Mosquito Repellant Fabrics

Preparation of Mosquito Repellent Fabrics

Abstract:
A mosquito repellent substrate includes a fabric which is impregnated with a repellent carrier composition. The carrier composition includes a mosquito repellent (e.g. permethrin, prallethrin etc.), binder, emulsifier and cross linker. The carrier composition is applied as a finish or printed onto the fabric.

1. Introduction

1.1 About Mosquitoes

Mosquito-borne diseases, such as malaria, dengue fever and yellow fever, have plagued civilization for thousands of years. There are many kind of mosquitoes, each of which has a different habitat, behavior and preferred source of blood. About ten of these species are so numerous, and such vicious biters of man and animals, that an organized mosquito control is necessary because mosquitoes are not a nuisance as biting insects, but are also involved periodically in transmitting disease to humans and animals.
Only female mosquitoes bite. When adult mosquitoes emerge from the aquatic stages, they mate, and the female seeks a blood meal to obtain the proteins for the development of her eggs. After a blood meal is digested and the eggs are laid, the female mosquito depending on her stamina and the weather may repeat this process many times without mating again. They usually feed every 3 to 4 days; in a single feeding, a female mosquito typically consumes more than its own weight in blood. Male mosquitoes feed primarily on flower nectar. He lives for only a short time after mating. Certain species of mosquitoes prefer to feed at twilight or nighttime; others bite mostly during the day.
Mosquitoes home in on people because they are giving off carbon dioxide, lactic acid, body odor and also heat. Mosquitoes use carbon dioxide and lactic acid like sign posts to our body - following them until they find our skin and they bite us.

1.2 About Mosquito Repellents

1.2.1 Permethrin

Permethrin is a human-made synthetic pyrethroid. It does not repel insects but works as a contact insecticide, causing nervous system toxicity that leads to the death or "knockdown" of the insect. The chemical is effective against mosquitoes, flies, ticks, and chiggers. Permethrin has low toxicity in mammals, is poorly absorbed by the skin, and is rapidly inactivated by ester hydrolysis.
Density: 1.19 g/cm³
Chemical Formula: C21H20Cl2O3
Boiling Point: 200°C

1.2.2 Prallethrin

Prallethrin is also a pyrethroid. It works on the same principle as permethrin. It has been found to be more effective on Indian mosquitoes than permethrin.
1.2.3 DEET
DEET is N,N-Diethyl-m-toluamide. It works by evaporation, creating a shield a few inches above the area of application. The repellent vapor confuses mosquito so they can’t locate a target host.

1.2.4 Eucalyptus oil

It works on the same principle as DEET.
Chemical name:
1,3,3-Trimethyl-2-oxabicyclo[2.2.2.]-octane

2. Objective

The main aim is to fix one or a combination of the above mentioned mosquito repellents to the fabric.

3. Challenges

All the above mentioned repellents have no affinity for fabrics as such, so a system was required to keep them attached to the fabric. Also the system was required to withstand repeated washing. The prepared fabric should have the desired level of efficacy against mosquitoes and it should last even after repeated washings.

4. Experiment

Samples were prepared using permethrin, prallethrin and eucalyptus oil using various combinations of their concentrations and methods of fixing. The various recipes used are mentioned below.
4.1 Recipe I
• With Eucalyptus as Mosquito Repellent
1) Binder – 6%
2) Eucalyptus oil – 2%
3) DAP (Di-ammonium Phosphate) – 1%
4) Water – 91%

Initially, the samples were padded in the padding mangle and then dried at 80oC. Then curing was done at 120oC. But, the smell of eucalyptus oil, which is the main factor in repelling mosquitoes was found to be absent from the samples. Hence, the process was modified and only padding and drying at room temperature was carried out.

4.2 Recipe II
• With permethrin / prallethrin Oil
1) Binder – 10%
2) Emulsifier (Lissapol – N) – 2%
3) Oil – 0.5%
4) Cross linker – 2%
5) DAP – 1%
6) Water – make to 100%
The samples were padded with the above recipe and then dried at 80oC and cured at 120oC. The above recipe was also tried with increasing the oil concentration from 0.5% to 2%, 3% and 5%.

4.3 Recipe III
• Printing
1) Binder – 15%
2) Permethrin / Prallethrin Oil – 0.5%
3) Emulsifier – 2%
4) Pigment – 5%
5) Cross linker – 2%
6) DAP – 1%
7) Thickener – make to 100%
In this method, it has been tried to mix the mosquito repellent with the print paste and then samples were prepared by screen printing. The printed samples were dried at 80oC and cured at 120oC.

The samples prepared by using the above recipes were washed under the following conditions:
Temperature of washing: 60oC
Time of washing: 30 minutes
Washing was carried out in HTHP machine using a 5gm/l solution of an Industrial Detergent.

4.4 Testing of the samples

Both washed and unwashed samples have been sent for testing and the test is based on contact bioassays using recommended WHO Pesticide Evaluation Scheme (WHOPES) procedures which state the testing method as follows:

Female mosquitoes, aged 5–8 days, are released in a tunnel (square section 25 cm x 25 cm) made of glass, 60 cm length (Figure 5). At each end of the tunnel, a 25-cm square cage is fitted and covered with polyester netting. At one third of the length, a disposable cardboard frame is placed with the treated fabric sample. The surface of fabric “available” to mosquitoes is 400 cm2 (20 cm x 20 cm), with nine holes each 1 cm in diameter: one hole is located at the centre of the square; the other eight are equidistant and located at 5 cm from the border.

In the shorter section of the tunnel, bait is placed, unable to move. In the cage at the end of the longer section of the tunnel, 100 females are introduced. Females are free to fly in the tunnel but have to make contact with the piece of treated fabric and locate the holes in it before passing through, to reach the bait.

After 15 hours, the mosquitoes are removed and counted separately from each section of the tunnel and the immediate mortality is recorded. Live females are placed in plastic cups with honey solution; delayed mortality is recorded after 24 hours. During tests, cages are maintained at 27 °C + 2 °C and 80% + 10% relative humidity under subdued light.
Several tunnels will be used simultaneously, one tunnel with untreated fabric always being used as a negative control. Blood feeding inhibition is assessed by comparing the proportion of blood fed females (alive or dead) in treated and control tunnels. Overall mortality is measured by pooling the immediate and delayed (24-hour) mortalities of mosquitoes from the two sections of the tunnel.

Washed fabric that cause mortality >80% and or blood-feeding inhibition (BFI) >90% in tunnel tests meet the criteria to pass the testing.

Results

The samples were tested using WHOPES standards in the laboratory. The results are summarized in the table 1.1.

Reference:
1. Fabrics with insect repellent and a barrier; Document type and document number: United States Patent 5252387;
2. Flake proof fabric; Document Type and Number: United States Patent 4833006;
3. Synergistic effect of amylopectin-permethrin in combination on textile fabrics; Document Type and Number: United States Patent 5089298;
4. Wearable insect repellent patches; Document Type and Number: United States Patent 20060188538;
5. Insect repellent substrate for headwear: Document Type and Number: United States Patent 20030150467;