Monitoring the melt-extrusion transesterification of ethylene-vinylacetatecopolymer by self-modeling curve resolution analysis of on-line near-infrared spectra

The transesterification of molten ethylene-vinylacetate (EVA) copolymers by octanol with sodium methoxide as catalyst in an extruder has been monitore d by on-line near infrared (NIR) spectroscopy. A total of 60 NIR spectra we re acquired for 37 min with the last spectrum recorded 31 min after the add ition of octanol and catalyst was stopped. The experimental spectra show st rong baseline fluctuations which are corrected for by multiplicative scatte r correction (MSC). The chemometric methods of the orthogonal projection ap proach (OPA) and multivariate curve resolution (MCR) were used to resolve t he spectra and to derive concentration profiles of the species. The detaile d analysis reveals the absence of completely pure variables which leads to small errors in the calculation of pure spectra. The initial estimation of a concentration that is necessary as an input parameter for MCR also presen ts a non-trivial task. We obtained results that were not ideal but applicab le for practical concentration control. They enable a fast monitoring of th e process in real-time and resolve the spectra of the EVA copolymer and the ethylene-vinyl alcohol (EVAL) copolymer to be very close to the reference spectra. The chemometric methods used and the decomposed spectra are discus sed in detail.