Foamed open-cell structures

While we are dealing mostly with open-cell foams, control of the degree of openness also has an effect on tensile properties. Saunders reported on the control of open-cell structures by the addition of a stannous catalyst. They showed maxima... 

The open cell structure of carbon foam with its greater than 90% porosity and chemical inertness at temperatures below 500°C suggests its use as a filtration media for corrosive liquids and a dispersant for gases. 

Flexible foams are resilient open-cell structures with densities varying from 25—650 kg/m3, depending on the choice of the raw materials. Most flexible foams are produced in the form of a slab or bun in a continuous process in widths up to 2.4 m and thicknesses up to 1.2 m. A liquid foamable mixture is pumped onto a conveyor, which moves through a tunnel where reaction and foaming occur (101). Similar mixtures can be placed in a mold and allowed to foam. This process is used in the manufacture of automobile seats (see Foamed plastics). 

Flexible Polyurethane. 1 hcse foams are produced from long-chain, lightly branched polyols reacting wilh a diisocyanale. usually toluene diisocyanale (TDI), to form an open-celled structure wilh free air flow during flexure. During manufacture these foams arc closely controlled for proper density, ranging from 17 to 80 kg/ml (0.8-5 Ibs/ft ). to achieve the desired physical properties and cost. 

Foam structures consist of at least two phases, a plastic matrix and gaseous voids or bubbles. A closed-cell or open-cell structure is formed, with cellular walls enclosing the gaseous voids. In closed cell foams, the gas cells are completely enclosed by cell walls, while in open-cell foams, the dispersed gas cells are unconfined and are connected by open passages. Plastic can be stabilized against cell rupture by crosslinking (Chapters 1 and 2). 

Understanding the link between microstructure in PDMS foams and the mechanical performance is crucially important for the development of ageing trends that allow long term qualification. The plots in Figure 13 show force decay curves for a series of siloxane foam samples with varying closed cell contents. The trend demonstrates the time dependent nature of the measurement of physical properties. This creates an additional source of variation and if possible then it should be eradicated by the production of 100% open cell structures. 

In order to prepare wood substitutes and materials with open-cell structures, the so-called water-filled oligomeric foams are used These foams are obtained by mixing the OFM-monomeric composition with water until an emulsion is formed which is hardened after the addition of an initiator and activator. As a result, a white rigid material is obtained which is a spatial network copolymer with uniformly distributed micro-inclusions of water (2—5 nm). Optimal strength is reached at 50-60% of water, although the amount of water may be as high as 90%. At optimal water concentration, the cell walls withstand cryolitic destruction till 34 K. At 7 mass % of water the apparent denaty of the material reaches 250—9(X) kg/m and it resembles natural wood in appearance and in some properties. 

Considerable information has been accumulated regarding the relationdiip between the portion of open cells and the technical properties of oligomeric foams 83-85) xhere are considerably less data available on the relationship between the amount of open cells and other morphological parameters of RO foams, for example apparent density. Reticular foams based on RO are not considered in this survey because the open-cell structure is created by secondary processing of finished products and not during foaming. 

Epoxy foams are rigid. Some are predominantly of closed-cell structure and some of open-cell structure. Current efforts may lead to... 

The cells of the structure can be either closed or open. The former type is like a foam, in that the matrix can geometrically be compared with the continuous phase of the foam, which consists of thin lamellae and Plateau borders. Here we have thicker lamellae or walls, and beams (struts, ribs) where two lamellae meet if the cells are filled with gas we can call the system a solid foam. Open cells occur when the lamellae contain holes now we speak of a sponge. Some types of sponge structures merely consist of beams. Most plant tissues (see, e.g., Figure 9.4) consist of closed cells that are mainly filled with an aqueous liquid. 

Flame retardant flexible foams are very difficult to obtain due to the low crosslink density, low aromaticity, open cell structure and long polyolic aliphatic chains. Generally, flame retardants flexible foams are produced with additive flame retardants, for example with powdered melamine + tris (2-chloropropyl) phosphate [14]. 

Silicone foam thus formed has an open cell structure and is a relatively poor insulating material. Cell size can he controlled by the selection of fillers, which serve as bubble nucleating sites. The addition of quartz as a filler gready improves the flame retardancy of the foam chat yields of >65% can he achieved. Because of its excellent flammability characteristics, Silicone foam is used in building and construction fire-stop systems and as pipe insulation in power plants. Typical physical properties of silicone foam are listed in Table 10. 

Rigid foams tend to be closed cell in nature, and this characteristic is necessary for some of the typical application areas such as thermal insulation and floatation aids. Some rigid foams do exist however with an open cell structure such as the phenol-fonnaldehyde-based horticultural and floral foams. 

Cellular rubber may be described as an assembly of a multitude of cells distributed in a rubber matrix more or less uniformly. The cells may be interconnected (open cells) as in a sponge or separate (closed cells). Foam rubber made from a Uquid starting material such as latex, described earKer, is of open-cell type. Cellular products made from solid rubber are commonly called sponge (open cell structure) and expanded rubber (closed cell structure). 

Foamed network structures (lofted structures) are also prepared in a compression press using Radlite technology. In this case, after applying full temperature and pressure for the requisite 2-A min, the platen gap is opened 1.5 times the original setting (for primarily open-cell structure) or 1.1-1.2 times the... 

Accidentally produced foams exhibit an irregular, open-cell structure. Interconnected, randomly sized and shaped voids often vary in size, shape and distribution from one area of a foam to another. 

Foam neoprene is similar to open-cell neoprene in that it is a compressible material with intercormecting cells. Its main area of application is for cushioning, for example, in mattresses, seating, and carpet underlay. Because of the good heat and oil resistance of neoprene, it has also found application as a railroad car lubricator. This absorbent open-cell structure provides a wicking action to deliver oil to the journal bearings. 

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