Rheological behaviors and electrical properties of nanocomposites based on poly(ethylene-co-methyl acrylate) and multi-walled carbon nanotubes

Nanocomposites based on pristine and functionalized multi walled carbon nanotube (MWNT) and three commercial grades of poly(ethylene-co-methyl acrylate) (EMA) copolymers containing 9, 24 and 30 wt% methyl acrylate (MA), respectively have been prepared. The influences of pristine MWNTs (u-MWNTs), carboxyl and hydroxyl functionalized MWNTs (f-MWNTs) on rheological, electrical and electromagnetic shielding characteristics have been investigated. Storage modulus (in dynamic shear) value increases especially at higher frequency levels due to increased polymer-filler interactions. In both steady shear and capillary flow, the nanocomposites register a slightly higher viscosity than neat EMAs, depending on the type of MWNTs present in the matrix. All nanocomposite systems represent an increase in elastic response with increasing frequency. Morphological studies exhibit that increased MA content leads to superior dispersion of functionalized MWNTs in EMA matrix. The nanotube networks are also sensitive to the steady shear deformation particularly at high temperature. Morphological studies also exhibit that MWNTs become more aligned along longitudinal direction after extrusion leading to improved dispersion. f-MWNTs based nanocomposites exhibit higher conductivity and lower resistivity than that of the pure EMA. A sharp transition from an electrically insulating to a semi conductive composite is observed at 2 wt% -OH functionalized MWNTs loading, especially in EMA24 and EMA30. This is ascribed due to the possible H-bonding interaction between MWNTs and matrix. The electromagnetic interference (EMI) shielding effectiveness (SE) of the nanocomposites has also been investigated. A high value of SE (~15 dB) for hydroxyl functionalized MWNTs with EMA24 has been realistic for an engineering application.