| Résumé | In structural clay-containing polymeric nanocomposites (CPNC) ca. 2 – 5 wt% clay is dispersed in polymer matrix: thermoplastic, thermoset or elastomeric. Since most clay/polymer systems are antagonistically immiscible, in analogy to immiscible polymer blends, a two-step compatibilization is required: (1) intercalation of clay into organoclay and (2) addition of functional compatibilizer(s). The volume of these compatibilizing species usually is larger than that of clay itself. These additives affect the thermodynamic, rheology and other performance characteristics of CPNC. Since the system is immiscible, i.e., sensitive to stresses during the compounding and forming stages, the reproducibility of behavior may be a problem. Furthermore, from the chemical and physical points of view the natural and synthetic clays are complex. The purified natural clay may contain 2-5 wt% contaminants (humic derivatives, quartz, gypsum, dolomite, ...), whereas the synthetic ones may be a mixture of different crystallographic forms (e.g., lamellar and needle-like). Both types of clay have polydispersed platelets shape and size. Accordingly, characterization of CPNC should start with that of clay, its platelet size, their inherent dispersibility (absence of interlamellar crystalline welding) and presence of contaminants. CPNC are being characterized by the rheological methods in the solid and molten state. Their mechanical, barrier, dielectric and other properties are determined following the standard methods. However, the use of the high pressure dilatometry (HPD) is relatively rare, even when this is the simplest way for determining the free volume and the thermodynamic interaction parameters as well as the key engineering quantities: the thermal expansion and compressibility coefficients. The HPD measurements are important, especially in view of the kinetic nature of transitions (vitrification, crystallization) that stretches into the non-equilibrium melt. An overview of the method and results obtained for CPNC with amorphous or semi-crystalline polymeric matrices are described. |
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