Polymer clay nanocomposites mechanical properties

Polymer-clay nanocomposites (PCN) are a class of hybrid materials composed of organic polymer matrices and organophilic clay fillers, introduced in late 1980s by the researchers of Toyota (Kawasumi, 2004). They observed an increase in mechanical and thermal properties of nylons with the addition of a small amount of nano-sized clays. This new and emerging class of pol miers has found several applications in the food and non-food sectors, such as in constmction, automobiles, aerospace, military, electronics, food packaging and coatings, because of its superior mechanical strength, heat and flame resistance and improved barrier properties (Ray et al., 2006). 

Polymer clay nanocomposites have, for some time now, been the subject of extensive research into improving the properties of various matrices and clay types. It has been shown repeatedly that with the addition of organically modified clay to a polymer matrix, either in-situ (1) or by melt compounding (2), exfoliation of the clay platelets leads to vast improvements in fire retardation (2), gas barrier (4) and mechanical properties (5, 6) of nanocomposite materials, without significant increases in density or brittleness (7). There have been some studies on the effect of clay modification and melt processing conditions on the exfoliation in these nanocomposites as well as various studies focusing on their crystallisation behaviour (7-10). Polyamide-6 (PA-6)/montmorillonite (MMT) nanocomposites are the most widely studied polymer/clay system, however a systematic study relating the structure of the clay modification cation to the properties of the composite has yet to be reported. 

Since Nylon-6/clay nanocomposites with excellent thermal and mechanical properties were reported by many scientists and polymer/clay nanocomposites have attracted much attention. The improvements in thermal. 

Polymer clay nanocomposites are already used in many applications to enhance existing properties of a particular material, and development should be focused on the true multifunctional materials. Certainly, clay nanocomposites will continue to be used for enhanced mechanical, flammability, and gas barrier properties, but fundamental limits in clay chemistry prevent them from being used easily in applications requiring electrical/ thermal conductivity or optical properties. Similarly, combinations of... 

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. 

In recent years, a new and emerging class of clay-filled polymers called Polymer-Clay Nanocomposites (PCN) was developed. Properties such as superior mechanical strength, reduction in weight, increased heat-resistance and flame retardancy, improved barrier properties against oxygen, carbon dioxide, ultraviolet light, moisture and volatiles, as well as conservation of flavor in drinks and beverages are achievable with these novel composites [17-21]. 

Flame retardant intumescent formulations have been developed using charring polymers PA6, thermoplastic polyurethanes (TPUs), and hybrid clay-PA6 nanocomposites as carbonisation agents. The advantage of the eoncept is to obtain FR polymers with improved mechanical properties and to avoid the problem of migration and solubility of the additives. 

The addition of nanoparticles to synthetic rubber resulting in enhancement in thermal, stiffness and resistance to fracture is one of the most important phenomena in material science technology. The commonly used white filler in mbber industry are clay and silica. The polymer/clay nanocomposites offer enhanced thermo mechanical properties. Bourbigot et al. observed that the thermal stability of polystyrene (PS) is significandy increased in presence of nanoclay [75]. Thermal and mechanical properties of clays multiwalled carbon nanotubes reinforced ethylene vinyl acetate (EVA) prepared through melt blending showed synergistic effect in properties [76]. 

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. 

Since the publication of Toyota s pioneering work on polymer-silicate (or clay) nanocomposites, the preparation of polymer clay nanocomposites has attracted intense interest in the materials science community [1-6]. By introducing a few weight percent of clay into the polymer matrix, many properties of these nanocomposites will be improved, such as mechanical properties [7], thermal stability [8], and flam retardance [9],... 

Nowadays, ordered inorganic/organic PNs with a finely tuned structure have displaced a lot of traditional composite materials in a variety of applications because the intimate interactions between components can provide enhancement of the bulk polymer properties (i.e., mechanical and barrier properties, thermal stabihty, flame retardancy, and abrasion resistance). The reinforcing nanoparticle/ polymer adhesion is of primarily importance, as it tunes the final properties of the nanocomposite. Polymer/clay nanocomposites (PCNs) meet this demand due to the platelet-type dispersion of the clay filler in the organic matrix [1]. 

Mechanical Behavior. Being able to improve strength and stiffness with limited alteration of toughness is a goal readily achievable with polymer-clay nanocomposites (see Mechanical Properties Reinforcement). 

Following the appropriate pathway, in situ polymerization has allowed the preparation of a large variety of polymer-clay nanocomposites with interesting functional and/or mechanical properties. For instance, a doped PPy-synthetic hec-torite nanocomposite exhibits conductivity from about 10 to 10 S/cm (155). In gena-al, monomers showing affinity to be adsorbed by smectites, e.g., hydrophilic species, can produce infracrystalline homocondensations. Other monomers, such as acrylonitrile, are also easily intercalated in smectites, because such molecules are directly associated to the interlayer cations M" (M" = Li +, Na, etc.) through —C N—M"+ ion-dipole interactions (156-158). The action of "Y-irradiation (156) or thermal (158) treatments can induce the polymerization... 

Eventually, regarding the nano-hydro)yapatite filler, like the polymer/ clay nanocomposites, the good dispersion of inorganic fillers in the PHBV inevitably benefits the improvement of the mechanical properties of the materials. Furthermore, the study also pointed out the enhanced material bioactivity since this specific property is expected for the repair and replacement of bone. 

Polymer/clay nanocomposites exhibit remarkable improvement in material properties relative to unfilled polymers or conventional composites. These improvements can include increased tensile modulus, mechanical strength, and heat resistance and reduced gas permeability and flammability [1], There are various methods of preparing polymer/clay nanocomposites (i) in situ polymerization, (ii) solution intercalation, (iii) melt intercalation, and (iv) in situ template synthesis [2],... 

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