Quality Control of Silicone rubber

Importance of the topic

Determining vinyl content in silicone rubber is crucial for controlling cross-linking density, mechanical properties, and product performance. Traditional gas chromatography methods require chemical reagents, extensive sample preparation, and skilled analysts, resulting in lengthy analysis times and higher operational costs.

Study objectives and overview

This work evaluates visible-near infrared (Vis-NIR) spectroscopy as a rapid, reagent-free alternative for quantifying vinyl groups in silicone rubber. The performance of the Vis-NIR approach is compared against the standard acid-conversion gas chromatography (GC) method.

Methodology

Silicone rubber samples were measured in transflection mode across 400–2500 nm without any chemical pretreatment. A 1 mm gold diffuse reflector defined a consistent path length, while the DS2500 Slurry Cup ensured easy sample placement and cleaning. Spectral data were collected and processed in Vision Air Complete software to develop multivariate calibration models linking NIR predictions to GC reference values.

Used instrumentation

• DS2500 Solid Analyzer (400–2500 nm spectral range)
• DS2500 Slurry Cup (simplified sample handling)
• Gold diffuse reflector, 1 mm path length
• Vision Air 2.0 Complete software (data acquisition and model development)

Main results and discussion

The calibration model achieved a coefficient of determination (R²) of 0.989, with a standard error of calibration of 0.0076 % and cross-validation error of 0.0089 %. Correlation diagrams demonstrated strong agreement between Vis-NIR predictions and GC reference values. Each NIR measurement took under one minute, compared to approximately 60 minutes for the GC workflow, including sample preparation.

Benefits and practical applications

• Rapid, reagent-free analysis (< 1 minute per sample)
• Minimal sample preparation and straightforward operation
• Reduced labor, training, and consumable costs vs. GC
• Suitability for at-line or online quality control in silicone manufacturing

Future trends and applications

Advances in chemometric algorithms and machine learning may further refine predictive accuracy and expand the method to other polymer additives and contaminants. Portable or inline Vis-NIR systems could enable real-time monitoring and automated process control in diverse industrial environments.

Conclusion

Vis-NIR spectroscopy with the DS2500 Solid Analyzer offers a fast, cost-effective, and accurate solution for quantifying vinyl content in silicone rubber. By eliminating reagents and drastically reducing analysis time compared to GC, this approach enhances quality assurance and production efficiency.