Morphology,mechanical properties and electromagnetic shielding effectiveness of poly(styrene‐b‐ethylene‐ran‐butylene‐b‐styrene)/carbon nanotube nanocomposites: effects of maleic anhydride,carbon nanotube loading and processing method

Nanocomposites based on poly(styrene‐b‐ethylene‐ran‐butylene‐b‐styrene) (SEBS) and carbon nanotubes (CNTs) (SEBS/CNT) as well as SEBS grafted with maleic anhydride (SEBS‐MA)/CNT were successfully prepared for electromagnetic shielding applications. Both SEBS/CNT and SEBS‐MA/CNT nanocomposites were prepared by melt compounding and were post‐processed using two different techniques: tape extrusion and compression moulding. The different nanocomposites were characterized by Raman spectroscopy and rheological analysis. Their mechanical properties, electrical properties (10^-2–10⁵ Hz) and electromagnetic shielding effectiveness (8.2–12.4 GHz) were also evaluated. The results showed that the CNT loading amount, the presence of MA in the matrix and the shaping technique used strongly influence the final morphologies and properties of the nanocomposites. Whilst the nanocomposite containing 8 wt% CNTs prepared by compression moulding presented the highest electromagnetic shielding effectiveness (with a value of 56.73 dB, which corresponds to an attenuation of 99.9996% of the incident radiation), the nanocomposite containing 5 wt% CNTs prepared by tape extrusion presented the best balance between electromagnetic and mechanical properties and was a good candidate to be used as an efficient flexible electromagnetic interference shielding material. © 2018 Society of Chemical Industry     

In situ Spinel Expansion Design by Colloidal Alumina Suspension Addition

The incorporation of nano powders into refractory castables it is not a straightforward procedure, due to their agglomeration and sintering drawbacks. Considering the alumina grain size effect on the in situ spinel formation and the associated overall volumetric expansion, alumina–magnesia refractory castables containing different alumina sources were evaluated by the assisted sintering technique. Reducing the size of fine tabular alumina (<200 μm) led to lower expansion levels, indicating the main role of alumina grain size in this property. Regarding the reactive aluminas (nano alumina powder, hydratable alumina, and colloidal alumina), the composition containing colloidal alumina performed remarkably better, leading to the lowest in situ spinel expansion level as a consequence of its high sinterability. The use of nano scaled alumina suspensions was the most suitable alternative to inhibit the shortcoming of nano powder agglomeration. Conversely, the castable containing the nano alumina powder did not behave as expected. The present work pointed out that the use of nano powders in refractory castables is only feasible if the compound is fully dispersed. Otherwise, cheaper raw materials could provide even better results than those of nano agglomerated powders.     

Ultrafine grinding of sugar cane bagasse ash for application as pozzolanic admixture in concrete

Sugar cane bagasse ash, a byproduct of sugar and alcohol production, is a potential pozzolanic material. However, its effective application in mortar and concrete requires first the controlled use of grinding and classification processes to allow it to achieve the fineness and homogeneity that are required to meet industry standards. The present paper investigates the role of mill type and grinding circuit configuration in grinding in laboratory- and pilot plant-scale on the particle size, specific surface area and pozzolanic activity of the produced ashes. It was observed that, although different size distributions were produced by the different mills and milling configurations, the pozzolanic activity of the ground ash was directly correlated to its fineness, characterized by its 80% passing size or Blaine specific surface area. From a low pozzolanic activity of less than 50% of the as-received ash, values above 100% could be reached after prolonged grinding times. Electric power requirements to reach the minimum pozzolanic activity were estimated to be in the order of 42 kWh/t in an industrial ball mill. Incorporation of an ultrafinely-ground ash in a high-performance concrete in partial replacement of Portland cement (10, 15 and 20% by mass) resulted in no measurable change in mechanical behavior, but improved rheology and resistance to penetration of chloride ions.     

Does creatine supplementation improve the plasma lipid profile in healthy male subjects undergoing aerobic training?

   

We aimed to investigate the effects of creatine (Cr) supplementation on the plasma lipid profile in sedentary male subjects undergoing aerobic training.     

A novel,efficient procedure for acylation of cellulose under homogeneous solution conditions

Commercially available cellulose (Avicel PH101) was successfully acylated under homogeneous solution conditions by the following novel procedure: 2.0 g of cellulose and 5.0 g of LiCl were introduced into a glass reactor, magnetic stirring was started, the pressure was reduced to 2 mmHg, the temperature was raised to 110°C in 30 min, and the reactor was kept under these conditions for another 30 min. N,N‐Dimethylacetamide, 60 mL, was introduced, atmospheric pressure was restored, and the temperature was raised to 150°C in 30 min. The system was kept under these conditions for 1 h, then the temperature was decreased to 40°C; in 2 h a clear cellulose solution was obtained. Acid anhydride was added, and the solution was stirred at 60°C for additional 18 h. Acetates, propionates, butyrates, and acetate/butyrate mixed ester were prepared with excellent reproducibility of the degree of substitution, from 1 to 3. The degree of polymerization of cellulose is negligibly affected by these reaction conditions. The distribution of the acetyl moiety among the three OH groups of the anhydroglucose unit follows the order C₆ > C₂ > C₃. Features relevant to the industrial application of this novel procedure are discussed. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 1355–1360, 1999     

Evaluation of the occurrence of mechanical constriction of the Arc in A-TIG welding of austenitic stainless steels

This paper evaluates indications of arc constriction by the thermal and electrical insulation caused by oxides of a single component in A-TIG welding of austenitic stainless steels. Changes in arc dimensions, in its electric voltage and in weld bead morphology caused by three oxide fluxes (SiO₂, Cr₂O₃ e Al₂O₃) applied with two surface densities (30 e 60 g/m2), and with and without a flux-free central strip (of 1, 2 and 4 mm) were studied. Results showed no significant change in the width of the electric arc for the experimental conditions used, therefore not supporting a possible mechanical constriction in the electric arc by oxide electrical and thermal insulation. Lateral filming indicated that the arc is delayed by the fluxes with silica causing the strongest effect. The presence of a clean central strip in the flux layer decreased weld penetration and weld bead cross section, besides the reduction of the width of the bead. Therefore, the results of the present work seem to support Marangoni convection as the main mechanism responsible for increasing penetration in A-TIG welding of stainless austenitic steels.     

Secondary Metabolic Profile as a Tool for Distinction and Characterization of Cultivars of Black Pepper (Piper nigrum L.) Cultivated in Pará State,Brazil

This study evaluated the chemical compositions of the leaves and fruits of eight black pepper cultivars cultivated in Pará State (Amazon, Brazil). Hydrodistillation and gas chromatography–mass spectrometry were employed to extract and analyze the volatile compounds, respectively. Sesquiterpene hydrocarbons were predominant (58.5–90.9%) in the cultivars “Cingapura”, “Equador”, “Guajarina”, “Iaçará”, and “Kottanadan”, and “Bragantina”, “Clonada”, and “Uthirankota” displayed oxygenated sesquiterpenoids (50.6–75.0%). The multivariate statistical analysis applied using volatile composition grouped the samples into four groups: γ-Elemene, curzerene, and δ-elemene (“Equador”/“Guajarina”, I); δ-elemene (“Iaçará”/“Kottanadan”/“Cingapura”, II); elemol (“Clonada”/“Uthirankota”, III) and α-muurolol, bicyclogermacrene, and cubebol (“Bragantina”, IV). The major compounds in all fruit samples were monoterpene hydrocarbons such as α-pinene, β-pinene, and limonene. Among the cultivar leaves, phenolics content (44.75–140.53 mg GAE·g⁻¹ FW), the enzymatic activity of phenylalanine-ammonia lyase (20.19–57.22 µU·mL⁻¹), and carotenoids (0.21–2.31 µg·mL⁻¹) displayed significant variations. Due to black pepper’s susceptibility to Fusarium infection, a molecular docking analysis was carried out on Fusarium protein targets using each cultivar’s volatile components. F. oxysporum endoglucanase was identified as the preferential protein target of the compounds. These results can be used to identify chemical markers related to the susceptibility degree of black pepper cultivars to plant diseases prevalent in Pará State.     

Master batch approach for developing PVDF/EVA/CNT nanocomposites with co-continuous morphology and improved electrical conductivity

Conducting polymer composites constituted by co-continuous poly (vinylidene fluoride) (PVDF)/ ethylene- vinyl acetate copolymer (EVA) blends with multiwalled carbon nanotube (CNT) were prepared by melt mixing using different procedures. The effect of the master batch approach on the conductivity, morphology, mechanical, thermal and rheological properties of PVDF/EVA/CNT nanocomposites was compared with that based on one step mixing strategy. The selective extraction experiments revealed that CNT was preferentially localized in the EVA phase in all situations, even when PVDF@CNT master batch was employed. Nanocomposites prepared with EVA@CNT master batch displayed higher conductivity, whose value reached around 10⁻¹ S m⁻¹ with the addition of 0.56 vol% of CNT. The better electrical performance was attributed to the better distribution of the filler, as indicated by transmission electron microscopy and rheological behavior. The electrical and rheological behavior were also investigated as a function of the CNT content.