Effect of conducting carbon black on the photostabilization of injection molded poly(propylene-co-ethylene) containing TiO_2

摘要

The photoelectrochemical process initiating degradation during outdoor exposure of polymers containing TiO_2 has previously been assigned to the reaction of an excited electron in the conductive band of TiO_2 with atmospheric O_2. This reaction generates the superoxide radical O_2~-, which promotes polymer oxidation. Conducting carbon black (CCB) was used in substitution of the non conducting grade (CB) to minimize the photodegradation of injection molded parts made of TiO_2 containing poly(propylene-co-ethylene), such as car bumpers. Analysis by light reflectance and specular reflectance in the mid-infrared region using a self-organizing map (SOM) revealed that the formulation with CCB presented less photodegradation. Visual observation and comparative optical micrography showed that samples with CCB exhibited lower surface whitening than samples with CB. Addition of CCB to samples without TiO_2 does not contribute to polymer stabilization. We propose that the stabilization effect associated with CCB is a consequence of the deactivation of the TiO_2 photoexcited electron by CCB.