Thermoplastics, fire retardants

As with other so-called engineering thermoplastics, the polyacetals are available modified with glass fibre, and may contain fire retardants, and some grades are blended with PTFE. In 1982 Hoechst introduced blends of polyacetals... 

Literatures are available on POSS-polymer composites synthesized from different thermoplastics [71-74]. These composites are lightweight and show good fire retardancy, thermal stability, and mechanical reinforcement. Literatures on POSS-rubber composites are yet to come in a big way. 

FIRE RETARDANT FILLERS. The next major fire retardant development resulted from the need for an acceptable fire retardant system for such new thermoplastics as polyethylene, polypropylene and nylon. The plasticizer approach of CP or the use of a reactive monomer were not applicable to these polymers because the crystallinity upon which their desirable properties were dependent were reduced or destroyed in the process of adding the fire retardant. Additionally, most halogen additives, such as CP, were thermally unstable at the high molding temperatures required. The introduction of inert fire retardant fillers in 1965 defined two novel approaches to fire retardant polymers. 

In most applications, polyester and vinyl ester resins are used as the matrix materials. Epoxies are also used, although they require longer cure times and do not release easily from the pultrusion dies. Hence, thermosetting resins are most commonly used with pultrusion, although some high-performance thermoplastics such as PEEK and polysulfone can also be accommodated. In addition to the resin, the resin bath may contain a curing agent (initiator, cf. Section 3.3.1.2), colorants, ultraviolet stabilizer, and fire retardant. 

In addition to the fire retardant fillers which are effective in their own right, a number of mineral fillers are used as components of fire retardant systems for thermoplastics. The principal one is antimony oxide. 

Electrical and office equipment enclosures, such as computer cases, copier cases and telecommunications equipment, are conventionally prepared from thermoplastic resins such as PC, ABS, and poly(propylene). These materials have the advantageous properties of toughness, flexibility and the ability to meet the UL specifications by including fire retardant additives. 

Joseph, P. and Ebdon, J. R., Recent developments in flame-retarding thermoplastics and thermosets, in Fire Retardant Materials, Horrocks, A. R. and Price, D. (Eds.), 2000, Woodhead Publishing Limited, Cambridge, U.K., pp. 220-263. 

The use of polyols such as pentaerythritol, mannitol, or sorbitol as classical char formers in intumescent formulations for thermoplastics is associated with migration and water solubility problems. Moreover, these additives are often not compatible with the polymeric matrix and the mechanical properties of the formulations are then very poor. Those problems can be solved (at least partially) by the synthesis of additives that concentrate the three intumescent FR elements in one material, as suggested by the pioneering work of Halpern.29 b-MAP (4) (melamine salt of 3,9-dihydroxy-2,4,8,10-tetraoxa-3,9-diphosphaspiro[5,5]-undecane-3,9-dioxide) and Melabis (5) (melamine salt of bis(l-oxo-2,6,7-trioxa-l-phosphabicyclo[2.2.2]octan-4-ylmethanol)phosphate) were synthesized from pentaerythritol (2), melamine (3), and phosphoryl trichloride (1) (Figure 6.4). They were found to be more effective to fire retard PP than standard halogen-antimony FR. 

This is the second most widely used fire-retardant filler. It is more expensive than aluminum hydroxide, but has a higher decomposition temperature (about 300°C), making it more suitable for use in thermoplastic applications where elevated processing temperatures are encountered. 

Hornsby, P.R. and Watson, C.L., Aspects of the mechanism of fire retardancy and smoke suppression in metal hydroxide filled thermoplastics, IOP Short Meetings Series No 4, Institute of Physics, London, U.K., April 1997, p. 17. 

Melamine diborate (MB), known in the fire-retardant trade as melamine borate, is a white powder, which can be prepared readily from melamine and boric acid. It is partly soluble in water and acts as an afterglow suppressant and a char promoter in cellulosic materials. Budenheim Iberica79 claims that, in a 1 1 combination with APP, MB (10%-15%) can be used for phenolic bound nonwoven cotton fibers. In general, melamine borate can be used as a char promoter in intumescent systems for various polymers including polyolefins or elastomers. However, its low dehydration temperature (about 130°C) limits its application in thermoplastics that are processed at above 130°C. Melamine borate is also reported to suppress afterglow combustion in flame-proofing textiles with APP or monoammonium phosphate to meet the German DIN 53,459 and Nordtest NT-Fire 002.80... 

Le Bras, M. and Bourbigot, S. 1998. Fire retarded intumescent thermoplastics formulations, synergy and synergistic agents-a review. In Fire Retardancy of Polymers—The Use of Intumescence, Le Bras, M., Camino, G., Bourbigot, S., and Delobel, R. (Eds.), Cambridge, London The Royal Society of Chemistry, pp. 64—75. 

Bourbigot, S. Le Bras, M. Breant, P. et al. Zeolites New synergistic agents for intumescent fire retardant thermoplastic formulations—criteria for the choice of the zeolite. Fire Mater. 1996, 20, 145-154. 

Burning may be considered another means of oxidation. Non-burning plastics are a must in commercial constructions according to building codes and are often required for automotive, electronic, and electrical applications. From the numerous thermoplastics, only the halogen-containing polymers, polyamides, polycarbonate, poly(phenylene oxide), polysulfone, and polyimides are self-extinguishing. Even these, such as poly (vinyl chloride), may become flammable when plasticized with a flammable plasticizer. Fire control can be the key to volume use of plastics. Polyester panels, urethane foam, and PVC tarpaulins account for nearly 90% of all fire retardants consumed. Consumption in 1967... 

In our studies we found that phosphonic acids (16), phosphinic acids (25), and phosphine oxides (17) are additives capable of imparting fire retardant properties to thermoplastic polymers. Tables I and II present data for some of these compounds when added to polyethylene or to poly (methyl methacrylate). The concentration reported is not necessarily the lowest effective concentration for the additive in the polymer. These additives also were effective in other thermoplastic polymers such as polystyrene, impact polystyrene, polypropylene and ABS. The compounds were completely compatible with the polymers. 

The mechanism of action of flame retardants in thermoplastic materials (polyethylene, polypropylene, polystyrene, cellulosics, PMMA, etc.) is unknown and is certainly quite complex. Broido (7) presented a good example in the difficulties of explaining how fire retardants work. He found that materials which were most effective in preventing flaming combustion of cellulose were also effective in causing sugar cubes to support flame ... 

The thermoplastic polymers we studied included the polyolefins as polyethylene and polypropylene the polyacrylates and methacrylates as poly (methyl methacrylate) styrene polymers including both clear and impact types and acrylonitrile-butadiene-styrene (ABS) plastics. Fire retardance was evaluated by the D-635 procedure as described previously (19). 

PCTs have chemical and physical features closely resembling those of PCBs [1, 10]. They are non-oxidizing, inert, permanently thermoplastic, of low volatility, non-corrosive to metals, not hydrolysed by water, and resistant to aggressive and corrosive chemicals like alkalies and strong acids. They impart fire retardant properties to other materials [1]. Most PCTs were produced as tech-... 

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