Reducing acrylamide precursors in raw materials derived from wheat and potato

A review of agronomic and genetic approaches as strategies for the mitigation of acrylamide risk in wheat and potato is presented. Acrylamide is formed through the Maillard reaction during high-temperature cooking, such as frying, roasting, or baking, and the main precursors are free asparagine and reducing sugars. In wheat flour, acrylamide formation is determined by asparagine levels and asparagine accumulation increases dramatically in response to sulfur deprivation and, to a much lesser extent, with nitrogen feeding. In potatoes, in which sugar concentrations are much lower, the relationships between acrylamide and its precursors are more complex. Much attention has been focused on reducing the levels of sugars in potatoes as a means of reducing acrylamide risk. However, the level of asparagine as a proportion of the total free amino acid pool has been shown to be a key parameter, indicating that when sugar levels are limiting, competition between asparagine and the other amino acids for participation in the Maillard reaction determines acrylamide formation. Genetic approaches to reducing acrylamide risk include the identification of cultivars; and other germplasm in which free asparagine and/or sugar levels are low and the manipulation of genes involved in sugar and amino acid metabolism and signaling. These approaches are made more difficult by genotype/ environment interactions that can result in a genotype being "good" in one environment but "poor" in another. Another important consideration is the effect that any change could have on flavor in the cooked product. Nevertheless, as both wheat and potato are regarded as of relatively high acrylamide risk compared with, for example, maize and rice, it is essential that changes are achieved that mitigate the problem.

Platinum nanoparticle-modified electrodes, morphologic, and electrochemical studies concerning electroactive materials deposition

The present work describes the synthesis of platinum nanoparticles followed by their electrophoretic deposition onto transparent fluorine-doped tin oxide electrodes. The nano-Pt-modified electrodes were characterized by voltammetric studies in acidic solutions showing a great electrocatalytic behavior towards H(+) reduction being very interesting for fuel cell applications. Morphological characterization was performed by atomic force microscopy on different modified electrodes showing a very rough surface which can be tuned by means of time of deposition. Also, nickel hydroxide thin films were galvanostatically grown onto these electrodes showing an interesting electrochemical behavior as sharper peaks, indicating a faster ionic exchange from the electrolyte to the film.

Evaluation of the Cohesive Strength Between Resin Composite and Light-curing Characterizing Materials

Purpose: To evaluate the cohesive strength between composite and different light-curing characterizing materials (LCCM), which were prepared using the intrinsic technique.Materials and Methods: One hundred composite specimens were made by using a prefabricated Teflon device, and a layer of LCCM was applied at the interface. The specimens were divided into 5 groups (n = 20): group 1 (control), no LCCM was used; group 2: application of White Kolor Plus Pigment (Kerr) LCCM; group 3: White Tetric Color Pigment (Ivoclar/Vivadent) LCCM; group 4: Brown Kolor Plus Pigment (Kerr) LCCM; group 5: Black Tetric Color Pigment (Ivoclar/Vivadent) LCCM. All materials were used according to the manufacturers' instructions. Specimens were submitted to a tensile test in a universal testing machine (EMIC DL-200MF) to evaluate the cohesive strength at the composite interface. Data were subjected to one-way ANOVA and Tukey's test (alpha = 5%).Results: ANOVA showed a p-value = 0.0001, indicating that there were significant differences among the groups. The mean values in MPa (+/- standard deviation) obtained for the groups were: G1: 28.5 (+/-2.74)a; G2: 23.5 (+/-2.47)b; G3: 20.3 (+/-2.49)b; G4: 10.5 (+/-2.40)c; G5: 9.66 (+/-3.06)c. The groups with the same letters presented no significant differences. The control group presented statistically significantly higher cohesive strengths when compared to the other groups. The groups in which Brown Kolor Plus Pigment and Black Tetric Color Pigment LCCM were used showed significantly lower cohesive strengths when compared to the groups in which White Kolor Plus Pigment and White Tetric Color Pigment LCMM were used.Conclusion: The use of LCCM produced with the intrinsic technique reduced the cohesive strength of composite.

Coloring ionic trapping states in WO3 and Nb2O5 electrochromic materials

Complex electro-optical analysis is a very useful approach to separate different kinetic processes that occur during ionic insertion reactions in electrochromic oxide materials. In this paper, we use this type of combined technique to investigate ionic and optical changes in different oxide host systems, i.e., in two oxide hosts, specifically WO3 and Nb2O5. A comparison of their electro-optical responses revealed the presence of an ionic trapping contribution to the kinetics of the coloring sites, which was named here as coloring ionic trapping state. As expected, this coloring trapping process is slower in Nb2O5 since the reduction potential of Nb2O5 is more negative (more energy is needed for a higher degree of coloration). A phenomenological solid-state model that encompasses homogeneous charge transfer and valence trapping was proposed to explain the coloring ionic trapping process. Basically the model is able to explain how ionic dynamics at low frequency region, i.e., the slower kinetic step, controls the coloring kinetics, i.e., how it is capable to regulate the coloring rates.Optical transient analyses demonstrated the possibility of the presence of more than one coloring ionic trap, indicating the complexity of the processes involved in coloration phenomenon in metal oxide host systems. (C) 2008 Published by Elsevier Ltd.

Characteristics of the double-torsion test to determine the R-curve of ceramic materials

Double-torsion tests were carried out on a commercial ceramic floor tile to verify whether this test is suitable for determining the R-curve of ceramics. The instantaneous crack length was obtained by means of compliance calibration, and it was found that the experimental compliance underestimates the real crack length. The load vs. displacement curves were also found to drop after maximum loading, causing the stress intensity factor to decline. The R-curves were calculated by two methods: linear elastic fracture mechanics and the energetic method. It was obtained that the average values of crack resistance, R, and the double of the work of fracture, 2 · γwof, did not depend on notch length, a0, which is a highly relevant finding, indicating that these parameters were less dependent on the test specimen's geometry. The proposal was to use small notches, which produce long stable crack propagation paths that in turn are particularly important in the case of coarse microstructures.

NUMERICAL AND ANALYTICAL VERIFICATION OF A MULTISCALE COMPUTATIONAL MODEL FOR IMPACT PROBLEMS IN HETEROGENEOUS VISCOELASTIC MATERIALS WITH EVOLVING DAMAGE

Composites are engineered materials that take advantage of the particular properties of each of its two or more constituents. They are designed to be stronger, lighter and to last longer which can lead to the creation of safer protection gear, more fuel efficient transportation methods and more affordable materials, among other examples. This thesis proposes a numerical and analytical verification of an in-house developed multiscale model for predicting the mechanical behavior of composite materials with various configurations subjected to impact loading. This verification is done by comparing the results obtained with analytical and numerical solutions with the results found when using the model. The model takes into account the heterogeneity of the materials that can only be noticed at smaller length scales, based on the fundamental structural properties of each of the composite’s constituents. This model can potentially reduce or eliminate the need of costly and time consuming experiments that are necessary for material characterization since it relies strictly upon the fundamental structural properties of each of the composite’s constituents. The results from simulations using the multiscale model were compared against results from direct simulations using over-killed meshes, which considered all heterogeneities explicitly in the global scale, indicating that the model is an accurate and fast tool to model composites under impact loads. Advisor: David H. Allen

Modeling and simulations of some anisotropic soft-matter systems: from biaxial to chiral materials

We have modeled various soft-matter systems with molecular dynamics (MD) simulations. The first topic concerns liquid crystal (LC) biaxial nematic (Nb) phases, that can be possibly used in fast displays. We have investigated the phase organization of biaxial Gay-Berne (GB) mesogens, considering the effects of the orientation, strength and position of a molecular dipole. We have observed that for systems with a central dipole, nematic biaxial phases disappear when increasing dipole strength, while for systems characterized by an offset dipole, the Nb phase is stabilized at very low temperatures. In a second project, in view of their increasing importance as nanomaterials in LC phases, we are developing a DNA coarse-grained (CG) model, in which sugar and phosphate groups are represented with Lennard-Jones spheres, while bases with GB ellipsoids. We have obtained shape, position and orientation parameters for each bead, to best reproduce the atomistic structure of a B-DNA helix. Starting from atomistic simulations results, we have completed a first parametrization of the force field terms, accounting for bonded (bonds, angles and dihedrals) and non-bonded interactions (H-bond and stacking). We are currently validating the model, by investigating stability and melting temperature of various sequences. Finally, in a third project, we aim to explain the mechanism of enantiomeric discrimination due to the presence of a chiral helix of poly(gamma-benzyl L-glutamate) (PBLG), in solution of dimethylformamide (DMF), interacting with chiral or pro-chiral molecules (in our case heptyl butyrate, HEP), after tuning properly an atomistic force field (AMBER). We have observed that DMF and HEP molecules solvate uniformly the PBLG helix, but the pro-chiral solute is on average found closer to the helix with respect to the DMF. The solvent presents a faster isotropic diffusion, twice as HEP, also indicating a stronger interaction of the solute with the helix.

Advanced polymeric materials for applications in technical equipment for snow sports

The thesis is divided in three chapters, each one covering one topic. Initially, the thermo-mechanical and impact properties of materials used for back protectors have been analysed. Dynamical mechanical analysis (DMTA) has shown that materials used for soft-shell protectors present frequency-sensitive properties. Furthermore, through impact tests, the shock absorbing characteristics of the materials have been investigated proving the differences between soft and hard-shell protectors; moreover it has been demonstrated that the materials used for soft-shell protectors maintain their protective properties after multi-impacts. The second chapter covers the effect of the visco-elastic properties of the thermoplastic polymers on the flexural and rebound behaviours of ski boots. DMTA analysis on the materials and flexural and rebound testing on the boots have been performed. A comparison of the results highlighted a correlation between the visco-elastic properties and the flexural and rebound behaviour of ski boots. The same experimental methods have been used to investigate the influence of the design on the flexural and rebound behaviours. Finally in the third chapter the thermoplastic materials employed for the construction of ski boots soles have been characterized in terms of chemical composition, hardness, crystallinity, surface roughness and coefficient of friction (COF). The results showed a relation between material hardness and grip, in particular softer materials provide more grip with respect to harder materials. On the contrary, the surface roughness has a negative effect on friction because of the decrease in contact area. The measure of grip on inclined wet surfaces showed again a relation between hardness and grip. The performance ranking of the different materials has been the same for the COF and for the slip angle tests, indicating that COF can be used as a parameter for the choice of the optimal material to be used for the soles of ski boots.

Thermoelectric properties in phase-separated half-Heusler materials

The conversion of dissipated heat into electricity is the basic principle of thermoelectricity. In this context, half-Heusler (HH) compounds are promising thermoelectric (TE) materials for waste heat recovery. They meet all the requirements for commercial TE applications, ranging from good efficiencies via environmentally friendliness to being low cost materials. This work focused on the TE properties of Ti0.3Zr0.35Hf0.35NiSn-based HH materials. This compound undergoes an intrinsic phase separation into a Ti-poor and Ti-rich HH phase during a rapid solidification process. The resulting dendritic microstructure causes a drastic reduction of the thermal conductivity, leading to higher TE efficiencies in these materials. The TE properties and temperature dependence of the phase-separated Ti0.3Zr0.35Hf0.35NiSn compound were investigated. The TE properties can be adjusted depending on the annealing treatment. The extension of annealing time for 21 days at 1000 °C revealed a reduction of the thermal conductivity and thus an enhancement of the TE performance in this sample. An increase of annealing temperature caused a change of the phase fraction ratio in favor of the Ti-rich phase, leading to an improvement of the electronic properties. rnInspired by the TE properties of the Ti0.3Zr0.35Hf0.35NiSn HH compound, the performance of different n- and p-type materials, realized via site substitution with donor and acceptor elements was examined. The fabrication of a TE n- and p-type material pair based on one starting compound can guarantee similar TE and mechanical properties and is enormous beneficial for device engineering. As donor dopants V, Nb and Sb were tested. Depending on the lattice position small doping levels were sufficient to attain distinct improvement in their TE efficiency. Acceptor-induced doping with Sc, Y and Co caused a change in the transport behavior from n- to p- type conduction, revealing the highest Seebeck coefficients obtained in the MNiSn system. rnThen, the long-term stability of an exemplary n- and p-type HH compound was proven. Surprisingly, the dendritic microstructure can be maintained even after 500 cycles (1700 h) from 373 to 873 K. The TE performance of both n- and p-type materials showed no significant change under the long-term treatment, indicating the extraordinary temperature stability of these compounds. Furthermore both HH materials revealed similar temperature-dependence of their mechanical properties. This work demonstrates the excellent suitability of phase-separated HH materials for future TE applications in the moderate temperature range.rn

Chemical composition in phosphate materials from the ocean floor

Content, distribution patterns, and speciation of Cl in phosphorites and bone phosphate from the ocean floor, as well as in a set of samples from the land are studied. Total Cl content varies from 0.05 to 4.25% in phosphorites and from 2.48 to 2.75% in recent phosphate-bearing sediments. Recent phosphorites are enriched in Cl relative to ancient ones. Bound Cl content (not extractable by washing), which increases with lithification, varies from 0.17 to 0.60% in ocean and land phosphorites and from 0.02% to 1.30% in bone phosphate. Na content in most samples is higher relative to Na of NaCl due to its incorporation into the crystal lattice of apatite. However, the opposite relationship is observed in some samples indicating partial Cl incorporation into the anion complex of phosphate. Behavior of Cl in phosphorites from the present-day ocean floor is controlled by early diagenetic processes, whereas the role of weathering, catagenesis, and hydrogeological factors may be crucial for phosphorites on continents.

Thermogravimetric analysis of the pyrolysis of several materials used in the preparation of commercial cigarettes

Comunicación presentada en forma de póster en el "12th Mediterranean Congress of Chemical Engineering", Barcelona (Spain), November 15-18, 2011

GCMC-surface area of carbonaceous materials with N-2 and Ar adsorption as an alternative to the classical BET method

In this paper we apply a new method for the determination of surface area of carbonaceous materials, using the local surface excess isotherms obtained from the Grand Canonical Monte Carlo simulation and a concept of area distribution in terms of energy well-depth of solid–fluid interaction. The range of this well-depth considered in our GCMC simulation is from 10 to 100 K, which is wide enough to cover all carbon surfaces that we dealt with (for comparison, the well-depth for perfect graphite surface is about 58 K). Having the set of local surface excess isotherms and the differential area distribution, the overall adsorption isotherm can be obtained in an integral form. Thus, given the experimental data of nitrogen or argon adsorption on a carbon material, the differential area distribution can be obtained from the inversion process, using the regularization method. The total surface area is then obtained as the area of this distribution. We test this approach with a number of data in the literature, and compare our GCMC-surface area with that obtained from the classical BET method. In general, we find that the difference between these two surface areas is about 10%, indicating the need to reliably determine the surface area with a very consistent method. We, therefore, suggest the approach of this paper as an alternative to the BET method because of the long-recognized unrealistic assumptions used in the BET theory. Beside the surface area obtained by this method, it also provides information about the differential area distribution versus the well-depth. This information could be used as a microscopic finger-print of the carbon surface. It is expected that samples prepared from different precursors and different activation conditions will have distinct finger-prints. We illustrate this with Cabot BP120, 280 and 460 samples, and the differential area distributions obtained from the adsorption of argon at 77 K and nitrogen also at 77 K have exactly the same patterns, suggesting the characteristics of this carbon.

Quantum effect induced reverse kinetic molecular sieving in microporous materials

We report kinetic molecular sieving of hydrogen and deuterium in zeolite rho at low temperatures, using atomistic molecular dynamics simulations incorporating quantum effects via the Feynman-Hibbs approach. We find that diffusivities of confined molecules decrease when quantum effects are considered, in contrast with bulk fluids which show an increase. Indeed, at low temperatures, a reverse kinetic sieving effect is demonstrated in which the heavier isotope, deuterium, diffuses faster than hydrogen. At 65 K, the flux selectivity is as high as 46, indicating a good potential for isotope separation.

Comparison of nitrogen adsorption at 77 K on non-porous silica and pore wall of MCM-41 materials by means of density functional theory

Nitrogen adsorption on a surface of a non-porous reference material is widely used in the characterization. Traditionally, the enhancement of solid-fluid potential in a porous solid is accounted for by incorporating the surface curvature into the solid-fluid Potential of the flat reference surface. However, this calculation procedure has not been justified experimentally. In this paper, we derive the solid-fluid potential of mesoporous MCM-41 solid by using solely the adsorption isotherm of that solid. This solid-fluid potential is then compared with that of the non-porous reference surface. In derivation of the solid-fluid potential for both reference surface and mesoporous MCM-41 silica (diameter ranging front 3 to 6.5 nm) we employ the nonlocal density functional theory developed for amorphous solids. It is found that, to out, surprise, the solid-fluid potential of a porous solid is practically the same as that for the reference surface, indicating that there is no enhancement due to Surface curvature. This requires further investigations to explain this unusual departure from our conventional wisdom of curvature-induced enhancement. Accepting the curvature-independent solid-fluid potential derived from the non-porous reference surface, we analyze the hysteresis features of a series of MCM-41 samples. (c) 2005 Elsevier Inc. All rights reserved.

A study in radiopaque polymeric materials

The problems associated with x-ray-transparent denture base are defined and conventional approaches to their solution are assessed. Consideration of elemental absorption parameters leads to the postulation that atoms such as zinc, and bromine, may be effective radiopacifiers over at least part of the clinical x-ray spectrum. These elements had hitherto been considered too light to be effective. Investigation of copolymers of methylmethacrylate and p-bromostyrene revealed no deleterious effects arising from the aromatically brominated monomer (aliphatic bromination caused UV destabilisation). For effective x-ray absorption a higher level of bromination would be necessary, but the expense of suitable compounds made further study unjustifiable. Incorporation of zinc atoms into the polymer was accomplished by copolymerisation of zinc acrylate with methylmethacrylate in solution. At high zinc levels this produced a powder copolymer convenient for addition to dental polymers in the dough moulding process. The resulting mouldings showed increasing brittleness at high loadings of copolymer. Fracture was shown to be through the powder particles rather than around them, indicating the source of weakness to be in the internal structure of the copolymer. The copolymer was expected to be cross-linked through divalent zinc ions and its insolubility and infusibility supported this. Cleavage of the ionic cross links with formic acid produced a zinc-free linear copolymer of high molecular weight. Addition of low concentrations of acrylic acid to the dough moulding monomer appeared to 'labilise' the cross links producing a more homogeneous moulding with adequate wet strength. Toxicologically the zinc-containing materials are satisfactory and though zinc is extracted at a measurable rate in an aqueous system, this is very small and should be acceptable over the life of a denture. In other respects the composite is quite satisfactory and though a marketable product is not claimed the system is considered worthy of further study.