Polymers are macromolecules that contain long repeating chains of subunits. The form, structure, and composition of a single polymer establish its properties, so it is important to characterize these parameters in an accurate manner. Polymers are often synthesized into solid forms like sheets and fibers. The properties of these polymer varieties are majorly influenced by their texture, crystal structure, and crystallinity which can be examined using X-ray diffraction (XRD). As all of these polymers typically contain low X-ray absorption, large d-spacings, and a certain degree of preferred orientation (texture), transmission scattering with a 2D detector (XRD2) is considered to be a perfect way to define the samples.
Measurement of Polypropylene Samples
Analysis was carried out for polypropylene samples gathered from an extruded tube and a sheet. Measurements of the samples were carried out in transmission with a D8 DISCOVER, equipped with the PILATUS3 2D detector, and the IµS micro-focus source. A 300 micron-collimator was utilized for this purpose. Beamstops were not required due to the detector’s high count rate capability.
Scattering patterns were obtained at a close sample-to-detector distance, to increase both speed and scattering coverage at an extended distance, to achieve the perfect peak resolution. At larger distances a number of images were obtained from varied diffraction angles to collect the full diffraction pattern. The sample–to-detector distance was instantly detected, and specific detector aberration corrections were not needed, making it possible to carry out both of the measurements in an effortless manner.
Measurement of Polypropylene Samples
Figure 1 shows the images obtained with a sample-to-detector distance of 2.7 cm for 5 minutes, with 360° gamma coverage to 2θ = 30°, with restricted gamma coverage to 2θ=56°. This coverage is best suited for high throughput and mapping applications.
The resolution was maximized by pushing back the detector to a detector distance of 7 cm, and 3 images were collected, 2θ=-20°, 0°, +20° resulting in 360° gamma coverage to 2θ = 30°. Figure 2 depicts the images collected from these measurements.
Figure 1. Images of two polypropylene samples collected with a sample-to-detector distance of 2.7cm.
Figure 2. Images of two polypropylene samples collected with a sample to detector distance of 7cm.
To execute additional analysis the images depicted in Figure 2 were added to DIFFRAC.EVA, and combined into a standard 2θ plot. In addition to phase identification, peak width, associated with the microstrain and crystallite size of the polymer, can also be leveraged to gain a better understanding about the effects of processing on the material’s structure.
A radial integration of the (110) polypropylene reflection, placed at about 14°2θ is shown in Figure 3. Polar integration of the images is depicted in Figure 4. It is possible to measure the degree of the orientation by measuring the FWHM of the reflections in the radial integration.
Figure 3. Radial Integration of the images shown in Figure 2.
Figure 4. Polar Integration of the images shown in Figure 2.
Significant morphological data, like texture, can be easily overlooked when standard 1-dimensional (1D) systems are used. With very large 2 theta and gamma coverage, the morphological data is present in every single measurement executed with the D8 DISCOVER integrated with PILATUS3 detector in a 2-dimensional (2D) iffraction (XRD2) configuration.
This information has been sourced, reviewed and adapted from materials provided by Bruker AXS Inc.
For more information on this source, please visit Bruker AXS Inc.