Formulation of Emulsifiable Concentrates

From the above discussion, it is dear why the choice of surfactants for ECs is still made on a trial and error basis. Once this choice is made, an extensive work is required to optimise the composition to produce an acceptable product that satisfies the criteria of spontaneous emulsification and stability under practical conditions. In many cases, it is also essential to add other components such as 

As mentioned above, testing of ECs is carried out using fairly simple procedures. The most common procedure is that based on the recommendation of the World Health Organization (W.H.O.), which was originally designed for DDT emulsifi-able concentrates. The W.H.O. specification states, 

The emulsion is kept at 29-31 °C for one hour and examined for any creaming or separation.  

The reason for the above procedure is because both temperature and water hardness have a major effect on the performance of ECs. This was illustrated previously [8], showing the effect of water hardness on the amount of cream that separates 

The above dependence of the performance of ECs on water hardness and temperature may be related to the dependence of emulsifier properties on these parameters. This is discussed in more detail in Chapter 6. Nonionic surfactants are particularly sensitive to these parameters. For example, the solubility in water and, therefore, the effective HLB number of a typical nonionic surfactant decreases as the temperature or salt content of the solution increases. This is evident from the decrease in c.m.c. and cloud point with increasing salt concentration and/or temperature [10, 11]. 

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