Influence of fillers on mechanical properties of ATH filled EPDM during ageing by gamma irradiation

International audienceThe presence of a significant content of fillers accelerates the degradation of ATH filled EPDM subjected to gamma irradiation at room temperature. Above the melting temperature of the EPDM, this induces a decrease in the apparent mechanical reinforcement of the fillers. This also promotes de-cohesion mechanisms which leads to an increase in the strain at break with irradiation dose. It is not clear whether the use of a filler treatment attenuates this accelerating effect or not; however, part of this treatment remains efficient at a high dose and seems also to delay but not suppress the occurrence of de-cohesion mechanisms at large strain. Moreover, at room temperature, i.e. below the melting temperature, all the consequences of ageing by gamma irradiation are strongly attenuated by the presence of a semicrystalline microstructure, the morphology of which is not too strongly modified by irradiation. (C) 2010 Elsevier Ltd. All rights reserved

Complex dependence on the elastically active chains density of the strain induced crystallization of vulcanized natural rubbers, from low to high strain rate

Strain Induced Crystallization (SIC) of Natural Rubbers (NR) with different network chain densities (¿) is studied. For the weakly vulcanized rubber, the melting stretching ratio ¿m at room temperature is the lowest. This is correlated with larger crystallites in this material measured by in situ WAXS, suggesting their higher thermal stability. SIC kinetics is then studied via stretching at various strain rates (from 5.6 × 10-5 s-1 up to 2.8 × 101 s-1). For the slowest strain rates, SIC onset (¿c) is clearly the lowest in weakly vulcanized rubber. By increasing the strain rate, ¿c of the different materials increase and converge. For the highest strain rates, ¿c values still increase but less rapidly for the weakly vulcanized sample. This complex dependence on the elastically active chains (EAC) density of SIC has been confirmed by in situ WAXS during dynamic experiments and interpreted as a consequence of both the polymer chain network topology and of the entanglements dynamics.Peer ReviewedPostprint (author's final draft

Développement et caractérisation mécanique de membranes silicone architecturées

International audienceDes applications médicales nécessitent l'élaboration de membranes à anisotropie de comportement mécanique. La présente étude vise à proposer une solution à partir d'un seul matériau constitutif. Le principe repose sur la création de membranes architecturées en créant localement au niveau du Volume Elémentaire Représentatif des hétérogénéités de réticulation aux motifs contrôlés. Un matériau silicone est choisi pour la réalisation de ces membranes, à la fois pour sa facilité à le modifier chimiquement et ses propriétés élastomériques intrinsèques. Le degré de réticulation du silicone est maitrisé localement par irradiation UV d'un photo-inhibiteur avant vulcanisation : les zones irradiées réagissent moins en hydrosilylation, générant une phase plus élastique. Cette manipulation permet la création de membranes aux propriétés architecturées de par le contrôle local du degré de réticulation du réseau polymère

Characteristic-time of strain induced crystallization of crosslinked natural rubber

International audienceReal time Wide-Angle X-ray Scattering (WAXS) measurements during cyclic tensile tests at high strain rates (from 8 s−1–280 s−1) and at room temperature on crosslinked Natural Rubber (NR) are performed thanks to a specific homemade device. From the observed influence of the frequency on the crystallization index at the maximum sample elongation, a characteristic crystallization time is deduced. This is done taking into account the material self-heating during such unusually high strain rates. Two regimes for the dynamic process of strain induced crystallization are evidenced. For the NR tested, the obtained characteristic time is around 20 ms when the material average elongation during the cyclic test is above a critical elongation value λc. λc is the minimum elongation needed to induce crystallization during low strain rate tensile tests. Moreover, a rapid increase of this characteristic time is found when the average elongation decreases below this critical value

Strain induced crystallization and melting of natural rubber during dynamic cycles

Strain-induced crystallization (SIC) of natural rubber (NR) is studied during dynamic cycles at high frequencies (with equivalent strain rates ranging from 7.2 s-1 to 290 s-1). The testing parameters are varied: the frequency, the temperature and the stretching ratio domain. It is found that an increase of the frequency leads to an unexpected form of the CI–¿ curve, with a decrease of the crystallinity during both loading and unloading steps of the cycle. Nevertheless, the interpretation of the curves needs to take into account several phenomena such as (i) instability of the crystallites generated during the loading step, which increases with the frequency, (ii) the memory of the previous alignment of the chains, which depends on the minimum stretching ratio of the cycle ¿min and the frequency, and (iii) self-heating which makes the crystallite nucleation more difficult and their melting easier. Thus, when the stretching ratio domain is above the expected stretching ratio at complete melting ¿melt, the combination of these phenomena, at high frequencies, leads to unexpected results such as complete melting at ¿min, and hysteresis in the CI–¿ curves.Peer ReviewedPostprint (author's final draft

Polymer Chain Generation for Coarse-Grained Models Using Radical-Like Polymerization

International audienceThis paper presents major improvements in the efficiency of the so-called Radical-Like Polymerization (RLP) algorithm proposed in ”Polymer chain generation for coarse-grained models using radical-like polymerization” [J. Chem. Phys. 128 (2008)]. Three enhancements are detailed in this paper: (1) the capture radius of a radical is enlarged to increase the probability of finding a neighboring monomer; (2) between each growth step, equilibration is now performed with increasing the relaxation time depending on the actual chain size; (3) the RLP algorithm is now fully parallelized and proposed as a “fix” within the “Lammps” molecular dynamics simulation suite

Coarse-Grained Lattice Modeling and Monte Carlo Simulations of Stress Relaxation in Strain-Induced Crystallization of Rubbers

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European aerosol phenomenology - 8 : Harmonised source apportionment of organic aerosol using 22 Year-long ACSM/AMS datasets

Organic aerosol (OA) is a key component of total submicron particulate matter (PM1), and comprehensive knowledge of OA sources across Europe is crucial to mitigate PM1 levels. Europe has a well-established air quality research infrastructure from which yearlong datasets using 21 aerosol chemical speciation monitors (ACSMs) and 1 aerosol mass spectrometer (AMS) were gathered during 2013-2019. It includes 9 non-urban and 13 urban sites. This study developed a state-of-the-art source apportionment protocol to analyse long-term OA mass spectrum data by applying the most advanced source apportionment strategies (i.e., rolling PMF, ME-2, and bootstrap). This harmonised protocol was followed strictly for all 22 datasets, making the source apportionment results more comparable. In addition, it enables quantification of the most common OA components such as hydrocarbon-like OA (HOA), biomass burning OA (BBOA), cooking-like OA (COA), more oxidised-oxygenated OA (MO-OOA), and less oxidised-oxygenated OA (LO-OOA). Other components such as coal combustion OA (CCOA), solid fuel OA (SFOA: mainly mixture of coal and peat combustion), cigarette smoke OA (CSOA), sea salt (mostly inorganic but part of the OA mass spectrum), coffee OA, and ship industry OA could also be separated at a few specific sites. Oxygenated OA (OOA) components make up most of the submicron OA mass (average = 71.1%, range from 43.7 to 100%). Solid fuel combustion-related OA components (i.e., BBOA, CCOA, and SFOA) are still considerable with in total 16.0% yearly contribution to the OA, yet mainly during winter months (21.4%). Overall, this comprehensive protocol works effectively across all sites governed by different sources and generates robust and consistent source apportionment results. Our work presents a comprehensive overview of OA sources in Europe with a unique combination of high time resolution (30-240 min) and long-term data coverage (9-36 months), providing essential information to improve/validate air quality, health impact, and climate models.Peer reviewe