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The Unique Material For Imaginative Applications

Wed, 11/07/2007 - 5:10am

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Reticulated Polyurethane Foam filters, cushions, pads, wicks, scrubs, seals, absorbs, dampens, protects – and more.
Reticulated polyurethane foam is both unique and versatile. It is produced in a wide range of densities and pore sizes—measured in Pores Per Inch (PPI), a nominal measure of voids to solid material per linear inch—to meet virtually thousands of different applications for commercial, consumer, industrial, medical and military uses. Reticulated foam is light in weight, strong, resistant to most chemicals, and is easily fabricated into almost any shape.
An Explosive Gas Mixture And A Controlled Flame

Foam with optimized pore sizes and densities is engineered specifically for explosion suppression and surge/noise mitigation, making them suitable for use in fuel tanks.

The reticulation process converts controlled pore foam into fully open media. This can be done by one of two ways; either a chemical method or by a thermal process. In the thermal process, a block or “bun” of polyurethane foam is placed in a large vacuum pressure vessel that is evacuated and filled with an explosive gas mixture. The gas mixture is ignited and a controlled flame front passes through the foam bun, rupturing the cell membranes and leaving the skeletal structure intact.

Reticulated polyurethane foam is commonly found in the fuel tanks of military aircraft where it is used to prevent catastrophic explosions from hostile fire.

The thermal method can be applied to a greater variety of polyurethane materials than the chemical process, typically both polyester and polyether polyurethane materials. Thermal processing produces material with a smooth, clean appearance that can be important for some clinical and medical applications, such as in defoamers or blood oxygenators. It also has the added benefit of doubling the tear and tensile strength of the foam after reticulation.

Thermal processing is easily repeatable from batch to batch, and once processed the reticulated foam is then sold to fabricators who produce a wide range of end products, such as filters, seals, liquid reservoirs, gaskets, fuel tank protectors, cushioning material and many others.

A Dip Into A Chemical Bath
When reticulation is performed by means of chemicals, the polyurethane is passed through a caustic bath. The caustic solution dissolves the polyurethane’s window membranes, leaving behind a three-dimensional skeletal structure with few or no membranes between strands. The resulting reticulated polyurethane foam must be washed, rinsed, and dried to remove any residue of the caustic solution.

Unfortunately, this approach leaves a trace powder residue of the caustic solution behind in the reticulated foam, which makes materials processed by liquid means unsuitable for certain (typically medical) applications. The chemical approach is also not suitable for certain types of polyurethane materials, notably polyether polyurethane materials. Since it is a process of dissolving, the post-reticulated strands that remain are very weak with much lower physical properties than those of thermal reticulation.

Touching The Void
Reticulated polyurethane has another key advantage: high void volume. The void volume, or ratio of total voids to total solid material, can be as high as 98 percent in some end products, with high surface areas of as large as 200 ft 2 per cubic foot of reticulated polyurethane foam. Changes in the number of pores per inch and the sizes of the pores determine the permeability of the final material and provide a measure of design flexibility. Typical pore sizes may range from 4 to 120 PPI.

The foam is incorporated into disposable cardiotomy and venous reservoirs used for open-heart surgery, it removes air from blood before reinfusion into a patient

Good elongation characteristics, high tensile strength, and high tear strength of reticulated polyurethane foam all contribute to its versatility for fabrication, supporting such techniques as cutting, shaping, stapling, tacking, stitching, cementing, laminating and grommeting. Although the material is inherently impervious to microbial organisms, it can also be manufactured with permanent fungicidal/bactericidal additives for increased control of microbial activity as well as conductive or non-conductive electrical properties.

Make It Applicable
The uses for reticulated polyurethane foam are many and include familiar items such as speaker grills, shoe polish bottle tips, paint brushes, supermarket produce counter mats, cosmetic applicators and literally thousands of others. But the material has many lesser-known applications, some of which are vital to health and safety. For example, reticulated polyurethane foam is incorporated into disposable cardiotomy and venous reservoirs used for open-heart surgery, providing the critical function of removing air from blood before reinfusion into a patient.

Thousands of products use reticulated polyurethane foam, many of which you encounter everyday including speaker grills, shoe polish bottle tips and paint brushes.

The chemical-resistant nature of reticulated polyurethane foam allows it to be used for a wide range of industrial applications, including filtering air in humidifiers, bacteria filters, vehicle air cleaners and engine inlet prefilters.

Another major application for reticulated polyurethane foam includes its use for outdoor cushioning materials at public facilities such as stadiums and resorts where seating comfort is important. Cushioning Grade reticulated foam drains water like a sieve yet retains all the seating comforts of other foam seating materials. Cushions produced with this material may be used immediately after rain, washing or morning dew.

The Few, The Proud, The Reticulated Polyurethane Foam
Reticulated polyurethane foam is commonly found in the fuel tanks of military aircraft,small attack ships, and ground vehicles where it is used to prevent catastrophic explosions from hostile fire or when accidents occur (such as a static spark during over-the-wing refueling operations). It is also mandated for use in the fuel tanks of competition racecars for the same reason—to prevent explosions in case of a crash.

These special versions of reticulated polyurethane foam with optimized pore sizes and densities are engineered specifically for explosion suppression and surge/noise mitigation, making them suitable for use in fuel tanks of any vehicle with the possibility of a fuel tank explosion. They have precise and repeatable pore sizes, reduced weight and displacement and excellent static dissipation properties. They are also resistant to most fuels.

Another interesting application for reticulated polyurethane foam is its use in metal casting, in the production of ceramic filters to eliminate impurities from the pouring process. The foam serves as a sacrificial catalytic substrate. It is first coated with ceramic slurry and then baked to remove the foam and fuse the ceramic, creating a rigid ceramic part. Molten metal flows through the ceramic part (which acts as a filter) during the casting process to remove impurities and control the rate of flow.

Compressing Foams
When compressed, reticulated polyurethane foam materials exhibit somewhat different properties than in their uncompressed states, and this characteristic can be used to advantage in many applications. Compression ratios as high as 20:1 can be used to achieve extremely high void volumes of 95 percent or more in filtering, reservoiring and wicking applications.

For example, the uniform texture of the foam materials makes them ideal for ink rollers and in ink cartridges for computer printers. The excellent filtration qualities of reticulated polyurethane foam provide a rigorous flow path and more impingement surfaces to trap particulate matter, with high breathability, wicking, capillary action and high strength. When compressed, a high-performance reticulated polyethylene foam material will still maintain a relatively high void volume.

For additional information, contact Philip Laut at plaut@crestfoam.com or visit www.crestfoam.com.

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