ADDITIVES | HIGH DENSITY COMPOUNDS
Right:
Magnetite iron oxide (Fe3
O4
is a black lustrous powder offering a density of 5.2 g/cm3
)
ride and bismuth trioxide. Magnetite is proving to be an increasingly useful high density filler for plastic compounds, according to Dr Chris DeArmitt, an industry consultant and President of Phantom Plastics. “Com- pared with typical mineral fillers, advantageous properties include greater Mohs hardness, electrical conductivity and higher volumetric heat capacity, while it is also both attracted by a magnet and microwave heatable,” he says. “In addition, it [magnetite] is
there is a need for such a product. Known as DenzFlex, it is a high purity synthetic iron oxide that can also replace expensive pigments,” DeArmitt says. He adds that at least one other source is understood to be evaluating and consider- ing an entry into the polymer market.
Other factors influencing
the take-up of magnetite in polymers include processing. “There is a drive for finer
PHOTO: PHANTOM PLASTICS
x-ray opaque and can be used to block radiation. In terms of adding density to polymers, a 40 wt% loading of magnetite is equivalent to a 10.3 vol% loading and can provide a polymer density of 1.34 g/cm3
filler loading of calcium carbonate or talc, the increase in density is 37%,” he says. At higher filler levels the increase is even more
pronounced. At an identical filler loading of 41 vol% – which is 80 wt% for magnetite and 68 wt% for calcium carbonate and talc – a polymer density of 2.66 g/cm3
can be achieved, an increase of
Below: MagniF magnetite fillers from LKAB Minerals are used in automotive sound deadening components
196%. The comparable figure for the mineral fillers is an 82% increase,” DeArmitt explains. However, a number of issues are potentially holding back wider use of magnetite in polymer compounds. “New sources of magnetite are needed,” DeArmitt says. “There are not many sources of high purity magnetite in the world suitable for use as speciality fillers for polymers.” DeArmitt works with Arctic Minerals, which
offers its MagniFlex magnetite black iron oxide for polymer applications. It recently also developed a red iron oxide-based product based on haematite. “This was recently introduced to the market and is already seeing significant sales, indicating that
particles because current iron oxides are a little coarser than we
would like. Finer particle size means better impact resistance, higher elongation to break and better surface finish,” DeArmitt says. He explains that the most prevalent magnetite
– an increase of 49%. For the equivalent wt%
products in the market are coarse compared to other speciality fillers, with a mean size of 15 microns up to a top size of 45 microns. “New products now being launched include a magnetite with a mean size of around 10 microns and a top size of 30 microns. No new processing methods are required. However, it does require a further investment in more energy to mill finer. Neverthe- less, the new finer forms of magnetite are cheaper than incumbent courser types, primarily due to optimised logistics,” he says. Magnetite has FDA indirect food contact
approval. It can also be surface treated to help processing or to enhance properties. “Iron oxides can be treated with stearic acid or silane type treatments. Surface treatments lead to better impact resistance and improved flow. This means higher loadings are possible and because iron oxides are relatively hard, surface treatments can lower wear,” DeArmitt says. Another supplier of Magnetite is LKAB Miner-
als. According to Rob Lammertink, the company’s Director Polymers & Coatings, the key to formula- tion of high density polymer compounds is achieving an optimal cost/performance balance. He says its MagniF magnetite grades can be used as a filler in a wide range of polymers and rubbers to provide a level of density that is difficult to achieve with other standard mineral products. High filler levels can also be reached without surface treatment of the filler particles. MagniF is described as a pure and fine greyish- black powder milled from magnetite mined and processed at LKAB Mineral’s resources in the north of Sweden. Primarily used for its high density,
66 COMPOUNDING WORLD | May 2019
www.compoundingworld.com
PHOTO: LKAB MINERALS
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