Active flame-retardant fillers

A second type of filler, called active flame-retardant fillers, is considered more effective than inert particles. Its operating mode involves not only fuel dilution, but also an additional cooling or heat sink effect. Indeed, these compounds are able to decompose at elevated temperature via eudothermic reactions which absorb energy and tend to slow down thermal degradation of the composite. Besides, inert gases (water vapour, carbou dioxide) are formed by the filler decomposition and contribute to diluting the concentration of combustible volatiles in the flame-environment. Common active flame retardant fillers are ... 

Use Glass, ceramics, iron-free aluminum and aluminum salts, manufacture of activated alumina, base for organic lakes, flame retardants, mattress batting. Finely divided form (0.1-0.6 microns) used for rubber reinforcing agent, paper coating, filler, cosmetics. 

Fillers such as magnesium hydroxide and aluminum trihydroxide are used as flame retardants because their decomposition product - water -is an active ingredient in flame retardancy. These fillers are discussed in detail in Chapter 12. 

Unsaturated polyester resins are mainly made by condensing a dibasic acid (1,2-propanediol) with an anhydride (maleic or phthalic anhydrides), by forming ester linkages between the dibasic acid (or their anhydrides) and glycols. Then a reactive monomer (mostly styrene or vinyl toluene, MMA or diallyl phthalate) is used to crosslink the system when needed. Unsaturated denotes the uncompleted chemical activity (double bond) in the original structure, which are used for crosslinking afterwards. In this context, an excess of styrene as the crosslinker (10 to 50 %) is usually added to have it ready in the system, as well as to reduce the viscosity. There are also certain accelerators used (such as, cobalt naphthenate or tertiary amines like dimethyl aniline) to facilitate the cure at ambient temperatures. In addition, there may be pigments, fillers, various inhibitors, accelerators, stabilisers and flame retardants, added to the system. Polymerisation is activated whenever a catalyst (i.e., benzoyl or methyl-ethyl-ketone peroxide) is added. 

The types of additives discussed here lead to important physical changes. Thus blowing agent use permits the production of cellular structures flame retardants improve thermal and combustion characteristics pigments and colorants change the aesthetic aspect while physical and mechanical properties are modified by active fillers and reinforcements. 

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