Mechanical reinforcement of a high-performance aluminium alloy AA5083 with homogeneously dispersed multi-walled carbon nanotubes

Dense and homogeneous multi-walled carbon nanotube/metal composites are prepared by powder metallurgy. The distribution of the nano-reinforcements in the matrix is studied by scanning electron microscopy and Raman spectroscopy. The mechanical properties of the composites are determined by means of static tensile tests and Vickers micro-hardness measurements. We show that a homogeneous dispersion of the nanotubes at the micron scale is required in order to improve the mechanical properties of the metal matrix composite. This can be achieved using ball-milling through the mechanisms of plastic deformation and cold-welding. Accordingly, we report significant improvements to the mechanical properties of composites prepared with a high-performance aluminium alloy AA5083 matrix.     

Monodisperse polymer beads as packing material for high-performance liquid chromatography

A novel approach to monodispersed porous polymer beads allowing accurate control over a broad range of pore size distribution has been developed. It involves the use of monodispersed template particles which are used as polymeric porogens in the suspension polymerization of monomers such as styrene and divinylbenzene. The size uniformity of the template particles is retained by the final porous beads. The porous properties of the final beads are determined in large part by the characteristics of the porogenic mixture such as its composition, the molecular weight of the polymeric porogen, as well as the relative amount of monomers, polymeric and low molecular weight porogens used.     

Radical grafting of polar monomers onto polypropylene by reactive extrusion

Polypropylene (PP) was functionalized in the melt by grafting polar monomers using an internal mixer and a corotating twin‐screw extruder. 2,5‐Bis(tertbutylperoxy)‐2,5‐dimethylhexane (Luperox 101) and dicumyl peroxide (DP) were the used radical initiators. The polar monomers were itaconic acid (IAc), 2‐octen‐1‐ylsuccinic anhydride (OY), 2‐hydroxyethyl methacrylate (HEMA), and 3‐allyloxy‐1,2‐propanediol (AP). Grafting was quantified by FTIR combined to Elemental Analysis. Grafting degree depends mainly on monomer and initiator natures and concentrations. Grafting degree maxima were 3.9, 2, 9.5, and 3.9 wt %, respectively, for IAc, OY, HEMA, and AP. Some properties of the modified PP were evaluated. Thermal analysis indicated that the polarity of PP increased by grafting reaction and size‐exclusion chromatography showed that the grafting was not accompanied by a significant M_w and viscosity decrease. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Homogeneous dispersion of SiO2 nanoparticles in an hydrosoluble polymeric network

The main difficulty still encountered in the elaboration of polymer/silica nanocomposites is the control of the nanoparticles dispersion homogeneity and the stability of the nanoparticle dispersion in the surrounding substance. The innovative point of this work is the elaboration of hybrid networks in aqueous solution performed with ASE (alkali swellable emulsion) thickeners grafted with silica nanoparticles. The thickening ability of the polymer should favour silica nanoparticles dispersion in fluid matrices. Two ASE copolymers were realised by copolymerisation in emulsion of MA (methacrylic acid) and EA (ethyl acrylate) and/or TFEM (trifluoroethyl methacrylate). The substitution of a part of EA by TFEM gave fluorinated ASE copolymers. Their free acid functions were then coupled with different ratio of amine functionalized silica nanoparticles to afford nanocomposites. The amounts of silica nanoparticles in the copolymers were determined by thermogravimetric experiments. Depending on the silica nanoparticles/copolymer ratio in basic aqueous solutions we achieved stable translucent gel like aqueous suspensions of silica nanoparticles containing 1 wt.% of the polymer/SiO₂ nanocomposite.     

Poly[ethylene‐co‐(vinyl alcohol)]‐graft‐poly(ε‐caprolactone) Synthesis by Reactive Extrusion, 1 ‐ Structural and Kinetic Study

Chemical modification of EVOH in the molten state at 185 °C by a grafting from process of poly(ε‐caprolactone) in batch was studied. ¹H NMR was used to characterize the structure evolutions of PCL grafts. In addition to grafting reactions, dynamic covalent transesterification reactions between EVOH residual alcohols and the polyester grafts led to a redistribution of the PCL grafts length. up to 27 and SR up to 80% were obtained. Experiments made in a corotating mini twin‐screw extruder also confirmed these results. The effect of the alcohol to caprolactone ratio and catalyst concentration (SnOct₂) on kinetic evolution showed that few minutes were necessary to complete the polymerization. A kinetic model was proposed and adequate conditions for the synthesis by reactive extrusion were defined.

     

Epothilones as lead structures for the synthesis-based discovery of new chemotypes for microtubule stabilization

Epothilones are macrocyclic bacterial natural products with potent microtubule-stabilizing and antiproliferative activity. They have served as successful lead structures for the development of several clinical candidates for anticancer therapy. However, the structural diversity of this group of clinical compounds is rather limited, as their structures show little divergence from the original natural product leads. Our own research has explored the question of whether epothilones can serve as a basis for the development of new structural scaffolds, or chemotypes, for microtubule stabilization that might serve as a basis for the discovery of new generations of anticancer drugs. We have elaborated a series of epothilone-derived macrolactones whose overall structural features significantly deviate from those of the natural epothilone scaffold and thus define new structural families of microtubule-stabilizing agents. Key elements of our hypermodification strategy are the change of the natural epoxide geometry from cis to trans, the incorporation of a conformationally constrained side chain, the removal of the C3-hydroxyl group, and the replacement of C12 with nitrogen. So far, this approach has yielded analogs 30 and 40 that are the most advanced, the most rigorously modified, structures, both of which are potent antiproliferative agents with low nanomolar activity against several human cancer cell lines in vitro. The synthesis was achieved through a macrolactone-based strategy or a high-yielding RCM reaction. The 12-aza-epothilone ("azathilone" 40) may be considered a "non-natural" natural product that still retains most of the overall structural characteristics of a true natural product but is structurally unique, because it lies outside of the general scope of Nature's biosynthetic machinery for polyketide synthesis. Like natural epothilones, both 30 and 40 promote tubulin polymerization in vitro and at the cellular level induce cell cycle arrest in mitosis. These facts indicate that cancer cell growth inhibition by these compounds is based on the same mechanistic underpinnings as those for natural epothilones. Interestingly, the 9,10-dehydro analog of 40 is significantly less active than the saturated parent compound, which is contrary to observations for natural epothilones B or D. This may point to differences in the bioactive conformations of N-acyl-12-aza-epothilones like 40 and natural epothilones. In light of their distinct structural features, combined with an epothilone-like (and taxol-like) in vitro biological profile, 30 and 40 can be considered as representative examples of new chemotypes for microtubule stabilization. As such, they may offer the same potential for pharmacological differentiation from the original epothilone leads as various newly discovered microtubule-stabilizing natural products with macrolactone structures, such as laulimalide, peloruside, or dictyostatin.     

Consumption of fish from a contaminated lake strongly affects the concentrations of polybrominated diphenyl ethers and hexabromocyclododecane in serum

Very high concentrations of polybrominated diphenyl ethers (PBDE) have been reported in fish from Lake Mj?sa in Norway. This study was performed to examine the serum concentrations of PBDE and hexabromocyclododecane (HBCD) in consumers of fish from this lake and to investigate possible relationships between serum concentrations, self-reported fish intake and calculated total dietary PBDE exposure. Serum concentrations of the sum of the seven PBDE (BDE-28, 47, 99, 100, 153, 154 and 183) were significantly higher than those of a reference group of Norwegians eating only food with background levels of contamination (medians: 18 ng/g lipids men, 8.4 ng/g lipids women). The median dietary intake of Sum 7 PBDE was 2549 ng/day (30 ng/kg body weight/day), the highest dietary intake of PBDE reported. The contribution from fish caught from the contaminated lake comprised 98.7% of the total dietary exposure. For men, serum levels of PBDE were strongly correlated with the calculated dietary exposure, except for BDE-209. This suggests that sources other than the diet are important for human BDE-209 exposure. The median serum HBCD concentration was 4.1 and 2.6 ng/g lipids for men and women, respectively, and was also found to be associated with consumption of fish from Lake Mj?sa.     

Dropwise condensation heat transfer on ion implanted aluminum surfaces

Stable dropwise condensation (DWC) of saturated steam has been achieved on an aluminum alloy Al 6951 disc with an average surface finish of about 0.15 μm by means of ion beam implantation technology with an ion dose of 10¹⁶ N⁺ cm^?2 and an implantation energy of 20 keV. Measurements of the condensation heat transfer coefficient at steam pressures of 1200 and 1400 mbar were carried out as a function of surface subcooling on vertical plates of the same material which is commonly used for heat transfer equipment. Probably due to alloy inhomogeneities, only on about 50% of the plate surface DWC could be achieved, resulting in a maximum enhancement factor of 2.0 for DWC in comparison with theoretical values calculated by a corrected form of the Nusselt film theory. The heat transfer coefficient increases with increasing steam pressure and decreases with increasing surface subcooling. Furthermore, it was shown that condensation heat transfer cannot be enhanced if the ion implantation does not induce DWC. For the investigations, two different condensers have been used, one for the stability tests on discs and one for the heat transfer measurements on plates.     

Self‐Defensive Biomaterial Coating Against Bacteria and Yeasts: Polysaccharide Multilayer Film with Embedded Antimicrobial Peptide

Prevention of pathogen colonization of medical implants is a major medical and financial issue since infection by microorganisms constitutes one of the most serious complications after surgery or critical care. Immobilization of antimicrobial molecules on biomaterials surfaces is an efficient approach to prevent biofilm formation. Herein, the first self‐defensive coating against both bacteria and yeasts is reported, where the release of the antimicrobial peptide is triggered by enzymatic degradation of the film due to the pathogens themselves. Biocompatible and biodegradable polysaccharide multilayer films based on functionalized hyaluronic acid by cateslytin (CTL), an endogenous host‐defensive antimicrobial peptide, and chitosan (HA‐CTL‐C/CHI) are deposited on a planar surface with the aim of designing both antibacterial and antifungal coating. After 24 h of incubation, HA‐CTL‐C/CHI films fully inhibit the development of Gram‐positive Staphylococcus aureus bacteria and Candida albicans yeasts, which are common and virulent pathogens agents encountered in care‐associated diseases. Hyaluronidase, secreted by the pathogens, leads to the film degradation and the antimicrobial action of the peptide. Furthermore, the limited fibroblasts adhesion, without cytotoxicity, on HA‐CTL‐C/CHI films highlights a medically relevant application to prevent infections on catheters or tracheal tubes where fibrous tissue encapsulation is undesirable.