Nouryon: A New Biodegradable Polymeric Dispersant for Crop Protection Formulations

Regulations play an important role in formulation design and available technologies. Some of the versatile tools like Nonylphenol ethoxylates (NPE), N-Methyl-2-pyrrolidones (NMP) have been banned and authorities have a list of substances they continuously evaluate. Recently, European Chemical Agency (ECHA) has been evaluating styrenated phenol. Based on available information and screening data, styrenated phenol meets the criteria for very bioaccumulative (vB), persistent (P) and possibly very persistent (vP) in the environment. ECHA states that the substance has also the potential for endocrine disrupting properties and is investigating which may affect tristyrylphenol derivatives and their use in crop protection formulations.

ECHA has also submitted a restriction proposal for microplastic particles that are intentionally added to mixtures used by consumers or professionals. The persistence and the potential for adverse effects or bioaccumulation of microplastics is a cause for concern. Derogations are proposed for polymers that occur in nature, polymers that meet criteria for minimum (bio)degradability which makes (bio)degradability an important property in selecting formulation aids in crop protection formulations.

Dispersancy is an important functionality in retaining physical stability of formulations which in return enhances bio-efficacy. Typical dispersing agents are surfactants and/or polymers. For a good dispersant, adsorption efficiency to solid substrate (AI) is an important criterion. It is known that polarizable aromatic groups in the hydrophobe of a dispersant can provide good substantivity to the actives. Thus, dispersants based on tristyrylphenol (TSP) or nonylphenol (NP) are commonly used and show good efficiency. Unfortunately, these types of chemistries, as noted, are under regulatory scrutiny. Thus, there is a need to develop sustainable dispersing agents.

In addition to efficient adsorption, the surfactant molecules need to provide either electrostatic or steric stabilization (ideally both) to function as a good dispersant. Thus, anionic surfactants are most commonly used as primary dispersant and due to the versatility of ethoxylated phosphate ester, this type of chemistry is used extensively. Advantage of this type of chemistry is that it is highly tunable. One can do that by selecting different hydrophobes (linear, branched, saturated and unsaturated), as well as degree of ethoxylation. Phosphate esters are prepared by reaction of an alcohol with either polyphosphoric acid or phosphorus pentoxide. Using phosphorous pentoxide results in formation of both mono and diester, which is desirable, since presence of diester is important for dispersion (see Table 1 below).

In the search for a versatile and sustainable dispersing agent for crop protection, a series of surfactants were synthesized and evaluated by varying the hydrophobe as well as degree of alkoxylation, with the following desired outcome:
• Performance equivalent or better in a wide range of actives compared to current leading dispersants
• Non endocrine disruptor
• Biodegradable
• Low eye irritation
• Low aquatic tox
 
Our assessment has showed that shorter hydrophobes are preferred for biodegradability, but unfortunately shorter hydrophobes generally result in poor performance. Propoxylation (PO) of the molecule in addition to ethoxylation (EO) mitigated the issue. However, even with presence of PO, there is a limit to the size of the hydrophobe. In addition, branching of the hydrophobe was found to be important. Molecules with branched hydrophobe resulted in SC’s with desirable stable viscosity. Thus, optimizing the molecule in terms of size of the hydrophobe, degree of propoxylation and ethoxylation as well as reaction route resulted in Agrilan 1015, a biodegradable dispersant that performs as well or better than TSP based dispersant and had improved toxicity profile.

Biodegradability of Agrilan 1015 as well as a competitor product based on Ethoxylated TSP-phosphate ester (TSP-PE) was also evaluated. The Figure 1 below shows the comparative data. Both Agrilan 1015 and TSP-PE contain propylene glycol and the initial sharp rise in biodegradation is due to the presence of propylene glycol. Comparison of the data clearly shows Agrilan 1015 continues to biodegrade even after 12 weeks, whereas for TSP biodegradation levels out after three weeks and most of the degradation is due to propylene glycol. Thus, Agrilan 1015 can be designated as inherently biodegradable and not persistent, whereas TSP is almost non-biodegradable and persistent.
Evaluation of Agrilan 1015 in SC formulations was carried out using various actives and was compared to a leading commercial dispersant based on TSP (TSP-PE). The formulation used to prepare these SC’s is shown in Table 2. All SCs were subjected to two weeks stability at elevated temperature (54 ^oC).

Evaluation of the SC properties showed that the new dispersant, Agrilan 1015, afforded similar or better performance to the commercial dispersant (an example data for suspensibility is shown in Figure 3). Figure 2 shows a comparative picture between Agrilan 1015 and TSP-PE after two weeks storage stability at 54 ^oC. 

Agrilan 1015 was also tested in seed treatment formulations, particularly for FS and showed excellent performance that resulted in high color saturation for selected pigments.

Eye irritation of Agrilan 1015 was also evaluated using an InVitro method (Bovine Corneal Opacity and Permeability, BCOP). An InVitro score of significantly less than 3 indicated that this product is non-irritating. In addition, aquatic tox was also assessed using an in-house “Algae growth inhibition” method. The results indicate that this product is not expected to be acutely toxic to aquatic organism.

In summary, Agrilan 1015 is a new biodegradable dispersant for aqueous systems, such as SC and FS. It offers low toxicity with ‘clean’ label-contains no classified ingredients. It is designed by a unique patent protected technology. In addition, it can be used as wetting agent and an emulsifier in EW and SE formulations.

Some additional information

 
Characteristics
-    Appearance: Clear Liquid
-    Viscosity: Pourable
-    Solid Content: 50%
-    pH: 5.5-6.5

Regulatory Status
•    TSCA and FIFRA listing under consideration
•    Meets REACH polymer exemption
•    Listed in China and Japanese Chemical Inventory



This article will be published in AgroPages '2020 Formulation & Adjuvant Technology ' magazine to be published this May. 

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