Super-tough And Electrically Conductive High-density Polyethylene Nanocomposite

Recently, carbon nanotubes(CNT) have intrigued tremendous interests inscientifc research for their unique structures. For their quasi-one-dimensionalstructures and excellent electrical properites, CNT can greatly improve theelectrical conductivity of insulative polymer at a low CNT content, and thatmakes them be ideal conductive fillers. But CNT-filled polymeric compositesoften have disadvantages of low fracture toughness. As a result, how toprepare composites with excellent electrical properties and mechanicalproperties (especially fracture toughness) becomes a focus research area.Rubber and elastomer are usually used to improve the fracture toughness ofplastics, but they woold decrease the tensile strength and Young’s modulus ofplastics.In this dissertation, CNT are used as conductive fillers to increase theelectrical conductivity of high-density polyethylene (HDPE), and calciumcarbonate (CaCO3) are incorporated with as a third phase to enhance fracturetoughness and Young’s modulus. Meanwhile the third phase also plays a roleof volume exclusion, which decrease the amount of CNT without damagingthe high electrical conductivity of conductive composite. To increase thetoughening effectiveness, active calcium carbonate treated with stearic acid bythe manufacturer are used and further coated with coupling agent. The mainworks are as follows:1. Calcium carbonate treated with different amount of coupling agent areused to prepare HDPE/CaCO3composites, the effect of CaCO3loading onimpact strength of binary composite is investigated. A conclusion is drown that composite containing30wt%CaCO3which are treated with3wt%coupling agent has the maximum impact strength, about190%higher than thatof matrix.2. HDPE/CNT composites are prepared as a function of CNT loading.Observed from the SEM micrographs, most of CNT are well dispersed,although agglomerations still existed. The percolation threshold of CNT isabout4.5wt%. Electrical conductivity has a biggest jump when CNT contentchanging from2wt%to4wt%, about10orders of magnitude. The addition ofCNT greatly decreases impact strength and elongation at break of composites.Comparing to matrix, when6wt%CNT are added, electrical conductivity getsa improvement of15orders of magnitude but impact strength and elongationat break decrease by34%and40%respectively.3. HDPE/30wt%CaCO3/CNT ternary composites with changing contentof CNT were prepared. SEM micrographs show that CNT disperse in thematrix between calcium carbonate particles, the inorganic solid particles doplay a role of volume exclusion. Electrical conductivities of ternarycomposites are higher than that of HDPE/CNT binary composites at any CNTcontent, especially when CNT content is3wt%, electrical conductivity ofternary composite raise by up to5orders of magnitude. The percolationthreshold of ternary composites drops to3.5wt%. To further investigate theeffect of CaCO3loading on the mechanical and electrical properties of ternarycomposites, HDPE/CaCO3/3wt%CNT composites are prepared, in whichCaCO3particles are treated with3wt%coupling agent. The results show thatelectrical conductivity gradually increases with increasing CNT content.While composite with30wt%CaCO3has the highest impact strength, furthermore CaCO3particles have negative effect on impact strength of composite.