(559f) The Extent of Filler's Organo-Modification and the Resulting Morphology and Thermo-Mechanical Properties of Poly(ε-caprolactone)/Clay Nanocomposites

The development of polymer/clay nanocomposites has attracted significant interest in recent years due to the exceptional physical property improvements that these materials often exhibit, at relatively low filler loadings. In order to achieve these benefits, efficient dispersion levels of the reinforcing agent is a prerequisite, so that the high aspect ratio and surface area of the clay particles are fully utilized and the resulting nanocomposite properties are isotropic. In general, the inorganic filler neither has good interaction with the organic polymer to achieve good dispersion, nor adequate adhesion, and, as a result, surface organic treatments are common. Organic modifier's packing density within the silicate galleries is a very important factor regarding the dispersibility of the clay into the matrix and the properties of the final hybrid material.

The present study was undertaken to elucidate the effect of the surfactant concentration on the thermo-mechanical behavior of poly(ε-caprolactone) (PCL) nanocomposites. Hybrids were prepared by the addition of montmorillonite modified by hexadecylammonium cation concentrations equivalent to 0.3-3.0 times the cation exchange capacity (CEC) of the mineral. Dispersion of the organomodified clay (C16MMT) into the polymer matrix was achieved by the melt intercalation technique. The structural characteristics of the as-prepared composites were investigated by X-ray diffraction (XRD) and their thermal properties were studied by thermogravimetry (TGA) and differential scanning calorimetry (DSC). The influence of the amphiphilic cation concentration on the material's mechanical properties was explored in tensile loading conditions, while dynamic mechanical and thermal analysis (DMTA) was performed in bending mode.

The results showed that surfactant concentration higher than 50% the clay CEC was necessary in order for the organomodified clay to fully disperse into the polymer matrix at nanoscale level. Intermediate surfactant level reinforces the thermal stability of the hybrid by increasing the onset decomposition temperature. Furthermore, an increase of the clay modification degree enhances the compatibility between the mineral and the matrix leading to a significant improvement of the composite's stiffness without sacrificing polymer ductility. In conclusion, the amphiphilic cation concentration was found to play a major role in controlling the structure at nanoscale level and the thermo-mechanical properties of the hybrid material.

Acknowledgements

This work was supported by the Region of Western Macedonia (Greece) through the PEP grant with MIS 105545 to I. Z.

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