The modification and characterization of an x-ray diffractometer for the study of polymer fibers and films

The two objectives of this research were to modify a commercially available X-ray transmission diffractometer assembly for the study of polymer fibers and films and to characterize the instrumental correction factors for the unite The performance of the modified diffractometer was compared to the performance of the single-crystal orienter currently used in the Polymer Engineering Department at the University of Tennessee at Knoxville. The data acquired from a flat-film diffraction pattern were used to generate a reference standard for comparison with the diffractometer and the single-crystal orienter.

The determination of the optimum thickness for a specimen of polymer sheet or film is readily accomplished by the standard methods. The optimum thickness for a fiber is complicated by the void inclusion encountered in mounting the specimen. A method for estimating the effect of the void volume was established and confirmed by experimental data.

One of the primary uses of the transmission diffractometer is to study the crystallite orientation of polymer specimens. The standard method which makes use of an azimuthal scan at a fixed Bragg angle is an extension of the technique of making an azimuthal scan of a flat-film diffraction pattern with a densitometer. The azimuthal instrumental broadening for the diffractometer was found to be strongly dependent on the Bragg angle at the lower angles and nearly independent at the higher angles. The source of the broadening was found to be the vertical divergence of the incident X-ray beam. A model was developed from which the first-order estimate of the effect was found to be in good agreement with the experimental data. As a result, an empirical broadening correction can be made and applied to the azimuthal data for determination of the unbroadened azimuthal profile to aid in the calculation of the Hermans-Stein orientation functions.