodium hydroxide (0.1014mol/L), anhydrous ethanol, phenolphthalein indicator.

Iii. Experimental Methods

3.1 Preparation for the Experiment

The electrode slope correction was carried out using calibration solutions with PH values of 4.01, 7.00, and 9.21 respectively to ensure that the electrode slope was above 90%.

3.2 Confirmation of the Experimental Endpoint

Weigh approximately 0.8g of the sample, dissolve it in anhydrous ethanol, then add 5 drops of phenolphthalein indicator. Titrate manually until the phenolphthalein indicator changes color. Place the PH composite electrode in the solution and determine the PH value at the color change point to determine the titration endpoint of the endpoint titration method.

3.3 Sample testing

Weigh 0.8g of the sample, accurate to 0.0001g, and place it in a titration cup. Dissolve it in an appropriate amount of anhydrous ethanol, stir evenly, and then use a pH composite electrode as the working electrode. Titrate with 0.1M sodium hydroxide until the color change endpoint of the indicator appears. At the same time, conduct a blank test.

The parameters of the titrator are set as shown in Table 1

Table 1 Titration Parameter Settings

Iv. Results and Discussion

4.1 Experimental Results

The experimental results are shown in Table 2

Table 2 Test Results

4.2. Conclusion

The acid value of the sample tested this time is 22.14mgKOH/g. The data has good repeatability, is safe and efficient, and can well replace manual detection.