We investigated the influence of fillers on the deterioration of polyoxymethylene resin (POM) in ozone generated by electric discharge. The extent of deterioration was evaluated by studying the weight and thickness changes, three-point flexural strength, appearance and molecular weight of the resin. The weight and thickness of the material linearly decreased after the incubation period ; each surface gradually roughened by chalking. Flexural strengths are decreased with decrease in exposed time. Size exclusion chromatography measurements indicated that the degradation of POM by ozone proceeded via corrosion-layer formation and was limited to layers near the specimen surface, whereas the inner layer showed barely any deterioration. The corrosion rate was estimated from the thickness of the corrosion layer and residual thickness of the uncorroded layer. The flexural strength after exposure could be predicted from this estimated corrosion rate. In this study, even after adding fillers, no significant delay was observed in resin deterioration by ozone.
To clarify the origin of rapid degradation of polypropylene (PP)-based composites with inorganic fillers, infrared microscope study was performed for PP/SiO2 composites. Thermal and photo degradations of PP were greatly enhanced around SiO2 particles, as a result of facile volatilization of stabilizer from loosely connected interfaces between the PP matrix and SiO2 particles. Organic modification of SiO2 surfaces improved the connection at the interfaces and notably suppressed the volatilization of stabilizer. Thus, the critical role of interfacial structures was reported for the first time in the degradation and stabilization of PP-based composites.