Published: Jan 2001
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Surface active agents are used to formulate active ingredients for crop protection and are used in either liquid or solid form. The trend is to also incorporate wetting agents in the formulation in order to achieve bio-efficacy enhancement thus lowering the surface tension of the spray solution, resulting in uniform wetting and spreading when in contact with leaf surfaces. Often these wetting agents will produce a high level of foaming in the spray tank. This is undesirable due to the fact that an overflowing spray tank can cause a worker exposure problem.
Foam is extremely complex consisting of polydisperse gas bubbles separated by draining films. These films exhibit complicated hydrodynamics involving the distinct rheology of air-liquid surfaces and, for thin films, colloidal interaction forces. The nature of the foam film collapse processes that are intrinsic to foam are still not well understood. Antifoams are generally hydrophobic, finely divided insoluble materials and, therefore, their presence further complicates the complexities associated with foam. In the case of perfluorinated acids, the agent is solubilized in the foam film and drastically reduces the surface tension between the air-liquid interfaces. Theories of the antifoam mechanism appear to fall into two broad categories: those requiring the antifoam to be surface active at the air-liquid surfaces of the foaming liquid and those that do not.
A multiplicity of antifoams is known; however, these products are unstable under conditions such as high shear temperatures, long-term storage, acid, alkaline and highly ionic medium. Chemistry based on a perfluorinated acid has shown to overcome the previously mentioned issues. In addition, this new compound has the great advantage of being water soluble.
This new compound (Figure 1 ) is highly surface active with an extremely low surface tension of 19 mN/m measured on a 0.1% aqueous solution. The antifoaming behavior is related to the effect of the surface tension in the foam films leading to film rupture.
This paper explains the advantages of perfluoroalkylphosphinic and perfluoroalkylphosphonic acids as a high performance antifoam versus an organo-silicone antifoam.
perfluoroalkylphosphinic acid, perfluoroalkylphosphonic acid, water soluble, antifoam, organo-silicone, perfluorinated alkyl, film rupture, polyderschaum, kugelschaum, unstable, metastable, detergents, drainage, surface elasticity, surface rheology, film thickness, ASTM method, GIFAP code, compatibility, crop protection, formulations process, surface active agent, surface tension, solubilized
Technical Manager, Crop Protection, NAFTA, Clariant Corp., Charlotte, NC