Carbon Nanotubes Modified With Corona Plasma And Their Applications In Epoxy Resin

Among the numerous strategies of modifying carbon nanotubes (CNTs), plasma treatment has its advantages of nonpolluting, time-saving, and the plasma-induced graft polymerization of vinyl monomers has been found to be an extremely attractive method of chemical modification of CNTs. Unfortunately, these plasma treatment methods are generally executed at pressures below one atmosphere in the apparatuses, which restricts the scaled-up in industry. On the contrary, corona discharge can be carried out at room temperature and work well at normal atmosphere. In this study, corona discharge was firstly used to modify multi-walled carbon nanotubes (MWCNTs). The effect of the modification on the structure, morphology and properties of CNTs was also investigated as well as on the properties of MWCNTs/epoxy composites.Firstly, MWCNTs were modified by corona discharge and then heat-treated in the air. The influences of corona discharge parameters such as treatment time and processing power were investigated. The results of energy dispersive x-ray analysis (EDX) and thermo-gravimetric analysis (TGA) indicated the introduction of oxygen-containing functional groups onto the surface of the MWCNTs after heat treatment. The water contact angle tests showed that the hydrophobicity of the MWCNTs was decreased to some extent. The static water contact angle was reduced from 146°to 122°when the time of the corona discharge treatment reached 3 min at the processing power of 200 W. The enhanced thermo-mechanical and mechanical properties of epoxy composites filled with the corona-discharge treated MWCNTs were observed. The modified MWCNTs conferred better properties on the composites than the pristine MWCNTs because of the improved dispersion of MWCNTs in matrix and the enhanced interfacial interaction between the treated MWCNTs and epoxy.Secondly, corona discharge was applied to initiate the graft polymerization of glycidyl methacrylate (GMA) and 2-hydroxyethyl methacrylate (HEMA) monomers onto the surface of MWCNTs at atmospheric pressure. The results of transmission electron microscopy (TEM) and field emission scanning electron microscopy (FE-SEM) indicated that MWCNTs were encapsulated by polymers and a core-shell like structure was formed. The grafting degree depended on the processing time of corona discharge and the concentration of vinyl monomers, as demonstrated by TGA. The dispersibility of the polymer grafted MWCNTs (PGMA-g-CNTs and PHEMA-g-CNTs) in both ethanol and acetone was dramatically improved.Thirdly, the effect of polymer grafted MWCNTs on the curing behavior of epoxy/triethanolsmine (TTA) system was studied using differential scanning calorimetry (DSC). The results demonstrated that the polymer grafted MWCNTs had greater influence on the curing reaction than the pristine MWCNTs (P-MWCNTs). The curing activation energy of the epoxy/TTA system was apparently decreased by the addition of polymer grafted MWCNTs. Additionally, the curing activation energy of epoxy/TTA/PHEMA-g-CNTs was lower than epoxy/TTA/PGMA-g-CNTs.Subsequently, nanocomposites of epoxy resin filled with various MWCNTs were prepared. The enhanced mechanical and thermal properties of epoxy nanocomposites filled with the polymers grafted MWCNTs were observed. The grafted MWCNTs conferred better properties on the composites than the pristine MWCNTs because of the improved dispersion of MWCNTs in matrix and the enhanced interfacial interaction between them. It was also found that PGMA-g-CNTs can improve the mechanical and thermal properties of the nanocomposites more effectively than PHEMA-g-MWCNTs. The addition of 0.5wt% of PGMA-g-CNTs yielded 58.9% increase of flexural strength, which was higher than the presence of PHEMA-g-CNTs and P-MWCNTs.Finally, poly (styrene-co-maleic anhydride) (SMA) grafted multi-walled carbon nanotubes (SMA-g-CNTs) was prepared via in situ syntheses under 60Co y-ray irradiation. The chemical structure and morphology of grafted MWCNTs was investigated by Fourier transform infrared spectroscopy, TGA, TEM and Raman spectroscopy. The effect of SMA-g-CNTs on mechanical and thermal properties of MWCNTs/epoxy was also observed. The results demonstrated that the addition of SMA-g-CNTs yielded better mechanical and thermal properties of MWCNTs/epoxy, which was attributed to the improved dispersion of MWCNTs in epoxy and the enhanced interfacial interactions between them. The reinforcement of MWCNTs/epoxy composites was further improved by the amination of SMA-g-CNTs. In addition, hydroxyl functionalized CNTs were fabricated in 0.5M KOH/ethanol solution using a single-step radiation method. The dispersion of MWCNTs in both ethanol and acetone was dramatically improved after hydroxylation, which was revealed by ultraviolet-visible spectroscopy and digital photos.