Optimization Of Rotor Structure Of Two Rotor Continuous Mixer And Their Application In The Preparation Of Masterbatch Of LLDPE Based Thermally Conductive Microporous Film

When preparing particle filled polymer composites,the effects of the filler characteristics and the external field on the microstructure are major factors to determine the properties of composites.In this thesis,the influence of alumina content and particle size on the micro structure and rheological properties of linear-low-density-polyethylene/alumina（LLDPE/Al2O3）composites were analyzed.On this basis,a viscosity prediction model and a thermally conductive predicition model considering the thermal resistance of interface were established.Focusing on the two rotor continuous mixer,the cross-section configuration and three-dimensional structure of the mixer rotor were studied,and three rotor structures with different mixing characteristics were proposed.According to the morphology evolution characteristics of composites in the mixing process,the whole process simulation of the solid conveying and melt mixing of the two rotor continuous mixer were carried out by using the discrete element and finite element analysis software.The flow field parameters and mixing effect of the optimized rotor structures were simulated and experimentally evaluated.On this basis,with the help of the optimized rotors,the masterbatch for thermally conductive microporous films were prepared and their properties were studied.The optimized rotor was successfully applied to the industrial device for the production of masterbatch of microporous films.The main research contents and results are as follows:（1）The dispersion and distribution characteristics of Al2O3 particles with different content and particle size in the composites were analyzed by SEM,and the effects of Al2O3 particle content and particle size on the apparent viscosity,complex viscosity and dynamic rheological properties of the composites were analyzed by testing the steady-state and dynamic rheological properties.Based on the Carreau viscosity model of LLDPE,a rheological prediction model of filled composites including the content and particle size of Al2O3 particles was established.It provided a good foundation for more accurate numerical simulation results of the mixing process of filled polymers.（2）Based on the statistical analysis of the microsturcture of LLDPE/Al2O3 composites and the principle of heat transfer,a thermally conductive predicition model of filled composites considering the thermal resistance of interface was established.Then the accuracy of the model was evaluated by means of heat conduction experimental test and heat conduction process simulation analysis.The results showed that compared with the existing prediction models,the thermally conductive prediction model established in this thesis has higher accuracy under certain conditions when the content of thermally conductive filler is relatively high and the particles contact each other to form a local thermal conductivity path.（3）In order to improve the mixing efficiency by increasing the number of times of materials passing through the high shear zone at the top of the screw edge,the effects of the cross section and the three-dimensional geometric model of mixer rotors on the dispersed and distributed mixing process were studied by analyzing the flow process of the material in the mixing chamber.The fitting model of the rotor cross section profile curve was proposed,and the three-dimensional space surface of the rotor was optimized.Three rotor configurations with different hybrid characteristics were designed.In order to improve the mixing efficiency by strengthening the calendaring effect between rotors,a selection criterion of relative phase angle between a pair of rotors was proposed.Based on the coupling of discrete element and finite element,the simulation method for the whole process of the two rotor continuous mixer including solid conveying and mixing zone and melt mixing zone was established,in which the average velocity of particles at the outlet section of solid conveying counted using EDEM software was taken as the velocity of the melt material inlet during the POLYFLOW finite element simulation of the melt mixing zone.（4）The whole process simulation of solid conveying mixing characteristics and melt mixing characteristics of two rotor continuous mixer was carried out.The solid conveying mixing characteristics,melt mixing flow field characteristics and the dispersion and distribution mixing effects of materials with the three designed rotors were analyzed.The blending modification experiments of LLDPE/Al2O3 composites were carried out with three kinds of rotors respectively.By means of SEM,plate rheometer and the tensile testing machine,the microstructure,rheological properties and mechanical properties of the samples were characterized,and the mixing effect and mixing characteristics of the three rotors were evaluated.Simulation and experimental studies showed that,M2 rotor had stronger dispersion and distribution mixing ability,and the dispersion and distribution mixing effect of M1 rotor was relatively weak,and the mixing process was relatively soft,M3 rotor had moderate dispersion and distribution mixing effect,but its residence time distribution was the narrowest,and its self-cleaning performance was relatively good.（5）The LLDPE/CaCO₃/Al₂O₃ composites were prepared by two rotor continuous mixer with the M2 rotor.The effects of Al2O3 content and preparation process on the properties of the composites and microporous films were studied.The results showed that,when the initial tensile ratio of the films exceeds 200%,a small number of spherical Al2O3 particles peel off from LLDPE,which lead to form micropores at the interface.With the increase of tensile ratio,more micropores appear around Al2O3 particles,and the size of micropores become larger gradually.Compared with the stretched film without Al2O3,when the mass ratio of LLDPE/CaCO3/Al2O3 was 50/35/15 and the microporous films were prepared by casting process with a stretching ratio of 200%,the strength of the films along and vertical to stretching directions was increased by 8%and 15%respectively,the water vapor transmittance was increased by 20%,and the thermal conductivity of the films was increased by more than 61%.This result meets the relevant requirements of national standards and industrial standards.On this basis,the engineering scale-up work was carried out,and the high-efficiency mixing rotor applied to the industrial production of microporous film masterbatch was successfully developed,which solved the key problem of mixing equipment in the production of microporous film masterbatch.