additives feature | Mineral modifiers
products are used when talc does not provide enough dimensional stability, reinforcement, warpage and shrinkage reduction, or heat distortion temperature. “The distinct flaky shape of Mica HLP 100 works against warpage for high dimensional stability,” reports Mayer. Glass-fibre filled PA6 can experience anisotropic shrinkage that leads to warpage. A KMI study showed that replacing a portion of the glass fibre with KMI’s Mica HLP 100 (a micronized phlogopite mica) reduced shrinkage overall and made shrinkage more balanced while maintaining tensile modulus. Although HDT decreased compared to the higher glass-fibre content formulation, the HDT was much better than a formula that used glass spheres to replace a portion of the glass fibre. The mica formulation was also better than the glass sphere formulation in terms of modulus and shrinkage. Wollastonite is a high aspect-ratio mineral with a
LKAB’s phlogopite mica PW80 has a very high aspect ratio, delivering good strength and modulus
LKAB’s investment in a world-scale processing plant
enables it to supply even the largest customers, adds DeArmitt. Other LKAB minerals include UltraCarb, which is a blend of huntite and hydromagnesite that is finding success as a halogen-free flame retardant (see Compounding World, August 2013), and magnetite for sound and vibration damping (which will be covered in more detail in a future issue). At the Compounding World Forum 2013, Jim Harper,
Kärntner Montanindus- trie offers platy phlogopite mica (left) and high aspect-ratio wollastonite (right)
applications development manager at Imerys, described the advantages of mica in polymers and explained how particle size affects properties. Increasing particle size improves notched Izod impact resistance and heat deflection temperature (HDT). Small particle sizes can be used for class A surfaces, but larger sizes might have some reflecting effect, he noted. The use of mica in polyethylene (PE) and PP is
growing, because these polymers are increasingly used as substitutes for other polymers, where they require additives, including mineral modifiers, to boost proper- ties, notes Veronika Mayer, application management at Kärntner Montanindustrie (KMI). In PP, KMI’s mica
needle-like structure that can be used for reinforce- ment, thermal and dimensional stability, and scratch resistance. A recent KMI study of its Wollastonite Submicro 4-15 grade shows a significant improvement in scratch and mar performance, especially compared to common extender fillers, says Mayer. Halloysite is another high aspect-ratio mineral. It is an aluminosilicate clay that occurs in a naturally exofoliated, hollow, nanotubular structure. A new source for halloysite is I-Minerals, which has a measured resource in Idaho that is in the feasibility stage of development. The company is developing a grade with 70% halloysite and another with 90% (the remainder being kaolinite). The I-Minerals halloysite is composed of variable lengths of tubes, many of which are 4-5 micron in length and approximately 0.10 microns in diameter. This translates to an aspect ratio of 40 to 50 which is very high, even compared to other halloysites, notes Linda Koep, market development manager at I-Minerals. Applications for such high aspect-ratio tubes include polymer reinforcement and reducing CTE in coatings. Other published uses for
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COMPOUNDING WORLD | August 2014
www.compoundingworld.com
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