Green Solvent-Based Antimicrobial Microemulsions: Formulation and Evaluation of Methyl Ester-Camphor Oil Systems for Surface Cleaning

The design of eco-friendly antimicrobial preparations is one of the crucial issues to be considered in terms of resolving the health- and ecological-related problems related to the use of traditional synthetic disinfectants. The study presents the development and an overall analysis of new green solvent based antimicrobial microemulsions using neem oil methyl ester, camphor oil, and ethoxylated vegetable oils as totally bio-based materials. Surfactants of different hydrophilic-lipophilic balance (HLB) (9.7, 11.7 and 12.5) were added to two oil blends (80:20 and 60:40 camphor oil to neem oil methyl ester) to create both the oil-in-water (O/W) and water-in-oil (W/O) microemulsion systems. Pseudo-ternary phase diagrams were plotted to establish stable microemulsion areas and twelve formulations were properly characterized based on physicochemical characteristics such as pH, density, conductivity, particle size, and stability. Dynamic light scattering examination showed that the size of the particles varies between 81.90 nm and 189.2 nm, and all of the preparations showed very good thermodynamic stability in 30 days. The testing of antimicrobial efficacy under the requirements of EN 1040:2005 standards showed a strong activity against Staphylococcus aureus and Escherichia coli, where log reductions were 2.90 to >4.35 and the percentage reductions were 99.87% to >99.99% on a 5-minute contact. It is worth mentioning that the Blend-1 JO-5 formulation (80:20 oil blend with HLB 11.7) showed the best antimicrobial activity with more than 4.35 log reduction to S. aureus. The findings support the argument that methyl ester solvents and fully bio-based microemulsion systems in soil cleaning applications can be used to offer an alternative to the synthetic disinfectants, as these systems are stable and can offer effective and efficient systems to counteract microorganisms, at the same time being environmentally sound.