Foamed production methods

Methods for foam production are numerous, depending to a great extent on the material used and the desired morphology. Metals, glasses, and ceramics all can be converted to foams with controlled physical characteristics by utilizing one of several foam production methods. Polymeric microcellular foams arc emphasized in this chapter and methods for their pr uction are addressed. 

Foam Products. Latices are made into foams for use in cushioning appHcations. The latices are frothed with air and then chemically coagulated for thick appHcations, or heated to induce coagulation for thinner appHcations. The latter method allows for infinite pot life during production (see Foamed plastics). 

In more recent years, molded flexible foam products are becoming more popular. The bulk of the molded flexible urethane foam is employed in the transportation industry, where it is highly suitable for the manufacture of seat cushions, back cushions, and bucket-seat padding. TDI prepolymers were used in flexible foam mol ding ia conjunction with polyether polyols. The introduction of organotin catalysts and efficient siHcone surfactants faciHtates one-shot foam mol ding, which is the most economical production method. 

Gafa and Lattanzi [6] determined the foaming power of commercial surfactants including AOS, LAS, AS, and SAS in 1 g/L solutions at 40°C according to a modified Ross-Miles method [66]. Their data, shown in Table 24, show that the best foaming products are the AOS and AS compounds followed by LAS and SAS. 

Olefins or alkenes are defined as unsaturated aliphatic hydrocarbons. Ethylene and propylene are the main monomers for polyolefin foams, but dienes such as polyisoprene should also be included. The copolymers of ethylene and propylene (PP) will be included, but not polyvinyl chloride (PVC), which is usually treated as a separate polymer class. The majority of these foams have densities <100 kg m, and their microstructure consists of closed, polygonal cells with thin faces (Figure la). The review will not consider structural foam injection mouldings of PP, which have solid skins and cores of density in the range 400 to 700 kg m, and have distinct production methods and properties (456). The microstructure of these foams consists of isolated gas bubbles, often elongated by the flow of thermoplastic. However, elastomeric and microcellular foams of relative density in the range 0.3 to 0.5, which also have isolated spherical bubbles (Figure lb), will be included. The relative density of a foam is defined as the foam density divided by the polymer density. It is the inverse of the expansion ratio . 

Patent Number US 5391581 A 19950221 PRODUCTION METHOD OF FOAMED PARTICLES OF UNCROSSLINKED ETHYLENE-BASED RESIN... 

Patent Number US 5350544 A 19940927 METHOD OF PREPARING A CROSSLINKED, POLYETHYLENE FOAM PRODUCT BY SURFACE EXPANSION OF A FOAM... 

Two techniques allow determination of the compressibility of foam. The methods are related and the application dictates which method better defines the quality of the product. For example, for furniture cushions, indentation force deflection (IFD) is a more common test technique than compression force deflection. Both methods determine the amount of force required to compress a foam to a percentage of its thickness. In the IFD test, the plunger that compresses the foam is smaller than the foam sample. This presumably correlates to a person sitting in the center of a chair cushion. 

Chlorofluorocarbon Alternatives. There still is no completely satisfactory propellant for use in the aerosol method of foam production. Chloroflu-orocarbons, still widely used, are harmful 10 atmospheric ozone and low molecular weight hydrocarbons, now popular, e g., in producing shaving cream, are explosive and promote the greenhouse effect. See also Fluorine. 

Polyurethane formulations cover an extremely wide range of stiffness, hardness, and densities. The performance properties of polyurethane can be widely modified by selecting appropriate raw materials, catalysts and auxiliary compounds, by employing various production methods and/or by employing various methods for further processing and/or for shaping the final products. Therefore, polyurethanes have wide applications such as elastomer, coating, adhesive, foam, and leather. 

The simplest technique for determination of the average by volume expansion ratio (and density) is the direct measurement of the total foam volume and the liquid volume in it (or its mass). Using barbotage methods for foam production the foaming process can be run until the initial solution is completely transformed into foam. Foam expansion ratio and its density are calculated by the formula... 

The production of foams was extensively discussed along with many of the unique difficulties that such systems present. Many advanced characterization techniques and methods for foam production were detailed. Used in conjunction with nano filled PDMS, the development of confident ageing predictions should be possible. 

Foams can be made by releasing a gas within a foamable liquid. For example, the opening and pouring of a bottle of soda releases pressurized CO2 gas, producing foam bubbles. Chemical reactions can also generate bubbles within the liquid. Other methods of foam production are to force both liquid and gas through a packed column (Khan et al. 1988), to spray foamable liquid onto a screen on which a fan is blowing (Aubert et al. 1986), or to use the foam-extrusion process (Han 1981). 

Molding. This method is used for producing molded-foam products such as pipe coverings, window frames, chair shells, and picture frames. 

---