XRD investigation of three types of polyethylene films with ARL EQUINOX 100 X-ray Diffractometer

Importance of the Topic

Polyethylene (PE) is the most widely produced plastic, accounting for over one-third of global polymer output. Its versatile properties make it indispensable in packaging, consumer goods and industrial applications. Understanding crystallinity and microstructure through rapid benchtop X-ray diffraction (XRD) enables quality control, material development and optimization of mechanical performance.

Objectives and Study Overview

This application note evaluates three common PE film types – high-density (HDPE), low-density (LDPE) and linear low-density (LLDPE) – using the Thermo Scientific ARL EQUINOX 100 benchtop XRD system. The goals are to:

• Determine percent crystallinity and crystallite size of each film variant
• Compare results for two sample series (B and C) per film type
• Demonstrate the speed and resolution capabilities of the EQUINOX 100 for polymer analysis

Methodology

Film samples were mounted in windowed cardboard frames and placed in a stationary reflection holder. XRD patterns were collected from 0°–115° 2θ using Co Kα radiation (λ = 1.78897 Å) with a 1-minute acquisition time. Raw data were processed using whole pattern fitting (WPF) via Rietveld refinement in MDI JADE 2010 with the ICDD PDF-4+ database.

Instrumentation Used

Thermo Scientific ARL EQUINOX 100 X-ray Diffractometer equipped with a low-wattage Cu (50 W) or Co (15 W) micro-focus source and curved position sensitive detector (CPS) for simultaneous, real-time peak measurement. The compact design requires no external water chiller, facilitating laboratory and field deployment.

Main Results and Discussion

Analysis of percent crystallinity and crystallite size revealed:

• HDPE films exhibited the highest crystallinity (87–90 wt %) with crystallite sizes of ~200–307 Å, consistent with their linear molecular structure and high density (>0.941 g/cm³).
• LDPE films showed intermediate crystallinity (52–55 wt %) and smaller crystallites (~138–162 Å) due to extensive short-chain branching and lower density (0.910–0.940 g/cm³).
• LLDPE films appeared predominantly amorphous in the studied films (<1 wt % crystalline) with crystallite sizes of ~33–181 Å, suggesting orientation effects in the thin film that limit coherent diffraction from short branches.

The rapid 1-minute measurements and low instrument background enabled reliable quantification of amorphous and crystalline fractions, as well as determination of crystallite dimensions and fit quality (R-factor ~12–14 %, Goodness of Fit ~1.1–1.4).

Benefits and Practical Applications

Benchtop XRD analysis of PE films delivers:

• Fast, accurate assessment of crystallinity for process control and product specification
• Non-destructive evaluation of film quality in production and research settings
• Support for formulation screening, aging studies and mechanical property optimization

Future Trends and Applications

Advances in detector technology and data processing will further reduce analysis times and improve sensitivity to low-crystallinity phases. Integration with in-line and at-line systems can enable real-time monitoring of polymer extrusion and film formation. Coupling XRD with complementary techniques (e.g., DSC, FTIR) will deepen insights into structure–property relationships and support development of sustainable, bio-based polyethylenes.

Conclusion

The Thermo Scientific ARL EQUINOX 100 benchtop XRD platform offers rapid, high-resolution analysis of PE film crystallinity and microstructure. One-minute measurements yield reliable quantification of crystalline and amorphous content, as well as crystallite size, making it an ideal tool for both laboratory research and quality assurance in polymer manufacturing.

References

1. Ceresana Research. Market Study: Polyethylene – HDPE. May 2012.
2. Ceresana. Market Study: Polyethylene – LDPE (2nd edition). October 2014.
3. Ceresana. Market Study: Polyethylene – LLDPE (2nd edition). November 2014.