Mechanical properties of carbon filler-reinforcement of poly(ethylene-co-octene) membranes

Mixed matrix membranes, consisting of a dispersion of filler particles within a polymeric matrix, are potentially suitable to combine the exclusive advantages in separation performance of both inorganic and polymeric materials. Chemical structure, surface chemistry, size, and aspect ratio are the most important variables for filler selection, whereas filler-polymer compatibility and filler distribution are the key points for an effective membrane preparation [1]. The elastomeric poly(ethylene-co-octene) was chosen owing to its higher permeability than other semi-crystalline analogous polyolefins (polyethylene and polypropylene) [2]. Mixed matrix membranes based on poly(ethylene-co-octene) containing up to 30 wt % of virgin or oxidized multi-walled carbon nanotubes (CNTs) and carbon fibres (CFs) were prepared and characterised [3]. The deformation rate-dependence of the Young's modulus was determined in the fully reversible elastic deformation range using square samples to verify the sample homogeneity. In some cases, a slight non-uniformity of the sample was observed, presumably due to flow-induced orientation of the CFs or CNTs in a preferential direction during the preparation of the samples. Thus, whereas the modulus itself depends strongly on the filler content, the deformation rate dependence of the modulus decreases only slightly with filler content, i.e., the typical viscoelastic behaviour is slightly depressed by the presence of stiff, yet purely elastic, fillers. The strongest reinforcement effect is observed for the carbon fibers, especially at high concentration.