PET Clay Nanocomposites by In-situ Polymerization

Hua Deng, Ke Wang, Qin Zhang, Feng Chen, and Qiang Fu 

Research activities in nanomaterials have increased dramatically over the last decade. Nanocomposites based on polymers have been considered as one of the most important methods to modify polymer matrices at the nanometer level [1]. These materials differ from conventional materials not only thanks to the properties of the nanofillers, but also to their extreme small size and large surface area which allow them to have much more interaction with the polymer matrix than conventional composites. 

In-situ Synthesis of Poiymer Nanocompo tes, First Edition. Edited by Vikas Mittal. 

Polyethylene terephthalate (PET) as one of the most important engineering thermoplastics has a wide range of apphcations in the areas of fibers, clothes, soft drink bottles, etc., due to its low cost and high performance. Thus, any improvement for PET in terms of its crystallization, antistatic, fire retardant, barrier, and mechanical properties could enhance its potential for industrial application [14]. 

Several methods including melt compounding, solution-based process, and in-situ polymerization could be used for the preparation of PET/clay nanocomposites. In-situ polymerization involves swelling of clays in a liquid monomer, or a monomer solution, followed by polymerization initiated thermally or by the addition of a suitable compound in the presence of intercalated/exfoUated days. It is considered as one of the best methods to produce polymer nanocomposites based on day because relativdy small-sized monomers could be easily intercalated into day layers before polymerization. Then, further polymerization between days could easily lead to weU-dispersed clay in the polymer matrix. Furthermore, day could be added into the redpe for the polymerization process thus, no further process is needed to reahze industrial application. 

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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]. 

Nanocomposite conventional mesoscale fibers (textile fibers that carry nanoparticulate filler) are produced via conventional fiber-spinning techniques by incorporating well-dispersed nanoparticles into the spinning dope. For instance, an intercalated poly(ethylene terephthalate) (PET)/organo-montmorillonite (MMT) nanocomposite prepared by in situ polymerization of the polyester in the presence of MMT clay was successfully melt spun into microfibers (Guan, G.-H., et al. 2005). Melt-spun conventional fibers of... 

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