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 o f diffusion, swelling and dehydration of formulated PVC films containing di fferent levels (10-30%) of dioctylphthalate (DOP) plasticiser and 5% of a f ungicide, N-(fluorodichloromethylthio)phthalimide, fluorfolpet. The diffusi on rates and swelling levels are well correlated, implying that the mobilit y of water (measured using either simple Fickian or dual-mode models) is st rongly dependent on the 'free volume' created by changing chain microstruct ure and flexibility as the polymer swells and becomes more rubbery. Both di ffusion rates and degrees of film swelling show a maximum at 20-25% DOP con centration. However, T-g falls monotonically as the polymer is plasticised. Thus the water dynamics land the previously discovered leaching of fluorfo lpet) depends not only on the chain mobility but also on the degree to whic h 'free volume' is created in the presence of increasing amounts of DOP. Mu tual solubility of the formulation components is likely to play a role, and the presence of phase separation at similar to 20% DOP cannot be ruled out . (C) 2001 Elsevier Science Ltd. All rights reserved.