additives feature | Conductive carbon blacks the lower the moisture pick-up.
“As opposed to furnace blacks, the Imerys Graphite & Carbon proprietary production process delivers very graphitic carbon blacks [which are] quite hydrophobic. This factor, maybe in conjunction with additional effects from the granule form, would explain the out-perfor- mance of Ensaco250G versus other conductive carbon blacks with low surface area.”
Moisture pick-up of different carbon blacks Source: Imerys
Low moisture content and low moisture pick-up of a carbon black is crucial to guaranteeing high system stability. “High moisture can hinder carbon black feeding, can result in poorer dispersion in the polymer matrix – also meaning weaker mechanical properties, and occurrence of surface defects – and failure in water-sensitive polymers and applications,” Van Bellingen says. She further notes that while conductive compounds containing water-sensitive carbon blacks may require special aluminium packaging, this is not necessary with carbon blacks with low moisture pick-up. “The low moisture pick-up (maximum 0.3%) and the high purity level (an especially low level of basic traces, in the ppm range) make Ensaco250G conductive carbon black very suitable for sensitive polymers like polycar- bonates and polyesters, and moisture-sensitive polymers in general,” Van Bellingen explains. High-end applications such as conductive PC carrier tapes, for example, demand very low levels of moisture and contaminants.
Van Bellingen also says that Ensaco conductive carbon blacks match the severest purity requirements relating to polycyclic aromatic hydrocarbons (PAH), such as benzo[a]pyrene (BAP). “Originating from some rubber industry guidelines, low PAH/BAP content of individual ingredients is becoming a topic of concern for plastics compositions,” she says.
Comparison of moisture pick-up of two types of carbon black with low surface area but different levels of structure
Source: Imerys During mixing, the low surface area eases the
wetting of the carbon black, while the high structure facilitates de-agglomeration. “High-structure blacks enable the establishment of a continuous path for the electrons into the fi lled polymer at a lower concentra- tion than lower structure blacks would do,” Van Bellingen notes. “Providing a good dispersion can be achieved, the use of a conductive carbon black will help reduce the negative impact of the fi ller on the plastics mechanical performances. “ Van Bellingen also cites tests that have shown
evidence of the infl uence of the surface area on the moisture content and moisture pick-up of a carbon black: the lower the surface area of the carbon black,
32 COMPOUNDING WORLD | November 2014
Polycyclic aromatic hydrocarbons are a group of organic compounds classifi ed as toxic to the environ- ment and harmful to human health. They result mainly from incomplete combustion of organic matter. “PAHs accumulate in industrial carbon black pigments used to modify the conductivity of polymers,” says compounding company Grafe, which has separately announced the development of reduced-PAH conductive compounds; it says that they meet standards required by the GS seal for tested quality in Categories 1–2.
The GS seal sets the maximum PAH level in relation
to mass depending on a given product’s application. PAHs can be absorbed through skin contact, the lungs and via food. Grafe says that to be listed in Category 2, the total amount of PAH in a substance must be lower than 10 mg/kg and the maximum of levels of BAP, which are particularly critical, must not exceed 1 mg/kg. Another compounder that has been expanding its
www.compoundingworld.com
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