Interactions between PVC and binary or ternary blends of plasticisers : effect on processing and properties
A statistically based mixture design was used to plan experiments on plasticiser blends in PVC compounds. This work investigates compatibility, the extrusion characteristics at different shear rates and the properties of these compounds. Seventeen different plasticisers, spread over five binary and twelve ternary plasticiser systems, were screened for their compatibility. Standard methods such as the solid-gel transition temperature and the FloryHuggins interaction parameter were used. For the binary blends of different plasticiser families, the interactions correlate with increasing differences of the solid-gel transition temperature of the monomeric plasticisers used. If the blend contains a polymeric plasticiser, the interaction decreases with increasing differences in the solid-gel transition temperature. The mechanistic theory of Doolittle enables the interactions of ternary and higher plasticiser systems by using PVC in compositions of binary ones to be assessed. UNIFAC-FV was used to predict the F1ory-Huggins interaction parameter of single plasticisers and of the ternary plasticiser system DOP-DOA-DOS. For plasticisers under investigation, the same relative order of compatibility ranking was obtained using either the solid-gel transition temperature or UNlF AC-FV. The latter was also applied to predict the Gibbs free energy of mixing for a series of monomeric and polymeric plasticisers. For the various ternary systems, some physical properties such as heptane extraction showed an excellent correlation with the solid-gel transition temperature. For a selection of eight ternary plasticiser systems, the ease of fusion during processing on a Haake Rheometer was evaluated A clear relationship was found between the kneader data at the fusion peak and the solid~gel transition temperature, except for the ODPP and C911P containing systems. These systems showed a good correlation between the kneader data and the solid-gel transition temperature and shear viscosity of the compound or viscosity of the plasticiser. Finally, the extrusion characteristics of five ternary plasticiser mixtures were determined. These characteristics were also found to dependent on the solid-gel transition temperature. In some cases, however, the extrusion characteristics also depended on other variables, such as shear viscosity and bulk density of the compounds used.