Emulsion concentrates EWs

Many agrochemicals are formulated as O/W emulsions, referred to as emulsion concentrates (EWs). These systems offer many advantages over the self-emulsifiable oils (ECs). Being aqueous-based, they produce less safety hazard to human operators, and may be less phytotoxic to plants. 

Among several applications of emulsions the most important are listed here Food emulsion, e.g. mayonnaise, salad creams, deserts, beverages, etc. Personal care and cosmetics, e.g. hand creams, lotions, hair sprays, sunscreens, etc. Agrochemicals, e.g. self-emulsifiable oils which produce emulsions on dilution with water, emulsion concentrates (EWs) and crop oil sprays. Pharmaceuticals, e.g. anaethetics of O/W emulsions, lipid emulsions, double and multiple emulsions, etc. Paints, e.g. emulsions of alkyd resins, latex emulsions, etc. Dry cleaning formulations - these may contain water droplets emulsified in the dry cleaning oil that is necessary to remove soils and clays. Bitumen emulsions - emulsions prepared stable in the containers but when applied to the road chippings they must coalesce to form a uniform film of bitumen. Emulsions in the oil industry - many crude oils contain water droplets (e.g. North Sea oil) and these must be removed by coalescence fol-... 

It can be seen from the above short discussion that agrochemical formulations are complex multiphase systems and their preparation, stabilization and subsequent application require the application of the basic principles of colloid and interface science and this is the objective of the present part [1, 2]. It will start with a section on surfactants and the physical properties of their solutions. This is followed by a section on the interfacial aspects of agrochemical formulations including adsorption of surfactants and polymeric surfactants at the air/liquid, liquid/liquid and solid/liquid interfaces. The stabilization of dispersions, both electrostatic and steric, is discussed in the next section. The basic principles of colloid and interface science are illustrated in detail by considering emulsion concentrates (EW s) and suspension concentrates (SC s). A summary will be given on microemulsions and controlied release of agrochemical formulations. 

Three main classes may be distinguished, namely anionic, cationic and amphoteric [3, 4]. A useful technical reference is McCutcheon [5], which is produced annually to update the list of available surfactants. A recent text by van Os et al. [6] listing the physicochemical properties of selected rmionic, cationic and nonionic surfactants has been published by Elsevier. Another useful text is the Handbook of Surfactants by Porter [7]. It should be mentioned also that a fourth class of surfactants, usually referred to as polymeric surfactants, has been used for many years for preparation of EW s (emulsion concentrates) and SC s (suspension concentrates) and their stabilization. 

The major classes of pesticides in use in the Region are organochlo-rine and organophosphorus compounds, Ccirbamates, pyrethroids and bacterial larvicides. Organophosphorus compounds are the most common, followed by pyrethroids. Insecticides are available in a variety of formulations, including emulsifiable concentrates (EC), wet-table powders (WP), dustable powders (DP), suspension concentrates (SC), oil-in-water emulsions (EW) and capsule suspensions (CS). 

The specification of suspoemulsions is covered by the FAO-Manual (5 Ed. 1998) [1] and most regulatory bodies (specifically in the EU) base their data requirements on the test methods described therein. It is important to recognize that the characterization of SE s is not just the addition of all available methods useful for suspension concentrates (SC) or emulsions (EW). 

Applications of Dithiopyr to paddy grown Oryza are targeted to control Echino-chloa spp. Dithiopyr can be formulated into several different formulations, including an emulsion in water (EW) containing 240 g a.i. an emulsifiable concentrate (EC) up to 120 g a.i. and a wettable powder (WP) with 40% a.i. In addition, granular formulations are available. 

Steric repulsion results from the presence of adsorbed layers of surfactants and/or polymers. The use of natural and synthetic polymers (referred to as polymeric surfactants) for stabilization of suspension concentrates and emulsions (EW s) plays an important role in agrochemical formulations. Polymers are particularly important for preparation of concentrated dispersions, i.e. at high volume fraction ( j of the disperse phase,... 

Microemulsions are quite distinct from macroemulsions (EW s). With emulsions, increasing the mechanical energy and increasing surfactant concentration usually results in the formation of smaller droplets which become kinetically more stable. With microemulsions, neither mechanical energy nor increasing surfactant concentration can result in its formation. The latter is based on a specific combination of... 

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