FT-NIR-Spectroscopy for Process Monitoring of Polymers

Significance of the Topic

Real-time control of polymer production is critical for achieving total quality management and zero-defect operation in the plastics industry. Fast, reliable and non-invasive analytical methods are essential to monitor chemical reactions and material flows, reduce waste and ensure consistent product quality.

Objectives and Study Overview

This application note demonstrates the use of FT-NIR spectroscopy to monitor polymer processes inline. A case study on polyethylene film production illustrates how molecular information from near-infrared spectra can be used to track chemical and physical properties during polymerization, extrusion and film winding.

Methodology and Instrumentation

The study employs a MATRIX-F FT-NIR process spectrometer paired with fiber-coupled probe heads. Two probe designs are used:

• Transmission probes with stainless steel or Hastelloy housing and sapphire windows for translucent liquids.
• Diffuse reflection probes for scattering or opaque samples such as polymer melts, powders and pellets.

Spectral data are streamed to process control software (CMET) and can be output via 4–20 mA, Modbus, Profibus DP or OPC DA for automated feedback.

Main Results and Discussion

Inline FT-NIR monitoring enabled:

• Real-time tracking of polymerization progress, with clear density (red) and Melt Flow Index (blue) profiles.
• Early detection of deviations in chemical parameters (OH-number, NCO-content, acid value, residual monomer).
• Quality control checkpoints before extrusion and on the finished film to identify defects.

The molecular specificity of the NIR spectra allowed simultaneous evaluation of chemical and rheological properties, reducing analysis time from hours to seconds.

Benefits and Practical Applications

The FT-NIR approach offers:

• Non-destructive, inline analysis without process interruption.
• Rapid feedback to minimize off-spec production and waste.
• Simultaneous measurement of multiple chemical and physical parameters.
• Flexibility to retrofit existing processes via fiber optics.

This method is particularly valuable for QA/QC in polymerization, extrusion, molding and film production.

Future Trends and Opportunities

Advances in probe design for higher temperatures and pressures will extend FT-NIR monitoring to more challenging processes. Integration with Industry 4.0 platforms, machine learning for predictive analytics and expanded probe multiplexing are expected to further enhance process understanding and control.

Conclusion

FT-NIR spectroscopy using robust process probes and MATRIX-F instrumentation provides a powerful solution for inline polymer monitoring. Its molecular insight, speed and seamless integration into control systems support improved quality, reduced waste and greater process efficiency.

References

No external literature references were provided in the source application note.