Evaluation of Techniques for Determination of Hydroxyl Value in Materials for Different Industrial Applications

Abstract

When some materials need to be characterized, the hydroxyl number (IOH) determination is especially useful, mainly for those applied in the aerospace field. Usually, this characterization is performed by wet chemistry, using methodologies involving several steps, such as derivatization. This is a time-consuming and costly step. On the other hand, when the analysis is performed by Fourier transform infrared (FT-IR) spectroscopy, the most used region is the medium infrared (MIR) and transmission techniques are usually employed. However, FT-IR methodology developed error is usually not discussed. FT-IR methodology was developed in near infrared (NIR) and MIR regions, including non-conventional techniques, such as universal attenuated total reflection (UATR) and transflectance (near infrared reflection accessory [NIRA]), and transmission, to determine IOH in surfactants, used in aerospace catalysts/cosmetic products, and polyesters, applied in paints. According to the samples’ characteristics, surfactants were analyzed by transmission/solution and, as received, by NIRA. Polyesters were analyzed by UATR and NIRA, as received. The IOH values for all samples were also measured by wet chemistry and/or potentiometry (supplier’s data) and used as reference. Good linear correlations were observed between 0.939 and 0.976, being considered with good precision, and between 88% (NIRA) and 98% (MIR) of the results were explained by developed methodologies.

Natural Oil Polyol from High-Oleic Palm Oil─Reaction Kinetics and Monitoring Using Near-Infrared Spectroscopy

“…The best correlation with the hydroxyl value obtained from titration was observed within the 2038 to 2092 nm interval. This region of the spectra is related to combination bands of hydroxyl groups, , and it has been previously used for the spectroscopic quantification of polyols and alcohols. , The corresponding parity plots of the oxirane and hydroxyl values of calibration samples obtained from titrimetric and correlated NIR spectra are presented in Figure . As noticed, no systematic error was evidenced as deviations were randomly distributed around the entire interval.…”

“…This is normally carried out using time-consuming and waste-generating titrimetric methods that involve the use of strong inorganic acids, highly reactive and harmful acetic anhydride, and highly toxic pyridine. , Alternatively, greener and safer spectroscopic methods could be implemented to monitor reaction progress. For instance, both oxirane and hydroxyl groups can be quantitatively analyzed by mean of Fourier transform infrared (FTIR) and near-infrared (NIR) spectroscopy. − In particular, NIR has different advantages such as little or no sample preparation, low cost, and less time consuming. Also, it enables multiple analyses from a single spectrum .…”

Properties of Hydroxyl‐Terminal Polybutadiene (HTPB) and Its Use as a Liner and Binder for Composite Propellants: A Review of Recent Advances

“…Regarding the characterization of these HTPB‐based materials, non‐conventional FT‐IR spectroscopy techniques can be of great value, as we have previously reported [161]. Moreover, the fact that there are few studies in the near‐infrared (NIR) region, or even the absence of researches with specific accessories such as reflectance, NIRA generates great interest for further research in the resin characterization field.…”