Thermosets flammability

The binder system of a plastic encapsulant consists of an epoxy resin, a hardener or curing agent, and an accelerating catalyst system. The conversion of epoxies from the Hquid (thermoplastic) state to tough, hard, thermoset soHds is accompHshed by the addition of chemically active compounds known as curing agents. Flame retardants (qv), usually in the form of halogens, are added to the epoxy resin backbone because epoxy resins are inherently flammable. 

Thermosets and thermoplastics behave differently from each other in fires. Thermosets do not melt when heated but may well undergo further crosslinking. The presence of such additional crosslinks hinders movement of any volatile degradation products through the polymer matrix. Hence the combustion zone tends to be starved of fuel and for this reason thermosets tend to be relatively non-flammable. 

Flammability. Presence of chlorine, fluorine, bromine, or phosphorous in a polymer reduces flammability. Thermosets are more flame-resistant than thermoplastics. 

SCHEME 2.5 Initial chain scissions in polyester.53 (From Levchik, S.V., Thermosetting polymers, in Plastics Flammability Handbook, Troitzsch, J. (ed.), Hanser, Munich, 2004, pp. 83-98.)... 

The predominant mode of action of phosphorus-containing flame retardants (both additives and reactives), when present in thermoplastics or thermosets, is considered to be in the condensed phase. Generally, as with cellulose, flammable gas generation is reduced and char formation is promoted. In some cases, the char cohesiveness is also enhanced. The retention of phosphorus in the chars in... 

The mechanical strength and operating temperature of plastics are low compared with that of metals. The mechanical strength, and other properties, can be modified by the addition of fillers and plasticisers. When reinforced with glass or carbon fibres thermosetting plastics can have a strength equivalent to mild steel, and are used for pressure vessels and pressure piping. Unlike metals, plastics are flammable. Plastics can... 

The polymer eomponent, whieh is a thermosetting resin, forms eross-linked bonds between chains of molecules, whieh enhanees the eharacteristic of the produet. Unsaturated polyesters and vinyl esters are primarily used as resin systems. Epoxies are also used in some eases, but the eure eyele is longer. Phenolic resins have gained importanee these days because of their inherent properties, especially in applications that require lower flammability, reduced smoke generation, and higher thermal stability. New resin systems such as... 

Thermosets. Fire retardancy in thermosetting polymers is achieved largely by the use of reactive fire retardants because the common fire-retarding additives lack permanence. The flammability of thermosetting materials can be reduced by the additions of inorganic fillers and/or reactive flame retardant components. Flame-retardant vinyl monomers or other cross-linking agents are also frequently employed. 

EXPLOSION and FIRE CONCERNS combustible NFPA rating Health 1, Flammability 2, Reactivity 1 flammable when exposed to heat or flame moderately explosive upon exposure to heat or flame autopolymerizes explosively with aeid catalysts to form a thermoset-... 

Thermoset composite systems of phenol and formaldehyde, some of which can he substituted for a number of structural applications can also be considered as engineering plastics and they have been in use for a very long time. In recent applications, improved urea - melamine resins have been used as matrices more and more for composite systems, because of their non-melting, high thermal and chemical resistances, hardnesses, mechanical-dimensional stabilities and low flammabilities. 

Reinforced thermoset composites of UP are used extensively because of their non-melting, high thermal and chemical resistances, hardness, mechanical properties, dimensional stabilities and low flammabilities. 

Polymers in their raw state are usually technically unsatisfactory in one respect or another, such as their stability to light or heat, or their processability, or flammability, or colour, or opacity, or antistatic characteristics, etc., and they simply could not be used in commercial applications successfully without the incorporation of one or more additives [2] to modify behaviour. The additives are often present at very low concentrations (0.1-3 parts per hundred of resin, by weight) and are called stabilizers, UV absorbers, viscosity modifiers, lubricants, fire retardants, pigments, etc. Fillers may be present at 50 or even 150 parts per hundred of resin, by weight. Thermosetting resins tend to have fewer additives of the kind... 

HMIS Health 3, Flammability 1, Reactivity 1 Uses Coupling agent for plastics effects immobilization of enzymes sizing of glass fibers for making laminates filler for thermosets, thermoplastics as primer or additive, esp. in epoxy, phenolic, PU, vinyl plas-tisols and imide systems in food-pkg. adhesives Regulatory FDA 21CFR 175.105... 

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