EVALUATION OF THE ORIENTATION COEFFICIENT FOR THE C-AXIS IN POLY(ETHYLENE-TEREPHTHALATE) FIBERS

The literature methods for the determination of the mean of the crysta llite orientation distribution for the c axis, that is of the orientat ion coefficient f(c), for poly(ethylene terephthalate) (PET), based on the azimuthal scan of the (($) over bar 105) reflection, are reviewed . These methods appear unsuitable for samples presenting the ''tilted orientation''; that is, the molecular chain axis inclined by some degr ees with respect to the fiber axis, as frequently occurs for PET fiber s. A new method for the determination of f(c) for PET, also based on t he azimuthal scan of the (($) over bar 105) reflection (which can be a pplied also to samples with ''tilted orientation''), is proposed. This method implies as a first step the determination of the tilt angle, f or which the complete fiber pattern is required. A possible simplifyin g assumption, which allows use of the sole azimuthal (($) over bar 105 ) profile and makes the method also applicable to poorly oriented samp les (for which the determination of the tilt angle is not easy), is al so discussed. (C) 1995 John Wiley and Sons, Inc.