Modulated-temperature thermomechanical analysis

By employing a ‘modulated-temperature’ heating programme composed of a series of heat-isotherm stages, it is possible to separate the change in dimensions of an oriented material during heating into two contributions: a thermally ‘reversing’ component which is due to linear thermal expansion and a ‘non-reversing’ part arising from relaxation to the disordered state on heating aboveT _g. Some preliminary results for biaxially drawn poly(ethylene terephthalate) film are presented. These experiments were carried out at the Thermal Methods & Conservation Science Laboratory, Department of Chemistry, Birkbeck College, University of London.