Modification of carbon nanotubes for key potential applications as reinforcement in nanocomposite

M. ESCOBAR; R. CANDAL; G.H. RUBIOLO; S. GOYANES

Rio de Janeiro, Brasil

Congreso; 4thInternacional conference on science and technology of composite materials. COMAT 2007; 2007

Several factors have to be considered in order to succeed in the use of carbon nanotubes (CNT) as reinforcements in polymer matrixes. The most important are: adequate functionalization (type and degree), wettability and well dispersion of the CNT into the polymeric matrix. The functional groups should be chemically compatible with the polymeric matrix. Wettability can be accomplished by tunings the matrix and CNT surface polarity. The previous factors contribute to obtain a good dispersion of CNT. An interesting way to prevent CNT-CNT contact, is to “decorate” the CNT with foreign materials, as silica nanoparticles. Silica nanosphere and CNT could increase the composite hardness, but they display an opposite behavior with respect to electrical and thermal conductivity. In this context we report a new route to obtain either silica nanoparticles grown through Multi Wall Carbon Nanotube (MWCNTs) or fluorinated carbon nanotubes (F-MWCNTs) starting from the same precursor. Essentially, the MWCNT were growth by pyrolisis of acetylene using Chemical Vapor Deposition method (CVD) on iron nanoparticles included into a silica matrix prepared by sol-gel process. Purification process involves several steps, including treatments with concentrated sulfuric acid, hydrofluoric acid (to dissolve silica matrix) and, eventually, hydrochloric acid. The characteristics of the final products depend on several parameters, as H2SO4/HF molar ratio, reaction time, and composition of the rinsed solution. Silica nanoparticles are obtained by a disolution-reprecipitation method, by adding acidulated water immediately after the HF treatment. The dissolved silica is hydrolyzed and precipitated in the form of spherical particles onto the CNT. If concentrated HCl is used as rinsed agent the dissolved silica is not hydrolyzed and the reprecipitation process is avoided. The remnant silica dissolved in the hydrochloric solution is eliminated in the washing procedure. In this case, controlling the reaction time, fluorinated MWCNTs (fluor-nanotubes) can be obtained.