Synthesis and properties of poly(ether urethane) membranes filled with isophorone diisocyanate-grafted carbon nanotubes

A three-step surface treatment of multi-walled carbon nanotubes (MWCNTs) was used to enhance the mechanical and transport properties of poly(ether urethane) (PEU) film. The original MWCNTs were first carboxylated via a mixture of sulfuric and nitric acids to obtain MWCNT grafted to a -COOH group (MWCNT-COOH), then further hydroxylated via thionyl chloride and 1,6-hexanediol to obtain MWCNT grafted to 1,6-hexanediol (MWCNT-OH), and finally treated via isophorone diisocyanate (IPDI) to obtain MWCNT grafted to IPDI (MWCNT-IPDI), which had a similar structure to the hard segments of PEU. Fourier-transform infrared spectroscopy revealed that the functional group -IPDI was successfully grafted onto MWCNTs. Then the prepared MWCNT-IPDI was blended with PEU in a tetrahydrofuran solution to obtain the final transparent MWCNT-IPDI/PEU membranes. All the membranes were characterized by Instron, DMA, DSC and water vapor permeability (WVP). The results showed a remarkable enhancement of mechanical properties and glass-transition temperature of the hard-segments of PEU by adding only small amount of MWCNT-IPDI. For example, the tensile strength was increased from 26.2 MPa for pure PEU to 42 MPa for composites containing 0.3 wt% of MWCNT-IPDI, and the storage modulus was improved from 1500 MPa for pure PEU to 2350 MPa for composites containing 0.5 wt% of MWCNT-IPDI. Very interestingly, a largely improved WVP of PEU film has been achieved by mixing with MWCNT-IPDI. The WVP was increased from 646 g/m2 24 h for the pure PEU to 856 g/m2 24 h for the composites containing 0.3 wt% of MWCNT-IPDI, and to 1180 g/m2 24 h for the composites containing 0.8 wt% of MWCNT-IPDI.