iFormulate: Agrochemical Formulation — A Future Without Microplastics?

Dr Jim Bullock
Director at iFormulate Ltd

In recent years, much attention has been paid to the environmental problems caused by plastic pollution and in particular, by microplastics - small pieces of plastics which may be found in the environment and in the food chain. The EU defines microplastics as being¹:

″Particles containing solid polymer, to which additives or other substances may have been added, and where at least 1% w/w of particles have all dimensions between 0.1µm and 5mm, or for fibres, a length of between 0.3µm and 15mm and a length to diameter ratio of more than 3.″

After a period of fact-finding and consultation lasting several years², the European Commission published a draft Regulation (amendment to REACH) in 2022. This would place restrictions on microplastics intentionally added at 0.01% or more by weight. Excluded from the restrictions would be natural polymers, biodegradable polymers and polymers with at least 2 g/l solubility in water. ECHA published the draft amendment to the REACH Regulation in August 2022. The proposal is going to the EU Parliament, and it is expected that there will be a transitional period of five years after entry into force for uses of agricultural and horticultural products.

Although much of the microplastic contamination we see in the environment has its origin in packaging materials and car tyres, product formulation plays a role too. These restrictions will be especially relevant for cosmetics, household products and agrochemicals. However, with the elimination of plastic microbeads from cosmetics, the spotlight has moved onto other industries and application areas. So first, let’s take a look at the challenges for formulators of agrochemicals who may be tasked with removing many of the polymer materials used in products such as microencapsulated formulations, seed treatments and slow-release fertilisers.

Microencapsulated Pesticide Formulations

Pesticide active ingredients may often be encapsulated in a polymer shell in order to provide controlled release properties in the field or to improve environmental or operator safety. Typical pesticide microcapsules are polymeric, with particle diameters in the range of 1 – 20 µm. The most common current microencapsulation technology makes use of interfacial polymerisation with isocyanate and amine monomers which react to form polyurea. In general, this type of polymer is not biodegradable and is therefore a candidate for replacement. Although other encapsulation technologies such as complex coacervation may use naturally occurring materials such as gum arabic and gelatin, a crosslinking step is typically applied in order to make robust microcapsules, and the resulting polymer is therefore potentially no longer seen as natural.

Pesticide Granules

Granular, solid pesticide formulations may be applied via a spray tank - in which case they are water-dispersible granules - or they are applied dry (e.g., by direct in-furrow application). In general, water dispersible granules will contain dispersing agents and other polymeric materials which are typically water-soluble and – although formulators should check this – are therefore unlikely to be caught by the microplastics definition. On the other hand, granules for dry application may contain binders which are intended to slow down and control the breakdown of the granule in order to sustain the release of the active ingredient over a period of time. The polymers used as binders - such as polyvinylpyrollidone - may potentially not be natural, biodegradable or of high solubility and therefore replacements may be sought here too.

Seed Treatments

Seeds are frequently coated with crop protection materials, fertilizers or other bioactive components that are released in the soil after the seed is sown. As with pesticide granules, polymeric binders such as carboxymethyl cellulose may be used to control the release of the active substances and again these could be included within the definition of microplastics.

Slow-Release Fertilisers

In a similar way to pesticide granules and seed treatments, some solid fertiliser granules are coated in order to slow the release of fertiliser into the soil. Whereas some granules are coated with thermoplastics like polyolefins, poly(vinylidene chloride) and polyurethane, which could fall within the definition of restricted microplastics, other granular products are coated with molten sulphur which, not being polymeric, is likely to fall outside the microplastics definition.

Possible Solutions

As a result of the challenge to replace microplastics in several applications, a number of possible solutions have emerged. One recent publication tackled the challenge of biodegradability of polyurea microcapsules formed by interfacial polymerisation³. In this example a typical oil-soluble isocyanate monomer MDI (methylene diphenyl diisocyanate) was used but the water-soluble amine was replaced by naturally derived chitosan oligosaccharide (COS). Because COS is biodegradable, this sort of polymer could potentially fall outside EU definition of microplastics.

The use of naturally derived polymers (biopolymers) for controlled release agrochemicals has been suggested as an alternative to synthetic polymers. A number of different materials have been proposed as ″nanocarriers″ for fertilisers and pesticides including alginate, cellulose, chitosan, lignin, poly(lactic acid) and polypeptides⁴. One specific example of a biologically derived targeted release technology is the proposed use of liposomes based on plant-derived lipids which were used to deliver nutrients through the leaf into the target plant⁵. In a further example, nanoparticles of chitosan (a naturally derived polysaccharide) were used to deliver zinc as a micronutrient using foliar application or seed treatment⁶.

In the field of seed treatments, microplastic-free products are now being marketed, e.g., by Incotec⁷. The topic of replacing microplastics in seed treatments has also been the subject of recent patent applications, including an application from Croda (Incotec’s parent company) which describes a seed coating formulation claimed to be microplastic-free which contains a natural rosin resin, a starch derivative and a wax dispersion⁸. Also active in developing microplastic-free alternatives for seed coatings is Solvay, whose Peridiam^® Quality 3001 product is claimed to have comparable application properties to conventional coatings⁹.

Meanwhile, a completely different approach to the challenge of microencapsulation has been taken by Eden Research by using ready-made natural capsules. Their Sustaine^® microcapsules are produced from empty yeast cells and can be used to encapsulate pesticide active ingredients such as fungicidal terpenes. Such a product has been commercialised as Mevalone^®10.

Summary

The need to replace microplastics in agrochemical formulations has posed a significant challenge for formulators and technologists in the sector. Although a dominant new replacement technology has not yet emerged, there are already a large number of new innovations emerging onto the market or in earlier stages of innovation. These innovations have their basis in a wide variety of different approaches, and it is this variety that gives cause for optimism that the industry will be able to meet the requirements of the regulator when the time comes. A further positive factor is that this challenge is not only being faced by agrochemical companies. Very similar challenges are being faced by formulators of cosmetics and household products. As in other areas of innovation, it is to be hoped that looking to other industries for inspiration and ideas will help accelerate the pace of change.

Finally, in this article we have provided some general background about the legislative approach in the EU. Whether, how and when these or similar regulations apply to you or your products will depend on a number of factors including the field of application and the territory that your products are marketed in. Before taking any action related to microplastic replacement, you should first seek advice from a regulatory specialist.
 

¹ Draft EU Commission Regulation https://ec.europa.eu/transparency/comitology-register/screen/documents/083921/1/consult?lang=en
² European Chemicals Agency https://echa.europa.eu/hot-topics/microplastics
³ Yu et al, ″Preparation of Polyurea Microcapsules by Interfacial Polymerization of Isocyanate and Chitosan Oligosaccharide″. Materials (Basel, Switzerland). 2021 Jul;14(13):3753. https://doi.org/10.3390/ma14133753
⁴ Machado et al, ″Biopolymer-based nanocarriers for sustained release of agrochemicals: A review on materials and social science perspectives for a sustainable future of agri- and horticulture″. Advances in Colloid and Interface Science, Volume 303, May 2022, 102645 https://doi.org/10.1016/j.cis.2022.102645
⁵ Karny et al, ″Therapeutic nanoparticles penetrate leaves and deliver nutrients to agricultural crops″. Nature Scientific Reports, 2018 https://doi.org/10.1038/s41598-018-25197-y 
⁶ Choudhary et al, ″Zinc encapsulated chitosan nanoparticle to promote maize crop yield″. International Journal of Biological Macromolecules Volume 127, 15 April 2019, Pages 126-135 https://doi.org/10.1016/j.ijbiomac.2018.12.274
⁷ Incotec https://www.incotec.com/en-gb/sustainable-seed-solutions/microplastic-free-seed-coatings
⁸ European Patent Application EP4090712A1 (Croda)
⁹ ″Solvay: Microplastics restriction, biologicals… How regulations and trends in seed treatment create opportunities for the development of new seed coatings?″. Agropages, June 2022 https://news.agropages.com/News/NewsDetail---43073.htm
¹⁰ Eden Research https://www.edenresearch.com/technology/sustaine.aspx

This article will be published in AgroPages '2023 Formulation & Adjuvant Technology ' magazine to be published this May.

If you'd like to share your company's story and products/solutions. Please contact Grace Yuan via: grace@agropages.com