E. Pesce

Rotational Molding of Polyamide-6 Nanocomposites with Improved Flame Retardancy

Abstract The aim of this work was to develop polyamide-6/ organic-modified montmorillonite (omMMT) nanocomposites for the production of hollow parts by rotational molding. Particular emphasis was placed on the mechanical and flame retardancy properties needed for the fabrication of vessels for flammable liquids. The morphology of the melt compounded nanocomposites, produced by melt compounding, was investigated by X-ray diffraction measurements (WAXD), and Transmission Electron Microscopy (TEM) showed an exfoliated structure. Rheological measurements were used in order to verify whether the viscosity of materials was adequate for rotational molding. While thermomechanical analysis has revealed that neat PA6 and its nanocomposites were not suitable for rotational molding, due to the very low thermal stability of the polymer, the addition of a thermal stabilizer, shifted the onset of degradation to higher temperatures, thus widening the processing window of both PA6 and PA6 nanocomposites. Large-scale vessel prototypes were obtained by rotational molding of thermo-stabilized PA6 and its nanocomposites, and samples extracted from the rotomolded parts were characterized with respect to physical and mechanical properties. It was found that the PA6 nanocomposites exhibited significant improvements at cone calorimeter tests in comparison with neat PA6.

Particle size dependence of resonant-tunneling effect induced by CdS nanoparticles in a poly(N-vinylcarbazole) polymer matrix

CdS nanoparticles of different sizes were synthesised in poly(N-vinylcarbazole) and studied in device structures glass/indium tin oxide (ITO)/PVK:CdS/Al. Electrical bistability and negative differential resistance (NDR) effects were observed in the current-voltage characteristics. In addition, the devices showed a considerable enhancement of the current magnitude. A dependence of the current conduction on the nanoparticle size and size distribution in the polymer was studied through electrical impedance measurements. The study revealed the importance of the charge effects of the nanoparticles resulting in a bistable behavior. A resonant tunneling current model was proposed to explain the NDR and its relation with the nanoparticle size and size distribution.

Luminescent nanocomposites of conducting polymers and in-situ grown CdS quantum dots

Luminescent PVK:CdS and P3HT:CdS nanocomposites with enhanced electrooptical properties have been synthesized. The nucleation and growth of CdS nanoparticles have been obtained by the thermolysis of a single Cd and S precursor dispersed in the polymers. The size distribution and morphology of the nanoparticles have been studied by TEM analyses. Monodispersive and very small nanoparticles of diameter below 3 nm in PVK and 2 nm in P3HT, have been obtained. The application of such nanocomposites as emitting layers in OLED devices is discussed.

Microstructural analysis of ultra-thin nanocomposite layers fabricated by Cu+ ion implantation in inert polymers

Ion implantation was used to fabricate ultra-thin nanocomposite subsurface layers in inert polymers for applications in mechanics, optics and electronics [1]. Amorphous polycarbonate substrates were implanted at room temperature with low energy Cu+ ions of 60 keV, at 1 μA/cm2 and with doses in a range from 1×1016 to 1×1017 ions/cm2. The nanocomposite surfaces were investigated by transmission electron microscopy (TEM), X-ray diffraction (XRD), optical absorption spectroscopy and electrical conductivity. Cross-section transmission electron microscopy (XTEM) was used to analyze the microstructure and morphology of the Cu-implanted region. TEM experiments show that nanocrystals are formed at ion doses of 1×1016 ions/cm2 (Figure1). The ionimplanted nanocrystals are located at about 50nm–80nm below the polymer surface, in accordance with TRIM calculations (projected range of 75nm and straggling of 20nm). However, at higher ion doses (5×1016 ions/cm2) a continuous thin nanocrystalline copper films is produced. Figure 2 (b) shows the grazing-incidence XRD patterns (incidence angle = 1°) recorded prior and after Cu-implantation in polycarbonate as well as the corresponding diffraction difference curve. The observed diffraction peaks correspond to copper (cubic phase) in accordance with the ICDD (card no. 851326; JCPDS-ICDD 2000). The XTEM image (Figure 2a) shows a continuous polycrystalline copper films below the polycarbonate surface; the lattice fringes are well observed in the Cu film. Optical absorption spectra show a surface plasmon resonance at 2eV suggesting the formation of nanocrystalline Cu films. This characteristic SPR peak is well pronounced for doses of 5×1016 ions/cm2, while at higher doses the SPR peak is smeared out.