Study of the migration of PVC plasticizers

An accelerated method has been set up in order to study the capacity of migration of different commercial plasticizers from flexible PVC parts towards other media kept in contact with it; in this case, polystyrene (PS) has been used as example. This process may occur during the storing or shipping of this type products and could modify their properties or their aesthetic appearance. The test consists in maintaining during 1 week the flexible PVC item in contact, under a given pressure, with a polystyrene sheet at 50 °C. After this time, the PVC and the PS are separated and the thermal degradation of the PS is then studied in a thermobalance under nitrogen atmosphere, using Curie metals as internal standards. The study of the pyrolysis behaviour can be used in order to evaluate the amount of plasticizer migrated. Several samples must be analysed in order to obtain reliable results. The behaviour of plasticizers of different chemical families (i.e. phthalates and citrates) and molecular weights, has been studied. Although the plasticizer loss is not observed as a sharp process in the loss weight versus temperature curve (due to the existence of plasticizer fractions which seem to interact differently with the polymer), clear conclusions can be obtained regarding the amount of migrated plasticizer and the temperature of the process, which increases with the molecular weight of the plasticizer. The type of the plasticizer has also a significant effect and the citrates have higher migration capacity than phthalates.