Rigid foam Open cell

Definition Types include flexible, semirigid, and rigid foams, open- or closed-cell foams, and high-... 

Closed-cell foams are most suitable for thermal insulation and are generally rigid, while open-celled foams are best for car seating, furniture, bedding and acoustical insulation, among applications. These are generally flexible. 

Foams can be flexible or rigid, with open or closed cells, reinforced or not. Their properties depend on ... 

Foamed polymers. Thermosets and thermoplastics formed into low density, cellular materials containing bubbles of gas. Rigid foams have their gas bubbles in closed cells, inhibiting flexibility flexible foams have the bubbles in open cells, permitting the gas to escape as the foam is flexed. 

Rigid foams generally have closed.cells," flexible foams have open cells so the air can escape during Hexing. 

The dimensional stability of low density, water blown rigid PU foams for pour-in-place thermal insulation applications was improved by the use of a phthalic anhydride based polyester polyol containing a dispersed cell opening agent. The foam systems obtained allowed some of the carbon dioxide to be released through the cell windows immediately after filling of the cavity, and to be rapidly replaced by air. Studies were made of the flowability, density, open cell content, dimensional stability, mechanical properties, thermal conductivity and adhesion (particularly to flame treated PE) of these foams. These properties were examined in comparison with those of HCFC-141b blown foams. 21 refs. 

Moreover, flexible foams are characterized by utilization of special emulsifiers in their synthesis yielding an open-cell architecture, whereas for rigid foams emulsifiers are chosen that create more closed-cell structures. As diisocyanate for both types, the commercially available mixture of 80% 2,4-toluene diisocyanate and 20% 2,6-toluene diisocyanate is especially suitable. If foam formation is to take place at room temperature, and especially when hydroxy compounds with secondary hydroxy groups are used [poly(propylene glycol)s], the presence of a catalyst is generally required (see Sect. 4.2.1). 

The newer open-cell foams, based on polyimides (qv), polybenzimidazoles, polypyrones, polyureas, polyphenylquinoxalines, and phenolic resins (qv), produce less smoke, are more fire resistant and can be used at higher temperatures. These materials are more expensive and used only for special applications including aircraft and marine vessels. Rigid poly (vinyl chloride) (PVC) foams are available in small quantities mainly for use in composite panels and piping applications (see Flame retardants Hrat-rrststantpot.ymf.rs). 

Foamed plastics can be classified in different ways, for instance by their nature (flexible vs. rigid), chemical composition of the matrix, density, cell size, cell structure (open-celled vs. closed-celled), processing method, and dimensions. It is the aimed combination of these properties that determines the final application of the cellular polymer. As an example, open-celled ultra-low density foams are highly desirable for acoustical insulation, while rigid foams with closed-cells and elevated densities are preferred as load-carrying core materials in composite materials. 

When plastics are foamed to low densities, containing more air than polymer, they acquire unique new properties and applications. Major uses are in crash padding and thermal insulation. Closed-cell foams are outstanding for flotation, rigidity, and insulation while open-cell foams are outstanding for softness, resilience, and comfort. 

Soft, very flexible vinyl foams used for garment insulation, upholstery and similar applications are made by this CBA process. The more rigid foams used as underlays for rugs and flooring can also be made by this method, but require different plastics and lower plasticizer contents. Open-cell chemically blown vinyl foams generally have densities in the range of 5 to 30 lb/ft3. 

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. 

Hence, one of the most probable reasons for the formation of open cells, including microcells, due to water vapor is given in The mechanism described there, however, does not explain the formation of closed microcells which we observed in the structure of rigid phenolic foams The formation of these microcells is apparently connected with specific features of foaming and hardening kinetics in oligomeric compositions. 

According to Thomas elastic polymers often produce open-cell foamed plastics, whereas rigid polymers generally form closed-cell materials. However, there are many exceptions to this rule, owing to the variety of blowing techniques. Closed-cell structures are more likely to be produced from polyurethanes, epoxy resins, silicones, poly(vinyl chloride), polystyrene, etc., whereas open-cell materials mainly result from phenolic and carbamide foamed plastics. 

Foams made from vinyl resins are of two types, open-cell and closed-cell. The open-cell foams are soft and flexible, whUe the closed-cell foams are predominantly rigid. Both types are made from plastisols, which are suspensions of finely divided resins in a plasticizer. The polymer does not dissolve appreciably in the plasticizer until elevated temperatures are used. 

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

This Navy specification covers a single class of foam, nominal density 2.0 Ib/ft rigid unicellular polyurethane foam, and the materials required for preparation by the foam-in-place technique. Requirements cover density, compressive strength, volume change after heat aging, humidity aging, compressive set, unicellularity (% open cells, max.), oil resistance, and fire resistance. 

Whether the cells are closed (as in rigid foams) or open (as in flexible foams). 

The most Important distinction is between closed- and open-cell foams. In closed-cell (unicellular) foams, each gas bubble is separated from the others by thin walls of polymer these foams are optimal for flotation applications, structural rigidity, and thermal insulation. In open-cell foams, the cells are all interconnecting, and fluids and especially air can flow freely through the foam structure these are optimal for sponge products and for soft flexible materials. In the extreme case, when the last few remaining cell walls (windows) have been chemically dissolved out of an open-cell foam, it is sometimes called "reticulated."... 

The effect of the gas on mechanical properties depends on the paradox of closed- versus open-cell construction. In a closed-cell foam, mechanical deformation compresses the gas, so the gas contributes to rigidity and strength of the plastic product. In an open-cell foam, on the other hand, the fluidity of air permits it to rush out when the foam is deformed and to rush back when the deformation is released therefore, the foam contributes to the softness, flexibility, and resilience of the plastic product. 

Shock absorbance, both in flexible open-cell foams because of the rush of escaping air, and in rigid foams because of the conversion of kinetic energy into potential energy during crushing of cell walls to create new surface. 

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. 

A closed-cell foam makes a better buoy or life jacket because the cells do not fill with liquid. In cushioning applications, however, it is desirable to have compression to cause air to flow from cell to cell and thereby dissipate energy, so the open-cell type is more suitable. Foamed plastics can be produced in a wide range of densities—from 0.1 Ib/ft. (0.0016 g/cm ) to 60 Ib/ft. (0.96 g/cm )—and can be made flexible, semirigid, or rigid. 

Freon 11 blows to give closed cell structures whereas water produces open cells through carbon dioxide. This formulation is typical for a rigid foam for thermal insulation purposes. The heat build-up due to the reaction exotherm (about 80 kj/mole for formation of urethane groups) is sufiiciently dissipated through the open cell to avoid thermal degradation. 

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