Determination of moisture content of polyamide 66 directly from combination region near-infrared spectra



The hygroscopic nature of polyamide (PA) polymers motivates the development of analysis tools for use in assessing their moisture content. Among possible analysis techniques, near-infrared (near-IR) spectroscopy is non-destructive, requires little or no sample preparation, and is compatible with sample thicknesses on the order of mm. The work reported here makes use of transmission near-IR spectroscopy in the combination region (5000–4000 cm−1) to develop a protocol for assessing the moisture content of PA 66 samples directly from their spectral intensities after preprocessing with the standard normal variate transform and partial least-squares. The method is compatible with online or continuous monitoring applications and can be calibrated without the use of destructive reference measurements such as thermogravimetric analysis. The long-term calibration performance of the technique is evaluated, and on a scale of 0–100% moisture uptake, the standard error of prediction is found to average 1.4% over 6 months. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40645.