Nano-clays strength

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 ... 

The impact strength of clay-polymer nanocomposites either increases, decreases or remains unaltered by the nano-clay incorporation. The impact strength is not altered much by the presence of nano-clay, as reported elsewhere [21]. A special co-intercalation type of organoclay was used. In another study, an improvement in impact property is noticed while incorporating nano-clay in PP matrix [58]. The Izod impact strength of PP and CPN is shovm in Figure 9.37. 

The incorporation of dimethyl-dialkyl ammonium treated montmoril-lonite clay does not alter the impact toughness in sub-zero temperatures, whereas the addition of nano-clay improves the strength at higher temperatures. However, the fracture toughness of nanocomposites and neat epoxy increases when they are treated with sea water for 180 days. The... 

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 use of layered silicate nano-particles (i.e., clay), which have a much larger surface area (-750 mVg) and a much higher aspect ratio (>200) than conventional, macro-sized fillers, to reinforce polymers, has drawn a great deal of attention in recent years [14-18]. Adding a small amount of nano-clay can dramatically improve a number of properties such as stiffness and strength, thermal and dimensional stability, flame retardance, and barrier properties [17,18]. Thus, the introduction of nanoclay into WPCs could prove interesting from the perspective of improving their mechanical properties and flame retardance, which are desirable effects, particularly... 

The foam density variations of the foamed WPCs with different contents of wood fiber as a function of die temperature are shown in Figure 4. With no gas injection, the density reduction may be due to the volatiles (e.g., moisture or extractives) generated from WF during processing. The addition of 1% exfoliated nano-clay particles decreased slightly the foam density of the composites. This may be because nano-clay particles increase the melt strength and thereby the possibility of gas escape from the extrudate skin decreases. 

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). 

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). 

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. 

Nano-composites are the subject of intense research for a number of properties such as improved barriers to gas, higher mechanical strength, and improved flame retardancy. Plate-like particles of special clays, one nanometre (one billionth of a metre) thick by 1000 nanometres in diameter, are being studied as FRs in plastics by the US National Institute for Standards and Technology (NIST), Gaithersburg, Maryland. Initial research showed that the addition of as little as 5% of nano-sized clay particles could produce a 63% reduction in the... 

Composites are widely used in such diverse areas as transportation, construction, electronics and consumer products. They offer unusual combinations of stiffness, strength and weight that are difficult to attain separately from the individual components. The advent of nanoscience and nanotechnologies has continuously provided the impetus pushing for the development of materials with fascinating properties and a rich variety of applications. Polymer-clay (PC) nanocomposites represent a new class of materials based on reinforcement of polymeric materials by dispersion of nano-scale clay particles at molecular level in the polymer matrix. Because of their nanometer size features, nanocomposites possess unique properties typically not shared by their more conventional miaocomposite counterparts and therefore offer new technology and business opportunities. 

---