Analysis of polymers using near-infrared spectroscopy

Significance of the Topic

Near-infrared spectroscopy (NIR) enables rapid, nondestructive analysis of polymer and plastic materials
across a wide range of chemical and physical parameters without sample preparation.
Over 120 case studies demonstrate NIR’s value in process monitoring, quality control and material identification.

Study Objectives and Overview

This bulletin presents real-world examples of NIR applications using Metrohm instruments in polymer production
and formulation. Key goals include tracking chemical endpoints, assessing raw-material purity and optimizing product consistency.

Methodology and Instrumentation

• Sampling modes: transmission, diffuse reflectance and interactance using cuvettes, probes and sample cups
• Spectral range: 1100–2500 nm (some studies extend to 400–2500 nm)
• Data analysis: multivariate calibrations (PLS, MLR), derivative pretreatments and library matching
• Instrument platforms: Metrohm XDS RapidLiquid Analyzer, DS2500 Solid Analyzer, XDS SmartProbe Analyzer and Process Analyzer

Key Findings and Discussion

• Quantitative parameters: hydroxyl and acid values in polyols and polyesters; melt flow/index; viscosity; density; moisture; extractables; monomers and additives
• Process monitoring: real-time reaction endpoints; curing degree of thermosets; inline process control of polymerization
• Compositional analysis: copolymer and comonomer ratios; plasticizer, stabilizer and antioxidant levels; blend homogeneity
• Qualitative characterization: polymer type identification; coating detection; contamination screening; product classification
• Physical measurements: film and layer thickness; particle size effects; surface coatings and binder levels

Benefits and Practical Applications

• Inline or at-line monitoring provides immediate process feedback
• No sample preparation accelerates throughput and reduces lab workload
• Nondestructive testing preserves valuable materials
• Improved product consistency with reduced waste and rework
• Broad applicability across plastics, elastomers, composites, coatings and packaging

Future Trends and Opportunities

• Integration of compact NIR sensors into automated production lines
• Advanced chemometric and machine-learning calibration models
• Handheld and miniaturized fiber-optic probes for field and at-site testing
• Extension to new polymer chemistries, composites and recycled materials
• Industry 4.0 integration: digital twins, cloud analytics and real-time quality assurance

Conclusion

NIR spectroscopy, as demonstrated in Application Bulletin AB-414, delivers a versatile and robust platform for rapid polymer analysis.
It supports comprehensive monitoring of chemical composition, physical properties and process endpoints, enabling significant
efficiency gains, quality improvements and cost savings in polymer manufacturing.

Reference

Application Bulletin AB-414: Analysis of Polymers Using Near-Infrared Spectroscopy