Copper(0)-mediated radical polymerisation in a self-generating biphasic system

Herein, we demonstrate the synthesis of well-defined poly(n-alkyl acrylate)s via copper(0)-mediated radical polymerisation in a self-generating biphasic system. During the polymerisation of n-butyl acrylate in DMSO, the polymer phase separates to yield a polymer-rich layer with very low copper content (ICP-MS analysis: 0.016 wt%). The poly(n-butyl acrylate) has been characterized by a range of techniques, including GPC, NMR and MALDI-TOF, to confirm both the controlled character of the polymerisation and the end group fidelity. Moreover, we have successfully chain extended poly(n-butyl acrylate) in this biphasic system several times with n-butyl acrylate to high conversion without intermediate purification steps. A range of other alkyl acrylates have been investigated and the control over the polymerisation is lost as the hydrophobicity of the polymer increases due to the increase in alkyl chain length indicating that it is important for the monomer to be soluble in the polar solvent

Hyperelastic behavior of modified sepiolite/SEBS thermoplastic elastomers

International audienceThin elastomer films of styrene-ethylene-butylene-styrene block copolymer (SEBS) filled with sepiolite nanofibers nanocomposites were prepared by a dip-coating process. To increase the SEBS/Sepiolite elastomer performances, a new strategy of surface modification of sepiolite by SEBS polymer chains has been developed. In a first part the surface modification of sepiolite was characterized by FTIR and TGA. In a second part the mechanical properties of the filled SEBS films were assessed. Measurements of tensile properties and tear strength were carried to evaluate the impact of the sepiolite modification. These results are discussed in taking account the filler dispersion and the quality of the SEBS/sepiolite interface. The surface modification of the sepiolite nanofibers shows an interesting improvement of the tear strength without major modifications of SEBS matrix intrinsic hyperelastic behavior

Polymérisation radicalaire contrôlée de l'[alpha]-fluoroacrylate de n-butyle

MONTPELLIER-BU Sciences (341722106) / SudocSudocFranceF

Kinetic and thermodynamic parameters guiding the localization of regioselectively modified kaolin platelets into a PS/PA6 co-continuous blend

International audienceThis article highlights the role of kinetic and thermodynamic parameters on the localization of modified kaolin platelets into a high interfacial tension co-continuous PS/PA6 blend after extrusion, injection molding and annealing. Three kinds of copolymers were synthesized and grafted on kaolin: poly(styrene-co-(methacryloyloxy)methyl phosphonic acid) copolymer (P(S-co-MAPC1(OH)2)), polystyrene terminated 3-(mercaptopropyl)triethoxysilane, (ETS-PS) and poly(styrene-co-3-methacryloxypropyltrimethoxysilane) copolymer, (P(S-co-MPS)). Those copolymers were distinguished by (1) the nature of their functional groups (phosphonic acid that reacts only with aluminol groups or alkoxysilane that reacts with both silanol and aluminol groups), (2) the amount of functional groups and (3) their molecular weights. After functionalization the kaolin samples (K1, K2 and K3, respectively) were analyzed by FTIR, TGA and Py-GC/MS to evaluate the grafting. It was shown that P(S-co-MAPC1(OH)2) and P(S-co-MPS) copolymers grafted on kaolin led to highly anisotropic K1 and K3 kaolin platelets, respectively. Then, 50/50/5 PS/PA6/Ki samples (i = 0 to 3) were processed as follows: (1) kaolin platelets were dispersed (via solvent cast) into the PS phase. Then, (2) PS + kaolin were melt mixed by microcompounder with PA6, then (3) the PS/PA6/Ki were injection molded into disks and finally (4) they were annealed (via dynamic or quiescent annealing). Thanks to the high shear rate and longtime of mixing during extrusion (microcompounder), all the kaolin platelets (unmodified K, K1, K2 and K3) crossed the interface and were localized in the PA6 phase. All Ki kaolin stayed in the PA6 phase during injection. However, after annealing (quiescent or dynamic), the localization of the nanoplatelets was guided by thermodynamic parameters, and SEM analysis revealed the segregation of K1 and K3 kaolin platelets at the polymers interface, with a high tendency to impede polymer phases coalescence. Hence, modified K1 and K3 kaolin are promising compatibilizing agents for a co-continuous PS/PA6 blend

Graphene and graphite chemical modifications to perform electrical conductive polymer nanocomposites

International audienceThe last decade, graphene attracted much attention thanks to its 2D structure, high aspect ratio and high surface area. These intrinsic properties made it one of the most promising filler for the development of high added-value polymer nanocomposites [1], [2]. However, graphene nanoparticles are difficult to disperse in polymer matrices. Chemical modification is one of the solutions to improve the dispersion of graphene in polymers. The aim of our study is to tune the chemical modification to improve graphene or graphite dispersion while achieving a high electrical conductive polymer nanocomposite. The chemical modification used is a versatile method based on « grafting onto » functionalization with a previously synthesized copolymer. This functionalization is performed in several steps: (1) oxidation via Hummers or nitric acid attack, (2) “grafting onto” of a copolymer (P(MMA-co-HEMA)) and (3) reduction to recover the high electrical conductivity. The present study is focusing on the characterization of the graphene and graphite chemical modification. Raman spectroscopy reveals high defect concentration due to the strong oxidation and formation of sp3 bonds. XRD allows to show the structure modification (intercalation or exfoliation of the platelets). AFM and SEM allowed to show the exfoliation and the reduction can be quantify by coupling EDX with SEM. TGA, FTIR and Py-GC/MS characterizations proves the chemical modification and the amount of grafted copolymer. Finally, electrical measurements on powders were carried out to determine the impact of chemical modifications on electrical properties

Effect of modified graphene localization in PMMA/PS nanocomposites on electrical properties

International audienc

Effect of modified graphene localization in PMMA/PS nanocomposites on electrical properties

International audienc

h-BN Modification Using Several Hydroxylation and Grafting Methods and Their Incorporation into a PMMA/PA6 Polymer Blend

International audienceHexagonal boron nitride (h-BN) has recently gained much attention due to its high thermal conductivity and low electrical conductivity. In this study, we proposed to evaluate the impact of the modification of h-BN for use in a polymethylmethacrylate/polyamide 6 (PMMA/PA6) polymer blend. Different methods to modify h-BN particles and improve their affinity with polymers were proposed. The modification was performed in two steps: (1) a hydroxylation step for which three different routes were used: calcination, acidic treatment, and ball milling using gallic acid; (2) a grafting step for which four different silane agents were used, carrying different molecular or macromolecular groups: the octadecyl group (Si-C18), propyl amine group (Si-NH2), polystyrene chain (Si-PS), and PMMA chain (Si-PMMA). The modified h-BN samples after hydroxylation and functionalization were characterized by FTIR and TGA. Py-GC/MS was also used to prove the successful graft with Si-C18 groups. Sedimentation tests and multiple light scattering were performed to assess the surface modification of h-BN. Granulometry and SEM observations were performed to evaluate the particle size distribution after hydroxylation. After the addition of Si-PMMA modified h-BN into a PMMA/PA6 co-continuous blend, the morphology of the polymer blend nanocomposites was characterized using SEM. The calculation of the wetting parameter based on the surface tension measurement using the liquid drop model showed that h-BN dispersed in the PA6 phase. Grafting PMMA chains onto hydroxylated h-BN particles combined with an adequate sequence mixing led to a successful localization of the grafted h-BN particles at the interface of the PMMA/PA6 blend

Nanotubes d’Halloysite (HNTs) comme retardateurs de flamme dans des mélanges PE/EVA pour des applications en câblerie

International audienceDe nouvelles réglementations pour la protection de la santé et de l’environnement comme les Euroclasses poussent les industriels de la câblerie à se renouveler. Ils se doivent d’intégrer ces normes tout en continuant à améliorer les propriétés mécaniques et électriques, ainsi que le comportement au feu et le vieillissement des câbles. A l’heure actuelle, les matériaux utilisés pour les gaines des câbles sont des mélanges de polymères chargés en hydroxyde d’aluminium (ATH) ou en polyphosphate d’ammonium (APP). Des taux de charges élevés sont nécessaires pour améliorer le comportement au feu, cependant ils impactent défavorablement la flexibilité de la gaine ou sa sensibilité à l’eau. L’approche menée dans le cadre du projet HAREDY vise à améliorer les performances au feu des matériaux et également à retarder leur vieillissement hygro- et hydrothermique

Comportement au feu de formulations pour câbles électriques après vieillissement sous rayonnement gamma

National audienceLes câbles constituent une source importante de départ et de propagation de feux, c’est pourquoi ils doivent être ignifugés. Si leur comportement au feu est évalué après fabrication, la durabilité dans le temps du traitement ignifuge a jusqu’à présent été peu évaluée alors que ceux-ci doivent rester en service pendant plusieurs décennies tout en étant soumis à des environnements potentiellement agressifs. Ce manque de connaissances peut être particulièrement critique, par exemple dans le cas des centrales nucléaires dont la durée de vie va être prolongée au-delà de 40 ans 1 . Il a été montré que, selon sa nature et le type de vieillissement, le comportement au feu d’un matériau peut être dégradé, maintenu ou même parfois amélioré 2. Dans cette étude, une formulation commerciale pour un câble de nouvelle génération, à base de PE/EVA ignifugé par trihydroxyde d’aluminium, a été injectée sous forme de plaques. Ces plaques ont été soumises à différentes conditions de vieillissement (température, exposition aux UV et rayonnement gamma) dans le but d’évaluer leur comportement au feu à l’aide d’essais au cône calorimètre. Les résultats mettent en particulier en évidence une modification sensible et délétère du comportement au feu du matériau lorsqu’il a été soumis à des doses d’irradiation gamma pouvant être atteintes après plusieurs décennies d’exposition à un faible débit de rayonnements ionisants. Le matériau subit une forte déformation après ignition, due à la réticulation de la fraction polyéthylène sous l’effet du rayonnement gamma 3 . Dans un second temps, les câbles constitués de cette gaine seront évalués afin de vérifier que les phénomènes observés sur la gaine se produisent également sur les câbles