Organic acid-treated cotton and polyamide 6,6 fabrics for antibacterial water filtration

A water decontamination process is necessary to eliminate pathogenic microorganisms from contaminated water. In high-volume processing, microorganisms have to be effectively deactivated in minutes during water flow to reduce costs. This work proposes a novel strategy for water purification: cotton and polyamide 6,6 fabrics were treated with some organic acids (citric, maleic and tannic acids) and tested in various conditions as a cheap water filter for biological disinfection against Gram-positive (i.e. Staphylococcus aureus) and Gram-negative (i.e. Escherichia coli) bacteria. The treated samples were first evaluated by applying the standard ASTM E2149- 2013 method to assess their antimicrobial properties: the fabrics treated with tannic acid did not show good antibacterial activity against the Gram-negative bacterium. In contrast, citric and maleic acids reached excellent results in bacterial reduction for both the species tested. Hence, since a good antibacterial water filtration must be effective against all the microorganisms, citric and maleic acids were selected and also tested in a continuous flowing condition simulating a real filtration process. Both cotton and polyamide 6,6 treated with citric acid registered the fastest antibacterial activity against S. aureus, reaching bacterial reduction values equal to or higher than 98.6 % already after 3 filtration cycles of filtration. Instead, the same treated specimens needed more than 10 cycles to show significant antibacterial performances as water filter systems against the Gram-negative bacterium E. coli. The treatment with maleic acid revealed interesting results: all the specimens tested gave complete sterilization in 6 filtration cycles against both the species considered, underlining the capability of this organic acid to act as a promising water filter system. The functionalized fabrics were characterized by microscopy, infrared spectroscopy and through contact angle and water absorption time measurements.