Retardant fillers

Flame-Retardant Filler. Demand has increased for Mg(OH)2 as a nonhalogenated, flame-retardant filler for thermoplastics used in the aerospace, microelectronics, and cable and wire manufacturing industries (90). Producers of nonhalogenated, flame retardant fillers include Kyowa, Aluisuisse-Lonza (Magnifin product line), Morton, and a Dead Sea Periclase/Dead Sea Bromine joint venture (91). 

Numerous variations in composition, appHcation method and surface treatment, and properties of Mg(OH)2-containing flame-retardant fillers are disclosed in the patent Hterature (92—95). Smoke-suppressant foams incorporating Mg(OH)2 are useful as roof insulation slabs (96). Mg(OH)2 is contained... 

After formulation with a flame retardant filler such as alumina trihydrate Al203 3H20, hydrated silica or calcium carbonate, a peroxide curing agent and... 

FIRE RETARDANT FILLERS. The next major fire retardant development resulted from the need for an acceptable fire retardant system for such new thermoplastics as polyethylene, polypropylene and nylon. The plasticizer approach of CP or the use of a reactive monomer were not applicable to these polymers because the crystallinity upon which their desirable properties were dependent were reduced or destroyed in the process of adding the fire retardant. Additionally, most halogen additives, such as CP, were thermally unstable at the high molding temperatures required. The introduction of inert fire retardant fillers in 1965 defined two novel approaches to fire retardant polymers. 

Anon. Martinal as a Flame-retardant Filler for Cables. 

Flame retardant fillers have been used for many years in thermosets, but have only recently begun to make an impression in the thermoplastics area due to the need to develop products sufficiently stable to withstand the higher processing temperatures involved. 

In addition to the fire retardant fillers which are effective in their own right, a number of mineral fillers are used as components of fire retardant systems for thermoplastics. The principal one is antimony oxide. 

It is self evident that mineral fillers need to be stable at the temperatures (up to 350 °C) experienced in processing thermoplastics. Most fillers are stable to much higher temperatures and so this is not usually an issue. However, it is a very important topic for flame retardant fillers which function by decomposing endothermically with the release of inert gasses. To be effective, this decomposition must occur near to the temperature at which the polymer begins to decompose and release flammable volatiles. This is usually not too much above the processing temperature in the case of thermoplastics and hence the exact temperature at which decomposition commences is of great importance. The size and position of the endotherm and the rate at which the inert gas is released are also of importance to the flame retardant effect itself [23]. 

Aluminium hydroxide has a Moh hardness of about 3 and a specific gravity of 2.4. It decomposes endothermically with the release of water at about 200 °C and this makes it a very useful flame retardant filler, this being the principal reason for its use in polymers. The decomposition temperature is in fact too low for many thermoplastics applications, but it is widely used in low smoke P VC applications and finds some use in polyolefins. For these applications low aspect ratio particles with a size of about 1 micron and a specific surface area of 4-10 m g are preferred. The decomposition pathway can be diverted through the mono-hydrate by the application of pressure, and this may reduce the flame retardant effect [97]. This effect can be observed with the larger sized particles. Although it is chemically the hydroxide, it has for many years been known as alumina trihydrate and by the acronym ATH. 

The viscoelastic properties of polypropylene melts containing magnesium hydroxide fire retardant fillers have been studied using parallel plate dynamic rheology [36]. In this work the filler variants differed in particle size, surface area and morphology, ranging from approximately spherical particles formed... 

A major drawback to the industrial use of fire-retardant fillers is the high addition levels needed in most polymers to confer adequate fire retardancy. This can detrimentally influence processability and melt rheology, and, when used in load-bearing situations, the presence of the filler generally... 

In this chapter, an overview is presented of the principal fire-retardant filler types, including details of their origin, characteristics, and application. Consideration will then be given to their mechanism of action both as flame retardants and as smoke suppressants, and to means for potentially increasing their efficiency using synergists and nanoscale variants. 

The following properties are ideally required for the successful commercial use of a fire-retardant filler 1... 

TABLE 7.1 Current and Potential Fire-Retardant Fillers Candidate Material Approximate Onset Approximate Enthalpy ... 

This is the second most widely used fire-retardant filler. It is more expensive than aluminum hydroxide, but has a higher decomposition temperature (about 300°C), making it more suitable for use in thermoplastic applications where elevated processing temperatures are encountered. 

Boehmite is, in effect, partly decomposed aluminum hydroxide, where two-thirds of the water has been removed. Although it has been promoted as a fire retardant in its own right, but because of the relatively low water content, does not seem to be very effective for this purpose. However, it does seem to have some potential in mixtures with other fire-retardant fillers and this is where it is now being targeted.6... 

It is well known that freshly formed oxides have high surface areas and in addition, can be cata-lytically active,52 thereby promoting both carbon deposition and subsequent oxidation processes.53 The reduced combustion rate arising from the effects of the fire-retardant filler also contributes to lowering the rate of smoke evolution and, by improving oxygen to fuel ratios, further limits levels of smoke density.1... 

Using this concept, it has been shown by cone calorimetry that over a 3 min combustion period, 3 and 6 mm thick laminated structures, made with different fire-retardant skin and unfilled core combinations can give similar resistance to ignition and comparable HRR and smoke extinction area (SEA) results to fully fire-retardant compositions (Table 7.4). Mechanical properties, in particular impact strength, were also found to be greatly enhanced by this approach, since less fire-retardant filler is present in the material. Whereas this approach has been demonstrated to be effective with hydrated fillers, it is applicable to all fire-retardant types. 

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