Open-cell foams

Open-arc furnaces Open-celled foam Open-circuit potential Open-mold processes Open-pit mining Operating line... 

Fig. 5. Scanning electron micrographs of hoUow fiber dialysis membranes. Membranes in left panels are prepared from regenerated cellulose (Cuprophan) and those on the right from a copolymer of polyacrylonitrile. The ceUulosic materials are hydrogels and the synthetic thermoplastic forms a microreticulated open cell foam with a tight skin on the inner wall. Pictures at top are membrane cross sections those below are of the wall region. Dimensions as indicated.

At small strains the cell walls at first bend, like little beams of modulus E, built in at both ends. Figure 25.10 shows how a hexagonal array of cells is distorted by this bending. The deflection can be calculated from simple beam theory. From this we obtain the stiffness of a unit cell, and thus the modulus E of the foam, in terms of the length I and thickness t of the cell walls. But these are directly related to the relative density p/ps= t/lY for open-cell foams, the commonest kind. Using this gives the foam modulus as... 

N,N -Dimethy l-ZV.A -dinitrosoterephthalamide (V) Terephthalamide N2,H20, CO2 90-105 180 Low exotherm on decomposition but low decomposition temperature restricts use largely to open-cell foams. 

Bulk microstructure Continuous channels Between fibers Complex foam to vertically oriented channels Closed cell to open cell foam None... 

Some of the key factors that lead us to select polyurethane foam for upholstery are its durability, resilience, and controllable hardness (or softness, depending on your point of view). Vibration dampening and shock absorbance are important attributes in automobile and public transportation seating. Open cell foams are preferred for these applications because they allow for air and moisture transport, which improve the comfort of passengers who may occupy a seat continuously for several hours. This inherent breathability is also a valuable attribute in mattresses. Shock absorbance plays a key role in selecting flexible polyurethane foams for the packaging of fragile items. 

In another study, Chen and Zhao [55] demonstrated that by using a Ni-Cr alloy metal foam as the cathode DL (and current collector), instead of a CFP or CC, the performance of a DMFC can be enhanced significantly due to the improvement of the mass transfer of oxygen and overall water removal on the cathode side. Fly and Brady [56] designed a fuel cell stack in which the distribution layers were made out of metal foams (open cell foams). In addition, more than one foam (with different porosity) could be sandwiched together in order to form a DL with variable porosity. 

Micromechanics theories for closed cell foams are less well advanced for than those for open cell foams. The elastic moduli of the closed-cell Kelvin foam were obtained by Finite Element Analysis (FEA) by Kraynik and co-workers (a. 14), and the high strain compressive response predicted by Mills and Zhu (a. 15). The Young s moduli predicted by the Kraynik model, which assumes the cell faces remain flat, lie above the experimental data (Figure 7), while those predicted by the Mills and Zhu model, which assumes that inplane compressive stresses will buckle faces, lie beneath the data. The experimental data is closer to the Mills and Zhu model at low densities, but closer to the Kraynik theory at high foam densities. 

Patent Number US 5859076 A 19990112 OPEN CELL FOAMED ARTICLES INCLUDING SILANE-GRAFTED POLYOLEFIN RESINS... 

Describes open cell foamed articles including silane-grafted single-site initiated polyolefin resins. The olefin polymer resin can be a polyethylene, a copolymer of ethylene, a C3-C20 alpha-olefin, or a copolymer of ethylene, a C3-20 alpha-olefin and a C4-C20 diene. The open cell foamed articles have good cushioning properties and can be non-allergenic. 

Crystallisation of isotactic PP from homogeneous solution in supercritical propane yielded open-cell foams of high surface area. Their morphology usually consisted of microspheres with a dense core and a porous periphery... 

Brief details are presented on a PE multiporous thin sheeting of open cell foam structure. Planned production of the sheeting by Asahi Chemical and its application in refrigerators for water adsorption use is outlined. 

What are the advantages of open-celled foams and how do they differ from closed-cell foams ... 

In recent years, we have become integrated into the much larger world of polyurethanes, but we have always begun our investigations with a focus on the surface chemistry. While our studies have been on the full range of polyurethane chemistries and the full range in which polyurethanes are produced, the chemical aspects in which we are most interested are foams (the bulk of polyurethane production), specifically open-celled foams, and more specifically products known in the industry as reticulated foams. 

This chapter introduces readers to the versatility of polyurethane polymers without spending too much time on the chemistry. The next chapter will discuss a more classical view of the molecule and how it is developed. Our point, however, is to present a functional view of this system. We have examined its physical characteristics, focusing our attention on the uniqueness of reticulated foams. All the chemical points we have made apply to all polyurethane polymers, whether they are open-celled foams, closed-cell foams, or thermoplastic elastomers. 

FIGURE 2.14 Conversion of open-cell foam to reticulated foam. 

Air flow is a measure of the resistance that a foam presents to air passing through it. Intuitively one would expect that large pore size presents less of an impediment to flow than small cells. This is indeed true and it is this method that quantifies the effect. It is obvious by now that air flow is an important property in the context of this book. Unfortunately, the ASTM tests were designed for the measurement of resistance to air flow only. Our interests focus on the flow of other fluids, specifically water, through the foam. Nevertheless, air flow represents a quick and precise way to determine the quahty of a foam. If you are not sure of the difference between a reticulated foam and an open-cell foam, this test will differentiate them. Reticulated foams offer much less resistance to flow than open-cell foams. 

Finally, catalysts are very useful in controlling air flow. By controlling the sizes of cells or by causing the windows between cells to burst (to produce an open-cell foam), catalysts represent important tools in the effort to control air flow-through. 

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 production of an open-cell foam by the techniques described above only partially covers the polyurethanes considered most useful in the context of this book. Open-cell foams are converted to reticulated foams by a postprocessing technique. Two techniques are used in the U.S. The oldest involves immersing the foam in a... 

PHTHALIC ACID AND OTHERBENZENEPOLYCARBOXYLIC ACIDS] (Vol 18) -open-cell foams [INSULATION, THERMAL] (Vol 14)... 

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