Composite membranes containing carbon nanofibers (CNFs) and Matrimid were prepared by a solution-casting method. Prepared Matrimid–CNF composite membranes were characterized with X-ray diffraction, thermogravimetric analysis, differential scanning calorimetry, Fourier transform infrared spectroscopy, scanning electron microscopy, transmission electron microscopy, and mechanical testing techniques. The mechanical properties of the composite membranes increased over that of the pristine polymeric membranes. To develop a broad fundamental understanding of the connection between the composite architecture and gas-transport properties, both the gas-permeability and gas-separation characteristics were evaluated. The gas-transport properties of the Matrimid–CNF composite membrane was measured with a single gas-permeation setup (He, H2, N2, CH4 and CO2) at ambient temperature with the variable-volume method. The incorporation of CNFs (0.5–10 wt %) into the Matrimid matrix resulted in approximately a 22% reduction in the gas permeation of various gases, (H2, He, CO2, N2, and CH4). Moreover, an improvement of 1.5 times in the gas selectivity was observed for CO2/CH4, H2/CH4, He/CH4, and H2/N2 compared to pristine polymeric membrane. Hence, such polymer–CNF composite membranes could be suitable for gas-separation applications with high purity requirements. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46019.

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