In-line rheo-polarimetry: A method to measure in real time the flow birefringence during polymer extrusion

This work presents a new optical detection system, an in-line rheo-polarimeter, to measure in real time polymer flow birefringence during extrusion. The total transmitted cross polarized light intensity is measured, converted into optical path difference, which is corrected for the transparent glass windows stress birefringence and then converted into the polymer flow birefringence in real time. To validate the in-line measurements, a bench assessment was done using cast sheets of polycarbonate with known optical path difference as standards. The flow birefringence of polystyrene was measured in-line during the extrusion process, attaining values up to −4 × 10−4, close to those found in the literature. The flow birefringence of various polystyrene samples was measured in-line during the extrusion showing the effect of increasing molecular weight on the polymer chain orientation.