Flammability reduction

Zammarano M, Kramer RH, Harris R, Ohlemiller TJ, Shields JR, Rahatekar SS, Lacerda S, Gilman JW. Flammability reduction of flexible polyurethane foams via carbon nanofiber network formation. Polym. Adv. Technol. 2008 19 588-595. 

Poly(vinyl chloride) (PVC) has a high level of chlorine and as a result is considered inherently flame retardant. However, in many circumstances further improvement in flammability reduction of PVC is desired. An efficient way to enhance flame retardation of PVC is by the addition of Sb202 as a synergist. Additive retardants based on halogen and/or phosphorus are also employed. 

Flammability reduction of various plastics by flame-retardant... 

Phosphorus compounds should be added to an extent of 1.5 to 2 per cent of phosphorus content in the foam. Above this level, no further flammability reduction is gained. Even 1 per cent of phosphorus is satisfactory in the presence of 10 to 15 per cent of chlorine, and in fact, the phosphorus level can be decreased to 0.5 per cent at 4 to 7 per cent content of bromine. Halogen-containing polyurethane foams are preferably supplemented with antimony trioxide synergent. 

Flammability reduction by formation of particular chemical structures... 

Gilman, J. W., Harris, R. H., Shields, J. R., Kashiwagi, T., and Morgan, A. B. 2006. A study of the flammability reduction mechanism of polystyrene-layered silicate nanocomposite Layered silicate reinforced carbonaceous char. Polymers far Advanced Technologies 17 263-271. 

The investigation on the mechanisms of thermal stabilisation and flammability reduction in nanocomposites reveals that an addition of organoclays into a thermoset resin can substantially aid flame retardancy by encouraging the formation of a carbonaceous char in the condensed phase [118, 119]. The nanoscale dispersed lamellae of clay, either intercalated or exfoliated in polymer matrix, all enhance the... 

The researchers suggest that their work proposes a method for lowering the flammability of polymeric materials by modifying their morphology. With blends of polypropylene and ethylene/propylene terpolymer from 61.5 to 37.5% PP, a method for ecologically safe flammability reduction of composites has been shown. 

Miscellaneous chemicals are used to modify the flnal properties of rigid polyurethane foams. For example, halogenated materials are used for flammability reduction, diols may be added for toughness or flexibility, and terephthalate-based polyester polyols may be used for decreased flammability and smoke generation. Measurements of flammability and smoke characteristics are made with laboratory tests and do not necessarily reflect the effects of foams in actual fire situations. 

Processing conditions also strongly influence the flame-retardant behavior. For example, in the case of PS-based nanocomposites, extrusion above 180°C imder partially oxidative conditions yields an intercalated nanocomposite but with no flammability improvement, whereas the melt-extruded system at 170°C imder nitrogen or vacuum exhibits flame-retardant efficiency (41). The way thermal degradation of the organic modifier alters the flammability reduction mechanism has yet to be imderstood. 

Fuel tank flammability reduction means. Advisory circular AC No. 25.981-2A (2008), p 28... 

The type of nanocomposite structure or dispersion is controlled by many factors, all of which must be considered to produce a polymer nanocomposite successfully (Chapters 2 and 4) the extent of flammability reduction observed in a nanocomposite is due to the nanoflUer dispersion and polymer degradation chemistry (Chapters 3, 5, and 10). 

The mechanism of flammability reduction for polymer nanotube and nanofiber nanocomposites (Chapter 10) is similar to that for clays a nanofiUer-rich surface or barrier forms, which slows the rate of mass loss and therefore the rate of heat release. There is little reduction in the total heat release, indicating that the carbon nanoflbers and nanotubes only reduce the flammability of the... 

A trend that has already begun to arise is the use of multiple types of nanofillers in the same polymer to yield a multicomponent nanocomposite. Some workers have found that some types of nanofillers cannot bring all of the desired properties to the final material, so clays have been combined with multiwall carbon nanotubes to bring enhanced properties.The observation for most polymer additives is that they cannot be used for all applications in all polymers, and the same observation will surely be made about nanocomposites. A clay may be used to enhance the flammability performance, bnt it could also be combined with a conductive nanoflller to impart antistatic aspects or electrical conductivity in the final system. One potential way to look at the use of multiple nanoparticles is that each nanoparticle plays a complementary role in flammability reduction. For example, one could choose a clay for mass loss rate or fuel release reduction, but then use a colloidal particle to flu in the gaps between clay plates as the nanocomposite thermally decomposes. Perhaps even more useful, the colloidal particle could have catalytic or flame retardant properties that encourage... 

The use of nanocomposites to reinforce traditional composites has also been increasing and will continue to be a near-term trend. The emphasis for these applications, however, has been on additional mechanical reinforcement rather than flammability reduction.Since more traditional fiber-filled composites are exposed to fire risk scenarios, it makes sense to use a nanocomposite with the traditional composite to improve both mechanical and flammability performance. Of course, this does create an additional level of complexity, especially in handling the large increases in viscosity seen with nanocomposites used with thermoset composites. At this time, most nanocomposite-fiberglass/carbon fiber composites are used for military and aerospace applications, but the benefit of lightweight materials may also move these materials into automotive and mass transportation (e.g., bus, rail), where flammability performance is strongly needed. 

Since a polymeric material can reduce flammability and improve mechanical and thermal properties and possibly other properties as well, there is a great deal of promise that polymeric nanocomposites will not just meet this need for flammability reduction, but also exceed it, thus providing fire safely and improved properties for a wide range of consumer goods. 

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