DISCRIMINATION OF ETHYLENE VINYL ACETATE COPOLYMERS WITH DIFFERENT COMPOSITION AND PREDICTION OF THE CONTENT OF VINYL-ACETATE IN THE COPOLYMERS AND THEIR MELTING-POINTS BY NEAR-INFRARED SPECTROSCOPY AND CHEMOMETRICS/

Near-infrared (NIR) diffuse reflectance spectra have been measured by use of a rotating drawer for pellets of 12 kinds of ethylene/vinyl ace tate (EVA) copolymers with vinyl acetate (VA, the comonomer) varying i n the 7-44 wt % range. They are unambiguously discriminated from one a nother by a score plot of the principal component analysis (PCA) Facto r 1 and 2, based upon the NIR spectra pretreated by multiplicative sca tter correction (MSC). Principal component (PC) weight loadings for Fa ctor 1 show that the discrimination relies largely upon bands due to t he overtone and combination modes arising from the Vh unit. We have fo und one ''outlier'' in the score plot and elucidated its spectral char acteristics based upon PC weight loadings for Factor 2. Partial least- squares (PLS) regression has been applied to propose calibration model s which predict the VA content in EVA. The models have been prepared f or three kinds of pretreatment, the first derivative, the second deriv ative, and MSG; and four kinds of wavelength regions. The NIR spectra in the 1100-2200 nm region after the MSC treatment has given the best correlation coefficient and standard error of prediction (SEP) of 0.99 8 and 0.70%, respectively. The calibration models, prepared by NIR dif fuse reflectance spectroscopy for the pellet samples, are compared. wi th previously reported models by NIR transmission spectroscopy for the flowing molten samples, and viith those by Raman spectroscopy for the pellet samples. PLS regression has also allowed us to predict melting points of the copolymers with the correlation coefficient and SEP of 0.997 and 0.78 degrees C, respectively. (C) 1998 John Wiley & Sons, In c.