The Modeling Process Of Co-rotating Biaxial Eccentric Rotor Extruder And The Study On The Blending Process

Blending is the crucial step in the preparation of polymer composite system,while the blending effect determines the performance of polymer products.Therefore,the study of blending process,especially the blending process of polymer matrix composite system,shows great application value.Relevant researches indicate that compared with shear flow field,elongational flow field is more beneficial to the blending process.Based on elongational flow field,the vane type blending equipment,eccentric rotor blending equipment and biaxial eccentric blending equipment have outstanding blending effect.Studies on biaxial eccentric extruder,especially co-rotating biaxial eccentric extruder started late,therefore the blending mechanism of it remains unclear,which severely hinders its vast application.Because of the complex structure of the equipment for industrial manufacture,it is hard to study them.This paper analyzes,disassembles and simplifies the co-rotating biaxial eccentric rotor extruder used in industrial manufacture by using the idea of modeling and unitization,extracting its basic blending units,and developed a modeled co-rotating biaxial eccentric rotor blending equipment based on the above fundamental studies.Through the equipment,the characteristics of flow field,the characteristics and mechanism of distributed blending and dispersed blending in the blending process of co-rotating biaxial eccentric rotors were studied systematically for the first time.With the combination of theoretical analysis and numerical calculation,the flow field characteristic of the blending process in co-rotating biaxial eccentric rotor mixer is studied.According to the flow characteristics,the blending unit is divided into rotor-stator meshing region and rotor-rotor meshing region.The fluid flow in rotor-stator meshing region mainly occurs under the drag effect of rotors’ rotation,while the fluid in the rotor-stator meshing region mainly exchanges volume during the compression-release process of the chamber.In the rotor-stator meshing region,the shear flow dominates the position close to the rotor’s and the stator’s surface,while the elongation flow dominates the position away from the rotor’s and stator’s surface.In the rotor-rotor meshing region,the elongation flow is more conspicuous at the upper and lower ends of the region,and the shear flow is more obvious at the middle of the region.By combining pigment tracing method and numerical simulation,the blending characteristic and mechanism of co-rotating biaxial eccentric rotor mixer are studied.Compared with traditional blending method based on shear rheology,this method has great distributed blending capability.The uniformity of pigment distributed in the sample obtained by blending in the CERM at 10 rpm for 1 min is equal to that of the sample prepared by the traditional shear rheology method for 3 min under the same process.Moreover,the distributed blending capability of CERM is only affected by the non-Newtonian property of the fluid.The stronger the non-Newtonian property is,the worse the distributed blending effect would be.The distributed blending process shows a global-local parallel blending characteristic: the minor phase achieves global distributed blending in the volume exchange between chambers and local distributed blending in the expansive-convergent flow field.Both blending process go simultaneously.The mechanism of distributed blending is applicable to other blending equipment based on elongation rheology.By means of numerical simulation and experimental study,taking polyurethane/hexagonal boron nitride composite and polyurethane/starch composite as examples,the dispersed blending characteristic and mechanism of sheet solid fillers and melt droplets in the co-rotating biaxial eccentric rotor blending method were studied respectively.In this method,the h-BN filled thermal conductivity enhanced composite is prepared by peeling and dispersing,of which the thermal conductivity is enhanced by 20% compared with traditional methods,certifying its excellent dispersed blending capability.In addition,the increase of rotate speed and the prolongation of blending time within a certain limit could improve the effect of dispersed blending.For hexagonal boron nitride,crakes throughout the whole sheet first appear under the compressive stress generated by the divergent flow field.Then,the melt invades the inside of the fillers and tears them into small crushed particles with great dispersion efficiency.While for the melt droplets,fracture occurs in the whole blending chamber.The separation and aggregation of the melt droplets occur successively in the process of continuous expansive-convergent flow.