EFFECT OF X-RAY IRRADIATION ON THE THERMAL EXPANSION OF POLYMERS.

The coefficient of linear thermal expansion ( alpha ) of ordinary and X-ray irradiated samples of polyester, glass-fibre reinforced polyethylene and polytetrafluoroethylene, has been determined in the temperature range 30 to 200 degree C using a two-terminal capacitance technique. The temperature corresponding to the sudden increase in alpha of the X-ray irradiated samples are higher than those corresponding to the ordinary samples. The values of alpha for X-ray irradiated samples are smaller than those of ordinary samples for polyester and glass-fibre reinforced polyethylene over the entire temperature range of this study. For polytetrafluoroethylene the values of alpha of the X-ray irradiated sample are lower than those corresponding to the ordinary samples at lower temperatures, and this trend is reversed at higher temperatures. The results are explained in the light of the change in the polymer structure brought about by X-ray irradiation.