Preparation And Properties Of Conductive Composites Of Carbon Nanotube/Low Density Polyethylene/Polystyrene

Conductive polymer composites have been extensively used in many fields,such as electronic,energy and chemical engineering.The discovery of carbon nanotubes (CNTs)by Iijima in 1991 has brought a widespread research because of their unique electronic,mechanical and other properties.The application of carbon nanotube as conductive filler in polymer composites has been paid attention.In this thesis,A series of ternary and binary conductive polymer composites of polystyrene(PS),the low density polyethylene(LDPE)and multi-walled carbon nanotube(MWNT)were prepared by melt-mixing method.The work is summarized as following:1.The conductive properties of the binary composites of MWNT/PS and MWNTT/LDPE,as well as the ternary one of MWNT/LDPE/PS,were prepared via melt processing.The electrical percolation thresholds of MWNT/LDPE and MWNT/PS are 8 wt%and 6 wt%of MWNT loadings,respectively.whereas,the ternary multiphase of MWNT/LDPE/PS with a composition of LDPE/PS(50/50) exhibits a low electrical percolation,being 4 wt%MWNT loading.The positive temperature coefficient(PTC)effect of ternary conductive composites is similar to MWNT/LDPE,which is related to the LDPE domain's transition.2.Optical microscope and scanning electron microscope(SEM)were employed to observe the morphology of the conducive composites and the distribution of the carbon nanotubes in composites.As a result,the matrix polymers of LDPE and PS form co-continuous phases in polymer blends,and the carbon nanotubes preferably locate in LDPE phase and produce electrically conductive path.The formed "double percolation threshold" results in the decrease of the loading of conducting fillers,and the mechanical properties and processability of the multi-phase composites are thus improved.3.The measurement of dynamic rheology shows that the multiphase composites exhibit a very strong shear thinning effect.At low frequencies,the rheological behavior of the composites gives an obvious dependence of frequency for <3.0 wt% MWNT.At high frequencies,the fraction of MWNT has a slight influence on the rheological behavior of the composites.The results indicate a solid-like behavior formed in the composites,which suggests the formation of a nanotube network. Moreover,the addition of MWNT in the multiphase composite leads to the phase-separate temperature shifting to low temperature.4.The multiphase composites of MWNT/LDPE/PS exhibits a difference between rheological percolation and electrical percolation,being 3%and 4%loadings of the carbon nanotubes,respectively.We understand this difference in terms of the nanotube distance required for electrical conduction,as compared to the distance for impeding polymer motion.5.DSC was used to analyze the crystallization and to study crystalline kinetics of the ternary composites.The spectra and data indicate that the crystallization and melt behavior of MWNT/LDPE/PS is similar to MWNT/LDPE,revealing MWNT selectively located in LDPE domain.The addition of MWNT does not change the crystal form of LDPE;whereas,crystallization rate and crystallinity of the multiphase composites decrease due to LDPE molecular chain movement hindered by MWNT during crystallization.6.The addition of MWNT improves mechanical properties of the multiphase composites,resulting in the increase of tensile strength.