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| Issue date:01/12/2007 |
| ATA Journal for Asia on Textile & Apparel - Dec 2007 Issue |
| Source:Journal for Asia on Textile & Apparel |
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| Mosquito repellent textiles is one of the revolutionary ways to advance the textile field by providing the much-needed features of driving away mosquitoes, especially in the tropical areas, G. V. N. Shirish Kumar, Richa Maheshwari and K.H.Prabhu write. |
Many mosquito-borne diseases, such as malaria, dengue fever (DF), dengue hemorrhagic fever (DHF), chicken gunia and filariasis, are serious public health problems in tropical regions, especially in Africa and Asia. These diseases are transmitted to human beings through mosquito bite only. Since there is no effective vaccine available for the control of these diseases, prevention of mosquito bites is one of the main strategies to control or minimize incidence of these diseases.
People initially applied mosquito repellents on their skin directly as lotion. It is effective for a few hours and most of them can be harmful to human beings as they are coming in direct contact with the skin.
Due to these reasons, people now prefer mosquito repellent textiles, as they may remain effective for up to a week when applied to clothing. A repellent applied to clothing normally retains its effect longer than on skin because there is:
no loss by abrasion;
no loss due to skin absorption;
no removal of the active compound by sweating;
slower evaporation because of lower temperature, except when clothing is exposed to sunlight; and
better adherence to cotton and synthetic fibers.
There are many chemicals available for achieving mosquito repellency on textiles. But most of the chemicals are banned by World Health Organisation (WHO) due to their side effects on human beings and as well as their harmfulness towards environment. Therefore, researchers have shifted their focus towards natural mosquito repellents complied with the requirements of WHO.
Generally, cotton and nylon fabrics are treated with mosquito repellents since cotton is widely used as bed-sheets where nylon as mosquito nets.
Mosquito repellents primarily categorized into two groups: repellent insecticides and contact insecticides.
Repellent insecticides are substances mainly used to repel insects and pests rather than causing death. Several mosquito repellents are available in today's market, for instance, an estimated 110 million people safely use DEET worldwide each year.
Contact insecticides are substances that contain neuro-toxins for pests and insects, which are made unconscious when they come in contact with the insecticides.
Mosquito repellents are also divided into two groups, namely chemical repellents and natural repellents.
Chemical repellents
Developed by the US Department of Agriculture, Di-Ethyl Meta Toluamide (DEET) was first used by the military. It is applied as a skin lotion and its effectiveness last for four to five hours. DEET cannot be applied on fabrics, as it does not withstand even mild laundering.
It has recently been found that DEET may cause allergic problems, especially with infants and young children. There have been reports of cases of localized skin irritation, rashes, seizures, brain damage and even claims of one or two DEET-related fatal cases.
Allethrin is a chemical compound widely used in vaporizer repellents. Although it is safe, children are more susceptible to it, while malathion is an organophosphate insecticide that can cause acute and long-term neurological health problems.
At present, no chemical repellent is applied to the clothing and almost all repellents are designed to apply directly on the skin. However, most of chemical repellents are risk-born to people, leading to a need of developing natural and safe-to-human mosquito repellents, applicable to textile substrates.
Natural repellents
There are various natural mosquito repellents:
Citronella oil
Castor oil
Clove oil
Cedar oil
Rosemary oil
Peppermint oil
Lemongrass oil
Geranium oil
Chrysanthemum
Among them, chrysanthemum was found to be the best repellent.
Most amazingly, chrysanthemum remains its mosquito repellent capability even exposed to the environment for a long period of time, whilst other natural repellents lose their magic when exposed to sun, heat and/or rain.
Chrysanthemum can be extracted in three ways to become pyrethrum, which will be applied onto fabrics. By using water extraction, about 500 grams of flower is dried and then crushed to powder form. From this crushed powder take about five grams in 100 ml warm water and then soaked for about two hours. Finally the supernatant is taken and the residue is thrown off. The amount of water used may be reduced for extremely strong solution concentrations.
Another method is kerosene extraction. About 500 grams of dried flowers are soaked in four liters of kerosene for four hours. The kerosene will dissolve 71% of pyrethrum in 48 hours. After filtering through a fine mesh cloth, the extract is ready for application.
Alternatively, paraffin wax can be used. Dried flowers are soaked in paraffin for one day and occasionally stirred. The solution must be filtered before use. Alcohol extraction involves a procedure is similar to that of paraffin extraction. Alcohol extraction is possible but the resulting product has the disadvantage of evaporating very quickly.
From the above extraction procedures, water extraction is most widely considered and practiced. Kerosene extraction is not advisable as it is not eco-friendly. Paraffin's and alcohols are highly volatile and hence are not recommended. Therefore, the simple and most effective method of extracting pyrethrum both in terms of cost and process is by using water.
The extraction of pyrethrum with water can be done at different temperatures, 60℃ or 90℃. Out of the two extractions, the extraction done at 90℃ showed poor quality of the final extract solution than that of extraction done at 60℃. This shows that the rise in temperature beyond 70℃ has an adverse effect on the powdered extract. At the end of process the final extract is allowed to stand for at least two hours and then filtered off. The final clear solution is used for the finishing purposes.
Finishing of fabrics with pyrethrum
The pyrethrum can be applied to fabric in two ways:
Padding method
Exhaust method
In padding method, the fabric is simply impregnated in the extract solution followed by drying and then finally cured. In exhaust method, the fabric is treated with the solution for about an hour at 50℃-60℃ and then it is squeezed and dried.
Dosages of insecticide to different types of fabrics |
Both methods were quite effective, particularly the exhaust method, which shows satisfactory performance with both nylon and cotton and is less complicated than the padding technique. Nylon is finished only by exhaust technique, as it is difficult to withstand the stresses and strains in the padding technique.
The major disadvantage associated with this finish is slight yellowing problem. This result in tonal changes when this finish is applied to colored goods and the bleached fabric becomes slightly pale. Both cotton and nylon fabrics treated with pyrethrum, possess good wash fastness (finish remains after 5-10 washes).
In addition, dosages of insecticide vary with differing types of fabric.
Microencapsulation gives longer effect
For apparel designed for tropical climate where mosquitoes abound, there is a market for insect-repellent treatments that give a long-lasting effect. Microencapsulation of insect-repellent agents can be employed to provide a longer controlled release effect.
Thor SARL of France has developed a method to microencapsulate a synthetic pyrethroid called permethrin, which is a known insecticide. It is used particularly in military clothing for tropical climates.
Textiles treated with tea tree oil SPT microcapsules have been tested by the Carrol Loye Biological Research Institute, the US, and shown to demonstrate significant mosquito repellence properties. The natural organic ester plant oils act effectively as a nerve agent on insects. More importantly, recent research has shown that these have an unusual effect on mosquitoes, which is termed "jamming". This effect results in the "black box" that helps the mosquito search for victims being turned off. As a result, microencapsulated release of these plant oils has been found to significantly decrease the bites per minute in test boxes from 50 to virtually none.
Microencapsulated insect-resistant treatments are also used for textiles of natural protein fibers like wool and silk. Such finishes could provide long-term protection against the ravages wrought by the larvae of moths and particularly many types of beetles.
The microencapsulation finishes are not yet used extensively in the textile industry due to the prohibitive costs involved. More research is called for to produce more cost-effective mosquito repellent textiles that have a potential to become ultimately daily wear of people in the tropical areas, especially Asia.
Authors are researchers at the Department of Fibers and Textile Processing Technology, Mumbai University Institute of Chemical Technology, India.
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| Copyright © Adsale Publishing Limited. Any party needs to reprint any part of the content should get the written approval from Adsale Publishing Ltd and quote the source "ATA Journal for Asia on Textile & Apparel", Adsale Textile English Website - www.AdsaleATA.com. We reserve the right to take legal action against any party who reprints any part of this article without acknowledgement. For enquiry, please contact Editorial Department. |
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