Near Infrared Spectroscopy and Chemometrics Analysis of Linear Low-Density Polyethylene

Near infrared (NIR) diffuse reflectance spectra have been measured using a rotating drawer for pellets of 16 kinds of linear low-density polyethylene (LLDPE) with short branches and PE without any branches to propose a calibration model which predicts their density and to increase the understanding of NIR spectra of LLDPE. The density of the LLDPE samples investigated was in the range 0.911–0.925 g cm −3 . Partial least squares (PLS) regression has been applied to the original NIR spectra data set, their second derivatives and the spectra after multiplicative scatter correction (MSC) treatment to make up the models. The correlation coefficient was calculated to be 0.961, 0.965 and 0.970 for the original NIR spectra, their second derivatives and those with the MSC treatment, respectively, and the standard error of prediction ( SEP) was found to be 0.001 g cm −3 for all the cases. The regression coefficients plot for the calibration models shows that bands at 1192, 1376 and 1698 nm due to the overtone and combination modes of the CH 3 groups play important roles in the prediction of density.