**Microencapsulation concept**

Microencapsulation is a process by which individual elements of an active substance are stored within a shell, surrounded or coated with a continuous film of polymeric or inorganic material to produce particles in the micrometer to millimeter range, for protection and/or controlled release. The particles obtained by this process are called microparticles, microcapsules, and microspheres according to their morphologies and internal structure. For particles with a size range below 1 µm, the terms nanoparticles, nanocapsules, and nanospheres are often used. When average diameters higher than 1000 µm are obtained, the term "macrocapsules" is adequate. The nomenclature used to define the different elements of the encapsulated product includes terms for the shell, i.e., wall, coating, membrane material, and for the core material, i.e., active agent, payload, or internal phase. Various compounds from different origins such as dyes, proteins, fragrances, monomers, catalysts, etc. can be encapsulated with different types of wall material, including natural polymer (gelatin, cellulose, chitosan, etc.), artificial polymer (cellulosic derivatives, etc.), and synthetic polymers (polyamide, polyester, etc.), for a loading content between 5 and 90% of the microparticles in weight.

Microcapsules can exhibit a wide range of geometries and structures. The morphologies, geometries, or structures of the microcapsules depend mainly on the physicochemical characteristics of the core material and the process used to induce membrane formation. Thus, microparticles may have regular or irregular shapes, and their morphology may be described as mononuclear or core/shell structure, multinuclear or polynuclear particles, and matrix particle or microsphere. Microspheres consist of a polymeric network structure in which tiny particles of an active substance are distributed homogeneously, whereas microcapsules or

**V**

end-use.

**Controlled release**

compounds until final use.

**Compatibility**

core/shell structures exhibit a reservoir structure, i.e., the core substance is surrounded by a distinct layer. Furthermore, the layer and the core numbers are not limited to a single one; double-layered microcapsule shells, multilayer microcapsules, or dual-core particles are found in the literature, and the microparticles can also be obtained from clusters of microcapsules. The process choice and the formulation parameters, such as the polymer/solvent system, dictate their characteristics

According to the end-use, various characteristics of the microcapsules may be desired to design the final product. The size and shape of the particles, physicochemical properties of the shell, compatibility, and permeability are some of the main characteristics to consider in the choice the processes, taking in account the physicochemical properties of the active substance. The porosity of the shell is also

Some of the active substances used are chemically fragile, volatile, or unstable, and cannot be directly used without being entrapped in a capsule. One of the main advantages of using microencapsulation technology is its ability not only to protect active substances from the surrounding environment thereby increasing the shelf life of the product and its activity especially for fragrance or cosmetic applications, but also to prevent interaction with other compounds in the system or other components. The microcapsule shell capsules can prevent the evaporation of the volatile substance and protect both workers and end-users from exposure to toxic or hazardous substances; therefore, the active substances are handled more safely under this form before processing. They also transform a soluble compound in a temporarily insoluble form or realize the complex mixture of various components in a single capsule for a specific application. This process also allows masking an odor or an unpleasant fragrance of the active compounds during manufacture and

The use of microencapsulation technology for a controlled release application is one of the best ways to increase efficiency and minimize environmental damage. It can achieve a controlled delay of the release of the active substance until a stimulus is encountered at a specific rate, time, or situation, i.e., heating, moisture, mechanical pressure, etc. In this case, the shell acts as a protective barrier to prevent diffusion and mass loss of the active substance, and therefore maintain intact the core

The transformation of an active liquid into a pseudo-solid or powdered product can not only limit agglutination but also improve the mixing of incompatible compounds. Moreover, if one considers, for example, a textile application, the

as well as their functional properties.

**Benefits of microencapsulation**

controlled to complete the final application.

**Protection and shelf life enhancement**

core/shell structures exhibit a reservoir structure, i.e., the core substance is surrounded by a distinct layer. Furthermore, the layer and the core numbers are not limited to a single one; double-layered microcapsule shells, multilayer microcapsules, or dual-core particles are found in the literature, and the microparticles can also be obtained from clusters of microcapsules. The process choice and the formulation parameters, such as the polymer/solvent system, dictate their characteristics as well as their functional properties.
