Urethane foam

Polyurethane is pulverized to iacrease its bulk density, mixed with 30—80% of a thermoplastic mol ding material, gelled, and then granulated to give coated urethane foam particles 0.1 to 0.15 mm in size (48). The particle bulk density is three times that of the polyurethane, while the volume is 15% less. This material may be injection molded or extmsion molded into products (49). Other technologies for recycling polyurethanes have also been reported. 

The amount and physical character of the char from rigid urethane foams is found to be affected by the retardant (20—23) (see Foams Urethane polymers). The presence of a phosphoms-containing flame retardant causes a rigid urethane foam to form a more coherent char, possibly serving as a physical barrier to the combustion process. There is evidence that a substantial fraction of the phosphoms may be retained in the char. Chars from phenohc resins (qv) were shown to be much better barriers to pyrolysate vapors and air when ammonium phosphate was present in the original resin (24). This barrier action may at least partly explain the inhibition of glowing combustion of char by phosphoms compounds. 

Antagonism between antimony oxide and phosphoms flame retardants has been reported in several polymer systems, and has been explained on the basis of phosphoms interfering with the formation or volatilization of antimony haUdes, perhaps by forming antimony phosphate (12,13). This phenomenon is also not universal, and depends on the relative amounts of antimony and phosphoms. Some useful commercial poly(vinyl chloride) (PVC) formulations have been described for antimony oxide and triaryl phosphates (42). Combinations of antimony oxide, halogen compounds, and phosphates have also been found useful in commercial flexible urethane foams (43). 

Oligomeric 2-ChloroethylPhosphate. Akzo s Fyrol 99 [109640-81-5] is produced either by self-condensation of tris(2-chloroethyl) phosphate (82) or by insertion of phosphoms pentoxide into this phosphate (82) followed by ethoxylation. It is low in volatihty and useful in resin-impregnated air filters, in flexible urethane foam, rebonded foam, and stmctural foam. 

The product is a hquid recommended for flame retarding flexible urethane foams in furniture or automotive seating. It also appears to be useful in polystyrene foam, textile backcoating, and polyester resins. 

Blends of triaryl phosphates and pentabromodiphenyl oxide are leading flame-retardant additives for flexible urethane foams. A principal advantage is their freedom from scorch. 

Triphenyl phosphate [115-86-6] C gH O P, is a colorless soHd, mp 48—49°C, usually produced in the form of flakes or shipped in heated vessels as a hquid. An early appHcation was as a flame retardant for cellulose acetate safety film. It is also used in cellulose nitrate, various coatings, triacetate film and sheet, and rigid urethane foam. It has been used as a flame-retardant additive for engineering thermoplastics such as polyphenylene oxide—high impact polystyrene and ABS—polycarbonate blends. 

Phosphorus-Containing Diols and Polyols. The commercial development of several phosphoms-contaiuing diols occurred in response to the need to flame retard rigid urethane foam insulation used in transportation and constmction. There are a large number of references to phosphoms polyols (111) but only a few of these have been used commercially. 

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. 

One noteworthy neurotoxic response was demonstrated in laboratory pyrolysis studies using various types of phosphoms flame retardants in rigid urethane foam, but the response was traced to a highly specific interaction of trimethylolpropane polyols, producing a toxic bicycHc trimethylolpropane phosphate [1005-93-2] (152). Formulations with the same phosphoms flame retardants but other polyols avoided this neurotoxic effect completely. 

Usage of phosphoms-based flame retardants for 1994 in the United States has been projected to be 150 million (168). The largest volume use maybe in plasticized vinyl. Other use areas for phosphoms flame retardants are flexible urethane foams, polyester resins and other thermoset resins, adhesives, textiles, polycarbonate—ABS blends, and some other thermoplastics. Development efforts are well advanced to find appHcations for phosphoms flame retardants, especially ammonium polyphosphate combinations, in polyolefins, and red phosphoms in nylons. Interest is strong in finding phosphoms-based alternatives to those halogen-containing systems which have encountered environmental opposition, especially in Europe. 

Methylenebis(4-phenyl isocyanate). This compound is also known as methyl diisocyanate [101-68-8] (MDI) and is produced by the condensation of aniline and formaldehyde with subsequent phosgenation. Its principal end use is rigid urethane foams other end uses include elastic fibers and elastomers. Total formaldehyde use is 5% of production (115). 

Glycerol is used in nearly every industry. The largest single use is in dmgs and oral care products including toothpaste, mouthwash, and oral rinses (Table 3). Its use in tobacco processing and urethane foams remains at a fairly even consumption level. Use in foods and cosmetics is growing. 

Urethane Polymers. An important use for glycerol is as the fundamental building block ia polyethers for urethane polymers (qv). In this use it is the initiator to which propylene oxide, alone or with ethylene oxide, is added to produce ttifunctional polymers which, on reaction with diisocyanates, produce flexible urethane foams. Glycerol-based polyethers (qv) have found some use, too, ia rigid urethane foams. 

Glycols such as neopentyl glycol, 2,2,4-trimethyl-l,3-pentaiiediol, 1,4-cyclohexanedimethanol, and hydroxypivalyl hydroxypivalate are used in the synthesis of polyesters (qv) and urethane foams (see Foamed plastics). Their physical properties are shown in Table 1 (1 6). 

This reaction is catalyzed by hydrogen chloride and yields can be essentially quantitative when using either free phosphonic acid or its diesters. The flame retardant, Eyrol 6, produced by Akzo Chemicals, Inc. and used for rigid urethane foams, is synthesized as follows (24). 

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. 

A few percent TCNE added during formation of urethane foams imparts enough conductivity to dissipate electrostatic charges. Airplane fuel tanks filled with this foam stiU have about the same volume for fuel but do not build up static charges (29). 

This reaction is of importance in the manufaeture of urethane foams. 

DUNNOLS, I., Basic Urethane Foam Manufacturing Technology, Technomics, Westport, Conn. (1979)... 

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