Water clustering in polychloroprene

Water sorption has been studied gravimetrically for polychloroprene rubber samples, first at a fixed hygrometric ratio (98% HR) and several temperatures (25, 40, 60 and 80 °C) for samples of 1.8 and 3.8 mm thickness (Constant Temperature and Hygrometry, CTH experiments), then at fixed temperature (40 °C) and several hygrometric ratios ranging from 0 to 95% HR on samples of 0.1 mm thickness (DVS experiments). CTH experiments reveal an abnormal sorption behavior: after an apparently fickian transient period, the water absorption continues at almost constant rate, no equilibrium is observed after more than 2500 h, whatever the temperature. DVS experiments reveal a very low Henry's solubility but the formation of clusters at water activities higher than 40%. The water diffusivity is almost independent of activity below 50% HR and decreases rapidly when activity increases above 50%. Contrary to CTH experiments, equilibrium is reached in DVS and the difference is not simply linked to the well-known effect of sample thickness on diffusion rate. The results allow hypotheses such as hydrolysis or osmotic cracking to explain the abnormal sorption phenomenon to be rejected. It is suggested that clusters could be polymer-water complexes having a linear/branched structure able to grow without phase separation that could explain the reversibility of sorption-desorption cycles. The difference of behavior between thin 0.1 mm and thicker 1.8 or 3.8 mm samples could be due to an effect of swelling stresses

Oxidation of unvulcanized, unstabilized polychloroprene: A kinetic study

Thermal oxidation in air at atmospheric pressure, in the 80-140 °C temperature range and in oxygen at 100 °C in the 0.02-3 MPa pressure range, of unvulcanized, unstabilized, unfilled polychloroprene (CR) has been characterized using FTIR and chlorine concentration measurement. The kinetic analysis was focused on double bond consumption. A mechanistic scheme involving unimolecular and bimolecular hydroperoxide decomposition, oxygen addition to alkyl radicals, hydrogen abstraction on allylic methylenes, alkyl and peroxyl additions to double bonds and terminations involving alkyl and peroxy radicals was elaborated. The corresponding rate constants were partly extracted from the literature and partly determined from experimental data using the kinetic model derived from the mechanistic scheme in an inverse approach. Among the specificities of polychloroprene, the following were revealed: The rate of double bond consumption is a hyperbolic function of oxygen pressure that allows a law previously established for the oxidation of saturated substrates to be generalized. CR oxidation is characterized by the absence of an induction period that reveals the instability of hydroperoxides. The kinetic analysis also reveals that peroxyl addition is faster than hydrogen abstraction but slower in CR than in common hydrocarbon polydienes

Role of strain induced crystallization and oxidative crosslinking in fracture properties of rubbers

Tensile properties and crack propagation properties, especially critical strain energy release rate in mode I, GIC, have been used to investigate fracture properties of elastomers and their relationships with microstructure. These investigations were mainly based on a series of comparisons: first, the behaviour of polychloroprene rubber (CR), undergoing stress hardening due to strain induced crystallization (SIC) and oxidative crosslinking (OCL) was compared with that of chlorinated polyethylene (CPE), which undergoes SIC but not OCL, and with a polyurethane based on hydroxyl terminated polybutadiene (PU) which undergoes OCL but not SIC. Comparisons were also made on CR between fracture behaviour at ambient temperature, where SIC occurs and at 100°C where there is no SIC. Finally, oxidative crosslinking was used to vary in a continuous way the crosslink density in CR and PU, in order to evaluate the role of crosslinking in fracture behaviour. The results reveal the strong contribution of SIC to fracture strength. Crosslinking, even at low conversion, inhibits SIC which explains the sharp decrease of CR toughness in the early period of exposure to oxidation. When SIC has disappeared, it is possible to appreciate the effect of crosslinking on fracture behaviour. This effect, as evaluated from the density of deformation energy at rupture in tension or from GIC value, is almost negligible while the sample modulus increases regularly as a consequence of crosslinking. It appears that the toughness remains almost constant because it is under the influence of two contradictory phenomena: the negative effect of a reduction of ultimate elongation and the positive effect of a modulus increase. Such behaviour can be explained in terms of heterogeneous distribution of the lengths of elastically active chains. After long exposure, the sample behaviour becomes brittle, very high modulus values indicate that the samples approach, presumably in a heterogeneous way, the glassy state

Éditorial

Créée en 1984, la Revue Archéologique de l’Ouest s’apprête à célébrer son 35e anniversaire. L’éditorial ouvrant le tome 23 en 2006 rappelait le contexte de sa naissance, les conditions de sa croissance et les adaptations alors en cours. Avec ce volume, on passait en effet d’une structure associative reposant pour une large part sur le bénévolat à un organe d’édition et de diffusion professionnel. Douze années plus tard, de nouveaux ajustements apparaissent ..

294 Implementation time of a lipid lowering therapy in patients with dyslipidemia: results of Prysme study

Despite the availability of specific guidelines, the management of dyslipidemia in practice is not optimal.Objective and methodologyPRYSME, a non-interventional multicentre study carried out with 1226 general practitioners, aimed to describe the implementation time of a lipid lowering treatment according to cardiovascular risk level (primary objective) and to identify its determinants. Were eligible patients treated for a dyslipidemia diagnosed less than 2 years ago. Demographic and clinical characteristics and circumstances of diagnosis and treatment initiation were collected.Results3268 patients were included (mean age: 57 years old, males: 64%). 26% were obese and 45% overweight. Only 12% had no cardiovascular risk factors (CRF) at the time of dyslipidemia diagnosis. The most frequent CRF were arterial hypertension (50%), smoking (43%), family history of premature coronary heart disease (28%), HDL-c <0.4g/l (20%) whereas 15% of the patients had a personal history of cardiovascular disease. Dietary programs were initially implemented for 98% of the patients. More than 90% were treated with a statin. The implementation time of the treatment (evaluated according to the biological confirmation of dyslipidemia), according to the initial number of CRF, was as following:0 CRF1 CRF2 CRF≥ 3 CRFSecondary preventionTotal[-3;0] months34.3%28.6%27.1%29.3%49.1%33.1%]0;3] months23.1%26.2%26.4%24.0%21.9%23.9%> 3 months42.6%45.3%46.5%46.8%29.0%43.0%Chi-2 test : P<0.001The main determinant of an early implementation of a lipid lowering therapy (≤ 3 months) was secondary prevention (OR=1.8). The number of CRF had no significant impact.ConclusionThis study underlines the lack of awareness towards cardiovascular risk factors in the management of dyslipidemia, particularly while considering the implementation time of a lipid lowering therapy

Analyse géométrique des données : une enquête sur le racisme

In this paper, we present the data analysis processing of a survey about racism. The methodology is that of the analysis of structured data, inspired by specific comparisons in ANOVA, and applied to geometric data (Euclidean clouds). Its realization is done by means of the Language for Interrogating Data (LID) implemented in the EyeLID software.Dans cet article, nous présentons une démarche d'analyse statistique d'un questionnaire appliquée à une enquête sur le racisme. La méthodologie suivie est celle de l'analyse des données structurées, inspirée des comparaisons spécifiques en analyse de variance, et appliquée à des données géométriques (nuage euclidien). La mise en Ïuvre est réalisée grâce au langage d'interrogation de données (LID) implanté dans le logiciel EyeLID

Predictive ageing of elastomers: Oxidation driven modulus changes for polychloroprene

The oxidative ageing in the range of 60 °C–140 °C of sulfur vulcanized polychloroprene has been studied by FTIR spectroscopy (double bond consumption), modulus changes and oxygen absorption measurements. Experiments were carried out on thin films and thick samples to investigate both homogeneous and inhomogeneous (diffusion controlled) oxidation with the goal of establishing the underlying correlation between oxidative degradation chemistry and mechanical property changes. A correlation between oxidatively driven degradation chemistry and modulus is possible using the established approaches of rubber elasticity where an effective crosslinking yield due to double bond reactions is of the order of 30% for this material (i.e. the loss of 3 double bonds results in one effective crosslink associated with material hardening). It is then possible to predict modulus changes induced by oxidation for vulcanized and unstabilized polychloroprene rubber. A kinetic model is introduced with two propagation reactions (hydrogen abstraction and radical addition to double bonds) and two stabilization processes involving sulfur containing moieties from the vulcanization process. The kinetic scheme was solved and the relevant rate constants determined. This model can adequately predict modulus changes in films and thick samples as a function of time and spatially resolved

The MAORY first-light adaptive optics module for E-ELT

The MAORY adaptive optics module is part of the first light instrumentation suite for the E-ELT. The MAORY project phase B is going to start soon. This paper contains a system-level overview of the current instrument design

Prise en charge de l aponévrosite plantaire en soins primaires

L aponévrosite plantaire est une maladie prévalente en soins primaires. Après avoir présenté la pathologie, nous avons rapporté les résultats d une étude épidémiologique visant à décrire la population atteinte, étudier les modalités de diagnostic, répertorier les différentes thérapeutiques prescrites en soins primaires et évaluer leur efficacité à moyen terme. Un questionnaire a été transmis à 132 médecins de soins primaires en leur demandant de retourner un exemplaire à chaque patient inclus. Les 67 patients inclus ont été contactés par téléphone au minimum 3 mois après leur inclusion pour connaître l évolution de leur pathologie. Les patients qui consultaient pour une aponévrosite plantaire en soins primaires étaient non sportifs dans 69% des cas, de sexe féminin dans 57% des cas et de moyenne d âge 47 ans. Les médecins consultés ont fait le diagnostic cliniquement dans 70% des cas. Les orthèses plantaires ont été le plus souvent prescrites en première intention (84% des patients consultant pour la première fois). Elles ont été efficaces dans un tiers des cas mais un patient sur deux abandonnait le traitement à court ou moyen terme. En seconde intention, un traitement par ondes de choc externes a été prescrit chez 70% des patients qui reconsultaient et s est révélé efficace dans un cas sur deux. Les infiltrations ont été peu pratiquées. Enfin, 58% des patients étaient totalement soulagés après un suivi moyen de 406 jours. Pour comparer l efficacité des traitements les plus prescrits, des essais randomisés sont indispensables mais difficiles à mettre en place à cause du nombre nécessaire de patients à inclurePARIS12-CRETEIL BU Médecine (940282101) / SudocSudocFranceF