Plastics Industry and Talc
Plastics Industry uses highly pure, laminar talc to 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 yogurt 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 fiber: it reduces water absorption, shrinkage, deformation and creep. The elasticity modulus and shape retention temperature are improved.
The main reason for incorporating talc in plastics is to increase the stiffness (E-modulus). The degree of rigidity depends on the filling level, aspect ratio and fineness of the talc
2. THERMAL CONDUCTIVITY
Because of talc’s significantly higher thermal conductivity (compared to the polymer), the heat introduced and generated during processing is transmitted through the mixture more quickly. The heat is also transported out of the compound faster during cooling. Incorporating talc in a compound increases the thermal conductivity, resulting in faster production rates. Experience with filled polymers is that conductivity depends only on the filler content, within reasonable tolerances
The crystallisation of polypropylene is promoted by small amounts of preferably fine talc, which acts as a nucleating agent. Crystallisation starts at a higher temperature in the presence of talc, compared to unfilled PP. The impact strength is improved but this is primarily due to an increase in the crystallization of the PP and not the mechanical properties of the talc itself. There is also a change in modulus as a result of the change in crystallization.
4. IMPACT STRENGTH
Addition of mineral fillers will not generally improve impact strength. There are exceptions, for example the use of fine talc in PP compounds for car bumpers. In the latter case, 5 to 10% of fine talc is added. Impact strength decreases at higher loadings
5. DEFLECTION TEMPERATURE
In many applications such as in plastic parts for cars or packaging, rigidity is required at elevated temperatures. The heat distortion temperature (HDT) can be used to demonstrate how a mineral influences the stiffness of a plastic compound at elevated temperatures. Lamellar talc with high aspect ratio improves the deflection temperature of polyolefins to a greater extent than talc with a lower aspect ratio
6. CREEP RESISTANCE
Substantial reduction of creep is achieved with filled polymers in comparison to unfilled ones. Best results in our creep tests were obtained with fine platy talc. Various fillers and filler combinations reduced creep.
Information obtained from short-term tests of PP can be extrapolated to predict properties over a longer period of time at a constant temperature. The conventional short-term modulus is replaced in formulas by the creep modulus. The creep modulus, which is important increases the service life.
7. CHEMICAL RESISTANCE
Talc is water repellent and chemically inert. This is very important for the direct contact of mineral filled packaging material with food-stuffs. Migration tests are done with different stimulants (distilled water, 3% acetic acid, 10% ethanol and rectified olive oil).
NEW MARKETS FOR TALC-FILLED PLASTICS
The automotive and domestic appliances markets are still the dominating users of talc-filled compounds, but new markets are being developed. Their growth depends partly on the extent to which end-users actively seek alternative materials to PVC and PS. Markets of interest here include profiles, pipes and food packaging. Blanc Fixe Minerals has sound knowledge of the plastics industry offering high quality talc for present and emerging demands of the industry