MOLECULAR-ORIENTATION AND CONFORMATIONAL-CHANGES DUE TO UNIAXIAL-PLANAR DEFORMATION OF POLY(ETHYLENE-TEREPHTHALATE) FILMS

Conformational changes and chain axis orientation in poly(ethylene ter ephthalate) due to uniaxial-planar deformation (at constant width) at constant engineering stress in the range 1.2-5.5 MPa at temperatures i n the range 85-105-degrees-C have been studied by means of infrared sp ectroscopy. For all samples the state of orientation was frozen just a fter the deformation reached the equilibrium value at a draw ratio lam bda(p). For a given temperature there are two stress regimes, a lower one where lambda(p) decreases with increasing stress, corresponding to 'stretching with flow', and a higher one where lambda(p) increases wi th increasing stress, corresponding to 'crystallizing stretching'. It is shown that the crystallinity of the samples is uniquely related to the content of trans conformers and that the overall chain axis orient ation may be determined, to a good approximation, by determining the o rientation of the trans conformers; the chain axes associated with gau che conformers are effectively randomly oriented. Under conditions of 'crystallizing stretching' the content of trans conformers and the cha in axis orientation can be understood in terms of a rubber-like networ k extension if the drawing temperature is between 80-degrees-C (the gl ass transition temperature) and 95-degrees-C. At higher temperatures o f drawing, relaxation occurs in the amorphous phase. For all samples t here is an excellent correlation between the trans concentrations and the overall orientation, independent of whether relaxation or crystall ization occurs.