a b s t r a c t
Thin (60 l m) and thick (250 l m) samples of poly(ether ether ketone) were subjected to radiochemicalageing at 24 kGy h 1 dose rate for doses up to 30.7 MGy at 60 °C in air. FTIR spectrophotometry (hydroxyl and carbonyl build-up), ATR microscopy (oxidation proﬁles), ammonia gaseous treatment (determination of carbonyl nature), density, DSC (glass tran- sition temperature, cold crystallization and melting point changes), and gel content mea- surements (crosslinking) were conducted for examination of polymer degradation. Thin samples were shown to undergo principally chain scission process whereas thick ones undergo mainly crosslinking. This difference can be attributed to the kinetic control of oxi- dation by oxygen diffusion. A mechanistic scheme was proposed from radiochemical yields estimations.
Received 31 January 2005; accepted 11 April 2005 Available online 12 July 2005
The preceding papers of this series were devoted to the identiﬁcation and quantiﬁcation of the main chemical changes resulting from the radiochemicalageing of EPDM (77.9% ethylene, 21.4% propylene, 0.7% diene) and EPR (76.6% ethylene, 23.4% propylene) ﬁlms irradiated under oxygen atmosphere using 60 Co g-rays. It was shown that two processes are involved in the EPDM radio-oxidation. The random g-radiolysis of the polymer provides a constant source of macro-alkyl radicals that are likely to initiate a selective oxidation of the polymer through free-radicals reactions involving the abstraction of labile hydrogen atoms. In the present paper, infrared spectroscopy has been used to study the g-degradation of EPDM cross-linked with dicumyl peroxide and/or stabilised with two types of anti-oxidants (hindered phenol or amine-type). The results show that the anti-oxidants are not eﬃcient in preventing oxidation. To understand the lack of eﬃciency of the stabilisers, the impacts of the various formulations on the rate of degradation of EPDM against chain oxidation involved in thermal and UV ageing were also studied.
The previous model contains 40 kinetic parameters: 29 rate constants plus 11 yields. It is impossible to determine all these parameters in one single inverse approach. However, one can envisage determining them progressively from experimental results obtained, ﬁrst, in case of relatively simple radiochemicalageing, for instance PE and PP homopolymers radiolysis, then in case of more and more complex ones, such as PE and PP radiooxidation, ﬁrst in when oxygen excess, then oxygen is not in excess. Groups of kinetic parameters, which could be determined according to this method, are reported in Table 1 .
the beginning and is certainly due to chain scission whereas a moderate T g decrease is
observed for irradiation under vacuum. As proposed by Sasuga (Sasuga, 1988), polymer radio- degraded under anaerobic conditions would undergo mainly crosslinking meanwhile they would undergo chain scissions when they are degraded under aerobic (oxidative) conditions. The effect of atmosphere nature and the effect of thickness have the same origin linked to oxygen diffusion: thick samples present a diffusion limited oxidation (DLO), i.e. that their surface undergoes an oxidative degradation leading to chain scission meanwhile bulk undergoes an anaerobic radio-ageing generating radicals reacting only by coupling.
Keywords: bisphenol A polysulfone; radiochemicalageing; crosslinking; chain scissions; glass transition
Bisphenol A polysulfone (PSU) is widely used in nuclear plant engi- neering due to its interesting electrical insulation and mechanical performances at relatively high temperatures. Moreover, a rela- tively high resistance to ionizing radiations is expected owing to its aromatic character. PSU undergoes both chain scissions and crosslinking. The competition between these two phenomena de- pends on dose rate and temperature. 1 – 4 This paper is dedicated to
where q ( τ r i ) ( t ) is a second-order tensorial internal variable relative to phase ( r ) and collocation time τ i . Hence, a set of
N ∗ N p internal variables is deﬁned. This rewriting of the viscoelastic homogenization problem making use of Dirichlet series approximation does not provide a new framework for non-ageing behaviours. However, we can take advantage of this equivalence between the hereditary approach and an internal variables formulation to build an approximate incremental model for ageing viscoelastic materials.
underlying process of localization can be well understood with fig. 11: at the beginning of plastic strain, a shear band forms in the pellet, but its position can be influenced by the local state of the material (non aged zones are softer) and therefore be closer to one of the ends of the pellet. The band then tends to move towards the center of the pellet, but the shape of the pellet at 0.6% total axial strain is still asymmetric. This proves that there is a deterministic chaos effect: small variations of local state may lead to great variations of the final shape of the sample. As a general result, we have shown that asymmetrical deformation results from the heterogeneity of ageing in the UO 2 pellet. This heterogeneity is a necessary condition but not a sufficient condition, as the deformation can be symmetrical even for an aged and heterogeneous pellet.
More wetting causes further discharge, more carbonization, and finally, failure. The intensity of this effect of moisture is so dependent upon the surface condition that it is often separated from the aging mechanism and considered simply as a mode of failure .
Besides, moisture can contribute to a dominant mode of degradation that is very different from hydrolytic attack. When the environment includes rain, fog or any other form of condensate moisture, as well as voltage, a special type of deterioration occurs. It is the same process as in the failure mechanism, but now it determines the life and not simply the end of life, and the details are more important to understand. Leakage current flows across the surface and the heat generated causes a drying of the moisture film. A circumferential ‘dry-band’ forms, which partly interrupts the charge flow. Most of the applied voltage is supported by this dry-band, and arcs jump across it. These arcs are a type of discharge variously called ‘arclets’ or ‘scintillation’. They are fed by the current through the moisture film, so that they are hotter than partial discharge would be. They impinge on the insulation surface, causing an ambient of fast moving, transient high temperature spots, each lasting a few ms. While they last, the atmosphere in the area of the arcs is an ionized plasma with a temperature of thousands of degrees. The surface of the insulation will react chemically with the constituents of the plasma, and degrade with the heat, causing a spot of carbon or other conductive residue to form on the material surface. This localized degradation may become an attachment point for the arc terminus (the cathode spot) so that the rate of degradation becomes self-accelerating. The degradation zone extends itself from one electrode to the other, and the former insulator ceases to be an insulator. This is one possible way to view ‘surface tracking’. Essential features that must be maintained during the life of outdoor insulation are surface hydrophobicity in respect to water effects, and resistance to sunlight as a general requirement. Other Issues A number of other electrical properties can be important for insulations and dielectrics, de- pending on the application. Among them, bulk dielectric properties, encompassing conductivity, permittivity and dielectric losses are fundamental parameters for such materials. Changes that can be observed here are induced more by environmental parameters such as humidity and water uptake, UV exposure, thermal stresses than by pure electrical ageing.
Accelerating ferroic ageing dynamics upon cooling
Junyan Zhang 1,2,6 , Yunwei Mao 1,2,7 , Dong Wang 1,2 , Ju Li 1,2,3,4 and Yunzhi Wang 1,2,5
Once a structural glass is formed, its relaxation time will increase exponentially with decreasing temperature. Thus, the glass has little chance of transforming into a crystal upon further cooling to zero Kelvin. However, a spontaneous transition upon cooling from amorphous to long-range ordered ferroic states has been observed experimentally in ferroelastic, ferroelectric and ferromagnetic materials. The origin for this obvious discrepancy is discussed here conceptually. We present a combined
PREDICTION OF THE FORMATION OF SEGMENTED FLOW IN MICROSYSTEMS FOR RADIOCHEMICAL LIQUID-LIQUID EXTRACTION
One of the most important separation techniques in radiochemical procedures is solvent extraction. It involves concentrated acids and corrosive solvents that require microsystems built with robust materials. In the last decade, a growing interest in its use in microsystems has emerged because such systems allow a good control of both the interface area between aqueous and organic phases, and the contact time of the two phases. After a study of parallel flow , our goal is to understand and compare the formation of segmented flow for T, flow focusing, and co-flow junctions, and to predict the optimal design in order to enhance solvent extraction.
thermoset networks containing ester groups. Water-polymer interaction mechanisms were extensively covered in comparable cases such as PMMA where hydrolysis of acrylate groups [ 19e21 ] was observed, together with a Fick mechanism for water diffusion a [ 22 , 23 ] and the existence of clustering [ 24 ]. The case of water ageing of UDMA used as matrices for HT-HP composite remains for us unclear and needs hence to be explored. Moreover, the effect of varying the conversion degree with external polymerization pres- sure on water ageing was also scarcely addressed for such networks.
It is well known, for over half a century, that organic matrix composites (OMCs) can fail by ‘‘humid ageing’’, i.e. irreversible interaction with water in (atmo- spheric) vapor or liquid state. Two particular cases resulted in a considerable amount of research: (1) the case of high performance epoxy-carbon composites in military airplanes used in wet tropical environments, especially in Vietnam in the 1960–1975 period [ 1 ]; (2) the case of polyester-glass fiber boat hulls in the 1970s–1980s when pleasure sailing developed extensively. In principle, ageing problems in OMCs can involve one or several of the three components: the fibers, the matrix or the interface. It was immediately shown that, in both cases, fibers are impermeable to water and stable in the natural environments under consideration. Interfacial failure can occur but here, the weakest component is, no doubt, the matrix. It was also rapidly recognized that both cases correspond to two distinct modes of polymer-water interaction. Amine crosslinked epoxies do not react chemically with water, they fail by loss of mechanical processes linked to the water penetration and its swelling effect on the matrix. Polyesters react with water, the hydrolysis of ester groups cuts the network strands, that leads to polymer embrittlement, but the main consequence of hydrolysis is to generate small organic molecules eventually responsible for osmotic cracking (the blistering process, well known to boat users).
easily related to fabrication process or chemical composition, this theory can not explain either the case when yield drop is not observed.
As a result, the observed phenomena should be explained by an interaction between dislocation and some defects. As the strain softening behavior is related to a waiting time during which no deformation occurs and dislocations hence do not glide ([Lefebvre, 1976]), the point defects must be mobile. This excludes some barriers, such as dislocation forest, Lomer-Cottrell locks, or precipitates. However, the precise nature of the main migrating defects in UO 2 is not known. It could be vacancies, solute atoms or any other possible defect. For all these reasons, we used a simplified dynamic strain ageing theory based on [McCormick, 1988, Kubin and Estrin, 1990, Estrin and Kubin, 1991]. The main hypothesis is that some defects are attracted by dislocations (this process will be simply called ageing throughout this paper). Therefore, dislocations are slowed down by these defects. We will show in the next section, that the proposed model can explain the phenomena previously described, including strain softening, effects of temperature and strain rate, temperature sensitivity of the yield stress and strain rate sensitivity. Contrary to other dynamic strain ageing models, it can not although reproduce the Portevin - Le Chatelier effect.
providers and public health decision-makers need to understand more fully the value of vaccination and
to consider it as an important preventive tool in the promotion of successful ageing.
ß 2016 Elsevier Masson SAS and European Union Geriatric Medicine Society. All rights reserved.
Abbreviations: BADL, basic activities of daily living; IADL, instrumental activities of daily living; CMV, cytomegalovirus; HZ, herpes zoster; VZV, varicella zoster virus; PHN, post-herpetic neuralgia; ZBPI, Zoster Brief Pain Inventory; PCV, pneumococcal conjugate vaccine; HCPs, healthcare professionals.
The bleach-membrane chemical interaction shows a degradation of the polysulfone, in spite its well-known chemical stability. The degradation, which generates an embrittlement of the fibre, occurs by chains scission (determined by Size Exclusion Chromatography) with the hydroxyl radical OH formed in the bleach • solution. These chain scissions take place on the isopropylidene and sulfone groups to form final vinylidene and sulfonate groups respectively. Analytic investigations (IR and proton NMR) show that the degradation of additives happens separately without interfering on the ageing of the PSU but alters the behaviour of the fibre. The lifetime of the fibre depends on the total chlorine concentration of the ageing solution but also on its pH which drives the formation of hypochlorous acid and hypochlorite ion in great proportion, essential condition for the formation of hydroxyl radicals.
[2 , 13 , 20] . The identi ﬁcation of such oxidatively modiﬁed proteins (i.e. the oxi-proteome components), can give some insights into the mechanisms by which these damaged proteins accumulate and potentially affect cellular and/or tissular function during ageing or in disease conditions  . In this paper, the occurrence and characterization of carbonylated proteins was studied in hu- man rectus abdominis muscle obtained from young and old healthy donors. Although no signi ﬁcant differences in global protein car- bonylation was observed at the proteome level, we have used 2D gel electrophoresis based proteomic approaches to improve the resolution of individual proteins for the quantitative analysis of their carbonylation status and further identi ﬁcation of these major skeletal muscle proteins that are targeted by oxidative damage during human rectus abdominis skeletal muscle ageing.