Pet Nanocomposites

Biaxial stretching was reported to improve exfoliation of silicate layers within a PET matrix [67,68]. Rajeev et al. [67] employed a twin-screw extruder to produce PET 

Crystal content of the produced films also increased in the presence of the organoclays and higher degree of crystallinity was obtained for the samples containing the chain extender [74]. Mechanical properties in the machine direction of the neat PET and PET-based nanocomposites, with and without 

and TEM are widely used for morphological characterization of nanocomposites. Rheology has also been used extensively in complement to these techniques in several studies as it is very sensitive to the morphology of nanocomposites [23,75-80]. The summary of the most significant results from these studies is the transition from liquid-like to solid-like viscoelastic behavior for nanocomposites, even at low-volume fractions of silicate layers, as well as a strong shear-thinning behavior. The solid-like behavior has been attributed to the formation of a percolated network of clay particles that occurs at relatively low clay loading, due to the anisotropy of the particles, which prevents their free rotation and the dissipation of stress. 

By employing rheometry, detailed information about molecular-level changes in the stmcture (e.g., oxidation, degradation, cross-linking, etc.) can be obtained. In addition, the interactions between the nanoparticles and the matrix can also be detected and quantified. Another advantage of rheological methods is that they probe the bulk of nanocomposite materials on a significant volume of sample tested, which increases the reliability of the data. Finally, measurements are performed in the molten state, which can 

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For polyester, the reported work82 done in Sichuan University of China, involves adding MMT clay in a copolymer of poly(ethyleneterephthalate), which with a phosphorus-containing monomer could produce PET with higher thermal stability and char-forming tendency. However, fibers were not produced from this PET-nanocomposite polymers. 

An interesting observation is the reported decrease in melt viscosity of organo-clay composites, with respect to the matrix viscosity [46, 47]. Results reveal that PET nanocomposites behave quite differently in shear as opposed to elongation. 

Rheological studies of PET nanocomposites are not ample, but show very interesting features. In the low frequency range, the nanocomposites display a more elastic behavior than that of PET. It appears that there are some physical network structures formed due to filler interactions, collapsed by shear force, and after all the interactions have collapsed, the melt state becomes isotropic and homogeneous. Linear viscoelastic properties of polycaprolactone and Nylon-6 [51] with MMT display a pseudo-solidlike behavior in the low frequency range of... 

In the same manner, the crystallization behavior of SiO -PET nanocomposites is evaluated by means of DSC studies [33]. Basically polyethylene terephthalate is a crystalline polymer. The endothermic peak of the pure PET appears at 225°C and corresponds to melting temperature. The endothermic peak appears at high temperature for SiO -PET nanocomposite system. The data collected through DSC thermal analysis are given in Table 9.3. 

Table 9.3 DSC results of neat PET and SiO -PET nanocomposites. Reprinted from [33] with permission from Elsevier.

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]. 

Figure 1.16 Ring-opening polymerization of cyclic oligomers to generate PET nanocomposites. Reproduced from Ref [34] by permission from Elsevier.

Figure 5.8 (a) Mass (%) versus temperature and (b) derivative mass (DTG) versus temperature at a heating rate of 10°C/min for PET nanocomposites with OMMT. Reproduced from Ref [24] with permission. 

Sanchez-Garcia, M.D., Gimenez, E., Lagaron, J.M., 2007. Novel PET nanocomposites of interest in food packaging applications and comparative barrier performance with biopolyester nanocomposites. Journal of Plastic Film and Sheeting 23 (2), 133—148. 

Comparing the results of the neat PP and PP/PET nanocomposites with the PP/GF composites, a striking conclusion can be drawn. In the latter case, there is an extremely large error range (Table 11.1) indicating that some of the PP/GF samples have the same... 

Kim Bohwon, Koncar Vladan, and Devaux Eric. Electrical properties of conductive polymers PET -nanocomposites fibres. AUTEXRes. J. 4 no. 1 (2004) 9-13. 

At this point, we should also mention that this chapter is not intended to provide an extensive review of the polymer nanocomposites field - the reader interested in such reviews can refer to a number of related books [1 ], numerous compilations of relevant symposia and conference proceedings, or recent review articles [12-15,20,21]. This chapter is rather an attempt to establish design principles toward the formation of PET nanocomposites with layered silicates bearing thermally stable surfactants, as well as linking these design principles to the relevant underlying fundamentals. 

Because both melt-processing and polymerization of PET necessitate high temperatures (250-300 °C), it becomes obvious at the outset that any organically modified layered silicates that are intended as reinforcing fillers for PET should employ surfactants with appropriately high thermal stability. The typical alkylammoniums, for example, decompose below these temperatures. Two examples of higher-temperature surfactants that have been employed as modifiers for layered silicates in PET nanocomposites are pyridinium and phosphonium specifically, cetylpyridinium, via solution dispersion [22], and dode-cyltriphenylphosphonium, via in situ polymerization [23], In these two cases, both the... 

In this chapter, we focus on melt-processed PET/nanoclay nanocomposites, where the nanoclay is alkylimidazolium montmorillonite or alkylquinolinium montmorillonite. The chemical structures of these thermally stable alkyl cations are shown in Figure 4.1, and both the surfactants and the respective organically modified clays can be synthesized easily (see Section 4.5). These imidazolium and quinolinium surfactants satisfy all three requirements for application to melt-processable PET nanocomposites, as enumerated in Section 4.2.1. Specifically,... 

In summary, when surfactants are selected for nanofillers intended for PET nanocomposites, there are important requirements that should be met, substantially limiting the range of appropriate surfactants. As a first approach, alkylammoniums should be avoided, whereas alkylimidazoliums should be preferred. This last class of surfactants are applicable to high-performance nanocomposites beyond PET for example, they were successfully used in polystyrene and polyamide matrices [32], epoxies [35], and ABS polymers [36, 37], as well as for fillers other than clays, such as polyhedral oligomeric silsesquioxane (POSS) [38] and carbon nanoffibes [39]. 

As examples of the utilization of thermally stable imidazolium-based surfactants with mont-morillonite (MMT), allowing high-temperature melt-blending of PET nanocomposites. 

Figure 4.6 DMA analysis comparing unfilled PET homopolymer with melt-processed PET nanocomposites at 3 wt% inorganic loading, based on hexadecylimidazohum MMT (imig) and on 2MTL8 alkylammonium MMT (amig.s)- The storage modulus (G ) and the tan5 (G"/G ) are plotted.

Figure 4.7 Thennogravitometric analysis (TGA) of various PET nanocomposites employing clays with thermally stable organic surfactants (a,b) Melt-processed PET copolymer with hexadecylimi-dazolium MMT (c) Melt-processed PET homopolymer with various clays bearing hexadecylquino-Uniums [25]. (d) Solution-processed PET with cetylpyridinium MMT [22]. AH TGA was done under N2 flow.

Study [25] concluded that this fire performance is probably due to filler-induced increased char formation, because the reductions in PHRR are roughly comparable for all four composites, despite their morphological variations (ranging from very good nanoscale and mesoscale dispersions for the MMT-based nanocomposites to rather poor dispersions and conventional composite structures for the magadiite-based composites [25]). In addition, when the fire behavior of these PET nanocomposites [25] was compared with that of PS nanocomposites [47] (based on both alkylquinolinium- and alkylammonium-modified MMT), it was suggested that the thermally stable quinolinium surfactants are more effective in fire-resistance improvement than the alkylammonium surfactants [25]. 

A. Vassiliou, K. Chrissafis, and D. Bikiaris, Thermal degradation kinetics of in situ prepared PET nanocomposites with acid-treated multi-walled carbon nanotubes. Journal of Thermal Analysis and Calorimetry, 100 (2010), 1063-71. 

C. Byrne, T. McNally, and C. G. Armstrong, Thermally stable modified layered silicates for PET nanocomposites. Presented at Polymer Processing Society Americas Regional Meeting, Quebec, Canada, 2005. 

The incorporation of impermeable clay particles into PET (which is a semicrystalline polymer) can improve the barrier properties of PET nanocomposites towards gases and water vapor. This, in turn, results in outstanding property improvements in terms of a decreasing water permeability for food packaging and an increasing flame resistance. When a new system of saturated polyesters... 

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