Characterization of the oxygen scavenging capacity and kinetics of SBS films

Butadiene-containing polymers such as styrene-butadiene-styrene (SBS) block copolymers are of a potential use as oxygen scavenging polymers CUSP) in barrier applications. To evaluate their use in such applications, oxygen uptake was measured for films made of an SBS copolymer and four cobalt catalyst loadings with various thicknesses. The oxygen uptake was found to be kinetically limited for thin films while diffusion controls the uptake at long times for thick films. The thickness of the oxidized region at long oxidation times is termed the critical thickness L-c and was quantified by various analyses. Thin films (i.e.,L <= 2L(c)) oxidize fully and homogeneously, whereas heterogeneous oxidation typically occurs in thicker films (i.e., L > 2L(c)). A thin film model was used to extract the reaction rate parameters and a stoichiometric oxidation coefficient that describe oxygen uptake in the absence of diffusion limitation. An approximate moving-boundary model was developed to describe thick film oxidation behavior at long times and was found to be in semi-quantitation agreement with the measured uptake. (C) 2012 Elsevier Ltd. All rights reserved.