Use of an automated spring balance for the simultaneous measurement of sorption and swelling in polymeric films

In the present work a new experimental apparatus has been set up for simultaneous measurements of solubility, diffusion coefficient and polymer swelling in a single sorption experiment. To that aim a quartz spring balance has been coupled with a CCD camera, which allows the automatic recording of spring elongation and sample dilation during mass uptake. To test the apparatus, acetonitrile sorption into polyetherurethane has been investigated, at 40 °C and an activity range from 0 to 0.7. The experimental results have been then compared with sorption and dilation data obtained independently using other techniques. In all cases, the agreement between the different datasets is remarkable. The new apparatus proved to be able, for the cases considered, to simultaneously provide quantitative information on penetrant solubility and diffusivity as well as polymer dilation, with high sensitivity and good reproducibility. Errors directly due to this technique seldom exceed 1% in swelling evaluation and mass uptake; higher sources of uncertainties still affect the calculation of the average diffusion coefficient.