Detector óptico NIR in-line para monitoramento da degradação termomecânica do polipropileno durante a extrusão

Abstract

The present research aimed to develop an in-line NIR (near infrared) optical detector to monitor polypropylene (PP) thermomechanical degradation during extrusion. The optical detector monitors, in real time, the absorbance of OH and CH chemical bonds, specifically. Hydroperoxides, which contain an OH (hydroxyl) chemical bond, are one of the main thermomechanical degradation products that arise during PP extrusion. The absorption of electromagnetic radiation, through the OH and CH bonds, is monitored by an optoelectronic system installed immediately after the extrusion process, in the extruder die. The electromagnetic radiation emission system consists of an output module with NIR-emitting LEDs and an electronic radiation intensity control system. The electromagnetic signal is then converted into a voltage signal by the NIR receiver, amplified, converted from analog to digital, and finally transmitted to a computer via USB. A software is responsible for performing the processing and graphic display of the NIR receiver signals, monitoring the level of polymer degradation during extrusion. The optical detector was validated on a bench, monitoring the absorbance of specific chemical bonds present in the organic liquids carbon tetrachloride, ethanol, acetone and hexane. The validation included the monitoring of absorbance of PP polymeric films reprocessed in an extruder. In addition, the optical detector was validated in the extruder, by monitoring the absorbance, in the transient state, of previously reprocessed PP, as well as using a polypropylene/polyvinyl alcohol (PP/PVAl) polymer blend. Finally, the optical detector was used for in-line monitoring of the thermomechanical degradation of PP during the extrusion process.