Mixed modifier clays and their dispersion in solvent cast polycaprolactone nanocomposites

• The novel concept and development of Mixed Modifier Clay are introduced.
• Clay surface properties are tailored by utilizing more than one organo-modifier.
• Varying modifier concentrations allow clays hydrophobicity to be fine-tuned.
• Optimized clay dispersion in polymers by enhanced compatibilisation is achieved.
• Matrix development and detailed characterisation strongly support findings.

The concept and development of mixed modifier clays have been investigated in order to optimize clay dispersion within polymer matrices in general and polycaprolactone (PCL) in particular. A range of mixed modifier clays have been prepared by the inclusion of a second, more polar, organomodifier of much shorter chain length (Me3(CH2CH2OH)N+) within a benzyl(hydrogenatedtallowalkyl)dimethylammonium organoclay. The focus was to produce a range of organoclays with a systematic progression of selected polarities so that an optimum compatibility with the host polymer, PCL, could be achieved. The key to success was to attain that delicate balance where the long alkyl chains on the first modifier just overcame the layer–layer attraction whilst the second, shorter chain, modifier offered the potential to optimise the polarity of the clay surface and reduce the congestion in the interlayer space to ease polymer ingress. The organo-modification, subsequent polymer dissolution and casting were achieved using nitrobenzene as the solvent. X-ray diffraction (XRD) evidence, supported by, carbon/nitrogen analysis, proton nuclear magnetic resonance spectroscopy and thermogravimetry–mass spectroscopy, indicated that, when fully optimized, a homogeneous distribution of the two modifiers had been achieved within each individual interlayer space and that the amount of each modifier could be controlled. XRD data and transmission electron microscopy images confirmed that the extent of dispersion, of the mixed modifier clay in PCL, could be controlled to produce layered aluminosilicate–polymer systems that were either exfoliated, intercalated or a mixture of both.