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Beryllium will be one of the plasma-facing materials for ITER. It will have to sustain high fluxes of hydrogen isotopes and as a consequence significant amounts of tritium can be retained in the wall. For safety and operational reasons, the deuterium and tritium inventory in the vacuum vessel must be limited. As a consequence, hydrogen diffusion, trapping and solubility are of vital importance in assessing and modeling the plasma fuel retention into the wall. In order to understand these issues, point defects and the behavior of hydrogen in beryllium are investigated based on Density Functional Theory calculations. Although some data have already been acquired in the past, some of them disagree, which motivates further investigations. To do so, the formation energy and diffusion properties of point defects are investigated in the first part of this paper. In a second part, the solubility and diffusivity of hydrogen in beryllium are calculated. A diffusion coefficient is established in order to be used in Rate-Equation and Kinetic Monte-Carlo Kinetic models and to allow for comparison with experimental measurements. [ABSTRACT FROM AUTHOR]

Lignin was used as flame retardant for polybutylene succinate (PBS) biopolyester. Lignin was first demonstrated to weakly contribute to material flammability due to a high charring ability and a low heat release when burning. Alkali lignin was proved to be more interesting than organosolv lignin due to the release of sulfur dioxide during decomposition. When incorporated at a 20%wt loading in PBS, alkali lignin significantly reduces pHRR and promotes a thick charring behavior. Alkali lignin was successfully surface modified by grafting molecular or macromolecular phosphorous compounds. When blended with PBS, modified lignin was highlighted to further increase the barrier effect. Char promotion is accelerated and the resulting charred layer exhibits a higher cohesivity. Modified lignin appears as an interesting biobased flame retardant component. [ABSTRACT FROM AUTHOR]

Abstract: The aim of this study is to better understand the performance of binary blends of biodegradable polyesters when exposed to hygrothermal ageing, in order to overcome some of their limitations such as water resistance. For this, blends have been prepared by extrusion using two P(L)LA (l-poly-(lactic acid)) of different molecular weights and PɛCL (poly-ɛ-caprolactone). Mechanical properties over ageing are reported and compared to pure P(L)LA. Blending PɛCL to P(L)LA allowed to improve P(L)LA initial resilience. During ageing, crystallinity increase seemed to lower water uptake at short ageing times, while osmotic cracking was found to possibly occur in pure P(L)LA for long ageing times, thus increasing water uptake. Besides, P(L)LA/PɛCL blends water uptake remained constant over ageing. Finally, while P(L)LA resilience decrease could be related to chain scission, blend aptitude to elongation decrease was related to interphase decohesion, at long ageing times. Results showed P(L)LA molecular weight influence on both initial mechanical properties and water uptake. [Copyright &y& Elsevier]

Abstract: This paper describes a study, made in France, of the effect of warm pre-stressing (WPS) in the presence of semi-elliptical defects. Main objective was to confirm the validity of our approach which combines testing and modelling for analysing a more complex geometrical configuration than one with a simple crack under WPS conditions. This involved ad hoc tests on compact tension (CT) specimens of 18MND5 steel (equivalent to ASTM A533B plate) with semi-elliptical cracks: [•] The tests were conducted under isothermal and warm pre-stress conditions in order to quantify discrepancies associated with the shape of the defect and the type of thermal transient. [•] Different types of thermal transients were studied to assess any impact on the positive effect of warm pre-stressing. This involved also 3D modelling of tests in order to be able to apply either global approach with the use of the master curve and the Wallin method or local approach criteria with the modified Beremin model. It was confirmed the warm pre-stressing had an effect, even in the case of tests conducted at low levels of pre-stressing. The supporting numerical interpretations made demonstrated the ability of the simplified global approach (Wallin method) and the local approach (modified Beremin model) to predict the positive effects of warm pre-stressing. [Copyright &y& Elsevier]

Abstract: A study of the properties of short glass fibre reinforced thermoplastic composites based on poly(ethylene terephthalate), poly(butylene terephthalate) and polyamide-6,6 in an aggressive environment is reported. The influence of the fibre/matrix interface on the composite behaviour in a moist environment is especially studied. Competitive phenomena may explain differences observed according to the nature of the fibre surface treatment. Among them these characteristics may be an intrinsic fragility of some chemical interfacial bonds, the hydrophilicity of some chemical groups, the presence of long macromolecular chains neighbouring the interface or of a transcrystalline interfacial area. [Copyright &y& Elsevier]

Abstract: To study the effects of warm pre-stressing on the toughness of reactor pressure vessel steel, the “Commissariat à l’Energie Atomique”, in collaboration with “Electricité De France” and AREVA-NP, has made a study combining modeling and a series of experiments on large specimens submitted to a thermal shock or isothermal cooling. The tests were made on 18MND5 ferritic steel bars, containing a short or large fatigue pre-crack. The effect of “warm pre-stressing” was confirmed, in the two cases of a fast thermal shock creating a gradient across the thickness of the bar and for gradual uniform cooling. In both cases, no propagation was observed during the thermal transient. Fracture occurred under low temperature conditions, at the end of the test when the tensile load was increased. The failure loads then recorded were substantially higher than during pre-stressing. To illustrate the benefit of the WPS effect, numerical interpretations were performed using either global approach or local approach criteria. WPS effect and capability of models to predict it were then clearly shown. [Copyright &y& Elsevier]

Abstract: Silica particles of different physical properties (particle size, morphology and specific surface area) were introduced into an ethylene–vinyl acetate copolymer filled with an intumescent mineral fire retardant system containing magnesium hydroxide and organo-modified montmorillonites. The effect of silica particles on the cohesion and strength of the foamed combustion residue was studied by micro-indentation, concurrently with the characterization of material''s fire behavior. Silica particles seem to act as defects that generate cracks, decreasing the strength of the residue. This generation of cracks is connected to a lower cohesion of the residue, especially for silica particles of high specific surface area. In parallel, the presence of silica of high specific surface area, despite tending to decrease Time To Ignition, also improves self-extinguishing ability, thanks to a better thermal stability at higher temperatures, and reduces the maximum Heat Release Rate in cone calorimeter tests. [Copyright &y& Elsevier]

The mechanical properties and fire resistance of a recycled poly(ethylene terephthalate) were improved by using a specific treatment of the waste material and the incorporation of encapsulated red phosphorus in combination with co-additives. The use of red phosphorus has to be limited due to a negative influence on impact resistance and rate of heat release. Among several metal oxides, Al2O3 acts as a good co-synergist at a total loading of 5 wt.% due to its reactivity, high specific surface area and aluminium phosphate formation. The complementary use of glass fibres can also generate intumescence by improving the mechanical stability of the char layer. [Copyright &y& Elsevier]

A new silicophosphorylated filler was generated in situ in a molten PA66 copolymer during extrusion process with the aim to improve the fire behavior of the matrix. The filler was obtained in one step via hydrolysis–condensation reactions of SiDOPO precursor (DOPO, 9,10-dihydro-9-oxa-10-phosphaphenanthrene). The synthesis of the precursor is reported and characterized by NMR. A 29 Si NMR study of SiDOPO hydrolysis–condensation reactions in N-methylacetamide (NMA) solvent was also conducted. Thermal stability of Cop-PA/SiDOPO composite and the major degradation products were studied by thermogravimetric analysis coupled with Infrared spectrometry (TGA/FTIR). The Pyrolysis Combustion Flow Calorimeter (PCFC) and cone calorimeter were used to investigate the fire behavior of the composite. Results show that the nanocomposite exhibits a little earlier ignition but with a decrease around 33% of the peak of heat release rate (PHRR). The presence at low concentration of silicon (0.65 wt.%) and phosphorus (0.75 wt.%) promotes the formation of an expanded char layer that acts as a barrier. A reduction of about 18% in effective heat of combustion (EHC) values suggests an additional flame inhibition effect of phosphorus in the gas phase. [ABSTRACT FROM AUTHOR]

An organophosphorus silica filler was generated in situ the molten PA66 copolymer (Cop-PA) during extrusion process without adding solvents. Nanocomposites synthesis is based on hydrolysis–condensation reactions of diethylphosphatoethyltriethoxysilane precursor (SiP). The thermal stability of Cop-PA/SiP nanocomposites and the major degradation products were studied by thermogravimetric analysis (TGA) and TGA coupled with Infrared spectrometry (TGA/FTIR). The Pyrolysis Combustion Flow Calorimeter (PCFC) and cone calorimeter were used to investigate the fire behaviour of the nanocomposites. Results showed a decrease by more than 50% of the peak of heat release rate (PHRR) and the formation of an expanded char layer with the addition of only 0.91wt% of silicon and 0.96wt% of phosphorus by this original route of fillers dispersion. [ABSTRACT FROM AUTHOR]

Abstract: Transparent polycarbonate nanocomposites with improved fire behavior were prepared by incorporation of polyhedral oligomeric silsesquioxane (POSS) and resorcinol bis (diphenyl phosphate) (RDP) via melt blending. Flame retardancy performance was characterized using thermogravimetric analysis, pyrolysis combustion flow calorimeter and cone calorimeter. Simultaneous presence of RDP and POSS led to the decrease of the degradation rate and the increase of char residue due to the reaction of the additives with the decomposing polymer. This results in a significant reduction of flammability of polycarbonate. In cone calorimeter, the heat release rate as well as the smoke production rate were shown to strongly decrease due to a condensed phase mechanism that favored the formation of a cohesive char layer. Transparency evaluation was performed in both physical and psychophysical spaces. The two approaches give various assessment of transparency. Considering the perceived optical properties, it could be concluded that flame retarded PC is translucent rather than transparent. [Copyright &y& Elsevier]

Abstract: This paper investigates and compares the thermal degradation and fire reaction of different natural fibers and their corresponding biocomposites. Polybutylene succinate (PBS) was used as polymer matrix. Cellulose, hemp, flax, sugar cane and bamboo were used as natural fibers and ammonium polyphosphate (APP) was used as fire retardant agent. The influence of fiber type, fiber content and the addition of APP were investigated using TGA, PCFC and cone calorimetry. The incorporation of fibers in PBS reduces the thermal stability, and the time to ignition (TTI) of biocomposites, but it increases the mass residue corresponding to the formation of a char barrier. These results are ascribed to the components of fibers, and the flammability of the gas released by the lignocellulosic fibers. The fiber content does not influence the TTI, but affects significantly the peak of heat released rate (pHRR). Thus, a minimum content of fibers is required to form a protective barrier during fire test. The addition of APP in the biocomposite leads to hot hydrolysis of PBS and phosphorylation of flax. Hence, the fire retarded biocomposite forms a barrier layer due to the charring of the matrix and the preservation of the fiber skeleton and therefore shows a significant decrease of the pHRR. [Copyright &y& Elsevier]

Abstract: The detection of branched chains in thermally degraded thermoplastic polymers is far from simple, especially at a low conversion ratio, mainly because of the low sensitivity of commonly used laboratory analytical techniques. The objective of this article is to present an approach able to demonstrate the formation of such macromolecular structures during thermal degradation of molten PET at low oxygen partial pressures (typically for pressures lower than 9% of atmospheric pressure). Such ageing conditions are met during PET mechanical recycling by extrusion, and can be simply reproduced by sequential nitrogen/air tests in a rheometer cavity. The approach consists of a careful analysis of the complex shear modulus changes in a Cole–Cole diagram. Values obtained for Cole–Cole model parameter K′ indicate clearly an accumulation of branched chains in the melt with the time of residence in the reactor. [Copyright &y& Elsevier]

Abstract: Hygrothermal ageing has been investigated on glass fibre reinforced polyethylene terephthalate (PET) composites using complementary techniques and a multiscale approach in order to identify the different steps of the material''s degradation. For early ageing times (t <6h), DMTA tests give evidence of the plasticisation of the PET matrix. GPC measurements and acid end group titration show that the chemical degradation step of the composites occurs immediately and that the main degradation mechanism is random chain scission. The changes in morphology resulting from hydrolysis, investigated through DSC and SAXS experiments, reveal a decrease in the long period that may result from the diffusion of oligomers out of the spherulites. The water uptake for long ageing times is attributed to an interfacial debonding which induces an osmotic pressure in this area. Photomechanical measurements highlight the development of microcracks within the aged material that induced an increase in the variation of material volume. [Copyright &y& Elsevier]

• As the Kyowaglas burns, metallic lead (Pb) forms and accumulates at the top surface slowing down the heat transfer. • By the end of the combustion process, metallic lead undergoes an oxidation to form lead oxide (PbO) on the surface of the residue. • Leaded-compounds seems to slightly accelerate the decomposition of PMMA. • Leaded-compounds confers a significant thermal stability to PMMA. In the present work, the flammability of Kyowaglas is characterized experimentally. Kyowaglas is a lead-based composite used in glove boxes of nuclear facilities as a biological protection against radiation. It consists of 70% wt PMMA (Poly(Methyl Methacrylate)) and 30% wt leaded compounds. The aim of the study is to understand the role and impact of lead during the combustion of Kyowaglas in order to deepen knowledge of its thermal and fire behavior. A comparative study between Kyowaglas and virgin PMMA is conducted to better understand the effect of lead on the combustion process of these materials. Fire behavior is studied using cone calorimeter, pyrolysis-combustion flow calorimeter and thermogravimetric analysis. At different stages of cone calorimeter test, the samples and residues were examined and characterized using different experimental techniques like microscopy, spectroscopy, X-ray diffraction and calorimetry. Thermal analysis data show that lead seems to slightly accelerate the decomposition of PMMA under inert atmosphere. However, it confers significant thermal stability during a cone test due to the accumulation of lead on the surface of the sample. As the Kyowaglas burns, metallic lead is formed and accumulated at the top surface slowing down the heat transfer. At the end of the cone calorimeter test, lead oxide beads start to form on the surface of the residue due to the oxidation of metallic lead. [ABSTRACT FROM AUTHOR]

Abstract: An Environmental Stress Cracking test was used to investigate damage to glass fiber reinforced poly(lactic acid) based biocomposites. The study was performed in water. The main advantages were a significant decrease in experiment duration compared to natural, artificial or accelerated tests and an increase in the reliability of the results. Depending on the specific nature of the glass fiber used, significant types of failure behavior were observed. [Copyright &y& Elsevier]