Low Melting Point, High Electrolyte, Biodegradable: How Many Constraints Have Been Added to Dispersants in Three Years?

A high-load SC passes every specification on the bench, then cakes after two weeks at 54 °C.

The first reaction used to be that the wrong dispersant had been chosen. Over the past year or so, published technical material has begun asking something else first: what is the melting point of the active?

It is a small shift, but a real one. Reviewing three years of formulation technology articles published by AgroPages, one pattern recurs: the chemistry of dispersants has not changed much — polycarboxylates, lignosulfonates, naphthalene sulfonate condensates, EO/PO block copolymers, most of them decades old. What has changed is the set of conditions a dispersant is expected to satisfy at once.

Three years ago, a dispersant that dispersed the particles, held off sedimentation and stopped crystal growth was doing its job. Today it also has to keep a low-melting active from caking, survive a high-electrolyte system, and be readily biodegradable without failing heat storage.

Few new molecules, a great many new constraints. We take the three in turn.

1. Low-melting actives

Actives with low melting points soften, or partly melt, under production, storage or application conditions; particles agglomerate; the formulation cakes or gels. The trouble is that conventional dispersants are built for hard particles. Once a particle has softened, steric hindrance stops doing anything.

Clariant ran a model study on this using difenoconazole 400 g/L SC, putting four conventional dispersant types — acrylic copolymer, anionic tristyrylphenol surfactant, naphthalene sulfonate condensate and lignosulfonate — through two weeks at 54 °C. Nouryon described the same thing from the other side: in a high-load formulation of a low-melting, polymorphic fungicide, the product often passes initial testing, but after several weeks at elevated storage temperature the active grows larger crystals, viscosity climbs, sediment will not redisperse, and field performance turns erratic.

The crystallisation side has harder numbers. Working across metribuzin, acetamiprid, diuron, imidacloprid and propanil, LEVACO found that 0.5% w/w of a crystal growth inhibitor shifted the morphology from needles to spots — where the reference additive needed eight times the dose to match it.

The real change here is not that solutions appeared. It is that the problem is stated differently: no longer "the dispersant underperformed" but "this class of active has this failure pathway." Melting point, water solubility and polymorphism are all data you can look up. Once failure modes are sorted by physical property, they can be anticipated rather than discovered when the heat storage results come back.

2. High electrolyte

Salt-form actives, fertilisers, micronutrients, and the hardness ions the spray water brings with it. At high ionic strength, electrostatic repulsion is compressed, steric stabilisation weakens, and the dispersant's own solubility changes. The three effects compound, and a good many dispersants give out.

The constraint applies at both ends, in-can and in the tank, but the criteria differ: in-can is judged over months to two years of storage, tank-mix over tens of minutes of dilution stability and whether the nozzles block.

An anionically modified graft copolymer from Clariant used a saflufenacil plus glufosinate-ammonium SC/SL combination as its model, showing particle size growth well below the references under elevated-temperature storage. A dispersant from Wuxi Jingfung, developed originally for high-salt suspension systems containing glufosinate, glyphosate and choline chloride, later turned out to hold up in the tank as well, remaining compatible with almost every liquid fertiliser on the market — the two constraints meeting in a single product.

3. Biodegradability

This one comes from somewhere else. Not from the active, but from regulation.

The difficulty is that the two goals are physically opposed: a polymer that degrades in the environment will also degrade on the shelf. As published material puts it, biodegradable dispersants that also perform remain scarce, and usually cost something in storage stability. The readily biodegradable polymer dispersant BASF introduced in 2025 goes directly at that conflict, with performance validated in SC formulations using azoxystrobin, terbuthylazine, trifloxystrobin and others.

For formulators the significance runs past any single product. Biodegradability is moving from a differentiator to a condition of entry, and conditions of entry do not allow a performance discount.