Quality control of Bromobutyl rubber

Significance of the Topic

This application note addresses rapid quality control of Bromobutyl rubber (BIIR), a key elastomer in automotive and industrial applications. Traditional assays for parameters such as viscosity, bromine content and additives are time‐consuming and require reagents. Near‐infrared spectroscopy (NIRS) offers a reagent‐free, high‐throughput alternative.

Study Objectives and Overview

The study aimed to develop and validate a NIRS calibration model for simultaneous determination of multiple BIIR quality parameters. A dataset of 68 industrial BIIR samples was used to correlate spectral data with reference laboratory methods.

Methods and Instrumentation

• Samples: 68 Bromobutyl rubber specimens covering typical production variability
• Spectrometer: Metrohm DS2500 Liquid Analyzer covering 400–2500 nm
• Sampling: Disposable 8 mm vials, transmission mode, temperature‐controlled at 50 °C
• Software: Vision Air Complete for spectral acquisition and chemometric model building
• Reference methods: Mooney viscometer (viscosity), titration (bromine), oven‐drying (volatile matter), XRF (calcium stearate), NMR (functional bromide)

Key Results and Discussion

The calibration models delivered strong correlations between NIRS predictions and lab references:

• Mooney viscosity: R² = 0.73; SECal = 0.44 %; SECV = 0.61 %
• Bromine content: R² = 0.96; SECal = 0.046 %; SECV = 0.064 %
• Volatile matter: R² = 0.77; SECal = 0.046 %; SECV = 0.056 %
• Calcium stearate: R² = 0.95; SECal = 0.082 %; SECV = 0.153 %
• Functional bromide: R² = 0.96; SECal = 0.044 %; SECV = 0.060 %

The high R² values for bromine, stearate and bromide indicate precise quantification, while moderate values for viscosity and volatiles demonstrate acceptable performance for routine QC.

Benefits and Practical Applications

• Analysis time under one minute per sample
• No chemical reagents or extensive sample preparation
• Disposable vials simplify cleaning and reduce cross‐contamination
• Simultaneous multi‐parameter measurement enhances laboratory throughput
• Reduced operational costs and environmental impact

Future Trends and Opportunities

• Integration of NIRS in production lines for real‐time process control
• Expansion of calibration libraries to other rubber grades and additives
• Application of advanced chemometric and machine learning techniques for model refinement
• Automation of sampling using robotic interfaces for continuous monitoring

Conclusion

Near‐infrared spectroscopy using the DS2500 Liquid Analyzer provides a reliable, rapid, and eco‐friendly alternative to classical methods for BIIR quality control. The validated models enable simultaneous quantification of key parameters, streamlining laboratory workflows and improving operational efficiency.

Reference

• Metrohm Application Note AN-NIR-107, Quality control of Bromobutyl rubber