Influence of processing conditions on the leaching of thermal stabilizers from plasticized polyvinyl chloride in the presence of water

Abstract

Plasticized PVC formulations for pharmaceutical packaging contain calcium and zinc stearates, which are PVC heat stabilizers. It was found in the literature that these additives can migrate to some aqueous solutions, especially when the pH is alkaline, the best example being sodium bicarbonate solutions. So, the aim of this work was to demonstrate the correlation between the lubricant ability of these stearates and their further migration in fluids. For this purpose, we studied the migration of calcium and zinc stearates during an extrusion step, focusing essentially on slip phenomenon. We have demonstrated here that slip phenomenon occurs in the case of plasticized PVC heat stabilized by calcium and zinc stearates. The slip phenomenon amplitude increases with the total amount of stearates in the formulation and also when the extrusion temperature decreases. The analysis of a die insert through scanning electron microscopy coupled with an X-ray energy dispersive technique could allow us to see that the additive mainly responsible for the slip is calcium stearate. The analysis of the leachable components of the formulations migrating after steam sterilization in sodium bicarbonate solutions leads to conclude that zinc stearate also migrates to the metal surface of the die during extrusion, but in a lower extent than calcium stearate. So, a good correlation exists between the processing conditions, including essentially the stearate concentration and the extrusion temperature, and the migration of these additives from the extruded sample to aqueous solutions. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 70: 2391–2400, 1998