Determination of Temperatures of Polyamide 66 Directly from Near- Infrared Spectra

The commercial importance of polyamides (PAs) motivates the development of chemical analysis tools for use in characterizing their structure and properties. Near-infrared (IR) spectroscopy offers advantages in this regard because of its simplicity of sample preparation and compatibility with sample thicknesses on the order of millimeters. For applications in which the measurement of sample temperature is difficult with a conventional probe, the work presented here demonstrates the ability to determine the temperature of PA 66 directly from its near-IR spectrum. Temperature-induced changes in spectral shape in the 4000-5000 cm(-1) region are extracted through application of the discrete wavelet transform, and the resulting preprocessed spectra are submitted to partial least-squares regression to construct predictive models for temperature. These models are tested across different samples of PA 66 and over a time span of 7 weeks. Errors in predicted temperatures averaged 1.50 degrees C over the range of 21-105 degrees C. (c) 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40476.