Formulation professionals are increasingly facing big challenges in the development of new products containing a mixture of multisite active ingredients. In Brazil, where the climate is hot and humid for most of the year, conditions are perfect for the emergence of pests, which daily grow more resistant to the formulations available in the market. To keep a check on application dosages to reduce costs and waste, and damage to the environment, there is growing demand for the development of products that contain a mix of compounds with complementary biological activities for effective crop protection.
This is a challenge for developers, as often the active ingredients are incompatible. Some proposed mixes are hard to formulate. At this moment, the formulator must search for compatibility solutions within the portfolio of ingredients available through the suppliers of surfactants. Nowadays, we have at our disposal a wide range of materials approved by national regulators that can be used in the development of agrochemical formulations. When faced with perplexing cases, it is necessary to test compositions containing different chemical dispersants, solvents, emulsifi ers, wetting and rheology agents. In addition, sometimes it is necessary to try some unusual blends to solve a given problem.
In fact, there is no ready recipe for the compatibilization of active ingredients in a formulation, because compounds of different chemical natures also require surfactants of distinct natures. And in some cases, it is not possible to achieve the perfect balance just by choosing the “suitable” surfactants. At this moment, the formulator has an even bigger challenge—to choose a less conventional type of formulation instead of the most traditional ones.
A survey done by our regulatory affairs team presents clearly how reluctant we still are to use the less common formulation types. There are approximately 1,948 agrochemical formulations registered up to 2018 in Brazil. Of them, 1561 (i.e. 80%) are part of the big fi ve formulation types: Suspension concentrate (SC), emulsifi able concentrate (EC), soluble concentrate (SL), wettable dispersible granules (WG) and wettable powders (WP). The other 387 (i.e. 20%) are spread among 34 minor types of formulations. The circle chart presented below summarizes the distribution of the registered products by formulation types(As shown in Figure 1).
Although less explored, some types of formulations in this minor group have interesting properties, which can be the technological solution for challenging mixtures. In theory, it is possible to keep each of the compounds in different chemical environments in one pot, so there is no direct interaction between the active compounds at the same phase, resulting in a bipartite system, each one with the suitable surfactant chemistry. For example, in suspoemulsions (only 7 formulations registered in Brazil; 0.36% of total), an active ingredient co-exists as a suspension in an aqueous phase with another liquid water-insoluble active compound as an EW emulsion, or even an active dissolved in a water-immiscible solvent (also as an EW emulsion). This is a great strategy to reconcile liquidinsoluble compounds with insoluble solids in an aqueous-based formulation. The problem with complex formulations is the fact that the projects involve a much longer development period in the search for stability (shelf life), process and fi ne-tuning set of components.
Taking advantage of the less explored formulation types and the concept of "in can" adjuvancy towards performance improvement, the oil dispersions (OD, 13 registered in Brazil; 0.67% of total) are formulations with great potential. As the carrier oil (aromatic, paraffi nic, vegetable oils and methyl esters of vegetable oils) often acts as an adjuvant, it aids in a better spray retention, spreading and foliar uptake. This feature opens up the possibility of using smaller concentrations of the active ingredient to perform, as well as the traditional suspension concentrates (SCs) of higher concentrations. All this reflects in lower cost of the final product by replacing expensive active compounds with a cheaper set of solvents and surfactants.
Once a mix of active compounds becomes a really robust and physically and chemically stable formulation, we began a new journey that goes through a few more bottlenecks prior to registration. These bottlenecks are intrinsic to the development process and part of the praxis of a formulator chemist in order to achieve an approved formulation. One of the most important parameters to be achieved deals with the ecotoxicological profi le of formulated products, which must meet a series of guidelines and suitable values to get the registration approved3. We will not go into details about the ecotoxicological tests because it is beyond the scope of this article. However, there are general concerns that formulators keep in mind about the choice and combination of ingredients to ensure a lower ecotoxicological profile of the final product. Therefore, we are always looking for ingredients with good biodegradability and less danger to the environment. Ingredients with a renewable and eco-friendly profile are always welcome as candidates to introduce into new formulas. Nonetheless, being green is not enough. These greener alternatives must have equivalent performance, market availability and feasible cost. This is the only way to have a fi nal product, which is more sustainable but can still compete with products obtained from traditionally applied surfactants and raw materials. This is what we observe in the efforts made by the chemical specialties supplier companies, which are always releasing newer and modern materials trends.
Finally, it is evident that there are available tools and strategies to be adopted by formulation chemists in the search for solutions to complex mixtures of active ingredients. Choice of suitable components, use of underrated and sometimes forgotten formulation types, and partnership with suppliers of formulation ingredients are essential to meet the demands of the market and contribute to increased crop yield and productivity.