Quality Control of Polyamides

Importance of Topic

Polyamides are widely used in industrial and consumer products due to their mechanical strength and thermal stability. Monitoring key quality parameters such as relative viscosity, functional end groups, and moisture is critical for ensuring consistent performance and meeting regulatory standards. Traditional wet chemical methods are time-consuming and labor-intensive, motivating the adoption of rapid, non-destructive techniques like near-infrared (NIR) spectroscopy for streamlined quality control.

Objectives and Study Overview

This application note evaluates the ability of the DS2500 Solid Analyzer to simultaneously determine relative viscosity, amine and carboxyl end group contents, and moisture levels in polyamide pellets within one minute. The study aims to compare NIR predictions against established primary methods (viscometry, titration, Karl Fischer) to assess precision, accuracy, and overall feasibility in routine analysis.

Methodology and Instrumentation

Polyamide pellets were measured directly in a rotating DS2500 Large Sample Cup without sample preparation. Reflection spectra were recorded over 400–2500 nm using the DS2500 Solid Analyzer. Data acquisition and chemometric model development were performed with Vision Air Complete software. Calibration and cross-validation routines produced figures of merit to evaluate predictive performance.

Used Instrumentation

• DS2500 Solid Analyzer (Metrohm No. 2.922.0010)
• DS2500 Large Sample Cup (Metrohm No. 6.7402.050)
• Vision Air 2.0 Complete Software (Metrohm No. 6.6072.208)

Main Results and Discussion

High correlation was observed between NIR predictions and reference values for all parameters:

• Relative viscosity: R2 = 0.986, SECV = 0.055 dl/g
• Carboxyl end group: R2 = 0.972, SECV = 11.1 meq/kg
• Amine end group: R2 = 0.981, SECV = 4.1 meq/kg
• Moisture content: R2 = 0.991, SECV = 0.067 %

Compared to conventional methods, NIR spectroscopy reduces total analysis time from over 90 minutes per parameter to under one minute for all four metrics combined.

Benefits and Practical Applications

• Time and cost savings by eliminating chemical reagents and sample preparation.
• Non-destructive, operator-friendly workflow suitable for production environments.
• Rapid feedback enables real-time process control and quality assurance.

Future Trends and Opportunities

Integration of NIR analyzers into production lines for inline monitoring and automated feedback loops is expected to grow. Advances in miniaturized sensors, cloud-based chemometric model management, and machine learning algorithms will further enhance predictive accuracy and adaptability across diverse polymer grades.

Conclusion

The DS2500 Solid Analyzer combined with chemometric models provides a fast, reliable, and cost-effective alternative to traditional wet chemistry for polyamide quality control. Its high predictive performance for viscosity, end group content, and moisture within one minute positions NIR spectroscopy as a valuable tool for routine and online analysis.