The Observed Stability of PVC Particles in n-Butylchloride

Abstract

<p> The mechanism by which PVC particles remained stable in n-butylchloride was investigated.</p> <p> The PVC particles were made by aqueous emulsion polymerization with benzoyl peroxide initiator and polyvinyl alcohol surfactant. The particles were cleaned by ion exchange and their surface charge was found to be 0.068 ± 0.005 C/m^2. Dispersions of PVC in n-butylchloride were prepared by two methods. In the first, the particles were dried in an oven. The dried particles were redispersed in n-butylchloride via sonication. This produced a dispersion consisting of 0.26 kg/m^3 of PVC particles with an arithmetic volume average diameter of 317 nm and a standard deviation of 93 nm. The second method involved dialyzing the cleaned aqueous latex with methanol and then with n-butylchloride. The dialysis method was inferior to the sonication method. The dialysis method was time consuming, it produced a dispersion with large particle diameter, the dispersion was contaminated with water and methanol and surface species were removed by the methanol.</p> <p> The particles were found to be stabilized by an electrostatic mechanism. This was verified by observing that the particles migrated to the positive electrode when exposed to a potential difference of 1000 V. A surface potential of 0.203 V was calculated for the particles from mobility measurements and the Huckel equation.</p> <p> The charge separation that must occur to allow the particles to have the negative charge is hypothesized to be a result of organic molecules such as PVC-PVA oligomers that dissolve from the particles and form micelles. These molecules were readily soluble in methanol and only slightly soluble in n-butylchloride. As a result, when the dispersion was washed with methanol, the particles flocculated. The presence of these species in the dispersant was supported by evidence from ultra-violet, infra-red and nuclear magnetic resonance spectroscopy. The electronegative groups in the micelles provide a reasonably polar environment for hydrogen ions to exist. These hydrogen ions became the countercharge for the negatively charged particles.</p>