Effect of thermal damage on mechanical behavior and transport properties of self-compacting concrete incorporating polypropylene fibers

Explosive spalling of cementitious composites when it is heated from surface is considered to be the most dangerous effect of damage of concrete structures subjected to fire attack, especially when it occurs in restricted areas such as underground tunnels. The main objective of the study presented in this paper is to investigate the influence of high temperature on mechanical behavior, pore size distribution and transport properties of self-compacting concrete reinforced with polypropylene fibers (PPF). The experiment investigation was carried out using two mixtures with a constant water-to-binder ratio (w/b) of 0.37. Two SCCs mixtures were manufactured using an industrial cements according to European standard EN 197 1: CEM I 52.5?N (Portland cement), the difference between the mixtures is the presence of PPF. The amount of fibers used was fixed in 2?kg/m³, as recommends Eurocode 2 for high performance concrete to avoid explosive spalling. The specimens were subjected to various heating-cooling cycles from the room temperature 20?°C to 200?°C, 300?°C, 400?°C and 500?°C. The chloride resistance of the two SCC produced with the different mixtures in damaged and undamaged state are measured using a chloride migration test accelerated by an external applied electrical field. Intrinsic permeability is measured using the nitrogen gas. Klinkenberg approach is used for the determination of the intrinsic permeability. Torrent permeability measurement method was applied in this article, and a correlation was obtained between measure of intrinsic permeability and the Torrent permeability measurement. Finally, a relationship between thermal damage indicators and the increase in permeability and migration coefficients is also obtained.     

Exopolysaccharide from Pantoea sp. BCCS 001 GH isolated from nectarine fruit: production in submerged culture and preliminary physicochemical characterizations

Food Science and Biotechnology - Exopolysaccharide (EPS), as potential microbial base polysaccharide source, has plenty of applications due to its unique physicochemical structure. A Pantoea sp....     

Online ultrasonic film casting of LLDPE and LLDPE/clay nanocomposites

Transparent cast films of linear low density polyethylene (LLDPE) with nanoclay up to 10 wt % were prepared in one step process using an ultrasonically assisted compounding extruder operating at various ultrasonic amplitudes combined with film casting machine operating at various take up speeds. Thermal, rheological, morphological, and mechanical properties and gas permeability of these films were studied. Ultrasonic treatment introduced an increase in the complex viscosity and storage modulus and a reduction in the tangent loss of LLDPE/clay nanocomposite melts. Cast films prepared by ultrasonic treatment at an amplitude of 7.5 μm showed the highest mechanical properties in both the machine and transverse directions and the lowest oxygen permeability. X‐ray diffraction patterns along with the SEM and TEM images revealed the presence of the exfoliated structure due to the ultrasonic treatment for cast films containing up to 7.5 wt % of clay loading. NMR studies of LLDPE cast films showed an increase of branching due to the ultrasound treatment. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Bicomponent nanofibers from core–shell nozzle in gas jet spinning process

This work evaluates the use of a core–shell nozzle assembly in conjunction with gas jet spinning technique for production of bicomponent nanofibers from an immiscible polymer pair of polyvinylpyrrolidone (PVP) and poly(vinyl acetate) (PVAc) with three morphological forms—interpenetrating network (IPN), core–shell, and bilobal structurers—by varying the sets of miscible solvents offering different affinity for the polymers. Such fiber structures have strong potential in drug delivery and wound dressing applications. Solutions of PVP and PVAc in respective single solvents metered through a core–shell nozzle assembly meet at the exit of the nozzle and a liquid jet is initiated upon contact with a turbulent gas jet. The gas jet stretches the liquid jet into nanofibers. The results indicate that miscible solvent pairs with low affinity for one of the polymer component yield core–shell morphology with distinct polymer interfaces, while the miscible solvent pairs with high affinity for both polymers produce IPN morphology. Also, interchanging core and shell solutions does not alter the IPN morphology. Finally, bilobal nanofiber structures result from spinning of polymer solutions in miscible solvents with low affinity for the second polymer using a nonconcentric core–shell nozzle assembly. © 2020 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48901.     

Biosynthesis of xanthangum‐coated INPs by using Xanthomonas campestris

Synthesis of iron nanoparticles (INPs) with a biocompatible coating usually is a multistep process which requires harsh, special and protected reaction conditions. In the current experiment, the authors used Xanthomonas campestris cells to develop a facile method for fabrication of biocompatible INPs. Bacterial cells were supplied with ferric citrate as an iron precursor. Transmission electron microscopy micrographs exhibited that xanthan gum‐coated INPs are synthesised and deposited on the surface of X. campestris cells and produced nanoparticles were 20–80 nm in diameter with 41.7 nm mean particle size. Xanthan gum coating with about 7 nm thickness formed a clear hollow around each nanoparticle. According to thermogravimetric analysis, the coating was about 13.4% of the total INPs weight. Prepared particles had a zeta potential of −114 mv which is an ideal surface charge to make particles colloidally stable in aqueous matrixes. Xanthan gum‐coated INPs were non‐crystalline with low saturation magnetisation value of about 0.26 emu/g.Inspec keywords: nanoparticles, nanofabrication, iron, microorganisms, transmission electron microscopy, particle size, electrokinetic effects, surface charging, magnetisation, organic compoundsOther keywords: biosynthesis, xanthan gum‐coated INPs, Xanthomonas campestris cells, iron nanoparticles, biocompatible coating, bacterial cells, ferric citrate, transmission electron microscopy micrographs, mean particle size, thermogravimetric analysis, zeta potential, surface charge, saturation magnetisation, size 20 nm to 80 nm, Fe