Carbon foam flame retardant

Polycarbonates are prepared commercially by two processes Schotten-Baumaim reaction of phosgene (qv) and an aromatic diol in an amine-cataly2ed interfacial condensation reaction or via base-cataly2ed transesterification of a bisphenol with a monomeric carbonate. Important products are also based on polycarbonate in blends with other materials, copolymers, branched resins, flame-retardant compositions, foams (qv), and other materials (see Flame retardants). Polycarbonate is produced globally by several companies. Total manufacture is over 1 million tons aimuaHy. Polycarbonate is also the object of academic research studies, owing to its widespread utiUty and unusual properties. Interest in polycarbonates has steadily increased since 1984. Over 4500 pubflcations and over 9000 patents have appeared on polycarbonate. Japan has issued 5654 polycarbonate patents since 1984 Europe, 1348 United States, 777 Germany, 623 France, 30 and other countries, 231. 

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. 

Flame Retardance. The most important reason for phenolic foam being an excellent flame retarder is that the phenolic polymer is easily carbonized and the char part formed as a result is highly stabilized. This mechanism of char-formation is considered that of a multi-aromatic ring with chemically stabilized strong bond formed through a dehydrogenation reaction by heating and oxidation. 

Expanded polystyrene is also produced by extrusion of the melt containing a volatile solvent, or more recently carbon dioxide, through a slit. The pressure drop caused by the emergence of the molten polymer from the slit of the extruder allows the hot solvent to rapidly vaporize, and in the process expands the extruded shape to an extent related to the temperature and proportion of solvent used. When carbon dioxide is used as the blowing agent, its expansion on emergence of the melt from the slit can perform the same function. This product is referred to as extruded polystyrene foam. Some manufacturers incorporate a flame retardant into grades intended for construction. 

An important way of inhibiting the ignition of polymeric materials is to increase the formation of carbonaceous chars at the expense of combustible fuels. Ammonium phosphate has been used for many years as a flame retardant for cotton and is known to work by catalysing the formation of carbon and water. It is also effective in poly(urethane) foams which form a major component of much domestic upholstery. 

Intumescents function because, under fire conditions, they foam to produce an insulating carbon char which both protects the substrate from high temperatures and allows only a small proportion of polymer to be involved in the fire. Heat release can be controlled because the surface of the char nearest the flame will ablate, so absorbing energy. This contrasts with conventional flame retardants that absorb energy by endothermic chemical decomposition or liberation of water, or by altering the polymer s surface chemistry to slow down oxygen access. 

It has also been diseovered that potassium earbonate enhances the charring of polymers containing pentaerythritol-silica combinations as flame retardants. This has led to the discovery of base-catalysed intumescence of potassium bitartrate. Combinations of potassium bitaitrate and pentaerythritol show improved intumescence but carbon char oxidation by glowing combustion has remained a problem. Base catalysis is an attractive alternative to conventional acid-catalysed intumescent flame retardant systems as it could help to alleviate corrosion problems during polymer processing. Unfortunately, strongly basic residues also catalyse the oxidative destruction of the char-foam at high temperatures. 

Changing methods to produce flexible foam, by the replacement of fluorocarbon blowing agents in many cases with carbon dioxide, have brought consequences for the choice of flame retardant... 

When plastic or other materials that contain APP are exposed to an accidental fire or heat, the flame retardant starts to decompose commonly into polymeric phosphoric acid and ammonia. The polyphosphoric acid reacts with hydroxyl or other groups of a synergist to form an unstable phosphate ester. Dehydration of the phosphate ester then follows. Carbon foam is built up on the surface against the heat source (charring). The carbon barrier acts as an insulation layer, preventing further decomposition of the material. 

C in TG-FTIR measurement (792 cm ) of a brominated polystyrene sample [365]. On-the-spot TG-FTIR of PBT/octabromodiphenyl ether (MW 801 Da) detected the brominated diphenylether flame retardant at 275° C and terephthalic acid (the starting monomer of PBT) at 425°C [310]. Similar high-MW species have never been reported in TG-MS experiments the flame retardant was not observed in off-line TG-GC-FTIR-MS analysis. In an examination of an ABS/PC blend with 8% triphenylphosphate (TPP), in addition to the EGP, the SGPs for the specific wavenumber windows of TPP (900-1200 cm ), aromatic compounds (3000-3100 cm ), and carbon oxides originating from PC (2200-2300 cm ), were obtained. TPP evolving first was detected at about 150°C (detection limit 0.5 /xg/s) [310]. Anthony [366] has used FTIR spectroscopy to examine TG residues and diffuse reflectance as the means of sample preparation for the study of interactions between pyromellitate polyesters (smoke suppressants) and polyurethane foams. This was achieved by interrupting the thermal analysis at selected points on the TG curve. In... 

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