Cracking formation on the surface of extruded photodegraded polypropylene plates

The cracking formation during the photodegradation of polypropylene (PP) plates (1 mm thickness), with (PPOx) and without pro-oxidant [PP), has been investigated. The plates were produced by extrusion in an industrial production line and were exposed to ultraviolet radiation in the laboratory for periods of up to 480 hr. The samples were investigated by infrared spectroscopy- FTIR, optical light microscopy, differential scanning calorimetry (DSC) and X-ray diffraction (XRD). The results showed that the extension of photodegradation process is more intense for PPOx than for PP samples. For both samples, cracks were formed at the surface perpendicularly to the flow-lines. However the cracks frequency was different for both samples and sides of sample. The crack frequency was correlated with chain orientation, A(110); it was shown that lower degrees of orientation resulted in lower crack frequency. POLYM. ENG. SCI., 48:365-372, 2008. (c) 2007 Society of Plastics Engineers.

Effect of nitrogen on the corrosion-erosion synergism in an austenitic stainless steel

High temperature gas nitrided AISI 304L austenitic stainless steel containing 0.55 wt% N in solid solution, was corrosion, erosion and corrosion-erosion tested in a jet-like device, using slurry composed of 3.5% NaCl and quartz particles. Scanning electron microscopy analysis of the damaged surfaces, mass loss measurements and electrochemical test results were used to understand the effect of nitrogen on the degradation mechanisms. Increasing the nitrogen content improved the corrosion, erosion and corrosion-erosion resistance of the AISI 304L austenitic stainless steel. Smoother wear mark contours observed on the nitrided surfaces indicate a positive effect of nitrogen on the reduction of the corrosion-erosion synergism. (C) 2011 Elsevier Ltd. All rights reserved.

Influence of the Type of Quaternary Ammonium Salt Used in the Organic Treatment of Montmorillonite on the Properties of Poly(Styrene-co-Butyl Acrylate)/Layered Silicate Nanocomposites Prepared by In Situ Miniemulsion Polymerization

Hybrid latices of poly(styrene-co-butyl acrylate) were synthesized via in situ miniemulsion polymerization in the presence of 3 and 6 wt % organically modified montmorillonite (OMMT). Three different ammonium salts: cetyl trimethyl ammonium chloride (CTAC), alkyl dimethyl benzyl ammonium chloride (Dodigen), and distearyl dimethyl ammonium chloride (Praepagen), were investigated as organic modifiers. Increased affinity for organic liquids was observed after organic modification of the MMT. Stable hybrid latices were obtained even though miniemulsion stability was disturbed to some extent by the presence of the OMMTs during the synthesis. Highly intercalated and exfoliated polymer-MMT nanocomposites films were produced with good MMT dispersion throughout the polymeric matrix. Materials containing MMT modified with the 16 carbons alkyl chain salt (CTAC) resulted in the largest increments of storage modulus, indicating that single chain quaternary salts provide higher increments on mechanical properties. Films presenting exfoliated structure resulted in the largest increments in the onset temperature of decomposition. For the range of OMMT loading studied, the nanocomposite structure influenced more significantly the thermal stability properties of the hybrid material than did the OMMT loading. The film containing 3 wt % MMT modified with the two 18 carbons alkyl chains salt (Praepagen) provided the highest increment of onset temperature of decomposition. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 119: 3658-3669, 2011

Quantification of MgO surface excess on the SnO(2) nanoparticles and relationship with nanostability and growth

In this work, we experimentally showed that the spontaneous segregation of MgO as surface excess in MgO doped SnO(2) nanoparticles plays an important role in the system`s energetics and stability. Using Xray fluorescence in specially treated samples, we quantitatively determined the fraction of MgO forming surface excess when doping SnO(2) with several different concentrations and established a relationship between this amount and the surface energy of the nanoparticles using the Gibbs approach. We concluded that the amount of Mg ions on the surface was directly related to the nanoparticles total free energy, in a sense that the dopant will always spontaneously distribute itself to minimize it if enough diffusion is provided. Because we were dealing with nanosized particles, the effect of MgO on the surface was particularly important and has a direct effect on the equilibrium particle size (nanoparticle stability), such that the lower the surface energy is, the smaller the particle sizes are, evidencing and quantifying the thermodynamic basis of using additives to control SnO(2) nanoparticles stability. (C) 2010 Elsevier B.V. All rights reserved.

Influence of Water Content, Time, and Temperature on the Rheological Behavior of Polyethylene Terephtalate

In this work, the main factors affecting the rheological behavior of polyethylene terephtalate (PET) in the linear viscoelastic regime (water content, time delay before test, duration of experiment, and temperature) were accessed. Small amplitude oscillatory shear tests were performed after different time delays ranging from 300 to 5000 s for samples with water contents ranging from 0.02 to 0.45 wt %. Time sweep tests were carried out for different durations to explain the changes undergone by PET before and during small amplitude oscillatory shear measurements. Immediately after the time sweep tests, the PET samples were removed from the rheometer, analyzed by differential scanning calorimetry and their molar mass was obtained by viscometry analysis. It was shown that for all the samples, the delay before test and residence time within the rheometer (i.e. duration of experiment) result in structural changes of the PET samples, such as increase or decrease of molar mass, broadening of molar mass distribution, and branching phenomena. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 116: 3525-3533, 2010

Influence of the rubbery phase on the crystallinity and thermomechanical properties of poly(3-hydroxybutyrate)/elastomer blends

Poly(3-hydroxybutyrate) (PHB) is a very promising biopolymer. In order to improve its processability and decrease its brittleness, PHB/elastomer blends can be prepared. In the work reported, the effect of the addition of a rubbery phase, i.e. ethylene - propylene-diene terpolymer (EPDM) or poly(vinyl butyral) (PVB), on the properties of PHB was studied. The effects of rubber type and of changing the PHB/elastomer blend processing method on the crystallinity and physical properties of the blends were also investigated. For blends based on PHB, the main role of EPDM is its nucleating effect evidenced by a decrease of crystallization temperature and an increase of crystallinity with increasing EPDM content regardless of the processing route. While EPDM has a weak effect on PHB glass transition temperature, PVB induces a marked decrease of this temperature thank to its plasticizer that swells the PHB amorphous phase. A promising solution to improve the mechanical properties of PHB seems to be the melt-processing of PHB with both plasticizer and EPDM. In fact, the plasticizer is more efficient than the elastomer in decreasing the PHB glass transition temperature and, because of the nucleating effect of EPDM, the decrease of the PHB modulus due to the plasticizer can be counterbalanced. (C) 2010 Society of Chemical Industry

ANNEALING EFFECTS ON THE MICROSTRUCTURE OF FERRITIC-MARTENSITIC ODS-EUROFER STEEL

Oxide dispersion strengthened (ODS) ferritic/martensitic (FM) steels are promising candidates for structural applications in future fusion power reactors. In order to evaluate the thermal stability of 80% cold-rolled ODS-EUROFER, samples were annealed for 1 h at temperatures up to about 0.9 T(m), where T(m) is the absolute melting point. The characterization of the annealed samples was performed using transmission electron microscopy and electron backscatter diffraction. Results show that static recovery is the main softening mechanism of this steel when annealed below 800 degrees C. The volume fraction of recrystallized grains is quite small (below 0.10). Above 900 degrees C, martensitic transformation takes place causing pronounced hardening. Large M(23)C(6) particles are found at the grain boundaries after tempering at 750 degrees C for 2 h.

Medium carbon steel deep drawing: A study on the evolution of mechanical properties, texture and simulations, from cold rolling to the end product

Medium carbon steels are mostly used for simple applications; nevertheless new applications have been developed for which good sheet formability is required. This class of steels has an inherent low formability. A medium carbon hot rolled SAE 1050 steel has been selected for this study. It has been cold rolled with reductions in the 7-80% range. Samples have been used to assess the cold work hardening curve. For samples with a 50 and 80% thickness reduction, an annealing heat treatment has been performed to obtain recrystallization. The material has been characterized in the ""as received"", cold rolled and annealed conditions, using several methods: optical microscopy, X-ray diffraction (texture), Vickers hardness and tensile testing. The 50% cold rolled and recrystallized material has been further studied in terms of sheet metal formability and texture evolution during the actual stamping of a steel toecap that has been used to validate the finite element simulations. (C) 2008 Elsevier B.V. All rights reserved.

On the Steinmetz hysteresis law

The behavior of the Steinmetz coefficient has been described for several different materials: steels with 3.2% Si and 6.5% Si, MnZn ferrite and Ni-Fe alloys. It is shown that, for steels, the Steinmetz law achieves R(2)> 0.999 only between 0.3 and 1.2 T, which is the interval where domain wall movement dominates. The anisotropy of Steinmetz coefficient for non-oriented (NO) steel is also discussed. It is shown that for a NO 3.2% Si steel with a strong Goss component in texture, the power law coefficient and remanence decreases monotonically with the direction of measurement going from rolling direction (RD) to transverse direction (TD), although coercive field increased. The remanence behavior can be related to the minimization of demagnetizing field at the surface grains. The data appear to indicate that the Steinmetz coefficient increases as magnetocrystalline anisotropy constant decreases. (c) 2008 Elsevier B.V. All rights reserved.

Effect of the processing conditions and the addition of trans-polyoctenylene rubber on the properties of natural rubber/styrene-butadiene rubber blends

In this study, the influence of the processing conditions and the addition of trans-polyoctenylene rubber (TOR) on Mooney viscosity, tensile properties, hardness, tearing resistance, and resilience of natural rubber/styrene-butadiene rubber blends was investigated. The results obtained are explained in light of dynamic mechanical and morphological analyses. Increasing processing time produced a finer blend morphology, which resulted in an improvement in the mechanical properties. The addition of TOR involved an increase in hardness, a decrease in tear resistance, and no effect on the resilience. It resulted in a large decrease in the Mooney viscosity and a slight decrease in the tensile properties if the components of the compounds were not properly mixed. The results indicate that TOR acted more as a plasticizer than a compatibilizer. (c) 2008 Wiley Periodicals, Inc.

Effect of rolling on the residual stresses and magnetic properties of a 0.5% Si electrical steel

Cold-rolled (0-19% of reduction) 0.5% Si electrical steel sheets were studied in detail, including macro and micro residual stress measurements, crystallographic texture, dc-hysteresis curves and iron losses. Even for the smallest deformation, losses increase significantly, with large increase of the hysteresis losses, whereas the anomalous losses reduce slightly. The residual microstresses are similar to 150-350 MPa, whereas residual macrostresses are compressive, similar to 50 MPa. The large increase of the hysteresis losses is attributed to the residual microstresses. The dislocation density estimated by X-ray diffraction is in reasonable agreement with that predicted from the Sablik et al. model for effect of plastic deformation on hysteresis. The intensity of the texture fibers {1 1 1}< u v w > and < 110 >//RD (RD = rolling direction) increases with the reduction. (C) 2008 Elsevier B.V. All rights reserved.

Investigation on the intergranular corrosion resistance of the AISI 316L(N) stainless steel after long time creep testing at 600 degrees C

The effect of precipitation on the corrosion resistance of AISI 316L(N) stainless steel previously exposed to creep tests at 600 degrees C for periods of up to 10 years, has been studied. The corrosion resistance was investigated in 2 M H(2)SO(4)+0.5 M NaCl+0.01 M KSCN solution at 30 degrees C by electrochemical methods. The results showed that the susceptibility to intergranular corrosion was highly affected by aging at 600 degrees C and creep testing time. The intergranular corrosion resistance decreased by more than twenty times when the creep testing time increased from 7500 h to 85,000 h. The tendency to passivation decreased and less protective films were formed on the creep tested samples. All tested samples also showed susceptibility to pitting. Grain boundary M(23)C(6) carbides were not found after long-term exposure at 600 degrees C and the corrosion behavior of the creep tested samples was attributed to intermetallic phases (mainly sigma phase) precipitation. (C) 2007 Elsevier Inc. All rights reserved.

Effect of cerium (IV) ions on the anticorrosion properties of siloxane-poly(methyl methacrylate) based film applied on tin coated steel

This work investigates the influence of the addition of cerium (IV) ions on the anticorrosion properties of organic-inorganic hybrid coatings applied to passivated tin coated steel. In order to evaluate the specific effect of cerium (IV) addition on nanostructural features of the organic and inorganic phases of the hybrid coating, the hydrolytic polycondensation of silicon alkoxide and the radical polymerization of the methyl methacrylate (MMA) function were induced separately. The corrosion resistance of the coatings was evaluated by means of linear polarization, Tafel type curves and electrochemical impedance measurements. The impedance results obtained for the hybrid coatings were discussed based on an electrical equivalent circuit used to fit the experimental data. The electrochemical results clearly showed the improvement of the protective properties of the organic-inorganic hybrid coating mainly when the cerium (IV) was added to the organic phase solution precursor, which seemed to be due to the formation of a more uniform and densely reticulated siloxane-PMMA film. (C) 2010 Elsevier Ltd. All rights reserved.

Evaluation of the effect of ammonium carbamate on the stability of proteins

BACKGROUND: The use of the volatile salt ammonium carbamate in protein downstream processing has recently been proposed. The main advantage of using volatile salts is that they can be removed from precipitates and liquid effluents through pressure reduction or temperature increase. Although previous studies showed that ammonium carbamate is efficient as a precipitant agent, there was evidence of denaturation in some enzymes. In this work, the effect of ammonium carbamate on the stability of five enzymes was evaluated. RESULTS: Activity assays showed that alpha-amylase (1,4-alpha-D-glucan glucanohydrolase, EC 3.2.1.1), lysozyme (1,4-beta-N-acetylmuramoylhydrolase, EC 3.2.1.17) and lipase (triacyl glycerol acyl hydrolase, EC 3.1.1.3) did not undergo activity loss in ammonium carbamate solutions with concentrations from 1.0 to 5.0 mol kg(-1), whereas cellulase complex (1,4-(1,3 : 14)-beta-D-glucan 4-glucano-hydrolase, EC 3.2.1.4) and peroxidase (hydrogen peroxide oxidoreductase, EC 1.11.1.7) showed an average activity loss of 55% and 44%, respectively. Precipitation assays did not show enzyme denaturation or phase separation for alpha-amylase and lipase, while celullase and peroxidase precipitated with some activity reduction. Analysis of similar experiments with ammonium and sodium sulfate did not affect the activity of enzymes. CONCLUSION: Celullase and peroxidase were denatured by ammonium carbamate. While more systematic studies are not available, care must be taken in designing a protein precipitation with this salt. The results suggest that the generally accepted idea that salts that denature proteins tend to solubilize them does not hold for ammonium carbamate. (C) 2010 Society of Chemical Industry

AN ASSESSMENT ON THE USE OF THE DEBYE-HUCKEL EQUATION FOR THE THERMODYNAMIC MODELING OF AQUEOUS SYSTEMS CONTAINING POLYMERS AND SALTS

In this work, a study on the role of the long-range term of excess Gibbs energy models in the modeling of aqueous systems containing polymers and salts is presented. Four different approaches on how to account for the presence of polymer in the long-range term were considered, and simulations were conducted considering aqueous solutions of three different salts. The analysis of water activity curves showed that, in all cases, a liquid-phase separation may be introduced by the sole presence of the polymer in the long-range term, regardless of how it is taken into account. The results lead to the conclusion that there is no single exact solution for this problem, and that any kind of approach may introduce inconsistencies.