Particulate-Polymer Nanocomposites Processing

Particulate-polymer nanocomposites can be prepared by any one of the following general approaches  

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In the stated above treatment not only nanostructure integral characteristics (macromolecular entanglements cluster network density v, or nanocluster relative fraction cp j), but also separate nanoeluster parameters are important (see Section 15.1). In this case of particulate-filled polymer nanocomposites (artificial nanocomposites) it is well-known, that their elasticity modulus sharply increases at nanofiller particles size decrease [17]. The similar effect was noted above for REP, subjected to different kinds of processing (see Fig. 15.28). Therefore, the authors of Ref. [73] carried out the study of the dependence of elasticity modulus E on nanoclusters size for REP. 

Proceeding from the said above, the present work purpose is the theoretical treatment of particulate nanofiller aggregation process and elasticity modulus (reinforcement degree) particulate-filled polymer nanocomposites with due regard for the indicated effect within the framework of irreversible aggregation models and fractal analysis. 

The applicability of irreversible aggregation models for theoretical desc ription of particulate nanofiller particles aggregation processes in polymer nanocomposites has been shown. Analysis within the framewoik of the indicated models allows to reveal either factors influence on aggregation degree. 

In Figure 9.14 the dependence K (D ) is adduced, which has shown linear decay with growth in and at = 3, i.e., at nanostructure formation in Euclidean space, K = 0 and the structure of epoxy polymers does not undergo changes (formation of nanoclusters) in its creation process. Let us note that such treatment is confirmed by the data for particulate-filled polymer nanocomposites, for which the structure formation proceeds in Euclidean space and the polymer matrix dimension of nanocomposites is constant and equal to this parameter for a matrix polymer [40]. The similar, but weaker, dependence K (D ) was found for a linear amorphous polymer (polycarbonate, a dashed line in Figure 9.14), which is due to the absence of such a powerful factor as chemical crosslinking nodes network. 

By surveying the nanocomposites prepared so far, wear resisting polymer nanocomposites can be regarded as a successful example that brings the so-called nano-effect into full play. At a filler loading of less than 1%, the wear rate of the matrix was lowered by over thousands of times (Table 20.4). Similar enhancement due to the addition of small amounts of fillers is impossible to perceive in microcomposites. The developments in this aspect have broadened the application possibility of particulate composites and solved the dilemma arising from the contradiction between tribological performance improvement and processability deterioration, as often observed in microparticles filled composites. 

Hence, the stated above results have shown, that elasticity modulus change at nanoindentation for particulate-filled elastomeric nanocomposites is due to a number of causes, which can be elucidated within the frameworks of an harmonicity conception and density fluctuation theory. Application of the first from the indicated conceptions assumes, that in nanocomposites during nano indentation process local strain is realized, affecting polymer matrix only, and the transition to macrosystems means nanocomposite deformation as homogeneous system. The second from the mentioned conceptions has shown, that nano- and micro systems differ by density fluctuation absence in the first and availability of ones in the second. The last circumstance assumes that for the considered nanocomposites density fluctuations take into account nanofiller and polymer matrix density difference. The transition from nano to Microsystems is realized in the case, when the deformed material volume exceeds nanofiller particles aggregate and surrounding it layers of polymer matrix combined volume [49]. 

Several techniques such as intercalation of polymer from solution, in-situ intercalative polymerization, melt intercalation, direct mixture of polymer and particulates, template synthesis, in-situ polymerization and solgel process, are being employed for the preparation of polmer-layered silicate nanocomposites. Among them the most common and important approaches are in-situ polymerization, solution-induced intercalation method, and melt processing method, which are briefly discussed below. 

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