MATERIALS | MINERAL FILLERS
Right: Evonik’s Tegopren 6875 coating ‘hydropho- bises’ filler surfaces so effectively that high-density TiO2
will float on water
terms of different high performance fillers for high temperature polyamide grades, such as PA610, PA6T/6 and PA9T, with the goal to modify the properties.” A key element in the project is the application of
appropriate surface treatments. “Polymers usually have low surface tensions and low polarity. Water and minerals have high surface tensions and high polarity. If they are mixed together, the interfacial energy is high, and the phases tend to separate. Modifications of minerals by, for example, silanes or other organic molecules have the task of lowering this interfacial tension and making the phases compatible,” he explains. Emphasising the company’s extensive experi- ence in surface treatments on minerals, Sebö says it has tested various fillers, including kaolin, mica, and wollastonite, with different newly-developed temperature-resistant surface treatments suitable for the higher processing and working tempera- tures of HT-PAs. “The development showed us very interesting and promising results, for example, in the mechanical properties, especially in terms of elongation at break,” he says. Very good results in terms of elongation at break have been obtained with HPF’s Tremin 939 (long needle Wollastonite) in PA 610 and with Tremin 283 (short needle Wollastonite) in PA6T/6 the E-modu- lus is slightly reduced compared to the specimen with the standard coating. “The technology can be transferred to other thermoplastic materials, but at processing temper- atures over 330°C, which was the case for PA9T, there is no longer any effect visible from the surface coating,” says Sebö. Tests are still ongoing with other thermoplastic materials with much lower processing temperatures such as PA6 and PP, with the goal of improving processing and impact strength.
Improved dispersion
Dispersion is another challenge in compounding of mineral fillers and this can lead to agglomerates in the polymer matrix, which can result in high stiffness and low toughness of the final products. For some time, Evonik has been developing additives to improve the dispersion of fillers (organic as well as inorganic) in polymeric matrices. These additives, branded Tegomer and Tegopren, are based on organo-modified siloxane (OMS) chemistry. Evonik says the OMS chemistry allows higher filler loadings in combination with better melt flow and reduced abrasion in highly filled inorganic compounds. Tegopren 6875 was one of the first
30 COMPOUNDING WORLD | June 2021
surface treatment additives based on the OMS non-coupling technology. More recently, Evonik has launched Tegopren 6879, a bifunctional modified OMS containing a minor amount of silyl functionalities.
Similar to silane chemistry, the ethoxy groups
can react with the filler but they are claimed to generate almost no VOCs. “This surface treatment creates super-hydrophobic filler surfaces,” says an Evonik spokesperson. “It is not only suitable for oxides but interacts with carbonates and sulphates as well. On top of that, its functionality allows interaction with nitrogen/phosphorous-based flame retardants and organic pigments.” Evonik surface treatments have FDA and EC food contact regulation compliance and are suitable for use by filler manufacturers as well compounders. Compounders can apply them during the compounding process or using an external mixer, which will typically require lower concentrations. Filler manufacturers can use Evonik’s OMS emulsions, Tegopren 6875-45 and Tegopren 6879-50, as part of a water-based inline surface treatment.
CLICK ON THE LINKS FOR MORE INFORMATION: �
www.hudsonresourcesinc.com �
www.calcean.com �
www.nantbiogoods.com (Nant Bioplastics) �
https://asbury.com/ �
www.arcticminerals.com �
www.ima-europe.eu �
www.omya.com �
www.reverteminerals.es �
www.kmi.at (Kärntner Montanindustrie) �
www.hoffmann-mineral.com �
www.imerys.com �
www.trinityresources.ca �
www.quarzwerke.com (HPF The Mineral Engineers) �
www.evonik.com
www.compoundingworld.com
IMAGE: EVONIK
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