Julio Roberto Bartoli

Electrical percolation, morphological and dispersion properties of MWCNT/PMMA nanocomposites

Nanocomposites of poly (methyl methacrylate) (PMMA) and carbon nanotubes have a high potential for applications where conductivity and low specific weight are required. This piece of work concerns investigations of the level of dispersion and morphology on the electrical properties of in situ polymerized nanocomposites in different concentrations of multi-walled carbon nanotubes (MWCNT) in a PMMA matrix. The electrical conductivity was measured by the four point probe. The morphology and dispersion was analyzed by Transmission Electron Microscopy (TEM) and Small Angle X-ray Scattering (SAXS). The correlation between electrical conductivity and the MWCNT amount, presented a typical percolation behavior, whose electrical percolation threshold determined by power law relationship was 0.2 vol. (%) The exponent t from the percolation power law indicated the formation of a 3D network of randomly arranged MWCNT. SAXS detected that the structures are intermediate to disks or spheres indicating fractal geometry for the MWCNT aggregates instead of isolated rods. HR-TEM images allowed us to observe the MWCNT individually dispersed into the matrix, revealing their distribution without preferential space orientation and absence of significant damage to the walls. The combined results of SAXS and HR-TEM suggest that MWCNT into the polymeric matrix might present interconnected aggregates and some dispersed single structures.

Nanocomposites of acrylonitrile-butadiene-styrene/montmorillonite/styrene block copolymers: Structural, rheological, mechanical and flammability studies on the effect of organoclays and compatibilizers using statistically designed experiments

Previous study with nanocomposites of acrylonitrile-butadiene-styrene copolymer (ABS) and organophylized montmorillonite clays (OMMT) investigated the effect of clay modifiers polarities on their performance. Nevertheless, the literature has shown that the use of compatibilizers plays a key role in the dispersion of OMMT in polymeric matrices. Therefore, in the present work, ABS/OMMT nanocomposites compatibilized with styrenic block copolymers prepared by melt intercalation in a twin-screw extruder was studied. Nanocomposites formulations followed a 22 factorial design having different kinds of Cloisite OMMT (30B and 20A + 30B) and of compatibilizers (SBS and SEBS-g-MA) as independent variables. Structural (X-ray diffraction) and morphological (transmission electron microscopy) analyses of the nanocomposites showed a better clay dispersion, partially exfoliated, for ABS/30B/SBS than the intercalated morphology for ABS/20A30B/SEBS-g-MA. Rheological dynamic shear tests indicated a tendency to the formation of a percolating network structure for the ABS/OMMT/SBS nanocomposites, independently of nanoclay kind. Besides, these materials presented non-dripping effect on flammability tests. ABS/OMMT/SBS nanocomposites show also the best performance in both uniaxial tensile and dynamic shear storage moduli. These results are probably due to improved affinity between components. In conclusion, among the styrene block copolymers, SBS compatibilizer is more effective than SEBS-g-MA to improve the properties of ABS/OMMT-based nanocomposites.

Filmes ópticos poliméricos fluorados com índice de refração gradual

Fluorinated PMMA optical films were obtained using the CF4+H2 plasma polymerisation technique. The characterisation analysis: ESCA, RBS, FTIR, gravimetry, contact angle, refractometry and ellipsometry, revealed that a hydrofluorcarbon polymer was deposited on the optical films exposed to the plasma. Fluorine concentration increased gradually with the fluorinated film depth (0.43-0.49mm). A refractive index 1.42-1.43 was found on the surface of the fluorinated films, lower than the PMMA (1.49). This fluorinated layer could present a gradient refractive index, being reciprocal of the Fluorine concentration. The potential advantages to obtain graded-index polymer waveguides and optical fibres are loss reductions and higher transmission rates.

Effect of solvents on the morphology of PMMA films fabricated by spin-coating

A method to produce thin layer of PMMA (poly (methyl methacrylate) films by spin coating is reported. PMMA is dissolved in xylene, a mixture of MIBK-xylene ...

Organoclay nanocomposites of post-industrial waste poly(butylene terephthalate) from automotive parts

Polymeric nanocomposites are novel materials of huge interest owing to their favourable cost/performance ratio with low amount of nanofillers, improved thermal resistance, flame retardancy and mechanical properties in relation to their matrices. In this work, composites based on post-industrial waste or primary recycled poly(butylene terephthalate) and 5 wt.% of organic modified montmorillonite clays were melt compounded using a twin-screw extruder. A 22 factorial experimental design was used to study the compounding and processing variables: Organic modified montmorillonite with one or two hydrogenated tallow (initial basal spacing) and screw speed of the extruder. X-ray diffraction and transmission electron microscopy suggest that a partial exfoliation of the organoclay in the recycled poly(butylene terephthalate) matrix was achieved for organic modified montmorillonite with lower initial basal spacing. On the other hand, formulations containing organic modified montmorillonite with higher initial basal spacing showed only intercalated structure. The recycled poly(butylene terephthalate)–organic modified montmorillonite nanocomposites did not drip flaming material during burning tests. Storage of dynamic-mechanical, tensile and flexural moduli of the recycled poly(butylene terephthalate)–organic modified montmorillonite were improved when compared with both virgin and recycled poly(butylene terephthalate)s, mainly for nanocomposites formulated at a lower initial basal spacing organoclay. This could be related to a better diffusion of polymer into organic modified montmorillonite layers compared with the higher initial basal spacing organoclay. The improvements on the physical properties of recycled poly(butylene terephthalate) showed the feasibility to add value to primary recycled engineering thermoplastics with a very small amount of organic modified montmorillonite.

Development and characterisation of graded-index polymeric films for optical guides and sensors

Polymeric optical films were deposited by CF4+H2 plasma process. The polymeric films contain Fluorine increasing gradually with depth. As Fluorine reduces polymer refractive index it is concluded that the films refractive index is also varying gradually.

Thermal aging of an insulation EPR-rubber compound

The stability of an EPR (ethylene-propylene rubber) compound, used as power cable insulation (138 kV) and for downhole pump (petroleum well) cables, was studied under various conditions of thermal stress. Samples were subjected to temperatures in the 50-300 degrees C range, for periods as long as 1000 h. After these treatments, electric and tensile strengths of the samples were determined, and the samples were also examined by spectroscopic (photoacoustic, infrared) methods. Gases evolved during rubber heating were analyzed by gas chromatography. It was found that: (1) electric strength is reduced: 17% of original value after 1 h at 300 degrees C and 40% after 1000 h at 200 degrees C, but no changes were found after 1000 h at 150 degrees C; (2) paraffin, used as a processing additive in the compound, exudes at temperatures as low as 50 degrees C; the exudate is more oxidized than the input material; (3) Pb/sub 3/O/sub 4/, which is also a constituent of the compound, is reduced to PbO at higher temperatures; and (4) methane is prevalent in the gaseous mixture released by the heated compound.<<ETX>>