Shear flow effect on the crystalline forms in polyamide 6/montmorillonite nanocomposites

The influence of shear flow on the crystallization of polyamide 6/MMT nanocomposites prepared by melt intercalation process was investigated in detail by differential scanning calorimetry. The melted nanocomposites were controlled sheared in the steady and oscillatory shear flow, using a rotational rheometer, and cooled in an inert atmosphere. The effects of shear rate or frequency, clay concentration, and crystallization conditions on PA 6 crystalline phase development were studied. As expected, an opposite impact of shearing on γ‐phase formation in the nanocomposites and neat matrix was found. Surprisingly, a critical shear frequency for the onset of γ‐form crystallinity formation in the nanocomposites, increasing with the filler content as a consequence of polymer chains confinement within oriented clay platelets was found. At higher shear frequencies, the proportion of γ‐form in the nanocomposites increased dramatically with the clay concentration and reached 30–40%. The shear flow effects were influenced by cooling conditions, and more significant effect for rapidly cooled samples was observed. The isothermal crystallization at the solidification temperature 205°C reduced the γ‐form content. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Flame‐retardant effect of polyaniline coating deposited on cellulose fibers

Filtration paper was coated with a thin polyaniline film. The content of conducting polymer was 8.2 and 6.3 wt % for polyaniline hydrochloride and polyaniline base, respectively. After burning, the coated material retains the original fibrilar morphology of cellulose. The polyaniline coating converts to solid carbonaceous products. The resulting structure prevents the formation of gaseous carbon oxides by restricting the access of oxygen to cellulose. While the ash from the uncoated paper after burning is 0.005 wt %, the microtubular residue of polyaniline‐coated paper is 16–24 wt % of the original mass. The flame‐retardant performance of polyaniline and poly(1,4‐phenylenediamine) coatings was comparable both for the protonated forms and the corresponding bases. The conversion of polyaniline‐coated cellulose fibers to solid pyrolytic products was characterized by FTIR and Raman spectroscopies. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 2347–2354, 2005     

Streptomycetes cultured on glass beads: Sample preparation for SEM

We demonstrate the preparation of samples of streptomycetes (Streptomyces coelicolor, S. aureofaciens) cultured on glass beads (balotina) for scanning electron microscopy. The main trick of the method consists in immobilization of glass beads with low-melting agarose. The samples are then fixed in OsO(4) vapors followed by dehydration in vapors of absolute ethanol. No air-to-liquid transition during the sample preparation occurs. Consequently, whole cell cycle of streptomycetes in the term of mycelial morphology can readily be studied by this method.     

Eulerian-Lagrangian model for traffic dynamics and its impact on operational ventilation of road tunnels

This contribution deals with a computational Eulerian-Lagrangian model that simulates movement of cars inside a road tunnel and its impact on operational ventilation. The model simulates moving cars as discrete objects that “fly” through the tunnel. The objects are treated with a Lagrangian momentum equation and their velocity is solved along their trajectories that are determined by the shape of the roadway. The flow of the ambient air is solved with a commercial CFD code StarCD. Due to drag force, the cars virtually change their velocity, but the latter is continuously re-set to its original value. The momentum equation for the continuous phase contains an additional source term that results from the net efflux of momentum of cars when they enter and leave a particular control volume of the solution domain. The model by Jicha et al. (Int. J. Environ. Monit. Asses. 65 (2000) 343) can simulate cars moving at different speeds and traffic rates in individual traffic lanes. As a result we obtain flow rate generated by moving vehicles as a function of traffic speed and traffic rates. Turbulence was modelled using standard k-ε model with three different formulas for extra sources of the kinetic energy of turbulence that account for additional turbulence generated by moving vehicles. The traffic-induced turbulence shows a non-negligible effect on the total flow rate inside the tunnel. The model was validated with experimental data from Chen et al. (Int. J. Wind Eng. Ind. Aerod. 73 (1998) 99), where the small-scale tunnel 1:20 was investigated. The experiments were carried out with a moving belt carrying small car-like objects. The tunnel length was 20 m, the height 36.5 cm and the tunnel had two parallel lanes. Several traffic densities and speeds were simulated, namely 10,000, 20,000 and 30,000 cars/h per lane with speeds of 20 km/h and 40 km/h.     

The interaction of thin polyaniline films with various H‐phosphonates: Spectroscopy and quantum chemical calculations

The conducting form of polyaniline (PANI) is formed by doping of non‐conducting PANI base usually by protonic acids. An alternative way of doping, consisting in an interaction via hydrogen bonding, has been previously proven for H‐phosphonates. In this study, PANI base films are exposed to various H‐phosphonates, changes in the structure of the films are analyzed by ultraviolet–visible, infrared, and Raman spectroscopies and spectroscopic data are compared with quantum chemical calculations. According to our results, the interaction of the PANI base films with H‐phosphonates is realized by hydrogen bonding between the imine nitrogen of PANI and the hydroxy group of the H‐phosphonate tautomeric form, i.e., phosphite. This is in the contrast to the PANI powders doped with H‐phosphonates where both interacting phosphite and non‐interacting H‐phosphonate forms were observed. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46728.     

Bio-mechanochemical synthesis of silver nanoparticles with antibacterial activity

By using a bio-mechanochemical approach combining mechanochemistry (ball milling) and green synthesis for the first time, silver nanoparticles (Ag NPs) with antibacterial activity were successfully synthesized. Concretely, eggshell membrane (ESM) or Origanum vulgare L. plant (ORE) and silver nitrate were used as environmentally friendly reducing agent and Ag precursor, respectively. The whole synthesis took 30?min in the former and 45?min in the latter case. The photon cross-correlation measurements have shown finer character of the product in the case of milling with Origanum. UV–Vis measurements have shown the formation of spherical NPs in both samples. TEM study has revealed that both samples are composites of nanosized silver nanoparticles homogenously dispersed within the organic matrices. It has shown that the size and size distribution of the silver nanoparticles is smaller and more uniform in the case of eggshell membrane matrix implying lower silver mobility within this matrix. The antibacterial activity was higher for the silver nanoparticles synthesized with co-milling with Origanum plant than in the case of milling with eggshell membrane.     

Simplification of separation of the reaction mixture after transesterification of vegetable oil

A heterogeneous reaction mixture is formed by transesterification of vegetable oils. The reaction mixture contains mainly methyl esters of higher fatty acids and glycerol. From this mixture, biodiesel is gained by spontaneous sedimentation in the gravitational field. The sedimentation can be considerably accelerated by controlled addition of water. It was found that addition of small amounts of water to the crude reaction mixture significantly affected the mixture, and substantial changes in the speed of the separation took place. Considerable differences in the composition and quality of the ester and glycerol phases occurred. The optical properties (transmittance and refractive indices) of the heterogeneous reaction mixture are changed after addition of water; this change can be observed spectrophotometrically. This method is applicable to all types of vegetable oils including waste frying oils.     

Multiscale modelling of nanoindentation test in copper crystal

The nanoindentation test in the dislocation free crystal of copper is simulated by a nonlinear elastic finite element analysis coupled with both ab initio calculations of the ideal shear strength and crystallographic considerations. The onset of microplasticity, associated with the pop-in effect identified in experimental nanoindentation tests (creation of first dislocations), is assumed to be related to the moment of achieving the value of the ideal shear strength for the copper crystal. Calculated values of the critical indentation depth lie within the range of experimentally observed pop-ins in the copper crystal. The related indentation load is somewhat lower than that observed in the experiment.