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General information about the functions and chemistry of adjuvants for agrochemicals

Adjuvant functions

Adjuvants can have more than one function in improving the performance of a pesticide. Multiple functionality is caused by the following. A substantial number of adjuvant products are mixes of compounds differing in chemistry and function. For instance, a mix of ammonium sulphate and a polymer. Secondly, one chemical compound or type of compound may interact with different stages in the targeting of a pesticide. A polyoxyethylene tallow amine surfactant improves both the wetting of the leaf surface and the foliar uptake of glyphosate. One can discriminate between adjuvant-functions that have a direct influence on the availability of the active ingredient and adjuvant-functions that have an indirect influence on the availability.

Potential functions of adjuvants for agrochemicals.

Direct influence on availability of the active ingredient	Indirect influence on availability of the active ingredient
Reduction of drift	Prevents foaming
Reduction of volatilization	Influence on pH
Improved retention spray solution	Improves compatibility with other ai's
Increased foliar uptake ai	Hindering antagonistic effects by inorganic cations
Prevents wash-off during rain	Enhancing viscosity
	Marker for deposition of spray solution

Adjuvant Classes

A few hundred adjuvants are on the market in the USA and it is expected that the number of products will increase in Europe and elsewhere in the near future. For most products, the adjuvant producers provide limited information regarding the structure and concentration of compounds in an adjuvant product. In spite of this, a number of different classes can be distinguished (see table below).

Alkoxylation (with ethylene and/or propylene oxide) and esterification are frequently used methods to change the hydrophilic lipophilic balance, the molecular weight and the three-dimensional structure of the surfactant. Further, the degree of branching (alcohols), presence of unsaturated C-C bounds and the presence of functional groups like sulphate, phosphate and sulpho-succinate, are used to modify the physical-chemical properties.

The physical-chemical properties of an adjuvant determine its usefulness in a certain application. Different chemical structures may have similar physical-chemical properties required for a certain adjuvant function. That's why so many different structures are sometimes recommended for the same function.

Adjuvant classes.

Classes	Sub-classes
Emulsifiable oils	Mineral oil
	Seed oil (triglycerides)
	Alkoxylated triglycerides
Fatty acids from vegetable origin	Esterified
	Alkoxylated and esterified
Surfactants	Based on: alcohols, fatty acids, alkylphenols, alkylamines, sorbitol, sorbitan, trisiloxane, and alkylpolyglycosides
Salts	Ammonium sulphate, ureum, ammonium nitrate, calcium nitrate
Monoterpenic alcohols
Waxes	Acid wax, ester wax, ethoxylated acid wax
Phospholipids	soya phospholipids
Polymers	Polyacrylamides, polyethylene oxide, polyvinils