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. 2014 Jan 3;4(1):20-39.
doi: 10.3390/membranes4010020.

Carbon Nanotube- And Carbon Fiber-Reinforcement of Ethylene-Octene Copolymer Membranes for Gas and Vapor Separation

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Carbon Nanotube- And Carbon Fiber-Reinforcement of Ethylene-Octene Copolymer Membranes for Gas and Vapor Separation

Zuzana Sedláková et al. Membranes (Basel). .
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Abstract

Gas and vapor transport properties were studied in mixed matrix membranes containing elastomeric ethylene-octene copolymer (EOC or poly(ethylene-co-octene)) with three types of carbon fillers: virgin or oxidized multi-walled carbon nanotubes (CNTs) and carbon fibers (CFs). Helium, hydrogen, nitrogen, oxygen, methane, and carbon dioxide were used for gas permeation rate measurements. Vapor transport properties were studied for the aliphatic hydrocarbon (hexane), aromatic compound (toluene), alcohol (ethanol), as well as water for the representative samples. The mechanical properties and homogeneity of samples was checked by stress-strain tests. The addition of virgin CNTs and CFs improve mechanical properties. Gas permeability of EOC lies between that of the more permeable PDMS and the less permeable semi-crystalline polyethylene and polypropylene. Organic vapors are more permeable than permanent gases in the composite membranes, with toluene and hexane permeabilities being about two orders of magnitude higher than permanent gas permeability. The results of the carbon-filled membranes offer perspectives for application in gas/vapor separation with improved mechanical resistance.

Figures

Figure 1
Figure 1
Scanning Electronic Microscopy images of used fillers: carbon fibers (CFs) and carbon nanotubes (CNTs).
Figure 2
Figure 2
SEM images of fractured surface of EOC/CF composites (20 wt % CF) and EOC/CNT composites (25 wt % CNT).
Figure 3
Figure 3
Tensile strength (a), maximum deformation (b), and Young’s modulus (c), as a function of the concentration of CNTs, oxidized CNTs, and CFs in the EOC-based composite membranes.The average Young’s modulus and its standard deviation were obtained from measurements of both strips (4–7 specimens) and square samples (2 specimens). The right axis (c) gives the relative increment compared to the neat polymer. Tensile strength and maximum deformation were based on strips only. Lines are plotted as a guide to the eye.
Figure 4
Figure 4
Optical photographs showing the defects during the tensile test of the EOC sample containing 20% of oxidized CNTs. Image rotated by 90 degrees. (a) Small deformation; (b) Large deformation before rupture.
Figure 5
Figure 5
Young’s modulus as a function of the elongation rate for both neat EOC and EOC/CNTs or EOC/CFs composites. Sample length is 2 cm and width is 3 cm. (a) CNT; (b) ox-CNT; (c) CF. The solid lines represent the best fit of the experimental data with the power function given in Equation (5).
Figure 6
Figure 6
Powerlaw fluid factors K and n, obtained by fitting the experimental Young’s modulus of the composite membranes with Equation (5) as a function of the filler loading. Lines are plotted as a guide to the eye.
Figure 7
Figure 7
Gas permeability and corresponding ideal permselectivity for EOC/CNTs films (a,c) and EOC/CFs composite films (b,d) as a function of the carbon filler concentration. The spread in the data of repeated measurements is of the same order of magnitude as the symbol size. Lines in the permeability graphs correspond to the least squares fit of the experimental data with the Maxwell equation (Equation (6)). The lines in the selectivity graphs correspond to the calculated ratio of the fitted permeabilities.
Figure 8
Figure 8
Gas diffusion coefficients (a) and solubility coefficients (b) with the corresponding selectivities (c,d) for EOC/CNT films reported in Figure 7 as a function of the CNT concentration. The spread in data of repeated measurements is of the same order of magnitude as the symbol size.
Figure 9
Figure 9
Alkane permeability coefficient of EOC/CNT composite films (a) and toluene and ethanol permeability coefficient of EOC/CF composite films (b) as a function of the vapor activity; (c,d) corresponding solubility coefficients, calculated from Equation (4). Lines are plotted as a guide to the eye.
Figure 10
Figure 10
Time lag measurement of a neat EOC membrane with water vapor (p/p0 = 0.65) and with ethanol vapor (p/p0 = 0.57). T = 25 °C.

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