A.M. Visco

X-ray photoelectron spectroscopy of Au/Fe2O3 catalysts

Gold catalysts supported on iron oxide have been characterized by X-ray photoelectron spectroscopy (XPS). Depending on the method of preparation and pretreatment, different gold species have been detected on the catalyst surface. In the absence of thermal treatment, the XPS spectra of the impregnated samples show the formation of gold(III) (oxy)chloride species. No metallic gold is formed. Both metallic and oxidized gold species are instead present on the surface of the samples prepared by coprecipitation. Oxidized gold(III) species are predominant on the uncalcinated catalysts. After treatment at high temperature and/or under reaction conditions the amount of metallic gold increases. The XPS data have been correlated with the activity of the investigated catalysts in the oxidation of carbon monoxide at low temperature.

Influence of Ru precursor, support and solvent in the hydrogenation of citral over ruthenium catalysts

A series of ruthenium supported catalysts were prepared and investigated in the liquid-phase hydrogenation of citral. The mechanism of the reaction was found to be dependent on the Ru precursor, support and solvent used. On the sample prepared from RuCl3 the acetals of citronellal were formed with the subsequent hydrogenation of the isolated C=C double bond. On the samples obtained from precursors which do not contain chloride ions, citronellal was the main reaction product. Hydrogenation of the isolated C=C double bond was negligible. Using cyclohexane as solvent, a large amount of isopulegol was also obtained. The results of the hydrogenation of citral have been correlated to the presence of acid sites and incompletely reduced ruthenium which favour cyclization and acetals formation from citronellal. On the basis of the reported results, a reaction scheme for hydrogenation of citral over ruthenium catalysts is proposed.

Catalytic oxidation of carbon monoxide over Au/Fe2O3 preparations

Low temperature catalytic oxidation of carbon monoxide has been studied over Au/Fe2O3. On the coprecipitated samples the catalytic activity shows a maximum at a gold content of about 5%. Calcination of Au/Fe2O3 decreases the catalytic activity and the stability. The catalytic activity measured is the highest ever reported in the literature on Au/Fe2O3 preparations.

On the compatibilization of PET/HDPE blends through a new class of copolyesters

Polyethyleneterephthalate (PET) and polyethylene are incompatible polymers and their blends show, in general, poor properties. Compatibilization is then a necessary step to obtain blends with good mechanical and barrier properties. In this work different compatibilizing agents were used, i.e. a maleic anhydride elastomer and some new products containing graft-copolymers having polyester segments grafted onto polyethylene backbone chains. Both the functionalized elastomer and the new products drastically improve the morphology and the ductility of the blend. In the case of the modified elastomer the compatibilizing action has been attributed to the formation of H-bonds whereas the copolymers contained in the new products act as compatibilizing agents as they contain polyester segments and polyethylene segments with thermodynamic affinity with PET and polyethylene, respectively.

Wetting modifications of uhmwpe surfaces induced by ion implantation

Ultra-high-molecular-weight-polyethylene (UHMWPE) surfaces are characterized in terms of roughness and wetting. Changes in the surface morphology of the polymer were induced macroscopically by mechanical friction and microscopically by ion implantation. The ion irradiation was obtained by using 300 keV Xe+ beams with doses ranging between 1014 and 1015 ions/cm2. Roughness and wetting measurements were performed in order to investigate the UHMWPE surface properties before and after the surface treatments. The wetting angle of the polymeric surface increases with the decrease of the roughness and with the increase of the absorbed dose. Results are discussed from the point of view of the biological reactions that could degrade the UHMWPE biocompatible surfaces employed in different mobile prostheses.

Incorporation of Carbon Nanotubes into Ultra High Molecular Weight Polyethylene by High Energy Ball Milling

Multiwalled carbon nanotubes, CNTs (0.3–1.0 wt.%), were incorporated in the ultra high molecular weight polyethylene (UHMWPE) matrix by solid state dry mixing in order to avoid the use of high temperature, solvents, and materials pretreatments. Physical, morphological, and mechanical tests were performed on both the pristine materials and the nanocomposites. Experimental results showed that the CNTs are homogeneously dispersed into the polymeric matrix but no close interaction occurs between the two components. In fact, no appreciable mechanical or thermal improvement was observed. Instead, a bi-dimensional CNT conductive network was formed within the polymeric matrix, which increased its crystalline order.

Wear behaviour of UHMWPE reinforced by carbon nanofiller and paraffin oil for joint replacement

The majority of artificial joints incorporate biomedical grade Ultra High Molecular Weight Poly Ethylene (UHMWPE), whose wear is considered most important in controlling service time of the whole joint. The aim of this work was to improve wear resistance of UHMWPE through the addition of 0.5-2.0wt% of Carbon Nano Filler (CNF) and 2% wt of Paraffin Oil (PO) using ball milling (BM) and extrusion techniques (EX). The wear tests on these nanocomposites were conducted by a pin on disc in dry (air) and wet media (simulated synovial fluid or artificial lubricant, and bovine synovial fluid or natural lubricant). Mechanical tests (tensile and hardness), physical analysis (calorimetric, density, wet ability, roughness) and morphological observations were also performed. The experimental results showed that natural lubricant provides the greatest reduction in wear rate while the largest one occurred in air. Furthermore, the BM mixed nanocomposites with a filler load of 1.0% exhibited the best wear resistance among all the samples with an improvement of 42%, 64% and 83% in air, artificial and natural lubricant, respectively. This is due to its higher ductility and thermal features, and lower wet ability in the two lubricants.

Mechanical performance of electron-beam-irradiated UHMWPE in vacuum and in air

Ultrahigh molecular weight polyethylene (UHMWPE) was modified by a 5-MeV energy electron beam at different temperatures before, during, and after irradiation, both in air and in high vacuum. Wear resistance, hardness, and tensile strength of irradiated polyethylene were compared with those of untreated one. Physical analyses (like infrared spectroscopy and calorimetric analysis) were carried out to investigate about the changes in the material induced by irradiation. Experimental results suggested that structural changes (double bonds, crosslinks, and oxidized species formation) occur in the polymer depending on the environmental conditions of the irradiation. Mechanical behavior is related to the structural modifications. A temperature of 110 degrees C before, during, and after the in vacuum irradiation of UHMWPE produces a high amount of crosslinks and improves polymeric tensile and wear resistance, compared to that of the untreated material.

Effect of functional groups of multi-walled carbon nanotubes on the mechanical, thermal and electrical performance of epoxy resin based nanocomposites

This article concerns the effect of pristine, carboxylic and amino-functionalised carbon nanotubes used as filler in epoxy-based nanocomposites. The amount of carbon nanotubes was within the range 0.2–0.8 wt%. Their mechanical properties were investigated by means of flexural strength and resilience tests. The carbon nanotubes lead to an improvement of ductility and mechanical strength compared to the neat epoxy resin in the order: amino > carboxylic > pristine. The results of morphological, calorimetric, rheological and electrical conductivity tests suggest that this improvement is due to a good dispersion of the filler in the matrix and it occurs especially with low filler amounts (0.2–0.4 wt%) of amino carbon nanotubes. In the nanocomposites realised with amino-functionalised carbon nanotubes there is an interphase that creates a weak interfacial interaction between the filler and the epoxy resin. The thermal stability as well as the electrical conductivity of resin, is not appreciably improved after the addition of either functionalised carbon nanotubes.

Fiber Reinforced Polyester Resins Polymerized by Microwave Source

Polyester resin based composite materials are widely used in the manufacture of fiberglass boats. Production time of fiberglass laminate components could be strongly reduced by using an intense energy source as well as microwaves. In this work a polyester resin was used with 2% by weight of catalyst and reinforced with chopped or woven glass fabric. Pure resin and composite samples were cured by microwaves exposition for different radiation times. A three point bending test was performed on all the cured samples by using an universal testing machine and the resulting fracture surfaces were observed by means of scanning electron microscopy (SEM). The results of mechanical and microscopy analyses evidenced that microwave activation lowers curing time of the composite while good mechanical properties were retained. Microwaves exposition time is crucial for mechanical performance of the composite. It was evidenced that short exposition times suffice for resin activation while long exposure times cause fast cross linking and premature matrix fracture. Furthermore high-radiation times induce bubbles growth or defects nucleation within the sample, decreasing composite performance. On the basis of such results microwave curing activation of polyester resin based composites could be proposed as a valid alternative method for faster processing of laminated materials employed for large-scale applications.