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cited By 2; International audience; Based on the heterogeneous nature of semi-crystalline terpolymer and the important role that interface polarization plays for dielectric and electromechanical response, small molecular plasticizer bis(2-ethylhexyl) phthalate (DEHP) was introduced into electrostrictive terpolymer to improve electromechanical performances of electrostrictive terpolymer P(VDF-TrFE-CTFE). As expected, the introduced DEHP contributes to greatly increased dielectric permittivity at low frequency, decreased Young's modulus and moderately reduced dielectric breakdown strength of terpolymers, which are closely related with the increased mobility of polymer chains caused by DEHP. Consequently, DEHP modified terpolymers exhibit well improved electromechanical performance in contrast with pure terpolymer. The evolution of electromechanical performances of modified terpolymer with DEHP loading, electric field and frequency was well investigated for actuator applications. © 2016 Elsevier Ltd. All rights reserved.

We discuss the origin of the plateau modulus enhancement (χ) in semi-crystalline segmented block copolymers by increasing the concentration in hard segments within the chains (X HS). The message we deliver is that the plateau modulus of these thermoplastic elastomers is greatly dominated by the volume fraction (Φ) and the width (W) of crystallites according to χ–1 ~ ΦW in agreement with a recent topological model we have developed. We start by a quick review of literature with the aim to extract χ(Φ) for different chemical structures. As we suspected, we find that most of the data falls onto a mastercurve, in line with our predictions, confirming that the reinforcement in such materials is mainly dominated by the crystallite’s content. This important result is then supported by the investigation of copolymer mixtures in which Φ is fixed, providing a similar reinforcement, while the chains compositions is significantly different. Finally, we show that the reinforcement can be enhanced at constant Φ by increasing W for a given class of block copolymers. This can be done by changing the process route and is again in good agreement with our expectations.

In this paper, BGaN thin films with two different thicknesses were deposited on two different substrates and their surface morphologies were investigated. The amorphous glass and semi-crystalline polyethylene terephthalate substrates were selected. At the same time, two different deposition angles are selected with a view to the effect of deposition angle on surface morphology. The surface and optical properties were determined by using X-ray diffractometer (XRD), atomic force microscope (AFM), spectroscopic ellipsometry (SE) and optical interferometer. The thicknesses of thin films on substrates are about 30 nm and 40 nm. According to the atomic force microscope images, small-dimensional grains observed on relatively large grains. The roughness values of the thin films on the polyethylene terephthalate substrate are lower than on the glass substrate. © 2016 Elsevier Ltd

Arresting of segmental mobility in polymer systems on cooling from the melt was simulated by means of the Bond Fluctuation Model. In order to represent the behaviour of the system, three potentials were included: a Lennard-Jones potential, a bond length potential and a bond angle potential. The effect of the bond angle and bond length potential combination is to stretch the chains, while the Lennard-Jones potential leads to a lack of free volume which appears when temperature decreases. So, when a cooling ramp is applied, depending on the balance of these potentials, the system shows a transition in which molecules densely pack or, on the contrary, remains amorphous. Therefore, the choice in the weighting of these three potentials is a key point to simulate a physical system by using the Bond Fluctuation Model. © 2010 Elsevier Ltd. All rights reserved., The authors would like to acknowledge the support provided by the Conselleria d'Educacio of the Generalitat Valenciana through the GV/2009/033 project. This work was supported by the computer-time grant (No. 2003014) of the Centre de Ressources Informatiques de Haute Normandie (CRIHAN).

Two series of bio-based PBT copolyesters were obtained by polycondensation in the melt of 2,4:3,5-di-O- methylene-D-glucitol (Glux-diol) or dimethyl 2,4:3,5-di-O-methylene-D-glucarate (Glux-diester) with 1,4-butanediol and dimethyl terephthalate. The glucose-based bicyclic compounds used as comonomers were synthesized from commercially available 1,5-D-gluconolactone. The prepared PBT copolyesters had weight-average molecular weights in the 30 000–50 000 range; they had a random microstructure, and they were stable above 300 o C. The copolyesters containing less than 30% of sugar- based units were semicrystalline and were found to adopt the triclinic structure of PBT. These copolyesters with low contents in Glux were able to crystallize from the melt but at lower rates than PBT. The Tg value of PBT steadily increased with the incorporation of Glux units in the polyester chain with an increasing ratio of rv1.7 o C or rv1 o C per %Glux point, depending on which unit, the diol or the diacid, was replaced. The copolyesters hydrolyzed at higher rates than PBT, and those containing glucarate units displayed an appreciable susceptibility towards biodegradation. Ministerio de Economía y Competitividad MAT2009-14053-C02 MAT-2012-38044- CO3-03 AGAUR 2009SGR1469

This article discusses the interrelation between formulation, processing, and properties of biocomposites composed of a bioplastic reinforced with wood fibers. Polylactide (PLA) and polylactide/thermoplastic starch blends (PLA/TPS) were used as polymeric matrices. Two grades of PLA, an amorphous and a semicrystalline one, were studied. TPS content in the PLA/TPS blends was set at 30, 50, and 70 wt%. Two types of wood fiber were selected, a hardwood (HW) and a softwood (SW), to investigate the effect of the fiber type on the biocomposite properties. Finally, the impact of different additives on biocomposite properties was studied with the purpose to enhance the bioplastic/wood fiber adhesion and, therefore, the final mechanical performance. The biocomposites containing 30 wt% of wood fibers were obtained by twin-screw extrusion. The properties of the biocomposites are described in terms of morphology, thermal, rheological, and mechanical properties. Furthermore, the biocomposites were tested for humidity and water absorption and biodegradability. An almost 100% increase in elastic modulus and 25% in tensile strength were observed for PLA/wood fiber biocomposite with the best compatibilization strategy used. The presence of the TPS in the biocomposites at 30 and 50 wt% maintained the tensile strength higher or at least equal as for the virgin PLA. These superior tensile results were due to the inherent affinity between the matrices and wood fibers improved by the addition of a combination of coupling and a branching agent. In addition to their outstanding mechanical performance, the biocomposites showed high biodegradation within 60 days. POLYM. ENG. SCI., 54:1325-1340, 2014. © Her Majesty the Queen in Right of Canada 2013 © Her Majesty the Queen in Right of Canada 2013.

The thermally activated shape memory response of polymeric materials results from a combination of the material molecular architecture with the thermal/deformational history, or ‘programming’. In this work, we investigate the shape memory response of systems based on poly(e-caprolactone) (PCL) so as to explore the adoption of proper chemical and thermomechanical tailoring routes. Cross-linked semicrystalline PCL-based materials are prepared by different molecular architectures starting from linear, three- and four-arms star PCL functionalized with methacrylate end groups, allowing to tune the melting temperature, T m, ranging between 36 and 55 °C. The materials’ ability to display the shape memory is investigated by the application of proper thermomechanical cycles on specimens deformed at two different temperatures (23 and 65 °C, i.e. below and above the T m, respectively). The shape memory response is studied under dynamic thermal conditions in thermally activated recovery tests, to identify the typical transformation temperatures, and under isothermal conditions at given recovery temperatures, to monitor shape recovery as a function of time. All the specimens are capable of full recovery on specific thermal ranges influenced by both melting and deformation temperatures. Specimens deformed above T m are able to recover the whole deformation in a very narrow temperature region close to T m, while those deformed at room temperature display broader recovery processes, those onset at about 30 °C. Isothermal tests reveal that when the deformed material is subjected to a constant recovery temperature, the amount of recovered strain and the time required strongly depend on the particular combination of melting temperature, deformation temperature and recovery temperature.

The diacetalized diol 2,4:3,5-di-O-methylene-D-glucitol (Glux), a bicyclic compound derived from D-glucose, was used as a comonomer of 1,6-hexanediol in polycondensation in the melt with dimethyl terephthalate to produce a set of aromatic copolyesters (PHxGluxyT) with Glux contents ranging from 5 to 32%-mole. These sustainable copolyesters had molecular weights within the 12,000 to 45,000 g mol-1 range, and polydispersities between 2.0 and 2.5. They all had a random microstructure and displayed slight optical activity. PHxGluxyT showed a good thermal stability and were semicrystalline with both crystallinity degree and crystallization rate decreasing as the content in Glux increased. Conversely, Tg increased with the incorporation of Glux going from 8 oC in PHT to near 60 oC in the copolyester containing 32%-mole Glux. Compared to PHT, PHxGluxyT copolyesters showed not only an enhanced susceptibility to hydrolysis but also an appreciable biodegradability in the presence of lipases. Ministerio de Economía y Competitividad MAT2009-14053-C02 AGAUR 2009SGR1469

cited By 7; International audience; The fibrillar structure that develops upon drawing of semi-crystalline polymers has been investigated at room temperature by means of in situ SAXS for a series of ethylene copolymers crystallized through various thermal treatments. The long period of the microfibrils for any given material proved to be only dependent on the experimental conditions of the drawing. This suggested the occurrence of a destruction and reconstruction of the semi-crystalline structure via fragmentation accompanied with melting-recrystallization. However, the diameter of the microfibrils proved to keep the memory of the lamellar microstructure via a correlation with the content of interphase at the crystal-amorphous boundary. A physical explanation is proposed for these apparently antagonist findings. The memory of the lamellar semi-crystalline microstructure is completely erased in the microfibrils owing to the melting-recrystallization process. In contrast, the diameter of the fibrils keeps the memory of the chain topology to which a major role is ascribed in the strain-induced fragmentation of the crystalline lamellae. © 2012 Elsevier Ltd. All rights reserved.

Ionic conductivity, diffusion coefficients, mobility and ionic concentration for lithium salts dissolved in polymer electrolytes are determined by the modeling of the dielectric loss and spectra. Cation and anion diffusion coefficients are quantified using the Trukhan model depending on the assumed ratio of the cation to anion diffusion coefficients. Measurements are performed for polymer electrolytes consisting of polyethylene oxide (PEO) with dissolved LiClO 4 salts for different sample thicknesses and temperatures ranging from 5 to 105 °C, which comprises both the crystalline and amorphous phases of the composite electrolyte. A good phenomenological description of the dielectric loss spectra is obtained for both the semi-crystalline and amorphous phases. The fraction of mobile ions is estimated to vary from 0.002% at 25 °C (semi-crystalline phase) up to 0.05% at 80 °C (amorphous phase)., This research has been supported by the IMIDIC/2009/152 project, granted by the Generalitat Valenciana (Valencia, Spain) through the Institute for Small and Medium Industry (IMPIVA) and the European Union by FEDER funds. Dr. A. Munar acknowledges the support of the Ramon y Cajal programme08-18-463B-750, and Grant MAT2009-14602, Ministerio de Ciencia e Innovacion, Spain.

Several series of nanocomposites were prepared using a latex-based process, the main step of which consisted of mixing an aqueous suspension of exfoliated carbon nanotubes (CNTs) and a polymer latex. In the present work, a systematic study on the electrical properties of fully amorphous (polystyrene - PS) as well as semi-crystalline (isotactic polypropylene - iPP) nanocomposites containing either single-wall (SWCNTs) or multi-wall carbon nanotubes (MWCNTs) has been conducted. Percolation thresholds as low as 0.05 wt.% or 0.1 wt.% were observed for SWCNT/iPP and MWCNT/iPP nanocomposites, respectively. The formation of a conductive percolating network at such a low CNT concentration is favored by the high intrinsic conductivity and the low viscosity of the polymer matrix. The electrical percolation threshold of the iPP-based system was found to be lower than its rheological percolation threshold. Beyond the percolation threshold, MWCNT-based nanocomposites generally exhibited higher conductivity levels than those based on SWCNTs, most probably due to the higher intrinsic conductivity of the MWCNTs as compared to that of the SWCNTs. These excellent electrical properties, associated with the strong nucleating effect of the CNTs reported earlier [1,2], render this type of nanocomposites extremely attractive from a technological point of view. © 2010 Elsevier Ltd. All rights reserved.

Several series of nanocomposites were prepared using a latex-based process, the main step of which consisted of mixing an aqueous suspension of exfoliated carbon nanotubes (CNTs) and a polymer latex. In the present work, a systematic study on the electrical properties of fully amorphous (polystyrene - PS) as well as semi-crystalline (isotactic polypropylene - iPP) nanocomposites containing either single-wall (SWCNTs) or multi-wall carbon nanotubes (MWCNTs) has been conducted. Percolation thresholds as low as 0.05 wt.% or 0.1 wt.% were observed for SWCNT/iPP and MWCNT/iPP nanocomposites, respectively. The formation of a conductive percolating network at such a low CNT concentration is favored by the high intrinsic conductivity and the low viscosity of the polymer matrix. The electrical percolation threshold of the iPP-based system was found to be lower than its rheological percolation threshold. Beyond the percolation threshold, MWCNT-based nanocomposites generally exhibited higher conductivity levels than those based on SWCNTs, most probably due to the higher intrinsic conductivity of the MWCNTs as compared to that of the SWCNTs. These excellent electrical properties, associated with the strong nucleating effect of the CNTs reported earlier [1,2], render this type of nanocomposites extremely attractive from a technological point of view. © 2010 Elsevier Ltd. All rights reserved.

This paper presents a study of polyamide 6/sepiolite clay nanocomposite, obtained by melt compounding in a mini twin-screw extruder, and characterised in terms of morphology (SEM and TEM analysis) and mechanical properties of the composite, along with their crystallinity and crystal structure of the semi-crystalline matrix. The tensile test results are interpreted in terms of two micromechanical models: the Halpin-Tsai model for stiffness and the Pukanszky equation for yield stress, and compared with the results on polyamide 6/smectite montmorillonite (MMT) clay nanocomposites from selected publications. This comparison between sepiolite (fibre-like shape, 1D) and smectite (platelet-like, 2D) clays offers an interesting model-study on the effect of nanofiller shape and orientation on final mechanical properties. It shows that 1D fillers are expected to provide better reinforcement in the case of oriented systems, whereas platelets should be more efficient in isotropic composites. It was demonstrated that sepiolite has a higher reinforcing efficiency (higher effective aspect ratio) than MMT in PA6 and a good filler-matrix interface, due to strong hydrogen bonds between silanol groups on the sepiolite surface and amide groups of PA6. © 2009 Elsevier Ltd. All rights reserved.

This paper presents a study of polyamide 6/sepiolite clay nanocomposite, obtained by melt compounding in a mini twin-screw extruder, and characterised in terms of morphology (SEM and TEM analysis) and mechanical properties of the composite, along with their crystallinity and crystal structure of the semi-crystalline matrix. The tensile test results are interpreted in terms of two micromechanical models: the Halpin-Tsai model for stiffness and the Pukanszky equation for yield stress, and compared with the results on polyamide 6/smectite montmorillonite (MMT) clay nanocomposites from selected publications. This comparison between sepiolite (fibre-like shape, 1D) and smectite (platelet-like, 2D) clays offers an interesting model-study on the effect of nanofiller shape and orientation on final mechanical properties. It shows that 1D fillers are expected to provide better reinforcement in the case of oriented systems, whereas platelets should be more efficient in isotropic composites. It was demonstrated that sepiolite has a higher reinforcing efficiency (higher effective aspect ratio) than MMT in PA6 and a good filler-matrix interface, due to strong hydrogen bonds between silanol groups on the sepiolite surface and amide groups of PA6. © 2009 Elsevier Ltd. All rights reserved.

cited By 2; International audience; A new technique, the High Velocity Compaction (HVC) allows the processing of nascent semicrystalline powders via sintering. It implies several controlled energy impacts on a powder-filled die. The die is heated up to a temperature below the melting temperature of the powder. Sintering occurs thanks to dissipation of a part of impacts energy which allows local heating and thus melting of a fraction of the powder. The aim of this paper is to evaluate the spatial localization of the part of powder which is melted during HVC process in order to estimate the quality of interparticular welding: "the sintering quality" and to deduce the most probable sintering mechanism. Two polymer powders are tested: PolyOxyMethylene and Ultra High Molecular Weight Poly Ethylene. This objective has been reached in particular thanks to local measurements of mechanical properties which have been performed by nanoidentation. It has been observed that a fraction of the nascent polymer undergoes melting-recrystallization during the process. Then, it is demonstrated that melting-recrystallization is needed to achieve sintering that would occurs by diffusion and intertwining of the chains at the melted state and also cocrystallization during the cooling. In light of these two mechanisms, the sintering quality is discussed in order to have an insight of HVC possibilities to process different type of polymers. © Springer/ESAFORM 2008.

An overview on the synthesis, structure and properties of polyamides and aromatic copolyesters produced by using monomers derived from carbohydrates is provided. Two examples are selected for illustration: (a) aliphatic polyamides prepared from aldaric acids and (b) aromatic copolyesters containing alditols units. Polycondensation in solution of n-alkanediamines ( n taking even values from 6 to 12) with activated pentaric (l- arabino and xylo) and hexaric ( galacto and d- manno) acids bearing the secondary hydroxyl groups protected as methyl ether, afforded linear polyaldaramides PA- nSu with Mw oscillating between 25 000 and 150 000 g mol−1. They are stable above 300°C and are semicrystalline even so only PA- nMn are stereoregular. Melting temperatures of PA- nSu range between 140 and 230°C and most of them are able to crystallize from the melt at a rate that increases with the length of the polymethylene segment. Both melting and glass transition temperatures decrease with the content in sugar units. Spherulitic films, oriented fibers and lamellar single crystals could be obtained from PA -nSu. All these polyamides seem to adopt a common crystal structure made of hydrogen-bonded sheets with the sugar residue skewed to attain an efficient side-by-side packing of the polymer chains. Aromatic homopolyesters and copolyesters derived from terephthalic acid and mixtures of butylene glycol and O-methylated alditols were prepared by polycondensation in the melt with Mw in the 20 000–50 000 g mol−1 range and a random microstructure. The thermal properties of PBT containing alditols units are very depending on the sugar constitution and copolyester composition. In general they are thermally stable above 300°C and display crystallinity for contents in alditols up to 30%. Melting temperatures decrease with the content in alditols whereas an opposite trend is observed for glass transition temperatures. The crystalline structure of PBT is preserved in the crystalline copolyesters whereas a different crystal lattice is adopted by homopolyesters entirely made of alditol units. In general, polyamides and polyesters containing sugar derived units are widely soluble in organic solvents, markedly hydrophilic and more susceptible to hydrolysis than their parent polymers.