| Abstract: | The procedure of Southern and Porter has been used to prepare poly(ethylene terephthalate) segments by high-pressure extrusion in an Instron capillary rheometer at temperatures from 245° to 265°C. X-Ray measurements of crystalline orientation along the axis of long-growth segments showed that segment properties were controlled by the time-dependent crystallization of polymer melt in the rheometer reservoir. During the initial stage of extrusion, a highly oriented, translucent segment was generated by flow-induced crystallization. However, formation of the translucent morphology eventually stopped, and thereafter a poorly oriented, opaque segment was generated by solid-state extrusion. From wide- and small-angle x-ray scattering, differential scanning calorimetry, and density measurements, it was determined that the most perfect morphologies were prepared at an extrusion temperature of 265°C. In addition to having the highest degree of crystalline orientation, translucent segments extruded at 265°C have a peak melting point of 267°C and a crystallinity value of 62%. Hot-stage optical microscopy showed that the translucent segments contained axially aligned fibrous crystals whose birefringence persisted to 290°C. The exceptional thermal stability of the segments was corroborated by the results of shrinkage tests at temperatures near the melting point; even after 1 hr at 260°C, the shrinkage did not exceed 7%. The accumulated evidence suggests that the translucent segments contain an extended-chain component. |
