High Temperature Orientation Modification of Undrawn Polyester Filaments. Complex Influence of the Temperature and Tensile Stress

In the present work the complex influence of the temperature and tensile stress on the deformation behavior, birefringence and degree of crystallinity of undrawn poly (ethylene terephthalate) (PET) fibers was studied. Amorphous PET yarns were subjected on heat mechanical modification at constant temperatures in a narrow range above glass transition temperature from 80 0 C to 95 0 C combined with tensile stress with values from 0 MPa to 30 MPa. Birefringence measurements and differential scanning calorimetry (DSC) were used in order to identify the occurred as a result of the heat mechanical processing structural changes in the samples. The fibers birefringence was measured using a specialized device that allows quick and precisely determination of the birefringence of complex objects such as polymer fibers and films. It is established the influence of the superposition annealing temperature/tensile stress on the filaments dimensional changes, birefringence and degree of crystallinity.