The hydroxyl value is a critical parameter routinely measured by polyol manufacturers to determine the quality of their product. Users of these polyol products often depend on the manufacturer’s certification of quality to confirm the appropriateness of the material for their own manufacturing processes. The hydroxyl value measurement is a key criterion for this certification because it reflects critical properties of the polyol, particularly the polymer chain length and purity. These properties, in turn, reflect the physical properties of the material. Ultimately, the physical properties of the product dictate its suitability for the purposes of the end user.
Use of a material with inappropriate properties is usually very costly as it leads to the manufacture of products that are not within specifications, wasting production time and materials. Polyol manufacturers often use the measurement of the hydroxyl value as a critical in-process test to indicate the completeness of a polymerization reaction.
Traditionally, this test has been accomplished by a time consuming titration analysis. In such a testing scheme, samples are collected at specified times during the reaction process. These samples are then taken to a process or QC lab and the titration is performed. The results are calculated and feedback is communicated to the process operator(s). At that point, any necessary adjustments are made.
Titration analyses are labor-intensive and time-consuming. It takes a substantial amount of time to receive the test results and determine whether adjustments need to be made or if the test can be terminated. Also, titration analysis might not show problems with the product if such issues do not affect the hydroxyl value measurement.
Fourier transform near-infrared (FT-NIR) spectroscopy has become the method of choice, replacing titration for the measurement of the hydroxyl value in polyols. FT-NIR offers the advantages of speed, simplicity of operation and freedom from the use of noxious chemicals. Operators in the production area can potentially use the technique in an at-line mode. Such a method leads to rapid feedback which allows timely process adjustments and quicker detection of reaction end-points. This in turn saves time, improves efficiency and, ultimately, leads to cost savings.
Another advantage is that worker exposure to chemicals is greatly reduced by the implementation of FT-NIR methods. FT-NIR also has the potential to give analysts more comprehensive information about the product. Even if there is a problem that does not affect the hydroxyl measurement, FT-NIR can still detect deviations while a titration may not. Many times, polyol manufacturers must also measure other parameters related to the hydroxyl value. For example, polyester producers must measure acid number. FT-NIR has been proven to be advantageous for these measurements and other critical measurements for polyol products. Hence, the use of FT-NIR can help to streamline processes by allowing the measurement of multiple properties with one data collection event.
Read FT-NIR for Online Analysis in Polyol Production which describes the use of FT-NIR spectroscopy for the determination of the hydroxyl value and other critical polyol properties. FT-NIR measurements for all of these properties were shown to be both accurate and precise for near-line, at-line or QC lab determinations.
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