THE POSSIBILITIES OF MICROENCAPSULATED ANTIOXIDANTS FOR POLYMERS .1. A THEORETICAL-ANALYSIS

We consider the possibility of stabilising a polymer by using a low-molecular-weight, mobile and soluble antioxidant, trapped in a small volume fraction of encapsulant which releases it into the surrounding polymer to compensate for consumption or loss. Two models are discussed. In the 'matrix' model, the additive is dissolved in an encapsulant and its release is controlled entirely by the diffusion coefficient in the encapsulant. In the 'balloon' model, the pure additive is surrounded by a wall of encapsulant, through which it permeates. Modelling allows the required diffusion or permeation coefficients to be calculated for any chosen loss time. Purely diffusion-controlled loss would require improbably low diffusion coefficients, whereas the required permeabilities for balloon models are accessible. It is difficult to imagine a system for which the temperature coefficient of loss rate would be low enough to allow elevated temperature processing without loss of the additive.