Rheology of poly(propylene)/clay nanocomposites

The linear and nonlinear shear rheological behaviors of poly(propylene) (PP)/clay (organophilic‐montmorillonite) nanocomposites (PP/org‐MMT) were investigated by an ARES rheometer. The materials were prepared by melt intercalation with maleic anhydride functionalized PP as a compatibilizer. The storage moduli (G′), loss moduli (G″), and dynamic viscosities of polymer/clay nanocomposites (PPCNs) increase monotonically with org‐MMT content. The presence of org‐MMT leads to pseudo‐solid‐like behaviors and slower relaxation behaviors of PPCN melts. For all samples, the dependence of G′ and G″ on ω shows nonterminal behaviors. At lower frequency, the steady shear viscosities of PPCNs increase with org‐MMT content. However, the PPCN melts show a greater shear thinning tendency than pure PP melt because of the preferential orientation of the MMT layers. Therefore, PPCNs have higher moduli but better processibility compared with pure PP.© 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 2427–2434,2004     

Eco-friendly electronics,based on nanocomposites of biopolyester reinforced with carbon nanotubes: a review

ABSTRACT

Fabrication of electronic materials from nanocomposite of biopolyesters reinforced with carbon nanotubes can be regarded as the effective alternative for conventional nanocomposites consisting of non-biodegradable polymers. Commercial availability of biopolyester-based nanocomposites is limited because of their high cost compared to other polymers, but the factor of their compostable nature is worthless for environmental protection. Such nanocomposites have potential applications in biodegradable sensors, EMI materials, etc. In this review, the current progress of biopolyester/CNTs nanocomposites in the field of biodegradable electronics is reviewed and also the impact of CNTs dispersion on electrical, thermal and mechanical properties of eco composites is stipulated.     

Nonisothermal crystallization kinetics of poly(butylene terephthalate)/montmorillonite nanocomposites

The melt intercalation method was employed to prepare poly(butylene terephthalate) (PBT)/montmorillonite (MMT) nanocomposites, and the microstructures were characterized with X‐ray diffraction and transmission electron microscopy. Then, the nonisothermal crystallization behavior of the nanocomposites was studied with differential scanning calorimetry (DSC). The DSC results showed that the exothermic peaks for the nanocomposites distinctly shifted to lower temperatures at various cooling rates in comparison with that for pure PBT, and with increasing MMT content, the peak crystallization temperature of the PBT/MMT hybrids declined gradually. The nonisothermal crystallization kinetics were analyzed by the Avrami, Jeziorny, Ozawa, and Mo methods on the basis of the DSC data. The results revealed that very small amounts of clay (1 wt %) could accelerate the crystallization process, whereas higher clay loadings reduced the rate of crystallization. In addition, the activation energy for the transport of the macromolecular segments to the growing surface was determined by the Kissinger method. The results clearly indicated that the hybrids with small amounts of clay presented lower activation energy than PBT, whereas those with higher clay loadings showed higher activation energy. The MMT content and the crystallization conditions as well as the nature of the matrix itself affected the crystallization behavior of the hybrids. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 99: 3257–3265, 2006     

Thermal and surface characterization of polyurethane–urea clay nanocomposite coatings

This paper reports synthesis and characterization of polyurethane–urea (PU‐urea) and the nanocomposites derived from the PU‐urea with silicate clays. Organophilic montmorillonite cotreated by cetyl trimethyl ammonium bromide (CTAB) was synthesized and used to prepare PU‐urea/montmorillonite nanocomposites coatings. PU‐ureas were prepared from polyethylene glycol (PEG), polypropylene glycol (PPG), trimethylol propane (TMP), and 4,4′‐diphenylmethane diisocyanate (MDI) by reacting excess diisocyanate with polyether glycols. The excess isocyanate of the prepolymers was cured with atmospheric moisture. The synthesized moisture cured PU‐urea and nanocomposites were characterized by Fourier transform infrared (FTIR) spectroscopy, thermogravimetric analysis (TGA), differential scanning calorimetric (DSC), and angle resolved X‐ray photoelectron spectroscopy (AR‐XPS). The thermal stability of the PU‐urea nanocomposites was higher relative to the mother PU‐urea films. DSC results showed a slight enhancement in the soft segment glass transition temperature after 3 wt % clay loading. The surface properties showed an enrichment of the soft segment toward the surface. An enhancement in the hard segment composition in the nanocomposite coatings has resulted in enhancing the phase mixing process. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 2393–2401, 2006     

Synthesis and characterization of in situ polymerized segmented thermoplastic elastomeric polyurethane/layered silicate clay nanocomposites

Nanocomposites based on thermoplastic elastomeric polyurethane (TPU) and layered silicate clay were prepared by in situ synthesis. The properties of nanocomposites of TPU with unmodified clay were compared with that of organically modified clay. The nanocomposites of the TPU and organomodified clay showed better dispersion and exhibited superior properties. Exfoliation of the clay layers was observed at low organoclay contents, whereas an intercalated morphology was observed at higher clay contents. As one of major purposes of this study, the effect of the silicate layers in the nanocomposites on the order–disorder transition temperature (T_ODT) of the TPU was evaluated from the intensity change of the hydrogen‐bonded and free carbonyl stretching peaks and from the peak position change of the N? H bending peak. The presence of the organoclay increased T_ODT by approximately 10°C, which indicated improved stability in the phase‐separated domain structure. The layered silicate clay caused a tremendous improvement in the stiffness of the TPU; meanwhile, a reduction in the ultimate elongation was observed. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 3048–3055, 2006     

Characterization and preparation of new multiwall carbon nanotube/conducting polymer composites by in situ polymerization

Composites based on poly(diphenyl amine) (PDPA) and multiwall carbon nanotubes (MWNTs) were prepared by chemical oxidative polymerization through two different approaches: in situ polymerization and intimate mixing. In in situ polymerization, DPA was polymerized in the presence of dispersed MWNTs in sulfuric acid medium for different molar composition ratios of MWNT and DPA. Intimate mixing of synthesized PDPA with MWNT was also used for the preparation of PDPA/MWNT composites. Transmission electron microscopy revealed that the diameter of the tubular structure for the composite was 10–20 nm higher than the diameter of pure MWNT. Scanning electron microscopy provided evidence for the differences in the morphology between the MWNTs and the composites. Raman and Fourier transform IR (FTIR) spectroscopy, thermogravimetric analysis, X‐ray diffraction, and UV–visible spectroscopy were used to characterize the composites and reveal the differences in the molecular level interactions between the components in the composites. The Raman and FTIR spectral results revealed doping‐type molecular interactions and coordinate covalent‐type interactions between MWNT and PDPA in the composite prepared by in situ polymerization and intimate mixing, respectively. The backbone structure of PDPA in the composite decomposed at a higher temperature (>340°C) than the pristine PDPA (～300°C). This behavior also favored the molecular level interactions between MWNT and PDPA in the composite. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 3721–3729, 2006     

Using maleic anhydride grafted poly(lactic acid) as a compatibilizer in poly(lactic acid)/layered‐silicate nanocomposites

The goal of this work was to prepare exfoliated poly(lactic acid) (PLA)/layered‐silicate nanocomposites with maleic anhydride grafted poly(lactic acid) (PLA–MA) as a compatibilizer. Two different layered silicates were used in the study: bentonite and hectorite. The nanocomposites were prepared by the incorporation of each layered silicate (5 wt %) into PLA via solution casting. X‐ray diffraction of the prepared nanocomposites indicated exfoliation of the silicates. However, micrographs from transmission electron microscopy showed the presence of intercalated and partially exfoliated areas. Tensile testing showed improvements in both the tensile modulus and yield strength for all the prepared nanocomposites. The results from the dynamic mechanical thermal analysis showed an improvement in the storage modulus over the entire temperature range for both layered silicates together with a shift in the tan δ peak to higher temperatures. The effect of using PLA–MA differed between the two layered silicates because of a difference in the organic treatment. The bentonite layered silicate showed a more distinct improvement in exfoliation and an increase in the mechanical properties because of the addition of PLA–MA in comparison with the hectorite layered silicate. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 1852–1862, 2006     

Preparation and characterization of maleic anhydride‐g‐polypropylene/diamine‐modified clay nanocomposites

Polypropylene (PP)/montmorillonite (MMT) nanocomposites were prepared by compounding maleic anhydride‐g‐polypropylene (MAPP) with MMT modified with α,ω‐diaminododecane. Structural characterization confirmed the formation of characteristic amide linkages and the intercalation of MAPP between the silicate layers. In particular, X‐ray diffraction patterns of the modified clay and MAPP/MMT composites showed 001 basal spacing enlargement as much as 1.49 nm. Thermogravimetric analysis revealed that the thermal decomposition of the composite took place at a slightly higher temperature than that of MAPP. The heat of fusion of the MAPP phase decreased, indicating that the crystallization of MAPP was suppressed by the clay layers. PP/MAPP/MMT composites showed a 20–35% higher tensile modulus and tensile strength compared to those corresponding to PP/MAPP. However, the elongation at break decreased drastically, even when the content of MMT was as low as 1.25–5 wt %. The relatively short chain length and loop structure of MAPP bound to the clay layers made the penetration of MAPP molecules into the PP homopolymer phase implausible and is thought to be responsible for the decreased elongation at break. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 95: 307–311, 2005     

Characterization of polymer‐layered silicate (clay) nanocomposites by transmission electron microscopy and X‐ray diffraction: A comparative study

Several polymer‐layered silicate (clay) nanocomposites (PLSNs) were analyzed by transmission electron microscopy (TEM) and wide‐angle X‐ray diffraction (XRD) in an effort to characterize the nanoscale dispersion of the layered silicate. The PLSNs investigated included thermoset (cyanate esters) and thermoplastic polymers (polystyrene, nylon 6, and polypropylene‐g‐maleic anhydride). The results of this study reveal that the overall nanoscale dispersion of the clay in the polymer is best described by TEM, especially when mixed morphologies are present. XRD is useful for the measurement of d‐spacings in intercalated systems but cannot always observe low clay loadings (<5%) or be used as a method to identify an exfoliated nanocomposite where no XRD peaks are present (constituting a negative result). Most importantly, the study showed that XRD is not a stand‐alone technique, and it should be used in conjunction with TEM. Our studies suggest that new definitions, or a clarification of existing definitions, are needed to properly describe the diversity of PLSN nanostructures seen in various materials. Published 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 1329–1338, 2003     

Deformation behaviour during cold drawing of nanocomposites based on single wall carbon nanotubes and poly(ether ester) copolymers

Relationships between the macroscopic deformation behaviour and microstructure of a pure (PBT-b-PTMO) block copolymer and a polymer nanocomposite (PBT-b-PTMO + 0.2 wt% SWCNT) were investigated by simultaneous small- and wide-angle X-ray scattering (SAXS and WAXS) during tensile deformation using synchrotron radiation. The Young's modulus was found to be 15% higher for the nanocomposite than for the pure block copolymer as well as the yield strength, while the elongation-to-break was less than a half. This different behaviour can be explained by taking into account the different structural features revealed by SAXS and WAXS and thus considering that SWCNT act as anchors in the nanocomposite, sharing the applied stress with the PBT crystals and partially preventing the flexible, non-crystallisable PTMO chains to elongate.