Use of near-infrared spectrometry in control analyses of acrylic fibre manufacturing processes

Near-infrared (NIR) spectroscopy was used in control analyses for sodium thiocyanate and 90 : 10 (w/w) acrylonitrile-vinyl acetate copolymer in spinning solutions used for manufacturing textile acrylic fibres. NIR spectra were recorded in the transflectance mode, using fibre optics and a ceramic disk as reflecting surface. Partial least-squares regression (PLSR) was used to construct models for both analytes, using the test set for external validation. Second-derivative and standard normal variate (SNV) spectra led to simplified and more robust models than conventional spectra. Two PLS 1 models for the individual determination of the analytes and a PLS2 model for their joint simultaneous determination are proposed. The errors obtained for the validation samples were 1.6% for NaSCN and 2.6% for the copolymer. The robustness of the proposed calibration models was confirmed by using them in control analyses of samples manufactured several months after the models were constructed. (C) 1999 Elsevier Science B.V. All rights reserved.