Carbon black dispersion procedures

At the time of writing, a revision of ISO 11345 is near to completion. The main change is to expand the number of methods to 5 so that provision is made to make tests at lOOx magnification and also a separate procedure for large agglomerates. The new version covers dispersion of silica as well as carbon black and additional sets of standard photos have been included. 

In a second preparation procedure, referred to as dry state , the carbon black is resolved in a solvent and dispersed by ultrasonic treatment. Afterwards, the highly diluted suspension is dipped on a grid and treated as above. 

Testing procedure. Water is added to a blender, followed by ammonium hydroxide to adjust pH to the required level. Carbon black is added in 30 s with low speed mixing. Dispersing agent is added in portions from a burette under high speed dispersion. The endpoint is determined as 5 min of uninterrupted fluidity under high speed mixing. The total time of determination should not exceed 10 min. Standard methods. The method is described in Cabot Corporation Technical Report S-131. 

Carbon blacks are incorporated into polymeric media by one of two methods. The proper amount of carbon black may be dispersed directly into the polymer using a suitable mixing device. Far more common, however, is the masterbatch process in which carbon black is first dispersed into a carrier resin in concentrations of 30-50%. This concentrate is then let down (diluted) via the salt and pepper procedure attained by introducing a mixture of concentrate and polymer pellets into the mixing unit. The ratio of compound to pellets is adjusted to provide for the final carbon black loading. 

In the case of black polyolefin pipes, fittings, and compounds, test method ISO 11420 describes two procedures for assessment of carbon black particle and agglomerate size and dispersion for content of less than 3%. The method is applicable also to raw material in pellet form. 

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