Mineral modifi ers | additives feature
Jennifer Markarian reviews recent developments in
mineral modifi ers for
improving the properties and sustainability of
polymer compounds
Functional fi llers: making modifi cations with minerals
A wide range of minerals are used to increase polymer properties, moving beyond a role as fi llers and polymer extenders to functional modifi ers. High aspect-ratio minerals, such as mica, wollastonite and halloysite, boost properties, and some talc and calcium carbonate grades have the added benefi t of improving sustainability. Minerals are found in various shapes, and those with
a fi brous or platy nature have the potential to offer reinforcement. Mica, for example, is a platy mineral known as an effective reinforcement for nylons and also polyolefi ns, says Chris DeArmitt, business development manager for Polymers & Coatings at LKAB Minerals. The company, which was formerly known as Minelco, has a full range of muscovite and phlogopite micas and recently introduced even higher aspect ratio grades of these micas to take performance to the next level. Micas, when specially processed via wet milling, can yield aspect ratios of 100 or more. Phlogopite mica PW80, with an exceptionally high aspect ratio, is claimed to give the highest strength and modulus compared to other micas, wollastonites or talcs. “Testing in polyamides (PA) and polypropylene (PP)
showed it to be twice as effective as the same loading of talc,” reports DeArmitt. “In glass-reinforced PA6,6 used in under-the-hood applications, PW80 gave excellent reinforcement while retaining good impact resistance and was more cost-effective than many of the alterna- tives. Effective reinforcement gives the opportunity for increased quality, or one can achieve the same
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performance with lower density, which is vital for automotive applications.” Mica can be used to replace some of the glass fi bre
in PA6, resulting in lower warpage, better mouldability, smoother surface fi nish and better barrier. While the phlogopite is bronze in colour, an equivalent white muscovite mica grade called R90 is also available where colour is important. Mica also provides other properties, such as sound damping, UV protection, coeffi cient of thermal expansion (CTE) reduction and char formation (for fl ame retardancy). Mica improves barrier properties because the high
aspect ratio mineral creates a tortuosity effect whereby the permeant has to diffuse around the mineral plates, explains DeArmitt. In a high-performance thermoplas- tic coating application designed to protect the substrate from harsh chemicals, PW80 greatly increased barrier properties.
“Without PW80, a steam exposure test normally
results in failure within 48 hours. By adding PW80, the coating still has not failed after months of continuous testing,” says DeArmitt. “The potential of high aspect ratio plates is well known and has driven two decades of effort to exfoliate nanoclays with disappointing results. It turns out that the answer is much simpler; one can get the same benefi ts with mica and avoid the pitfalls, because mica processes just like standard reinforcements and performs extremely well without the need for surface treatments.”
August 2014 | COMPOUNDING WORLD 23
Mica is a platy mineral that provides effective
reinforcement for nylons and polyolefi ns
(photo: LKAB)
PHOTO: LKAB
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