Study On The Processing Process Of LLDPE/Al₂O₃ Composites

Melt-blending is the most widely used method for the preparation of polymer-composites,and the process is of great significance for obtaining high-performance composites.In this thesis,the processing of linear low density polyethylene and alumina(LLDPE/Al2O3)composites was studied by experiment and numerical simulations.In the previous research,the interaction between filler particles and matrix was not considered.and the dispersion and distribution process of the filler particles in the polymer matrix was inot analyzed in detail.In this thesis,based on the rheological study of LLDPE/Al2O3 composites.a modified rheological model considering the influence of Al2O3 loading and particle size was established.The processing of LLDPE/Al2O3 composites was studied by numerical simulations of continuous element method and discrete element method.The distribution and dispersion behavior of Al2O3 in LLDPE were analyzed.Finally,the effects of mixing process on the properties of LLDPE/Al2O3 composites were investigated by experimental methods.The main conclusions are as follows:(1)In the nano-Al2O3 filling system,the viscosity increases with the increase of the Al2O3 filling amount,and there is a mutation in the viscosity when the Al2O3 filling amount is 8%-10%,which arises from the formation of particle network structures within the system.In different particle size Al2O3 filling systems,nano-Al2O3 has a small surface area and higher surface energy,which mainly hinders the untangling of polymer molecular chains;micro-Al2O3 has lower surface energy,which mainly hinders the flow of molecular chains.The effect of nano-Al2O3 on the rheological behavior of the composite system is much greater than that of micro-Al2O3.(2)The material is conveyed forward by the screw in the conveying section of the two-rotor continuous mixer,and the"?"-shaped movement is carried out around the rotor in the mixing section.At the same time,the material back mixing occurs in the reverse spiral edge area and the spiral edge intersection area,which has a positive effect on the sufficient mixing of the materials;as the mixing time increases,the volume fraction of Al2O3 in the mixing chamber gradually approaches the initial volume fraction,and the fluctuation is small,the mixing of the materials is more uniform.(3)As the rotor speed increases,the Al2O3 has a better dispersion and distribution in the LLDPE matrix,the viscosity increases,and the mechanical properties also increase.However,when the rotation speed is increased from 700 rpm to 800 rpm,the viscosity and mechanical properties of the composites decrease.With the increase of the feed amount,the dispersion and distribution effect of Al2O3 in the LLDPE matrix gets better first and then deteriorates.The viscosity also increases first and then decreases.