HIGH DENSITY COMPOUNDS | ADDITIVES
Getting heavy with plastics
Polymer compounds tend to be light weight, at least compared to their main rivals, but there are applications where greater density is a benefit. Mark Holmes finds out more
While many applications for plastic compounds benefit from their lightweighting advantages, there are situations where adding density and weight to plastics is beneficial. In automotive, for example, high density polymer formulations are widely used to control interior noise and vibration. High density materials can also block x-rays, useful in some healthcare products. And the additional heft can create a perception of quality, adding a premium in certain packaging applications. Achieving high densities in plastics means high filler loadings. That may sound like a recipe for poor processability but the high density of the fillers in typical use means high weight percentage loadings convert to much lower volume percent loadings. As a consequence, processing is not compromised excessively. Several fillers are commonly used to add density to plastics. Barium sulphate, which is white in powder form and has a density of 4.0-4.5 g/cm3
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depending on purity, provides high density and radio opacity, making it useful for applications in sound dampening and x-ray visibility for medical implants. Magnetite iron oxide (Fe3
O4 O3
lustrous powder offering density of 5.2 g/cm3 Haematite iron oxide (Fe2
) is a black .
) is a coarse, shiny
gunmetal grey colour that, when ground below 5 microns in size, changes colour to rust red. With the same density as magnetite, it is normally less expensive than magnetite, making it an attractive alternative it is highly effective in sound deadening applications. As both magnetite and haematite fillers are oxidised forms of iron, both are immune from corrosion in the final plastic compound. Tungsten can be used where very high density compounds are sought, such as for lead replace- ment applications. It offers a density of 19.25 g/ cm3
. Other high denisty, radio-opaque filler options available to compound developers include bismuth subcarbonate, bismuth oxychlo-
May 2019 | COMPOUNDING WORLD 65
Main image: Magnetite is finding increasing interest as a high density filler for plastics
PHOTO: PHANTOM PLASTICS
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