Enhancing the efficacy and wash durability of permethrin-impregnated fabrics using coarse emulsion and nanoemulsion for adult mosquito (Culex pipiens L.) control

Permethrin is a common and effective insecticide used to treat fabrics for protection against mosquitoes. However, a significant limitation is that its potency quickly diminishes due to washing and environmental exposure, reducing the long-term durability of the treated fabrics. This study investigated the enhancement of residual properties using coarse emulsion and nanoemulsion formulations of permethrin, applied to military uniform fabrics. A stable permethrin nanoemulsion was successfully developed and characterized, exhibiting a mean droplet size of 159.10 ± 1.12 nm, a polydispersity index of 0.325, and a zeta potential of -15.4 mV. The role of a commercial acrylic binder was also evaluated at different permethrin-to-binder ratios (1:1, 1:3, and 1:5). HPLC analysis of permethrin residues after repeated laundering (1-50 washes) demonstrated that the incorporation of a binder significantly improved wash durability, with the 1:5 ratio achieving the most sustained permethrin retention. Bioassays against Culex pipiens adults revealed that the nanoemulsion formulation was significantly more effective than the coarse emulsion, achieving 95% knockdown and 90% mortality in WHO tube tests, compared to 60% knockdown and 70% mortality, for the coarse emulsion. The cone test also showed superior performance for the nanoemulsion. The results indicate that, the combination of a nanoemulsion formulation and an optimal binder ratio synergistically enhances the insecticidal efficacy and wash-fastness of permethrin-treated fabrics, offering a promising strategy for developing durable protective clothing for mosquito control.