Effective Mechanical Properties Of Polypropylene Filled With Micro/Nano Silica

The polymer composites filled with ceramic particles have been widely used in intelligence manufacturing,microelectronics and other fields.Among them,polypropylene(PP)composite filled with silica(SiO2)is one of the typical representative,which can be used as wire and cable materials,electrode barrier of lithium sulfur battery and so on.The excellent mechanical properties are the premise of the stable service of the related devices,so it is of great significance to characterize the effective mechanical properties of the composites.In this paper,the effective elastic modulus and tensile strength of the composites were theoretically characterized for the typical polymer matrix composites filled with micro/nano silica firstly.The samples of PP/SiO2 composites were prepared by melt-blending,and the mechanical properties of the composites were measured by tensile experiments.Furthermore,the 3D finite element models of PP/SiO2 composites were built and the mechanical properties were simulated.The results are as follows:(1)According to the Mori-Tanaka model and the ideal tensile strength model of composites,by considering the influences of the scale effects of the filler,the interface properties and the dispersion degree of the filler on the mechanical properties,the theoretical models of the effective elastic modulus and tensile strength of the composites were developed respectively.The interface strength between PP and SiO2 and the scale effects of mechanical properties of the composites can be predicted by the models.(2)Through the tensile experiment of PP/SiO2 composites,the trend of its elastic modulus and tensile strength with SiO2 mass fraction and filler particle size was obtained respectively,which was consistent with the theoretical prediction.The trend of its elastic modulus and tensile strength with the content of SiO2 are not consistent.When the content of SiO2 increases,the elastic modulus increases monotonously,while the tensile strength increases firstly and then decreases,and reaches the highest when the content of SiO2 is 2%;With the decreasing of the particle size of SiO2 from 10?m to 20nm,its elastic modulus and tensile strength also show the trend of increasing firstly and then decreasing.When the particle size of SiO2 is 50nm,both of them reach the highest.The microstructure observation shows that the nano fillers have better interface bonding with matrix than the micro fillers,but the agglomeration size of nano fillers is larger,which explains experimentally the influence mechanism of interface and agglomeration on the mechanical properties of the polypropylene composite filled with silica.(3)The corresponding three-dimensional finite element models of PP/SiO2 composites were established.The uniaxial tensile process was simulated,and the mass fraction and particle size of SiO2 were changed respectively.The trends of elastic modulus and tensile strength based on the simulation were consistent with the experimental and theoretical prediction.Considering the obvious damage debonding between the micro SiO2 and the matrix,the damage evolution process of the debonding was further simulated.It is found that the damage starts from the two poles of tensile particles and gradually extends to the equator.The influence of the interface thickness was also simulated.It is found that the elastic modulus and tensile strength of the composites both increase monotonously with the increasing of the interface thickness.