Home Education Fillers for Polymer Applications
In general, fire retardants are more expensive than their host polymers and are only added in order to meet regulatory requirements. If a particular polymer is used in a high-risk situation (mass transport, electrical and electronic, upholstered furniture, or certain construction applications) and it is too flammable, fire retardants may be incorporated to ensure that regulatory criteria are met.
The mid-1970s saw a surge in the commercial use of mineral fillers, due to legislation passed in the USA that required carpet backing to be of low flammability. ATH was found to be highly suitable for this purpose and its use has since infiltrated a multitude of other applications. In Europe, most of the market’s ATH is incorporated within polyolefins, due to the demand for “low smoke and fume” (LSF) electric cables, particularly in nondomestic buildings (in domestic buildings “PVC cables” are most common, although actually comprised of roughly equal portions of PVC, chalk, and plasticizer). Magnesium compounds, including MDH, were introduced into the plastics and polymers market in the late 1980s (Janshekar et al. 2011). The Western European ATH market in 2010 was valued at $232 million and that for magnesium compounds was $34 million (Janshekar et al. 2011).
Due to its relatively low decomposition temperature, ATH is limited to polymers that can be processed below 200 °C. Magnesium compounds present an attractive alternative and offer a wide range of applications and processing temperatures. Use of MDH is expected to increase as polypropylene replaces PVC in the automotive industry, where high temperatures require thermally stable materials. Hydromagnesite and huntite mixtures are used in a range of PVC compounds for cable and building products.
Table 6 End uses and applications for polymer - mineral filler composites
There are four types of ATH products on the market. Prices are given per kilogram based on value in 2010 (Janshekar et al. 2011).
Coarse - particle size = 40-80 ^m, $0.60-0.70 kg-1 Ground - particle size = 2.5-20 ^m, $0.50-1.00 kg-1 Precipitated - particle size = 0.8-2.5 ^m, $1.15-1.70 kg-1 Surface treated - e.g., silane, stearic acid - $1.72-2.40 kg-1
The selection of ATH type is based on the cost and performance requirements. Ground ATH tends to be selected when the performance to price ratio is advantageous over other fire retardant solutions, or where regulations require low smoke production. About half of ground ATH is used in thermosets, one fifth is used in carpet backings, another fifth goes into coatings and plaster, and the rest is used in paints and cable applications (Janshekar et al. 2011). Precipitated ATH is mainly used in the wire and cable industry, although its use in thermosets and rubber flooring is on the rise. The commercial use of surface treated ATH is small due to the high cost; however, it finds use in applications requiring increased water resistance (e.g., bathtubs made from unsaturated polyester or acrylic polymers) or particularly high loadings (Table 6).
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