Flexible foam

Reaction of these polyols with an excess of isocyanate yields isocyanate terminated materials which are then chain extended by an amine such as hydrazine (NH2NH2) or ethylenediamine. The fibre is usually spun from solution in dimethylformamide. 

Spandex fibres, because of their higher modulus, tensile strength and resistance to oxidation, as well as their ability to be produced at finer deniers, have made severe iiu-oads into the natural rubber latex thread market. They have also enabled lighter weight garments to be produced. Staple fibre blends with non-elastic fibres have also been introduced. 

Whereas the solid polyurethane rubbers are speciality products, polyurethane foams are widely used and well-known materials. 

However, subsequent polyesters were produced with low carboxyl values and gas evolution occurred by the reaction already mentioned when discussing the Vulkollans, that between isocyanate and water 

The isocyanate group may be terminal on a polyester chain or may be part of the unchanged di-isocyanate. The density of the product, which depends on the amount of gas evolved, can be reduced by increasing the isocyanate content of the reaction mixture and by correspondingly increasing the amount of water to react with the excess isocyanate (that is excess over that required for chain extension and cross-linking). 

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Commonly used isocyanates are toluene dhsocyanate, methylene diphenyl isocyanate, and polymeric isocyanates. Polyols used are macroglycols based on either polyester or polyether. The former [poly(ethylene phthalate) or poly(ethylene 1,6-hexanedioate)] have hydroxyl groups that are free to react with the isocyanate. Most flexible foam is made from 80/20 toluene dhsocyanate (which refers to the ratio of 2,4-toluene dhsocyanate to 2,6-toluene dhsocyanate). High-resilience foam contains about 80% 80/20 toluene dhsocyanate and 20% poly(methylene diphenyl isocyanate), while semi-flexible foam is almost always 100% poly(methylene diphenyl isocyanate). Much of the latter reacts by trimerization to form isocyanurate rings. 

Flexible foams are used in mattresses, cushions, and safety applications. Rigid and semiflexible foams are used in structural applications and to encapsulate sensitive components to protect them against shock, vibration, and moisture. Foam coatings are tough, hard, flexible, and chemically resistant. 

Rebound flexible foam Rebound hardness test Receptor... 

Polyurethane. SmaU quantities of polyurethane film are produced as a tough mbber-like film. Polyurethane is more commonly used to produce foamed sheet, both flexible and rigid. The flexible foam is used as cushioning in furniture and bedding the rigid foam is widely used for architectural insulation because of its outstanding thermal insulation efficiency (see Urethane POLYMERS). 

Diphosphates. Three 2-chloroethyl diphosphates have been sold commercially. These have low volatihty and good-to-fair thermal stabiUty, and are thus useful ia those open cell (flexible) foams which have requirements for improved resistance to dry and humid aging. 

The simplest was Olin s Thermolia 101, tetrakis(2-chloroethyl) ethylenediphosphate [33125-86-9] C QH2QCl40gP2 (77), used extensively ia flexible foams (78,79). This compound has been discontinued, reportedly because of by-product problems. 

Because of the bulky neo stmcture in the middle of the molecule, this compound has enhanced hydrolytic stabiUty in addition to low volatihty. It is useful in many types of flexible foam, as well as in adhesives and epoxy- or phenoHc-based laminates. 

Nonreactive additive flame retardants dominate the flexible urethane foam field. However, auto seating appHcations exist, particularly in Europe, for a reactive polyol for flexible foams, Hoechst-Celanese ExoHt 413, a polyol mixture containing 13% P and 19.5% Cl. The patent beHeved to describe it (114) shows a reaction of ethylene oxide and a prereacted product of tris(2-chloroethyl) phosphate and polyphosphoric acid. An advantage of the reactive flame retardant is avoidance of windshield fogging, which can be caused by vapors from the more volatile additive flame retardants. 

This phosphoms-rich oligomer can also be incorporated into polyurethanes. Combinations with Eyrol 6 permit the OH number to be adjusted to typical values used in flexible foam, urethane coating, or reaction injection mol ding (RIM) appHcations (115,116). 

One ASTM test procedure has suggested (24) that foamed plastics be classified as either rigid or flexible, a flexible foam being one that does not mpture when a 20 x 2.5 x 2.5 cm piece is wrapped around a 2.5 cm mandrel at a uniform rate of 1 lap/5 s at 15—25°C. Rigid foams are those that do mpture under this test. This classification is used in this article. 

The mechanical properties of rigid foams vary considerably from those of flexible foams. The tests used to characterize these two classes of foams are, therefore, quite different, and the properties of interest from an application standpoint are also quite different. In this discussion the ASTM definition of rigid and flexible foams given earlier is used. 

The properties of commercial rigid foamed plastics are presented in Table 2. The properties of commercial flexible foamed plastics are presented in Table 4. The definition of a flexible foamed plastic is that recommended by the ASTM Committee D 11. The data shown demonstrate the broad ranges of properties of commercial products rather than an accurate set of properties on a specific few materials. Specific producers of foamed plastics should be consulted for properties on a particular product (137,138,142). 

Table 4. Physical Properties of Commercial Flexible Foamed Plastics...

Compressive Behavior. The most kiformative data ki characterising the compressive behavior of a flexible foam are derived from the entire load-deflection curve of 0—75% deflection and its return to 0% deflection at the speed experienced ki the anticipated appHcation. Various methods have been reported (3,161,169—172) for relating the properties of flexible foams to desked behavior ki comfort cushioning. Other methods to characterize package cushioning have been reported. The most important variables affecting compressive behavior are polymer composition, density, and cell stmcture and size. 

Various geometric coring patterns ki polyurethanes (171,175) and ki latex foam mbber (176) exert significant influences on thek compressive behavior. A good discussion of the effect of cell size and shape on the properties of flexible foams is contained ki References 60 and 156. The effect of open-ceU content is demonstrated ki polyethylene foam (173). 

Tensile Strength and Elongation. The tensile strength of latex mbber foam has been shown to depend on the density of the foam (149,177) and on the tensile strength of the parent mbber (177,178). At low densities the tensile modulus approximates a linear relation with density but kicreases with a higher power of density at higher densities. Similar relations hold for polyurethane and other flexible foams (156,179,180). 

Tear Strength. A relation for the tearkig stress of flexible foams that predicts linear kicrease ki the tearkig energy with density and kicreased tearkig energy with cell size has been developed (177). Both relationships are verified to a limited extent by experimental data. 

Fillers (qv) are occasionally used in flexible slab foams the two most commonly used are calcium carbonate (whiting) and barium sulfate (barytes). Their use level may range up to 150 parts per 100 parts of polyol. Various other ingredients may also be used to modify a flexible foam formulation. Cross-linkers, chain extenders, ignition modifiers, auxiHary blowing agents, etc, are all used to some extent depending on the final product characteristics desired. 

Textile uses are a relatively stable area and consist of the lamination of polyester foams to textile products, usually by flame lamination or electronic heat sealing techniques. Flexible or semirigid foams are used in engineered packaging in the form of special slab material. Flexible foams are also used to make filters (reticulated foam), sponges, scmbbers, fabric softener carriers, squeegees, paint appHcators, and directly appHed foam carpet backing. 

Process and Equipment. Rigid polyurethane foam processes use the same high or low pressure pumping, metering, and mixing equipment as earher described for flexible foams. Subsequent handling of the mixture is deterrnined by the end product desired. 

Industrially, polyurethane flexible foam manufacturers combine a version of the carbamate-forming reaction and the amine—isocyanate reaction to provide both density reduction and elastic modulus increases. The overall scheme involves the reaction of one mole of water with one mole of isocyanate to produce a carbamic acid intermediate. The carbamic acid intermediate spontaneously loses carbon dioxide to yield a primary amine which reacts with a second mole of isocyanate to yield a substituted urea. 

The products from the continuous process (buns) are cut to shape for the particular appflcation, while the molded foams ate formed to shape during the mol ding process. The density of the continuous buns is traditionally between 16-32 kg/m (1-2 Ibs/ft ). Molded foams have densities greater than 32 kg/m. Flexible foams find appHcafions as automotive cushions, carpet underlay, furniture, seating, and bedding. 

Flexible foams are resiUent open-ceU stmctures with densities varying from 25—650 kg/m, depending on the choice of the raw materials. Most flexible foams are produced in the form of a slab or bun in a contiauous process in widths up to 2.4 m and thicknesses up to 1.2 m. A Hquid foamable mixture is pumped onto a conveyor, which moves through a tunnel where reaction and foaming occur (101). Similar mixtures can be placed in a mold and allowed to foam. This process is used in the manufacture of automobile seats (see Foamed plastics). 

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