Polymer clay nanocomposites experimental

Pooria Pasbakhsh, PhD, is currently a Lecturer at the School of Engineering, Monash University Sunway Campus, Malaysia. Dr. Pasbakhsk s research has been centered on the development and application of computational approaches and experimental tools for modern polymers, halloysite nanotubes, and polymer clay nanocomposites. 

Six of the eleven chapters are devoted primarily to the intercalation chemistry of smectite clays, the most versatile among all lamellar compounds. Two of these chapters are devoted to the experimental and theoretical aspects of the clay structures and surface chemistry, including chemical catalysis. Organo clays and polymer-clay nanocomposites, the adsorption of nitroaromatic compounds of environmental significance onto clay surfaces, photochemical processes, and pillared clays and porous clay heterostructures are the subjects of the remaining four chapters. These six chapters provide detailed discussions of the factors that influence access to the intragallery surfaces of the clay host and the materials properties of the resulting intercalates. 

As presented schematically in Figure 16, a second way to prepare polymer-clay nanocomposites via in situ polymerization consists of intercalation of the monomer (or a precursor of the monomer) in the form of a cation and then later addition of an initiator to induce/polymerization. Thus, the direct exchange of the interlayer cations of smectites by anilinium cations, followed by oxidation with (NH4)2S20g, could be an alternative procedure to reach the formation of PANI/clay nanocomposites. In this case, the experimental conditions allow the direct formation of PANI as a conducting emeraldine salt (152). 

The experimental data on barrier performance of polymer-clay nanocomposites can be divided into three categories. The first group includes systems that fit the tortuous path model reasonably well. The second category includes composites that exhibit relative gas permeabilities that are inferior to the tortuous path model predictions. The last group includes composites that exceed the performance predicted by the model. The following discussion will give specific examples of each of these categories with explanations for each type of behavior. 

The effect of polymer-filler interaction on solvent swelling and dynamic mechanical properties of the sol-gel-derived acrylic rubber (ACM)/silica, epoxi-dized natural rubber (ENR)/silica, and polyvinyl alcohol (PVA)/silica hybrid nanocomposites was described by Bandyopadhyay et al. [27]. Theoretical delineation of the reinforcing mechanism of polymer-layered silicate nanocomposites has been attempted by some authors while studying the micromechanics of the intercalated or exfoliated PNCs [28-31]. Wu et al. [32] verified the modulus reinforcement of rubber/clay nanocomposites using composite theories based on Guth, Halpin-Tsai, and the modified Halpin-Tsai equations. On introduction of a modulus reduction factor (MRF) for the platelet-like fillers, the predicted moduli were found to be closer to the experimental measurements. 

Alperstein D. Experimental and computational investigation of EVOH/clay nanocomposites. J Appl Polym Sci 2005 97 2060-2066. 

Under specific experimental conditions, such materials may be obtained as delaminated (or exfoliated) nanocomposites, which may be described as single inorganic slabs imiformly and randomly dispersed within a polymer matrix. Readers interested by the synthesis and the properties of these delaminated nanocomposites, especially in the field of clays, should see Nanocomposites, Polymer-Clay and other recent reviews (7-9). These materials have imusual and versatile properties, such as barrier materials and reinforced materials, (see Barrier Polymers Reinforcement). 

The properties of polymer nanocomposites are influenced by numerous factors including nanofillers type, purity, and the match between clay and CNT dimensions (length and diameter). These factors should be taken into account in the preparation of polymer nanocomposite, as well as in process of reporting and interpreting the experimental data. 

To clarify the mechanisms of the clay-reinforced carbonaceous char formation, which may be responsible for the reduced mass loss rates, and hence the lower flammability of the polymer matrices, a number of thermo-physical characteristics of the PE/MMT nanocomposites have been measured in comparison with those of the pristine PE (which, by itself is not a char former) in both inert and oxidizing atmospheres. The evolution of the thermal and thermal-oxidative degradation processes in these systems was followed dynamically with the aid of TGA and FTIR methods. Proper attention was paid also to the effect of oxygen on the thermal-oxidative stability of PE nanocomposites in their solid state, in both the absence as well as in the presence of an antioxidant. Several sets of experimentally acquired TGA data have provided a basis for accomplishing thorough model-based kinetic analyses of thermal and thermal-oxidative degradation of both pristine PE and PE/MMT nanocomposites prepared in this work. 

Several authors used the continuum mechanics for modeling conventional polymer composites as well as PNC. Ren and Krishnamoorti [2003] used a K-BKZ integral constitutive model to predict the steady-state shear behavior of a series of intercalated nanocomposites containing an organo-MMT and a disordered styrene-isoprene diblock copolymer. The model predicts the low-y shear stress properties calculated from the experimental linear stress relaxation and the relaxation-based damping behavior. However, as it does not take into account the effect of clay platelet orientation, it is unable to predict the shear stress behavior at intermediate y and the normal stress behavior at all y and clay contents. 

As stated in the introduction, this study is part of a more general project that deals with the synthesis, characterization, materials properties investigation, and molecular modelling of clay-polymer nanocomposites. This section presents die experimental and theoretical approaches used in this work. 

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