In order to test the applicability of colloid chemistry-based methods for the evaluation of latex stability, poly(vinyl acetate) latices were modified by copolymerization and emulsifier addition. The copolymerization with ethylene sulfonic acid sodium salt (ESASS) proved to be an effective procedure to enhance the latex stability. The addition of a nonylphenol-poly(ethylene oxide) sulfate ammonium salt (Hoe S2928) was less effective.
By these methods one series each was prepared with the amount of comonomer or emulsifier increased gradually. A different latex stability was obtained upon shearing and storage at 70°C, depending on concentration.
The different stability could easily be measured by practical methods, e.g., solids content and particle size distribution determined by Laser Aerosol Spectroscopy (LAS) and Photon Correlation Spectroscopy (PCS).
The data of critical Coagulation Concentration (CCC) with CaCl2 specified by turbidity measurements correlate with the stability determined by practical methods, as well as the determination of surface charges by polyelectrolyte titration with a Streaming Current Detector (SCD).
On the contrary, Zeta Potential determined by Mass-Transport Electrophoresis and Microelectrophoresis of the original, dialyzed or thoroughly cleaned latices did not correlate with latex stability. A good correlation, however, could be found between Zeta Potential and the other criteria of the latex stability during a coagulating titration with a cationic polymer.