Study On Measurement And Characterization Methods Of The Twin-Screw Blending Process Along The Extruder Using Near-Infrared Spectroscopy

The properties of polymer blends depend largely on the dispersion uniformity of the dispersed phase in matrix.At present,dispersion uniformity of blends is mainly characterized by off-line scanning electron microscopy(SEM)after shutdown sampling,which is timeconsuming,destructive,hysteretic,and can not fully reflect the true state of materials.Therefore,this paper proposes to use the in-line near-infrared spectroscopy(NIR)measurement technology to characterize the dispersion uniformity of blends along the extruder in twin-screw blending process,in order to obtain the dispersion evolution of blends in real time.This is of great significance for understanding the polymer blending process,improving the properties of blends,and promoting the development of in-line NIR measurement technology in the polymer field.In this article,the in-line NIR multichannel measurement system was firstly developed,and its performance and reliability were tested.Then,the system was applied to in-line measure the POE content of polypropylene(PP)/polyolefin elastomer(POE)blends during the twinscrew blending process.Using partial least squares(PLS)and linear support vector regression(LinearSVR)multivariate calibration method,the quantitative model of POE content was established respectively,and the optimal model was determined after comparing the model performance.Based on this model,the evolution process of POE content with 90,70,50,30,10 mass percent was tracked in real time.Afterwards,the dispersion uniformity of PP/POE blends along the extruder was characterized by in-line NIR multichannel measurement,and the result was compared with SEM images.Finally,the same method was used to characterize the PP/POE blending process under different component ratios and different screw speeds,effects of component ratio and screw speed on the dispersion uniformity of blends were also discussed.The results showed that: 1)the developed in-line NIR multichannel measurement system had good performance and reliability,it can be used for in-line monitoring of twin-screw polymer blending process.2)POE content measured by in-line NIR multichannel measurement system showed high accuracy,and the established LinearSVR model based on in-line NIR spectra of PP/POE can real-time monitor the change of POE content in blending process.3)The coefficient of variation(CV)of POE content at four windows measured by in-line NIR spectroscopy was 9.13%,6.26%,5.90% and 4.08%,respectively,which was consistent with the SEM characterization result of POE dispersion uniformity,thus proved the feasibility of characterizing the dispersion uniformity of polymer blends along the extruder using developed in-line NIR multichannel measurement system;4)The dispersion uniformity of blends along screw axis was different with varied component ratios or screw speeds.Under the same screw speed,the dispersion evolution of blends was faster and the dispersion uniformity of final product was better when the phase with lower viscosity was the dispersed phase and the phase with higher viscosity was the matrix.Moreover,in the twin-screw blending extrusion process,it is not the higher screw speed is,the more uniformly blends disperse,but there is a screw speed which makes the best mixing effect.