Real-time monitoring of poly(ethylene vinyl acetate) extrusion using At-Process Spectroscopy
susan Barnes, M Sibley, P Coates, H.G.M Edwards
IRC in polymer engineering
United Kingdom

Keywords: in-line, spectroscopy, EVA

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Analysis of polymer production processes using spectroscopic and ultrasonic techniques is becoming more prevalent. These at-process methods allow real-time information on a variety of melt characteristics to be collected for process monitoring and control.
This work will demonstrate real-time monitoring during extrusion of poly(ethylene vinyl acetate) random co-polymers with vinyl acetate (VA) content of 1- 40 wt %, using on-line transmission mid-infrared, in-line transmission near-infrared and in-line Raman spectroscopy. In-line ultrasonic measurements have been made simultaneously with these techniques, across the melt during single screw extrusion of the co-polymers. The efficiency of the respective methods for determination of VA content is investigated and multivariate chemometric analysis of the data acquired from each spectroscopic technique will be presented.
The spectral techniques of MIR, NIR and Raman can be used to analyze the differences between various polymer types, grades and blends, by analysing spectral changes associated with chemical bonds specific to each melt component. In P(EVA) co-polymer systems, discrimination of VA content relies heavily upon features arising from the C=O stretching and O=C-O bending modes of the VA as well as the C-C stretching modes of the ethylene unit.
Longitudinal ultrasonic velocity responds to changes in bulk modulus and density. In-line measurements on polymer melts will therefore allow real-time detection of VA content in EVA copolymers.