Interaction of partially soluble additives with polyvinylchloride: Solubility of stearates at high temperatures

Several problems concerning the molecular structure and the morphology of polyvinylchloride (PVC) have been extensively studied in the last 20 years [1], whereas relatively little is known on the kinetic and thermodynamic aspects of the interaction between the polymer and the additives which are commonly added to it. A typical PVC formulation, of the unplasticized type, may contain from 5 to 10 different additives such as lubricants, stabilizers, processing aids, etc. They are added to the resin and mixed, often at a temperature of about 100°C, to ensure a satisfactory distribution on the surface of the 100-150-um polymer grains. The resulting “dry blend” is then fed to the processing machine, usually a twin-screw extruder, where the original particles are converted into a continuous llmelt” in which the additives are assumed to be dispersed homogeneously.