Layered clay minerals. Basic research and innovative composite applications

Literature reveals that the nature of the clay minerals in clay-based polymer nanocomposites (CPN) is often disregarded or only reported in very general terms. The decisive clay mineral properties for high-performance CPN are highlighted. Many aspects should be taken into account when clay minerals are used for the preparation and optimization of CPN. Clay minerals (smectite, kaolinite, sepiolite) differ by class, but there are also differences within each species such as montmorillonite. Even montmorillonites of the same locality can differ in certain properties. The structural details of the clay minerals (composition, compensating cations) must therefore be carefully specified, so even small changes can be of influence in applications such as nanocomposites. The clay mineral particles are often modified to render them compatible with the polymer. In most cases, surfactants are used to render the surface hydrophobic, but this modification generally reduces or impedes delamination of the clay mineral particles into thinner or single layers. The most important step is therefore finding the optimal way of modification and adjusting the hydrophilic-lipophilic balance (HLB) to the polymer matrix. The HLB not only depends on the chemical nature of the surfactants but also on the surfactant/CEC ratio. The aspects discussed clearly indicate that CPN formation is an excellent example of modern Materials Science requiring the cooperation of scientists of different backgrounds, engineers and technologists. It is evident that Clay Technology can only be successful and of strong impact when the actual results of modern Clay Science will be fully established, (c) 2007 Elsevier Inc. All rights reserved.