Clay-polymer nanocomposites tensile properties

In one example, the tensile strength of polyamide 6 was increased by 55% and the moduli by 90%, with the addition of only 4wt% of delaminated clay. The enhanced tensile property of PCN suggests that nanocomposite performance is related to the degree of clay delamination, which increases the interaction between the clay layers and the polymers. Several explanations, based on the interfacial properties and the mobility of the polymer chains, have been given for this reinforcement. Kojima et al. reported that the tensile modulus improvement for polyamide 6-clay hybrid originated from a constrained region, where the polymer chains have reduced mobility. The dispersion and delamination of the clay were the key factors for the reinforcement. The delaminated nanocomposite structure produces a substantial increase in modulus. 

Clay-polymer nanocomposites, a new class of hybrids, came into the purview of researchers after their invention by the Toyota research group [7,8]. They found dramatic improvement in tensile properties of polymers by adding clay in small weight fractions. In continuation of this, other researchers have used various techniques to develop polymer nanocomposites with clay as reinforcement after proper organic treatment. 

The physical properties of a number of other polymer nanocomposites made with clays have been measured. Table 33.3 contains a selection of reported values for some of the most common polymers. Poly(ethylene terephthalate) (PET) and Poly(butylene terephthalate) (PBT) are the most commOTi commercial engineering polymers. The average increase in tensile modulus for most of the PET nanocomposites [21,22,24] is in the range of 35%. This is well below the prediction of a 95% increase for a 5% by weight nanocomposite utilizing Halpin-Tsai theory. The only exception was PET produced by in situ polymerization and tested as fibers [20]. In each one of these references it was acknowledged that full exfoliation had not been reached in the composite. It is reasonable to expect that substantial improvement in properties could be seen if full exfoliation were achieved. The reported increase in tensile modulus for PBT nanocomposites is only in the 36% range [23,24]. 

Le Digabel F, Boquillon N, Dole P et al (2004) Properties of thermoplastic composites based on wheat-straw lignocellulosic fillers. J Appl Polym Sci 93 428-436 Lee S -R, Park FI-M, Lim H et al (2002) Microstructuie, tensile properties, and biodegradability of aliphatic polyester/clay nanocomposites. Polymer 43 2495-2500 Lee SFI, Ohkita T, Kitagawa K (20(M) Eco-composite from poly(lactic acid) and bamboo fiber. Flolzforschung 58 529-536... 

Recently, a big window of opportunities has opened for polymer nanocomposites just to overcome the limitations of traditional microcomposites. Although, the chemistry of clay minerals and composites based on some nanoscale particles is known for several decades, the research and development of nanoscale-filled polymers has been skyrocketed in recent years, for numerous reasons. First, unprecedented combinations of properties have been observed in some polymer nanocomposites. For example, incorporation of isodimensional nanoparticles into thermoplastics increases the modulus, the yield stress, and the ultimate tensile strength (Sumita et al. 1983). 

Polycaprolactone can increase the tensile strength and impact strength but reduce the ultimate elongation, tensile modulus, and shrinkage of the thermoplastic starch (TPS) polymer (Avemous et al. 2000). Montmorillonite clay can improve the properties of TPS and create a biobased nanocomposite (Bordes et al. 2009 Aouada et al. 2011). 

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