Plasticization of poly(vinyl chloride) : PVC/plasticizer compatibility and its relationship with processing and properties of plasticized PVC
The compatibility of suspension PVC with a series of twelve different plasticizers was determined using the estimated values of compatibility predictors, such as the Hildebrand solubility parameter, as well as actual measurements of compatibility, such as the solid-gel transition temperature and the Flory-Huggins interaction parameter. Different relative orders of compatibility were obtained between the plasticizers studied using the two different approaches. Then, using the twelve different plasticized PVC compounds, the ease of fusion during processing (Brabender mixing and compression moulding) was evaluated and found to be closely related to the PVC/plasticizer compatibility. It was found that the more compatible the plasticizer, the more rapid the fusion during processing, but the higher the torque peak during Brabender mixing. It was also found that the temperature at the fusion peak in a Brabender torque rheometer is closely related to the various parameters used to measure the compatibility, (e.g. the solid-gel transition temperature, the interaction parameter, and the activity parameter). Finally, the rheological and tensile properties of plasticized PVC were determined and it was found that both the rheological and tensile behaviour are highly dependent on the level of fusion of the PVC compound, which in turn depends on the plasticizer type. However, once a high level of fusion is attained, these properties depend more on the viscosity of the plasticizer and the glass transition temperature of the compound.