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Coupling Agents In Treated Fillers
Jun 11, 2018

Coupling Agents in Treated Fillers


Mineral fillers, such as calcium carbonate (CaCO3), clays, silicas, mica, talc, alumina trihydrate (ATH) and titanium dioxide, account for the lion's share (about 90%) of the demand for fillers and extenders, with CaCO3 being by far the most commonly used filler. Non-mineral fillers and extenders include carbon black, glass beads and various organic materials.

Among the thermoplastics, PVC accounts for about 70% of the demand for fillers, with PP, nylon and polyester together accounting for another 20%. It is estimated that more than 2 million tonnes of treated fillers are consumed annually in the manufacture of thermoplastics. Natural calcium carbonate (treated with fatty acid) accounts for more than 80% of that total. In terms of volume, the main fillers treated with coupling agents for incorporation in thermoplastics are ATH, calcined clays, wollastonite (calcium metasilicate) and mica, together consuming about 2,500 tonnes of coupling agents per year.

The annual requirement for treated fillers in elastomers is reported to be in excess of 500,000 tonnes, of which about 70% employ coupling agents. More than 10,000 tonnes/year of coupling agents of various types are used, with silanes predominating for the treatment of precipitated silica and clays. In fact the use of precipitated silicas treated with sulphur-functional silanes (such as Degussa's 'Si 69') in rubbers represents the single largest market for any coupling agent. This silica/silane technology is best known for its application in 'green' car tyres but has also enabled silica-filled rubbers to be used in a variety of demanding applications such as industrial rollers and shoe soles.

For thermosets the picture is complicated by the prevalence of in-situ coating and the use of mineral fillers in conjunction with glass fiber. Annual treated filler usage is estimated at under 100,000 tonnes consuming less than 1000 tonnes of coupling agents, the main fillers being ATH, natural silicas and mica.