Orientation distribution in the noncrystalline regions of biaxially drawn poly(ethylene terephthalate) film: A chain‐intrinsic fluorescence study

Abstract

AbstractWe have studied development of the in‐plane distribution of “amorphous orientation” during sequential and simultaneous biaxial drawing of poly(ethylene terephthalate) film, using polarized intrinsic fluorescence. The machine direction (MD) draw ratio was always fixed at 3.5, and the transverse direction (TD) draw ratio was varied. The rate of increase in the proportion of TD‐oriented chains with increasing TD draw ratio is almost identical in the sequential and simultaneous processes up to a draw ratio of 2.7. At this point, sequential drawing starts to involve transverse realignment of MD‐oriented chains, which accelerates redistribution of orientation from the MD to the TD. Consequently, in sequential drawing, a “balanced” biaxial orientation distribution is achieved at a TD draw ratio significantly below the MD draw ratio, whereas at the same TD draw ratio in the simultaneous process, MD orientation remains dominant. At equal MD and TD draw ratios, the non‐crystalline chains in sequentially drawn film are predominantly oriented along the TD, but their orientation distribution is isotropic in simultaneously drawn film. High‐temperature annealing at fixed dimensions diminishes the proportion of TD‐oriented chains in films with transverse draw ratios < 2.5. We attribute this to a more highly developed crystallite network in the MD, which constrains orientational relaxation along the MD. A balanced distribution of amorphous orientation is directly responsible for achieving balanced tensile strength and balanced extensibility. © 1993 John Wiley & Sons, Inc.