Using an X-Ray Diffractometer to Determine Crystallite Size and Polymorphism

Polymer materials are utilized in a diverse array of processes, which each possess different requirements with regards to the resilience of the material. Due to its cost-effectiveness and availability, Polypropylene (PP) is one of the most prevalent materials.

The chemical and mechanical resilience of polymer materials is not only dependent on type and crystallinity, but additionally on the polymorphic structure and domain size (crystallite size, CS). Implementing β-PP in place of α-PP demonstrably enhances chemical resilience and impact strength alike, although the viscosity remains at a similar level to α-PP.

Instrument

The Thermo Scientific™ ARL™ EQUINOX 100 X-ray diffractometer engages a bespoke Cu (50 W) or Co (15 W) micro-focus tube fitted with mirror optics. These low wattage requirements negate the need for an external water chiller, as well as other peripheral infrastructure, and therefore permit the instrument to be effectively conveyed from the laboratory to the field, or between laboratories.

ARL EQUINOX 100 X-ray diffractometer.

Figure 1. ARL EQUINOX 100 X-ray diffractometer.

The ARL EQUINOX 100 (c.f. Figure 1) offers very rapid data acquisition rates in comparison to competing diffractometers, due to its distinctive curved position sensitive detector (CPS). The instrument calculates all diffraction peaks concurrently, and in real time, and is consequently ideally suited for both reflection and transmission calculations.

Experimental

For XRD experiments, a sheet sample of PP (Polypropylene) was analyzed in transmission geometry for five minutes under Cu-Kα radiation. The quality of the data acquired with benchtop ARL EQUINOX 100 is similar to the data deriving from conventional high-power floor standing apparatus.

Qualitative analysis was performed with the use of MDI JADE 2010, which was employed in collaboration with the ICDD PDF4+ Organic database. CS was ascertained through the execution of Le Bail fitting and Scherrer’s equation.

Results

Comparing the data to ICDD PDF4+ Organic database explicitly provides results comprising primarily β-PP (blue) and traces of α-PP (grey), while there is a divergence of domain sizes between β-PP (33 nm) and α-PP (10 nm) (c.f. Figure 2).

Diffraction pattern of β-PP (blue) and α-PP (grey).

Figure 2. Diffraction pattern of β-PP (blue) and α-PP (grey).

Conclusion

The ARL EQUINOX 100 benchtop XRD tool, used in collaboration with the MDI JADE 2010 software package, and ICDD pdf4+ Organic database, is an efficient screening solution, enabling the convenient determination of the crystallite size and the polymorphism of polymer materials.

The intergrowth structure of α- and β- PP is an essential component of the resulting material, which is broadly implemented in industrial processes.

Authors: Dr. Simon Welzmiller, Ju Weicai, Application Specialists XRD.

This information has been sourced, reviewed and adapted from materials provided by Thermo Fisher Scientific - Elemental Analyzers.

For more information on this source, please visit Thermo Fisher Scientific - Elemental Analyzers.

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