Wettable powders

Production of wettable powders (WP) is re­latively simple with moderate costs.

Physical-chemical characteristics

The physical-chemical characteristics of wettable powders, according to international speci­fications, have to comply with the following requirements:

• quick wetting

• complete dispersibility

• suspension stability

• low foaming

• no caking during storage

Formulations

Wettable powders can differ remarkably according to the active ingredient content, requested performances, appli­cation rates etc.

Typical composition are approximately as follows:

Components

Active ingredients

Each a.i. has particular physical-chemical characteristics. Therefore to choose the ad­ditives and inerts it is necessary to take into account several elements, partially listed in this section. The basic differences affecting the choice of additives are primarily the physical sta­te (solid or liquid), the chemical stability in environmental conditions, pH etc.

Absorbing anticaking fillers

The absorbing filler is usually a precipitated silica with a high absorptive power. Milled silica is preferable for formulations of absorbed a.i. which only need homogenization. Either diatomite or calcium silicate may be used. The percentage of absor­bent filler must be sufficient to lead to a dry, free-flowing powder, before and after tropical tests.

Fillers

There is a large choice: either natural mineral products such as kaolin, attapulgite, calcite, diatomite etc. The choice must be made according to the physical-chemical characteristics with consideration to the following properties.

• Fineness: particle size needs to be as low as possible in order to ob­tain a suitable suspensibility.

• pH and pK: these characteristics need to be chosen according to the chemical properties of the active ingredients in order to ensure the sto­rage stability.

• Free moisture: usually should be as low as possible to avoid degrada­tion of the active.

• Impurities: could give rise to degradation of the active and must be as low as possible.

• Cristalline silicas: are often present in a filler of natural origin, and their level should be as low as possible to avoid undue wear on the equipment.

• Anticaking property: is an especially important characteristic for the wettable powders of high active content, or when the active has a low melting point, to insure suitable free flowing.

Wetting agent

As the majority of actives have a hydrophobic nature, the surfactants are needed to provide rapid wetting and dispersion. The wetting agent should not produce stable foam to avoid problems during the field treatment.

Dispersing agent

Our dispersing agents are synthetically produced and show very high efficiency at low concentration. They also act as chelating and sequestering agents. Sometimes they are used in small amounts (0.5-1%) to improve activity of lignosulfonate salts.

Compatibility agent

When mixing wettable powders with EC in the tank mix, some flocculation may occurs. To make them compatible a designed polymeric component shall be used normally at 1-3% to provide the correct characteristics.

Antifoam

We have available an antifoam specially designed to solve the foaming problems of wettable powders by blending it after grin­ding or in the spraying tank. This antifoam is based on a silicone compound micro-encap­sulated in a soluble filler which releases the antifoam active when it is dispersed in water.