Production of wettable powders (WP) is relatively simple with moderate costs.
The physical-chemical characteristics of wettable powders, according to international specifications, have to comply with the following requirements:
no caking during storage
Wettable powders can differ remarkably according to the active ingredient content, requested performances, application rates etc.
Typical composition are approximately as follows:
|Solid a.i.||Liquid or waxy a.i.|
|Active ingredient(s)||up to 90%||up to 50%|
|Wetting agent||1 to 5%||1 to 5%|
|Dispersing agent||3 to 10%||3 to 10%|
|Stabilizer, compatibility agent, antifoam, stickers||0 to 5%||0 to 5%|
|Colloidal silica||0 to 15%||up to 40%|
|Fillers||up to 100%||up to 100%|
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.
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.
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.
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.
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.
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.
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