Molecular weight influence on shape memory effect of shape memory polymer blend (poly(caprolactone)/ styrene‐butadiene‐styrene )

The shape memory effect (SME) does not only concern the macroscopic structure. It concerns also the polymer structure at morphological, macromolecular, and molecular scales. This effect may depend on different physicochemical properties like morphology heterogeneity, chain rigidity, steric hindrance, chain polarity, free volume, cross-linking or entanglement density, molecular shape and weight, and so on. Hence, finding the relationship between the SME and these properties is very important. This can help to obtain the knowledge about the phenomenon origin and mechanism. One of the basic polymer properties, which can have direct SME, may be the molecular weight (Mw). The question here is: If the Mw of a shape memory polymer (SMP) changes, for different reasons like degradation, what will be the effect of this change on its SME. In order to answer to this question, the investigation is focused on an SMP blend of 40% poly(ɛ-caprolactone) (PCL) and 60% styrene-butadiene-styrene (SBS). Then, enzymatic hydrolysis is performed on this blend to change its Mw. It is shown that this change is only related to the variation in the Mw of PCL. After that, different samples with a distinct average Mw are prepared and characterized by various experimental methods. Shape memory tests are performed on these blends, and the recovery rate (Rr) for each of them is determined. It is found that when Mw of PCL decreases, its degree of crystallinity, its glass transition, and its melting temperatures, corresponding to the PCL phase, increase. However, the elongation at break of the blend declines with the reduction in Mw. The tests show that the alteration in the blend's Mw influences its SME. Indeed, Rr of the (PCL/SBS) mixture drops with the decrease in Mw of PCL

Perivascular Expression and Potent Vasoconstrictor Effect of Dynorphin A in Cerebral Arteries

BACKGROUND: Numerous literary data indicate that dynorphin A (DYN-A) has a significant impact on cerebral circulation, especially under pathophysiological conditions, but its potential direct influence on the tone of cerebral vessels is obscure. The aim of the present study was threefold: 1) to clarify if DYN-A is present in cerebral vessels, 2) to determine if it exerts any direct effect on cerebrovascular tone, and if so, 3) to analyze the role of κ-opiate receptors in mediating the effect. METHODOLOGY/PRINCIPAL FINDINGS: Immunohistochemical analysis revealed the expression of DYN-A in perivascular nerves of rat pial arteries as well as in both rat and human intraparenchymal vessels of the cerebral cortex. In isolated rat basilar and middle cerebral arteries (BAs and MCAs) DYN-A (1-13) and DYN-A (1-17) but not DYN-A (1-8) or dynorphin B (DYN-B) induced strong vasoconstriction in micromolar concentrations. The maximal effects, compared to a reference contraction induced by 124 mM K(+), were 115±6% and 104±10% in BAs and 113±3% and 125±9% in MCAs for 10 µM of DYN-A (1-13) and DYN-A (1-17), respectively. The vasoconstrictor effects of DYN-A (1-13) could be inhibited but not abolished by both the κ-opiate receptor antagonist nor-Binaltorphimine dihydrochloride (NORBI) and blockade of G(i/o)-protein mediated signaling by pertussis toxin. Finally, des-Tyr(1) DYN-A (2-13), which reportedly fails to activate κ-opiate receptors, induced vasoconstriction of 45±11% in BAs and 50±5% in MCAs at 10 µM, which effects were resistant to NORBI. CONCLUSION/SIGNIFICANCE: DYN-A is present in rat and human cerebral perivascular nerves and induces sustained contraction of rat cerebral arteries. This vasoconstrictor effect is only partly mediated by κ-opiate receptors and heterotrimeric G(i/o)-proteins. To our knowledge our present findings are the first to indicate that DYN-A has a direct cerebral vasoconstrictor effect and that a dynorphin-induced vascular action may be, at least in part, independent of κ-opiate receptors

Plastiques biosourcés et/ou biodégradables en fin de vie - Conditions et conséquences sur leur valorisation dans lesfilières actuelles de valorisation des déchets

The industrial demand for biosourced plastics is increasing because of the need to develop a societythat is less dependent on fossil resources. New products are developed to meet the demand forproduction of consumer goods and equipment as well as to meet regulatory and societal demands.Diversification of bioplastics requires consideration of their integration into current (and future)processes for the treatment and recovery of solid waste: mechanical recycling, chemical recycling,biological recovery of material and / or energy (composting, anaerobic digestion). Based on a detailedreview of the scientific and technical literature, as well as feedback from industrial experiments, thisstudy aims at identifying the consequences of the presence of bioplastics in the solid waste treatmentsectors and to identify research and development issues favoring their effective integration intocurrent and future value chains of circular resources.La demande industrielle de plastiques biosourcés et/ou biodégradables augmente au fil de la prise deconscience de la nécessité de développer une société moins dépendante des ressources fossiles. Denouveaux produits sont développés pour répondre à la demande de production de biens deconsommation et d’équipement, tout en satisfaisant les exigences réglementaires et sociétales. Ladiversification des matières plastiques nécessite de prendre en considération leur intégration dans lesfilières actuelles de traitement et de valorisation des déchets solides : filières de recyclage mécanique,filières biologiques de valorisation matière et/ou énergie (compostage, méthanisation) et filièrespouvant être amenées à se développer en se basant sur du recyclage chimique et biochimique. Baséesur une revue détaillée de la littérature scientifique et technique, de retours d’expériencesindustrielles, cette étude a pour objectif d’identifier les conséquences de la présence de plastiquesbiosourcés dans les filières de traitement des déchets solides citées ci-dessus. Il conviendra de cernerles enjeux de recherche et développement technologique favorisant leur intégration effective dans lesfilières actuelles et futures de valorisation circulaire des ressources

Mechanical properties of aluminium-based metal matrix composites reinforced with α-alumina platelets

The tensile properties of an aluminium-based metal matrix composite reinforced with [MATH]-alumina platelets were investigated from an experimental and a theoretical point of view. An increase in Young modulus, 0,2% proof stress, flow stress and ultimate tensile strength was observed over the unreinforced metal. These improvements were obtained at the expense of the tensile ductility. The experimental results were analyzed using both a dislocation model and a continuum model based on an iterative Eshelby method

Thermoelectric power applied to metallurgy: principle and recent applications

International audienceno abstrac

Ecomatériaux : les matériaux passent au vert

International audienc

Étude de la cinétique de précipitation des nitrures d’aluminium dans un acier bas carbone

Afin de déterminer une technique fiable de dosage des nitrures d’aluminium dans les aciers calmés aluminium, nous avons comparé différentes techniques : les dosages par PTE, par hydrogène à chaud, par dissolution électrochimique suivie d’une minéralisation, par dissolution électrochimique suivie d’une attaque sodique et le dosage de Beeghly. Ces techniques permettent de quantifier soit l’azote en solution solide, soit l’azote précipité. Nous avons étudié différents états de précipitation d’AlN : trois états durant la cinétique de précipitation à 700°C et deux états de réchauffage (1130 et 1250°C). Nous en avons déduit que les trois premières techniques semblent fiables alors que le dosage de Beeghly ne donne de bons résultats que pour les précipités formés à haute température

Influence of an ethylene-octene copolymer and of pollutants in (PP/EPR) blends

International audienceThe objective of this work was to study the effectiveness of commercial compatibilizers (E-EA-MAH copolymer) on the morphology of blends of polypropylene/ethylene polypropylene rubber (PP/EPR) (78/22) and metallocenic ethylene-octene copolymer (EOC) polluted by (poly (vinyl chloride) (PVC) and by an oil for engine. Blends of various compositions (with and without compatibilizer or pollutant), were prepared using a corotating twin-screw extruder. In both cases, the analyses of blend morphologies highlighted the poor adherence between the two phases in the uncompatibilized blends. Compatibilized polluted blends display better adherence between phases. Dynamic mechanical thermal analysis and differential scanning calorimetry show that the compatibilizer improves the adhesion between both phases and enables stress transfer at the interface

Mechanical characterization of LDPE/PLA blends/wood flour composites

In this work, biocomposites based on low density polyethylene (LDPE), a current thermoplastic, and polylactic acid (PLA), a biodegradable thermoplastic, blends were prepared in presence of various amounts of wood flour (0 to 40 wt %). For that purpose, the following LDPE/PLA/wood flour composites were considered: 20/80/0, 2080/5, 20/80/10, 20/80/20, 20/80/30, 20/80/40). The evolution of elongation at break, strength at break and Young's modulus was followed as a function of the wood flour concentration. The results showed that the properties of the considered composites depend on the level of wood flour