Effect of conducting carbon black on the photostabilization of injection molded poly(propylene- co-ethylene) containing TiO 2

Abstract

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.