Effect of compatibilizing agents on the mechanical properties of high‐density polyethylene/olive husk flour composites

The main objective of this research was to investigate the effect on the thermal and mechanical properties of the addition of two different compatibilizing agents, malefic anhydride‐grafted polyethylene (PE) [synthesized in a solution state (MAPE) and commercial (XA255)], to olive husk flour, high‐density polyethylene (HDPE) composites. The composites contain 30 wt % of olive husk flour and a variable proportion of compatibilizer (3, 5, and 7 wt %). The grafting reaction was followed by Fourier transform infrared, and the grafting degree was evaluated by means of titration. The effect of grafting on the thermal properties of MAPE was observed by ATG/DTG. The mechanical and thermal properties of the composite were investigated. A morphological study of the composite reveals that there is a positive effect of compatibilizing agent on interfacial bonding. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Silane-Grafted Isotactic Polypropylene Used as a Coupling Agent on Glass. Consequences on The Interfacial Adhesion

Functionalized isotactic polypropylenes have been synthetized in order to be used as coupling agents on glass fibers associated with a polypropylene matrix. This new way of interface toughening requires a grafting of such polymeric chains on the glass surface and a crystallization of these grafted chains at the same time in the same crystals as the polypropylene matrix (co-crystallization). Using a Ziegler-Natta polymerization, copolymers based on propene and two different types of dienes have been prepared. Such a synthesis allows one to change the functionality and the position of double bonds used to introduce the silane functions. A Speier hydrosilylation was used for this purpose with two kinds of silanes. Silane-functionalized oligopropenes were also prepared in order to compare the effect of the position of the silane functions on the glass/polypropylene adhesion: side chain or chain end positions. The characterization of these functionalized polypropylenes is described. Their ability to be grafted on a glass surface was checked by means of wetting measurements after extractions according to the hydrophobic nature of the polypropylene and the hydrophilic character of the glass. The co-crystallization of the pure and functionalized polypropylenes was demonstrated on blends. Two silane functionalized-PP were selected to study the glass fiber/PP adhesion by means of the microdroplet test.     

Factors Governing the Catalytic Reactivity of Metallic Nanoparticles

Some recent advances in catalysis by metals are reviewed illustrating the versatility of supported nanoparticles and their high potential to be major contributors to solve energetic or environmental issues of the ongoing century. Since the early structure sensitivity concept, progresses have brought new insights and guidelines on structure ‐ reactivity relationships such as strain effects, the ring‐capture model, the particle surface density effect, or the influence of crystallographic planes. These phenomena are proposed to play a key role in the catalytic cycle. Systematic studies are however still required to estimate their real relevance and their respective contributions according to the type of chemical reactions and of operating conditions.     

Power Loss Predictions in High-Speed Rolling Element Bearings Using Thermal Networks

In high-speed rolling element bearings (REB), the lubricant is used to separate the mating surfaces but also to cool down the parts while the system is in operation. In the context of optimizing oil circuits, a clear understanding of the lubricant cooling mechanisms is therefore required in order to reach a compromise between a good cooling capacity and the constraints on mass, size, and power. In this article, a model is presented that makes it possible to predict temperature distributions in high-speed thrust ball bearings. It is found that the prediction or measurement of global power loss cannot discriminate between several combinations of traction and drag forces. On the other hand, the predicted temperature distributions appear as very sensitive to the relative importance given to hydrodynamic rolling tractions or drag losses. Based on these findings, a methodology is suggested in order to define the most realistic power loss models to be used in high-speed REB simulations.     

Antimicrobial Activity of Nisin and Natamycin Incorporated Sodium Caseinate Extrusion‐Blown Films: A Comparative Study with Heat‐Pressed/Solution Cast Films

Antimicrobial edible films based on sodium caseinate, glycerol, and 2 food preservatives (nisin or natamycin) were prepared by classical thermomechanical processes. Food preservatives were compounded (at 65 °C for 2.5 min) with sodium caseinate in a twin‐screw extruder. Anti‐Listeria activity assays revealed a partial inactivation of nisin following compounding. Thermoplastic pellets containing food preservatives were then used to manufacture films either by blown‐film extrusion process or by heat‐press. After 24 h of incubation on agar plates, the diameters of K. rhizophila growth inhibition zones around nisin‐incorporated films prepared by solution casting (control), extrusion blowing or heat pressing at 80 °C for 7 min of nisin‐containing pellets were 15.5 ± 0.9, 9.8 ± 0.2, and 8.6 ± 1.0 mm, respectively. Since heat‐pressing for 7 min at 80 °C of nisin‐incorporated pellets did not further inactivate nisin, this indicates that nisin inactivation during extrusion‐blowing was limited. Moreover, the lower diameter of the K. rhizophila growth inhibition zone around films prepared with nisin‐containing pellets compared to that observed around films directly prepared by solution casting confirms that nisin inactivation mainly occurred during the compounding step. Natamycin‐containing thermoplastic films inhibited Aspergillus niger growth; however, by contrast with nisin‐containing films, heat‐pressed films had higher inhibition zone diameters than blown films, therefore suggesting a partial inactivation of natamycin during extrusion‐blowing.     

On the Impact of Linear Siloxanated Side Chains on the Molecular Self-Assembling and Charge Transport Properties of Conjugated Polymers

Herein reported is the impact of the functionalization of four different semiconducting polymer structures by a linear siloxane-terminated side-chains. The latter is tetrasiloxane (Si₄) or trisiloxane (Si₃) chains, substituted at their extremity to a pentylene linker. The polymer structure is based on 5,6-difluorobenzothiadiazole comonomer (PF2), a diketopyrrolopyrrole unit (PDPP-TT), a naphtalediimide unit (PNDI-T₂), and a poly[bis(thiophen-2-yl)thieno[3,2,b]thiophene (PBTTT). The properties of these siloxane-functionalized polymers are scrutinized and compared with the ones of their alkyl-substituted polymer analogues. The impact of the alkyl-to-siloxane chain substitution clearly depends on the molecular section of the side chains. When a branched 2-octyldodecyl chain (C₂₀) is replaced by a Si₄ chain of same molecular section, the greatest impact is the strong increase of the π-stacking overlap of the polymer backbones. This effect leads to a significative enhancement of the charge mobility values of the polymers. As in-plane and out-of-plane mobility are increased simultaneously, this π-overlap enhancement effect happens to be preponderant over the polymer orientation variations. When a linear tetradecyl chain (C₁₄) is replaced by a linear Si₃ chain of twice larger molecular section, the polymer structure is profoundly affected. While PBTTT-C₁₄ is crystalline and purely edge-on, PBTTT-Si₃ is mesomorphic and shows a mixed face-on/edge-on orientation.     

Electrical aging of polyurethane under ac voltage

The electrical aging of polyurethane under ac voltage has been investigated using Weibull statistical analysis. It is shown that the time to breakdown characteristic (V-t) of this polymer includes three zones corresponding, respectively, to the youth defects, the statistical dispersion of the intrinsic defects, and the real aging of the polymer. The variation of slope of the V-t curve is related to the change of the degradation mechanism. This degradation is governed by the action of partial discharges according to three stages: (1) the appearance of very fast discharges within the cavities; (2) the initiation of discharges resulting of a very thin layer of oxidation products; and (3) the formation of crystals having small dimensions leading to degradation by electrical tree. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Study by electrical conductivity and infrared spectrometry of the thermal stability of defective iron spinels with aluminium and chromium

Precipitation in defective chromium- or aluminium-substituted magnetites, \(\gamma - \left( {Fe_{\left( {8/3} \right) - \left( {8/9} \right)x}^{3 + } M_{\left( {8/9} \right)x}^{3 + } \square _{1/3} } \right)O_4^{2 - } \left( {M^{3 + } = Al^{3 + } ,Cr^{3 + } ;0< x< 2} \right)\) , and defective iron aluminium chromium spinels, \(\gamma - \left( {Fe_{8/9}^{3 + } Al_{\left( {8/9} \right)\left( {2 - x} \right)}^{3 + } Cr_{\left( {8/9} \right)x}^{3 + } \square _{1/3} } \right)O_4^{2 - } \) has been investigated by electrical conductivity and infrared spectrometry in the temperature range 600 to 1200° C. For highly γ-AI-substituted magnetites and γ-iron aluminium chromium spinels the transformation of the spinel lattice into an α-rhombohedral lattice has been found to be preceded by the formation of an intermediate phase at about 900° C with a high alumina content, approximately identical to disordered γ-Al₂O₃. It is only at higher temperatures (> 1100° C) that the formation of an α-rhombohedral phase is observed. In the case of γ-Cr-substituted magnetites, temperatures of only about 700° C are required for the transformation γ → α.