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SentroProc NIR - In-line Determination of Vinyl Acetate (VA) in Polymer Blend Polypropylene (PP)/Ethylene Vinyl Acetate Copolymer (EVA) Ranging from 0 to 10 % VA during an extrusion

Modifying and blending polymers in the melt is one of the most important procedures to influence material properties and the behavior while processing. The in-line process control requires fast, reliable, and robust analytical methods which do not interact with the material to be analyzed. Especially, the near infrared spectroscopy (NIR) can come up to these expectations. It is a powerful technique for the qualitative and quantitative analysis of primary and final products. It is also suitable for quantifying the composition of synthetic blends (composites, blends, additives). More-over, this method provides information on the transformation process of polymerization reactions. The investigation was aimed at determining the accuracy and the detection limit for the quantitative analysis of vinyl acetate in-line in the extruder.

Experimental Setup

The tests were done in a single screw extruder at 25 bar and 200° C. The system used for the NIR measurements is based on a NIR diode array spectrometer for the spectral range from 900nm to 1700nm. The spectrometer module is thermally stabilized. The spectrometer has no moving parts, making it mechanically robust. The spectrometer can be connected to the NIR transmission probes via two optical fibers. The fiber leading to the probe has a diameter of 400 µm whereas the fiber coming from the adapter to the spectrometer has a diameter of 600 µm. For the acquisation and prediction of spectral data our process software WinSpec which stores the spectra in the spc format is used.

The calibration was built using the GRAMS32 program and the PLSplus/IQ chemometric application from Galactic Ind. Corp. The spectra for calibration (shown below) are depicted over the entire concentration range.


The calibration file was loaded into the WinSpec Software and tested on three blends with 0,3%VA; 0,9%VA (figure 3) and 5%VA. The noise of the concentration values is less than 0.03 %.

The measurements proved that the different measuring times due to the change of averaging parameters did not significantly influence the quality of the spectra and the concentration values. This allows in-line measurements in the extruder in less than 5 seconds (100 spectra averaged) easily, enabling both an excellent and very fast process control.

We thank IPF Dresden, especially Mr. Dr. Fischer and Mr. Pigorsch, for the fruitful co-operation in this project.

The detailed version of this application will be published as an article in the magazine Prozess 10-2001, Verlag Vogel Life Science.

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