Quality Control of Polyols

Significance of the Topic

The hydroxyl number is a critical parameter for characterizing polyol quality in polymer production. Traditional titrimetric methods rely on toxic reagents and require significant sample preparation time. Implementing a chemical-free, rapid spectroscopic approach addresses safety, cost, and throughput concerns in industrial and laboratory environments.

Objectives and Overview of the Study

This application note evaluates the feasibility of using visible-near infrared (Vis-NIR) spectroscopy to determine the hydroxyl number of polyols according to ASTM D6342-12. The goal is to compare performance, speed, and operating costs against the established titration method (ASTM D4274-16) while eliminating hazardous reagents.

Methodology and Instrumentation

The study employed an XDS RapidLiquid Analyzer operating in transmission mode across 400–2500 nm. Samples were measured in disposable 4 mm pathlength vials at a controlled temperature of 30 °C. No chemical reagents or sample pretreatment were required. Calibration and prediction models were developed using Vision Air Complete software, correlating Vis-NIR spectra with reference titration values.

• XDS RapidLiquid Analyzer (Metrohm 2.921.1410)
• Disposable glass vials, 4 mm diameter (Metrohm 6.7402.010)
• Vision Air Complete spectroscopy software (Metrohm 6.6072.208)

Main Results and Discussion

Vis-NIR calibration yielded a correlation coefficient (R2) of 0.998 for hydroxyl number prediction. The standard error of calibration (SEC) was 1.28 mg KOH/g and the standard error of cross-validation (SECV) was 1.42 mg KOH/g. These figures of merit demonstrate accuracy and precision comparable to wet chemical titration. Analysis time was under one minute per sample, significantly faster than the five-minute titration protocol.

Cost analysis over one year for 10 daily analyses showed total running expenses of approximately $2 063 with NIR versus $18 188 using titration, driven by lower consumable costs and reduced operator time.

Benefits and Practical Applications of the Method

• Chemical-free operation enhances laboratory safety and environmental compliance.
• Rapid analysis reduces turnaround time and increases sample throughput.
• Lower consumable expenses and minimal maintenance decrease overall operating costs.
• Non-destructive testing preserves sample integrity for further analysis.

Future Trends and Potential Applications

Advancements in Vis-NIR instrumentation and chemometric algorithms are expected to enable inline process monitoring of polyol production. Integration with automated sampling systems and real-time data analytics will facilitate closed-loop quality control. Expansion of calibration libraries may extend the approach to other polymer precursors and complex formulations.

Conclusion

The Vis-NIR method offers a fast, accurate, and cost-effective alternative to titration for determining the hydroxyl number of polyols. Eliminating hazardous reagents and reducing analysis time improves safety and efficiency in quality control workflows, aligning with industry trends toward greener analytical solutions.