Polyurethanes Closed cell

Whilst rigid closed-cell polyurethanes are excellent thermal insulators they do suffer from a limited and often unsatisfactory level of fire resistance, even in the presence of phosphorus-containing and halogen-containing fire retardants. Considerable promise is now being shown by the polyisocyanurates, which are also based on isocyanate chemistry. 

The R s of a fibrous or cellular insulation like those in Table 2 generally decrease as the temperature increases. In the case of closed-cell polymeric foams like polyurethane nr pnlyisncyanurate board, the R may decrease if the insulation temperature drops below the condensation temperature of the blowing agent in the cells. This is because of changes in the gas- phase composition and therefore the gas-phase thermal conductivity. The R of insulations also depends on density when all other factors are constant. The relationship bett een R and density... 

One example is the use of rigid selfexpanding closed cell polyurethane foams as a method to inhibit corrosion of the interior surfaces of metal (steel, etc.) structural cavities exposed to seawater and moisture is one of many example of plastic providing corrosion protection. Unfilled metal cavities are a general feature of various structures or products used in the marine, building, electronics,... 

Property ASTM Test Phenolics Foamedin Syntactic Place Castable Polyvinyl Chloride Rigid Closed Cell Phenylene Oxide Foamable Resin Polycarbonate Polystyrene Medium-Density Foam Polystyrene Molded Extruded Polyurethane Rigid Closed Cell... 

Most rigid polyurethane foams have a closed cell structure. Closed cells form when the plastic cell walls remain intact during the expansion process and are not ruptured by the increasing cell pressure. Depending on the blowing process a small fraction (5-10%) of the cells remain open. Closed cell structures provide rigidity and obstruct gaseous or fluid diffusional processes. 

Rigid polyurethane foams can be made from either polyester or polyether prepolymers, which are crosslinked with polyfunctional isocyanates. The resulting foams are largely closed cell, with only about 5 to 10% of cells being open. Rigid polyurethane foams are widely used as insulation in commercial, residential, and industrial settings. 

Rigid polyurethane foams are mostly based on polyether alcohol and are highly cross-linked. Rigid foams are many times blown by halogenated alkanes like trichlorofluoromethane. These foams have closed cell structures and are used for thermal insulation. Semi-rigid foams are used in car crashpads and packaging. 

Foams are commercially produced several ways. Some polymerization processes produce their own foam. Polyurethanes, for example, are very exothermic. When they are formed, if a little water is present, CO2 will be a by-product. As the polymer forms, the CO2 will cause closed cell foam. As another example, a blowing agent can be injected into the molten polymer. The agent will later decompose, giving off a gas when the polymer is heated to melting. Epoxy resins are expanded into foams this way. 

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. 

Cellular Polyurethane. Composed principally of the catalyzed reaction product of pulyisocyanatc and polyhydroxy compounds, processed usually with fluorocarbon gas to form a rigid foam having a predominantly closed-cell structure. Under investigation by regulators. 

During synthesis of a polymer, particularly of polyurethane, gaseous products can appear. Therefore, a complete model of the process must take into account (at least in some cases) the possibility of local evaporation and condensation of a solvent or other low-molecular-weight products. Such a complex model is discussed for chemical processing of polyurethane that results in formation of integral foams in a stationary mold.50 In essence, the model is an analysis of the effects of temperature in a closed cell containing a solvent and a monomer. An increase in temperature leads to an increase in pressure which influences the boiling temperature of the solvent and results in an increase in cell volume. The kinetics of polymerization is described by a simple second-order equation. The... 

Most low density rigid polyurethane foams have a closed-cell content of >90%. Above 0.032 g/cm3, closed-cell content increases rapidly and is generally >99% above 0.192 g/cm3. Bun foam, produced under controlled conditions, has a very fine-cell structure, with cell sizes of 150—200 im. 

Properly ASTM Test Phenolic Chi onile Rigid Closed Cell Plienylcne Oxide Foam able Resin Polyethylene Medium- Polycarbonate Density Foam Polystyrene Polyurethane Rigid Closed Cell... 

Foams Wave by Mater-Bi, foamed sheet packaging is a biodegradable alternative to conventional protective foam packaging such as polystyrene, polyurethane and polyethylene. Wave by Mater-Bi is starch-based, and is expanded using water, extruded into sheets and then assembled into blocks that can be cut into any shape. The foams have a robust and resilient closed-cell structure. 

Low Temperature [-101 to -1°C (-150 to -l-30°F)] Cellular glass, glass fiber, polyurethane foam, and polystyrene foam are frequently used for this service range. A vapor-retarder finish with a perm rating less than 0.02 is required. In addition, it is good practice to coat all contact surfaces of the insulation with a vapor-retardant mastic to prevent moisture migration when the finish is damaged or is not properly maintained. Closed-cell insulation should not be relied... 

A polishing pad has a significant impact on the performance of the CMP process. It transports the slurry to the pad-wafer interface, impacts the polishing nonuniformity, and affects the global wafer and device planarity. Pads may consist of thin porous closed cell [28], open cell [29], or noncell [30] polyurethane material. The properties of polishing pad can be studied in detail... 

The moisture resistance, low cost, and low-density closed-cell structure of many cellular polymers resulted in their acceptance for buoyancy in boats, floating docks, and buoys. Because each cell is a separate flotation unit, these materials cannot be destroyed by a single puncture. Foamed-in-place polyurethane between thin skins of high tensile strength is used in pleasure craft [98]. Other cellular polymers that have been used where buoyancy is needed are produced from polystyrene, polyethylene, poly(vinyl chloride), and certain types of rubber. Foams made from styrene-acrylonitrile copolymers are resistant to petroleum products [99,100]. 

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. 

Cell size is a factor controlling not only the volumetric weight of a foam but also such an important morphological parameter as gas-filling (see Sect. 3.2). As follows from Fig. 21, when the cell size decreases (i.e. the number N of cells per millimeter increases, the gas-filling of polyurethane foam samples (2.5 cm thick) also decreases since the number of the closed cells increases. This has been confirmed by air stream resistance tests at a pressure drop of 0.25 mm HjO... 

Fig. 21. Gas permeability of foamed polymers as a function of cell size, in the coordinates air steam velocity v versus number of cells N per linear mm, in polyurethane foams based on polyethers (1) and polyesters (2, 3) (1), (2) closed cell foams, (3) reticulated foam ...

Surfactants. A surfactant is a major raw material for polyurethane foams. Surfactants play an important role in obtaining required cell structures, e.g., fine cells, coarse cells, closed cells, and open cells, and these cell structures then influence foam properties. 

In contrast, when polyurethane formation is too fast, the resulting foam cells are stable, cell membranes are not broken during foam rise, and closed cells are formed. The closed cells are the cause of shrunk foams, because the internal gas pressure becomes lower than the atmospheric pressure. 

Type I is closed-cell polyethylene and Type II is open-cell polyurethane. 

AMS 3574-85 Polyurethane, Foam-in-Place, Rigid, Closed Cell, for Helmet Liners, 7 pp... 

Approximately 80% of PU are manufactured as foams. Polyurethane foams are lightweight materials, consisting predominantly (>98%) of air (and gases in the case of closed-cell foams). Both the chemistry and the processing will have major effects on the final properties of the foam. Polyurethane foams can be used to form composites with almost all flexible or rigid facings. As the density of the foam increases, the suitability for demanding dynamic applications is improved. ... 

Polypropylene (G/F)/nylon 6,6 Polyurethane open/closed cell foam Polypropylene (mica filled/glass filled/mineral filled) Aluminum tube AA4343/AA3003 base Aluminum tube AA4343/AA3003 base Nylon 6,6/nylon 6/polypropylene Nylon 6,6/nylon 6 Polypropylene (GF)... 

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