Time-resolved X-ray wide angle scattering studies of the effect of draw rate and temperature on the development of orientation and crystallinity in PET

Abstract

A purpose-designed X-ray fibre diffraction camera has been used to record the variation in the wide angle X-ray scattering during the drawing and annealing of the organic polymer polyethylene terephthalate. Data were recorded at the Daresbury Laboratory Synchrotron Radiation Source using a Photonics Science electronic area detector interfaced to a Synoptics framegrabber as a series of frames with an exposure time of 40 ms for each frame. Frames could be displayed while the diffraction pattern was being accumulated allowing the experiment to be conducted in a genuinely real-time mode. The draw rate was varied from 20% per min to 72 000% per min and the draw temperature from 80°C to 140°C. The draw ratio in these experiments was designed to be 3.6:1. For the highest draw rates essentially all the change in the diffraction pattern was complete in less than 1 s. The degree of crystallinity and orientation observed in drawn samples depends on both the draw temperature and the draw rate. In particular for draw rates of 72 000% per min the high degree of orientation and crystallinity observed at a draw temperature of 80°C diminishes with increasing draw temperature until for draw temperatures of 140°C the pattern is essentially unoriented and non-crystalline.