Open cellular foam

A foamed plastic is called an open-cellular foam when its pores are interconnected with one another otherwise, this plastic is called a closed-cellular foam... 

Acknowledging these difficulties, researchers at LLNL proposed a nomenclature for open cellular foam structures called Low-Density MicroceUular Materials (LDMMs) [4]... 

Most published literature analyzed the elastic modulus of silica aerogels by drawing inspiration from the cellular solids models. For example, Ashby and Gibson (1997) describe the open cellular foam model compressive modulus to follow power law dependence on the relative density as shown in Eq. (5.1) where C and /i are geometric constants that depend on the topological features and microstructure undergoing cell wall bending as the dominant deformation. 

Foam Insulation Since foams are not homogeneous materials, their apparent thermal conductivity is dependent upon the bulk density of tne insulation, the gas used to foam the insulation, and the mean temperature of the insulation. Heat conduction through a foam is determined by convection and radiation within the cells and by conduction in the solid structure. Evacuation of a foam is effective in reducing its thermal conductivity, indicating a partially open cellular structure, but the resulting values are stiU considerably higher than either multilayer or evacuated powder insulations. 

Foamed polymeric materials can have either a closed or open cellular structure. Closed cells tend to be favoured when the pressure is maintained during the expansion. Both types are used for different applications, e.g., closed for thermal and sound insulation, open cell for soaking up liquids by capillary... 

The foam monoliths were a-Al203 samples with an open cellular, spongelike structure. We used samples with nominally 30 to 80 pores per inch (ppi) which were cut into 17 mm diameter cylinders 2 to 20 mm long. A 12 to 20 wt.% coating of Pt or Rh was then applied directly to the alumina by an organometallic deposition. 

By far the most studied PolyHIPE system is the styrene/divinylbenzene (DVB) material. This was the main subject of Barby and Haq s patent to Unilever in 1982 [128], HIPEs of an aqueous phase in a mixture of styrene, DVB and nonionic surfactant were prepared. Both water-soluble (e.g. potassium persulphate) and oil-soluble (2,2 -azo-bis-isobutyronitrile, AIBN) initiators were employed, and polymerisation was carried out by heating the emulsion in a sealed plastic container, typically for 24 hours at 50°C. This yielded a solid, crosslinked, monolithic polymer material, with the aqueous dispersed phase retained inside the porous microstructure. On exhaustive extraction of the material in a Soxhlet with a lower alcohol, followed by drying in vacuo, a low-density polystyrene foam was produced, with a permanent, macroporous, open-cellular structure of very high porosity (Fig. 11). 

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). 

Rodents chew through cellular polymers but do not ingest the foam as a foodstuff. The resistance to rot, mildew, and fungi is related to moisture absorption [64]. Therefore, open-cell foams support such growth better than closed-cell foams. High humidity and temperature are necessary for the growth of microbes on any plastic foam. 

ASTM D 1565-81 A Standard Specification for Flexible Cellular Materials Vinyl—Chloride Polymers and Copolymers (Open-Cell Foam), 9 pp (DOD Adopted) (FSC 9320) (MR) (Comm D-11)... 

Covers simulation of naturally occuning reactions such as oxidation or hydrolysis by humidity for open cellular latex and polyurethane foams. 

Cellular solids are a class of materials with low densities and novel physical, mechanical, thermal, electrical, and acoustic properties. Low-density cellular metals can feature a wide variety of topologies to include open-cell foam, closed-cell foam, hollow-sphere foam, periodic/optimized truss structures, and honeycomb. Metallic foams consist of air dispersed in a solid matrix, similar to polymer foams such as polystyrene or food foams such as whipped cream. Closed-cell foams feature solid faces such that each cell is independently sealed from its neighboring cells, whereas open-cell foams (also known as porous metals, metal sponges and truss-type materials) do not contain cell walls they only have cell edges. Hollow-sphere foams consist of an assembly of individual hollow spheres. 

ASTM D 1565, Flexible cellular materials Vinyl chloride polymers and copolymers (open cell foam). 1981. 

FIGURE 2.58 Schematic representations of section through different types of cellular polymer, (a) Low-density open-cell foam, (b) High-density closed-cell foam, (c) Single-component structural foam with cellular core and integral solid skin, (d) Multicomponent structural foam, (e) Fiber-reinforced closed-cell foam, (f) Syntactic foam. 

The glass transition temperature lies considerably above the temperature of use with rigid foams and considerably below the temperature of use with flexible foams. The cellular structure may be open, closed, or mixed. All cells are open to each other with open cellular structures. In contrast, each cell is sealed off or encapsulated from the other cells by a plastic wall in closed-cell structures. Structural foams are foams with a dense outer skin and an interior of lower density they are also called integral foams or self-skinning foams. In contrast to normal foams syntactic foams do not directly enclose the gas but contain small hollow bodies of glass, ceramics, or plastics which are under vacuum or are filled with a gas. 

The act of foaming a plastic material results in products with a wide range of densities. These materials are often termed cellular plastics. Cellular plastics can exist in two basic structures closed-cell or open-ceU. Closed-cell materials have individual voids or cells that are completely enclosed by plastics, and gas transport takes place by diffusion through the cell walls. In contrast, open-ceU foams have cells that are interconnected, and fluids may pass easily between the cells. The two structures may exist together in a material so that it may be a combination of open and closed cells. 

Open-cell foamed plastic n. A cellular plastic in which most of the cells are interconnected in a manner such that gases can flow freely from one cell to another. 

There are several types of foamed plastics including syntactic foam, closed-cell foam, and open-cell foam. Syntactic foam is a special type of plastic foam in which the cellular structure is formed by the use of smaU, hollow spheres made of resin, glass, or other hollow particles. The spheres are dispersed throughout a matrix of resin, usually thermosetting, which when cured resanbles a conventional foam plastic. Once mixed, syntactic foam may be cast or formed in place by a pouring or trowling action. 

By focusing on customer-driven development, American Aerogel has successfully commercialized a form of aerogel materials. Aerocore, a black organic monohthic open cellular rigid foam, can be produced with a wide range of properties and sizes. It can be used as a thermal insulator, acoustic attenuator, chemical support media, electrical conductor, and mechanical shock absorber. 

The open cell foams have a cellular network and the voids coalesce so that the solid (polymer matrix) and the fluid phases are continuous [4]. 

The bubble cells eventually ruptured with further expansion, resulting in open cellular structures that exhibited diverse, quite well-developed lamellar habits with thicknesses of less than 1 pm, the texture of which was characterized by orientation of the chains along the flow direction of the volatile phase. This agrees in general with the previous results of poly(butylene terephthalate, PBT) foams that comprised open cell structures (8). Oriented lamellae interconnected laterally were aJso seen. In contrast, an LDPE specimen that crystallized from... 

Metcalfe et al. (2003) tested cold hibernated elastic memory (CHEM) polyurethane for the treatment of lateral wall aneurysms on the carotid arteries of dogs. The SMP polyurethane was made in open cellular (foamy) structures with the glass transition temperature of 60 C. After 3 weeks, in vivo experiments showed that the CHEM foam led to improved aneurysm embolization, and a thick neoin-tima formation by favoring the ingrowth of cells. However, residual necks and recurrences were observed in some cases due to the incomplete filling of the vascular lumen. 

In the cellular model (Gibson, 1988), the porous solid is defined as a material built up of struts or plates, which form the edges and the faces of the cells. The most important structural characteristic of the cellular models is their relative density, which can be expressed as a function of the cell edge length, I and the size of the cross section, t. For an open cell foam made of cubic polyhedra, p/ps is proportional to (r//). Then, the elastic and the mechanical features have been calculated respectively E oc and Kic oc (p/ps). ... 

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