Thermoplastic composites play an important role in our society, as their properties
respond to a wide range of specific demands. They have, therefore, attracted considerable
interest from both industry and academic media.
When clays and polymers are compatible, the properties conferred by the filler to the
polymer matrix are comparable or exceed those of traditional materials. Since polyolefins are
hydrophobic and clays are hydrophilic, either the filler or the matrix must be modified as to
increase their compatibility. Modern approaches do not use only organically modified clays, but
also apply compatibilizing agents (e.g., units of maleic anhydride grafted onto polyethylene or
polypropylene chains) [1].
The high aspect ratio of the nanoclays provide a great interfacial area, thus enhancing
reinforcing properties. Silicates such as montmorillonite, hectorite, and saponite have a layered
structure that, upon exfoliation, leads to composites with very high stiffness and strength [2].
The most effective methods for preparing polymer-clay nanocomposites are melt
intercalation, in situ polymerization, and solution dispersion. The melt intercalation method is
the most convenient at industrial scale due to the continuous nature of the process and economic
factors. It was found that the orientation of clay in compatibilized polymer matrices (polymers
grafted with maleic anhydride) increased with increasing shear rate. The hydrogen bridges
between polymeric maleic anhydride units and oxygen-containing groups in the silicates may
significantly contribute to the clay intercalation. But for an effective clay exfoliation, the shear
stress addition was required.
From a scientific point of view, a comparative study of the structure and morphology of
polymer-clay composites obtained through different procedures is very useful when it comes to
explain composites properties and behavior.
New nanocomposites based on high density polyethylene (HDPE) and organically
modified nanoclay (Cloisite 20A) were obtained by two different methods, namely melt
compounding and solution blending, and their properties were comparatively studied in order to
establish the dependence of the clay degree of exfoliation/intercalation on the preparation
procedure.
References:
1. Bhattacharya, S.N.; Kamal, M. and Gupta, R. Polymeric Nanocomposites: Theory and Practice.
Carl Hanser Verlag, Munich, 2008.
2. Hetzera, Ma.; De Keea, D. Wood/polymer/nanoclay composites, environmentally friendly
sustainable technology: A review. Chemical Engineering Research and Design, 2008, 86, pp.
1083-1093.