Functionalized titanium dioxide (TiO 2 ) nanospheres with pimelic acid (TiO 2 -PA) were synthesized through a novel and effective route, where the goal was to promote a high percentage of b-crystal into a matrix of isotactic polypropylene (iPP) by the use of low amount of nucleating agent. The successful chemical attachment of pimelic acid onto the TiO 2 surface was indicated by the presence of a new band at 1575 cm -1 and an increase in the thermal stability of the PA of approximately 200°C, which were observed through infrared spectra and thermogravimetric techniques, respectively. The iPP nanocomposite was analyzed by differential scanning calorimetry and wide-angle X-ray diffraction in order to identify b-crystals. An exothermic peak at 152°C and a diffraction peak at 2h = 16.2°confirmed the ability of the TiO 2 -PA nanoparticles to promote the b-crystal phase in the iPP nanocomposite even at low percentages (0.1 % w/w).About 85 % of b-crystal content was promoted with the TiO 2 -PA particles, that was significantly higher than the 25 % obtained by unmodified TiO 2 particles. Moreover, from visco-elastic analysis, it is evident that TiO 2 -PA particles help to improve the dissipation energy by effect of the promoted b-crystal phase in the polymer composites. Likewise, the AFM images provide evidence of the incompatibility of TiO 2 particles with the iPP matrix showing protruding reliefs in comparison with the homogeneous topography of the iPP/TiO 2 -PA composite. This results were confirmed by SEM, where the exclusion of TiO 2 particles was evident.

Isotactic polypropylenes (iPP) with different melt flow indexes (MFI) were used to fabricate nanocomposites (NCs) with 10 wt % loadings of multi-wall carbon nanotubes (MWCNTs) using ultrasound-assisted extrusion methods to determine their effect on the morphology, melt flow, and electrical properties of the NCs. Three different types of iPPs were used with MFIs of 2.5, 34 and 1200 g/10 min. Four different NC fabrication methods based on melt extrusion were used. In the first method melt extrusion fabrication without ultrasound assistance was used. In the second and third methods, an ultrasound probe attached to a hot chamber located at the exit of the die was used to subject the sample to fixed frequency and variable frequency, respectively. The fourth method is similar to the first method, with the difference being that the carbon nanotubes were treated in a fluidized air-bed with an ultrasound probe before being used in the fabrication of the NCs with no ultrasound assistance during extrusion. The samples were characterized by MFI, Optical microscopy (OM), Scanning electron microscopy (SEM), Transmission electron microscopy (TEM), electrical surface resistivity, and electric charge. MFI decreases in all cases with addition of MWCNTs with the largest decrease observed for samples with the highest MFI. The surface resistivity, which ranged from 1013 to 105 Ω/sq, and electric charge, were observed to depend on the ultrasound-assisted fabrication method as well as on the melt flow index of the iPP. A relationship between agglomerate size and area ratio with electric charge was found. Several trends in the overall data were identified and are discussed in terms of MFI and the different fabrication methods.

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The influence of organomodified nanoclay (montmorillonite) on the crystallization and melting mechanisms of isotactic polypropylene (iPP) was studied. Films of both neat polymer and clay nanocomposites were prepared after molecular weight optimization through melt extrusion. Products exhibited the tactoidlike morphology since no compatibilizers were used. The effect of introduction of nanoclay within the polymer was studied through isothermal crystallization and linear heating. The results indicated that low nanoclay concentrations induce the formation of the β‐crystalline structure, its formation being inhibited with high nanoclay contents. Dynamic nonisothermal bulk crystallization experiments indicated that nanoclays act as nucleating agents of iPP. Isothermal, bulk crystallization studies indicated that the crystallization process (induction time and crystallization kinetics) is proportionally accelerated by the nanoclay presence. There was also an accelerated formation of secondary crystallization when nanoclays were present in high concentrations. POLYM. ENG. SCI., 47:1889–1897, 2007. © 2007 Society of Plastics Engineers

Bionanocomposites (BNCs) of waxy corn starch, glycerol, and graphene oxide (GO) or graphite oxide (GrO) were prepared by melt mixing. First, the GrO was pre-exfoliated in a water solution using ultrasound at 1 wt %. Small-angle X-ray scattering was used to determinate the interlaminar separation of GrO and transmission electron microscopy, Fourier infrared spectroscopy, and thermogravimetric analysis were used to characterized the GrO. Next, BNCs were characterized by X-ray diffraction, scanning electron microscopy, thermogravimetric analysis, and mechanical property measurements. A complete exfoliation of GrO was obtained in the waxy corn matrix. Amorphous X-ray patterns of the BNCs were observed, indicating that the exfoliated GO avoid the retrogradation of starch. According to scanning electron microscopy results, the BNCs showed an irregular texture and a good dispersion of GO, while thermoplastic starch showed a smooth morphology with a fragile structure. The BNCs exhibited higher thermal stability than thermoplastic starch. The tensile strength and the Young's modulus increased by 140% and 230% at a GO loading levels of 0.5% due to good interfacial interactions of GO and the waxy corn starch matrix.