Step-scan FTIR and photoacoustic detection to assess depth profile of photooxidized polymer

Abstract

The extent of degradation of photooxidized materials must be determined precisely in order to evaluate its lifetime. Generally, an heterogeneous degree of oxidation is recorded through the sample thickness. Because, oxidation can be much more important near the surface, a photoacoustic (PA) detection of the IR spectrum of the material appears particularly well adapted. A PA detector attached to a step-scan (SS) FTIR spectrometer was used to record the IR spectrum of a photooxidized styrene–isoprene copolymer. In order to evaluate the ability of this technique to perform a depth profile of an oxidized material, the sample was also analyzed using transmission micro-FTIR analysis of cross-sectioned layers. These two techniques allow a complete analysis of the material from its surface to its core. Our main finding is that a PA detection is more suitable to determine the superficial extent of degradation, whereas the micro-FTIR appears more adapted to analyze the bulk properties of the material.