Foamed particles, structure

Most food products and food preparations are colloids. They are typically multicomponent and multiphase systems consisting of colloidal species of different kinds, shapes, and sizes and different phases. Ice cream, for example, is a combination of emulsions, foams, particles, and gels since it consists of a frozen aqueous phase containing fat droplets, ice crystals, and very small air pockets (microvoids). Salad dressing, special sauce, and the like are complicated emulsions and may contain small surfactant clusters known as micelles (Chapter 8). The dimensions of the particles in these entities usually cover a rather broad spectrum, ranging from nanometers (typical micellar units) to micrometers (emulsion droplets) or millimeters (foams). Food products may also contain macromolecules (such as proteins) and gels formed from other food particles aggregated by adsorbed protein molecules. The texture (how a food feels to touch or in the mouth) depends on the structure of the food. 

Structural foams are usually produced as fabricated articles in injection molding or extrusion processes they vary in properties (see Table 10.2). Again, the most important structural variables are polymer composition, density, and cell size and shape. Structural foams have relatively high densities (more than 320 kg/m3), and cell structures are primarily comprised of holes, in contrast to the pentagonal dodecahedral structure characteristic of low-density plastic foams. Because structural foams are generally not uniform in cell structure, they exhibit a considerable variation in properties with particle geometry (see Table 10.5) [24] these relations can provide valuable guidance. 

Foams (cellular structures) made by expanding a material by growing bubbles in it [11]. A foam has at least two components. At a macroscopic scale, there are the solid and liquid phases. The solid phase can be a polymer, ceramic or metal. The fluid phase is a gas in most synthetic foams, and a liquid in most natural foams. At a microscopic scale, the solid phase may itself consist of several components. For example, the solid phase of an amorphous polystyrene foam has only one component. On the other hand, the solid phase of a polyethylene foam or a flexible polyurethane foam typically has two components. These components are the crystalline and amorphous phases in polyethylene foams, and the hard and soft phases formed by the phase separation of the hard and soft segment blocks in flexible polyurethane foams. The solid phase of a polyurethane foam may, in fact, have even more than two components, since additional reinforcing components such as styrene-acrylonitrile copolymer or polyurea particles are often incorporated [12,13]. The solid is always a continuous phase in a foam. Foams can generally be classified as follows, based on whether the fluid phase is co-continuous with the solid phase ... 

The acrylic foam-coated nonwoven fabrics produced in this manner are capable of continuous operation at temperatures of up to approximately 120 °C. However, they are not normally resistant to hydrolytic conditions, these leading to the collapse of the structure and hence, premature pressurisation. The latter notwithstanding, in view of the success of foam-coated structures operating in relatively safe conditions , the future will undoubtedly see more advanced products of this type, leading to sttuctures that are both more efficient in particle capture and also are capable of operation in more chemically and thermally challenging environments. 

Figure 6.2a and b show the structure of foamed and non-foamed spray-dried maltodextrin powder at drying temperature 200 °C, respectively (Rabaeva, 2012). On analyzing Fig. 6.2b, particle structures can be observed with voids and inner bridges, which are similar to the foamed droplet structure shown in Fig. 6.1c. 

Foamed particles of maltodextrin (Figs. 6.13b-6.15b) have a more uniform structure and spherical shape which affects the bulk and apparent densities. For foamed material, the larger the powder particles the smaller is the bulk density of the product (Tabs. 6.3 and 6.4). For non-foamed material, the voids between large particles in the bed are filled with smaller particles, which causes an increase in the... 

Light scattering is a very convenient method for evaluating particle size according to Eqs (5.5)-(5.7). It is also possible to visualize structure development over time, as shown in Figure 5.48, where coarsening proceeds over a period of time at elevated temperatures [35]. In the present studies a very interesting foam-like structure was discovered when a PCL/SAN (70/30) blend was prepared by precipitation... 

For increased power requirements, electrode constructions have been developed which bring the electronic conductors in closer contact with the active material particles first, around 1930, the sinter electrode [110], recently in sealed cells largely replaced by the nichel-foam electrode, and then, around 1980, the fiber structure electrode [111]. In order to take full advantage of their increased perform-... 

Apart from manifold structures, carbons can have various shapes, forms, and textures, including powders with different particle size distributions, foams, whiskers, foils, felts, papers, fibers [76, 77], spherical particles [76] such as mesocarbon microbeads (MCMB s) [78], etc. Comprehensive overviews are given, for example in [67, 71, 72], Further information on the synthesis and structures of carbonaceous materials can be found in [67, 70, 72, 75, 79]. Details of the surface composition and surface chemistry of carbons are reviewed in Chapter II, Sec. 8, and in Chapter III, Sec. 6, of this handbook. Some aspects of surface chemistry of lithiated carbons will also be discussed in Sec. 5.2.2.3. 

Although silicone oils by themselves or hydrophobic particles (e.g., specially treated silica) are effective antifoams, combinations of silicone oils with hydrophobic silica particles are most effective and commonly used. The mechanism of film destruction has been studied with the use of surface and interfacial tensions, measurements, contact angles, oil-spreading rates, and globule-entering characteristics for PDMS-based antifoams in a variety of surfactant solutions.490 A very recent study of the effect of surfactant composition and structure on foam-control performance has been reported.380 The science and technology of silicone antifoams have recently been reviewed.491... 

Structured products, such as cosmetics, detergents, surfactant foams, inks, paints, drugs, foods and agrochemicals, combine several functions and properties in a single product. Design of these structured products involve the creation and the control of the particle size distribution in operations such as crystallization, precipitation, generation of aerosols, and nanoparticles as well as... 

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