Characterization of paper finishes by use of infrared spectroscopy in combination with canonical variate analysis

The finishing process used by the paper industry involves subjecting the paper surface to the action of chemicals and physical treatments in a series of operations intended to provide an end-product suitable for its intended use. In this work, we studied various paper finishes by using infrared spectra processed with appropriate chemometric techniques. To this end, we used a wide range of paper samples supplied in various finishes (coated, offset and cast-coated) by several paper manufacturers. Fourier transform middle-infrared (FTIR) spectra for the paper samples were recorded by using an ATR module, and reflectance near-infrared (NIR) spectra with the aid of a fibre-optic probe. Both techniques are fast and require no sample pretreatment.The primary aim of this work was to develop a new methodology affording the accurate classification and identification of paper finishes in samples other than those used to construct the calibration model. To this end, we used the discriminant chemometric techniques principal component analysis (PCA) and canonical variate analysis (CVA), application of which was followed by that of the k-nearest neighbour algorithm to the samples in the prediction set. This procedure was also used to classify the coated samples into three subgroups. Both FTIR and NIR spectroscopy allowed most of the samples in the prediction sets to be accurately classified and identified.