Ash determination in polyethylene

Importance of the topic

Ash fillers composed of silicon, magnesium and iron oxides are added to polyethylene to tailor mechanical and thermal properties. Accurate determination of ash content is essential for quality control in polymer production and for ensuring consistency of product performance.

Goals and overview of the study

This study aims to develop and validate a rapid near infrared spectroscopy method for quantifying low levels of ash in polyethylene granulates. The performance of the NIR approach is compared to the standard thermogravimetric analysis reference method.

Methodology and instrumentation

One hundred and fifty four polyethylene samples with ash contents ranging from 0.07 to 0.12 weight percent were analyzed. NIR spectra were collected using a DS2500 Solid Analyzer equipped with a large sample cup under rotation to average particle size effects. Calibration model development and data acquisition were performed with Vision Air Complete software. Reference ash content was determined by TGA under nitrogen.

Main results and discussion

Vis NIR spectra were used to construct a prediction model for ash content. Calibration results showed a coefficient of determination of 0.77. Figures of merit indicated a standard error of calibration of 0.0055 weight percent and a cross validation error of 0.066 weight percent. These results demonstrate reasonable prediction accuracy for routine analysis, with some limitations at very low ash levels and the influence of sample heterogeneity.

Benefits and practical applications

• The NIR method delivers ash content results in less than one minute compared to approximately two hours by TGA
• Non destructive analysis with minimal sample preparation and no consumable gases
• Suitable for at line or inline quality control in production environments

Future trends and applications

• Extension of NIR calibration libraries to cover a broader range of fillers and polymer grades
• Integration of advanced chemometric and machine learning algorithms to improve prediction robustness
• Development of portable and process analytical technology implementations for real time monitoring

Conclusion

The application note demonstrates the feasibility of near infrared spectroscopy for rapid quantification of low ash levels in polyethylene granulates. The NIR approach offers substantial time savings and operational simplicity, making it an effective tool for routine quality control.

Reference

• Metrohm Application Note AN NIR 100 Ash determination in polyethylene, Metrohm AG