Rapid and nondestructive analysis of the ethylene content of propylene/ethylene copolymer by near-infrared spectroscopy

Abstract Near Infrared (NIR) spectroscopy has been successfully implemented for the rapid and nondestructive analysis of ethylene content in flake and pellet of propylene/ethylene copolymer. The change of copolymer structure due to the variation of ethylene content during copolymerization reaction resulted in systematic NIR spectral variations. By using a partial least squares (PLS) regression combined with second derivative algorithm, relevant spectral information was successfully extracted and correlated with conventional infrared (IR) method. The error of NIR spectroscopic method for determination of ethylene content was comparable to the reference IR method. With the help of rapid and nondestructive natures of NIR spectroscopy, ethylene content can be measured less than 2 min without a physical sample pretreatment and the copolymerization process can be optimally controlled by continuously reflecting the process status from the NIR measurement.