Polyethylene content determination in polypropylene pellets by NIRS

Importance of the Topic

This study addresses the challenge of quantifying polyethylene content in polypropylene pellets to improve recycled polyolefins quality and mechanical performance.

Objectives and Study Overview

The application note describes the development of a near-infrared spectroscopy (NIRS) method to rapidly determine PE levels in PP blends ranging from 0.5 to 35%. Calibration models were built and validated against gravimetric reference data.

Methodology and Instrumentation

A total of 54 polymer blends with known PE concentrations were prepared using a compounder. Spectra were acquired on an OMNIS NIR Analyzer Solid equipped with a rotating large cup to minimize sample heterogeneity.

• OMNIS NIR Analyzer Solid
• Large holder and 100 mm cup
• OMNIS Software with Quant Development license

Main Results and Discussion

Two calibration ranges were evaluated:

• Full range (0.5–35% PE): R2CV = 0.987, SECV = 1.10%.
• Narrow range (0.5–9% PE): R2CV = 0.950, SECV = 0.60%.

Smaller concentration ranges improve absolute error at the expense of applicability span.

Benefits and Practical Applications

NIRS offers rapid analysis (seconds per sample) compared to ~60 min per sample by DSC. This enables high-throughput QC of recycled polyolefins and potential determination of other properties such as density.

Future Trends and Opportunities

Potential developments include inline monitoring during extrusion, expanded chemometric models for copolymer blends, miniaturized sensors for on-site analysis, and integration with process control systems.

Conclusion

The NIRS method provides a fast, accurate, and non-destructive alternative for polyethylene quantification in polypropylene, supporting efficient recycling and quality assurance.

References

• No literature references provided in the original document.