High purity multi-walled carbon nanotubes: Preparation, characterization and performance as filler materials in co-polyimide hollow fiber membranes

Abstract

Functionalized MWCNTS were used as filler materials for the preparation of composite polymeric hollow fiber membranes based on the BTDA-TDI/MDI (P84) co-polyimide. As a first step high purity multi-walled carbon nanotubes (MWCNTs) were synthesized using a novel catalytic CVD (chemical vapor deposition) technique, which enables large-scale production at low cost, while maintaining high purity and exceptional material properties at the same time. Covalent modification of pristine MWCNTs was applied in order to optimize both their nanoscale morphology and their dispersion in organic solvents. The functionalization process introduced certain functional groups, namely phenol groups, on the external surface of the nanotubes. Both pristine and functionalized MWCNTs with phenol groups were characterized using a variety of techniques such as XRD, SEM, TGA and Raman spectroscopy. The functionalized nanotubes were found to result in a uniform dispersion in NMP solvent. The best dispersion was observed in the case of phenol-functionalized MWCNTs. The effect of the concentration of carbon nanotubes on the composite membranes was investigated by carrying out DSC, SEM and gas permeability experiments. The prepared composite membranes were crack free and they presented high permeability values and ideal helium–nitrogen selectivities. In addition, the gas permeance coefficients increased linearly with the MWCNT concentration suggesting an increase of the free volume of the polymer matrix.