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

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 PLS1 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.