Determination of carbon black content in HDPE — purge gas buoyancy effect

Oxygen and air have been interchangeably used as the purge gas in the determination of carbon black content in polyethylene. This study shows that accuracy of the carbon black filler content is significantly affected by the choice of oxygen as the purge gas used to oxidise the carbon filler. It is believed that the difference in the density of the oxygen give rise to the buoyancy effect. Air, having closer density to the initial nitrogen purge gas in the analysis, is the better choice for purge gas for accuracy of analysis and reproducibility of results.