Utilizing zero crossover points in the near infrared reflectance analysis of industrial polymers

Near infrared reflectance methods were developed for the analysis of polymer pellets and films. Second derivative spectra were used to minimize the effects of scattering and to enhance spectral features. Zero crossover points, places in the derivative spectra where there is negligible response to concentration changes, were employed to minimize interferences at the measuring wavelengths. Two examples illustrate the utility of this technique for industrial quality assurance analyses. The examples include the measurement of three hydrocarbon polymers, directly in transparent pellets, and the determination of 0.1% MEK in an acrylic film. Precision and accuracy were found to be at least equal to that of other methods, and time savings were considerable.