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New Dispersing Agents for Multi-active Formulations
Nov. 11, 2015
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Davide Secchi
life science division technical director
Agro Market is moving towards water based formulation at higher active ingredients concentration and with combinations of actives to improve treatment efficacy. Combination of different active ingredients – including those addressed to the same target but with different mode of action – is a key and sustainable strategy for a better pest control management and for increasing crop yield.
Combination of different pesticides can be achieved in two ways: by mixing two or more single active formulations in the farmer’s tank prior to spray or by building-in the different actives in a single well balanced formulation. The tank mix options are quite dangerous: there is a high risk of instability of the mixture that could lead to non-homogeneity, separation in the tank and misapplication. Whilst in the US farms are large and structured with expert agronomist that can supervise the preparation and application of risky tank-mix, for the majority of the farmers in the rest of the world built-in combinations of actives would be the logic solution; but that shifts the problem to crop protection companies and their formulators who are more and more facing new and very challenging tasks.
Suspension Concentrate (SC):
For non-water soluble active ingredients and amongst standard technologies used to formulate a pesticide, Aqueous Suspension Concentrate (SC) is probably the safer, the more sustainable and economical formulation. It consists of suspending one or more active ingredients in water. SC normally contains between 5 – 60% of active ingredient(s), one (or more) dispersing agent, a rheology modifier, optionally wetting agents.
The possibility of combining in a single formulation more than one active ingredient depends on the characteristics of the active ingredients and on the strength and flexibility of the dispersing agent used. In particular skilled formulators take into considerations: melting point, lipo/hidrophilicity (logPow), solubility in water, chemical stability at different pH and milling hardness of the actives.
On industrial scale SC production generally consists of the preliminary preparation of a pumpable slurry containing the different actives, the dispersing and wetting agents, antifoam and water. The slurry is then transferred to a wet mill to reduce the particle size of the actives below 10 μm. That milled preparation is later added with additives (e.g.: anti-freezing, preservatives), residual water and rheology modifiers. During milling the pressure and the temperature inside the milling chamber tend to increase; even very efficient cooling system often cannot keep the temperature under control. If the melting points of the actives are very different, the lower one can melt destroying its properties.
Active ingredients having different logPow could require different type of dispersing agents; moreover if hardness of the solids is different, the harder could not achieve a correct particle size. The possibility of milling more than one active in a single operation is strongly linked to the efficiency and flexibility of the dispersing agent used. Standard dispersing agents are anionic polymers (e.g.: lignosulphonate, alkyl-naphtalene sulphonate, tri-styrylphenol ethoxy phosphate) or non-ionic polymers (e.g.: EO/PO Copolymers, TSP alkoxylates); in the majority of the cases these molecules work quite well but can fail with very high concentrations or with active ingredients with big different physical-chemical characteristics. To overcome these problems a new generation of highly effective dispersing agents has been developed: they reduce the viscosity of the system improving the milling operation and its efficiency. They are compatible with other dispersing agents to obtain a synergic effect to improve suspensibility, blooming and formulation’s shelf life.
Multi Actives SC Formulation1:
A combination of 3 active ingredients with different characteristics has been chosen as a model to test efficacy of the new generation of dispersing agents. As shown in Figure 1 the LogPow of the ingredients varies from 0,83 (metamitron) to 3,3 (napropamide): that normally suggests we need different type of dispersing agents. Also melting points are very different with napropamide prone to melt; moreover napropamide is very hard to mill whilst metazachlor and metamitron are relatively soft. Milling them together with traditional dispersants (e.g.: TSP derivates) has been almost impossible. So far we would have suggested milling separately napropamide and adding it to the other actives but that would mean to double the production time and the consumption of energy.
Thanks to the new dispersing agent - Envi-Pol 871R, milling operations are easily carried out in a single step reaching the required particle size and a very low viscosity (15 seconds – Fordcup #4). As metamitron is quite soluble in water a crystal growth inhibitor, Emulson AG TRN141-05, has been added to the formulation to prevent any potential crystal formation during storage. Formulation is reported in Table 1. Formulation has being characterized according to FAO Specification for Aqueous Suspension Concentrate2 as reported in Table 2.
Milling efficiency has been monitored by measuring particle size at time zero using a laser nanosizer and after ageing (14 days at 54°C). Particle size profile at time zero and after ageing are portrayed in Figure 2, showing a negligible increase with time that guarantees the stability of the formulation for the entire shelf of the product.
Conclusions:
Strategies to improve pest control with safer and sustainable pesticides formulations include water based Suspension Concentrates (SC) containing more than one single active ingredients. That represents a new challenge for agrochemical formulators and new dispersing agents will be required. The results obtained in this study confirm the great potential of a new family of dispersing agents for the production of multi-actives SC and the possibility to close the existing technological gap.
References and notes:
(1) Davide Secchi, from New Dispersing Agents for High Load and Multi Active Formulations, paper presented at: Agrochemical Formulation Conference, Berlin 2014, C&C Europe (2014)
(2) FAO Pesticides Specification 7.31 AQUEOUS SUSPENSION CONCENTRATES (SC): http://www.fao.org/fileadmin/templates/ agphome/documents/Pests_Pesticides/Specs/JMPS_ Manual/7.31.doc
(3) CIPAC Methods MT 160 and MT 161: CIPAC Handbook
Source: AgroNews
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