In-line near-infrared spectroscopy : a tool to monitor the preparation of polymer-clay nanocomposites in extruders

Abstract

In-line diffuse reflectance and on-line transmission near-infrared spectroscopy (NIR) measurements are performed at the same location of the barrel of a twin screw extruder during the preparation of a polypropylene/clay nanocomposite. Their performance is evaluated by means of a 7-parameter chemometric model using off-line rheological and structural (FTIR) data obtained from samples prepared under different screw speed, compatibilizer content and clay loading, as well as a process-related thermomechanical index. Despite the higher variability of the diffuse reflectance signal, the two models present analogous high quality indices. The aptness of the reflectance measurements is thus validated, which has direct practical advantages, as this probe can be fixed in any typical melt pressure transducer port. The probe is then used for the real-time in-line monitoring of the production of the same nanocomposite but now using different throughputs, and the chemometric-based predictions are compared with experimental off-line characterization data. The nonlinear effect of throughput is correctly anticipated.