The prediction of orientation and crystallinity in drawn poly(ethylene terephthalate)

This paper describes the prediction of molecular orientation and fractional crystallinity in polymer products formed by deformation processes. The cal culations are carried out for poly(ethylene terephthalate) articles such as film and stretch-blow moulded bottles formed just above the glass transiti on temperature. They are based on the interpretation of realtime X-ray diff raction patterns obtained during and after drawing at speeds comparable wit h industrial processing(1), where crystallization occurs only after drawing has ceased. A parametric study reproduces trends observed in many experime ntal uniaxial draw studies, such as the increase in orientation and crystal linity with draw ratio, draw rate and decreasing temperature. The study als o demonstrates the increase of crystallinity from annealing or less rapid c ooling from the draw temperature. The prediction method has also been appli ed to the first draw stage of a biaxial film line, where temperature variat ions through the thickness and in the machine direction lead to orientation and crystallinity non-uniformity through the thickness. The predicted aver age crystallinity is in good agreement with experimental measurements for a range of process conditions.