Mechanical-Viscoelastic Characterization in Nanocomposites

Vera Realinho, Marcelo Antunes, David Arencon, and Jose I. Velasco 

Since the first studies of polymer-clay nanocomposites, carried out by the research team at Toyota Automotive Corporation, much research has been performed on the incorporation of low and high aspect ratio nanofillers in polymers, and these have already demonstrated their capability to improve mechanical properties and other important properties such as wear resistance and electrical resistivity [1 ]. However, high material costs, complex processes, and limitations in production technology hamper the production and application of these nanocomposites on a large industrial scale. 

Polymer Composites Volume 2, First Edition. Edited by Sabu Thomas, Rumvilla Joseph, Sant Kumar Malhotra, Koichi Goda, and Meyyarappallil Sadasivan Sreekala. 

All these aspects have been overviewed in the following sections, preceded by a summary of the main factors affecting the mechanical behavior of nanocomposites and some modeling approaches that have been proposed. 

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The dynamic mechanical thermal analyzer (DMTA) is an important tool for studying the structure-property relationships in polymer nanocomposites. DMTA essentially probes the relaxations in polymers, thereby providing a method to understand the mechanical behavior and the molecular structure of these materials under various conditions of stress and temperature. The dynamics of polymer chain relaxation or molecular mobility of polymer main chains and side chains is one of the factors that determine the viscoelastic properties of polymeric macromolecules. The temperature dependence of molecular mobility is characterized by different transitions in which a certain mode of chain motion occurs. A reduction of the tan 8 peak height, a shift of the peak position to higher temperatures, an extra hump or peak in the tan 8 curve above the glass transition temperature (Tg), and a relatively high value of the storage modulus often are reported in support of the dispersion process of the layered silicate. 

Very interesting studies of natural rubber reinforcement with ZnO nanoparticles were performed by scientists from India, under the direction of Sabu Thomas [62]. The goal of these studies was to characterize the viscoelastic behavior and reinforcement mechanism of ZnO nanoparticles introduced into the rubber matrix. They have presented a constrained polymer model based on a rubbery region and a ZnO nanoparticle. Very interestingly, the authors presented a core-shell morphology model and constrained polymer model to explain the constrained polymer chains in NR/ZnO nanocomposites [62]. Thanks to this research and the proposed models, it is possible to understand the behavior of nanofillers in the polymer matrix and maybe in the future to develop an ideal nanofiller for use in the rubber matrix. 

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