Orientation and crystallisation mechanisms during fast drawing of poly(ethylene terephthalate)

Synchrotron radiation has been used to record the diffraction patterns from Poly(ethylene terephthalate) for a range of draw rates (0.1 to 10sec(-1)) and temperatures (90 to 120 degrees C). The patterns were analysed to derive the development of the <P (2)(cos theta)> order parameter and the rates of crystallisation. The effects of temperature and draw rate can be unified with a WLF time-temperature shift factor. Comparison with estimates of chain relaxation processes show that, when the draw rate is faster than the chain retraction process, the onset of crystallisation is delayed until the end of drawing. Crystallisation is very sensitive to both temperature and orientation and has an approximate 4th power dependence on <P-2(cos theta)>.