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.