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The chemical structure, polymer mobility and mechanical properties are studied for a cross-linked amorphous poly(ether urethane) (PU) from glass transition to rubber elasticity for juvenile dry samples and for water-saturated states after exposure to humid air (r.h. = 29, 67, 95, 100%) at 60 ∘ C during 1 y of ageing. For saturated samples, network chain cleavage is the chemical ageing mechanism, but it is too weak and slow to affect on the physical properties significantly within 1 y. Water acts primarily in a physical manner. Within 1 d, H 2 O molecules replace part of the weak urethane H-bonds by H 2 O –urethane H-bonds and reduce all other physical interactions between network chains by solvating hydrophilic segments. Thus, the cooperative polymer mobility strongly amplifies: The gain of specific conformational entropy doubles across the caloric glass transition, which shifts by −17 K. A H 2 O concentration of only c H 2 O ≈ (0.4 ... 0.5) c H 2 O , max suffices for the major part of these fast rearrangements. Some part of the water slowly forms (during 3–4 months) a finely dispersed water-rich mixed phase with the PU chains. Except the new phase, these molecular processes of physical ageing strongly affect the mechanical properties at damage-free deformation. For dry PU in the glass transition, the shear modulus, μ relaxed (T), after viscoelastic stress relaxation only depends on the deformation-induced entropy change—like in the rubber elastic state. Within one month, water drastically decreases the viscoelastic response, as expected for plasticisation. However, μ relaxed (T) slightly grows in wet PU. H 2 O molecules cause these opposite trends by boosting the cooperative mobility (i.e. extension of the accessible conformational space and entropy by reduction in energy barriers) and by occupation of free volume compartments. Water quickly reduces the fracture parameters by about 50%. We explain that embrittlement by the H 2 O -induced facilitation of cooperative network chain motions, which let fracture proceed with less energy. In summary, our findings provide a detailed conception of the molecular effects the H 2 O molecules have on the PU network, and they explain the consequences for the mechanical properties. [ABSTRACT FROM AUTHOR]

Rubber components produced from nitrile butadiene rubber (NBR) are changing their material properties due to environmental influences. This is caused by irreversible changes occurring in the elastomer network which is known as chemical ageing. In this paper, ageing behaviour of NBR is investigated and modelled under the influence of different surrounding media as air and oil. Based on the previous works, in which chemical ageing was also modelled, a continuum mechanical approach is introduced here, whereby the rubber viscoelasticity is taken into account. Simulations using FEM are then carried out under different chemical and mechanical boundary conditions, and the proposed modelling approach is validated by means of tension set measurements. [ABSTRACT FROM AUTHOR]

Elastomers are used in almost all areas of industrial applications, such as tires, engine mounts, bridge bearings, seals or coatings. During their use in operation, they are exposed to different environmental influences. These include, in particular, climatic factors such as air oxygen, high temperatures, light (UV radiation) and the influence of media (e.g. oils, fuels). A very important result of these factors is the chemical ageing of elastomers. In this case, the elastomer degenerates and changes its chemical structure in the aged regions, which leads to an irreversible change in the material properties in connection with the reduction in its usability. In this paper, chemical ageing of nitrile butadiene rubber (NBR) is investigated. Especially in case of thermo-oxidative ageing at elevated operating temperatures, the ageing processes run inhomogeneously. These effects are known as diffusion-limited oxidation (DLO) and are associated with the diffusion–reaction behaviour of atmospheric oxygen with the elastomer network. For these reasons, NBR samples are artificially aged in air and subjected to different experimental methods, which are presented and discussed. Additional results from inhomogeneous mechanical tests and permeation tests indicate the causes of the DLO-effect, show the influence of chemical ageing and are subsequently used for parameter identification in relation to the diffusion–reaction equation. A continuum-mechanical modelling approach is also presented here, which describes the finite hyperelasticity, diffusion–reaction processes as well as chemical degradation and reformation of the elastomer network. This multifield problem leads to a system of partial and ordinary differential equations and constitutive equations and is solved within the finite element method. [ABSTRACT FROM AUTHOR]

Due to the rapid increase in their efficiencies, third generation photovoltaics rose to prominence in recent years, and became serious competitors to conventional silicon based and thin film solar cells. This work investigates various techniques to grow and/or deposit copper oxide (CuO) on a copper substrate for utilization as a counter electrode in dye sensitized solar cell (DSSC) applications. Copper has many attractive thermal, electrical and mechanical properties and is widely used in solar thermal applications, but its use is limited in solar photovoltaic cells. The experimental results reported herein have proven the success of growing an intrinsic copper oxide layer on a pure copper substrate. Among the methods, the chemical ageing process followed by heat treatment has resulted in a homogenous and adherent oxide layer that attenuated the electronic conductivity and chemical reactivity of pure, bare copper electrodes. These electrodes are incorporated into solar cells that are constructed and tested against a platinum reference cell. The cells showed comparable short circuit current to their platinum counterparts, with efficiencies of 0.2% compared with 0.5% for platinum under the same conditions. The copper counter electrode with the CuO deposition exhibited good promise, especially when comparing figures of merit (power generated/price) as a cheap and effective alternative to platinum in third generation solar cell applications. • This work presents various synthesis techniques of copper oxide on copper electrodes. • The electrodes are intended for dye-sensitized solar cell applications to replace platinum. • The novelty is the limited number of available investigations on copper oxide in third generation solar cells. • The figure of merit (FOM) for the electrodes is better in terms of power/price of the electrodes. [ABSTRACT FROM AUTHOR]

Due to their vibration isolation performance, elastomers are often used in industrial applications such as bearings or seals. In service, parts made of rubber are often exposed to high temperatures while undergoing dynamic mechanical loads. On the one hand, this may reduce the fatigue properties in an irreversible manner due to thermo-oxidative network degradation and reformation, which is known as chemical ageing. In a durability test at constant temperature, a rubber specimen that was already aged at elevated temperatures exhibits a different fatigue behaviour than an unaged specimen of the same material. Since this behaviour is determined by the temperature history prior to the durability test, it is an indirect effect. If, on the other hand, durability tests of unaged specimens are carried out under different elevated temperatures, the temperature also has an instantaneous effect on the material’s lifetime. This direct effect vanishes if the temperature is reduced to a certain level. This work deals with both the indirect (chemical ageing) and the direct effects of elevated temperatures on the fatigue life of a natural rubber (NR) under mechanical loads. Therefore, fatigue tests were performed to investigate the various effects of elevated temperatures on the fatigue life. A new model is proposed that takes into account these effects. This model may therefore help establish more realistic test procedures for component development and provide relevant information for improved fatigue life prediction concepts. [ABSTRACT FROM AUTHOR]

• PECH-based polyelectrolytes of different architectures were synthesized. • PECH undergoes chain scissions and dehydrochlorination reactions in alkaline medium. • Degradation reactions are favored by a high concentration of KOH electrolyte. • PECH crosslinking via DABCO limites both KOH uptake and degradation reactions. • A high crosslinked membrane is stable even it contains a high cationic sites amount. The chemical stability of anion exchange membranes (AEM) is crucial for the durability of the electrochemical devicesusing them. In this context, poly(epichlorohydrin)-based AEM were subjected to chemical degradation in the presence of a corrosive alkaline medium. Linear and cross-linked polyelectrolytes grafted with ammonium cations based on Quinuclidine and/or DABCO were first synthesized. They were characterized by an IEC comprising between 1.3 and 3.1 mmol/g, an ionic conductivity above 2 mS/cm and transport numbers between 0.71 and 0.89. Their chemical stability was then evaluated after immersion in 1 M to 8 M KOH solutions for 672 h at 50 °C. The evolutions of these characteristics as well as the molecular structure of the materials during this period inform on the chemical resistance of the polymer backbone as well as that of the cationic sites. The main degradation reactions have been identified as chains scission and Hofmann elimination, leading to the loss of the cationic groups. Nevertheless, these reactions can be limited by a high crosslinking density of the membrane, enhancing then its chemical stability despite a high ammonium group content. [ABSTRACT FROM AUTHOR]

This paper presents a study on the impact of sodium hypochlorite (NaClO) on the performance and fouling behavior of polysulfone (PSF) membranes. The performance of aged PSF membranes was studied under different transmembrane pressures (TMPs), and three critical TMPs including the pressure corresponding to critical flux (P C ), the pressure corresponding to critical filtration efficiency (P V ), and the pressure corresponding to the greatest retention ability (P R ) were innovatively proposed. In terms of an aged membrane, the filtration efficiency (η v ) and retention ability (R) were decreased, while, the enhanced sieving capacity (η s ) were experimentally proved. These are strongly related to modified surface properties and enlarged pore diameters of aged PSF membranes. The fitting results of Hermia’s model and critical flux analysis mutually verified that the formation of cake layer fouling on an aged PSF membrane surface was delayed. However, the specific fouling results indicated the aged membrane suffered a more severe pore block fouling. Moreover, the target plot also implied that the critical parameters (P C , P V and P R ) can serve as indicators of the evolution of membrane performance and fouling behaviors. [ABSTRACT FROM AUTHOR]

Chemical ageing of ultrafiltration membranes related to drinking water operation is not a new problem, but literature documenting sieving properties and fouling behaviors of aged membranes are scarce. This paper shows how the surface chemistry evolution of polysulfone (PSF) and polyvinylidene fluoride (PVDF) membranes can lead to the formation of distinct membrane properties when exposed to sodium hypochlorite solutions. The surface physicochemical evolutions of aged membranes are characterized based on chemical composition (ATR-FTIR and XPS), water contact angle analysis, and surface zeta potential test. The results indicate the ageing mechanism and evolutions between PSF and PVDF membranes are totally different. In addition, the retention ability and fouling propensity of the aged membrane are also investigated by three different kinds of foulant (Dextran/HA/BSA). Surface hydrophilization of aged PVDF membrane enhanced its retention toward neutral (Dextran) and hydrophilic charged foulant (BSA), but the fouling type of aged PVDF membranes remained the same, in spite of the initial flux increasing greatly. In terms of PSF membranes, pore enlargement could be verified by a seemingly inconsistent result of dextran sieving experiments and the decreased HA rejection rate. Moreover, the increased negative charge on aged PSF membrane surface have a great impact on its sieving property and fouling propensity, especially for the charged and hydrophilic BSA. With the regression data of Hermia's model, the main fouling type of aged PSF membranes was proven changed to pore blocking, and the changes can ascribe to its altered surface chemical characteristic and pore diameter. [ABSTRACT FROM AUTHOR]

In this study, the effects of accelerated ageing under pre-strain on the maximum elongation of composite solid propellants were investigated. The maximum elongation of aged composite solid propellants at different ageing times, temperatures and pre-strains were determined. An ageing model was developed to analyse the effects of pre-strain and temperature on model parameters. Results show that pre-strain can increase the maximum elongation significantly during accelerated ageing, and the increasing amplitude exhibits a linear relationship with ageing temperature and pre-strain. The physical tension effect caused by pre-strain is a cumulative effect of the stress on samples and shows obvious characteristics of stress relaxation. The relaxation time is independent of pre-strain and exhibits an exponential relationship with ageing temperature. The effect of pre-strain on chemical ageing is related to a critical temperature T C . For the HTPB propellant investigated in this study, the T C is between 65 °C and 70 °C. When the ageing temperature is below T C , pre-strains have almost no effect on the ageing rate constant for maximum elongation k ε ; however, at temperatures above T C , they may promote chain scission reactions and decrease k ε . [ABSTRACT FROM AUTHOR]

Polyether ether ketone (PEEK) composites and AISI 52100 steel are high-performance materials that are often selected for high stress tribological applications under solid and hydrodynamic lubrication. In this study, the viability of these materials as a pair for boundary-lubricated systems was evaluated. Tribo-tests to evaluate different characteristics were conducted: (i) the effect of metallic surface finish (1 µm polished, 9 µm polished, shot peened and ground); (ii) the effect of temperature (room temperature and 90 °C); and (iii) the effect of long-term PEEK exposure to lubricant oil (i.e., chemical ageing). An AMTI tribometer equipped with a hermetic chamber and a heating system was used for reciprocating sliding tests with a 10 mm stroke, 2 Hz frequency and 2 h duration. The tests used a cylinder-on-disc configuration (polymer on metal), a tetrafluoroethane atmosphere and a 100 N normal force. The wear tracks were analysed using a light interferometer, SEM and optical microscope to assess the wear mechanisms, including transfer film formation. The surface skewness and transfer film establishment were the main factors affecting the friction coefficient. In contrast, the wear of the PEEK composites was mainly affected by the surface bearing index and chamber temperature. Moreover, transfer films were observed only on counterbodies that had a surface roughness ( S q ) of at least 0.030 µm. Finally, accelerated ageing of PEEK composites was performed in an autoclave at 180 °C and 3 bar pressure for 7 days in the presence of an ester-based lubricant oil and tetrafluoroethane atmosphere. DSC, DTG and FTIR techniques indicated that the filler/matrix interfaces of the PEEK composites were dissolved by the ester-based lubricant oil. Chemical ageing showed a significant effect on the friction steady state regime. Instead of a stable value, the friction coefficients of the aged composites increased slowly and continuously. [ABSTRACT FROM AUTHOR]

Polymers are highly important in industrial applications such as bearings, seals, bonds and coatings. Since these components are used in various areas of engineering, it is obvious that they are exposed to different environmental influences such as mechanical stresses, temperature profiles and chemical or biological substances. Therefore, their properties change over time which leads to limited operating times. In this contribution, the chemical ageing of elastomers within air is examined. A representative example for this phenomenon is the thermo-oxidative ageing of elastomeric bearings in automobiles. After the state of the art is presented and highlighted by scientific data, the experimental equipment necessary for the thermo-oxidative ageing studies is introduced. According to that, experimental data are shown and analysed. From the theoretical point of view, a constitutive approach is formulated by evaluating the Clausius–Planck inequality. The model exhibits a physically-based structure such that a clear identification of all material parameters is possible and meaningful numerical simulations can be shown. The contribution is closed by a summary and outlooks to future trends and objectives. [ABSTRACT FROM AUTHOR]

Abstract: Membrane separation processes have become a basic unit operation for process design and product development. These processes are used in a variety of separation and concentration steps, but in all cases, the membranes must be cleaned regularly to remove both organic and inorganic material deposited on the surface and/or into the membrane bulk. Cleaning/disinfection is a vital step in maintaining the permeability and selectivity of the membrane in order to get the plant to its original capacity, to minimize risks of bacteriological contamination, and to make acceptable products. For this purpose, a large number of chemical cleaning/disinfection agents are commercially available. In general, these cleaning/disinfection agents have to improve the membrane flux to a certain extent. However, they can also cause irreversible damages in membrane properties and performances over the long term. Until now, there is considerably less literature dedicated to membrane ageing than to cleaning/disinfection. The knowledge in cleaning/disinfection efficiency has recently been improved. But in order to develop optimized cleaning/disinfection protocols there still remains a challenge to better understand membrane ageing. In order to compensate for the lack of correlated cleaning/disinfection and ageing data from the literature, this paper investigates cleaning/disinfection efficiencies and ageing damages of organic ultrafiltration membranes. The final aim is to provide less detrimental cleaning/disinfection procedures and to propose some guidelines which should have been taken into consideration in term of membrane ageing studies. To carry out this study, this article will detail the background of cleaning/disinfection and aging membrane topics in a first introductive part. In a second part, key factors and endpoints of cleaning/disinfection and aging membranes will be discussed deeply: the membrane role and the cleaning parameters roles, such as water quality, storing conditions, cleaning/disinfection/aging agents/conditions/protocols. The third and last part will be developed the parameters, methods and ways of characterization at our disposal and commonly used to develop and implement membrane cleaning and/or ageing studies. [Copyright &y& Elsevier]

With the increasing number of requirements on joinings, it gets more and more important to understand and predict an assemblies properties. Nowadays, in industrial applications, combinations of different materials get more common. In most of those cases, it is, besides other advantages, useful to connect such parts with adhesives to avoid local cells. Thus, the knowledge about the mechanical behaviour of adhesives over the whole time of utilisation is an essential element of engineering. As it is well known, ageing due to environmental influences such as oxygen, radiation, ozone and others plays a major role in polymers properties. So, for the prediction of applicability over the whole lifetime of a technical component, the change in mechanical properties due to ageing is necessary. In this contribution, we introduce a material model which takes into account the internal structure of an adhesive. Therefore, an interphase zone is introduced. In the interphase, which is developed due to the contact of an adhesive with an adherent, the materials properties change continuously from the surface to the centre of the joint, where the polymer is in a bulky state. Built up on this geometry dependency, the materials ageing as a function of the position is described. To model the change of the polymers state, we use a parameter representing chain scission processes and another one for the reformation of a new network. In a last step, the model is transferred into a finite element code for exemplary calculations. [ABSTRACT FROM AUTHOR]

This work shows how the mechanical properties, tensile and shear strength, are modified in different way if two different types of composite materials are immersed in toluen and sulfuric acid. The composites have a thermoplastic as matrix and one of them is reinforced with glass fiber and the other with carbon fiber. Also the important influence of the temperature has been tested in the case of the acid and specimens with holes have been tested to know their influence.El presente trabajo muestra la diferente influencia que sobre las propiedades mecánicas, resistencias a tracción y cortadura, tiene la inmersión en dos agentes químicos, tales como, tolueno y ácido sulfúrico de dos tipos diferentes de materiales compuestos, uno reforzado con fibra de vidrio y otro con fibra de carbono. En ambos casos la matriz empleada es un termoplástico de altas prestaciones denominado PEI. En el caso del ataque con el ácido se ha podido, asimismo, contrastar la importante influencia de la temperatura en la disminución de las resistencias y por último, también se han ensayado, a tracción, probetas que contenían agujeros pasantes para, en este caso, descartar que el aumento de la superficie de ataque aumentaba éste.

This article concerns the constitutive representation of one of the chemical ageing processes that occur in elastomers, chemo-thermomechanical ageing, which takes place as an irreversible, time-delayed chemical reaction when a medium diffuses into an unlike solid. This process is inhomogeneous in component parts of finite thickness, and as it can be thermally activated, ageing is accelerated on an increase in temperature. The application of multiphase continuum mechanics to these basic characteristics enables a thermodynamically coupled material model to be formulated, which is able to describe not only the viscoelasticity, but also the chemical decomposition and reformation processes that occur in the polymer network. The evolution principle of Liu-Müller is used to evaluate the thermomechanical consistency of the model obtained. Subsequent to this, the finite element method is applied to solve the resulting set of partial equations, which corresponds to a coupled multifield problem. The article closes with convincing simulations of illustrative examples. [ABSTRACT FROM AUTHOR]

This paper documents the discovery of waste engine oil residues in pavements across Ontario, Canada. We have found that recovered asphalts from a large majority of poorly performing contracts test positive for zinc through X-ray fluorescence (XRF) analysis. In contrast, neither the aggregates nor any of the well-performing asphalts showed any signs of the metal. Since zinc dialkyldithiophosphates are universal additives in engine oils, we inferred that the use of waste oil residues in asphalt must be widespread. Further analysis of 2008 quality assurance samples taken for the Ontario Ministry of Transportation substantiated this, with most samples testing positive for zinc. XRF analysis of straight waste oil residues suggests that typical modification levels are in the 5-20% range. The damaging effect of this additive through increased physical and chemical hardening is briefly discussed with reference to previous studies on unexplained, premature and excessive thermal cracking. [ABSTRACT FROM AUTHOR]

Rubber components usually exhibit changes in their mechanical properties that accumulate over their service life and often determine the need for replacement. This article deals with chemical ageing coupled with mechanical loading. During chemical ageing, changes in the chemical structure of the material lead to alterations in its stiffness and gradual evolution of permanent deformations. The dynamic network model is used to capture these changes together with the generalized Yeoh model as the strain energy potential. A new set of measurements is presented together with a multiple-step calibration procedure. • Chemical ageing of rubber results affects stress–strain relationship and permanent set. • Specimens ageing at elevated or room temperature in deformed state. • Two calibration procedures examined using both synthetic and real-world data. [ABSTRACT FROM AUTHOR]

Light absorbing organic carbon, a.k.a., brown carbon (BrC) is an important contributor to air quality deterioration and global radiative forcing. This work studied optical, chemical properties and sources of BrC in fine particles (PM 2.5) collected in Yangzhou, China. The light absorption coefficient at 365 nm of methanol-soluble organics (Abs 365,MSOC) and water-soluble organics (Abs 365,WSOC) were 13.50 ± 7.03 M/m and 6.08 ± 4.30 M/m, respectively. Mass absorption efficiency at 365 nm (MAE 365) of methanol-soluble BrC (1.12 ± 0.35 m2/g C) was also higher than water-soluble BrC (0.75 ± 0.29 m2/g C). For water-soluble BrC, both Abs 365 and MAE 365 generally decreased with increases of its oxygen-to‑carbon (O/C) ratios and oxidation states (OS c), indicative of photo-bleaching upon chemical ageing. Positive responses of Abs 365,WSOC and MAE 365,WSOC to nitrogen-to‑carbon (N/C) ratios and water-soluble organic nitrogen (ON) contents reveal that ON species are important BrC chromophores. A multiple linear regression model was applied to apportion Abs 365,WSOC to contributions of different factors resolved from positive matrix factorization on water-soluble organic aerosols (OA), and obtained MAE 365 values of different OA factors. Overall, primary OA sources including traffic (18.9%), biomass burning (23.7%), and cooking-related OA (10.5%) together dominated the Abs 365,WSOC despite their total mass contribution was only about one third (31.9%). The largest single contributor of Abs 365,WSOC , however, was the less-oxidized secondary OA (33.8%); the more-oxidized secondary OA factor dominated water-soluble OA mass (50.8%), yet its light absorptivity was the weakest and contributed only 13.1% of Abs 365,WSOC. Unlabelled Image • Methanol-soluble BrC has larger Abs 365 and MAE 365 values than water-soluble BrC • Chemical ageing can lead to photo-bleaching of water-soluble BrC • Nitrogen-containing organics are important BrC chromophores • Traffic OA had a higher mass absorption efficiency than that of biomass burning OA • Primary OA dominated Abs 365, WSOC , yet less oxidized secondary OA was also important [ABSTRACT FROM AUTHOR]