Automatic measurement of the absolute CTE of thin polymer samples: I - effect of multiple processing on thermal expansion of polypropylene films

A new design for a light spot position sensor is suggested. Details of the setup and calibration of the sensor are described. The sensor is used to enhance the efficiency of an optical dilatometer by automating its operation. The modified dilatometer is used to measure the coefficient of thermal expansion, CTE, of some thin metallic and polymeric samples. Thermal hysteresis behavior and CTE of multiple-reprocessed polypropylene films are measured and discussed. The discussion is supported by some morphological investigations for the reprocessed samples. It is found, in general, that reprocessing of polypropylene reduces its CTE by 6-22% in a temperature range Lip to 100degreesC. Polypropylene films that have been reprocessed three times showed minimum thermal expansion. (C) 2003 Published by Elsevier Ltd.