Reacting foam

In another variation of the process, the foaming mix is fed to the bottom of a cylinder and the foaming mixture is pushed upwards (the Vertifoam process). The mass of material above the reacting foam can be used to control density, whilst in addition volatiles and gases find it more difficult to escape from the system. The solidified cylinder of foam may then be sliced horizontally into large discs. 

Two streams of PUR chemicals collide with each other violently and under high pressure generally at 1,500 to 3000 psi (10.3 to 24.1 MPa) inside the mixer. When these impinging streams collide, the flow is very turbulent and the reaction begins. The stream exits the mixhead and is directed into the mold. After the pour a piston inside the mixhead scrapes the walls of the chambers completely clean so that no reacted foam is left inside the mixhead. 

In this paper, instrumental means are used to obtain a physical description of the rise of urethane foam and cell opening. Infrared analysis is used to identify the chemical species present in reacting foam and to determine the order and relative rates of reaction of these species. From these data, a reaction sequence model is deduced for the process of making stable, water-blown urethane foam. 

Infrared Analysis. Infrared analysis has been used to identify the chemical species present in reacting foam and to determine the order and relative rates of reaction of these species. 

Figure 8. Evolution of carbon dioxide from reacting foam, Formulation B, measured by infrared absorbance at 2320 cm 1.

Abstract. Infrared analysis of reacting foams has been used to determine the sequence of chemical reactions that occurs in the foaming process and to relate this sequence of reactions to the stages evident in the formation of foam measured by rate-of-rise techniques. A reaction sequence model has been developed in which at the earliest stage of foaming, out-of-phase carbamic acid and carbamic acid salts, formed by hydrolysis of isocyanate, are the main species present tending to stabilize the froth-like foam. These species are in turn converted into polyureas. In the latter stages of the reaction sequence, urethane formation becomes predominant as the foam develops substantial bulk modulus... 

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. 

Adipic acid is an irritant to the mucous membranes. In case of contact with the eyes, they should be flushed with water. It emits acrid smoke and fumes on heating to decomposition. It can react with oxidizing materials, and the dust can explode ia admixture with air (see Table 3). Fires may be extinguished with water, CO2, foam, or dry chemicals. 

In addition to the main acidulation reaction, other reactions also occur. Free calcium carbonate in the rock reacts with the acid to produce additional by-product calcium compounds and CO2 gas which causes foaming. Other mineral impurities, eg, Fe, Al, Mg, U, and organic matter, dissolve, the result being that the wet-process acid is highly impure. 

Diester/Ether Diol of Tetrabromophthalic Anhydride. This material [77098-07-8] is prepared from TBPA in a two-step reaction. First TBPA reacts with diethylene glycol to produce an acid ester. The acid ester and propylene oxide then react to give a diester. The final product, a triol having two primary and one secondary hydroxyl group, is used exclusively as a flame retardant for rigid polyurethane foam (53,54). 

These foams are produced from long-chain, Hghtiy branched polyols reacting with a diisocyanate, usuaUy toluene diisocyanate [1321 -38-6] (TDI), to form an open-ceUed stmcture with free air dow during dexure. During manufacture these foams are closely controUed for proper density, ranging from 13 to 80 kg/m (0.8—5 lbs/ft ), to achieve the desired physical properties and cost. 

Another type of polyol often used in the manufacture of flexible polyurethane foams contains a dispersed soHd phase of organic chemical particles (234—236). The continuous phase is one of the polyols described above for either slab or molded foam as required. The dispersed phase reacts in the polyol using an addition reaction with styrene and acrylonitrile monomers in one type or a coupling reaction with an amine such as hydrazine and isocyanate in another. The soHds content ranges from about 21% with either system to nearly 40% in the styrene—acrylonitrile system. The dispersed soHds confer increased load bearing and in the case of flexible molded foams also act as a ceU opener. 

The Kleber-Colombes rigid PVC foam (253,254) is produced by compression mol ding vinyl plastisol to react and gel the compound, followed by steam expansion. The process involves mixing, mol ding, and expansion. The formulation consists of PVC, isocyanate, vinyl monomers such as styrene, anhydrides such as maleic anhydride, polymerization initiators, FC-11, and nucleators. The ingredients are mixed in a Wemer-Pfleiderer or a Baker Perkins... 

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. 

In some resole appHcations, such as foam and foundry binders, a rapid cure of a Hquid resin is obtained at RT with strong acid. The reactions proceed in the same manner as those of novolak resin formation. Methylol groups react at ortho and para phenoHc hydrogen to give diphenyknethane units (41). 

There are explosion hazards with phthahc anhydride, both as a dust or vapor in air and as a reactant. Table 11 presents explosion hazards resulting from phthahc anhydride dust or vapor (40,41). Preventative safeguards in handling sohd phthahc anhydride have been reported (15). Water, carbon dioxide, dry chemical, or foam may be used to extinguish the burning anhydride. Mixtures of phthahc anhydride with copper oxide, sodium nitrite, or nitric acid plus sulfuric acid above 80°C explode or react violently (39). 

Polyall lene Oxide Block Copolymers. The higher alkylene oxides derived from propjiene, butylene, styrene (qv), and cyclohexene react with active oxygens in a manner analogous to the reaction of ethylene oxide. Because the hydrophilic oxygen constitutes a smaller proportion of these molecules, the net effect is that the oxides, unlike ethylene oxide, are hydrophobic. The higher oxides are not used commercially as surfactant raw materials except for minor quantities that are employed as chain terminators in polyoxyethylene surfactants to lower the foaming tendency. The hydrophobic nature of propylene oxide units, —CH(CH2)CH20—, has been utilized in several ways in the manufacture of surfactants. Manufacture, properties, and uses of poly(oxyethylene- (9-oxypropylene) have been reviewed (98). 

Water, in small amount, reacts with the diisocyanate to generate carbon dioxide, and amine and is used most frequendy as the foaming agent. Polyurethanes have been treated in detail in the Hterature (66—68). 

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