Agrochemicals, Paints and Coatings and Food Colloids

Tharwat F. Tadros

• Publisher: De Gruyter
• Year: 2018
• eBook ISBN: 9783110587562
• Edition: 1
• Topic: Physical Sciences
• Subtopic: Chemistry
• Index: Chemistry

Volume 4 of Formulation Science and Technology is a survey of the applications of formulations in a variety of fields, based on the theories presented in Volumes 1 and 2. It offers in-depth explanations and a wealth of real-world examples for research scientists, universities, and industry practitioners in the fields of Agrochemicals, Paints and Coatings and Food Colloids.

Part I: The formulation of agrochemicals

1Introduction to the formulation of agrochemicals

Agrochemical formulations include a wide range of systems suited to specific applications [1, 2]. Agrochemicals are usually effective at several grams to hundreds of grams of active ingredient per 1,000 m2. It is, however, difficult to apply such a small amount uniformly to the crop. The active ingredient is always first formulated in a suitable diluent such as water or an organic solvent and when the formulation is applied it is further diluted in the spray tank to ensure uniform deposition upon spraying. In some cases, an agrochemical is a water-soluble compound of which paraquat and glyphosate (both are herbicides) are probably the most familiar. Paraquat is a 2,2 bypyridium salt and the counter ions are normally chloride. It is formulated as a 20% aqueous solution which is simply diluted into water at various ratios (1 : 50 up to 1 : 200 depending on the application) upon application. To such an aqueous solution, surface active agents (sometimes referred to as wetters) are added which are essential for a number of reasons. The most obvious reason for adding surfactants is to enable the spray solution to adhere to the target surface and spread over it to cover a large area. However, this picture is an oversimplification since the surface-active agent plays a more subtle role in the optimization of the biological efficacy. Thus, the choice of the surfactant syste min an agrochemical formulation is crucial since it must perform a number of functions. To date, this choice is made by a trial and error procedure, due to the complex nature of application and the lack of understanding of the mode of action of the chemical. It is the objective of this book to apply the basic principle of colloid and interface science to agrochemical formulations, their subsequent application, and the optimization of their biological efficacy.

The main purpose of any agrochemical formulation is to make handling and application of the active ingredient as easy as possible. An important function of the formulation is to optimize its biological efficacy. In most cases, this is achieved by controlling the physical characteristics of the formulation and use of adjuvants. An important criterion for any agrochemical is its safety both to the crop and the agrochemical worker. This requires adequate control of the spray droplet spectrum, reduction of any drift and removal of any toxic effect on contact with the individual. These stringent requirements can be achieved through careful analysis of all the interfacial phenomena that are involved in application. The concept of “Pesticide Delivery System” (PDS) must be applied, whereby the active ingredients are made available to a specified target at a concentration and duration designed to accomplish an intended effect, i.e., obtain the fullest biological efficacy while minimizing various harmful effects.

Most agrochemicals are water-insoluble compounds with various physical properties, which have first to be determined in order to decide on the type of formulation. One of the earliest types of formulations are wettable powders (WP), which are suitable for formulating solid water-insoluble compounds that can be produced in a powder form. The chemical (which may be micronized) is mixed with a filler such as china clay and a solid surfactant such as sodium alkyl or alkyl aryl sulphate or sulphonate is added. When the powder is added to water, the particles are spontaneously wetted by the medium and, upon agitation, dispersion of the particles takes place. It is clear that the particles should remain suspended in the continuous medium for a period of time depending on the application. Some physical testing methods are available to evaluate the suspensibility of the WP. Clearly, the surfactant system plays a crucial role in wettable powders. In the first place, it enables spontaneous wetting and dispersion of the particles. Second, by adsorption on the particle surface, it provides a repulsive force that prevents aggregation of the particles. This process of aggregation increases the settling of the particles and may also cause problems upon application, such as nozzle blockage.

The second and most familiar type of agrochemical formulation is emulsifiable concentrates (ECs), as described in Chapter 2. This is produced by mixing one agrochemical oil with another one, such as xylene or trimethylbenzene, or a mixture of various hydrocarbon solvents [1]. Alternatively, a solid pesticide could be dissolved in a specific oil to produce a concentrated solution. In some cases, pesticide oil may be used without the addition of any extra oils. A surfactant system (usually a mixture of two or three components) is always added for a number of purposes. First, the surfactant enabl...

Table of contents

• Cover
• Title Page
• Copyright
• Preface
• Contents
• Part I: The formulation of agrochemicals
• Part II: The formulation of paints and coatings
• Part III: The formulation of food colloids
• Index