Influence of polishing time on thermo-oxidation characterization of isothermally aged PMR-15 resin

The effect of polishing time on measured oxidation thickness and elastic modulus of isothermally aged PMR-15 neat resin was investigated. A specimen aged 956 h in ambient air at 288 degrees C (550 degrees F) was selected for this study. Thermo-oxidation of the specimen results in a surface oxidation layer with different stiffness and polishing characteristics than the interior of the specimen. The specimen was repolished at consecutive time periods from a quick polishing time to extensive polishing time. A white light interferometer was used as a surface profiler to measure height variations from the specimen edges into the interior of the material. Subsequently, optical microscopy and nanoindentation experiments were conducted to correlate observations of oxidation thickness and elastic modulus measurements with polishing time. The modulus profiles obtained from nanoindentation experiments indicate formation of an outer brittle layer followed by a sharp drop in the transition region to the unoxidized interior. The oxidized material is polished at a greater rate than the unoxidized material. The maximum variation in the surface profile from polishing was limited to 5 mu m across the oxidation layer (similar to 150 mu m), which results in a slope of similar to 2 degrees over the oxidized region. Optical measurements of thickness of oxidized layer and transition region are in good agreement with the height and modulus profiles obtained using the interferometer and nanoindenter, respectively. Results from three techniques show that the measured oxidation thickness and elastic modulus are relatively independent of the polishing time. (c) 2007 Elsevier Ltd. All rights reserved.