Nano-clays modulus

Lan and Pinnavaia [6] showed that hybrid organic-inorganic composites exhibited mechanical properties superior to those for their separate composites. Dependence of tensile strength and modulus of epoxy nano-clay composites on the chain length of the clay-intercalated alkylammonium ions is shown in Fig. 28. The presence of the organoclay substantially increased both the tensile strength and modulus relative to the pristine polymer. The mechanical properties increased with any exfoliation in the order ... 

Figure 9.27 shows the influence of nano-clay incorporation on storage modulus of the epoxy nanocomposites. The increase in percentage of nano-clay in epoxy resin increases the storage modulus up to a certain weight fraction of nano-clay, above which it decreases the modulus, but it is still above the value of neat epoxy matrix. The loss modulus curve shows the variation of glass transition temperature with respect to nanoclay incorporation and the maximum value of glass transition temperature is noted for the clay content of 3 wt% [31]. 

Wt% of nano-clay Flexural Modulus MPa Tensile Modulus MPa Heat Distortion Temperature °C... 

It is well known that fillers can affect the level and type of crystallinity in polymers such as polypropylene and polyamides. Nano-clays are known to promote significant changes in crystallinity in polyamides [32]. Mixed results have been reported for polypropylene, with most studies reporting no changes in the level of crystallinity, but some orientation of the polymer crystallites. Where these effects are present, they could contribute to the modulus and yield strength. 

The effect of matrix types on the flexural properties of PVC/wood-flour composites is summarized in Table 2. The flexural strength and modulus of the composites were compared with a variation of nano clay contents in the matrix as well as the use of adhesion promoter (coupling agent). 

Diaminodecane and 1,10-decanedicarboxylic acid were polyconden-sated in the presence of an organophihc clay to polymerize a nylon 1012 clay nano composite [27]. X-ray diffraction and TEM observations revealed that the clay layers were exfoliated and uniformly dispersed in nylon 1012. The speed of crystallization of the nanocomposite increased compared with nylon 1012. Furthermore, the tensile strength and the elastic modulus in tension were improved, and the amount of absorbed water was decreased through the improvement of the barrier characteristics. 

It was reported that the compatibilizer normally gets adsorbed on the surface of the clay platelets and alters the interphase [92]. The tensile strength and tensile modulus are always good for CPN compared with PP. The nano-level dispersion of clay in PP plays a vital role in such an improvement. The stiffness of the silicate layers contributes to the presence of immobilized (or) partially immobilized polymer phases [93]. The orientation of the silicate layer and molecular orientation also play a vital role in the improvement of the stiffness. 

In Section 23.2 was discussed the theory of reinforcement of polymer and elastomers which refers to the Guth-Gold-Smallwood equation (Equation (23.1)) to correlate the compound initial modulus (E ) with the filler volume fraction ( ). Moreover, it was already commented on the key roles played by the surface area and by the aspect ratio (/). Basic feature of nanofillers, such as clays, CNTs and nanographites, is the nano-dimension of primary particles and thus their high surface area. This allows creating filler networks at low concentrations, much lower than those typical of nanostructured fillers, such as CB and silica, provided that they are evenly distributed and dispersed in the rubber matrix. In this case, low contents of nanofiller particles are required to mutually disturb each other and to get to percolation. Moreover, said nanofillers are characterized by an aspect ratio /that can be remarkably higher than 1. Barrier properties are improved when fillers (such as clays and nanographites) made by... 

Shen and co-workers [91] used nano-indentation to study the effects of clay concentration on the mechanical properties, such as hardness, elastic modulus and creep behaviour of exfoliated PA 6,6-clay nanocomposites. Results were compared with those obtained by DMA and tensile tests. 

In the case of rubber blend clay composites good state of exfoliation of the clay, sufficiendy strong filler-rubber interactions as well as the compatibility between different rubber phases are playing major role. The presence of intercalated organoclays restricts the mobility of the rubber chains due to their confinement between the layers. As the concentration of nano filler increases the loss modulus increased. This can be explained in terms of the friction between the filler particles and the rubber matrix when the filler particles are uniformly dispersed in the mbber matrix. The damping values are found to decrease with the amount of filler due to the restricted mobility of the polymer chains owing to the intercalation of polymer chains into the layers of silicates. 

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