Preparation of partially neutralized poly(acrylic acid) microspheres via inverse pickering suspension polymerization

Partially neutralized poly(acrylic acid) (PAA) microspheres have been prepared by Inverse Pickering Suspension Polymerization (IPSP) using 1,2‐dichlorobenzene (DCB) and hydrophobic fumed silica nanoparticles (HFSi‐NPs) as organic dispersing media and dispersing agent respectively. As crosslinker N,N'‐methylene bisacrylamide (MBAc), as initiator potassium persulfate (KPS) and sodium metabisulfite (SMBS) redox couple were used. Neutralization degrees were adjusted using 8N NaOH solution and polymerizations were initiated at 34°C. Water/oil phase ratio was set to 1/7 for all polymerizations. Morphology of prepared dry poly(acrylic acid) beads was examined by two microscopic methods, scanning electron microscopy (SEM) and optical microscopy. Prepared microsized polymer beads were observed as smooth and spherical in shape. Effect of neutralization degree (α) varied from 70% to 90% on absorptions in both distilled water and saline solutions, absorption under load (AUL) and crosslink density (CD) results were also investigated. POLYM. ENG. SCI., 59:162–169, 2019. © 2018 Society of Plastics Engineers     

Role of organic additives on non-aqueous tape casting of SiAlON ceramics

Suspensions consisting of precursor α/β SiAlON forming powders, azeotropic solvent mixture of 60 MEK/40E, dispersant, binder, and plasticizer were optimized for tape casting by rheological measurements and tape properties. Sodium tripolyphosphate (STPP) was introduced as a dispersant for low temperature applications of α/β-SiAlONs. Optimum STPP amount was determined as 0.012 g/m² (of the particle surface) for stable α/β-SiAlON suspensions. Different amounts of binder/plasticizer mixtures were added to the slurries and the effects on rheological and green tape properties were investigated. Green tapes with dibutyl phthalate (DBP), and plasticizer mixture, poly(ethylene glycol) (PEG) and DBP, exhibited centered cracks with high plasticity, on the other hand, polyvinyl butral (PVB) and PEG showed no crack but low plasticity. Therefore, many different parameters were found to be effective on final tape properties. In addition, tapes were prepared with 6 vol% PVB + PEG, sintered at 1800 °C for 2 h and exhibited almost 97%TD in room temperature applications of α/β SiAlONs.     

Enhancing thermal and ionic conductivities of electrospun PAN and PMMA nanofibers by graphene nanoflake additions for battery‐separator applications

The present study reports the fabrication and characterization of electrospun polyacrylonitrile (PAN) and polymethyl methacrylate (PMMA) nanofiber separators embedded with graphene nanoflakes. Different weight percentages (0, 2, 4, and 8 wt%) of graphene nanoflakes were dispersed in dimethylformamide (DMF) and ethanol using sonication and high‐speed agitations, and then PAN and PMMA powders were added to the dispersions prior to the mixing process. Ratios of 85:15 for DMF : PAN and 88:12 for ethanol : PMMA were chosen during the dispersion and dissolution processes. After the fabrication of the membranes via the electrospinning process, thermal, dielectric, ionic, and surface hydrophobic properties of the PAN and PMMA nanofiber separators were investigated in detail. Test results revealed that the physical properties, such as wettability, dielectric constant, ionic conductivity, and thermal conductivity values of the nanocomposite separators were significantly increased as a function of graphene concentrations. For example, the water contact angle, ionic conductivity, dielectric constant, and thermal conductivity values of the membranes were increased from 120° to 145°, 3.31 × 10^?4 to 5.52 × 10^?4 S/m, 3.5 to 8.5 W/m K, and 1.0 to 5.0 W/m K, respectively, when the graphene concentration was increased from 0% to 8% in PMMA. Similar trends were observed in the PAN fibers, as well. Lithium‐ion (Li‐ion) batteries have become the major source of power for portable electronic devices, and because separators are one of the major components of these batteries, the present alternatives can be an option for long‐lasting Li‐ion battery fabrications. Copyright © 2014 John Wiley & Sons, Ltd.     

Determination of textural deterioration in fish meat processed with electrospun nanofibers

Nano-applications are named as one of the novel methods, which provide many advantages like a larger contact area on the surface of fish fillets with less material. The goal of the study was to reveal the textural profile changes correlated with TPB growth of fish fillets coated with nanofibers having 2.47 ± 0.68 mV zeta potential value and 172 nm diameter. The difference of TPB count between control (CS) and the fish fillets treated with nanofibers (NG) reached 3.45 log CFU/g (p < .05) on the sixth day. The hardness value of CS was decreased (p < .05) (the decline: 68%) while the hardness of NG was found to be much more stable (the change: 42%). The highest change in springiness for CS and NG samples was determined as ~24 and ~15%, respectively, for 12 days. Cohesiveness values of CS were slightly increased, but those of the fish fillets coated with nanofibers were remarkably decreased. The coefficient of correlation analysis between TPB count and cohesiveness values was determined as “r = −.026 and r = .796” for CS and NG, respectively. Chewiness values of CS were significantly decreased (p < .05). However, chewiness values of the fish fillets coated with nanofibers were found as much more stable (p > .05). The results revealed that nanofiber coating limited the increase of TPB in fish fillets; it also better kept the textural profile of fish fillets as compared to CS stored at 4°C. The study could play a guiding role in further food nanotechnology applications in the industry and food science.     

Acrylamide–Sepiolite Based Composite Hydrogels for Immobilization of Invertase

ABSTRACT:  Novel composite hydrogels, poly(acrylamide)–sepiolite (PAS), poly(acrylamide/acrylic acid)–sepiolite (PAAS), and poly(acrylamide/itaconic acid)–sepiolite (PAIS) were prepared and used for the immobilization of invertase. The parameters of equilibrium swelling, diffusional exponent, and diffusion coefficient of these hydrogels were calculated from swelling experiments. Invertase was immobilized onto PAS, PAAS, and PAIS and immobilized invertases (PASI, PAASI, and PAISI) were prepared. Optimum pH values for free invertase, PASI, PAASI, and PAISI are found to be 5, 5.5, 4.5, and 6, respectively, and the optimum temperatures were 30, 50, 50, and 35 °C for free invertase PASI, PAASI, and PAISI. It was found that  K_m  values of free invertase, PASI, PAASI, and PAISI were 11.3, 41.0, 94.5, and 56.0 mM, respectively.  V _max values were 2 μmol/min for free invertase, 8.10 μmol/min for PASI, 1.30 μmol/min for PAASI, and 0.42 μmol/min for PAISI, respectively. The invertase immobilized hydrogels showed excellent, temperature, storage, and operational stability.     

Impact of sodium chloride on Escherichia coli O157:H7 and Staphylococcus aureus analysed using transmission electron microscopy

Abundant literature information is available on sodium chloride, NaCl, as an antimicrobial and a preservative, however, information on NaCl effects on bacterial cell morphology is lacking. The effect of NaCl, on Escherichia coli O157:H7 and Staphylococcus aureus cells individually grown in a laboratory medium was examined using transmission electron microscopy (TEM). Cultures were grown in brain heart infusion (BHI) broth containing dissolved 0%, 5%, or 10% (w/v) commercially obtained fine (FN) and extra coarse (EC) grade granular NaCl. The pathogens were incubated at 35 degrees C for 12 and 24 h. Then, a mixture of five strains of each pathogen per treatment was prepared. Samples were centrifuged, pellets collected, fixed immediately with glutaraldehyde, and prepared for TEM examination. Cells morphology on TEM micrographs verified that the magnitude of morphological damage to E. coli O157:H7 cells was significantly greater than that of S. aureus cells. More cell injury occurred as NaCl concentration increased from 5% to 10%. Generally, S. aureus maintained its cellular structure and no severe cell wall or plasma membrane damage and/or shrinkage was observed. At 10% NaCl, the damage to E. coli O157:H7 cells was extensive, and the pathogen seemed to have lost its cellular integrity. Although NaCl affected the morphology of E. coli O157:H7 and S. aureus, the coarse grade of NaCl seemed to have a milder effect with respect to cell damage, especially on S. aureus. The 24 h-old cultures were more susceptible to NaCl treatment compared to the 12 h-old cells. Thus, the age of the cells has an impact on their resistance to salt--the environmental stressor.     

Reactive gas condensation synthesis of aluminum nitride nanoparticles

Aluminum Nitride (AIN) nanoparticles were synthesized using a Reactive Gas Condensation (RGC) technique in which a mixture of ammonia (NH3) and nitrogen (N2) gases were used for the nitridation of aluminum. NH3 served as the reactive gas, while N2 served as both a carrier gas and the inert source for particle condensation. X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) analyses revealed that at reactive gas compositions greater than 10% NH3 in N2, samples were composed entirely of hexagonal AIN nanoparticles. Electron diffraction patterns showed single crystal hexagonal AIN structure. The particle size was controlled by varying the pressure of the gas mixture. AIN nanoparticles were dispersed in a liquid matrix to enhance thermal conductivity. Results showed that a minimal addition of AIN increased the thermal conductivity of hydrocarbon pump oil by approximately 27%. The thermal conductivity became constant after reaching a maximum above 0.01 wt% AIN. Temporal stability of AIN was studied by XRD. Samples exposed to air for extended periods of time and analyzed by XRD show no degradation of crystalline AIN nanoparticles.     

CHARACTERIZATION OF DISSOLUTION PRODUCTS FROM TWO TURKISH LIGNITES BY 1 H NMR, IR AND GC TECHNIQUES

Some structural features of the dissolution products from two Turkish lignites ( Beypazari and Tuncbi-lek lignites) have been investigated with proton nuclear magnetic resonance and infra-red spectroscopies and gas chromatography. The results indicate that, in general, no substantial changes occur in the structural characteristics of the soluble products obtained from different extraction conditions. This is true especially for preasphaltene and asphaltene fractions. On the other hand, some structural differences were observed in the compositions of oil fractions especially in the neutral fraction of oils from the different experimental conditions. The neutral oils from the low temperature and short time extractions are mainly consisted of alkylated aromatics and include a very small quantity of longer chain paraffins. Whereas the oils from the extractions at high temperatures and longer times include several long straight-chain paraffins (C15 - C32) with higher quantity. Hydrogen atmosphere is moderately effective for deoxygenation of the products. Dealkylation reactions for smaller molecules are insignificant but hydrogen atmosphere is relatively effective for the dealkylation of larger molecules. Higher temperature and longer extraction period accelerate the liquid phase pyrolysis.     

Characterization of phase transformations and shape memory behavior of Fe–27.79Mn–2.72Si (wt%) alloy by thermomechanical and thermal treatments

Magnetic properties and volume fraction of the phases of a Fe–27.79Mn–2.72Si (wt%) alloy have been investigated by Mössbauer spectroscopy. The microstructure has been investigated using transmission electron microscope, scattering electron microscope, and light optical microscope. The stress-induced martensitic transformation, shape memory behavior, and shape recovery processes have been studied through the differential scanning calorimetry (DSC), tensile, and bending tests. The specimen was treated by the repetition of small amount of tensile deformations at room temperature, followed by a subsequent annealing at 600 °C at every cycle for bending and tensile tests. During the tensile tests, Vickers hardness values were determined for every step of thermomechanical treatments. At low deformation rate, the shape memory effect is almost complete Bergeon et al. (A242:87, 1998), so low deformation rate was studied in this work. Bending test was another thermomechanical training procedure to see the recovery rate for this investigation.