Studies on thermal,mechanical, morphological,and viscoelastic properties of polybenzimidazole fiber reinforced high density polyethylene composites

High density polyethylene (HDPE) and polybenzimidazole fiber (PBI) composites were prepared by melt blending in a twin screw extruder. The thermomechanical properties of PBI fiber reinforced HDPE composite samples (1%, 4%, and 8%) of fiber lengths 3 mm and 6 mm were investigated using differential scanning calorimeter (DSC), universal testing machine, rheometer, and scanning electron microscopy (SEM). The effects of fiber content and fiber lengths on the thermomechanical properties of the HDPE‐PBI composites were studied. The DSC analysis showed a decrease in crystallinity of HDPE‐PBI composites with an increase of fiber loading. SEM images revealed homogeneous distribution of the fibers in the polymer matrix. The thermal behavior of the composites was evaluated from thermogravimetric analysis and the thermal stability was found to increase with the addition of fibers. The evidence of homogeneous distribution was verified by the considerably high values of tensile strength and flexural strength. In the rheology study, the complex viscosities of HDPE‐PBI composites were higher than the HDPE matrix and increased with the increasing of PBI fiber loading. POLYM. COMPOS., 5–13, 2016. © 2014 Society of Plastics Engineers     

Activity and stability enhancement of α-amylase treated with sub- and supercritical carbon dioxide

Various physical, chemical and genetic approaches have been applied in order to enhance enzyme stability and activity. In this study, the aim was to investigate the capability of sub- and supercritical carbon dioxide to alter the stability and activity of α-amylase as an alternative technique. The effects of operational parameters such as pressure (50-300 bar), temperature (28-80 °C), CO? flow (2-10 g min?1) and time (60-180 min) were evaluated in regard to the activity and stability of fungal based α-amylase from Aspergillus oryzea. The activity of untreated enzyme was determined as 17,726 μmol/ml/min. While both sub- and supercritical conditions enhanced the activity, the increase in flow rate had an adverse effect and the activity was decreased by 28.9% at a flow rate of 10 g min?1 under supercritical conditions. Nuclear magnetic resonance (NMR) spectra of untreated enzyme and treated samples exhibiting the lowest and the highest activities were almost identical except for the chemical shifts observed at the lowest activity sample from 4.0 to 4.4 ppm which were assigned to protons of hydrogen-bonded groups. Optimum conditions were determined as 240 bar, 41 °C, 4 g min?1 CO? flow and 150 min of process duration yielding 67.7% (29,728 μmol/ml/min) higher activity than the untreated enzyme providing fundamental basis for enzymatic applications.     

MC-LMAC: A multi-channel MAC protocol for wireless sensor networks

In traditional wireless sensor network (WSN) applications, energy efficiency may be considered to be the most important concern whereas utilizing bandwidth and maximizing throughput are of secondary importance. However, recent applications, such as structural health monitoring, require high amounts of data to be collected at a faster rate. We present a multi-channel MAC protocol, MC-LMAC, designed with the objective of maximizing the throughput of WSNs by coordinating transmissions over multiple frequency channels. MC-LMAC takes advantage of interference and contention-free parallel transmissions on different channels. It is based on scheduled access which eases the coordination of nodes, dynamically switching their interfaces between channels and makes the protocol operate effectively with no collisions during peak traffic. Time is slotted and each node is assigned the control over a time slot to transmit on a particular channel. We analyze the performance of MC-LMAC with extensive simulations in Glomosim. MC-LMAC exhibits significant bandwidth utilization and high throughput while ensuring an energy-efficient operation. Moreover, MC-LMAC outperforms the contention-based multi-channel MMSN protocol, a cluster-based channel assignment method, and the single-channel CSMA in terms of data delivery ratio and throughput for high data rate, moderate-size networks of 100 nodes at different densities.     

Slow, fast and flash pyrolysis of rapeseed

Pyrolysis experiments have been conducted on a sample of rapeseed to determine particularly the effects of pyrolysis temperature, heating rate, particle size and sweep gas flow rate on the pyrolysis product yields and their chemical compositions. The maximum oil yield of 73% was obtained at the final pyrolysis temperature of 550–600 °C, particle size range of +0.6–1.25 mm, and sweep gas flow rate of 100 cm³min⁻¹ (N₂) at flash pyrolysis conditions in tubular transport reactor. Chromatographic and spectroscopic studies on the pyrolytic oil showed that the oil obtained from rapeseed can be used as a renewable fuel and chemical feedstock.     

Relationships between acute toxicities of para nitrophenol (p-NP) and nitrobenzene (NB) to Daphnia magna and Photobacterium phosphoreum: physicochemical properties and metabolites under anaerobic/aerobic sequentials

In this study, the acute toxicities of nitrobenzene (NB) and para nitrophenol (p-NP) were investigated in a high rate sequential anaerobic migrating blanket (AMBR)/aerobic completely stirred tank reactor (CSTR) using Microtox and Daphnia magna tests. After sequential anaerobic and aerobic treatments, the inhibitions in the Microtox bacteria decreased from an initial 78.10-48.20% and 4.00%, respectively, in wastewater containing 40.00 mg/L p-NP. The inhibitions of the influent wastewater containing 60.00 mg/L NB decreased from 72.10% to 45.30% and to 4.00% after anaerobic and aerobic treatment, respectively. The acute toxicity removals were 94% and 93% in the effluent of the whole sequential system, for p-NP and NB, respectively. The acute toxicity in the influent was dependent on the parent NB and p-NP concentrations and ons their physicochemical properties such as hydrophobicity, octanol/water partition coefficient and vapour density for both Microtox bacteria and Daphnia magna while the toxicity in the effluent of the anaerobic reactor was strongly dependent on the metabolites of p-NP (p-amino phenol, phenol, NH(4)-N) and NB (aniline) for Microtox test. This effluent was not toxic to Daphnia magna.     

Decolorization of malachite green, decolorization kinetics and stoichiometry of ozone-malachite green and removal of antibacterial activity with ozonation processes

This study aimed to identify degradation intermediates and to investigate the stoichiometry of decolorization and degradation, decolorization kinetics, and removal of antibacterial activity of malachite green (MG) using ozonization processes. The decolorization of MG was optimal at an acidic pH value of 3 based on molecular ozone attack on MG molecules. The stoichiometric ratio of decolorization between ozone and MG was calculated to be 7.0 with a regression coefficient of 0.995, whereas the ratio for degradation was calculated as 13.1 with a regression coefficient of 0.998. With MG concentrations in the range of 0.30-1.82 mM, the concentration of decolorized MG increased with higher initial concentrations of MG, whereas the ozonolytic decolorization rates of MG, decreased with increasing initial concentration. The pseudo-first-order degradation rate constants (k') decreased with the initial concentration and ranged from 0.769 to 0.223 min(-1). Twelve different intermediates were produced during the ozonation of MG with ozonation times between 5 min and 30 min and were identified by GC-MS. Although 86% of MG in the reaction mixture was removed by ozonation after 10 min, the decrease of antibacterial activity was very low (10%) for Bacillus subtilis and Staphylococcus epidermidis because the degradation intermediates, phenol and benzoic acid, also have antibacterial activity. The antibacterial activity of both MG and its intermediates were removed successfully with ozonation times above 26 min.     

Distributed Resource Allocation for Femtocell Networks: Regret Learning with Proportional Self-belief

Femtocell networks promise improvement in network quality and performance for dense wireless networks, but will suffer from inter-cell interference if resource management is not properly employed. This paper presents distributed joint resource allocation (sub-channel and power) to address co- and cross-tier interference issues in two-tier heterogeneous femtocell networks. Due to uncoordinated nature of femtocell base stations (HeNB) deployment, the interactions among self-interested HeNBs are formulated using game-theoretical tools. Then, we designed individual utility function for every HeNB in order to enforce cooperative behaviour among HeNBs as well as to avoid cross-tier interference towards macrocell user equipments within HeNB coverage. Based on the designed utility function, we propose a fully distributed adaptive learning algorithm with a proportional self-belief concept that can lead to correlated equilibrium with fast and decisive convergence. Finally, performance analysis on the proposed algorithm done in simulated environment showed positive results indicating improvements in terms of co- and cross-tier interference mitigation as compared to generic regret-based learning scheme and utility functions.     

Determination of the group and phase velocities from time–frequency representation of Wigner–Ville

The experimental measurement of the group and phase velocities of some circumferential waves propagating around a thin elastic tube is a still complex operation. In this study, we show that the dispersion velocity can be determined from a time–frequency representation. We use the Wigner–Ville method by virtue of its interesting properties. On some time–frequency images, the symmetric (S0) and antisymmetric (A1) circumferential waves are identified. The group velocity dispersion estimated from these images is compared with that computed by the proper mode theory method. A good agreement is obtained. The phase velocity is also determined from the group velocity.     

All-organic PANI–DBSA/PVDF dielectric composites with unique electrical properties

Novel all-organic polymer high-dielectric permittivity composites of polyaniline (PANI)/poly (vinylidene fluoride) (PVDF) were prepared by solution method and their dielectric and electric properties were studied over the wide ranges of temperatures and frequencies. To improve the interface bonding between two polymers, dodecylbenzenesulfonic acid (DBSA), a bulky molecule containing a polar head and a long non-polar chain was used both as a surfactant and as dopant in polyaniline (PANI) synthesis. Synthesized conducting PANI–DBSA particles were dispersed in poly(vinylidene fluoride) (PVDF) matrix to form an all-organic composite with different PANI–DBSA concentrations. Near the percolation threshold, the dielectric permittivity of the composites at 100 Hz frequency and room temperature was as high as 170, while the dielectric loss tangent value was as low as 0.9. Like typical percolation system, composites experienced high dielectric permittivity at low filler concentrations. However, their dielectric loss tangent was low enough to match with non-percolative ceramic filler-based polymer composites. Maximum electrical conductivity at 24 wt% of PANI–DBSA was mere 10^?6 S/cm, a remarkably low value for percolative-type composites. Increase in the dielectric permittivity of the composites with increase in temperature from 25 to 115 °C for different PANI–DBSA concentrations was always in the same range of 50–60 %. However, the degree of increase in the electrical conductivity with the temperature was more prominent at low filler concentrations compared with high filler concentrations. Distinct electrical and their unique thermal dependence were attributed to an improved interface between the filler and the polymer matrix.     

Conducting nanocomposites of polyaniline/nylon 6,6/zinc oxide nanoparticles: preparation,characterization and electrical conductivity studies

Nanocomposites of polyaniline as a conducting polymer and main matrix, zinc oxide nanoparticles as inorganic filler and nylon 6,6 as supporting matrix were prepared by solution mixing process in a common solvent. DC electrical conductivity and its thermal stability at different temperatures under ambient atmospheric conditions were studied for the nanocomposites. The stability studies were carried out by two slightly different techniques, i.e., cyclic ageing and isothermal ageing. The results showed that the DC electrical conductivity of the nanocomposites decreased with increase in the content of zinc oxide nanoparticles whereas the thermal stability in terms of DC electrical conductivity retention was slightly improved in few cases but not for all samples. The advance analytical techniques such as Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy, transmission electron microscopy, thermogravimetric analysis and X-ray diffraction (XRD) were also used to characterize the selected samples. It was also observed that zinc oxide nanoparticles in the nanocomposites were homogeneously distributed; however, some clusters/aggregates were also present. The FTIR results showed the existence of some interaction between the individual components of the nanocomposites as evident from the little shift in the peaks of FTIR spectra. This result was also supported by XRD data.