What is Talc?
The term talc covers a wide range of natural rocks and minerals, most of which are magnesium silicates. The pure talc mineral is a hydrous magnesium silicate, Mg3Si3O10(OH)2, which theoretically is 31.7 percent MgO, 63.5 percent SiO2, and 4.8 percent H2O. The crystal structure of pure talc is a brucite sheet (Mg12O12H4) sandwiched between two silica (SiO2) sheets, to form talc layers that are superimposed indefinitely. Each layer is electrically neutral. Adjacent layers are held together only by weak van der Waals forces.
This crystal structure has two consequences. First, talcs tend to form in plates. This platy structure gives talc many of its reinforcing performance properties in plastics.
Second, the weak van der Waals forces between the layers in the crystal can be easily overcome by rubbing. When you rub talc, those brucite and silica layers slide over each other, and the talc feels slippery. This is one of the reasons it is used in body and baby powders.
How is Talc Formed?
Talc is an alteration mineral. It is formed by geological modification of some host rock. Most talc is formed from the alteration of magnesite (MgO) in the presence of excess dissolved silica (SiO2). Altering serpentine or quartzite can also form talc. The different alteration routes form talcs that have significant differences in chemistry, color, morphology and impurities.
Because of the alteration method of formation and the multiple routes of talc formation into talc deposits – even if they are close in distance – can be very different. Thus, in any general discussion of talc care must be taken in applying all attributes to all deposits. Most commercial talc properties can be readily identified by their chemistry and mineralogy. Not all deposits are suited for all applications. Talc is characterized by softness, hydrophobic surface properties, chemical inertness and a slippery feeling. Some commercial talc may be harder because of the presence of impurities and associated minerals such as dolomite, calcite, tremolite and quartz. Talc is inert in most chemical reagents.
Application of Talc
Talc – the “secret ingredient”: colourless, odourless, imperceptible – insoluble and inert. Yet highly effective for so many applications. Most people use products made from talc every day, however, they don’t realize that talc is in the product or the special role that it plays.
Talc In Plastics
Talc imparts a variety of benefits to polypropylene, for instance higher stiffness and improved dimensional stability. In automotive parts (under-the-hood, dashboard, bumper interiors and exterior trim), household appliances and white goods. It requires advanced milling technology to obtain the finest talc without diminishing the reinforcing power of its lamellar structure. Talc also is used for linear low density polyethylene (LLDPE) antiblocking and as a nucleating agent in semicrystalline polymers. In polypropylene food packaging applications, talc is a highly effective reinforcing filler.
Talc In Paints
Most paints are suspensions of mineral particles in a liquid. The liquid portion of the paint facilitates application but after the liquid evaporates the mineral particles remain on the wall. Talc is used as an extender and filler in paints. The platy shape of talc particles improves the suspension of solids in the can and helps the liquid paint adhere to a wall without sagging. Powdered talc is a very bright white color. This makes talc an excellent filler in paint because it simultaneously serves to whiten and brighten the paint. Talc’s low hardness is valued because it causes less abrasion damage on spray nozzles and other equipment when paint is applied.
Talc In Paper
Most papers are made from a pulp of organic fibers. This pulp is made from wood, rags and other organic materials. Finely-ground mineral matter is added to the pulp to serve as a filler. When the pulp is rolled into thin sheets the mineral matter fills spaces between the pulp fibers, resulting in a paper with a much smoother writing surface. Talc as a mineral fillers can improve the opacity, brightness and whiteness of the paper. Talc also can also improve the paper’s ability to absorb ink.
Talc In Cosmetics
Finely ground talc is used as the powder base of many cosmetic products. The tiny platelets of a talc powder readily adhere to the skin but can be washed off easily. Talc’s softness allows it to be applied and removed without causing skin abrasion.
Talc also has the ability to absorb oils and perspiration produced by human skin. The ability of talc to absorb moisture, absorb odor, adhere to the skin, and serve as a lubricant and produce an astringent effect in contact with human skin make it an important ingredient in many antiperspirant.
Talc In Rubber
Talc reduces the viscosity of rubber compounds, thereby facilitating the processing of moulded parts. It also improves extrudate qualities, increasing production rates and enhancing UV radiation resistance of exterior parts such as automotive profiles. In sealants and gaskets, they provide good compression resistance, while in pharmaceutical stoppers, they create a barrier against liquids. In cables, talc functions as insulators and in tire manufacture it makes excellent processing aids.
Talc In Pharmaceutical
Talc is suitable for food products. Talc mineral is inert and passes through the body without being digested. It is thus approved as a carrier for food colorings and as a separating agent in such products as rice, powdered dried foods, cheese, sausage skins or table salt. The hydrophobic talc particles attach themselves to those of the food, protecting them and preventing clumping. In pharmaceuticals, talc is used primarily as a basis for powders. It is employed as an active agent and auxiliary agent. Talc is also suitable as a lubricant in pills.