Determination of moisture content in impregnated paper using near infrared spectroscopy

The variations in the NIR spectra depending on moisture content have been investigated. For this purpose a number of oil impregnated paper samples were kept in four desiccators with relative humidity of 6.6, 11, 59.5 and 75.5% respectively. The obtained moisture content in the paper ranged from 1.7% up to 8%. The NIR spectra were measured on these samples as well as on a sample during moisture adsorption, thus obtaining moisture contents in a range of 0-2.4%. The measured spectra were then processed using multivariate analysis. Both the H₂O combination band at about 1950 nm and the O-H stretch first overtone at about 1450 nm were well identified and allowed for calibration of the NIR spectra against various moisture contents. The wavelengths in the ranges 1380-1515 nm and 1850-2220 nm were used for the calibration of the NIR spectra. A partial least squares model was developed for the estimation of moisture content in impregnated paper