LOSS OF ADDITIVES FROM POLYMERS - THEORETICAL-MODEL

The rate at which an additive is lost from the surface of its solution in a polymer is considered to depend upon three factors—the solubility of the additive, the rate at which it volatilizes from the polymer surface, and its diffusion coefficient within the bulk of the polymer. By adapting the mathematics of heat flow in a solid, the loss of additive from a polymer is mathematically modeled in terms of these three variables for bulk polymer and for film and fiber samples. Two cases are considered—loss of additive by volatilization or dissolution from the polymer surface and loss by precipitation on the surface from a supersaturated solution of the additive. The results are applied to a discussion of the relative importance of the three parameters under various conditions occurring or expected in practical application of additives as oxidation stabilizers for polyethylene and polypropylene. Copyright © 1979 John Wiley & Sons, Inc.