Garry Webb, general manager of Sumitomo Chemical, explains his company’s approach to aerosol product formulation.
Although many will know Sumitomo Chemical has its heritage in pyrethroid discovery, commercialisation and manufacture, over the years, during the commercialisation process for various pyrethroids, Sumitomo Chemical has built up significant expertise in aerosol technology.
Although aerosols may be viewed as old technology, the development of a high performing aerosol product requires significant expertise and knowledge, to combine a range of chemical and physical parameters in designing a product that delivers superior performance.
Synthetic pyrethoids (SPs) are ideal partners for aerosol technology, being largely oil-soluble and relatively fast acting on insects. Almost all aerosols used today in public health and consumer markets contain one or more synthetic pyrethroids and may be supplemented with synergists like piperonyl butoxide (PBO) or MGK264, which facilitate the uptake of the SP by the nuisance insect.
Most often a fast knockdown SP such as imiprothrin is combined with a strong kill agent such as deltamethrin, cypermethrin or permethrin to give the visual appearance of flushing out and fast knockdown, together with good residual activity on sprayed surfaces.
Formulating an aerosol is far more complex than a liquid spray product because of the complex inter- relationships between the insecticidal concentrate, the propellant, the can, the valve (the suction device) and actuator (the button and dispersion nozzle) and the cap.
The choice of formulation depends on the target insect and desired performance properties. Solvent- based formulations generally deliver the fastest performance, as the solvent containing the active quickly penetrates the insect cuticle. This
is particularly the case for crawling insect aerosols when the key target pest (the cockroach) has a particularly waxy cuticle.
Water based formulations tend to be used for flying insects, as they allow for a smaller droplet size, resulting in a better ‘hang-time’ in the air, creating an ‘insecticide cloud’ which the insect cannot avoid.
As the pyrethroids are dissolved in the solvent, residual performance on porous surfaces can be limited. However, the addition of silica to formulations allows small particles of silica coated in active to sit on porous surfaces, boosting performance.
Typically, a standard aerosol will have a solvent-based concentrate in an unlined can using LPG propellant. The can itself is typically made of lacquered tinplate (steel with a thin layer of tin). For water-based emulsions, epon-lined cans are required to avoid can corrosion or a corrosion inhibitor must be added to the formulation.
Conversely, some solvent-based formulations cannot be used with lined cans, as the solvent will dissolve the lining. Similarly, CO2based propellants are not normally used for water-based emulsions, as the propellant will form carbonic acid and corrode the can.
Most aerosols use LPG propellants in the formulation. These propellants generally mix well with the formulation and ensure an even spraying pressure through the life of the can. As the formulation is under pressure in the can, most of the propellant is mixed with the concentrate in a liquid phase, with only a small amount present as gas in the headspace of the can.
Using CO2 as a propellant is less common, as it does not dissolve well in most concentrate formulations. This results in a drop in pressure as the can is used up, meaning a weaker spray as the can nears empty. However, CO2 does provide other advantages, most notably in its lack of flammability in comparison to LPG propellants.
The type of propellant, the concentrate formulation and the ratio of concentrate to propellant all affect the pressure in the can and therefore the spray characteristics.
Valve, actuator and cap
The physical attributes of the release mechanism – the valve, actuator and cap – will modify the spray characteristics of a given formulation. The amount of product released per second and the shape of the orifice will determine droplet size and spray characteristics. Consider the differences between the fine droplet size of a water-based fly spray, designed for long ‘hang-time’ versus the solvent-based, high output, long- distance spray of a wasp aerosol, designed to coat and immobilise wasps in their nest immediately.
Sumitomo aerosol expertise
Sumitomo has a long history and expertise in both synthetic pyrethroids and aerosol technology. Here in Australia, Sumitomo Chemical has developed some unique aerosols for the PCO and public health markets. These products have unique insecticidal combinations, with higher loadings of active ingredients than typical supermarket brands, together with the best aerosol technology, to deliver professional results for the professional pest manager.
Sumiblast – utilises a retractable straw and 360 degree valve to allow spraying into cracks and crevices, whilst holding the can upside down. Sumiblast combines an ideal ‘flushing aerosol’ with potent spot treatment product. The Dengue response program in north Queensland has found a novel use for the product – deep spray penetration into household stormwater pipes that often harbour Aedes aegypti.
WaspJet – the high output, high active formulation combined with its specially designed nozzle, can immobilise wasps in their nests from a distance of up to 6m. Furthermore, combining the low electrical conductivity of the formulation with non-flammable CO2propellant means it can be used with confidence around electrical areas and has been well adopted by electricity utility companies.
Bedlam – ideal spot treatment product as part of any bed bug treatment program. With its new generation synergist, it performs on resistant strains and its water-based formulation avoids staining, making it an ideal option for mattress treatments.
Although some pest professionals avoid aerosols as they can give homeowners the impression pest control is a job they could do themselves, in a number of situations aerosols provide the best product option for the job. Explaining to homeowners that these products are not available in supermarkets should retain your level of professionalism. In commercial situations, such aerosols provide discrete, professional performance, delivering quick results and good value, to you and your clients. Aerosols are certainly a handy tool when you need to ‘perform under pressure’.
Garry Webb, General Manager, Sumitomo Chemical Professional Products