Matrix or Coating Materials

There are three main types of encapsulated products based on size roughly divided into  

Macro-coated powders with sizes larger than 0.1 mm 

Matrix microparticles or microcapsules with sizes in the range 0.1 -100 pm 

Nanoparticles or nanocapsules with sizes smaller than 0.1 pm 

Macro-coating is used mainly to stabilise fragrances or transform them from liquid to free-flowing solid powder. Microencapsulation or nanoencapsulation is the process of enclosing a substance inside a miniature capsule. These capsules are referred to as microcapsules or nanocapsules. The substance inside the capsule can be a gas, liquid or solid. The capsule wall can consist of various materials, such a wax, plastic or biopolymers like proteins or polysaccharides. 

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In the interfacial polymerization technique, a wall is formed from monomers that are dissolved in the two separated phases (oil and water phase) and they polymerize at the interface of emnlsion droplets. The use of these methods is limited, since the preferred matrix or coating materials are nonrenewable or nonfood grade, such as polyesters, polyamides, polyurethanes, polyacrylates, or polyureas, almost always accomplished by traces of toxic monomers (van Soest, 2007). 

This chapter provides a brief overview of a variety of biopolymers of natural origin available for the use as shell or coating materials in microencapsulation of actives. However, a detailed knowledge of the chemical and physical properties of the encapsulation material is required prior to use as a coating/tilm/matrix during the encapsulation process. The interaction between encapsulation material and actives needs careful consideration. Also, the economic considerations will remain crucial for the selection of the most appropriate encapsulant materials. 

The material (matrix) that ensures the protection and the controlled release of the entrapped bioactive compound in a microcapsule is called shell materiaL waU material, or coating material. 

Mechanical properties of materials have recently been correlated to cellular or tissue responses [74,75]. To date, studies have demonstrated that stem cells and tissue cells (such as skin, muscle, and brain cells) sense and respond to local matrix (e.g., extracellular matrix or synthetic material) stiffness through the formation of molecular adhesion complexes and changes in the actin-myosin cytoskeleton, which provide a feedback of the matrix stiffness for cell adhesion, motility, and differentiation [74]. For example, epithelial cells and fibroblasts on a collagen-coated polyacrylamide substrate that allows the stiffness to be altered (elastic moduli from 5 to 80Pa) revealed less cytoskeletal spreading and higher rates of motility or lamelhpodial activity on flexible... 

Figure 4.2 illustrates the fundamental concept of interface and interphase in a fiber-reinforced polymer matrix composite material system, as proposed by Drzal in 1983 [26]. This schematic concept may also be appHed for a biocomposite system. Once a sizing or coating material is applied to the region between the fiber and the matrix, there exists an interphase, which may be referred as a third phase. Two interfaces can exist between the reinforcing fiber and the polymer matrix. One is a fiber-size interface and the other is a polymer-size interface. 

The products can have a variety of shapes, such as spherical, oblong or irregular, can be monolithic or aggregates, and can have single or multiple walls. In Fig. 20.1 some typical morphologies of capsules are shown. The capsules consist of the coated or entrapped materials referred to as active, core material, fill, internal phase or payload (such as aroma chemicals). The coating or matrix material is called wall, membrane, carrier, shell or capsule. 

An example of such a reservoir matrix system is a rate-controlling membrane coated solid solution beads comprising (1) a hydrophobic long-chain fatty acid or ester material (2) a surfactant and... 

Cross-section structure. An anisotropic membrane (also called asymmetric ) has a thin porous or nonporous selective barrier, supported mechanically by a much thicker porous substructure. This type of morphology reduces the effective thickness of the selective barrier, and the permeate flux can be enhanced without changes in selectivity. Isotropic ( symmetric ) membrane cross-sections can be found for self-supported nonporous membranes (mainly ion-exchange) and macroporous microfiltration (MF) membranes (also often used in membrane contactors [1]). The only example for an established isotropic porous membrane for molecular separations is the case of track-etched polymer films with pore diameters down to about 10 run. All the above-mentioned membranes can in principle be made from one material. In contrast to such an integrally anisotropic membrane (homogeneous with respect to composition), a thin-film composite (TFC) membrane consists of different materials for the thin selective barrier layer and the support structure. In composite membranes in general, a combination of two (or more) materials with different characteristics is used with the aim to achieve synergetic properties. Other examples besides thin-film are pore-filled or pore surface-coated composite membranes or mixed-matrix membranes [3]. 

Silica powder, glass beads and fibres are commonly used for the reinforcement of plastics. The produced composite materials have an increased thermal and mechanical stability, compared to the pure polymeric material. In order to bind the inorganic filler to the organic matrix, silane molecules, with both an inorganic and organic side, are used. The silane may be mixed with the matrix and filler material in the composite preparation, or be coated onto the filler prior to mixing. The application... 

As mentioned earlier, suspensions of particulate rods or fibers are almost always non-Brownian. Such fiber suspensions are important precursors to composite materials that use fiber inclusions as mechanical reinforcement agents or as modifiers of thermal, electrical, or dielectrical properties. A common example is that of glass-fiber-reinforced composites, in which the matrix is a thermoplastic or a thermosetting polymer (Darlington et al. 1977). Fiber suspensions are also important in the pulp and paper industry. These materials are often molded, cast, or coated in the liquid suspension state, and the flow properties of the suspension are therefore relevant to the final composite properties. Especially important is the distribution of fiber orientations, which controls transport properties in the composite. There have been many experimental and theoretical studies of the flow properties of fibrous suspensions, which have been reviewed by Ganani and Powell (1985) and by Zimsak et al. (1994). 

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