In-Line Monitoring of Polymer Extrusion Processes by NIR Spectroscopy

Abstract

NIR spectroscopy has become an analytical tool frequently used in many chemical production processes. Its use in polymer processing applications such as polymer extrusion would greatly increase product quality. Parameters of interest in this application are composition of the processed polymer, moisture or reaction status in reactive polymeric systems, as well as rheological parameters such as melt flow index (MFI) or viscosity. The measurement of NIR spectra could provide a way to control the processes. For this purpose a transmission sensor was developed for the application of NIR spectroscopy to extrusion processes. This sensor includes fibre optical probes and a measuring cell that can be adapted to the various extruders for in-line measurements. In contrast to mid-infrared sensors, it uses optical quartz components, which provides a low-cost solution. Extrusion processes at temperatures up to 300°C and pressures up to 35 MPa have been investigated. The application of multivariate analysis for PE/PPblending demonstrated the performance of the system with respect to process monitoring. In this case deviations between predicted and actual polymer composition were below 2%. Together with an AOTF spectrometer that was also developed, the complete system is suitable for harsh industrial environments and could lead to improved extrusion processes.

Evaluation of the structure of polypropylene/montmorillonite nanocomposite by in‐line light extinction and color measurements during multiple extrusions

“…According to earlier works [11], the use of Cloisite® 20A and Cloisite®15A, which are recommended by the producers to be used in nonpolar polymer matrixes, lead to a low log‐normalized light extinction indicating a great level of tactoids' dissaglomeration/exfoliation, which is improved even still with the presence of the PP‐ g ‐MA compatibilizer. By using the light extinction detector, the state of dissaglomeration/exfoliation could be monitored without any lag of time, continuously and directly during the extrusion process [27–32]. During this work, the optical behavior of the PP/MMT nanocomposites was monitored continuously during up to 2 h of processing in the steady state.…”

Recent Prospects in the Inline Monitoring of Nanocomposites and Nanocoatings by Optical Technologies

“…Generally, in polymer processing, NIR is performed mostly in transmission mode [53] by using flow cell barrels between the extruder and die. The degree of exfoliation was determined offline as an indicator for the dispersion of the nanofillers in the polymer matrix (Polypropylene (PP) and Polyamide 6 (PA)) for different modified layered silicates and at different process conditions [54].…”

A Critical Overview of Sensors for Monitoring Polymerizations

“…Nagata et al,546 for example, developed an in‐line density sensor using NIR spectroscopy and predictive calibration models such as partial least squares. Rohe et al547 also used NIR spectroscopy to predict the MFI. They developed a transmission sensor for the application of NIR spectroscopy to extrusion processes.…”