Flame-retardant additives alumina trihydrate

Filled PVC compounds can be flame-retarded by alumina trihydrate. Figure 5.9 shows the burning time of flame-retarded PVC plasticized by 50 phr. of di-isooctyl phthalate. Extinction time after the ignition of a horizontal rod specimen at environmental temperature of 100 or 120 °C is plotted against the additive content. In Figure 5.10, differential thermal analysis (DTA) curves of the same PVC compounds are presented. 

Alumina trihydrate exerts its considerable flame-retarding effect only at a high proportion, i.e. when incorporated as a filler. For this reason, its application is essentially suitable in conventional filled compounds like polyesters, epoxy resins and PVC cable compounds, etc. " . The oxygen index of a polyester resin is plotted in Figure 5.4 against the proportion of this flame-retardant additive. 

For specific flame-retardant additives, see specific chemical type (e.g., alumina trihydrate). 

TrialkylPhosphates. Triethyl phosphate [78-40-0] C H O P, is a colorless Hquid boiling at 209—218°C containing 17 wt % phosphoms. It may be manufactured from diethyl ether and phosphoms pentoxide via a metaphosphate intermediate (63,64). Triethyl phosphate has been used commercially as an additive for polyester laminates and in ceHulosics. In polyester resins, it functions as a viscosity depressant as weH as a flame retardant. The viscosity depressant effect of triethyl phosphate in polyester resins permits high loadings of alumina trihydrate, a fire-retardant smoke-suppressant filler (65,66). 

Some inorganic fillers are used as flame retardants in rubber base formulations. Flame retardants act in two ways (1) limiting or reducing access of oxygen to the combustion zone (2) reacting with free radicals (especially HO ), thus acting as terminator for combustion-propagation reaction. The additives most widely used as flame retardants for polymers are antimony oxides and alumina trihydrate. 

Addition of fillers such as alumina trihydrate, antimony trioxide, molybdenum oxide [315], zinc borate and zinc borate complex [316] leads to increase in TS but decrease in elongation and NG migration/absorption. Addition of inorganic fillers also leads to increase in flame retardance. 

Dicylopentadiene Resins. Dicyclopentadiene (DCPD) can be used as a reactive component in polyester resins in two distinct reactions with maleic anhydride (7). The addition reaction of maleic anhydride in the presence of an equivalent of water produces a dicyclopentadiene acid maleate that can condense with ethylene or diethylene glycol to form low molecular weight, highly reactive resins. These resins, introduced commercially in 1980, have largely displaced 0 0-phthalic resins in marine applications because of beneficial shrinkage properties that reduce surface profile. The inherent low viscosity of these polymers also allows for the use of high levels of fillers, such as alumina trihydrate, to extend the resin-enhancing, flame-retardant properties for application in bathtub products (Table 4). 

Highly chlorinated paraffins can be used as secondary plasticizers to reduce flammability and smoke (48). Nonplasticizer additives to assist in flame-retarding plasticized PVC include antimony oxide, alumina trihydrate, zinc borate, and magnesium carbonate (49). 

In addition to smoke suppressors, reduced-smoking compounds are also available in a ready-to-process state. For example the Envirez grade of PPG Industries is a styrene-free polyester resin filled with alumina trihydrate. Its smoke production is between 10 and 100 according to ASTM E 84 measured in the Steiner Tunnel (cf. Fig. 3.93, Section 3.2.1), and its value in the NBS chamber (cf. Fig. 4.6, Section 4.1.1.4) is 89, while those of the conventional halogen-containing flame-retarded polyesters are 250 to 1100 (smoke production) and 102 (D value). 

Intumescents are said to have a key advantage over filler-type non-halogenated flame retardants in that they are effective at lower addition levels than traditional materials. For example, an intumescent based on ammonium polyphosphate will achieve the same level of protection at addition levels of 25 to 35 parts by weight (pbw) as atypical non-halogenated flame retardant, such as alumina trihydrate or magnesium hydroxide, at between 60 and 70 parts by polymer weight. 

The other, almost universaL additive is inorganic powdered fillers, used to increase viscosity, hardness, modulus, thermal conductivity, heat deflection temperature, opacity, and UV resistance, and to decrease exotherm, cure shrinkage, coefficient of thermal expansion, and cost. Calcium carbonate is the least expensive and most widely used. Clay gives higher electrical and chemical resistance. Talc gives high viscosity for gel coats and auto body repair. Alumina trihydrate gives flame retardance. 

Flame Retardants. Flame retardance can be built into the epoxy resin by use of tetrabromobisphenol A or anhydride curing agents containing phosphorus or halogen. It can also be helped by nonreactive additives such as alumina trihydrate or organo-halogens + antimony oxide. 

Metal hydroxides provide an important alternative to halogenated flame retardants. Aluminium trihydroxide, sometimes known as alumina trihydrate, is the most widely used of all FRs in plastics. Magnesium hydroxide is also finding increasing acceptance, and calcium hydroxide is being marketed as an additive for different reasons. 

Aluminium trihydrate (ATH) is also known as hydrated alumina. It is the most widely used FR additive in volume terms, representing 43% of all flame-retardant chemicals in volume (but only about 29% in value). As well as flame retarding and smoke suppressing, it is an economical filler/extender. In a fire, it undergoes an endothermic dehydration with a twofold action, simultaneously absorbing... 

Dispersion agents promote improved dispersion of fillers. This can be especially useful when high loadings of alumina trihydrate are required for low smoke, halogen-free flame-retardant formulations, but can also be effective in obtaining optimum performance from an impact modifier. A small addition to the resin allows more filler to be added without increasing the viscosity. 

Fillers and additives are specifically added to enhance the specific performance, reduce cost, change viscosity or improve processibility of resin systems (Owens Coming, 2003). Dry fillers usually make up the largest proportion (up to 50 wt%) of a resin formulation. Commonly used fillers in pul-trusion include calcium carbonate as a volume extender, alumina silicate or clay to build corrosion resistance and electrical insulation, and alumina trihydrate for better fiame or smoke retardation and electrical arc resistance. Additives are meant to tailor specific performance or properties. These typically include initiators to influence resin curing, mould release compounds such as metallic stearates or organic phosphate ester, antimony oxide for flame retardance, pigments for coloration and agents for surface smoothness and crack suppression. 

The role of mineral fillers in plastic compounds is changing. In the past they were used to reduce costs by replacing polymer content by a less expensive material. Now they have a more important role to play since their use can modify processing characteristics or the properties of the finished part. Other uses include their ability to reduce the content of more expensive additives, notably pigments, flame retardants and impact modifiers. Nanomaterials are coming to the fore as potential fillers along with the more traditional options of alumina trihydrate, barium sulfate, calcium carbonate, kaolin and talc. 

In general purpose applications competitively priced thermosets are used for the printed circuit board base material which is usually FR4 (Flame Retardant) . One of the main flame retardants used in America is to have tetrabromobisphenol-A reacted into the epoxy resin. Non-halogen systems include additives such as alumina trihydrate, alumina trihydrate/red phosphorus and aromatic phosphates. Flame retardant epoxy coatings are reported to use ammonium polyphosphate with char-forming additives. 

First there are additives which act to remove heat by endothermic decomposition and/or the generation of copious quantities of inert gases to dilute the combustible polymer degradation products. Materials such as alumina trihydrate (ATH) and magnesium hydroxide, which in toimage terms are by far the most widely used halogen-free flame retardants, work in this way. These additives are more fully described in the section Flame retardants inorganic oxide and hydroxide systems. ... 

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