Thermal, gas transport and antimicrobial properties of PEBAX®RNEW films loaded with imidazolium ionic liquids

The incorporation of imidazolium ionic liquids (ILs) in flexible films is useful to take advantage of ILs remarkable properties [1] in many industrial applications. Poly(ether-block-amide) (Pebax®Rnew) membranes were prepared by controlled solvent evaporation loading, up to 5 wt.%, two ILs 1-octyloximethyl-3-methylimidazolium hexafluorophosphate [OOMmim][PF6] and 1-hexadecyl-3-methylimidazolium dimethyl-5-sulfoisophthalate [Hdmim][DMSIP] [2]. The ILs were synthetized and characterized by 1H NMR, MALDI-TOF spectroscopy, Differential Scanning Calorimetry (DSC) and Thermogravimetric Analysis (TGA). The miscibility, morphology, wettability, gas transport, spectral and thermal properties of the obtained blends were investigated. TGA evidences a good thermal stability (>200 °C) for the membranes, while DSC reveals phase separation in the IL-loaded films, in accordance with the island-like surface morphology observed by Scanning Electron Microscopy (SEM) and with Fourier Transform Infrared (FTIR) analysis. Gas permeability tests shows that the films are defect-free, maintaining the original selectivity of the neat polymer with a reduction in the gas permeability due to the impermeable nature of the solid ILs crystals. The blend antimicrobial activity, tested against both Gram- (Escherichia coli, Pseudomonas fluorescens, Salmonella enterica) and Gram+ (Listeria monocytogenes and Bacillus subtilis) bacterial strains, depends on the chemical structure of the incorporated ILs. The smaller [OOMmim][PF6] only slightly lowers the hydrophobicity of the neat polymer and is readily released from the films. Instead, the [Hdmim][DMSIP], having a cation bearing a longer alkyl chain, induces a promising antimicrobial activity in the blends together with good hydrophilicity, permeability and thermal stability. Data on ILs release and biocompatibility/cytotoxicity suggest their application as antimicrobial coating on furniture for sterile environments/rooms, as filters for aerating systems and, at low concentrations of ILs (<=1%), in biomedical field.