Volume 4, Issue 3 (March 2007)
Water Dispersible Granule Formulations Containing a New Defoaming Agent
A common problem found when water dispersible granule (WG) formulations are dispersed in water is the generation of high levels of a persistent foam layer. This high level of foaming causes many difficulties for the users of WG products in agricultural sprays. The development of foam may cause spillage and loss of product as well as cause problems for tank mixing with other products. There is also a risk of uneven coverage of a spray solution containing foam, and the time taken for foam to subside can be inconvenient as well as lead to a risk of sedimentation of the suspended solid. The persistent foam problem in WG formulations is a direct consequence of the presence of a surfactant wetting agent (wetter) which is used in the formulation to aid immersion and dispersion of the granule in water and to help evenly distribute water throughout the powder matrix during manufacture of the formulation. Various approaches have been tried to overcome persistent foam in WG formulations in the past. These approaches include the use of tank-added defoaming agents, the inclusion of silicone and other common defoamer types in the formulation, and use of lower foaming wetters which are generally nonionic surfactants. These approaches have generally met with limited success or led to other difficulties. In many cases using enough of these defoaming additives to be effective in defoaming leads to reduced dispersion properties. One class of defoaming agent commonly used in WG formulations is the salts of long chain fatty acids, or soaps. These are, however, only moderately effective. It has now been found that the combination of fatty acid salts together with chelating agents and a polyacid polymer leads to greatly enhanced foam reduction. This improvement in defoaming comes with no additional loss of dispersion performance of the WG. The optimized defoaming blend is effective in WG formulations at a use rate of around 2 % by weight and can be used with all the commonly used types of surfactant wetting agents and dispersants in a wide range of active ingredients.