The method of measuring the acid value of acrylic emulsion was studied

0 Introduction
Water-based coatings with water as a solvent or dispersion medium, do not add volatile organic solvents, in addition to the characteristics of general coatings, but also has no odor, low toxicity and not easy to burn and so on, so it has become a hot topic of research and has received widespread attention. According to the different coating substrate resins, water-based coatings can be divided into epoxy, polyurethane, acrylic, aolic acid and other types, currently widely used in water-based polyurethane coatings and water-based acrylic coatings.
Chen Jinlian, etc. , using pre-emulsified semi-continuous seed emulsion polymerization legal system with excellent nuclear/shell structure performance of high hydroxycrystal content acrylic micro-emulsion, emulsion in the preparation process, nihilum monosome has an optimal dosing, too high or too low When the coagulation rate is increased, the content of nircoulium has a greater impact on the viscosity of the emulsion, when the content of the nipple base is low, with the increase of the content of the nipple base, the mucus of the emulsion increased significantly, when the content of the nipple-based increased to 2%, the increase in the mucus of the emulsion slowed down
C.
. Feng Libang and others synthesized UV-cured polyurethane-acrylic, and was meso-moderated from the emulsified water dispersion system, and examined the effects of niobium-based content, melision and isocyanate number on the performance of emulsion and lacquer film. Nabuurs and others studied the effect of acid monomers and acid values of acrylic dispersants in two-component water-based polyurethane coatings on the performance of lacquer film, and found that the selection of suitable acrylic dispersion types and acid values can be made without bubbles and defects. Zhangfa Ai and other s9 with hydroxypropyl acrylic emulsion as hydroxy-modified polycyanate paint, preparation of water-based two-part polyurethane coating, found that in the best application formula acid value of 15 mgKOH/g or less, acid value When smaller, for the paint film gloss has a greater impact, the more carbapenem group, the smaller the acrylic emulsion particle size, the formation of a coating film gloss is higher, but the more the better, when the acid value is higher than 25 mgKOH/g, the resulting coating film water resistance performance significantly reduced. In water-based acrylic and two-part polyurethane coatings, the acid value of acrylic has a greater impact on the performance of emulsions and paint films.
national standard using toluene and ethanol mixed solvent dissolved resin samples, with phenolic acid as an indicator to determine the resin acid value, in practice, we found that this method to detect emulsion polymerization legal emulsion sample acid value, mixed solvent will make the sample break milk and produce precipitation, the acid value test has a great impact, and due to the interference of emulsion color, phenolic acid indicator titration endpoint is not obvious, will produce a large error. In this study, thyriphenol blue was used as an indicator to determine the acid value of different types of acrylic emulsion samples dissolved by a mixture of ethanol and water solvents, and the effect of different alcohol-water ratios (alcohol volume/water volume) on emulsion particle size and acid value and the dilution ratio (solution fluid accumulation/emulsion quality) on emulsion acid values were studied.
1 Test Part
1.1 Raw Materials and Test Equipment
Waterless Ethanol: Analysis Purity; Potassium Hydroxide: Analysis Purity; Potassium Phthalates: Working Baseline Reagents; Thyriphenol Blue: Indicator Ind; BASF and Dow's pure propylene emulsion; Dow's phenylpropyl emulsion; Badfu's silicone propylene emulsion; Romenhas' acetate emulsion; DSM's polyurethane acrylic emulsion. Alkaline titration tube; ultrasonic cleaner; METTLER TOLEDO MS204S analytical balance; Malvern Zetasizer Nano-ZS90 granular meter.
1.2 Test Method
said that the sample was placed in a conical bottle, accurate to 1 mg, added 50 to 200 mL and dilution ratio of less than 200 mixed solvents, ultrasonic 10 min, to be completely dissolved sample, so that dissolved Cool the liquid to room temperature, add 10 drops of thyriphenol blue indicator to the sample solution, immediately titration with a potassium hydroxide solution to yellow to turn blue, at least 10 s does not disappear as the end point, note the consumption of potassium hydroxide dissolved liquid product (mL).
1.3 particle size to determine the size of
particle size: The particle size changes of acrylic emulsion samples with different alcohol water ratios were measured using the Malvern Zetasizer Nano-ZS90 granular meter.
2 Results and Discussion
2.1 Effect of alcohol-water ratio on pure propylene emulsion particle size
In the test, BASF pure propylene emulsion samples were first dissolved using a mixture of toluene and ethanol in the national standard, but the solvent completely broke the sample and produced flocculation particles, thus affecting acid value determination results. Subsequently, we used a mixture of different alcohol-water ratio solvents to dilute the dissolved emulsion sample, to investigate the effect of titration on the emulsion particle size, the results can be seen in Figure 1.
As can be seen from Figure 1: In the process of determination of pure propylene emulsion particle size, when the alcohol-water ratio is less than 4, with the increase of alcohol-water ratio, the emulsion particle size will increase somewhat, but the entire solution system is still emulsion state, when the alcohol-water ratio reaches 5, there are flocculation particles produced.
2.2 Effect of alcohol-water ratio on pure propylene emulsion acid value
In the test, different alcohol-water ratio dissolved pure propylene emulsion samples were used to investigate the effect of pre- and post-titration on emulsion acid value, and 2 parallel measurements were made, the results of which are shown in Figure 2.
As can be seen from Figure 2: when the pure propylene emulsion acid value is measured, when the alcohol-water ratio is between 1.5 and 4.0, the resulting acid titration result is basically stable, but the alcohol-water ratio is 5.0, flocculation particles will be produced in the emulsion, which will have an impact on the repeatability and accuracy of the determination results. Therefore, for pure propylene emulsions, an accurate and stable acid value ratio of 1.5 to 4.0 alcohol can be used.
2.3 Effect of dilution ratio on emulsion acid value
On the basis of alcohol-water ratio of 1.5, the effect of pure propylene emulsion dilution on acid value was examined, and 2 parallel measurements were made, the results of which are shown in Figure 3.
Visible by Figure 3: Acrylic emulsion acid value determination, dilution ratio has no effect on acid value determination, but the total volume of the solution is too small or dilution ratio is too large to affect the end point judgment, thus affecting the acid value results, so the total volume of the solution can be selected 50 to 200 mL and dilution ratio is less than 200, so that the sample can be completely dissolved.
2.4 method applicable range verification
the current market commonly used acrylic emulsion mainly includes pure propylene emulsion, phenyl propylene emulsion, silicate emulsion, acetate emulsion and polyurethane acrylic and other categories, the test selected the above emulsion samples for method verification, to determine its applicable scope. Using a series of different alcohol-water ratios, the total volume of the solution is selected from 50 to 200 mL and the dilution ratio is less than 200, and the acid value of different types of emulsion samples is determined, and the results are found in Table 1.
can be seen from Table 1: When the alcohol-water ratio is between 1.5 and 4.0, pure propylene emulsion, silicone propylene emulsion and polyurethane acrylic emulsion are produced without flocculation particles, and the acid results are more accurate and stable; 1.5, emulsion flocculation is more serious, although with the increase of alcohol-water ratio, the acid value change is not much, but emulsion flocculation affects the repetitive stability of the results, while for phenyl-propylene emulsion, alcohol-water ratio is greater than 1.5, emulsion flocculation is more serious, and has a great impact on acid value results. Therefore, the mixed solvent dissolved with a choice of alcohol-water ratio of 1.5 determines several large acrylic emulsion samples with a total volume of 50 to 200 mL and a dilution ratio of less than 200, resulting in more accurate and repeatable acid results.
3 Conclusion
1) Because the national standard acid value measurement method is not suitable for the determination of acrylic emulsion acid value, this study uses alcohol and water as a mixed solvent, investigates the effect of different alcohol-water ratio on pure propylene emulsion particle size and acid value, when the alcohol-water ratio is between 1.5 and 4.0, the emulsion status is stable and the acid value results are accurate.
2) On the basis of alcohol-water ratio of 1.5, the effect of mixed solvent on emulsion dilution ratio was examined, and the dilution ratio had no effect on acid value determination, but in order not to affect the judgment of the end point, the total volume of the solution can be selected 50 to 200 mL and the dilution ratio is less than 200, so that the sample is completely dissolved.
3) Comprehensive test results, for pure propylene emulsion, phenyl emulsion, silicone propylene emulsion, acetate emulsion and polyurethane acrylic acid several commonly used acrylic emulsion acid determination, using thyriphenol blue as an indicator, choose 1.5 times the alcohol water ratio mixed solvent dissolved sample, the total volume of 50 to 200 mL and dilution ratio of less than 200 conditions, can obtain more accurate and stable acid results.