Strain induced crystallization in vulcanized natural rubber containing ground tire rubber particles with reinforcement and nucleation abilities

Strain induced crystallization (SIC) of peroxide vulcanized natural rubber (NR)/ground tire rubber (GTR) composites is studied by combining mechanical and microstructural characterization techniques. It is found that the incorporation of GTR into the NR matrix leads to more effective reinforcement at large strains at room temperature in the NR/GTR composites as compared to the neat NR. It is attributed to (i) the presence of the GTR particles acting as reinforcing fillers owing their high carbon black content, and (ii) the nucleating effect of the GTR for SIC in the NR matrix inducing further reinforcement through the generation of an increasing number of oriented crystallites that behave as supplementary reinforcing fillers

Confinement and distribution of the composition in semicrystalline/amorphous miscible blends of PEKK/PEI: a calorimetry study

International audienceBy combining small-angle X-ray scattering and differential scanning calorimetry measurements, we analyze the widening of the glass transition measured for miscible mixtures of semicrystalline PEKK chains and fully amorphous PEI chains. The calorimetric analysis reveals that the amorphous interlamellar phase is subject to confinement effects. In addition, we measure wide composition distributions for the amorphous interlamellar and interfibrillar phases. We quantitatively identify, through careful analysis of the signals, the fraction and average composition of each amorphous phase and the composition distribution. We conclude that the final distribution of the polymer chains that do not crystallize in the interlamellar and interfibrillar phases results from the crystallization dynamics of the mixtures

Mechanical reinforcement and memory effect of strain-induced soft segment crystals in thermoplastic polyurethane-urea elastomers

An amorphous poly(urethane-urea) copolymer composed of 70 wt% poly(ethylene oxide) (PEO) soft segments (SS) (Mw = 2000 g mol−1) and 30 wt% cycloaliphatic hard segments (HS) was subjected to in-situ X-Rays during tensile deformation. Mechanical hardening at room temperature was attributed to strain induced crystallization (SIC) of the PEO SS through the multiplication of aligned crystallites. The permanent nature of these crystals after stress removal indicates a certain mechanical stability, which we related here to the concomitant effect of superstraining of the SS crystallites and the HS reorganization upon deformation. This is in marked contrast to previous studies which reported the crystalline phase to be temporary upon unloading. A manifestation of such enhanced stability is the memory effect evidenced by an increased crystallizability of PEO segments during incremental cyclic loading. These results offer a way to (i) tune the mechanical properties of TPUs via the formation of mechanically stable pre-oriented SS crystals and to (ii) tune the thermally/water activated shape memory properties of TPUs (shape fixity, kinetics of shape memory recovery)

Cerebral imaging in infectious endocarditis: A clinical study

International audienceBACKGROUND:Because neurological failure is the most frequent extra-cardiac complication in Infectious Endocarditis (IE), a brain computerised tomography (CT) scan is usually performed. The benefits of magnetic resonance imaging (MRI) have not been clearly established. This study aims to clarify the prevalence and type of cerebral lesions in IE detected using MRI and to compare them with those detected using CT scans.METHODS:In the Grenoble University Hospital, patients diagnosed with definite or possible endocarditis according to Duke's criteria were screened from 2010-2012. Brain CT and MRI were performed as soon as possible after diagnosis.RESULTS:Of the 62 patients with IE who underwent at least one cerebral imaging within 3 weeks of diagnosis, Streptococcus (29) and Staphylococcus (14) were the main micro-organisms present. Twenty-eight (45%) patients underwent cardiac surgery. Eight (13%) died before discharge. Twenty (32%) had neurological symptoms. A brain CT-scan was performed on 53 (85%) patients and a MRI was performed on 43 (69%) patients. CT was pathological in 26 (49%) patients, whereas 32 (74%) MRI demonstrated abnormalities. The MRI lesions were classified as follows: ischaemia (48%), microbleeds (34%), haemorrhages (16%), abscesses (9%) and microbial aneurysms (4%). Of the 37 patients who underwent both MRI and CT examinations, ischaemia (48% vs 35%) and microbleeds (34%) demonstrated the difference between the two imaging methods.CONCLUSION:Through the early diagnosis of cerebral damage, even in asymptomatic cases, MRI may have a role in the IE management, influence any surgical decision and assist in prognosis assessment

Stiff, strong, tough, and highly stretchable hydrogels based on dual stimuli-responsive semicrystalline poly(urethane-urea) copolymers

There has been a considerable interest in developing stiff, strong, tough, and highly stretchable hydrogels in various fields of science and technology including biomedical and sensing applications. However, simultaneous optimization of stiffness, strength, toughness, and extensibility is a challenge for any material, and hydrogels are well-known to be mechanically weak materials. Here, we demonstrate that poly(ethylene oxide)-based dual stimuli-responsive semicrystalline poly(urethane-urea) (PU) copolymers with high hard segment contents (30 and 40%) can be utilized as stiff, strong, tough, and highly stretchable hydrogels with an elastic modulus (4-10 MPa) tens to hundreds of times higher than that of conventional hydrogels (0.01-0.1 MPa), strength (7-13 MPa) and toughness (53-74 MJ·m-3) fairly comparable to those of the toughest hydrogels reported in the literature, and stretchability beyond 10 times their initial length (1000-1250%). In addition, the shape-memory program has been used to tune the room temperature stiffness and strength of the studied PU copolymers. Finally, the materials show fast shape recovery (less than 10 s) during both heat- and water-activated shape memory cycles, which can be adjusted by a simple modulation of the hard segment content and/or soft segment molecular weight. Our findings may be of interest in emerging biomedical and sensing applications

Cooperative Synthesis of Raspberry‐Like Covalent Organic Framework‐Polymer Particles with a Radial Single‐Crystal Grain Orientation

International audienceAbstract Despite many efforts devoted toward the design of covalent organic frameworks (COFs) at the framework level by selecting the building blocks, their organization in the nano to meso regimes is often neglected. Moreover, the importance of processability for their applications has recently emerged and the synthesis of COF nanostructures without agglomeration is still a challenge. Herein, the first example of hybrid COF‐polymer particles for which polymers are used to manipulate the 2D COF growth along a specific direction is reported. The study examines how the nature, chain‐end functionality, and molar mass of the polymer influence the shaping of hybrid 2D boronate ester‐linked COF‐polymer particles. Catechol‐poly(N‐butyl acrylate) leads to the self‐assembly of crystallites into quasi‐spherical structures while catechol‐poly(N‐isopropylacrylamide) mediates the synthesis of raspberry‐like COF‐polymer particles with radial grain orientation. Scanning and transmission electron microscopies (SEM and TEM) and 4D‐STEM‐ACOM (automated crystal orientation mapping) highlight the single‐crystal character of these domains with one plane family throughout the particles. Interestingly, the presence of PNIPAm on the particle surface allows their drying without co‐crystallization and enables their resuspension. Kinetic investigations show that catechol‐P n BuA acts as a modulator and catechol‐PNIPAm induces a template effect, introducing supramolecular self‐assembly properties into particles to create new morphologies with higher structural complexity, beyond the framework level

Electron Beam Processing as a Promising Tool to Decontaminate Polymers Containing Brominated Flame Retardants

Electron Beam (EB) irradiation was utilized to decontaminate model systems of industrial polymers that contain a brominated flame retardant (BFR). Acrylonitrile-butadiene-styrene (ABS) and Polycarbonate (PC) are two types of polymers commonly found in Waste Electrical and Electronic Equipment (WEEE). In this study, these polymers were exposed to EB irradiation to degrade DecaBromoDiphenylEther (DBDE), one of the most toxic BFRs. Fourier-transform infrared spectroscopy analysis demonstrated an 87% degradation rate of DBDE for the ABS-DBDE system and 91% for the PC-DBDE system following an 1800 kGy irradiation dose. Thermal analysis using Differential Scanning Calorimetry revealed the presence of crosslinking in ABS and a minor reduction in the glass transition temperature of PC after EB processing. Polymers exhibited thermal stability after photolysis, as indicated by thermogravimetric analysis. In summary, EB irradiation had no impact on the overall thermal properties of both polymers. High-resolution mass spectrometry analysis has confirmed the debromination of both ABS-DBDE and PC-DBDE systems. Therefore, the results obtained are promising and could offer an alternative approach for removing bromine and other additives from plastic E-waste

Lipase-catalysed polycondensation of levulinic acid derived diol-diamide monomers: access to new poly(ester-co-amide)s

International audienceResearch toward bio-based polymers is an expanding field due to environmental concerns. A library of new aliphatic diol-diamide monomers with different chain lengths between the two amido groups was synthesized from sustainable levulinic acid and various linear aliphatic diamines (C 2-C 10). The monomers were prepared by diacylation of the diamines followed by reduction of the ketones to alcohols. These secondary diols were successfully recognized by an enzyme and polymerised in solution through a lipase-catalysed polycondensation. Poly(ester-co-amide)s with number-average molecular weights (M n) in the range of 1300-7200 g mol −1 were obtained, with dispersities between 1.5 and 1.8. An improvement of the M n value was observed upon increasing the monomer chain length. The variation of the aliphatic diol allows modulating the thermal properties of the final polymers. The glass transition temperatures were found to be between −23°C and 0°C. The polymers containing a long aliphatic segment (C 8-C 10) were able to crystallize (melting temperature of 90-97°C). TGA analyses showed that the ester linkages degrade at lower temperatures than the amide bonds. The stability of the latter was found to be higher when the number of methylene units increased from 2 (355°C) to 10 (378°C). This kind of biopolymer could be used as a drug delivery system or for tissue engineering applications. † Electronic supplementary information (ESI) available. Se

Atomic force microscopy as a suitable tool for probing the polar axis direction in electroactive P(VDF-co-TrFE) films at the nanoscale

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Étude de l'adhésion interfaciale dans les composites piézoélectriques à matrice fluoropolymère

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