Morphology, polymer clay

Solvent-polymer and solvent-clay interactions are very important in determining the morphology of polymer/clay nanocomposites. There are many reports describing the preparation of PNCs by solution mixing [65, 231-235]. Ho and Glinka [38]... 

It was also noticed by the same authors19 that the incorporation of the OMMT in EVA instead of PA6, keeping constant the global composition, led to a strong decrease in heat released, but with a different evolution of HRR as a function of time. This was ascribed to different morphologies of clays (mixed intercalated/exfoliated versus completely exfoliated) for the polymer blend. Consequently, the formulation process of complex FR systems involving polymer blends and made up of nanoparticles in combination with FRs seems crucial. 

Schematic illustration of clay and CNTs morphology in chitosan nanocomposites is shown in Figure 4.8. In the composites based on chitosan/CNTs containing 0.4 wt % CNTs, nanotubes can be well dispersed in chitosan, but no filler network could be formed due to its low concentration (Figure 4.8a). In the composites based on chitosan/clay containing 3 wt % clay, formation of 2D clay platelets network is possible (Figure 4.8b). In chitosan/clay-CNTs ternary nanocomposites, ID CNTs are confined in 2D clay platelets network, which results in a much jammed and conjugated 3D clay-CNTs network (Figure 4.8c). The interactions and networks in the system can be divided into (1) clay-clay network, (2) clay-CNTs network, (3) CNTs-polymer-clay bridging, (4) polymer-polymer network. The formation of different networks and interactions could be the main reason for the observed synergistic reinforcement of CNT and clay...

Figure 4.8. Schematic illustration of morphology of clay and CNTs in chitosan nanocomposites (a) chitosan/0.4% CNTs (b) chitosan/3% clay (c) chitosan/3% clay/0.4% CNTs. The interaction and networks in the system could include (1) clay-clay network (2) clay-CNTs network (3) CNTs-polymer-clay bridging (4) polymer-polymer network. Reprinted with permission from ref (42).

The reinforcement of polypropylene and other thermoplastics with inorganic particles such as talc and glass is a common method of material property enhancement. Polymer clay nanocomposites extend this strategy to the nanoscale. The anisometric shape and approximately 1 nm width of the clay platelets dramatically increase the amount of interfacial contact between the clay and the polymer matrix. Thus the clay surface can mediate changes in matrix polymer conformation, crystal structure, and crystal morphology through interfacial mechanisms that are absent in classical polymer composite materials. For these reasons, it is believed that nanocomposite materials with the clay platelets dispersed as isolated, exfoliated platelets are optimal for end-use properties. 

The previous session has shown that the preparation method has a fundamental role in the dispersion of the nanofiller and the morphology of the polymer/clay nanocomposite. Different degrees of dispersion are obtained for different systems and, to a lesser extent, even within the same sample (Figure 12.12). 

Fig. 2 Schematic representation of different structure of and morphologies of polym clay...

The main issue in processing of polymer/clay nanocomposites is to achieve sufficient interaction between the nanofiller and the polymer so as to achieve a favourable morphology. Due to the laminar structure of the most common nanoclays, the morphology of nanocomposites can be classified in three different types depending on the structure of the nanoclays and the interaction with the polymer chains aggregated, intercalated and exfoliated. Figure 8.2 shows the three possible morphologies of a polymer/clay nanocomposite. 

Figure 8.2 Possible morphologies of a polymer/clay nanocomposite.

F.C. Bragan9a, L.F. Valadares, C.A.P. Leite, F. Galembeck, Counterion effect on the morphological and mechanical properties of polymer-clay nanocomposites prepared in an aqneous medium. Chemistry of Materials 19 (2007) 3334-3342. 

L. Urbanczyk, et al., Batch foaming of SAN/clay nanocomposites with SCCO2 a very tunable way of controlling the cellular morphology, Polymer 51 (15) (2010) 3520-3531. 

However, not all of the manifold structural or morphological details influence the ultimate mechanical properties to the same degree. There are details which determine properties more than other ones, ie, there are so called property determining structures. Besides, it is not sufficient to study the average structure and morphology of a material, but the variation of morphological details or extreme sizes of the details have to be known. Smaller structural details have become increasingly important for a defined improvement of mechanical properties with a shift from details on the micrometer scale to details on the nanometer scale, eg, in block copolymer or nanocomposites, Polymer-Clay. 

Gain O, Espuche E, Pollet E, Alexandre M, Dubois P. Gas barrier properties of poly(e-caprolactone)/clay nanocomposites Influence of the morphology and polymer/ clay interactions. J Polym Sci, Part B Polym Phys 2004 43 205-214. 

Fig. 3 Schematic illustration the morphologies of polymer/clay composites...

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