982 resultados para antiwear additives


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Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

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Recycled polymer matrix composites reinforced with wood flour can be a viable alternative for the replacement of wood and virgin polymers in materials used in floors, door frames, windows and external cladding. The objective of this research was to determine some physical and mechanical parameters of composite made with Pinus taeda and elliottii wood flour (WF) and recycled polypropylene (PP), without the use of compatibilizers or additives. The composites were separated into four traits, namely 100% PP, 90% PP with 10%, WF 80% PP with 20% WF and 70 % PP with 30% WF. The characterization of the composite followed the standards ASTM D-638-10, ASTM D256-00, ASTM D570 -98, ASTM D1238 -10 and ASTM G 155-05, it was also employed the surface analysis by scanning electron microscopy. The dimensional stability tests showed satisfactory results. Even the composite with a higher percentage of wood flour (30%) had a flow index of 10 MFI, considered compatible with that observed for PP (polypropylene) virgin by standard ASTM D 1238-10. The inclusion of wood flour (FM) afforded composites with good mechanical characteristics which can be applied in manufacture of different materials, specifically employed outdoors.

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Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

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The aim of this study was to evaluate the ability of conventional toothpastes (1100 ppm F) supplemented with sodium trimetaphosphate (TMP) in demineralization. Blocks of enamel were selected and then divided into seven experimental groups of 12: toothpaste without F and TMP (placebo), toothpaste with 1100 ppm F (1100), and toothpaste with 1100 ppm F supplemented with TMP-1 % (1100 1 % TMP), 3 % (1100 3 % TMP), 4.5 % (1100 4.5 % TMP), 6 % (1100 6 % TMP), and 9 % (1100 9 % TMP). Blocks were subjected to five pH cycles (demineralizing/remineralizing solutions) at 37 °C and treated with toothpaste slurries twice daily, after which the blocks were maintained for 2 days in fresh remineralizing solution. Following treatments, surface hardness (SHf) and cross-sectional hardness were determined for calculating the integrated loss of subsurface hardness (ΔKHN). The fluoride present in the enamel was also measured. The SHf and ΔKHN measurements showed that supplementation with 3 % TMP was the most effective (p < 0.001) and showed greater concentration of F in the enamel (p < 0.001). Addition of 3 % TMP to a conventional toothpaste (1100 ppm F) showed greater efficacy in reducing enamel demineralization. Fluoride toothpastes containing trimetaphosphate possess good anticaries potential required to reduce the prevalence of dental caries in high-risk patients.

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Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

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In this research the aim was produce and evaluate a plastic composite using recycled polypropylene (PP) and fibers from sugarcane bagasse residues (SC), without the use of additives. This analysis was based on laboratorial tests for physical and mechanical characterization, according to the standards ASTM D256-00, D638-101 and D570-98 were analyzed: water absorption, thickness swelling, impact resistance, tensile strength and its correspondent deformation. For comparison it was elaborated three different compositions: 100% PP; 80% PP+20%SC; 70%PP+30%SC. The results indicate a positive correlation with the content of fiber and water absorption and thickness swelling. In the tension tests, the composites with fibers increase the value of resistance for physical efforts, bringing advantages as durability and integrity of the material, showing a viability of the composites.

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In this research the aim was produce and evaluate a plastic composite using recycled polypropylene (PP) and fibers from sugarcane bagasse residues (SC), without the use of additives. This analysis was based on laboratorial tests for physical and mechanical characterization, according to the standards ASTM D256-00, D638-101 and D570-98 were analyzed: water absorption, thickness swelling, impact resistance, tensile strength and its correspondent deformation. For comparison it was elaborated three different compositions: 100% PP; 80% PP+20%SC; 70%PP+30%SC. The results indicate a positive correlation with the content of fiber and water absorption and thickness swelling. In the tension tests, the composites with fibers increase the value of resistance for physical efforts, bringing advantages as durability and integrity of the material, showing a viability of the composites.

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Fewer and fewer Americans produce their own food, yet consumers demand and enjoy a food supply that is flavorful, nutritious, convenient, readily available, safe, abundant, varied, and reasonably priced. Food additives and technology make that possible. This research publication covers what food additive are, why are they used, how they are regulated, and what can individuals do when they are concerned about food additives. It also contains a guide to food additives table.

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The aim of this study was to evaluate the erosive potential of orange juice modified with food-approved additives: 0.4 g/l of calcium (Ca) from calcium lactate pentahydrate, 0.2 g/l of linear sodium polyphosphate (LPP) or their combination (Ca+LPP) were added to a commercially available orange juice (negative control, C-). A commercially available calcium-modified orange juice (1.6 g/l of calcium) was the positive control (C+). These juices were tested using a short-term erosion in situ model, consisting of a five-phase, single-blind crossover clinical trial involving 10 subjects. In each phase, subjects inserted custom-made palatal appliances containing 8 bovine enamel specimens in the mouth and performed erosive challenges for a total of 0 (control), 10, 20, and 30 min. Two specimens were randomly removed from the appliances after each challenge period. Enamel surface microhardness was measured before and after the clinical phase and the percentage of surface microhardness change (%SMC) was determined. Before the procedures, in each phase, the subjects performed a taste test, where the juice assigned to that phase was blindly compared to C-. Overall, C+ showed the lowest %SMC, being the least erosive solution (p < 0.05), followed by Ca+LPP and Ca, which did not differ from each other (p > 0.05). LPP and C- were the most erosive solutions (p <0.05). Taste differences were higher for C+ (5/10 subjects) and Ca (4/10 subjects), but detectable in all groups, including C- (2/10 subjects). Calcium reduced the erosive potential of the orange juice, while no protection was observed for LPP. Copyright (C) 2012 S. Karger AG, Basel

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The objective of this study was to evaluate the effects of adding alkalis on the fermentative pattern, aerobic stability and nutritive value of the sugarcane silage. A completely randomized design with 6 additives in two concentrations (1 or 2%), plus a control group, totalizing 13 treatments [(6x2)+1] with four replications, was used. The additives were sodium hydroxide (NaOH), limestone (CaCO3), urea (CO(NH2)(2)), sodium bicarbonate (NaHCO3), quicklime (CaO) and hydrated lime (Ca(OH)(2)). The material was ensiled in 52 laboratory silos using plastic buckets with 12 L of capacity. Silos were opened 60 days after ensiling, when organic acids concentration, aerobic stability and chemical composition were determined. The Relative Biological Efficiency (RBE) was calculated by the slope ratio method, using the data obtained from ratio between desirable and undesirable silage products, according to the equation: D/U ratio = [lactic/(ethanol + acetic + butyric)]. All additives affected dry matter, crude protein, acid detergent fiber, neutral detergent fiber contents and buffering capacity. Except for urea and quicklime, all additives increased the in vitro dry matter digestibility. In general, these additives altered the fermentative pattern of sugarcane silage, inhibiting alcoholic fermentation and improving lactic acid production. The additive that showed the best RBE in relation to sodium hydroxide (100%) was limestone (89.4%). The RBE values of urea, sodium bicarbonate and hydrated lime were 49.2%, 47.7% and 34.3%, respectively.

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USE OF ADDITIVES IN THE WOOD BIODEGRADATION BY THE FUNGUS Ceriporiopsis subvermispora: EFFECT IN THE MANGANESE PEROXIDASE-DEPENDENT LIPID PEROXIDATION. Ceriporiopsis subvermispora is a selective fungus in the wood delignification and the most promising in biopulping. Through the lipid peroxidation initiated by manganese peroxidase (MnP), free radicals can be generated, which can act in the degradation of lignin nonphenolic structures. This work evaluated the prooxidant activity (based in lipid peroxidation) of enzymatic extracts from wood biodegradation by this fungus in cultures containing exogenous calcium, oxalic acid or soybean oil. It was observed that MnP significant activity is required to promote lipid peroxidation and wood delignification. Positive correlation between prooxidant activity x MnP was observed up to 300 IU kg(-1) of wood.

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Objectives: To evaluate the effect of additives on the water sorption characteristics of Bis-GMA based copolymers and composites containing TEGDMA, CH(3)Bis-GMA or CF(3)Bis-GMA. Material and methods: Fifteen experimental copolymers and corresponding composites were prepared combining Bis-GMA and TEGDMA, CH(3)Bis-GMA or CF(3)Bis-GMA, with aldehyde or diketone (24 and 32 mol%) totaling 30 groups. For composites, barium aluminosilicate glass and pyrogenic silica was added to comonomer mixtures. Photopolymerization was effected by 0.2 wt% each of camphorquinone and N,N-dimethyl-p-toluidine. Specimen densities in dry and water saturated conditions were obtained by Archimedes' method. Water sorption and desorption were evaluated in a desorption-sorption-desorption cycle. Water uptake (%WU), water desorption (%WD), equilibrium solubility (ES; mu g/mm(3)), swelling (f) and volume increase (%V) were calculated using appropriate equations. Results: All resins with additives had increased %WU and ES. TEGDMA-containing systems presented higher %WU, %WD, ES, f and %V values, followed by resins based on CH(3)Bis-GMA and CF(3)Bis-GMA. Conclusions: Aldehyde and diketone led to increases in the water sorption characteristics of experimental resins.

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Yolk color and egg white (albumen) cleanliness and viscosity are important parameters by which consumers judge the quality of eggs. This study aimed to investigate changes in albumen viscosity during storage of eggs for up to 36 days from two different commercial laying hen strains (Carijo Barbada and Isa Brown) fed a diet containing annatto (1.5 and 2.0%) or a synthetic additive without synthetic colorants (control). Analyses of humidity, albumen height, pH, viscosity, foam formation, and stability were carried out on eggs. Carijo Barbada strain had smaller albumen, lower humidity and higher egg white viscosity than Isa Brown strain; however, with storage, viscosity lowered significantly on both strains. Initially, the addition of 2.0% of annatto or a synthetic additive increased viscosity in both strains, but with storage only the control maintained longer viscosity. Lower viscosity did not change foam density and stability.

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Polystyrene latex particles modified at the surface with different hydrophilic functional groups were prepared by miniemulsion polymerization and applied to control the crystallization of zinc oxide in aqueous medium. The effects of both latex structure and concentration on the crystal growth, morphology, crystalline structure, and properties of the resulting zinc oxide were analyzed. Depending on the latex additive used, micro- and submicrosized crystals with a broad variety of morphologies were obtained. Among the studied latexes, the carboxyl-derived particles were shown to be a convenient system for further quantitative investigations. In this case, as the additive concentration increases, the aspect ratio of the crystals decreases systematically. Latex particles are assumed to adsorb preferentially onto the fast growing {001} faces of ZnO, interacting with the growth centers and reducing the growth rate in [001]. When zinc oxide is precipitated in the presence of latex, the polymer particles become incorporated into the growing crystals and polymer–inorganic hybrid materials are obtained. These materials are composed of an inorganic and largely undisturbed crystalline matrix in which organic latex particles are embedded. Increasing amounts of latex become incorporated into the growing crystals at increasing overall concentration in the crystallizing system. Photoluminescence (PL) spectra were measured to obtain information on defect centers. Emission spectra of all samples showed a narrow UV peak and a broad band in the green-yellow spectral region. The former emission is attributed to exciton recombination, whereas the latter seems to be related with deep-level donors. Latex appears to be a quencher of the visible emission of zinc oxide. Thus, compared to pure zincite, ZnO–latex hybrid materials show a significantly lower PL intensity in the visible range of the spectrum. Under continuous photoexcitation, a noticeable dynamic behavior of the PL is observed, which can be related to a photodesorption of adsorbed oxygen. These surface-adsorbed oxygen species seem to play a crucial role for the optical properties of the materials and may mediate the tunneling of electrons from the conduction band to preexisting deep-level traps, probably related to intrinsic defects (oxygen vacancies or interstitial zinc). The polymer particles can block the sites where oxygen adsorbs, and the disappearance of the “electron-shuttle” species leads to the observed quenching of the visible emission. Electron paramagnetic resonance (EPR) provided additional information about crystal defects with unpaired electrons. Spectra of all samples exhibit a single signal at g ≈ 1.96, typical for shallow donors. Contrary to the results of other authors, no correlation was possible between the EPR signal and the visible range of PL spectra, which suggests that centers responsible for the visible emission and the EPR signal are different.