(159e) The Effect of Glow-Discharge Plasma and Muffle Furnace Heating on the Surface Chemistry of Kaolinite

Kaolinite is commonly used as a coating in the paper industry, and as a filler in the plastics industry. Therefore it is crucial that the particles are not flocculated. In order to achieve a stable system the surface chemistry is manipulated such that strong repulsive inter-particle forces are present. Traditionally, concentrated suspensions of kaolinite are prepared using polyelectrolytes to impart stability.

This paper then investigates the changes in the surface chemistry of a commercial kaolinite after treatment in a muffle furnace and in glow-discharge plasma.

The effect of both forms of treatment on the zeta potential of the kaolinite was investigated by electroacoustics, using an Acoustosizer II (Colloidal Dynamics). The muffle furnace heating lead to a decrease in the magnitude of the zeta potential at the natural pH, and after titration it was seen that the zeta potential was negative over the range 2.75 ? 10. Both techniques revealed that no iso-electric point was found, rather a minima in the magnitude of the zeta potential was observed at a pH of 3.5. This minima is shifted to higher pH values after increased temperature treatment. Plasma treatment induced changes of the zeta potential to more positive values. This can indicate a successful change in the surface charge due to the etching of the surface by reactive species of plasma gas.

Analysis of the surfaces of the kaolinite particles was also performed by the use of a DVS Advantage (SMS UK Ltd) which determined the affinity of the surface to water via gravimetric means. Both the muffle furnace and plasma treated kaolinite had a lower water uptake than the untreated kaolinite implying changes to the hydrophobic/hydrophilic nature of the kaolinite surfaces.