Processing foaming

Foamed polystyrene - which is also known as expanded polystyrene - is used extensively in a variety of applications, ranging from packaging peanuts to insulation board and single-use cups and plates. We produce it by two processes foam extrusion and bead expansion. Both types of expanded polystyrene consist of closed cells, i.e., bubbles with continuous walls. We can visually distinguish the two types of foam by the fact that products made by the expanded bead process consist of discrete beads that are welded together... 

In microbiological processes, foaming occurs more often than in chemical ones since many metabolic processes produce surfactants, the process frequently takes place in a 3- or 4-phase systems (G/L/(S)/microorganisms) and intensive aeration or gas evolution (fermentation processes) is often involved. This often leads to the situation that foam evolution cannot be controlled any more. 

In 2005, Japanese company Kaneka developed the first beads-process, foamed resin moulded product, which is based on polylactic acid. The new KanePearl product has the strength and shock-absorbing properties of existing beads-process, foamed polystyrene products. 

Lemlich, R., Adsubble Processes Foam Fractionation and Bubble Frac-... 

Figure 4. Photomicrograph of an enhanced oil recovery process foam containing emulsified crude-oil droplets. The droplets have traveled within the narrow lamellae to accumulate and sometimes coalesce in the plateau borders of the foam, where they are held preferentially. The presence of such emulsified oil droplets in the foam structure has a destabilizing effect on the foam.

Foamed carbon is also nongraphitizable. The cell structure of the polymer foam remains intact upon careful carbonization and densities lower than 0.1 g/cm- are obtainable. The thermal conductivity is just above that of plastic foams, but foamed carbon can be used at much higher temperatures. Its relatively low compressive strength can be increased by impregnation with pyrolytic carbon, although the thermal conductivity increases at the same time. By comparison with glassy carbon, foamed carbon is easy to work, so that the shape does not have to be established at the start of the process. Foamed carbon is corrosion resistant, as are all carbon modifications. 

Silk yam is normally degummed in the hank form. In the pack (beck), the hanks are normally hung on polished wood or metal rods which are submerged in the bath and turned by hand. Alternatively, hank and spray dyeing machines can also be used for degumming of silk in yam form. In the foam boiling process foam produced by soap bath comes m contact with silk and thus causes degumming. 

Detergency Manual dishwashing suds Machine dishwashing suds Commercial bottle-cleaning process foam Machine clothes-washing suds... 

The initial material for the foam catalyst may be any metal or alloy capable of existing, under normal conditions, in the metallic state (Cu, Ag, Ni, W, steel, Nichrome, etc.), or ceramics of various composition. Corrosion-resisting Nichrome and stainless steel are preferable materials of the foam support for deep oxidation processes. Foam ceramics is the most stable to corrosion however, it is brittle and can be broken under hard operating conditions. 

But in many industrial processes foam is an annoying factor. Cans cannot be filled properly, surfaces show defects, production processes are interrupted or slowed down. Then foam destroying substances, so called defoamem are added. The phenomenon of foam is not limited to water-based systems only. Also solvent-based or solvent-free systems sometimes do have air entrapments and a deaeration is essential for proper performance and appearance. Before taking a look into how foam can be destroyed it is necessary to understand how foam is stabilised, and which substances bring this about -because pure liquids do not foam ... 

Obtained forms of foamed plastics are blocks, sheets, slabs, boards, molded products, and extruded shapes. These plastics can also be sprayed onto substrates to form coatings, foamed in place between walls (i.e., poured into the empty space in liquid form and allowed to foam), or used as a core in mechanical structures. It has also become possible to process foamed plastics by conventional processing machines like extruders and injection-molding machines. 

To make an emulsion or a foam, droplets or bubbles have to be generated from the interface between the two immiscible phases. This is usually done in a homogenizer, where droplets or bubbles continuously breakup and recoalesce. The droplet or bubble size is ultimately determined by the timescales of the breakup and recoalescence processes. Foams may also be produced by supersaturating a liquid with a gas. This can be realized by gas-producing microorganisms or by dissolving gas in a liquid under pressure, whereafter the pressure is released as happens when opening a bottle of beer. 

Foam Injection Processes. Foams can be injected in to a reservoir for mobility control or for blocking and diverting. The foam can thus act to reduce the effects of ... 

Since surfactin causes foaming during fermentation process, foam fractionation can be used for the recovery of surfactants. A bioprocess for the enhanced production of surfactin from a medium containing glucose and metal cations along with continuous removal of product by foam fractionation has been established by Cooper et al. which is shown in Figure 14.9. 

The adsorption at the water-air interface is used in separation and concentration processes (foam separation and flotation extraction) [87]. To remove the traces of metals that are present in the anionic form, the method of foam fractionation is used. (The foam is formed during air bubbhng through the water solution of hexade-cyltrimethylammonium bromide) [88]. In this process the selectivity coefficients are determined by the anion hydration energies. 

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