J. $oc. Cosmetic Chemists, 21, 85-98 (Feb. 4, 1970) Microencapsulation Techniques Applications and Problems HERMAN NACK, B.Ch.E.* Presented May 8, 1969, New York City $ynopsis--A number of techniques have been developrid for cncapsulating small particles •anging in size from a few microns or less to about 2000 /z. In addition, there are other factors which must be given careful consideration in the development of suitable micro- encapsulated products, such as: physical and chemical properties of the core material and wall material post-treatment of capsules interaction of capsules and substrate storage conditions release mechanisms and economics. MICROENCAPSULATION processes of interest in the cosmetics field include: aqueous phase separation, nonaqueous phase separation, interfacial polymerization, multiorifice rotating cylinder, fluidized-bed spray-coating, melt prilling in a fluidized bed, spray drying, dif- [usional exchange, and meltable dispersion. 1 NTRODUCTION Interest in the application of microencapsulation technology in a wide variety of fields continues to run high. Recent research activities and commercial applications publicly disclosed include: detoxicants for treatment of uremia (1) flavor and aroma constituents in foods (2) dye precursors for graphic products (3) slow-release pharmaceuticals (4, 5) slow-release fertilizers (6) and perfumes (7). Undoubtedly, there are many applications that have not been disclosed, but have been and are being studied in laboratories all over the world. This paper has been prepared with the objective of providing in- formation on some of the significant elements and physical and chemical factors of concern in microencapsulation processes and systems. Descrip- tions of selected processes and discussion of some of the problems and potentials of this technology are presented. Battelle Memorial Institute, 505 King Avenue, C'•lumbus, Ohio. 85

86 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS There are numerous reasons for considering microencapsulation for a given problem and some of these are: to change the physical charac- teristics of a core material (for example from liquid to "powder") to provide controlled release of capsule contents to permit mixing and storage of reactive or incompatible materials to mask taste or color and to reduce volatility. MAJOR ELEMENTS OF MICROCAPSULE SYSTEMS CoTe The core phase, and consequently the capsule itself, may represent a wide range of possible configurations. Some of these are shown in Fig. 1. Operations that may be required in preparation of suitable cores clude: spheroidization, prilling, emulsification, grinding, and atomiza- tion. Selection of the preferred technique of core preparation may be of considerable importance as the configuration of the resulting capsule may strongly influence the performance of the capsular product in the end use application. A. LIQUID or GASEOUS CORE SPHERICAL O SOLID WALL CORE SOLID CORE IRREGULAR • SOLID WALL PARTICLE C. LIQUID SLURRY CORE LIQUID PHASE SUSPENDED SDLIDS SOLID WALL D. SPHEROIDIZED SOLID CORE SOLID MATRIX DISPERSED SOLIDS SOLID WALL E. MULTIPLE WALL CAPSULES •O FIRST SHELL "' i• CORE SECOND SHELL Figure 1. Capsule configurations