SORPTION ISOTHERMS FOR METHANOL, BENZENE AND ETHANOL ON POLY(VINYL ACETATE) (PVAC)

The sorption isotherms for three organic solvents on PVAc have been me asured via the isopiestic method using a simple inexpensive device wit h a spring inside the measuring chamber as the force sensor. A robust steel spring was used successfully instead of the sensitive quartz spr ing described in the literature. The sample was a thin aluminium foil coated with a thin polymer layer to yield a short diffusion path lengt h and sufficient equilibrium load at an acceptable tare mass. This ena bled equilibrium to be attained within 1-2 h. The experimental data ma y be well described by the Flory-Huggins theory. The interaction param eter was fitted as a linear function of the volume fraction. Temperatu re was of no significant influence within the range 20-50 degrees C or at 60 degrees C, respectively. The sorption isotherms can also be pre dicted by the UNIFAP (UNIFAC for polymers) method without the use of e xperimental data. PVAc exhibits highly sorptive behaviour, e.g. 10 wt. % methanol at 80% activity. The measuring device employed may be usefu l for the study of adsorbents that can be coated as a film onto alumin ium foil or exist as a thin film themselves (e.g. membranes).