Nanocomposite formation mechanical property improvements

To the extent that they are valid, the observations above bear significant implications for the possibilities of mechanical property improvements via nanocomposite formation. Specifically ... 

General purpose plastics are characterized for being used in low cost applications due to the ease of processing and low level of mechanical exigency. One way to add value to these commodities is nanocomposite formation, aiming to improve their properties (Anadao et al 2011). 

By analogy with the works which dealt with cellulose micro crystal-reinforced nanocomposite materials, microcrystals of starch [95] or chitin [96, 97] were used as a reinforcing phase in a polymer matrix. Poly(styrene-co-butyl acrylate) [95,96], poly(e-caprolactone) [96], and natural rubber [97] were reinforced, and again the formation of aggregates or clustering of the fillers within the matrices was considered to account for the improvement in the mechanical properties and thermal stability of the respective composites processed from suspensions in water or suitable organic solvents. 

For more than a decade, numerous research studies have been carried out on the flame-retardant properties conferred by nanoparticles and mainly by organo-modified layered silicates (OMLS). Earlier work at Cornell University and National Institute of Standards and Technology in the United States showed that nanocomposites containing OMLS reduced polymer flammability and enhanced the formation of carbonaceous residue (char).14 Owing to a strong increase in polymer viscosity, impairing processability, and also due to the breakdown of ultimate mechanical properties, the acceptable rate of incorporation for nanoparticles to improve flame retardancy is generally restricted to less than 10 wt %. 

The mechanical properties of the C3, C6, and Cl2 nanocomposites were all significantly better than those of the neat phenolic resin, even if a very small amount of the silicate was used. Among the nanocomposites prepared, the organically modified MMT-resol systems showed better mechanical properties than those of the unmodified MMT-resol system. This improvement was attributed to the formation of an end-tethered structure due to the reaction of the carboxylic acid of the organic modifier with the methylol group of the phenolic resin. Thermogravimetric analysis reported by Byun and coworkers showed that the nanocomposite systems had similar thermal stability to that of the neat polymer. 

Studies indicate the formation of an intercalated morphology in the nanocomposites due to favorable interactions between the polymer matrix and the clay. The morphology of the nanocomposite is intricately linked to the amount of silicate in the system. With clay content >15 wt%, mechanical properties are further improved but the formation of an apparent superlattice structure correlates with a loss in the electrical properties of the nanocomposite [25]. 

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