Structural changes in composite surface material after dry polishing.

The purpose of this study was to investigate the properties of composite materials that had been heated to temperatures which may occur during dry polishing. Bulk composite material was submitted to thermal analysis from R.T. to 200 degrees C. Two distinct stages of thermal reaction in this range could be identified. One at approximately 70 degrees C, which could be related to a further initiating of unreacted groups, and one above 100 degrees C, which could be related to the glass transition. The glass transition was also observed microscopically. Hardness measurements were carried out on the warm material at different temperatures as well as on the material being cooled down to R.T. With temperature rise, a continuous increase in hardness and abrasion resistance could be demonstrated. The observed phenomena for bulk material are related to the properties measured on dry polished surfaces.