Quality Control of Polyols

Importance of the topic

The hydroxyl number is a critical quality parameter for polyols used in polyurethane and other polymer production. Accurate and rapid determination of this parameter ensures consistent product performance, reduces waste, and supports regulatory compliance. Traditional titration methods employ toxic and corrosive reagents, creating safety and environmental concerns.

Objectives and Study Overview

This study aimed to demonstrate a chemical-free method for measuring the hydroxyl number of polyols according to ASTM D6342-12. Using Vis-NIR spectroscopy with the XDS RapidLiquid Analyzer, the goal was to achieve fast, reliable, and cost-efficient predictions without hazardous reagents or extensive sample preparation.

Methods and Methodology

Polyol samples were analyzed in transmission mode over the wavelength range of 400–2500 nm. Measurements were performed at a controlled temperature of 30 °C using 4 mm disposable glass vials. No sample preparation or added chemicals were required. Spectral data were recorded and processed using Vision Air Complete, and calibration models were built against reference titration values following ASTM D6342-12.

Used Instrumentation

• XDS RapidLiquid Analyzer (400–2500 nm, built-in temperature control)
• Disposable glass vials, 4 mm path length
• Vision Air Complete software for data acquisition and chemometric model development

Main Results and Discussion

Calibration models yielded a correlation coefficient (R2) of 0.998, with a standard error of calibration (SEC) of 1.28 mg KOH/g and a standard error of cross-validation (SECV) of 1.42 mg KOH/g. Correlation diagrams showed excellent agreement between Vis-NIR predictions and titration reference values. Each analysis required less than one minute, and reproducible spectra were ensured by stable measurement conditions.

Benefits and Practical Applications

• Eliminates toxic reagents such as p-toluenesulfonyl isocyanate and tetrabutylammonium hydroxide
• Rapid, under-one-minute analysis without sample preparation
• Substantially reduced running costs (approx. $2,063 vs. $18,188 per year for 10 analyses/day)
• Improved laboratory safety and environmental sustainability

Future Trends and Opportunities

Vis-NIR spectroscopy can be extended to other polymer quality parameters and raw materials. Integration into inline process control will enable real-time monitoring. Emerging chemometric and machine-learning techniques are expected to enhance prediction accuracy and robustness. Greater automation and digital workflows will further streamline quality assurance in industrial settings.

Conclusion

The chemical-free Vis-NIR approach using the XDS RapidLiquid Analyzer offers a fast, accurate, and cost-effective alternative to traditional titration for hydroxyl number determination in polyols, fulfilling ASTM D6342-12 requirements while enhancing safety and reducing operational expenses.