Influence of dehydration on the dielectric and structural properties of organically modified montmorillonite and halloysite nanotubes

Abstract The dielectric behaviours of organically modified montmorillonite (Cloisite-20) and nanosized tubular halloysite (Dragonite-HP) were investigated using broadband dielectric spectroscopy (BDS) under dehydration conditions up to 200 °C. The thermal and structural properties of both tested clay minerals were also initially examined in the as-received and dehydrated samples. Dragonite-HP was shown to lose 2.2 mass% of the adsorbed and interlayer water up to 200 °C. The dehydration of Dragonite-HP also caused the tightly connected tubular layers to unfold, thereby increasing the specific surface area and the total pore volume. Cloisite-20 lost only 1.1 mass% of its adsorbed water during dehydration due to the presence of an organic modifier, bis(hydrogenated tallow alkyl)dimethyl. Its presence led to decreases in the specific surface area and total pore volume of Cloisite-20 relative to those of pristine montmorillonite. BDS revealed that the dielectric constant (e') and dissipation factor (tan δ) of the thermally treated Dragonite-HP increased and that the volume resistivity (ρv) decreased within one order of magnitude in the temperature range of − 40 to 90 °C. In contrast, the e' of the thermally treated Cloisite-20 increased by two orders of magnitude, the tan δ increased by more than three orders of magnitude, and the ρv decreased by five orders of magnitude. The values of e', tan δ and ρv measured via BDS demonstrate that the dielectric properties of Dragonite-HP at a standard industrial frequency of 50 Hz and under a typical operating temperature range are more advantageous than those of Cloisite-20. This finding is very promising for the possible use of Dragonite-HP as a nanofiller for clay/polymer nanocomposites intended for cable core insulation manufacturing.