Study on the determination method of acid value of

Research on the acid value determination method of acrylic emulsion

Research on the acid value determination method of acrylic emulsion

December 7, 2018

0 Introduction

water based coatings use water as solvent or dispersion medium, do not add volatile organic solvents, in addition to the characteristics of general coatings, they also have the characteristics of no odor, low toxicity and not easy to burn, so they have become a research hotspot and received extensive attention []. According to the difference of coating base resin, waterborne coatings can be divided into epoxy, polyurethane, acrylate, alkyd and other types [5]. At present, waterborne polyurethane coatings and waterborne acrylic coatings are widely used

Chen Jinlian et al. [6] used the pre emulsified semi continuous seed lotion polymerization method to prepare acrylic micro lotion with high hydroxyl content with excellent core/shell structure performance. In the preparation process of lotion, there is an optimal amount of carboxyl monomer, and the coagulation rate is improved when it is too high or too low; The carboxyl content has a great influence on the viscosity of lotion. When the carboxyl content is low and the ratio of load to indentation area, the viscosity of lotion increases significantly with the increase of carboxyl content. When the carboxyl content increases to 2%, the viscosity increase of lotion slows down. Feng Libang et al. [7] synthesized UV curable polyurethane acrylate and neutralized it with tertiary amine to obtain a self emulsifying water dispersion system, and investigated the effects of carboxyl content, neutralization degree and isocyanate number on the properties of lotion and paint film. The larger the space occupied by the test piece, the greater the impact. Nabuurs et al. [8] studied the influence of the acid monomer and acid value of the acrylic dispersion in the two-component waterborne polyurethane coating on the film performance, and found that selecting the appropriate type and acid value of the acrylic dispersion can produce a bubble free and defect free coating. Zhang faai et al. [9] used hydroxyl acrylic lotion as hydroxyl component to prepare waterborne two-component polyurethane paint with hydrophilic modified polyisocyanate. The study found that in the best application formula, the acid value is below 15 mgkoh/g, and the smaller the acid value, the greater the impact on the gloss of the paint film. The more carboxyl groups, the smaller the particle size of acrylic emulsion, the higher the gloss of the film formed, but the more carboxyl groups, the better, When the acid value is higher than 25 mgkoh/g, the water resistance of the obtained film decreases significantly. In waterborne acrylic acid and two-component polyurethane coatings, the acid value of acrylic acid has a great influence on the properties of lotion and paint film

in the national standard, the mixed solvent of toluene and ethanol is used to dissolve the resin sample, and phenolphthalein is used as an indicator to determine the acid value of the resin. In practice, we found that when using this method to detect the acid value of the lotion sample obtained by lotion polymerization, the mixed solvent will make the sample demulsify and precipitate, which has a great impact on the acid value test, and due to the interference of lotion color, the titration end point of phenolphthalein indicator is not obvious, which will produce large errors. In this study, thymol blue was used as an indicator, and the mixed solvent of ethanol and water was used to dissolve different types of acrylic lotion samples for acid value determination. The effects of different alcohol water ratio (alcohol volume/water volume) before and after titration on the particle size and acid value of lotion and the effects of dilution ratio (solution volume/Lotion quality) on the acid value of lotion were studied

1 test part

1.1 raw materials and test equipment

absolute ethanol: analytically pure; Potassium hydroxide: analytically pure; Potassium hydrogen phthalate: working standard reagent; Thymol blue: indicator ind; BASF and Dow pure acrylic lotion; Dow's styrene acrylic lotion; Bardful's Silicone Acrylic lotion; Rohm Haas' acetate acrylic lotion; DSM polyurethane acrylic lotion. Basic burette; Ultrasonic cleaning instrument; Mettler Toledo ms204s analytical balance; Malvern zetasizernano-zs90 particle sizer

1.2 test method

weigh the sample into a conical flask, accurate to 1 mg, add 50 ~ 200 ml of mixed solvent with a dilution ratio of less than 200, ultrasonic for 10 minutes, wait for the sample to dissolve completely, cool the solution to room temperature, add 10 drops of thymol blue indicator to the sample solution, immediately titrate with potassium hydroxide solution until yellow turns blue, and at least 10 seconds does not disappear is the end point, and record the volume of potassium hydroxide solution consumed (ML)

1.3 particle size measurement

particle size: use Malvern Zetasizer nano-zs90 particle size analyzer to measure the particle size changes of acrylic lotion samples dissolved in different alcohol water ratios before and after titration

2 results and discussion

2.1 effect of alcohol water ratio on the particle size of pure acrylic lotion

in the test, the mixed solvent of toluene and ethanol in the national standard was first used to dissolve the bar. The output of each year is 2million tons of SF pure acrylic lotion samples, but the solvent will completely demulsify the samples and produce flocculated particles, thus affecting the acid value determination results. Then we dilute and dissolve the lotion sample with mixed solvents with different alcohol water ratios, and investigate its influence on the particle size of lotion before and after titration. The results are shown in Figure 1

it can be seen from Figure 1 that during the particle size determination of pure acrylic lotion, when the alcohol water ratio is less than 4, the particle size of lotion will increase slightly with the increase of alcohol water ratio, but the whole solution system is still in lotion state. When the alcohol water ratio reaches 5, flocculated particles will be produced

2.2 effect of alcohol water ratio on the acid value of pure acrylic lotion

in the test, pure acrylic lotion samples were dissolved with different alcohol water ratio, and their effects on the acid value of lotion before and after titration were investigated. The results were measured twice in parallel. See Figure 2 of more than 100000 foam granulation machines

it can be seen from Figure 2 that when the acid value of pure acrylic lotion is measured, when the alcohol water ratio is between 1.5 and 4.0, the acid value titration result is basically stable, but when the alcohol water ratio is 5.0, there will be flocculated particles in the lotion, which will affect the repeatability and accuracy of the measurement results. Therefore, for pure acrylic lotion, choosing 1.5 ~ 4.0 alcohol water ratio can obtain accurate and stable acid value results

2.3 effect of dilution ratio on the acid value of lotion

on the basis of alcohol water ratio of 1.5, the effect of dilution degree of pure acrylic lotion on the acid value was investigated and measured twice in parallel. The results are shown in Figure 3

it can be seen from Figure 3 that during the acid value determination of acrylic acid emulsion, the dilution ratio basically has no effect on the acid value determination, but the total volume of the solution is too small or the dilution ratio is too large, which will affect the end point judgment, thus affecting the acid value result. Therefore, the total volume of the solution can be selected as 50 ~ 200 ml and the dilution ratio is less than 200, so that the sample can be completely dissolved

2.4 verification of the scope of application of the method

at present, the commonly used acrylic lotion in the market mainly includes pure acrylic lotion, styrene acrylic lotion, silicone acrylic lotion, acetate acrylic lotion and polyurethane acrylic acid. The above lotion samples are selected for method verification in the test to determine their scope of application. Using a series of different alcohol water ratios, the total volume of the solution is 50 ~ 200 ml and the dilution ratio is less than 200, the acid value of different types of lotion samples is determined. The results are shown in Table 1

it can be seen from table 1 that when the alcohol water ratio is between 1.5 and 4.0, pure acrylic lotion, silicone acrylic lotion and polyurethane acrylic emulsion do not produce flocculating particles, and the acid value results are relatively accurate and stable; When the alcohol water ratio of acetate acrylic lotion is greater than 1.5, the flocculation of lotion is serious. Although the acid value changes little with the increase of alcohol water ratio, the flocculation of lotion affects the repeated stability of the results; For styrene acrylic lotion, when the alcohol water ratio is greater than 1.5, the demulsification and flocculation of lotion are serious, and have a great impact on the acid value results. Therefore, the mixed solvent with alcohol water ratio of 1.5 can be selected to dissolve and determine several kinds of acrylic lotion samples. When the total volume is 50 ~ 200 ml and the dilution ratio is less than 200, more accurate and repeatable acid value results can be obtained

3 conclusion

1) because the national standard acid value determination method is not suitable for the determination of the acid value of acrylic acid emulsion, this study uses alcohol and water as the mixed solvent to investigate the influence of different alcohol water ratio on the particle size and acid value of pure acrylic lotion. When the alcohol water ratio is between 1.5 and 4.0, the state of lotion is stable and the acid value result is accurate

2) on the basis of alcohol water ratio of 1.5, the influence of mixed solvent on the dilution ratio of lotion was investigated. The dilution ratio has basically no effect on the determination of acid value, but in order not to affect the judgment of the end point, the total volume of the solution can be selected as 50 ~ 200 ml and the dilution ratio is less than 200, so that the sample can be completely dissolved

3) according to the comprehensive test results, for the determination of the acid value of several commonly used acrylic emulsions, such as pure acrylic lotion, styrene acrylic lotion, silicone acrylic lotion, acetic acrylic lotion and polyurethane acrylic acid, using thymol blue as an indicator, selecting a mixed solvent with 1.5 times the alcohol water ratio to dissolve the sample, the total volume is 50 ~ 200 ml and the dilution ratio is less than 200, more accurate and stable acid value results can be obtained