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Polyimides rank among the most heat-resistant polymers and find application in a variety of fields, including transportation, electronics, and membrane technology. The aim of this work is to study the structural, thermal, mechanical, and gas permeation properties of polyimide based nanocomposite membranes in flat sheet configuration. For this purpose, numerous advanced techniques such as atomic force microscopy (AFM), SEM, TEM, TGA, FT-IR, tensile strength, elongation test, and gas permeability measurements were carried out. In particular, BTDA–TDI/MDI (P84) co-polyimide was used as the matrix of the studied membranes, whereas multi-wall carbon nanotubes were employed as filler material at concentrations of up to 5 wt.% All studied films were prepared by the dry-cast process resulting in non-porous films of about 30–50 μm of thickness. An optimum filler concentration of 2 wt.% was estimated. At this concentration, both thermal and mechanical properties of the prepared membranes were improved, and the highest gas permeability values were also obtained. Finally, gas permeability experiments were carried out at 25, 50, and 100 ◦C with seven different pure gases. The results revealed that the uniform carbon nanotubes dispersion lead to enhanced gas permeation properties.
The main scope of this work is to develop nano-carbon-based mixed matrix celluloseacetate membranes (MMMs) for the potential use in both gas and liquid separation processes. Forthis purpose, a variety of mixed matrix membranes, consisting of cellulose acetate (CA) polymerand carbon nanotubes as additive material were prepared, characterized, and tested. Multi-walledcarbon nanotubes (MWCNTs) were used as filler material and diacetone alcohol (DAA) as solvent.The first main objective towards highly efficient composite membranes was the proper preparationof agglomerate-free MWCNTs dispersions. Rotor-stator system (RS) and ultrasonic sonotrode (USS)were used to achieve the nanofillers’ dispersion. In addition, the first results of the application of thethree-roll mill (TRM) technology in the filler dispersion achieved were promising. The filler material,MWCNTs, was characterized by scanning electron microscopy (SEM) and liquid nitrogen (LN2)adsorption-desorption isotherms at 77 K. The derivatives CA-based mixed matrix membranes werecharacterized by tensile strength and water contact angle measurements, impedance spectroscopy,gas permeability/selectivity measurements, and water permeability tests. The studied membranesprovide remarkable water permeation properties, 12–109 L/m2/h/bar, and also good separationfactors of carbon dioxide and helium separations. Specifically, a separation factor of 87 for 10%He/N2feed concentration and a selectivity value of 55.4 for 10% CO2/CH4feed concentrationwere achieved.
Three different types of carbon nanomaterials, SWCNTs, MWCNTs and GNPs were prepared, modified, characterized, and their dispersibility behavior in three different solvents was evaluated. The carbon nanotubes were synthesized by using the well-known chemical vapor deposition method and the graphene nanoplatelets by wet physicochemical treatment techniques. Their characterization was accomplished by using various advanced techniques, such as powder X-ray diffraction and Raman spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy and N2 adsorption at 77 K. Furthermore, the carbon nanostructures were modified via plasma treatment and wet chemical surface modification in order to enhance their dispersion characteristics, for achieving more homogenous suspensions and therefore to be remained dispersed over a reasonable period of time without any sedimentation. The effect of treatment parameters and the use of different solvents were thoroughly studied mainly by optical methods, but also by using the DIN/EN classified ISO method of oil absorption and UV–Vis spectroscopy. The enhanced dispersion rate is observed in both CNTs and GNPs materials following their surface treatment, especially when using the solvent n-methyl-2-pyrrolidone. The aforementioned studied nanomaterials are perfect candidate fillers for preparing polymeric mixed matrix membranes.