Preparation of durable insecticide cotton fabrics through sol–gel treatment with permethrin
Introduction
The application of functional finishes to textile fabrics has led to the development of textile products with advanced properties, such as antibacterial [1], [2], [3], [4], UV protection [5], [6], fire protection (flame retardant textiles) [7], self-cleaning [8], hydrophobicity [9] or combinations of various properties in one fabric (multifunctional textiles) [10].
Sol–gel nanocomposite hybrids [11], [12], [13] have been shown to enable the chemical modification of natural fibres like cotton. Mild processing conditions are required and single-step processing, employing conventional machinery used in industrial textile finishing, such as pad application or exhaust processes, is usually enough to impart multifunctional properties to the finished fabrics [14]. Importantly, sol–gel nanocoatings exhibit excellent adhesion on cotton, attained through condensation between the –OH groups of the hydrolyzed silanes and those present on the surface of cellulose [12], [14].
The resulting transparent oxide layers can act as a carrier for embedded functional additives, such as organic compounds, inorganic particles or polymers [13]. The additives or active substances can be homogeneously incorporated into and immobilized in the sol–gel nanosol coatings, leading to new applications for functional fabric finishes, like the slow release of insecticides in insect-repellent textiles [15].
Insect-borne diseases afflict hundreds of millions of people each year and represent a significant portion of overall infectious diseases, which globally rank second among all causes of death. Vaccines and therapeutic drugs have yet to be developed to treat many of these diseases, so preventive measures must be taken to control these insects and avoid contact with them. Public health agencies worldwide consider insect-repellent textiles to be an increasingly important component in reducing the incidence of insect-borne infectious diseases such as malaria, West Nile virus, encephalitis, dengue fever, Lyme disease and many others [16], [17], [18], [19], [20].
Permethrin is a synthetic insecticide/repellent commonly used to treat clothing, netting, camping gear and military uniforms and to provide protection from mosquitoes, ticks, sand flies, fleas and other such disease-bearing insects. In spite of being effective against all stages of insect growth, permethrin is one of the least toxic insecticides to humans and the only one registered by the US Environmental Protection Agency (EPA) for use on clothing and in agricultural and pharmaceutical applications in the United States [16], [17].
Permethrin or other pyrethroid insecticides are generally incorporated into cotton based textiles either by dipping/spraying of the fabrics or by polymer-coating [18]. While the treatment by spraying is very simple, it results in a low laundering durability and it is difficult to control the quantity of permethrin on the textile. On the other hand, durable and effective insect-repellent coatings have been developed by using the polymer-coating method [19], [20], [21]. Nevertheless, these studies do not analyse the effect of the coatings on the textile properties, that is, handling and drapability, which are of crucial importance for clothing applications. In this sense, treatments with toxic formaldehyde-urea resins or other synthetic polymers dramatically alter the comfort and visual and tactile properties of cotton based fabrics.
In this study, we present an industrially viable procedure for the fabrication of comfortable and durable insecticide textiles based on the sol–gel technique. Permethrin was embedded into cotton fabrics by a silicon oxide nanocoating applied by conventional padding followed by curing (Fig. 1). The effect of the process parameters, such as silica precursor content and permethrin/silica precursor ratio, on the insect-repellent activity, textile properties and stability during washing was studied.
This new method provides the possibility of fine tuning the amount of insecticide incorporated. This point is critical since the maximum dosage of permethrin in clothing recommended by the World Health Organization (WHO) is 500 mg/m2.
Thanks to the high laundering durability, strong anti-mosquito effect and ease of application, the permethrin-containing sol–gel coatings presented in this study, could be proposed as an alternative to well-established treatments for cotton textiles [16], [17], [18], [19], [20], [21].
Section snippets
Materials
The textile substrate used in this study was a satin weave cotton fabric bleached without optical brightener, purchased from EMPA Test Materials. The characteristics of the fabric were 24 yarns and picks/cm with a weight of 210 g/m2.
Permethrin (provided by Zell Chemie Internacional, S.L) was used as the active principal substance. The most remarkable physicochemical properties are a density of 1.29 g/cm3, a decomposition temperature of 252 °C, low solubility in water (0.006 mg/L at 20 °C) but
Results and discussion
The objective of this study was to obtain a permethrin-containing cotton textile with high fastness/durability of the insecticide effect without altering its comfort and visual and tactile properties. For this purpose, we studied sol–gel process parameters, such as the solid content in the sol–gel formulation and the permethrin/TEOS w/w ratio. Moreover, controlling the fabrication process parameters is important to fine tune the amount of insecticide incorporated into the fabrics in order not
Conclusions
We developed an industrially viable procedure for the fabrication of durable insect-repellent textiles based on the sol–gel technique. Permethrin was embedded into cotton fabrics by a silicon oxide nanocoating applied by conventional padding followed by curing. This new method allows the amount of insecticide incorporated in the fabrics to be fine-tuned by simply adding the proper amount of it to the sol–gel solution. The application of the nanosol coating allows the fabric flexibility and
Acknowledgments
The financial support of this work was provided by the MICINN (Spanish Government) through the projects BIA2011-26288 and PID-600300-2009-12 project named INSEPLATEX. The authors would like to thank also Selina Koskela for her contribution in the experimental section.
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