Degree of sheathing

On the left you can see an amixon® apparatus for coating crop protection chemicals. The degree of coating is a measure of the portion of the particle surface that is covered by a shell layer. It describes how completely a core material has been coated. A high degree of coating means a closed and uniform coating layer.

The degree of coating can be described by the coated surface area:

θ = A_coated​​ / A_total​

• θ is the degree of coating
• A_coated​ is the coated surface area 
• A_total​ the total particle surface area

In practice, the degree of coating is often described by the mass fraction of the coating layer:

w_coat ​= ​m_coat​​ / m_total

• w_coat​ is the mass fraction of the coating
• m_coat​ is the mass of the coating layer 
• m_total​ is the total mass of the coated particle

The effectiveness of the coating is described by the encapsulation efficiency:

η_enc ​= ​ m_core,enc​​ / m_core,total

• η_enc​ is the encapsulation efficiency, 
• m_core,enc​ the effectively coated core mass 
• m_core,total​ the total core mass

A high degree of coating improves storage stability, dosability, and the controlled release of active substances or propellants. A low degree of coating can lead to premature reaction, moisture uptake, or dust formation.

The degree of coating is specifically adjusted in the chemical, food, pharmaceutical, battery, and detergent industries.