Determination of the degree of crystallinity in PE using ARL X’TRA Companion X-ray Diffractometer

Significance of the Topic

The degree of crystallinity in polyethylene critically influences its mechanical strength, thermal stability and optical clarity. Accurate quantification of crystalline and amorphous phases guides material selection and quality control in polymer manufacturing and research.

Objectives and Overview

This study demonstrates a routine method for determining the degree of crystallinity (DoC) and average crystallite size in polyethylene (PE) using X-ray diffraction (XRD). By applying one-click Rietveld analysis on the Thermo Scientific ARL X’TRA Companion, the workflow is optimized for both industrial QA/QC and research environments.

Used Instrumentation

The following equipment and software were employed:

• Thermo Scientific ARL X’TRA Companion benchtop X-ray diffractometer
• θ/θ goniometer (160 mm radius) in Bragg–Brentano geometry
• 600 W Cu Kα X-ray source (λ = 1.5418 Å)
• Divergence and Soller slits with beam knife for air-scatter reduction
• Solid-state pixel detector (55 × 55 µm pitch) for rapid data acquisition
• Profex software (BGMN) for individual peak fitting and Rietveld quantification

Methodology

A medium-density PE sample was mounted in a fixed holder and scanned in reflection mode using Cu Kα radiation for a 3-minute acquisition. Individual peaks corresponding to amorphous halo and crystalline reflections were deconvoluted in Profex. The integrated intensities yielded the DoC, while the Scherrer equation provided average crystallite sizes.

Main Results and Discussion

The analysis produced a degree of crystallinity of 62.3 %, consistent with typical MDPE values. The average crystallite size of the crystalline domains was calculated as 13.3 nm. The high precision of the pixel detector and optimized slit configuration ensured clear separation of amorphous background and crystalline peaks.

Benefits and Practical Applications

The XRD approach offers:

• Non-destructive, rapid assessment of polymer crystallinity
• Sensitivity to low crystallinity levels and structural details
• Automated one-click analysis to streamline QA/QC workflows
• Capability to inform processing parameters and end-use performance

Future Trends and Opportunities

Emerging developments include integration of in situ XRD for real-time process monitoring, coupling with thermal analysis for simultaneous DSC–XRD, and application of machine learning to accelerate peak deconvolution and phase identification.

Conclusion

The ARL X’TRA Companion X-ray diffractometer reliably quantifies crystallinity and crystallite size in polyethylene. Its user-friendly interface and automated analysis modules make it ideal for industrial quality control and advanced polymer research.

References

1. N. Doebelin, R. Kleeberg, Journal of Applied Crystallography, 2017, 48, 1573–1580.