Numerical Simulation For Inorganic Substances/Polymers In Blending And Extrusion Process Of Twin Screw Extruder

The variability,adaptability and excellent mixing performance brought by the modular structure of the intermeshing co-rotating twin-screw extruder have been widely used in polymer processing such as molding,blending,modification,and reactive extrusion.For high-efficiency mixing elements,a reasonable screw combination can greatly improve the mixing capacity of the extruder to achieve different mixing effects.This article first uses POLYFLOW software to perform numerical simulation analysis on the three-dimensional steady-state flow field of the PP/CaCO₃ composite extrusion process,visually observe the dispersion effect of nanoparticles in the polymer melt,compare and analyze the flow field effects of three different screw combinations.Among them,the screw combination with the staggered angle of 45°meshing block has the strongest shearing effect on most of the particles in the flow field;then comes to the meshing block with the staggered angle of 60°and the screw combination with a staggered angle of 90°is the weakest,while the twin screw with a staggered angle of 90°has the strongest stretching effect on the melt.The effect of the flow field in the three screw combinations on the dispersion of inorganic nanoparticles in the PP matrix is compared and analyzed.As the screw continues to extrude the material,the particle size of the agglomerated inorganic nanoparticles in the three screw combinations changes significantly.The particle size distribution curve of the twin screw with a staggered angle of 45°meshing block is lower than that of the other two screw combinations.The number of small agglomerates and fragments that are broken and exfoliated due to flow field shear is the largest.Therefore,the dispersion effect of inorganic nanoparticles in the PP melt in the twin screw with the staggered angle of 45°meshing block turns out to be the best.Besides,a mathematical model of the flow behavior of PP/CaCO₃ blends is given in this paper.According to the rheological properties of the blends,the Bird-Carreau model and the Arrhenius approximate equation are used to characterize the change of composite viscosity with shear rate and temperature,respectively.The finite element method is used to simulate the extrusion process of the PP/CaCO₃ blend in the twin screw under non-isothermal conditions,the relevant boundary conditions and temperature conditions are established,and the component transportation method is used to solve the concentration of particles in the extruder during the mixing process.The concentration change and quantitative characterization were carried out to equate the distribution and mixing process of calcium carbonate particles and other enhancement phases in the mixing process;the distribution and mixing during the blending process are also solved by the tracer particle method,and the results showed that the tracer particle method was consistent with the results obtained by the component transportation thus the calculation cost is saved.The influence of different CaCO₃content on the particle concentration deviation is simulated and calculated:as the content of CaCO₃ increases,the viscosity of the blend increases,which is not conducive to the dispersion of particles.When the content of CaCO₃ is 10%,an ideal dispersion and mixing effect can be obtained.Based on the theoretical basis of twin-screw non-isothermal simulation,the physical properties of the blend with a CaCO₃ content of 10%are selected,and the three-dimensional non-isothermal model of the PP/CaCO₃ blending extrusion process under different screw combinations is established,and the particle tracing method is preferred in this simulation.The two-phase distribution mixing process is studied,and the meshing block with increasing stagger angle is added between the inlet forward threaded element and the outlet reverse threaded element.It is found that when the staggered angle is 45°,the dispersed phase is the best in the polymer.Therefore,this screw combination is selected to explore the influence of different rotation speeds(60rpm,90rpm and 120rpm respectively)on the dispersibility of particles in the polymer matrix.The results showed that increasing the screw rotation speed is beneficial to improve the dispersion and mixing of particles during the extrusion process.Finally,the temperature field,viscous thermal field and viscosity distribution of the screw combination at a screw speed of 120 rpm are solved.The increase in flow field temperature during the non-isothermal extrusion process is mainly due to viscous heat generation,which is affected by screw shear and temperature.The viscosity of the material at the top of the screw ridge and the kneading block is smaller,whereas the viscosity heat value is larger.In summary,when the staggered angle of the engaging blocks in the screw assembly is 45°and the rotation speed is set as 120 rpm,it is most conducive to the dispersion of 10%CaCO₃ particles in the PP matrix.