Novel eco-friendly antimicrobial coatings for use in healthcare and sport textiles
Due to an increase in consumer awareness on environmental and health problems that can arise with synthetic materials and processes used within the textile industry there is a need for novel ‘green’ textiles. The rise in antibiotic-resistant microorganisms within recent years has led to 30,000 deaths in the EU every year, this has led to an increased need for novel antimicrobials (Cassini, Alessano et al., 2016). Synthetic biocides like triclosan and silver have been extensively used in the textile industry but new regulations by the EU Directive 98/8/EC, have now enforced the elimination and withdrawal of many commonly used biocides which are toxic and harmful to humans and the environment (Gao and Cranston, 2008; Gouveia, 2010; Kramer et al., 2006). Plant derived antimicrobials like essential oils (EOs) are therefore an attractive eco-friendly alternative for use in textile finishing (Alihosseini, 2016). Although EOs have regained popularity in recent years, with many studies dedicated to the antimicrobial potentials, (especially citrus-based EOs), few have been focused on their use in blends and encapsulation methods for their application on textiles. Due to EOs physicochemical properties, their development of functional fabrics is met with formulation challenges such as volatility and oxidative degradation and must therefore be protected before they can be used functionally. Screening of ten EOs by disk diffusion and subsequent evaluation of minimum inhibitory concentrations (MICs) and fractional inhibitory concentrations (FICs) showed that a 1:2 blend of L. cubeba (litsea) and Citrus Limon (lemon) EO respectively had the most efficacy in synergy, being inhibitory against Staphylococcus aureus, Escherichia coli, Staphylococcus epidermidis, Pseudomonas aeruginosa and Trichophyton rubrum compared to the individual EOs. The litsea-lemon EO blend was encapsulated (30% concentration) with natural biopolymers chitosan (0.05-1% w/v) and sodium alginate (0.1 % w/v) by using an emulsification method, without the presence of a surfactant. Gas Chromatography-Mass Spectroscopy (GC-MS) analysis revealed citral and limonene to be the major compounds found in the EOs, their presence also confirmed by Fourier Transform Infrared (FTIR) analysis. In vitro, the release of citral and limonene from the emulsion was examined using a dissolution method and the release profiles were characterised by initial burst release, followed by a slow controlled release of citral and limonene from emulsions; 70.11% of limonene was released within 10 min for a 1% w/v chitosan emulsion, whilst only 4.91% of citral was released within the same time. Fresh 1% chitosan-EO blend emulsions were then used to treat cotton and polyester using a soak-pad-dry method. Promising results were observed when time-kill assays were carried out on the treated fabric using the plate count method adapted from BS EN ISO 20743:2013, with 100% reductions observed at zero contact time (CT) for S. epidermidis, at 5 min for S. aureus and E. coli. Mosquito repellency was also assessed for EO-emulsion treated cotton which demonstrated 71.43% repellency to female mosquito Aedes aegypti compared to a repellency of 52.94% by neat EO-impregnated cotton. EOs show promise in their application as antimicrobials for the development of natural and eco-friendly functional textiles and should be further explored as alternatives to current synesthetic based finishing.
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