Particulate-Filled Polymer Composites 1 Modulus

As it is known [13, 14], the scale effects are often found at the study of different materials mechanical properties. The dependence of failure stress on grain size for metals (Holl-Petsch formula) [15] or of effective filling degree on filler particles size in case of polymer composites [16] are examples of such effect. The strong dependence of elasticity modulus on nanofiller particles diameter is observed for particulate-filled elastomeric nanocomposites [5], Therefore, it is necessary to elucidate the physical grounds of nano- and micromechanical behavior scale effect for polymer nanocomposites. 

According to the theories on reinforcement of polymer melts and elastomers by particulate fillers, " the initial modulus of a filled rubber composite is given by diflerent contributions. Figure 2.8 reports the dependence of the shear complex modulus on the strain amplitude. 

While unique properties, such as dimensional stability or increased hardness and modulus, are the usual motivation for exploiting particulate filled composites, special attention must be paid to other mechanical properties, such as yield and ultimate strength and fracture toughness [1 ]. Due to the low adhesion between non-polar hydrophobic polymer matrix and hydrophilic filler surface, the interfacial debonding is very frequently the first step of failure in these materials [2]. Mainly for this reason the effective application of particulate composites is first of all determined by the interfacial interaction between polymer and filler. 

Nanocomposites are composed of a polymer matrix and layered silicate platelets having approximately 1 nm thickness and large aspect ratio. In the last two decades, nanocomposites have attracted much attention from both industry and academia, because they may offer enhanced mechanical and/or physical properties (e.g., high modulus and high heat-distortion temperature) that are not readily available from conventional particulate-filled thermoplastic polymers. One of the advantages of such nanocomposites lies in that the concentration of layered silicates required is much lower (say, less than 7 wt%) than that (e.g., 40-60wt%) required for the conventional particulate-flUed thermoplastic composites to achieve a similar property enhancement. The lower specific gravity of nanocomposites as compared to conventional thermoplastic composites can offer potential cost benefits as well. 

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