Expansion and shrinkage of fibers. Load- and temperature modulated TMA measurements temperature calibration of fiber attachments

The thermal behavior of a drawn PET fiber has been investigated by thermomechanical analysis, TMA, and by differential scanning calorimetry, DSC. Above the glass transition temperature of 79 degrees C, the fiber shrinks to a maximum of 8% of the initial length. Temperature modulated TMA enabled the separation of the thermal expansion from the overlapping shrinkage during the first heating and to calculate the expansivity, alpha(e) and the shrinkage coefficient, alpha(s), independent of each other. Young's modulus, E, was measured by TMA with modulation of the tensile stress. Hence, it was possible to record the behavior of alpha(e), alpha(s) and E during the structural changes by combining both modulations in a single measurement. A new technique was developed to calibrate the sample temperature. With this, accurate control of the modulated temperature of the specimen was achieved, independent of the changing heating rate.