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The effects of the incorporation of multiwalled carbon nanotubes (MWNT) with a diameter range of 10−30 nm on the shear-induced crystallization behavior of poly(butylene terephthalate) (PBT) were investigated under myriad shearing and loading conditions employing principally the small-amplitude oscillatory shear flow. Upon shearing, the presence of MWNTs leads to the crystallization of the PBT nanocomposites at temperatures that are higher than the crystallization temperature of unfilled PBT. The Avrami analysis of the shear-induced crystallization data of PBT nanocomposite samples indicated that the kinetics of the crystallization depend on both the temperature and the concentration of the MWNTs. When the MWNTs were replaced with ∼70 μm graphite particles at similar volume loading levels the crystallization behavior of the PBT/graphite suspension samples did not differ from that of pure PBT. These findings emphasize that one primary mechanism associated with the significant changes in the mechanical properties observed upon the compounding of nanoparticles into various semicrystalline polymers is the change in the crystallization behavior of the polymer as affected by the presence and the concentration of the nanoparticles and the associated changes in the microstructural distributions of the nanocomposite.

There is growing interest in the incorporation of nanoparticles into engineering polymers to improve various functional properties. However, ultimate properties of nanocomposites are affected by a large number of factors including the microstructural distributions that are generated during processing. In this work, polyamide-11 (PA-11) (also known as nylon-11) nanocomposites are generated with carbon nanostructures employing a solution crystallization technique at multiple polymer and nanoparticle concentrations, followed by drying, molding, uniaxial stretching and the analysis of the microstructural distributions and tensile properties of the nanocomposites. The morphology of crystals of PA-11 encapsulating the nanoparticles changed from nano-hybrid shish-kebabs at low polymer concentration (0.02 wt % PA-11 in solvent) to spherulites at high polymer concentration (10 wt % PA-11 in solvent). The drawing down of nanocomposite films at draw ratios ranging from 2 to 5 at 100 C resulted in a shift of the PA-11 polymorph from the generally-encountered a phase to the technologically interesting c phase (which is the crystal phase attributed to the piezoelectric and pyroelectric properties of PA-11). The drawing down also increased of the tensile modulus and yield stress of the nanocomposite films. In contrast, the a phase was conserved at a drawdown temperature of 150 C, which was attributed to the resulting smaller normal force, i.e., the normal stress difference and the higher temperature allowing the partial relaxation of some of the macromolecules. These findings illustrate how PA-11 can be structured in the presence of carbon nanotubes and nanofibers to achieve enhanced functionality, which could broaden the application areas and utility of this polymer.

Poly(vinylidene fluoride) (PVDF) is a semicrystalline thermoplastic polymer that is of interest for sensor, actuator and biomedical applications because of its piezoelectric and pyroelectric properties, as well as outstanding mechanical and chemical properties. Although it is known that the shear-induced crystallization behavior of nanocomposites can be significantly affected by the presence of nanoparticles, the effects of the incorporation of carbon nanotubes on the deformation-induced crystallization and associated morphology development of PVDF have not been previously investigated. Here the dynamics of the shear-induced crystallization of carbon nanotubes incorporated in PVDF were investigated using simple shear flow. The shear-induced crystallization behavior was affected by the deformation rate, temperature, and the concentration of the carbon nanotubes. Time-dependence of linear viscoelastic properties indicated that the presence of multi-walled carbon nanotubes (MWNTs) in PVDF greatly altered the shear-induced crystallization kinetics of PVDF, while no significant changes in crystallization behavior were observed for pure PVDF samples sheared under similar conditions. Upon increase of the concentration of the MWNTs the crystal size of PVDF decreased while its rate of crystallization increased in conjunction with an increase of the beta phase crystallization. Overall, these findings suggest that the shear-induced crystallization of PVDF nanocomposites (and in general flow-induced crystallization effects associated with the thermo-mechanical history experienced by the nanocomposite during processing) should be integral parts of attempts to generate a comprehensive understanding of the development of the microstructural distributions and the coupled ultimate properties of polymer nanocomposites.

Microporous polyvinylidene fluoride (PVDF) and PVDF nanocomposite membranes were prepared via an isothermal immersion precipitation method using two different antisolvents (ethanol and water). The structure and morphology of the resulting membranes were investigated by wide angle X-ray diffraction (WAXD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and differential scanning calorimetry (DSC). The effects of the type of the antisolvent and the presence of multiwalled carbon nanotubes (MWNTs) on membrane morphology and the crystal structure developed within the membranes were studied. The crystallization of the PVDF upon immersion precipitation occurred predominantly in the α-phase when water is used as the antisolvent or in the absence of the carbon nanotubes. On the other hand, β-phase crystallization of the PVDF was promoted upon the use of ethanol as the antisolvent in conjunction with the incorporation of the MWNTs. The morphology and the total crystallinity of the PVDF membranes were also affected by the incorporation of the MWNTs and the antisolvent used, suggesting that the microstructure and the ultimate properties of the PVDF membranes can be engineered upon the judicious selection of crystallization conditions and the use of carbon nanotubes.

There is tremendous interest in using low loadings of multiwalled carbon nanotubes (MWNTs) to enhance the multifunctional properties of polymers, with functionalization often pursued to increase the dispersion and effective reinforcement of MWNTs within the polymer. In our interest to understand the effect of MWNT functionalization on Poly (butylene terephthalate) (PBT) crystallization kinetics, morphology and mechanical properties, nanocomposites were fabricated with both as-received and carboxyl group (-COOH) functionalized MWNTs. Initial results indicate as-received and functionalized nanotubes alter the crystallization temperature and crystal size for quiescent samples. In addition, isothermal crystallization studies using an Advanced Rheometric Expansion System (ARES) show that the addition of MWNTs increases the rate of PBT crystallization. However, functionalization was found to decrease the rate of nanocomposite crystallization as compared to nanocomposites samples prepared using pristine MWNTs, suggesting that nanotube functionalization weakens the nucleation effect observed in the nanocomposite samples. These results suggest that semicrystalline polymer nanocomposite crystallization kinetics and morphology can be significantly influenced by nanoparticle functionalization and chemistry. Further study of how these changes impact the rheological and multifunctional properties of semicrystalline nanocomposite systems are ongoing.

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