Flame-retardant rigid foams

Flame-Retardant Rigid Urethane Foams. The major applications of rigid urethane foams are in the appliance and building industries. The latter requires strictly flame-retardant rigid foams, because serious rigid urethane foam fires have been reported in the housing, construction, and ship-building industries. 

Flame-retardant rigid foams can be classified by the testing methods employed, but the results do not reflect actual fire situation. Fire-retardant rigid urethane foams can be prepared by using flame retardants of the additive type, reactive type, or a combination thereof. A review of flame retardants for polyurethane foams has been prepared by Hilado (154). 

Another route to flame-retardant rigid foams is the use of flame-retardant polyether polyols which contain phosphorous and halogen (reactive type). In recent years, due to the fire-gas toxicity caused by halogen-, phosphorous- or nitrogen-containing flame retardants, other types of flame-retardants which do not produce toxic gases are being developed. 

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. 

Witte, A. and Krieger, W., (Clariant GmbH), Halogen-free, pentane-blown, flame-retardant rigid polyurethane foam and a process for its production, U.S. Patent, 2001 6 593 385. 

Sivriev, C. Zabski, L. Flame retarded rigid polyurethane foams by chemical modification with phosphorus-and nitrogen-containing polyols. Fur. Polym. J. 1994, 30, 509-514. 

The high flammability and toxic-gas generation of flexible and rigid urethane foams have been major problems in the urethane-foam industry, and accordingly considerable efforts have been focused on the production of substantially flame-retardant flexible foams. 

All the triazinic polyols discussed here, have a high thermostable triazinic structure and a high nitrogen content, which gives inherently flame retardant, rigid PU foams [24]. 

A flame retarded rigid PU foam needs around 20-25% chlorine or 5-6% bromine or 1.5-2% phosphorus [1, 2, 4, 11]. During the history of PU many reactive flame retardants were developed, but only a few are used effectively in practice. 

Bromine containing polyols are very effective, reactive flame retardants. One of the most representative bromine polyols used in rigid and flexible flame retardant PU foams is 2,3 dibromobutene diol (Figure 18.3) [25] ... 

Very interesting reactive flame retardants were used successfully in the fabrication of flame retardant rigid PU foams by Solvay under the name of Ixol polyols. These polyols are triols based on epichlorohydrin and brominated unsaturated diol. Ixol polyols have chlorine, bromine and phosphorus in each structure [3, 44, 45]. 

Flame retardant rigid PU foams, due to their high aromaticity, and high crosslink density are easier to be obtain. An aromatic polyol has a supplementary contribution to improving the fire resistance (for example Mannich polyols, novolak polyols, triazinic polyols based... 

Dong, J.L. et al. 2007. Preparation of Flame-retardant Rigid Polyurethane Foam. China Plastics 21(12) ... 

Melamine cyanurate flame retardant, rigid PU foam Bis (2-chloroethyl) 2-chloroethylphosphonate Diethyl N,N-bis (2-hydroxyethyl) aminomethylphosphonate Diethyl... 

Tris (P-chloroethyl) phosphate plasticizer, flame retardant rigid PU foams Tris (P-chloroethyl) phosphate plasticizer, flame retardant rubber Diphenylcresyl phosphate plasticizer, flame retardant thermosets Tris (P-chloroethyl) phosphate plasticizer, flame retardant vinyl foams t-Butylphenyl diphenyl phosphate plasticizer, flame retardant vinyl nitrile foams t-Butylphenyl diphenyl phosphate plasticizer, flame retardant wood-resin composites... 

Chlorinated polyether Polysulphone Polytetrafluoroethylene Epoxy resin, amine-cured Epoxy resin, anhydride-cured The same filled with 65% of quartz flour The same filled with 65% of Al(OH)8 Epoxy resin, glass-laminated Epoxy resin, cycloaliphatic Expanded polystyrene Expanded polystyrene, flame-retardant Expanded polystyrene, extruded profile The same with flame-retardant Rigid polyurethane foam The same with flame-retardant Polysiocyanurate foam Flexible polyurethane foam Paraffin (candle)... 

Hilado conducted a comparative study on the flammability of great many flame-retarded polyurethane foam grades. The flammability of rigid polyurethane foams are markedly reduced by formation of an isocyanurate structure. The exploitation of this possibility is detailed in Section 5.1.5. 

A number of sugar-based polyols (e.g. derived from sucrose, a-methyl glucoside, dextrose, sorbitol, etc.) containing phosphorus in the form of phosphate, phosphite or phosphonate linkages have been reported for use in flame-retardant, rigid urethane foams (52-59). Recent reviews on flame-retardant urethanes incTu3e those of Papa ( 2) and Frisch and Reegen ( 3). 

Dimethyl Propylphosphonate (DMPP) [18755-43-6]. This liquid additive was recently introduced by Bayer as LEVAGARD DMRR, an alternative to the chloroalkyl phosphates for flame-retarding rigid polyurethane foams. 

Xu Wei, Wang Guojian, and Zheng Xiaorui. Research on highly flame-retardant rigid PU foams by combination of nanostructured additives and phosphorus flame retardants. Polym. Degrad. Stab. Ill no. 0 (2015) 142-150. 

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). 

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. 

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. 

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. 

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 the 1990s novel polyols included polyether-esters, which provided good prerequisites for flame retardancy in rigid foams and polyether carbonates with improved hydrolysis stability. 

There is also growing interest in multi-phase systems in which hard phase materials are dispersed in softer polyether diols. Such hard phase materials include polyureas, rigid polyurethanes and urea melamine formaldehyde condensates. Some of these materials yield high-resilience foams with load deflection characteristics claimed to be more satisfactory for cushioning as well as in some cases improving heat resistance and flame retardancy. 

Tris(2-chloroethyl) phosphate is used as a flame retardant in plastics, especially in flexible foams used in automobiles and furniture, and in rigid foams used for building insulation. No data on occupational exposure levels were available. Tris(2-chloroethyl) phosphate has been detected in drinking-water, river water, sea water and sediments in various parts of the world (IARC, 1990). 

The newer open-cell foams, based on polyimides (qv), polybenzimidazoles, polypyrones, polyureas, polyphenylquinoxalines, and phenolic resins (qv), produce less smoke, are more fire resistant and can be used at higher temperatures. These materials are more expensive and used only for special applications including aircraft and marine vessels. Rigid poly (vinyl chloride) (PVC) foams are available in small quantities mainly for use in composite panels and piping applications (see Flame retardants Hrat-rrststantpot.ymf.rs). 

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