Metal oxide fillers, such as titanium dioxide (TiO2), are heavily utilized in polymeric coatings and plastics for opacification, pigmentation, and mechanical enhancement. It is well known that the photoreactivity of TiO2 can contribute to the degradation of the surrounding polymer matrix, due to the generation of electron-hole pairs that further react to form redox species. The aim of the present study is to examine the effects of the type (i.e. surface treatment) and concentration of filler on the degradation of two polymer systems, a degradable epoxy amine and a stable acrylic urethane. Electron paramagnetic resonance (EPR) spectroscopy is applied to study the generation of radicals from the polymer and the filler. The EPR spectra from filled polymer films with different loadings of TiO2 and diverse photoreactivity were analyzed to assess their contribution to photodegradation. A change in EPR signals from trapped holes and electrons on/in TiO2 surface/lattice are observed from the filled polymer samples and a correlation between these TiO2 surface species with the stability of the polymer-TiO2 system under intense UV exposure was established. It was found that a more stable EPR signal, or more efficiently trapped charge, indicates that photoinduced holes and/or electrons could have higher potential to participate in the photocatalytic reaction, which causes more severe degradation patterns in the films.
Proceedings Title: ACS Polymeric Materials: Science and Engineering Preprints
Conference Dates: August 16-20, 2009
Conference Location: Washington, DC
Pub Type: Conferences
EPR, photoreactivity, polymer, degradation, UV, TiO2