Right: Carbon black remains the popular choice for
additives | Electrically conductive More hydrophilic conductive carbon blacks will keep
conductive and antistatic plastics
high moisture content in the compound, Van Bellingen says. “High moisture can not only hinder the carbon black feeding, with resulting poorer dispersion, related weaker mechanical properties and uneven conductivity, but it can also create high levels of permanent moisture to stay trapped in the compound, which in turn may generate bubbles and surface defects in the end application.” The company makes its Ensaco grades using a
proprietary production process that is said to differ from the most widely used furnace process. Van Bellingen says this process delivers a unique combination of ‘high structure’ and ‘low surface area,’ which guarantees an excellent dispersion of the conductive carbon black in plastics. She says regular furnace blacks are produced by a process that always delivers higher surface area at the same level of high structure, or only lower surface area at lower structure levels (see Compounding World, November 2015, page 27 for more on carbon black developments).
Doping with metals Mackinac Polymers has taken a quite different approach to obtaining electrical conductivity in plastics. Its path lies mid-way between those of inherently conductive polymers (polyaniline, for example) and compounds containing metallic additives. The company has developed technology for incorporating nano-scale conductive transition metals directly into the polymer backbone or onto side chains during the polymerisation process. It says conductivity of materials produced this way is much more controllable and uniform than is possible by incorporating conductive additives during the compounding process. Don Phillips, president of The Mackinac Group and Partner in Mackinac Polymers, claims the Mackinac
The Imerys Graphite & Carbon process delivers very graphitic carbon blacks with a very low number of oxygenated groups on their surface. This makes them much more hydrophobic than furnace blacks of the same surface area, which appear to have a higher surface oxygen content.
Source: Imerys Graphite & Carbon
30 COMPOUNDING WORLD | April 2016
technology has important advantages over conventional compounding technology for production of conductive materials. For one, while some conductive compounds may require additive levels anywhere from 20 to 80%, Mackinac conductive polymers typically contain 3-5%, so the original properties of the polymer are largely retained. Mackinac’s original intention was to act as technical
consultants to major polymer producers for develop- ment of conductive grades incorporating its technology, with the partner licensing the Mackinac technology. However, Phillips says polymer makers have, by and large, preferred to stick with their own in-house developments. As a result, it has now changed its business model to work directly with processors and OEMs, developing materials for specifi c applications and contracting out production of the materials to strategic partners (whose names remain confi dential). The company is also currently working with com- pounders on masterbatches. “We would provide a super functionalised base polymer (PP, PE, TPU, PC, ABS, etc) to the compounder,” Phillips says. “The compounder could then mix in additional additives for colour, strength, or whatever, to create the end product. Or they could blend our masterbatch with virgin material to create different levels or grades of functional material. We have been speaking with several compounders in recent months and we have got a lot of interest. We currently have around 60 projects in the queue.” Phillips says the conductive plastics project sprang out of a contract the company was involved in several years ago to develop a “heavy acrylic” that could be used as an alternative to glass for beer mugs. During the development, Mackinac chemists discovered that they could link bismuth (which could provide the extra density) into the backbone of the polymethylmeth- acrylate (PMMA).
Mackinac works with various conductive materials, including iron oxide (Fe3O4
), copper, silver and alumini-
um, as well as graphene. The nanoparticulate compo- nent can be composed of one or more organometallic
www.compoundingworld.com
PHOTO: IMERYS GRAPHITE & CARBON
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