Effect Of Polyethylene Branching Structure On Dispersion Of Inorganic Filler In Polyethylene Matrix

The final properties of composites mainly depend on the dispersion of the filler in matrixs.In this study,two types of inorganic fillers(talc and calcium carbonate)with different microstructures were mixed with four kinds of polyethylene(HDPE,LDPE,LLDPE and mPE)which have the different branching structures.The effects of contents of filler and difference branching structure of polyethylene on the dispersibility of filler particles in the matrixs were studied by dynamic rheological tests and SEM.And the melting and crystallization behavior of different composites were characterized by DSC.Furthermore,the influence of different dispersion situation on the mechanical properties of the composites was invesitigated.The results are as follows:The results show that the addition of high content of talc had a significant influence on the dynamic rheological behavior of the system of HDPE,LLDPE and mPE,which exhibited a significant Payne effect in small strain region.The storage modulus is very sensitive to the change of frequency in low frequency region,showing the solid-like behavior,which indicated that the agglomeration of amounts of talc occurred in the three high-filling systems.For the system of LDPE with long chain structures,the Payne effect and solid-like behavior didn’t appear in the small strain region and the low frequency region.Moreover,a more significant shear thinning behavior appears in the high frequency region.SEM show that,in the matrix of HDPE/Talc,LLDPE/Talc and mPE/Talc,there were different sizes of gaps between Talc powder and the matrix and talcum agglomeration phenomenon was more obvious.For LDPE/Talc,the fracture surface was very smooth which did not exist unexposed talcum particles,and there was no gap between the two phases.According to the results of DSC,for all composites,the addition of talc could improve the crystallinity and crystallization rate in the low-filling system,for LDPE/Talc,with the increase of the content of talc,the crystallinity and crystallization rate were gradually improved.The results of mechanical testing showed that mechanical properties of the low-filling system were improved.In contrast,when the content of talc was higher,the mechanical properties decreased obviously due to the agglomeration of talc in HDPE/Talc,LLDPE/Talc and mPE/Talc.For LDPE/Talc with large number of long chain structures,the mechanical properties decreased slightly which was due to thegood dispersion of Talc.In general,the rheological behavior PE/CaCO3 composites were similar to PE/Talc composites.But when the content of CaCO3 was 30 vol% in LDPE/CaCO3,the system has a significant Payne effect and solid-like behavior,and the mechanical properties was also decreased obviously which is may be due to the higher specific surface area of CaCO3 was easier to form the agglomeration phenomenon than talc.There is a more pronounced Payne effect in the filler filling system which did not modify with coupling agent.From the SEM micrographs,it also could be seen that the system was easier to form the agglomeration behavior,and the compatibility of the matrix and filler was also worser.