Vibrational spectroscopic and ultrasound analysis for the in-process monitoring of poly(ethylene vinyl acetate) copolymer composition during melt extrusion

Over the last decade, the demands for higher through-put in production, process optimisation and quality control in the polymer manufacturing industry has led to the implementation of a wide range of process analytical technologies. Techniques such as near-infrared (NIR) spectroscopy, Raman spectroscopy and ultrasound have become indispensable analytical tools for in-process monitoring allowing a molecular specific understanding of material characteristics, rheology and process trends. This paper reports the combined application of these three analytical techniques for assessment of co-polymer melt composition in-line during single screw extrusion to an accuracy of 0.16 wt%. The work demonstrates monitoring and characterisation of a series of ethylene vinyl acetate (EVA) random co-polymers with varying vinyl acetate (VA) content ranging from 2.0 to 43.1 wt%. The sensitivity of each technique to changes in copolymer composition and its ability to acquire real-time process data has been determined. Robust multivariate calibrations suitable for real-time predictions of VA content during processing have been developed and tested.