Functions and Applications
The five main properties of talc that make it a unique substance for industrial and domestic applications are:
- Lamellarity (composed of platelets that slide off each other)
- Softness (unctuous and non abrasive)
- Chemical inertness
- Affinity for organic chemicals
Talc is used as an anti-sticking agent, an anti-caking agent, a lubricant, a carrier, a thickener, a strengthening filler, a smooth filler, and an adsorbent.
In many industrial processes, talc is used to prevent two materials from sticking together. Talc powdering of moulds is widely used for example in tyre manufacturing or foundry applications. Certain foodstuffs or conveyor belts are also powdered with talc, to excellent effect. Similarly, chip boards are powdered to stop them from sticking together in storage.
Talc is extensively used in animal feed. It wraps each feed particle, setting up a natural barrier that stops moisture escaping from or entering the treated feed. Talc also improves the fluidity of the material, which helps to keep equipment clean (minimising bacteria proliferation), lowers energy consumption, reduces production stoppages, and makes the operatorís job safer.
Talc is used as a lubricant in pharmaceuticals for example. As well as not reacting with active ingredients, it facilitates the ingestion of solid drugs (pills, powders, etc). Talc also helps mould and demould pills. It is widely used as a lubricant in the transport of dry materials.
The chemical inertness of talc is of obvious interest for carrier applications. Excipients in pharmaceuticals and cosmetics (dry or moist) are a classic example. Apart from its inertness, talc also has the advantage of not generating bacterial growth and of releasing fragrances progressively. Carriers are also critical in applications such as fertilisers and plant protection. Adding talc to active ingredients results in a well managed release, allowing the practical and safe handling of very small and very large quantities of active substances.
Talc is able to influence the viscosity of water- and solvent-based formulations. In paints for example, it increases covering power, improves flow and prevents settling. It also improves the adhesion and final mechanical properties of the coating. Talc enables paints, with the necessary low viscosities, to be formulated with significantly less organic solvents. The use of talc in the formulation of a range of liquid products (paint, cosmetics, glues, etc.) also contributes to controlling sedimentation rates during storage.
Talc is used to reinforce various types of resins, principally polypropylene (PP). Although the talc used in such applications is finely ground, it nevertheless maintains its lamellar structure. This gives the PP the best trade-off between rigidity and impact strength. Applications include domestic appliances, food packaging films and, above all, automotive components such as bumpers and dashboards. Talc is also used as a semi-reinforcing filler in rubber. Talc's properties bring benefits to ceramics (household, construction, refractory and technical). It reduces firing time and temperature, improves vitrification and consequently the resistance of the ceramic. It also improves thermal shock resistance, particularly important in catalytic exhausts.
Talc's smoothness is appreciated in products that require suppleness and smoothness. A typical example is colouring pencils which, for a smooth and regular effect, must be robust, but at the same time softer than the paper. In terms of volume, talc is also the principal ingredient in putties, particularly polyester putties where it improves adhesion and sandability.
Talc's adsorption properties, i.e. adsorbing onto the surface only, are key in a number of applications, particularly pitch control in paper making where talc is used to absorb organic impurities (pitch, unwanted anions) which are sticky. Talc also greatly improves printing runnability. As a filler in paper, it increases smoothness and machinability, reduces friction, abrasion and porosity. In paper coating, it helps to improve ink transfer, finish feel and legibility of printing. Talc's adsorption properties are also valuable in the treatment of waste water by the activated sludge method. Providing an adequate support surface, talc platelets actually "ballast" the bacteria used in such treatments, thereby improving sedimentation and avoiding the release of bacteria in the final clean effluent.