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SUSPO-EMULSION TECHNOLOGY

Steve Broadbent, regional director of Ensystex, explains the science behind suspo-emulsion (SE) formulation technology.

A suspo-emulsion (SE) formulation is one of the more recent formulation breakthroughs. It allows formulation chemists to blend together active ingredients with very different solubility profiles.

The resulting product is actually two different formulations combined into one bottle, through the use of two different formulation phases, an emulsion in water (EW) phase and a suspension concentrate (SC) phase.

Maxxthor Turbo is an example of a suspo-emulsion product.

An aqueous suspo-emulsion is essentially a mixture of water- insoluble active constituents dispersed in a water-based solution; where one (or more) of the active constituents is a solid, formulated as a suspension form (SC) and one (or more) of the actives is an oil, formulated as an emulsion in water (EW).

Thus the resulting product is actually two different formulations combined in the one bottle – an emulsion in water (EW) phase and the suspension concentrate (SC) phase. The resulting product is then diluted with water for use.

This allows mixtures of active constituents to be used to provide a broader spectrum pest control product. Formulating the active ingredients together eliminates the need for tank mixing (which can lead to incompatibilities).

Like other aqueous liquid formulations, suspo-emulsions are easy to handle and measure, dust free, non-flammable and mix easily with water.

In particular, this technology allows formulation chemists a method to put together in the same water-based formulation, two or more active constituents with very different physico-chemical characteristics.

For the development of a suspo-emulsion, the solid and liquid active constituents must all be insoluble in the aqueous (water) phase. This is required to avoid crystal growth and ensure long-term stability. The concentration of actives is expressed in g/L of each active in the final product.

Suspo-emulsions are usually prepared by creating each formulation component separately, a suspension concentrate (SC) with the solid active constituent(s), and then creating a concentrate emulsion with the liquid or low melting point active constituent(s) (EW).

The emulsion-in-water phase is created by dissolving the oil-soluble actives in a suitable oil, and then emulsifying this with water. It is then stabilised with hydro-colloids. The resulting emulsion consists of the oil liquid droplets containing the active constituent(s) dispersed in the water.

These two formulations are then mixed together under normal agitation. In this way the characteristics of the formulation are controlled very well.

Consequently, the surfactants consisting of emulsifiers, dispersing agents and wetting agents that form the basic components of each formulation, need to be carefully selected. The formulation chemist must take into account the fact that the two formulations will be blended together, so the compatibility between the different components is very important.

These surfactants play several important roles in determining the properties of the final product and its long-term stability.

They ensure the solid particles in suspension are dispersed into the water phase by reducing the oil/water interface tension, they electrostatically stabilise the micronised particles to avoid flocculation, aggregation or coalescence and they ensure the long-term stability of the micronised particles in suspension.

They also impact on the compatibility of the suspension with the emulsion in both the concentrated and diluted state.

Monopropylene glycol or glycerine are also required to prevent the formulation from freezing. Thickeners and anti- foaming agents are also added to perfect the final product.

The final formulation must be stable for at least two years without any significant change of viscosity, phase separation or agglomeration between droplets and solid particles. The presence of a supernatant water layer on the surface is acceptable, providing only slight agitation is needed for the re-homogenisation.

Typically, stability is tested using accelerated ageing tests; two weeks storage at 54°C and one week at 0°C. The aged samples are then checked to ensure there is no chemical degradation of the active constituents, no sedimentation in the bottle, and that the viscosity has not changed by more than 10% compared to the initial value. Particle sizes must also be checked to ensure that no crystal growth, flocculation, or droplet size increase has occurred.

Steve Broadbent, Ensystex, Regional Director

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