With improved flammability

WHANG PEARCE Polymers with Improved Flammability Characteristics 267... 

It is known that increased char yield is usually associated with improved flammability behavior ( 1). This can be understood if one considers that the volatile flammable products can only diffuse with difficulty through the char, and that the thermal conductivity of a porous char layer is relatively poor (2). The structure of the polymer can contribute to the amount of char formed based on the character of the functional groups present and the nature of the backbone (2,3). Ritchie ( ) found that for a series of unsaturated polyesters and their copolymers, the temperatures at which carbon dioxide is eliminated was in the range of 280 to 345°C depending on the structure of the polyester. Aliphatic polyesters and their copolymers have less thermal... 

It has been reported that approximately 12 persons are killed and 120 are severely injured because of fire every day in Europe. Fire has considerable impact on the environment in terms of destmction of substructures and production of toxic and/or corrosive compounds such as CO, dioxins, HCN, and polycyclic aromatic compounds. Consequently, it is necessary to limit this kind of risk by designing new materials with improved flammability properties. Nowadays, many companies (building and civil engineering, transportation, cable-making and electrotechnical material, etc.) are directly concerned with this topic. 

In summary, new brominated flame retardants have essentially met the challenge for thermoplastics that do not meet current requirements (e.g. a V-0 rating) without additives. More stringent flammability requirements for advanced materials and applications, coupled with improved test methodology (e.g. lOa-b) may shift the focus of research to other approaches. 

Polyimide and Melamine. These are both low density, essentially open-cell foams used as pipe insulations, particularly those involved with fluids operating at temperatures up to 530 K. Because these foams operate at higher temperatures and have improved flammability characteristics compared to other foams, they are also used for some aircraft and marine applications. 

Since disperse dyes diffuse very slowly into PES fibers, efforts have been made to increase the rate of dye strike by chemical or physical alteration of the fiber. The fiber is also modified to reduce the pilling tendency, to increase shrinkage and elasticity, and to reduce flammability. Such modified fibers exhibit improved dye receptivity. Fibers with improved dyeability can be dyed with disperse dyes at boiling temperature without a carrier or with basic dyes when they are modified with acidic components (5-sulfoisophthalic acid). Fibers of this type are used if dyeing cannot be carried out easily above 100°C (e.g., in the case of floor coverings, articles made of PES-wool blends, stretch materials, and cord). Strongly crimped PES bicomponent fibers are produced for special purposes. These fibers are normally also dyeable at the boil and without a carrier [136, 137, 138],... 

The flammability properties of an intumescent fire retardant PP formulation with added MH has been investigated.65 The results show that the intumescent flame-retardant ammonium polyphosphate-filled PP has superior flammability properties but gives higher CO and smoke evolution. The addition of MH was found to reduce smoke density and CO emissions, in addition to giving superior fire resistance. PP filled with ammonium polyphosphate, pentaerythritol, and melamine has given improved flammability performance, without reducing its mechanical properties. 

ABS foam provides properties that include impact, heat, and chemical resistance low mold shrinkage rates good long-term dimensional stability and platability. Improved flammability characteristics are possible either by alloying (blending) with PVC or polycarbonate, or by... 

Intrinsically non-flammable polymers are few, but phenolic resins have a good reputation both in Are and smoke performance, which has resulted in their becoming increasingly favoured for reinforced plastics structures, for example, underground transport, where such concerns are greatest. Polyether ether ketone (PEEK) is also a low fire and smoke polymer. Unsaturated polyesters, vinyl esters and epoxy resins bum readily, but modified versions are available with improved behaviour. For example, both bromine and chlorine are used extensively in the form of chlorendic (HET) acid, tetrachlorophthalic anhydride (TCPA) and tetrabromo-phthalic anhydride (TBPA) which can be reacted into the polyester in small quantities and can act as permanent (non-migrating) flame retardants. 

Hazardous Decomp. Prods. Combustion boron oxide reaction with water releases methane NFPA Health 4, Flammability 4, Reactivity 3 Storage Handle only in sealed, purged systems store cylinders below 55 C away from direct sunlight, precipitation, mech. damage Uses Synthesis reagent as reactor fuel additive/surf. treatment doping material in semiconductor materials in amorphous devices for depositing a p-type silicon-carbon alloy with improved optical props. 

This present English edition is not a direct translation of the Hungarian version. It has been thoroughly revised, principally because of the continuing rapid development of plastics. A couple of years is enough for the manufacture of a range of novel resins and products with markedly improved flammability characteristics. Brand-new concepts and products have appeared in the interval since the Hungarian edition was published, so that some chapters had to be completely re-written. The other chapters have also been carefully revised and supplemented as necessary. 

Work in Italy by Montell (now part of Basell) and Turin University examined the optimum mix of melamine with other mineral fillers to obtain the best balance of properties. The addition of melamine to mineral FRs for polypropylene improves flammability behaviour as measured by UF94 and eliminates the afterglow phenomenon. However the melamine is not sufficiently thermally stable and requires special precautions in processing. It does, though, lower the compound density, which is an economic advantage and allows use of cheap inert fillers such as clay or talc. 

Europeans are enthusiastic about hydrocarbons like cyclopentane as blowing agents, and have not had too many problems with their flammability. Replacing 10% of the pentane by isobutane is said to allow the production of foams with improved insulation and mechanical properties and lower material costs. US manufacturers have observed the success of the European hydrocarbon policy and its safety record (despite fears about flammability) and are also beginning to use pentane. Several producers in South America, Australia and much of Asia have already moved to hydrocarbons, which are sold by petrochemical companies and their subsidiaries. Market share held by hydrocarbons is over 50% in some sectors of the foamed plastics industry. 

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. 

Compounding can assist with the limited combustible requirements mentioned above. Although j ackets made with perfluoroplastic have been around since the advent of the plenum specifications, their market share has declined due to low productivity and relatively high cost. New products that combine compounding technology with the inherently low fuel load of perfluorinated polymers promise to open new windows for jacket compounds that possess the low flammability of perfluorinated resins combined with improved processibility. 

Although the incorporation of microscale particles as fillers into polymers has been well explored scientifically, the decrease in size of particles to nanometers, and the simultaneous increase in interface area, results in extraordinary new material properties.In one such application, the flammability properties of polymers have been improved with the addition of nanoscale particles. These filled nanocomposites provide an attractive alternative to conventional flame retardants. At present, the most common approach to improving flammability is the use of layered silicates such as clays, as described in Chapter 3. However, there are many different shapes and types of nanoparticles. (Here, a nano scale particle is defined as having at least one dimension on the nanometer scale.) When all three dimensions are on the order of nanometers, we are dealing with true nanoparticles, such as spherical silica particles, having an aspect ratio of 1. Another type of nanoparticle has only one dimension on the nanometer scale. Such nanoscale... 

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