A study of The use of Manuka Honey and Methylglyoxal to Impart Antimicrobial Activity to Wool Textiles and Polymers

Methylglyoxal (MGO), which is an ingredient in New Zealand Manuka honey (MH) possesses unique antimicrobial properties against a broad range of bacteria. MGO has been determined to have a low minimum inhibitory concentration against bacteria. This provides a new opportunity to develop the use of this compound as a natural antimicrobial agent to impart such antimicrobial properties to wool textiles. This is the focus and detailed research work of this thesis. Also, its application to paper and polymer surfaces has been investigated briefly.

Due to their protein-based structure and porosity, woollen textiles provide a hospitable host for the growth of microorganisms. This microbial growth on such textiles can pose an undesirable health risk to humans and can negatively affect textile sales. the textile market. Similarly, microbial growth on other substrates such as walls, floors and various equipment can also pose health risks. There are a number of antimicrobial treatments on the market, but with the move to more natural-based antimicrobial agents, there is an opportunity to capture the natural antimicrobial properties of MH and particularly the active ingredient MGO, as a natural antimicrobial agent in wool textiles and paper and polymer substrates.

This research developed a novel approach and methodology to incorporate MH and also MGO itself as an isolated component and antimicrobial agent of MH, into the wool fibres and chemically bonding it to the fibre proteins. This approach commenced with determining the extent of uptake of MH, based on its MGO concentration, and MGO itself into wool fibres. The extent of MH and MGO uptake has been determined with High-Performance Liquid Chromatography (HPLC). This uptake was studied over a range of MH and MGO concentrations and temperatures using loose top wool, yarn and finished wool fabric. An increase in temperature from room temperature up to 80 °C resulted in significantly higher amounts of MGO and MH being absorbed by the wool. Also, higher concentrations of the initial MGO and MH solutions accelerated the uptake rates and resulted in higher uptake amounts. The relatively slow diffusion rate of MGO into the wool necessarily required a long period of time, up to 14 days, for the particular uptake to generally reach the saturation level. The maximum amounts of MH and MGO that were incorporated into wool fibres in this study were 21.2 mg g-1 and 299 mg g-1 wool, respectively.

The chemical interactions between MGO and MGO in MH with the wool fibres have been characterised by Fourier-Transform Infrared (FTIR) spectroscopy, Differential Scanning Calorimetry (DSC) and Thermogravimetric Analysis (TGA). FTIR spectra showed that the MGO absorption by the wool changed the intensity of particular peaks between 2,000 and 700 cm-1 characteristic of the wool proteins, and the NH stretching peaks of the wool at 3,270 cm-1. The TGA and DSC analyses showed a thermal stability of the wool after MGO absorption and the likely formation of new bonds, probably H-bonds, between the MGO and the wool. Confirming these findings, the MGOWool and MH-Wool showed a resistance against MGO leaching on washing with water, where less than 1% (relative) of MGO leached out. These results suggest the MGO is likely chemically bound to the wool fibres through hydrogen bonding.

The MGO-Wool and also MGO-paper composites produced in a similar way with MGO-Wool, exhibited antimicrobial activities against Gram-positive Staphylococcus aureus (S. aureus) and Gram-negative Escherichia coli (E. coli). The MGO-Wool showed bacteriostatic properties for all composites even after three months of being synthesised. This opens up potential applications for the use of MH and MGO in antimicrobial woollen apparel, medical textiles and bandages.

In addition, MGO was incorporated into samples of an acrylic polymer NeoCryl® XK-98 and a polyurethane, Kamthane K-5000, polymer resin, respectively. The interaction of MGO with the respective polymer chains resulted in similar hydrogen bonding between MGO and the polymers. At high MGO concentrations this bonding was confirmed by the presence of a new endothermic peak in the DSC pattern. The addition of MGO also modified the polymer surface and resulted in a more hydrophobic surface with an increased water droplet contact angle of 87.5°. The new polymer compositeswere successfully tested against S. aureus and E. coli microbes and were shown to exhibit antimicrobial properties.