(321d) Characterization of Oxygen Scavenging Films Based On Butadiene-Containing Polymers

Butadiene-containing polymers, such as styrene-butadiene-styrene block copolymers and 1,4 polybutadiene are of use as oxygen scavenging polymers (OSP) in barrier applications. As part of an evaluation of this use in such applications, films of these polymers were oxidized catalytically at four catalyst loadings and various thicknesses. Oxidation led to formation of crust layers at the film outer surfaces. Gas permeabilities of the crust layers are 2-3 orders of magnitude lower than those of neat, un-oxidized polymers. The diffusion-controlled oxidation creates a transient moving boundary that separates the oxidized and un-oxidized regions. Maximum oxygen uptake was measured to understand the kinetics and oxidation capacities of OSP systems and extracted from thin film experiments.

The thickness of the oxidized regions at long oxidation times is called the critical thickness, and it reaches a maximum at a certain catalyst loading. Films that are thinner than the critical thicknesses will oxidize fully and homogeneously. Results from three methods of analysis: 1) Thickness Model Analysis, 2) Inverse Thickness Analysis, and 3) SEM Imaging Analysis, all indicate a similar critical thickness value in each OSP system. Critical thicknesses appear related to the values of maximum uptake. Critical thicknesses set the upper OSP thickness limit in future diffusion-controlled oxidation systems, such as multi-layered and blend films.