Infrared-ATR studies of the hydration and dehydration of formulated PVC films

We have used FTIR-ATR spectroscopy to measure the water uptake, the rates of diffusion, swelling and dehydration of formulated PVC films containing different levels (10–30%) of dioctylphthalate (DOP) plasticiser and 5% of a fungicide, N-(fluorodichloromethylthio)-phthalimide, fluorfolpet. The diffusion rates and swelling levels are well correlated, implying that the mobility of water (measured using either simple Fickian or dual-mode models) is strongly dependent on the ‘free volume’ created by changing chain microstructure and flexibility as the polymer swells and becomes more rubbery. Both diffusion rates and degrees of film swelling show a maximum at 20–25% DOP concentration. However, Tg falls monotonically as the polymer is plasticised. Thus the water dynamics (and the previously discovered leaching of fluorfolpet) depends not only on the chain mobility but also on the degree to which ‘free volume’ is created in the presence of increasing amounts of DOP. Mutual solubility of the formulation components is likely to play a role, and the presence of phase separation at ∼20% DOP cannot be ruled out.