In‐line monitoring of component content of polypropylene/polystyrene blends during melt extrusion using Raman spectroscopy

Abstract

AbstractAt present, the component content measured by off‐line methods, which are hysteresis, destructive, and unrepresentative for the whole sample, makes it hard for real‐time monitoring of the performance of products in the process of polymer blending and modification. Therefore, in this paper, Raman spectroscopy as a real‐time measurement technology is applied for in‐line monitoring of component content of polypropylene/polystyrene (PS) blends during melt extrusion. Prior to performing an analysis of PS content in polypropylene/PS blends, the signal to noise ratio and relative standard deviation are evaluated with respect to the effects of screw speed, sampling distance of laser spot to melt surface, and single scan time in order to optimize sampling conditions. Owing to this, for quantitative analysis of PS content, different wavenumber ranges and pretreatment methods are used to develop the optimal partial least squares model, which is compared with the optimal partial least squares model of PS content based on off‐line infrared spectroscopy. It is concluded that in‐line Raman spectroscopy determination of PS content shows comparative accuracy and predicting ability, which is achieved exhibiting calibration results that coefficient of determination (R2) and root mean square error of cross‐validation are 0.9998 and 0.438 wt.% and prediction results that R2 and root mean square error of prediction are 0.9993 and 0.725 wt.%. What is more, in‐line monitoring system of Raman spectroscopy is successfully applied to measure PS content variation process from 80 to 50 wt.% then to 20 wt.%.