An energy-based model for the wear of UHMWPE

An energetic approach to model the wear of tribological systems in which one of the components of the pair is polymeric is presented in this work. Experimental data, obtained in ultra-high molecular weight polyethylene (UHMWPE) pin-on-disk tribological tests, showed that a linear correlation between the wear rate of the polymer and the dissipated energy exists, independently of the lubricant, of the material used as counterbody and of the surface finishing of both polymer and counterbody. This fact strongly suggests that, in UHMWPE-based tribological systems, energy dissipation is mainly caused by the elasto-plastic deformation and wear of the polymer. Based on this assumption, it is developed a mathematical model that yields for a physical interpretation of the parameters of the experimental wear vs. energy correlation. These parameters are intrinsic wear properties of the polymer and can be used for the optimization of polymer-based tribological systems.     

Analysis of the electrical transport,conductivity, and dielectric relaxation behavior of La0.75 Ba0.10 Sr0.15 Fe O2.875-δ (δ = 0.375 and 0.50) brownmillerite oxides

The topotactic reduction of La_0.75Ba_0.10Sr_0.15FeO_2.875 with titanium metal leads to a new isostructural material of the composition La_0.75Ba_0.10Sr_0.15FeO_2.875-δ (δ?=?0.375 and 0.50). XRD analysis of phases confirms that the obtained compound adopts a brownmillerite-type structure. A slight distorted monoclinic P2/m was found to describe the crystal structure. The transport properties have been investigated by current–voltage (I–V). The electric and dielectric measurements were carried out covering a wide range of temperature (300–600 K). Our materials display semiconducting properties as well as mixed ionic and electronic conductivity. At high temperatures, the activation energy values proved to be around 907–630 meV, which refers basically to oxygen vacancies conduction. The analysis of dielectric properties and dielectric losses (ε’, tanδ) of both compounds vs temperature at different frequencies demonstrates two relaxer attitudes. A low dielectric loss and low electrical conductance were displayed. Relying upon these values, these materials stand for perfect candidates for micro-electronics devices.

     

Fanconi Anemia Patients from an Indigenous Community in Mexico Carry a New Founder Pathogenic Variant in FANCG

Fanconi anemia (FA) is a rare genetic disorder caused by pathogenic variants (PV) in at least 22 genes, which cooperate in the Fanconi anemia/Breast Cancer (FA/BRCA) pathway to maintain genome stability. PV in FANCA, FANCC, and FANCG account for most cases (~90%). This study evaluated the chromosomal, molecular, and physical phenotypic findings of a novel founder FANCG PV, identified in three patients with FA from the Mixe community of Oaxaca, Mexico. All patients presented chromosomal instability and a homozygous PV, FANCG: c.511-3_511-2delCA, identified by next-generation sequencing analysis. Bioinformatic predictions suggest that this deletion disrupts a splice acceptor site promoting the exon 5 skipping. Analysis of Cytoscan 750 K arrays for haplotyping and global ancestry supported the Mexican origin and founder effect of the variant, reaffirming the high frequency of founder PV in FANCG. The degree of bone marrow failure and physical findings (described through the acronyms VACTERL-H and PHENOS) were used to depict the phenotype of the patients. Despite having a similar frequency of chromosomal aberrations and genetic constitution, the phenotype showed a wide spectrum of severity. The identification of a founder PV could help for a systematic and accurate genetic screening of patients with FA suspicion in this population.     

The effect of lowering salt on the physicochemical,microbiological and sensory properties of São João cheese of Pico Island

São João cheeses with varying curd dry salting treatments were made with decreasing levels of salt (sodium chloride): 4 (control), 3, 2 and 1% (w/w), along with the salt‐free version. The cheeses were ripened at 11 °C over a 40‐day period, and the effect of lowering salt on the physicochemical, microbiological and sensory properties of the cheese was studied. Reduced salt resulted in a concomitant moisture decrease with protein increase, ash and sodium reduction among experimental cheeses at the same ripening day, but there were no significant differences in pH, acidity and fat, or in the microbiological quality. Triangle tests indicated perceptible differences between test and control cheeses at the level of 2% NaCl (w/w) or less, but not with the cheese salted with 3 g NaCl/100 g. Considering the sensory, the physicochemical and the microbiological results, the cheese formulated at 3% NaCl (w/w) (presenting a reduction of 25% in salt) is feasible on an industrial scale, being indistinguishable by the regular consumer.     

Co-combustion of coal and sewage sludge: Chemical and ecotoxicological properties of ashes

The co-combustion of sewage sludge (SS) and coal is widely used for the treatment and thermal valorization of SS produced in wastewater treatment plants. The chemical and ecotoxicological properties of the ashes produced in this thermal treatment have not been fully studied. Two combustion tests were performed in a fluidized bed combustor. Colombian coal was used as fuel in test A. A blend (1 + 1) of this coal and a stabilized SS (Biogran^®) was used in a second test B. Samples of the bottom and fly ashes trapped in two sequential cyclones were collected. The characterization of the ashes was focused on two main aspects: (1) the bulk content of a set of metals and (2) the characterization of eluates produced according to the European Standard leaching test EN 12457-2. The eluates were submitted to an ecotoxicological characterization for two bio-indicators. In what concerns the bulk content of ashes, both combustion tests have produced ashes with different compositions. The ashes formed during the co-combustion test have shown higher concentrations of metals, namely Cr, Cu, Ni, Pb, Zn and Fe for all ashes. The leaching test has shown low mobility of these elements from the by-products produced during the combustion and co-combustion tests. Cr and Cr(VI) were mainly detected in the eluates of the 1st cyclone ashes produced in both combustion tests and in the 2nd cyclone ashes produced in the co-combustion test.Considering the ecotoxicity assays, the eluates of bottom and fly ashes for both combustion and co-combustion tests have shown low ecotoxic levels. The micro-crustacean Daphnia magna was generally more sensitive than the bacterium Vibrio fischeri. CEMWE criterion has allowed to classify the bottom ashes for both combustion and co-combustion tests as non-toxic residues and the fly ashes collected in both cyclones as toxic.     

Topography of collapsed triglyceride monolayers on glass

The stability and conformation of tripalmitin (TP) and triolein (TO) Langmuir‐Blodgett (LB) monolayers on glass were investigated using Atomic Force Microscopy (AFM). Compression isotherms revealed that TP reached the solid state at 15 mN m⁻¹, with a trident conformation. LB deposition of the monolayer on the glass surface was performed at the solid state (30 mN m⁻¹) with a transfer ratio close to 1. The TO monolayer collapsed in the liquid‐expanded phase at 13 mN m⁻¹. LB deposition was performed at 11 mN m⁻¹ with a transfer ratio of 1.4. The LB films were imaged by AFM (tapping mode). The TO monolayer collapsed in amorphous droplets. TP presented tiny amorphous drops plus crystalline shapes with unit layers of a thickness of 40—46 Å, corresponding to the long spacing of the β and α polymorphic forms. TP monolayer thus collapsed in aggregates to form crystalline structures. The thickness of the first step was mostly 86 Å, but sometimes 68 Å steps were observed, while the transferred monolayer generally reorganizes as a tuning fork in a regular crystalline unit, but can also remain as a trident, providing a hydrophobic support for upper layers. This findings supply backing for technical processes such as the interpretation of fat fractionation by microfiltration membranes, based on triglyceride/solid interaction statements.     

Absorbed water in the cork structure. A study by thermally stimulated currents,dielectric relaxation spectroscopy,isothermal depolarization experiments and differential scanning calorimetry

This paper reports on a modification of the dielectric properties of cork which occurs as a consequence of heating above 60° C or evacuation for several days. This phenomenon was observed using different experimental techniques (thermally stimulated currents, dielectric relaxation spectroscopy, isothermal depolarization experiments and differential scanning calorimetry), and the corresponding kinetics were analysed. It was observed that the original properties of cork were recovered if the sample was exposed to room air for several weeks. It is suggested that the reported modification of the dielectric properties arises from desorption, induced by heating or evacuation, of water molecules absorbed in the cork structure.     

The molecular relaxation mechanisms in cork as studied by thermally stimulated discharge currents

The dielectric relaxation mechanisms present in cork have been investigated in the temperature range -100 to 100 °C using the technique of thermally stimulated discharge currents. A relaxation mechanism was detected which showed a compensation behaviour as observed for the -relaxation (or glass transition relaxation) of synthetic polymers and which lead us to attribute to cork a glass transition-like temperature of 18 °C. One lower temperature mechanism was also observed, with low activation enthalpy and entropy, which is presumably originated by local motions (internal rotations) of polar molecular groups. An upper T _g relaxation of higher intensity was also detected which was attributed to large-scale non-cooperative motions of polymeric segments.     

Functionalization of chitosan membranes through phosphorylation: Atomic force microscopy,wettability, and cytotoxicity studies

Grafting negatively charged groups such as phosphates is a well‐known strategy for inducing the deposition of apatite‐like layers under simulated physiological conditions. In this investigation, chitosan was phosphorylated in an attempt to enhance its osteoconduction. Chitosan membranes were phosphorylated at 30°C with the H₃PO₄/Et₃PO₄/P₂O₅/butanol reaction system for periods up to 48 h. This method is an alternative to the phosphoric acid/urea/dimethylformamide phosphorylation method, which involves the use of much higher temperatures. In this study, the effects of the phosphorylation reaction time on the surface morphology and surface free energy of phosphorylated membranes were investigated with atomic force microscopy and static‐contact‐angle measurements, respectively. In addition, the modified membranes were evaluated with respect to their cytotoxicity toward bone cells through the incubation of human osteoblastic cells with extracts of the materials for two different periods: 24 and 120 h. The results revealed a reduction of the average surface roughness at the nanometer scale with increasing phosphorylation reaction time. Wettability studies showed an increase in the polar component of the surface free energy with increasing reaction time as a result of the increase in the phosphate surface concentration. Cytotoxicity studies revealed no cytotoxic effect of phosphorylated membranes on osteoblastic cells, regardless of the incubation period. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 276–284, 2006     

Ionic Liquid with Silyl Substituted Cation: Thermophysical and CO2/N2 Permeation Properties

Novel functionalized ionic liquid (IL) combining an imidazolium‐based cation with branched alkyl chain bearing silyl group, 1‐methyl‐3‐(2‐methyl‐3‐(trimethylsilyl)propyl)imidazolium ([Si?C₁?C₃‐mim]⁺), and bis(trifluoromethylsulfonyl)imide ([NTf₂]^?) anion was synthesized and its thermophysical properties (density, viscosity, surface tension, surface entropy and enthalpy, thermal stability) were studied in a wide temperature range and compared with those of ILs having linear alkyl ([C_n‐mim][NTf₂]) and siloxane ([(SiOSi)C₁mim][NTf₂]) side chains. It was found that at 25 °C [Si?C₁?C₃‐mim][NTf₂] is a liquid with dynamic viscosity of 224 cP (224 mPa s) and density of 1.32 g cm^?3. The presence of side branched alkyl chain with trimethylsilyl end‐group prevents crystallization of IL and leads to higher viscosities and lower densities in comparison with commonly known [C_n‐mim][NTf₂] (n=2–4). As surface excess enthalpy was found to be in the lower end of the usual range of values for ILs, the interactions between silyl‐functionalized cation and [NTf₂] anion can be considered as relatively weak. Finally, [Si?C₁?C₃‐mim][NTf₂] was used for the preparation of polymer supported ionic liquid membranes (SILMs) and their CO₂ and N₂ permeation properties at 20 °C and 100 kPa were determined: permeability PCO₂=311, PN₂=12 Barrer, diffusivity DCO₂=115×10¹², DN₂=227×10¹² m² s^?1 and CO₂/N₂ permselectivity αCO₂/N₂=25.3.