Anchored quaternary ammonium salts adsorbed on polyurethane film surfaces

Abstract

A flexible, thermoset and transparent polyurethane (PUR) film with high glass transition temperature, has been deployed as a substrate for anchoring anti-bacterial molecular layers. These layers are formed by adsorbing, from an aqueous solution, a silyl anchoring quaternary ammonium salt (AQAS) with a long alkyl chain (C18) onto the PUR film surface, followed by thermal curing at 160 °C. The presence of AQAS adsorbed on the PUR film surface is confirmed by the appearance of a distinctive N1 s level XPS peak at 402 eV, attributed to quaternary nitrogen (N+). The carbonyl groups on the PUR surface appear to be the main surface binding sites for the adsorbed AQAS molecules. This interpretation is validated by the relative decrease in the intensities observed for the ν (CO) at 1700 cm−1 in the infrared spectra, and decreases in the intensity of the C1 s binding energy peak for CO at 289 eV in the XPS spectra of the PUR following AQAS adsorption. Leaching studies suggest a chemisorbed first layer and several leachable higher layers of oligomeric forms of AQAS. A PUR surface incorporating a blended polydimethylsiloxane additive exhibits similar adsorptive capacity to pristine PUR. However exposing the PUR films to oxygen plasma treatment prior to AQAS adsorption leads to a higher coverage of the adsorbate on the PUR surface. The anchoring quaternary ammonium salt (AQAS) in this current work has established potencies against a wide range of critical organisms. Antibacterial assays adapted from the JIS 2801 wet fomite method confirm the potency (3-log reduction) of these PUR-AQAS films against Staphylococcus aureus and Escherichia coli.