Thermal sensitive shape recovery and mass transfer properties of polyurethane/modified MWNT composite membranes synthesized via in situ solution pre-polymerization

Polyurethane/multiwalled carbon nanotube (MWNT) composite membranes with thermal sensitive shape memory and mass transfer properties were synthesized via in situ pre-polymerization from concentration pretreated MWNT in DMF (N,N-dimethylformamide). Composite membranes were made from these polyurethane/MWNT solutions by casting them into Teflon plates. SEM photographs demonstrated that the MWNT distributed relatively homogenously in polyurethane matrix at low content and preferred to align in the membrane 2-dimension plane. The shape recovery and mass transfer properties of the prepared membranes were studied. Thermo-mechanical cyclic tensile testing results suggested that the shape recovery ratio increased prominently at below 2.0 wt% of MWNT because of the MWNTs high interaction with the hard segments; however at 3.0 wt% MWNT content, the shape recovery ratios decreased which can be ascribed to the relatively inhomogeneous distribution of MWNT and the decrease phase separation of the polyurethane at this high MWNT content. The water vapor permeability (WVP) studies showed that at below the soft segment melting transition temperature, at 0.25 wt% MWNT content, the WVP of the composite membrane decreased because the nano-sized MWNT acting as nucleating agent, thus, enhanced soft segment ordered crystal structure. In contrast, with increasing MWNT content, the WVP increased because in one aspect, MWNT constrained the forming of ordered soft segment phase structure; in another aspect, the straight MWNT with large aspect ratios offered a relatively straight “free” pathway for water molecule diffusion on the surface of MWNT or inside MWNT to pass through. At temperature above the soft segment phase melting transition temperature, the WVP increased markedly with increasing MWNT content. This could also be attributed to the pathway effect of MWNT by forming a channel through which water molecules could diffuse rapidly.