**Chapter 7 111**

Lag, Constant and Decay Release Characteristic of St-PVOH Encapsulated Urea as a Function of Coating Thickness Using Different Empirical Models *by Chigozie Francolins Uzoh and Stone Raphael Odera*

Preface

The term microencapsulation comes from the Greek "mikros," which means small, and from the Latin "en" and "capsula," which mean respectively in and a small box. This technology refers to the formation of polymer particles with diameters ranging from nanometers to millimeters, containing an active substance regardless of its physical state, i.e., in solid, liquid, or gaseous form, and which may have several types of morphologies. Over the past two decades, microencapsulation has been a growing field with applications in many technological disciplines. However, the principle of encapsulation is not new; biochemistry is one of the great founding principles of life, and the presence of a membrane allows the containment of essential molecules in cells. Nature is full of examples of encapsulation, from the macro- to the nanoscale, to protect material from the surrounding environment, such as a seed in a coat, a bird's egg, or a cell in a membrane. Thus, the development of microencapsulation processes is similar to an imitation of nature, to design innovative systems to immobilize, structure, or release the active ingredient. Since encapsulation has applications in various industrial fields, many definitions depend on the needs in a specific field. The most general definition probably corresponds to the trapping of a compound or system in a dispersed material for its immobiliza-

tion, protection, transfer control, structuring, and functionalization.

manometric scale, which is used in some advanced markets.

The development of the field of microencapsulation is closely linked to the progress of many advanced technologies to produce an innovative component for a specific application or industrial field, and thus to create a new application or market for products. One of the benefits of microencapsulation is that it combines various technologies from other unrelated industrial fields, which are combined to develop a new product. Also, in recent decades, the development of microencapsulation technology has also been accompanied by the reduction of particle size to the

The first mechanical microencapsulation technologies were developed at the end of the nineteenth century, and more particularly from spray coating and drying. It was only in the 1930s that the first attempts at phase coacervation microencapsulation were made by Bungenburg de Jong and Kass. A few years later, B. Green, a research chemist at the National Cash Register Company in Dayton, became interested in this technology and studied how the concept of microencapsulation could have a potential application in document copying. From the concept of phase coacervation developed by Bungenburg de Jong and Kass, he prepared the first gelatin-based microcapsules. The development of this technology from the laboratory to industrial scale took several years, and it was not until 1951 that NCR introduced the first carbonless copy paper. Green filed a patent for microencapsulation on June 30, 1953.

At the end of the 1950s, microencapsulation was gradually introduced in the

pharmaceutical and chemical sectors. Since then, microencapsulation processes and technologies have been continuously improved, modified, and adapted for various purposes and/or uses. Thus, the development of new methods and the expansion

**Introduction to microencapsulation**
