Quality control of polyols

Importance of the topic

Polyols are essential intermediates in the production of polyurethanes and other polymers. The hydroxyl value is a critical quality indicator that influences polymer properties and end-use performance. Traditional wet-chemical assays require reagents, generate waste, and take over 15 minutes per sample. A rapid, reagent-free analytical technique is needed to streamline quality control and accelerate decision-making.

Objectives and overview of the article

This whitepaper presents a pre-calibrated Near-Infrared Spectroscopy (NIRS) solution for the determination of hydroxyl value in polyols, compliant with ASTM D6342-12 and ISO 15603:2011. Key goals include:

• Delivering a turnkey calibration model based on extensive real-product spectra
• Enabling non-specialist operators to perform accurate measurements
• Reducing analysis time and cost per sample

Methodology and instrumentation used

The approach employs Metrohm’s DS2500 Near-Infrared Analyzer combined with Vision Air software and disposable vial holders. Major components:

• DS2500 NIR Analyzer for rapid spectral acquisition
• Pre-calibration model built on a large dataset of authentic polyol spectra
• Vision Air software offering simple pass/fail operation and advanced SOP management
• 8 mm disposable vials for non-destructive sample handling

Main results and discussion

The pre-calibration model yielded robust performance immediately after installation:

• Hydroxyl value prediction range: 16–1180 mg KOH/g
• Standard error of calibration (SECV): 13.9 mg KOH/g
• Correlation coefficient (R²): 0.994

Analyses are completed within 30 seconds without sample preparation, saving over 15 minutes per sample versus conventional wet-chemical methods. The method’s accuracy, reproducibility, and compliance with industrial QA/QC standards were confirmed. Calibration updates with customer samples can extend the model to additional parameters such as acid value or moisture.

Benefits and practical applications of the method

• Cost Reduction: Eliminates solvents, reagents, and waste-disposal expenses
• Speed and Convenience: Delivers results in under a minute with no chemical handling
• User Accessibility: Non-chemists perform routine checks; authorized users manage SOPs and data review
• Environmental Impact: Fully chemical-free, non-destructive analysis with minimal health and ecological risks

Future trends and possibilities

Adoption of NIRS pre-calibrations is expected to expand through:

• Integration into on-line and at-line process monitoring systems
• Expansion of calibration libraries to encompass broader polymer chemistries and quality parameters
• Enhanced connectivity and data analytics within Industry 4.0 frameworks
• Development of user-customizable calibration modules for niche applications

Conclusion

Pre-calibrated NIR spectroscopy represents a powerful alternative to traditional hydroxyl value assays in polyols, offering rapid, accurate, and reproducible results with minimal training and resource requirements. Metrohm’s DS2500 solution streamlines QA/QC workflows, reduces operational costs, and supports sustainable laboratory practices while ensuring compliance with ASTM and ISO standards.

References

• ASTM D6342-12: Standard Test Method for Hydroxyl Number of Polyols by Near Infrared Spectroscopy
• ISO 15603:2011: Plastics—Polyols—Determination of hydroxyl value
• ASTM D4274-14: Standard Test Method for Analysis of Alcohols and Polyols by Gas Chromatography