Phenolic fatty acid-based epoxy curing agent for antimicrobial epoxy polymers

Abstract

Epoxy resins are one class of important reactive pre-polymers used in the coating industry. To manufacture epoxy resins with antimicrobial properties, active quaternary ammonium groups are often introduced into the polymeric backbones following resin polymerization reactions for structure modification. However, these complicated approaches associated with these types of reactions make the commercialization of the antimicrobial epoxy polymers uneconomical, impractical and inconvenient. Besides, quaternary ammonium groups are undesirable because the hydrophilicity of the groups makes the resins less water-resistant. In order to simplify the development of antimicrobial epoxy polymers, we prepared an amide by reacting novel bio-based phenolic-branched fatty acids with ethylenediamine. The resulting amide was cured into a commercial epoxy resin -- diglycidyl ether of bisphenol A (DGEBA), which was solution-cast into epoxy polymer films. The antimicrobial activities of the resulting epoxy polymer films were investigated. The crude phenolic branched fatty acid amides (PBC-FAAs) as curing agents were separated and characterized by thin-layer chromatography, proton nuclear magnetic resonance (1H-NMR), gas chromatography-mass spectrometry (GCMS), liquid chromatography-mass spectrometry (LC/MS) and Fourier-transform infrared spectroscopy (FT-IR). The thermal and mechanical properties of the polymer films were also investigated by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and dynamic mechanical analysis (DMA). Cured epoxy films prepared from purified PBC-FAA exhibited antimicrobial activity against Listeria innocua. However, the crude, unpurified PBC-FAA-cured epoxy film showed much more promising antimicrobial activity against both Listeria innocua (Gram positive) and Escherichia coli (Gram negative).