Reticulated foam

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Reticulated foam is a very porous, low density solid foam. 'Reticulated' means like a net. Reticulated foams are extremely open foams i.e. there are few, if any, intact bubbles or cell windows. In contrast, the foam formed by soap bubbles is composed solely of intact (fully enclosed) bubbles. In a reticulated foam only the lineal boundaries where the bubbles meet (Plateau borders) remain.

Contents

Foam before reticulation (left), after reticulation (right) Reticulated foam.JPG
Foam before reticulation (left), after reticulation (right)

The solid component of a reticulated foam may be an organic polymer like polyurethane, a ceramic or a metal. These materials are used in a wide range of applications where the high porosity and large surface area are needed, including filters, catalyst supports, fuel tank inserts, and loudspeaker covers.

Structure and properties

Weaire-Phelan structure 12-14-hedral honeycomb.png
Weaire–Phelan structure

A description of the structure of reticulated foams is still being developed. While Plateau's laws, the rules governing the shape of soap films in foams were developed in the 19th century, a mathematical description of the structure is still debated. The computer-generated Weaire–Phelan structure is the most recent. In a reticulated foam only the edges of the polyhedra remain; the faces are missing. In commercial reticulated foam, up to 98% of the faces are removed. The dodecahedron is sometimes given as the basic unit for these foams, [1] but the most representative shape is a polyhedron with 13 faces. [2] [3] Cell size and cell size distribution are critical parameters for most applications. Porosity is typically 95%, but can be as high as 98%. [4] Reticulation affects many of the physical properties of a foam. Typically resistance to compression is decreased while tensile properties like elongation and resistance to tearing are increased. [5]

Production

Robert A. Volz is credited with discovering the first process for making reticulated polyurethane foam in 1956 while working for the Scott Paper Company. [6] Production of reticulated polyurethane foam is a two-step process that begins with the creation of conventional (closed-cell) polyurethane foam, after which cell faces (or "windows") are removed. To do so, the fact that the higher surface area and lower mass of cell faces compared with cell struts (or edges) makes them much more susceptible to both combustion and chemical degradation is exploited. Thus, closed-cell foam is either filled with a combustible gas like hydrogen and ignited under controlled conditions, or it is exposed to a sodium hydroxide solution to chemically degrade the foam, which will remove cell windows whilst sparing the edges. [7]

Reticulated ceramic foams are made by coating a reticulated polyurethane foam with an aqueous suspension of a ceramic powder then heating the material to first evaporate the water then fuse the ceramic particles and finally to burn off the organic polymer. [4]

Reticulated metal foam can also be made using polyurethane foam as a template similar to its use in ceramic foams. Metals can be vapor deposited onto the polyurethane foam and then the organic polymer burned off. [8]

Applications

Reticulated foams are used where porosity, surface area, low density are important.

Related Research Articles

Polyurethane Polymer composed of a chain of organic units joined by carbamate (urethane) links

Polyurethane refers to a class of polymers composed of organic units joined by carbamate (urethane) links. In contrast to other common polymers such as polyethylene and polystyrene, polyurethane is produced from a wide range of starting materials (monomers) and is therefore a class of polymers, rather than a distinct compound. This chemical variety allows for polyurethanes with very different physical properties, leading to an equally wide range of different applications. These include: rigid and flexible foams, varnishes and coatings, adhesives, electrical potting compounds, and fibres such as spandex and PUL. Of these, foams are the largest single application, accounting for 67% of all polyurethane produced in 2016.

Neoprene Family of synthetic rubbers

Neoprene is a family of synthetic rubbers that are produced by polymerization of chloroprene. Neoprene exhibits good chemical stability and maintains flexibility over a wide temperature range. Neoprene is sold either as solid rubber or in latex form and is used in a wide variety of commercial applications, such as laptop sleeves, orthopaedic braces, electrical insulation, liquid and sheet-applied elastomeric membranes or flashings, and automotive fan belts.

Foam Form of matter

Foams are materials formed by trapping pockets of gas in a liquid or solid.

Polyurea Class of elastomers

Polyurea is a type of elastomer that is derived from the reaction product of an isocyanate component and a synthetic resin blend component through step-growth polymerization. The isocyanate can be aromatic or aliphatic in nature. It can be monomer, polymer, or any variant reaction of isocyanates, quasi-prepolymer or a prepolymer. The prepolymer, or quasi-prepolymer, can be made of an amine-terminated polymer resin, or a hydroxyl-terminated polymer resin.

Memory foam Component primarily utilized for making cushions or mattresses

Memory foam consists mainly of polyurethane with additional chemicals that increase its viscosity and density. It is often referred to as "viscoelastic" polyurethane foam, or low-resilience polyurethane foam (LRPu). The foam bubbles or ‘cells’ are open, effectively creating a matrix through which air can move. Higher-density memory foam softens in reaction to body heat, allowing it to mold to a warm body in a few minutes. Newer foams may recover their original shape more quickly.

Syntactic foam Composite material filled with low-density spheres

Syntactic foams are composite materials synthesized by filling a metal, polymer, or ceramic matrix with hollow spheres called microballoons or cenospheres or non-hollow spheres. In this context, "syntactic" means "put together." The presence of hollow particles results in lower density, higher specific strength, lower coefficient of thermal expansion, and, in some cases, radar or sonar transparency. A manufacturing method for low density syntactic foams is based on the principle of buoyancy.

A polyol is an organic compound containing multiple hydroxyl groups. The term "polyol" can have slightly different meanings depending on whether it is used in food science or polymer chemistry. Polyols containing two, three and four hydroxyl groups are diols, triols, and tetrols, respectively.

Ethylene-vinyl acetate Chemical compound

Ethylene-vinyl acetate (EVA), also known as poly (PEVA), is the copolymer of ethylene and vinyl acetate. The weight percent of vinyl acetate usually varies from 10 to 40%, with the remainder being ethylene. There are three different types of EVA copolymer, which differ in the vinyl acetate (VA) content and the way the materials are used.

Metal foam

A metal foam is a cellular structure consisting of a solid metal with gas-filled pores comprising a large portion of the volume. The pores can be sealed or interconnected. The defining characteristic of metal foams is a high porosity: typically only 5–25% of the volume is the base metal. The strength of the material is due to the square–cube law.

Foam rubber

Foam rubber refers to rubber that has been manufactured with a foaming agent to create an air-filled matrix structure. Commercial foam rubbers are generally made of synthetic rubber, natural latex or polyurethane. Latex foam rubber, used in mattresses, is well known for its endurance. Polyurethane is a thermosetting polymer that comes from combination of Methyl di-isocyanate and polyethylene and some other chemical additives.

Nanofoam

Nanofoams are a class of nanostructured, porous materials (foams) containing a significant population of pores with diameters less than 100 nm. Aerogels are one example of nanofoam.

Ceramic foam is a tough foam made from ceramics. Manufacturing techniques include impregnating open-cell polymer foams internally with ceramic slurry and then firing in a kiln, leaving only ceramic material. The foams may consist of several ceramic materials such as aluminium oxide, a common high-temperature ceramic, and gets insulating properties from the many tiny air-filled voids within the material.

Printed electronics Electronic devices created by various printing methods

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A blowing agent is a substance which is capable of producing a cellular structure via a foaming process in a variety of materials that undergo hardening or phase transition, such as polymers, plastics, and metals. They are typically applied when the blown material is in a liquid stage. The cellular structure in a matrix reduces density, increasing thermal and acoustic insulation, while increasing relative stiffness of the original polymer.

Building insulation materials

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In civil engineering, concrete leveling is a procedure that attempts to correct an uneven concrete surface by altering the foundation that the surface sits upon. It is a cheaper alternative to having replacement concrete poured and is commonly performed at small businesses and private homes as well as at factories, warehouses, airports and on roads, highways and other infrastructure.

Solid State of matter

Solid is one of the four fundamental states of matter. The molecules in a solid are closely packed together and contain the least amount of kinetic energy. A solid is characterized by structural rigidity and resistance to a force applied to the surface. Unlike a liquid, a solid object does not flow to take on the shape of its container, nor does it expand to fill the entire available volume like a gas. The atoms in a solid are bound to each other, either in a regular geometric lattice, or irregularly. Solids cannot be compressed with little pressure whereas gases can be compressed with little pressure because the molecules in a gas are loosely packed.

Bioceramic

Bioceramics and bioglasses are ceramic materials that are biocompatible. Bioceramics are an important subset of biomaterials. Bioceramics range in biocompatibility from the ceramic oxides, which are inert in the body, to the other extreme of resorbable materials, which are eventually replaced by the body after they have assisted repair. Bioceramics are used in many types of medical procedures. Bioceramics are typically used as rigid materials in surgical implants, though some bioceramics are flexible. The ceramic materials used are not the same as porcelain type ceramic materials. Rather, bioceramics are closely related to either the body's own materials or are extremely durable metal oxides.

Titanium foams exhibit high specific strength, high energy absorption, excellent corrosion resistance and biocompatibility. These materials are ideally suited for applications within the aerospace industry. An inherent resistance to corrosion allows the foam to be a desirable candidate for various filtering applications. Further, titanium's physiological inertness makes its porous form a promising candidate for biomedical implantation devices. The largest advantage in fabricating titanium foams is that the mechanical and functional properties can be adjusted through manufacturing manipulations that vary porosity and cell morphology. The high appeal of titanium foams is directly correlated to a multi-industry demand for advancement in this technology.

References

  1. ↑ "The "shape" of our foam". Crest Foams. Archived from the original on 2010-05-09. Retrieved 2009-09-30.
  2. ↑ "Structure of random monodisperse foam" (PDF). Archived from the original (PDF) on 2010-06-16. Retrieved 2010-10-28.
  3. ↑ "A new counter-example to Kelvin's conjecture on minimal foams" probably referring to Gabbrielli, Ruggero (August 2009). "A new counter-example to Kelvin's conjecture on minimal surfaces". Philosophical Magazine Letters. 89 (8): 483–491. Bibcode:2009PMagL..89..483G. doi:10.1080/09500830903022651. S2CID   137653272.
  4. 1 2 Gliganic, Robert (February 21, 2008). "Where Reticulated Polyurethane Foam's a Fit". MachineDesign.com. Retrieved 2009-09-30.
  5. ↑ Blair, E. Allen (1967). Cellular plastics: proceedings of a conference, Natick, Massachusetts, April 13-15, 1966. National Academy of Sciences. p. 141. Retrieved 2010-12-02.
  6. ↑ "Hall of Fame". Polyurethane Foam Association. Archived from the original on 2009-07-18. Retrieved 2009-09-30.
  7. ↑ "Reticulated foam". United Foam. Archived from the original on 2009-06-22. Retrieved 2009-09-30.
  8. ↑ Queheillalt, Douglas T.; Derek D. Hass, David J. Sypeck, Haydn N.G. Wadley, DD.; Sypeck, DJ.; Wadley, HN. (2001). "Synthesis of open-cell metal foams by templated directed vapor deposition" (PDF). Journal of Materials Research. 16 (4): 1028–1036. Bibcode:2001JMatR..16.1028Q. doi:10.1557/JMR.2001.0143. S2CID   711787. Archived from the original (PDF) on 2018-12-11.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  9. 1 2 3 4 5 Curti, Michael C. "A Multifaceted Foam". Crest Foam Industries. Archived from the original on 2009-11-20. Retrieved 2009-09-30.
  10. ↑ Thomson, Tim (2004). Polyurethanes as specialty chemicals: principles and applications. CRC. p. 99. ISBN   978-0-8493-1857-3 . Retrieved 2009-09-30.
  11. ↑ Bennett, J. Michael. "Novel Halon Alternative Concepts – Synergistic Development of Public and Private Sectors" (PDF). National Institute of Standards and Technology. p. 3. Archived from the original (PDF) on 2010-05-31. Retrieved 2009-10-01.
  12. ↑ Gliganic, Robert. "The Unique Material for Imaginative Applications". Product Design and Development. Archived from the original on 2013-01-31. Retrieved 2009-09-30.
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