Large amount of mineral and vegetable oils are used as adjuvants in order to improve biological efficacy of fungicidal and/or herbicide formulations. These substances must be uniformly dispersed in aqueous spray to provide their homogeneous distribution onto the treated surface in the field. Therefore, they are usually formulated as emulsifiable concentrate or eventually as concentrated macroemulsion and diluted with water short before application.
In the case of mineral oils the classical and traditional formulation comprises nonylphenol ethoxylates as emulsifiers.
Fatty alcohol ethoxylates are also used as emulsifiers for these systems, as described for example in U.S. Pat. No. 4,966,728 (BASF).
There is currently high demand to replace mineral oil with vegetable oils since they are less phytotoxic, and have better ecotoxicological profile and environmental impact.
Transesterified triglycerides and vegetable oils are well known adjuvants and are normally used in aqueous spray in emulsified form, usually obtained from emulsifiable concentrate.
Also, numerous tank-mix adjuvant based on methyloleate are described in the form of emulsifiable liquid which upon dilution with water form kinetically stable oil-in-water macroemulsions.
Vegetable oils and/or methylated vegetable oils (transesterified triglycerides) require more sophisticated emulsifier system than mineral oils, particularly when fluid oil-in-water macroemulsions must be prepared.
Low viscous emulsifiable liquid which upon dilution with water form kinetically stable oil-in-water macroemulsions show main disadvantages, since often creamy or oily separation occurs and hence good homogenisation of the product is required before application.
Therefore it is highly desirable to obtain adjuvants based on vegetable oils and/or methylated vegetable oils in the form of fluid microemulsions.
Submicron droplets or microemulsion systems are described in adjuvants for pharmaceutical applications (for example in U.S. Pat. No. 6,451,325 and U.S. Pat. No. 6,299,884).
Microemulsions for agrochemical applications are also described in the patent literature.
U.S. Pat. No. 6,589,913 describes agrochemical glyphosate formulations which show microemulsion structure.
U.S. Pat. No. 5,905,072 describes microemulsions as adjuvants for systemic fungicides containing methyl esters of fatty acids, and specific mixtures of non-ionic and anionic surfactants.
The use of alkyl(oligo)glycosides in microemulsions comprising an oil phase and an agrochemical is described for example in U.S. Pat. No. 6,255,253.
The presence of various surfactants in microemulsions is known not only to influence the stability of the composition, but also to possibly enhance the biological activity of the agrochemical formulation.
It is known that, when a dilute aqueous composition of pesticide is applied to foliage by conventional hydraulic spraying, the presence of surfactants in the dilute aqueous composition can alter the size distribution of the spray droplets, typically increasing the percentage of spray volume in the form of small droplets and reducing the percentage of spray volume in the form of large droplets.
As smaller droplets have lower momentum than larger droplets, these smaller droplets are less likely to rebound from a foliar surface and consequently are more likely to be retained on that surface.
Spray retention can also be facilitated by adhesion between surfactant molecules in a spray droplet and the foliar surface, which in most plants is waxy and hydrophobic.
This adhesion reduces not only rebound but also run-off of spray droplets from the foliar surface.
Surfactants also tend to increase the area of contact between a spray droplet and a foliar surface, and in many cases enhance penetration of a systemic pesticide from the droplet into and through cuticles of leaves to reach internal leaf tissues.
The molecules of systemic pesticide compound must go through several barriers.
Among these, one of the most important is believed to be the lipophilic cuticle on the foliar surface to which the pesticide is applied.
It has therefore been theorised that it would be desirable to place the pesticide compound into an amphiphilic medium which would keep better compatibility between the lipophilic cuticle and the pesticide, and thereby facilitate penetration of pesticide into and through the cuticle.
Amphiphilic carrier can be easily built using surfactants.
Through these and perhaps other effects, amphiphilic materials including surfactants have long been known to increase the biological effectiveness of pesticide, and to act as adjuvants.