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See detailLes polyendocrinopathies de type I, aspect épidémiologique
Beckers, Albert ULg

Scientific conference (1993, May 14)

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See detailLes polyendocrinopathies de type I
Beckers, Albert ULg

Scientific conference (1994, April 08)

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See detailLes polyendocrinopathies de type I
Beckers, Albert ULg

Scientific conference (1995, February 23)

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See detailPolyester layered silicate nanohybrids by controlled grafting polymerization
Lepoittevin, Bénédicte; Pantoustier, Nadège; Alexandre, Michaël ULg et al

in Journal of Materials Chemistry (2002), 12(12), 3528-3535

Poly( epsilon-caprolactone) (PCL) layered silicate nanohybrids were synthesized by ring opening polymerization of epsilon-caprolactone according to a well-controlled coordination-insertion mechanism ... [more ▼]

Poly( epsilon-caprolactone) (PCL) layered silicate nanohybrids were synthesized by ring opening polymerization of epsilon-caprolactone according to a well-controlled coordination-insertion mechanism. Montmorillonites were surface-modified by non functional (trimethylhexadecylammonium) and hydroxy functional alkylammonium cations, i.e., (2-hydroxyethyl) dimethylhexadecylammonium. The hydroxy functions available at the clay surface were activated into tin( II or IV) or Al(III) alkoxide initiators for lactone polymerization, thus yielding surface-grafted PCL chains. The surface-grafted PCL chains were recovered by an ionic exchange reaction with lithium chloride and they were analyzed by size exclusion chromatography. The PCL molar mass was measured as a function of the hydroxy content of the clay that was modulated by exchanging the Na cations with mixtures of non-functional and hydroxy functional ammonium cations of different compositions. Nanohybrids were also characterized by small-angle X-ray diffraction, transmission electron microscopy and thermogravimetry. The PCL molar mass and the nanocomposite morphology (i.e., exfoliation and/or intercalation) were readily tuned by the content of the hydroxy groups available at the clay surface. Surface-grafted aluminium trialkoxide species proved highly efficient in initiating polymerization that leads to PCL chains of controlled molar mass and narrow molecular weight distribution with polydispersity indices as low as 1.2. [less ▲]

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See detailPolyester nanoparticles presenting mannose residues : toward the development of new vaccine delivery systems combining biodegradability and targeting properties
Rieger, Jutta ULg; Freichels, Hélène ULg; Imberty, Anne et al

in Biomacromolecules (2009), 10(3), 651-657

We report the synthesis of fully biodegradable polymeric nanoparticles presenting mannose residues at their surface and their interaction with lectins. A simple and versatile method was used to reach the ... [more ▼]

We report the synthesis of fully biodegradable polymeric nanoparticles presenting mannose residues at their surface and their interaction with lectins. A simple and versatile method was used to reach the surface functionalization of poly(d,l-lactic acid) (PLA) nanoparticles by mannose moieties: It consists in using an amphiphilic mannosylated poly(ethylene oxide)-b-poly(-caprolactone) (PEO-b-PCL) diblock copolymer as a bioresorbable surface modifier in a simple nanoprecipitation-evaporation procedure. The size and zeta potential of the nanoparticles were found to depend on the molar copolymer/PLA ratio, demonstrating the influence of the copolymer on the formation of the nanoparticles. The bioavailability of the mannose residues as specific recognition sites on the nanoparticle surface could be demonstrated by a modified enzyme-linked lectin assay (ELLA) using biotin-labeled lectins which interact specifically with α-d-mannopyrannoside derivatives. Besides specific interaction by lectin−mannose complex formation, nonspecific adsorption of the proteins on the nanoparticle surface was observed. These results were fully supported by isothermal titration calorimetry experiments which suggested that the balance between specific and nonspecific interactions can be controlled by the amount of glycosylated polymer used for the preparation of the nanoparticles. Such nanoparticles are expected to be specifically recognized by mannose receptors, which are highly expressed in cells of the immune system. The targeting properties of these carrier systems combined with their potential adjuvant effects due to their size in the range of 200−300 nm make them attractive candidates as vaccine delivery systems. [less ▲]

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See detailPolyester-based microcarriers with enhanced surface properties for tissue engineering
Markvicheva, Elena; Privalova, Anna; Sevrin, Chantal ULg et al

Poster (2014, June 17)

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See detailPolyéthylène - Mise au point de techniques analytiques sur Catalyseurs et Prépolymères au Chrome
Olive, Gilles ULg

Master's dissertation (1993)

Situation du sujet Les sujets de mon stage étaient: - Mise au point d'une méthode de dosage de l'aluminium dans les catalyseurs au chrome - Mise au point d'une technique analytique (FX) sur les ... [more ▼]

Situation du sujet Les sujets de mon stage étaient: - Mise au point d'une méthode de dosage de l'aluminium dans les catalyseurs au chrome - Mise au point d'une technique analytique (FX) sur les prépolymères Parmi les différentes qualités de polyéthylène, notamment celle destinée à l'extrusion-souflage, on peut utiliser un catalyseur à base de chrome. Pour des raisons de cinétique et de sélectivité on modifie ces catalyseurs soit par du titane, soit par de l'aluminium. Or pour éviter tout problème, notamment les points chauds dans le réacteur, et pour obtenir la qualité désirée, il est nécessaire de bien connaître la composition du catalyseur. Le dosage du chrome et du titane ne pose pas de problème, alors que le dosage de l'aluminium fournit des résultats très inférieurs à la réalité. Par ailleurs, dans le procédé phase gaz BP, la prépolymérisation du catalyseur permet un meilleur contrôle de la morphologie, donc de la fiabilité. Lors de polymérisation, on doit connaître exactement la quantité de catalyseur injecté. pour cela, il faut savoir de façon précise le taux d'avancement du prépolymère. Il est donc nécessaire de faire une série d'étalons pour la FX, car la méthode actuelle (taux de cendres qui nécessite 1 heure pour donner le résultat) n'est pas applicable pour le suivi d'un atelier. Les résultats obtenus Analyse de l'aluminium dans les catalyseurs Après avoir comparé les différentes méthodes actuelles, et effectué quelques essais pour déterminer la meilleure méthode, une longue série de points (11 au total) fut réalisée afin d'évaluer la fiabilité d'une nouvelle méthode. Il ressort de cette étude que: - l'ajout d'acide chlorhydrique permet de mieux solubiliser l'aluminium - il n'est pas nécessaire de mettre 20% d'acide fluorhydrique, 10% suffisent pour solubiliser la silice et le chrome - en absorption atomique, il faut bien homogénéiser l'échantillon et avoir des étalons récents. Une fois cette étude terminée et les différentes vérifications effectuées sur des souches catalytiques bien connues, l'étude d'homogénéité de lot a pu commencer. Malgré le faible nombre de points, on remarque que dans un même fût le pourcentage d'aluminium ne varie que de 0.01% Synthèse de prépolymères étalons La synthèse des deux séries d'étalons destinés à la FX a permis de dégager les remarques suivantes: - il faut faire attention à la vanne de fond de réacteur. Celle-ci crée un volume mort dans lequel le catalyseur peut tomber et ne réagit plus - les prépolymères doivent toujours être manipulés et conservés à l'abri de l'air, sinon ils se dégradent et ne peuvent plus servir pour recaler la dérive normale de la FX - il faut bien vérifier l'homogénéité des prépolymères et des pastilles sinon on a des erreurs de l'ordre de 40% sur la mesure. [less ▲]

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See detailPolyethylene-layered silicate nanocomposites prepared by the polymerization-filling technique: synthesis and mechanical properties
Alexandre, Michaël ULg; Dubois, Philippe ULg; Sun, Tao et al

in Polymer (2002), 43(8), 2123-2132

Polyethylene-layered silicate nanocomposites were prepared by the in situ intercalative polymerization of ethylene by the so-called polymerization-filling technique and analyzed by transmission electron ... [more ▼]

Polyethylene-layered silicate nanocomposites were prepared by the in situ intercalative polymerization of ethylene by the so-called polymerization-filling technique and analyzed by transmission electron microscopy (TEM), X-ray diffraction analysis (XRD), differential scanning calorimetry, dynamic mechanical analysis and tensile testing. Non-modified montmorillonite and hectorite were first treated by trimethylaluminum-depleted methylaluminoxane before being contacted by a Ti-based constrained geometry catalyst. The nanocomposite was formed by addition and polymerization of ethylene. In the absence of a chain transfer agent, ultra high molecular weight polyethylene was produced. The tensile properties of these nanocomposites were poor and essentially independent of the nature and content of the silicate. Upon hydrogen addition, the molecular weight of the polyethylene was decreased with parallel improvement of the tensile and shear moduli, in relation to the filler content. The exfoliation of the layered silicates was confirmed by XRD analysis and TEM observation. The mechanical kneading of the molten nanocomposites resulted in the partial collapse of the exfoliated structure driven by the thermodynamic stability of the layered filler. [less ▲]

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See detailThe POLYGAL project : optimization of food conservation using a combination of lactates and polyphenols.
Dure, Rémi ULg; Ladeuze, S.; Martin, E. et al

Poster (2009, November)

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See detailLa polygamie devant la Cour d'arbitrage
Carlier, Jean-Yves ULg

in Journal du Juriste (2005), 42(1), 1

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See detailPolygeneration and HVAC
Andre, Philippe ULg; Adam, Ch.; Aparecida Silva, Cl. et al

Conference (2005, April)

Decentralized cogeneration may help in energy conservation if a large enough amount of heat can be actually recovered. This restriction is becoming more and more severe because of the growing ... [more ▼]

Decentralized cogeneration may help in energy conservation if a large enough amount of heat can be actually recovered. This restriction is becoming more and more severe because of the growing effectiveness of modern power plants. Re-conversion of heating into cooling is not competitive with the use of modern vapor compression chillers. It may just help to extend a little the time during which the co-generation plant can be effectively used. A co-generation plant should not be sized above 30% of the maximal heating power in order to stay energy efficient. The results of a long term case study are summarized in the paper. These results show the incidence of the plant over-sizing : in this case, the system is consuming more than a classical solution [less ▲]

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See detailPolyhedral properties for the intersection of two knapsacks
Louveaux, Quentin ULg; Weismantel, Robert

in Mathematical Programming (2008), 113(1), 15-37

We address the question to what extent polyhedral knowledge about individual knapsack constraints suffices or lacks to describe the convex hull of the binary solutions to their intersection. It turns out ... [more ▼]

We address the question to what extent polyhedral knowledge about individual knapsack constraints suffices or lacks to describe the convex hull of the binary solutions to their intersection. It turns out that the sign patterns of the weight vectors are responsible for the types of combinatorial valid inequalities appearing in the description of the convex hull of the intersection. In partic- ular, we introduce the notion of an incomplete set inequality which is based on a combinatorial principle for the intersection of two knapsacks. We outline schemes to compute nontrivial bounds for the strength of such inequalities w.r.t. the intersection of the convex hulls of the initial knapsacks. An extension of the inequalities to the mixed case is also given. This opens up the possibility to use the inequalities in an arbitrary simplex tableau. [less ▲]

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See detailPolyimide foams derived from a high Tg polyimide with grafted poly(α-methylstyrene)
Hedrick, James L; DiPietro, R.; Plummer, C. J. G. et al

in Polymer (1996), 37(23), 5229-5236

A new route to high-Tg, thermally stable polyimide foams has been developed. Foams were prepared by casting microphase-separated graft copolymers comprising a thermally stable main chain, polyimide, and a ... [more ▼]

A new route to high-Tg, thermally stable polyimide foams has been developed. Foams were prepared by casting microphase-separated graft copolymers comprising a thermally stable main chain, polyimide, and a thermally labile graft, poly(α-methylstyrene). The copolymer compositions were designed so that the thermally labile block would be the dispersed phase. This can unzip to its monomer upon heating, and the decomposition product diffuses out of the film, leaving pores embedded in a matrix of the thermally stable component. The copolymers were synthesized through either the poly(amic acid) precursor, followed by chemical cyclodehydration to the imide form, or the poly(amic alkyl ester) precursor followed by thermal imidization. The decomposition of the α-methylstyrene in the block copolymer was studied by thermogravimetric, dynamic mechanical and thermomechanical analyses. Mild decomposition conditions were required to avoid rapid depolymerization of the α-methylstyrene and excessive plasticization of the polyimide matrix. The foams showed pore sizes with diameters ranging from less than 20 nm to over 1 µm, depending upon the synthetic route employed, and the reduction in the mass density was generally consistent with the starting composition. [less ▲]

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See detailPolyimide nanofoams from aliphatic polyester-based copolymers
Hedrick, James L; Carter, K. R.; Richter, R. et al

in Chemistry of Materials (1998), 10(1), 39-49

High-temperature polymeric foams were prepared using compositionally asymmetric microphase-separated block copolymers where the major component is thermally stable and the minor component is thermally ... [more ▼]

High-temperature polymeric foams were prepared using compositionally asymmetric microphase-separated block copolymers where the major component is thermally stable and the minor component is thermally labile. Upon thermal treatment, the dispersed phase undergoes thermolysis leaving pores the size and shape of which are dictated by the initial copolymer morphology. The driving force behind the survey of aliphatic polyesters as possible labile blocks stems from their quantitative degradation into low-boiling, polar degradation products. Poly(lactones), as a general class of materials, degrade by a backbiting process producing, primarily, monomer and cyclic oligomers. A ring-opening synthetic route to poly(lactones) affords oligomers of predictable molecular weight, narrow molecular weight distribution, and controlled end-group functionality. Block copolymers were prepared using monofunctional caprolactone and valerolactone oligomers and a high-Tg polyimide. Microphase separation was observed in all cases, and the lactone blocks did not crystallize. Thermal decomposition of the caprolactone block was accomplished by heating the copolymer to 370 °C for 5 h. Significant density reductions were found with pore sizes in the 60−70 Å range. [less ▲]

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See detailPolyimide nanofoams from caprolactone-based copolymers
Hedrick, James L; Russell, T. P.; Sanchez, M. et al

in Macromolecules (1996), 29(10), 3642-3646

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See detailPolylactide (PLA) designed with desired end-use properties: 1. PLA compositions with low molecular weight ester-like plasticizers and related performances
Murariu, Marius; Da Silva Ferreira, Amalia; Alexandre, Michaël ULg et al

in Polymers for Advanced Technologies (2008), 19(6), 636-646

Polylactide (PLA) is an attractive candidate for replacing petrochemical polymers because it is biodegradable and produced from annually renewable resources. Characterized by high tensile strength ... [more ▼]

Polylactide (PLA) is an attractive candidate for replacing petrochemical polymers because it is biodegradable and produced from annually renewable resources. Characterized by high tensile strength, unfortunately the brittleness and rigidity of PLA limit its applicability. For a great number of applications such as packaging, fibers, films, etc., it is of high interest to formulate new grades with improved flexibility and better impact properties. In this objective, a specific PLA grade (L/D isomer ratio of 96:4, high molecular weight) was melt-mixed with selected plasticizers: bis(2-ethylhexyl) adipate (DOA), glyceryl triacetate (GTA), and tributyl O-acetylcitrate (TBAC). Their effect on the molecular, thermal, and mechanical properties of PLA was investigated for content up to 20wt% plasticizer and the results were correlated with a particular attention to the relationship between property and application. Using the solubility and interaction parameters, a tentative evaluation of the product that could act as the most effective plasticizer for PLA has been performed and the obtained results have been corroborated with the materials physical properties. Excellent mechanical performances were obtained using the plasticizer having the lowest molecular mass (GTA) and the best interaction parameter. In relation to plasticizer amount/nature, the glass transition temperature of PLA (62-C) is decreased by plasticizing by more than 30-C, whereas better impact properties and lower stiffness are measured. The optimal formulations targeted to the final applications are clearly characterized by specific end-use properties: improved crystallization rates (PLA-DOA); high elongation at break and tensile strength (PLA-GTA, PLA-TBAC), medium to high impact properties (PLA-DOA, PLA-GTA) compositions. [less ▲]

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See detailPolylactide (PLA) – A new way of production
Jacobsen, Sven; Degée, Philippe; Fritz, Hans-Gerhard et al

in Polymer Engineering & Science (1999), 39(7), 1311-1319

Poly(lactide) (PLA), a biodegradable aliphatic polyester with excellent properties for different polymer applications, has been used mostly in the biomedical field, mainly because of its high price ... [more ▼]

Poly(lactide) (PLA), a biodegradable aliphatic polyester with excellent properties for different polymer applications, has been used mostly in the biomedical field, mainly because of its high price, resulting from expensive polymerization and purification techniques. Although this polymer can play a major role in future markets for biodegradable polymers, the current high price has to be reduced significantly to at least $4 US/kg. Therefore, this paper aims to partially review the polymerization techniques traditionally used in PLA synthesis and to propose new developments that enable us to produce these polymers by an innovative process for just a portion of the costs traditionally charged, using reactive extrusion techniques in a closely intermeshing co-rotating twin screw extruder. This paper gives an overview of attainable mechanical properties and future markets. [less ▲]

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See detailPolylactide (PLA)-CaSO4 composites toughened with low molecular weight and polymeric ester-like plasticizers and related performances
Murariu, Marius; Da Silva Ferreira, Amalia; Pluta, Miroslaw et al

in European Polymer Journal (2008), 44

Large amounts of stable b-anhydrite II (AII), a specific type of dehydrated gypsum and a by-produc tof lactic acid production process, can be melt-blended with bio-sourced and biodegradable polylactide ... [more ▼]

Large amounts of stable b-anhydrite II (AII), a specific type of dehydrated gypsum and a by-produc tof lactic acid production process, can be melt-blended with bio-sourced and biodegradable polylactide (PLA) to produce economically interesting novel composites with high tensile strength and thermal stability. To enhance their toughness, while preserving an optimal stiffness, selected low molecular weight plasticizers (bis(2-ethylhexyl) adipate and glyceryl triacetate) and polymeric adipates with different molecular weights have been mixed with a specific PLA (L/D isomer ratio of 96/4) and 40 wt% of AII using an internal kneader. Addition of up to 10 wt% plasticizer into these highly filled compositions can trigger a fourfold increase of the impact strength with respect to the compositions without any modifier, cold crystallization properties and a significant decrease of their glass transition temperature. Moreover, these ternary compositions (PLA–AII–plasticizer) are clearly characterized by easier processing, notable thermo-mechanical performances and good filler dispersion. This study represents a new approach in formulating novel melt-processable polyester grades with improved characteristic features using PLA as biodegradable polymer matrix. [less ▲]

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See detailPolylactide implants and bacterial contamination: an animal study
Mainil-Varlet, Pierre; Hauke, Christian; Maquet, Véronique et al

in Journal of Biomedical Materials Research, Part A (2001), 54(3), 335-343

Although bioresorbable aliphatic polyesters derived from lactic acid are now used clinically as sutures, bone-fracture fixation devices and sustained-release drug-delivery systems, very little is known ... [more ▼]

Although bioresorbable aliphatic polyesters derived from lactic acid are now used clinically as sutures, bone-fracture fixation devices and sustained-release drug-delivery systems, very little is known about their behavior in the infected environment. The aim of the present study was to compare the resistance to infection of two polylactide implants with different degradation characteristics, and to evaluate the influence of a bacterial challenge on their mechanical and physicochemical properties. Various quantities of a beta-haemolyzing strain of Staphylococus aureus (V 8189-94) were inoculated into the medullary cavity of rabbit tibiae, and an extruded polylactide rod composed of either P(L)LA (Poly(L-Lactide)) or P(L/DL)LA (Poly(L/DL-Lactide)) was then inserted. Animals were sacrificed four weeks after surgery. The tibiae and implants were removed under sterile conditions and evaluated microbiologically by culturing. The severity of infection was graded according to positive colony-forming units in the bone. The mechanical properties of the retrieved implants were assessed by 4-point bending and shear tests, performed in compliance with the ASTM D790 standard and their physicochemical characteristics also were characterized. P(L)LA and P(L/DL)LA implants were equally resistant to local infection, their mechanical and physicochemical properties being unaffected by bacterial challenge. Hence, once an infection has become established, the release of bactericidal/bacteriostatic by-products during implant degradation does not appear to affect its natural course. The release of bactericidal/bacteriostatic degradation products at the implantation site is unlikely to affect the natural course of an established infection. [less ▲]

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See detailPolylactide macroporous biodegradable foams by solid-liquid and liquid-liquid phase separation
Maquet, V; Schugens, C; Grandfils, Christian ULg et al

Conference (1995, May 22)

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