Talc for Plastics and Rubber
Highly pure, laminar talc for plastic and rubber enhances the performance of polyolefin compounds such as polypropylene (PP).
The possible applications are virtually infinite. Talc is not only used in automotive plastics and household appliances, but also in food packaging such as acid-resistant keep-fresh packs and yoghurt pots, in laptop housings and in window profiles.
For example, used in PP pipes, say, for sewage water, talc increases rigidity, creep strength and impact resistance (particularly at low temperatures). This makes PP/talc the environmentally friendly alternative to PVC.
In motor vehicles, talc in polymer compounds stabilizes fenders and makes dashboards more scratch-resistant. It gives the plastic parts under the hood the strength they need.
Over the last 20 years, the market for wood-plastic composites (WPCs) has also developed strongly. Here too, talc offers decisive advantages in combination with the natural fibre: it reduces water absorption, shrinkage, deformation and creep. The elasticity modulus and shape retention temperature are improved.
Talc increases the modulus of elasticity of PP compounds and thus the stiffness of structures. This is the main function of talc in plastic. Talc grades with a high aspect ratio, i.e. an especially platy, laminar structure, are most efficient here. The fineness of the talc particles and the filler content (the proportion of talc in the overall mixture) also influence rigidity.
The addition of mineral fillers does not generally increase impact resistance. There are however, exceptions, such as the use of fine talc (like Finntalc M05SL) in polypropylene bumpers. In this case, 5 - 10% is added. Greater proportions result in a renewed drop-off in impact resistance.
Polypropylene/talc compounds are moulded into plastics parts, e. g. automotive bumpers. It is important that the parts are dimensionally stable and exhibit as little shrinkage as possible after moulding. The same goes for warpage or thermal expansion. A pure talc, with a low loss of ignition and a high aspect ratio, helps keep plastics parts dimensionally stable.
PP compounds are dyed in all imaginable colours. To enable reproducible colour hues, the colour of the talc should vary as little as possible. Finntalc from the talc manufacturer Mondo Minerals is purified using a highly sophisticated, self-developed talc flotation process that is closely monitored to ensure that the product is highly consistent.
Pure, soft talc acts as a lubricant, reducing the mechanical impact of the scratch as it happens. Grey talc can reduce the visibility of scratches.
Talc provides much higher heat conductivity than polymers. The heating and cooling of compounds is accelerated, cycle times are reduced, and productivity is improved.
Talc is the softest mineral of all, with a Mohs hardness of 1. Pure, chlorite-free talc grades result in extremely low abrasion values and thus high tool service life in compounding and extrusion.
Talc and particularly pure, fine, laminar grades significantly improve the creep strength of polymers. From our studies, we can make long-term predictions of creep strength with a high level of confidence. This is important, for example, with pipes that are buried in the soil, under load. Enriching polypropylene with talc is essential in order to prevent such products from deforming over the long term.
The crystallization of polypropylene is efficiently promoted by small amounts of extremely fine talc (e.g. with a median particle diameter of 2 µm or less). After the addition of talc, nucleation sets in at a higher temperature. Thus, the advantages of partial crystallization can be utilized in a much more targeted manner where desired. The addition of small amounts of talc also improves impact resistance.
Talc improves the mechanical properties of rubber compounds. It reduces gas permeability and electrical conductivity, increases resistance to UV radiation and provides good compression resistance. Also, processing is improved because of a decrease in rubber viscosity.