DIFFUSION OF ADDITIVES AND PLASTICIZERS IN POLYVINYL-CHLORIDE) .1. 1-2 DOUBLE DISK METHOD FOR OBTAINING THE DIFFUSION-COEFFICIENT OF ADDITIVES IN POLYMERS

A simple expression has been obtained for the change with time, t, of the difference, (A0 - A1), between the radioactivity of the two faces of a disc of material made by joining a disc containing radioactive diffusant to a similar disc containing no radioactive material. It is shown, for the special case where one of the discs is twice as thick as the other, that linear plots of ln(A0 - A1) vs t should be obtained almost from the very beginning of the experiment and that the slope of these plots should be - π2D/l2, where l is the total thickness of the double disc. The diffusion coefficients for dibutyl tin dilaurate in a variety of plasticized poly(vinyl chloride)s over a range of temperatures have been obtained from plots of this kind; the validity of this simple method has been confirmed by computer calculations. © 1979.