National Activities - UK Sustainable Surfactants Renewable Feedstocks for the 21st Century - The Role of Renewables in Crop Protection

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Integrated Crop Protection & Biological Control : National Activities - UK : Starch : Sugar : Vegetable Oil/Fat



Competitive Industrial Materials from Non-Food Crops
Sustainable Surfactants: Renewable Feedstocks for the 21st Century
Wednesday 4 November 1998, Central Science Laboratory Agency, Sand Hutton, York

The Role of Renewables in Crop Protection
Dr Susan Critchley, Zeneca Agrochemicals, UK

Renewable alternatives to traditional, fossil-based chemicals, may be natural or a mixture of natural and synthetic chemicals. When considering the use of renewables in crop protection products, one expects the effects of the chemical to be similar to those currently in use. This paper discussed a typical formulation, ‘Herbicide EC’ (emulsifiable concentrate of herbicide), in terms of what goes into the bottle and the choices that can be made in relation to those contents. In particular, performance related aspects were reviewed.

A good crop protection product will improve yields by reducing competition. The active ingredient alone cannot provide the desired end result in a crop protection product, the formulation must:

• be stable in the bottle
• dilute to form a spray suspension
• spread and stick to the target
• dry down to form a stable concentrate

The types of chemicals required to provide these properties include formulation stabilisers (emulsifiers, solvents/diluents and rheology modifiers) and bio-enhancers (adjuvants, such as wetters/spreaders, penetrants and ‘stickers’). A typical Herbicide EC will contain a synthetically derived active ingredient, as well as two emulsifiers, an adjuvant and a solvent, all of which could be naturally or synthetically derived.

Emulsifiers have a number of roles within the product. When the concentrate is mixed with water, a uniformly distributed oil/water emulsion should be formed in the spray tank. This should produce a fine spray that will coat the target evenly with the oil-soluble active ingredient. There are literally hundreds of ionic, non-ionic and blends of emulsifiers available. These are usually selected on the basis of HLB (measure of relative affinity to water/oil) – an oil/water emulsion requires an HLB of 8-13. Ideally an emulsifier will:

• be amphiphilic (attracted to both water and oil)
• work at low concentrations
• adsorb quickly
• stabilise droplets
• be soluble in continuous phase
• reduce interfacial tension (bloom)

A suitable solvent will have properties including the following:

• dissolve the active ingredient
• high flash point
• miscible with emulsifiers
• water immiscible
• low toxicity

The choice of solvent may be influenced by factors other than physical performance. There are many solvents available including aromatic and aliphatic mineral oils, fatty alcohols and derivatives (e.g. esters), and specialty solvents (e.g. alkyl pyrrolidones). However, there are relatively few adequate renewable solvents.

Table 1. Emulsifiers and solvents suitable for use in a typical Herbicide EC formulation.

	Synthetic	Renewable / Hybrid
Emulsifiers	alkyl phenol ethoxylates (APEs)	alkyl polyglucosides (APGs)
	branched fatty acid ethoxylates (FA EOs)	sucrose esters
		sorbitan esters ethoxylates (EOs)
	block co-polymers	linear fatty acid ethoxylates
Solvents	aromatics	alkylated vegetable oils
	dearomatised solvents

The main drivers when choosing ingredients are: functionality, flexibility and effectiveness; cost and global availability; low batch to batch variation; regulatory aspects; and hazard classification. Renewables offer biodegradability, new opportunities for products and new functionality. However, they show natural variability and can be more expensive, less flexible and more complex than their synthetic alternatives. Batch to batch variation can be a particular problem in formulations containing emulsifiers. In addition to variations in renewables from the same source (due to variation in growing conditions, etc.), variations will occur between products with similar chemical structures from different sources (animal or vegetable), or during refining and processing of the raw material. This can be accommodated by altering surfactant levels (increasing the amount of surfactant used) or by mixing emulsifiers.

Given a choice, manufacturers would prefer to choose a renewable material. However, in reality the range of components meeting the required criteria is relatively narrow. There is an opportunity for the raw material suppliers to fill this gap.

Contacts

Contact

• Sue FINLAY / DEFRA Organic Farming and Industrial Crops Division / UNITED KINGDOM

Participant

• LINK Secretariat BBSRC / UNITED KINGDOM