Fire-retardant fillers efficiency

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 combination of melamine with hydrated mineral fillers can improve the fire retardancy behavior of PP, eliminating at the same time the afterglow phenomenon associated with these fillers used in isolation.70 Similarly in EVA copolymer, antimony trioxide used in combination with metal hydroxides has been reported to reduce incandescence.56 Chlorinated and brominated flame retardants are sometimes used in combination with metal hydroxides to provide a balance of enhanced fire-retardant efficiency, lower smoke evolution, and lower overall filler levels. For example, in polyolefin wire and cable formulations, magnesium hydroxide in combination with chlorinated additives was reported to show synergism and reduced smoke emission.71... 

Kimura et al. [107] made a light resistant formulation of a block E-P copolymer by extruding it at 220 °C with Mg(OH)2, and 2-hydroxy-4-octoxybenzophenone. The injection molded product (at 800 kg cm pressure) shows fire retardation also due to MgO filler and the benzophenone derivative is an efficient UV absorber. 

High efficiency in char formation is one of the reasons for the strong performance of Mg(OH)2 and A1(OH)3 as fire retarding additives. This performance can still be enhanced by surface coating the fillers with zinc hydroxystannate. Sb2O3 is volatized from the material and therefore does not affect char formation. Formation of char is an effective method of increasing the fire resistance of materials. The material which forms carbonaceous char has a reduced ability to supply the gaseous fuels required to fuel the fire. 

In general, when compared with the conventional polymer composites, polymer nanocomposites exhibit significant improvements in different properties at relatively much lower concentration of filler. The efficiency of various additives in polymer composites can be increased manyfold when dispersed in the nanoscale. This becomes more noteworthy when the additive is used to address any specific property of the final composite such as mechanical properties, conductivity, fire retardancy, thermal stability, etc. In case of polyolefin/LDH nanocomposites, similar improvements are also observed in many occasions. For example, the thermal properties of PE/LDH showed that even a small amount of LDH improves the thermal stability and onset decomposition temperature in comparison with the unfilled PE [22] its mechanical properties revealed increasing LDH concentration brought about steady increase in modulus and also a sharp decrease in the elongation at break [25]. While in this section, fire-retardant properties and electric properties of polyolefin/LDH nanocomposite were described in detail. 

Limiting oxygen index (LOI) is the parameter most frequently used to characterize the improvements in fire retardancy. " " " " " Table 12.2 gives a summary of data obtained for various fillers. The data in Table 12.2 show that even the addition of very common and inexpensive fillers such as calcium carbonate or talc increases the LOI value. From the data presented, Sb203 and Mg(OH)2 are the most efficient in increasing LOI. 

Magnesium hydroxide filler treated with magnesium stearate has improved filler/matrix interaction and maleic anhydride functionalized EPR increased impact strength. The composition is very efficient in fire-retarded PP [20]. 

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