Novel surface treatment, functionalization and hybridization of carbon nanotubes and their polymer-based composites

With unique physical, mechanical and transport properties, carbon nanotubes (CNTs) have attracted much interest in different fields, and they hold the promise of delivering exceptional mechanical properties and multi-functional characteristics. However, if these materials are to be utilized as effective reinforcements in polymer composites, proper dispersion and good interfacial bonding between the CNTs and the polymer matrix have to be guaranteed. The objectives of this project are to employ new surface treatment and functionalization techniques to promote CNT dispersion and interfacial adhesion with polymer matrix. A method based on silanization process is proposed for the functionalization of CNTs. The effects of CNT functionalization are investigated on the dispersion characteristics, mechanical and electrical properties of epoxy matrix nanocomposites containing different contents of CNTs. The results confirm that samples with functionalized CNTs show much better dispersion in epoxy matrix with associated improved mechanical properties than those without functionalization. A simple chemo-mechanical method is also proposed for amino functionalization of CNTs. Ball milling in the presence of ammonium bicarbonate allows the introduction of functional groups, like amine and amide groups, onto the CNT surface. The semiconducting behavior of the CNTs is converted from p-type to n-type after ball milling, with associated increase in electrical conductivity of CNTs. The amino functionalized CNTs are employed as template to prepare well-defined silver decorated CNTs (Ag@CNTs). Then the Ag@CNTs are employed as conducting fillers in epoxy to produce electrically conducting nanocomposites. The electrical, mechanical and thermal properties of the nanocomposites are investigated and compared with those containing pristine and functionalized CNTs. It is shown that the electrical conductivity of nanocomposites containing Ag@CNTs is significantly higher than those containing pristine and functionalized CNTs, and this enhancement is not at the expense of mechanical and thermal properties of the nanocomposites, confirming the advantage of the Ag@CNTs as effective conducting filler. Nanocomposites containing hybrid fillers of CNTs and carbon black (CB) were developed, aiming at enhancing the electrical conductivity of the composites with balanced mechanical properties, and significantly lowering the cost of the final product. A lower percolation threshold was achieved for the nanocomposites filled with hybrid fillers of 0.2wt% CNTs and 0.2wt% CB. CB also improved the ductility and thermomechanical performance of the hybrid nanocomposites while maintaining high modulus and strength, confirming the synergic effect of CB as an effective multi-functional filler