Evonik: Sustainable Surfactants for Crop Protection Solutions

The agricultural market is under increasing pressure as consumers ask for food containing lower, or no amounts of residual chemicals, but at the same time growers need to prevent the development of pathogens and pests resistant to active ingredients. Regulators demand less agrochemical input and some chemical pesticides have already been phased-out.

Well-known in the agrochemical market, Surfactants are used in formulations and as tank mix adjuvants. The benefits of adjuvants are important in plant protection products from pesticide formulation to storage, tank-mix dilution, spraying, targeting and finally acting on the pest. In water-based formulations, their main task is to decrease surface tension resulting in better wetting of the dispersed particle in water and more stable formulations. In oil-based formulations, emulsification properties support the quality of the emulsion ensuring higher stability and lower droplet size. In tank mix dilutions for all kinds of formulations, surfactants prolong physical stability as they reduce the surface tension of water. Targeted delivery is the main purpose of surfactants during spraying, which enhances efficacy and decreases the active amount needed. Targeted delivery is achieved by: 1) reducing driftable particles 2) enhancing adhesion and retention of spray droplets on the plant. 3) Improving uptake and penetration of active ingredients, and 4) increasing rain fastness.

However, regulatory pressure is rising with additives like NPE based solutions phased-out globally. With the agrochemical market demanding innovative, more sustainable additives, Evonik has developed benign surfactants which enable a more environmentally friendly plant protection.

New adjuvants that comply with eco-toxicological, safety and sustainability criteria provide solutions to support the plant protection industry. Evonik is introducing sustainable and biodegradable adjuvants in the following four classes: Wetting agents and multifunctional additives based on biodegradable trisiloxanes, polyglycerolester and sophorolipids.

Due to their chemistry, the way these novel surfactants work is different. Roughly speaking, the lower the surface tension of spray droplets the better adhesion and retention on the leaf. Water with 72 mN/m gives a strong bounce off of spray droplets. Trisiloxanes help to reach the lowest surface tensions and Evonik has developed readily biodegradable  trisiloxanes based on a unique patented technology. The reduction of water surface tension down to 21 mN/m facilitates the best adhesion and retention of droplets on very difficult to wet surfaces. Due to their special phase behavior in water, they provide superspreading of water, solutions and dispersions to ensure the best coverage of contact actives on surfaces thanks to the contact angle of 0°. This also enables the highest biological efficacy. In contrast to other superspreading trisiloxanes, these biodegradable trisiloxanes have no ecotoxolocial classification and are not dangerous goods for transportation.

BREAK-THRU^® S 301 is soluble in water and many oils, so it can be used in all kinds of liquid formulations and as a tank mix adjuvant to give excellent adhesion and retention of spray droplets. Commercially available products with living microbial actives rarely contain surface-active molecules, and alongside the low wetting and low dispersing properties of solid formulations in water, can often provide low and inconsistent field performance. BREAK-THRU^® S 301 can be used as a carrier liquid in dispersion concentrates for increased shelf life of living microbial products. As a tank mix additive, BREAK-THRU^® S 301 leads to a better dispersion of microbial actives in the spray solution, and to excellent wetting in the application, helping increase the efficacy of microbial-based pesticides.

BREAK-THRU^® SD 260 is developed specifically for use in WP – formulations for chemical pesticides or for biopesticides. The product is the first water soluble, solid trisiloxane to provide humectant properties, and to offer excellent wetting properties as it includes BREAK-TRHU® S 301. The addition of 1 - 5% w/w BREAK-THRU® SD 260 to the powder or granules of biopesticides significantly increases the surfactant properties of the final tank-mix dilution. At a concentration of 0.1 w/w-% it reduces the surface tension of water to 22 mN/m and the humectant property supports the field efficacy of the microbes.

Unique readily biodegradable adjuvants based on polyglycerol esters and sophorolipids fulfill modern requirements for all types of plant protection products and consist of a natural carbon source. They reduce the surface tension of water down to 30-35 mN/m. Incoming droplets solutions with such surface tensions normally show a strong and fast receding effect from the contact line, often leading to bounce off and loss of spray droplets. The new action is based on the interaction of the hydrophobic emulsified droplets with the cuticle leading to a so called ‘pinning effect’ preventing the droplet receding from the contact line of the water droplets. These droplets also stick to the surface so retention is excellent. It’s well-known that polyglycerol esters and sophorolipids lead to a swelling of the cuticle wax which improves the penetration through the cuticle. This facilitates the uptake of lipophilic and hydrophilic active ingredients through the cuticle and epidermal cells (see Figure 1 and Figure 2). This physico chemical interaction of the bio-based molecules with the cuticle wax can be shown nicely with confocal laser scanning microscopy as reported previously [ Haensel, et. al. (2015) Polyglycerolester as Sticker Penetrant Adjuvant ]. For systemics and contact active ingredients these products are well suited, and due to their hydrolytic stability these surfactants can be used for water-based and oil-based formulations.

 

 

This article was initially published in AgroPages '2019 Formulation & Adjuvant Technology ' magazine. Download the PDF version of the magazine to read more articles.