Application of Raman Spectroscopy for In-Line Measurement of Dispersion Uniformity of Polypropylene–Polystyrene Blends During Melt Extrusion

Abstract

At present, there is a widespread phenomenon that product quality is difficult to monitor during the process of polymer melt modification such as blending, filling, and reinforcement. In consideration of this problem, this paper proposes an in-line Raman spectroscopy technique for measuring dispersion uniformity of polystyrene (PS) in polypropylene (PP)/PS blends during melt extrusion. On the basis of the optimal partial least squares (PLS) calibration model for quantitative determination of PS content in PP/PS, the fluctuations of PS content in extruding PP/PS with a mass percentage of 70 : 30 at different screw rotation speeds were predicted. The coefficient of variation (CV) of PS content at each screw rotation speed was obtained to accurately compare the dispersion uniformity, which was in agreement with the PS dispersion result characterized by the scanning electron microscope (SEM). In addition, the sensitivity of the measurement was validated by calculating the CV of PP/PS with mass percentages of 69 : 31 and 71 : 29. All of the above demonstrated that the in-line measurement system of Raman spectroscopy was able to accurately measure the dispersion uniformity of PS during the blending extrusion of PP/PS and demonstrated good sensitivity to minor changes in the blends composition.