Stirring Duration Research Articles

Enhancement of biogas production by co-digestion of potato pulp with cow manure in a CSTR system.

Anaerobic digestion (AD) process is a well-established method to generate energy from the organic wastes both from the environmental and economical perspectives. The purpose of present study is to evaluate energy production from potato wastes by incorporating cow manure into the process. Firstly, a laboratory pilot of one-stage biogas production was designed and built according to continuously stirred tank reactor (CSTR) system. The setup was able to automatically control the environmental conditions of the process including temperature, duration, and rate of stirring. AD experiment was exclusively performed on co-digestion of potato peel (PP) and cow manure (CM) in three levels of mixing ratio including 20:80, 50:50, 80:20 (PP:CM), and 0:100 as control treatment based on the volatile solid (VS) weight without adding initial inoculums. After hydraulic retention time (HRT) of 50 days on average 193, 256, 348, and 149 norm liter (LN) (kg VS)(-1), methane was produced for different mixing ratios, respectively. Statistical analysis shows that these gas productions are significantly different. The average energy was determined based on the produced methane which was about 2.8 kWh (kg VS)(-1), implying a significant energy production potential. The average chemical oxygen demand (COD) removal of treatments was about 61%, showing that it can be leached significantly with high organic matter by the employed pilot. The energy efficiency of 92% of the process also showed the optimum control of the process by the pilot.

Magnetic Force Microscopy Characterization of Superparamagnetic Iron Oxide Nanoparticles (SPIONs)

The present study was aimed to develop dimethylaminoethyl methacrylate based nanoparticulate drug delivery system using nanoprecipitation method and optimize the process parameters using Plackett-Burman factorial design to yield least average particle size and narrow sized particle distribution without filtration or centrifugation process. Twelve experimental runs involving 11 process parameters at higher and lower levels were generated using Design-Expert. Factorial design result has shown that (a) Except stirring duration all other process parameters significantly influence the average particle size; (B) Except β-cyclodextrin concentration, aqueous phase volume and organic phase volume, all other process parameters significantly influence the polydispersity index; and (C) Except polymer concentration and poloxamer 407 concentration, all other process parameters do not significantly influence the zeta potential. The average particle size, polydispersity index and zeta potential of the prepared dual drug loaded nanoparticles were well within acceptable limits and found to be in the range of 47 to 87 nm, 0.14 to 0.28 and 22 to 39 mV, respectively. Surface morphology examination has shown that the prepared nanoparticles were spherical in shape. The developed dimethylaminoethyl methacrylate based nanoparticulate drug delivery system can be routinely used to fabricate narrow sized polymeric nanoparticles without filtration or centrifugation process.

Development of Dimethylaminoethyl Methacrylate Based Nanoparticulate Drug Delivery System Using Nanoprecipitation Method and Optimization of Process Parameters Using Plackett-Burman Factorial Design

The present study was aimed to develop dimethylaminoethyl methacrylate based nanoparticulate drug delivery system using nanoprecipitation method and optimize the process parameters using Plackett-Burman factorial design to yield least average particle size and narrow sized particle distribution without filtration or centrifugation process. Twelve experimental runs involving 11 process parameters at higher and lower levels were generated using Design-Expert. Factorial design result has shown that (a) Except stirring duration all other process parameters significantly influence the average particle size; (B) Except β-cyclodextrin concentration, aqueous phase volume and organic phase volume, all other process parameters significantly influence the polydispersity index; and (C) Except polymer concentration and poloxamer 407 concentration, all other process parameters do not significantly influence the zeta potential. The average particle size, polydispersity index and zeta potential of the prepared dual drug loaded nanoparticles were well within acceptable limits and found to be in the range of 47 to 87 nm, 0.14 to 0.28 and 22 to 39 mV, respectively. Surface morphology examination has shown that the prepared nanoparticles were spherical in shape. The developed dimethylaminoethylmethacrylate based nanoparticulate drug delivery system can be routinely used to fabricate narrow sized polymeric nanoparticles without filtration or centrifugation process.

Magnetic Properties and Microstructures of Polyethylene Glycol (PEG)-Coated Cobalt Ferrite (CoFe<sub>2</sub>O<sub>4</sub>) Nanoparticles Synthesized by Coprecipitation Method

Magnetic nanoparticles of cobalt ferrite (CoFe2O4) have been synthesized by co-precipitation method with various synthesis temperatures, concentration of NaOH and stirring duration. The results showed that nanoparticles have well crystallized structure with various grain sizes which depend on synthesis parameters. The grain size increased with increasing synthesis temperature, decreasing concentration of NaOH and decreasing stirring duration. Magnetic characterization of CoFe2O4 nanoparticles measured by Vibrating Sample Magnetometer (VSM) showed that coercive field was decrease with the decreasing of particle size. The saturation and remnant magnetization showed increasing when crystallinity increased. However, it also depends on presence of α-Fe2O3 phases and their grain size. Based on magnetic characterization analysis, sample with parameter of synthesis temperature 80°C, concentration of NaOH 5 M and stirring duration 120 minutes have been selected to be modified using polyethylene glycol (PEG)-4000. XRD and TEM analysis showed that surface modification with PEG-4000 could increase the crystallinity of nanoparticles, decrease agglomeration and control the shape to more spherical. VSM analysis showed that modification PEG-4000 could decrease the saturation magnetization which is due to the existence of α-FeO(OH) and γ-FeO(OH) phases from bonds at interface of CoFe2O4 as confirmed by XRD and Furrier Transform Infra Red (FTIR) analysis. Keywords: magnetic nanoparticles, CoFe2O4, copresipitation, PEG-4000

Polyethylene glycol as an alternative polymer solvent for nanoparticle preparation

Solvent toxicity is one of the major drawbacks in the preparation of polymeric nanoparticles today. Here, polyethylene glycols (PEGs) are proposed as non-toxic solvents for the preparation of polymeric nanoparticles. Based on a preparation process similar to the solvent displacement technique, several process parameters were examined for their effects on the properties of the prepared nanoparticles by this method to achieve the optimum preparation conditions. The investigated parameters included polymer type and concentration, volume and temperature of the dispersing phase, methods of dispersing the solvent phase into the non-solvent phase, duration and speed of stirring and washing by dialysis. Ammonio methacrylate copolymer (Eudragit RL), poly-lactide-co-glycolide (PLGA), and PEG-PLGA were found to be successful polymer candidates for the preparation of nanoparticles by this method. Nanoparticles with diameters ranging from 80 to 400 nm can be obtained. The encapsulation efficiencies of bovine serum albumin, and lysozyme as model proteins were ranging from 7.3±2.2% to 69.3±1.8% depending on the strength of polymer-protein interaction. Biological assays confirmed a full lysozyme activity after the preparation process. PEG proved to be a suitable non-toxic solvent for the preparation of polymeric protein-loaded nanoparticles, maintaining the integrity of protein.

Enhanced biological nutrient removal in sequencing batch reactors operated as static/oxic/anoxic (SOA) process

An innovative static/oxic/anoxic (SOA) activated sludge process characterized by static phase as a substitute for conventional anaerobic stage was developed to enhance biological nutrient removal (BNR) with influent ammonia of 20 and 40 mg/L in R1 and R2 reactors, respectively. The results demonstrated that static phase could function as conventional anaerobic stage. In R1 lower influent ammonia concentration facilitated more polyphosphate accumulating organisms (PAOs) growth, but secondary phosphorus release occurred due to NOx(-) depletion during post-anoxic period. In R2, however, denitrifying phosphorus removal proceeded with sufficient NOx(-). Both R1 and R2 saw simultaneous nitrification-denitrification. Glycogen was utilized to drive post-denitrification with denitrification rates in excess of typical endogenous decay rates. The anoxic stirring duration could be shortened from 3 to 1.5h to avoid secondary phosphorus release in R1 and little adverse impact was found on nutrients removal in R2.

Doxorubicin-Loaded (PEG)3-PLA Nanopolymersomes: Effect of Solvents and Process Parameters on Formulation Development and In Vitro Study

This study is focused on the preparation of doxorubicin-loaded nanopolymersomes (PolyDoxSome) and assessment of the effects of various solvents and process variables on the size and drug loading during preparation of formulation. PolyDoxSome was prepared by nanoprecipitation method using amphiphilic (PEG)₃-PLA copolymer, and the formation of polymersomes was assessed by dynamic light scattering and optical and transmission electron microscopy and evaluated for in vitro release profile and in vitro cytotoxicity. A systematic investigation indicated that solvent composition, order of addition, aqueous phase, copolymer concentration, and external energy input have significant influence on size and dispersity of PolyDoxSome. Under optimized conditions, PolyDoxSome had a size range of 130-180 nm with PDI < 0.2, a zeta potential ∼-8 mV, and a drug loading at ∼11% w/w with an encapsulation efficiency at ∼53% w/w. In vitro release profile of PolyDoxSome at 37 °C demonstrated that doxorubicin release was pH dependent and gave higher release at pH 5.5 in comparison to the release at pH 7.4 (similarity factor, f₂ < 50). PolyDoxSome exhibited enhanced cellular uptake of doxorubicin compared to free doxorubicin solution in MCF-7 cell line and showed a better cytotoxicity of doxorubicin at equivalent dose in nanopolymersomes. In conclusion, size and dispersity were strongly influenced by duration of magnetic stirring and overall composition of organic/aqueous media; however, size and dispersity were retained against different degrees of dilution. PolyDoxSome was able to control the release of doxorubicin in pH dependent manner and effectively deliver the drug in active form to MCF-7 breast cancer cells.

Influence of processing parameters on the quality of soycurd (tofu)

Tofu, a non-fermented soybean curd is a nutritious and digestible product with a high quality protein. Tofu making procedure includes soaking of beans, grinding, filtering, boiling, coagulating and moulding. The flavour, quality and the texture of tofu produced is significantly influenced by its processing parameters. Studies were carried out on the processing parameters like solid content of milk, thermal treatment of soybeans with sodium bicarbonate, stirring time after adding coagulant and moulding of tofu on the texture and quality of tofu. Our studies showed that the texture of the final product depended on the solid content of milk before coagulation. Pretreatment of soybeans with sodium bicarbonate, for 10min and milk obtained with low solid content of 7° Brix resulted in regular, smooth textured tofu with less beany flavour. Duration of stirring during coagulation and moulding parameters had a significant effect on the yield of tofu. Stirring the milk after adding the coagulant for 5s before settling and pressing the tofu with a load of 1,000g initially for 15min followed by 500g for another 15min, yielded (22.6g/100ml of milk) soft textured firm tofu.

SYNTHESIS AND CHARACTERIZATION OF CHEMICALLY GROWN ULTRALONG HEXAGONAL ZnO NANOTUBES

Ultralong zinc oxide nanotubes have been synthesized on glass substrate by a simple chemical bath deposition. The nanotubes are hexagonal with the core diameter about ~200 nm. The length of the nanotubes was about 10 μm. No specific alignment of the nanotubes on the glass substrate was observed. The morphology of the nanostructures depends highly on the concentration of zinc acetate solution, duration of mechanical stirring, and temperature during synthesis. Depending upon these experimental conditions nanorods and nanotubes were observed. The material was structurally characterized using grazing incidence X-ray diffraction, showing hexagonal unit cell structure. Transmission electron microscopy results revealed that the walls of the nanotubes are hexagonal. Room temperature photoluminescence spectrum shows a strong violet emission at ~420 nm from the ZnO nanotubes due to transition between zinc interstitial and zinc vacancy level. These results will be very useful in optoelectronic and nanophotonic device applications.

Experimental studies and phase field modeling of microstructure evolution during solidification with electromagnetic stirring

Thixocasting requires manufacturing of billets with non-dendritic microstructure. Aluminum alloy A356 billets were produced by rheocasting in a mould placed inside a linear electromagnetic stirrer. Subsequent heat treatment was used to produce a transition from rosette to globular microstructure. The current and the duration of stirring were explored as control parameters. Simultaneous induction heating of the billet during stirring was quantified using experimentally determined thermal profiles. The effect of processing parameters on the dendrite fragmentation was discussed. Corresponding computational modeling of the process was performed using phase-field modeling of alloy solidification in order to gain insight into the process of morphological changes of a solid during this process. A non-isothermal alloy solidification model was used for simulations. The morphological evolution under such imposed thermal cycles was simulated and compared with experimentally determined one. Suitable scaling using the thermosolutal diffusion distances was used to overcome computational difficulties in quantitative comparison at system scale. The results were interpreted in the light of existing theories of microstructure refinement and globularisation.

A simple way of shape-controlled synthesis of ZnSe nanocrystals : nanodots, nanoflowers, and nanotubes

By introducing aliphatic amines in high concentration, the shapes of ZnSe nanocrystals could be controlled through different stirring duration of zinc precursors.

Study of the Effect of an Antifoaming Agent on the Evaporation of the Components During the Stirring of a Coating Dispersion Containing a Volatile Agent

The main objective of this work was to evaluate the evaporation of coating liquids containing a volatile component (ethanol) and an aqueous polymer dispersion under well‐controlled circumstances. The influence of different concentrations of a polydimethylsiloxane type antifoaming agent was studied. In consequence of to its low interfacial tension, it can form a layer on the surface of a liquid, and the effect of this was studied by determination of the quantity of the stirred liquid that was evaporated. The effects of different operational factors were compared by means of factorial designs. It was conluded that the presence of ethanol in the liquid changed not only the extents of the effects of the factors, but also their relative importance as concerns the evaporation process. The highest difference in effect of a given factor was detected for the stirring rate, while the lowest difference was observed for the duration of stirring. A high concentration of Dimeticon decreased the extent of evaporation, but not significantly. Thus, the alterations in the effects of the operational factors were not very substantial either. It may be stated that this antifoaming agent does not result in a relevant change in the evaporation in these systems containing ethanol as a volatile component. Accordingly, primarily the operational parameters must be considered during the formulation of these compositions. This information helps towards the design of an appropriate stirring device, because our results indicate that open systems are not adequate and it is known that hermetically closed tanks make atomization impossible. Hence, determination of the critical control points of coatings with a liquid containing a volatile component cannot be avoided because the vapour of such materials can be very dangerous.

Electromagnetic Stirring Processing and its Influence on Mechanical Properties of ZL102(or Al-Si) Alloy

Al-Si alloy was melted by using vacuum induction melting furnace heated with medium-frequency induction and stirred simultaneously under Lorentz force. The experimental results were discussed with respect to the theoretical analysis of the Lorentz force on the molten alloy. It was found that Si phase tends to homogenize and aggregate along the direction of axis in the alloy under the effect of Lorentz force. With increasing stirring duration, Rod-shaped Si phase has a tendency to break and passivate on the edge. Vickers hardness measurement indicated that the microhardness of Al-Si alloy was improved after electromagnetic stirring. This result can be mainly attributed to the improvement in spheroidization of Si phase and aluminum phase.

Study on the thermal and mechanical properties of epoxy–nanoclay composites: The effect of ultrasonic stirring time

Epoxy–clay nanocomposites were synthesized with organophilic montmorillonite and diglycidyl ether of bisphenol A by using the in-situ polymerization under ultrasonic treatment. The clay layers were found to be separated further with the increase in the duration of ultrasonic stirring as measured from the X-ray diffraction measurements. Thermogravimetric analysis provided the fact that the maximum thermal decomposition temperatures increased with the increase in the duration of ultrasonic stirring. However, both the glass transition temperature and the storage moduli of the composites decreased with the increase of ultrasonic stirring time as measured from the dynamic mechanical analysis.

Microencapsulation of dehydroepiandrosterone (DHEA) with poly(ortho ester) polymers by interfacial polycondensation

An original encapsulation process of DHEA was developed, based on the formation of poly(ortho ester) membrane from interfacial polycondensation in an oil-in-oil emulsion. First, the formation of poly(ortho ester) (POE) in solution under anhydrous conditions between a polyol, a lactide diol and a diketene acetal (3,9-diethylidene-2,4,8,10-tetraoxaspiro-[5.5]-undecane) was studied in order to determine the structural and thermal characteristics of the POE polymer. The optimization of the formation of a fine and stable emulsion with the required size distribution was performed in relation with the type of the internal and external phases, the type and the concentration of the surfactant and the stirring rate and duration. The diffusion of monomers and DHEA was evaluated by GC-MS analysis in order to determine the mechanisms of the membrane formation. Finally the synthesis of poly(ortho ester) DHEA-loaded microcapsules was performed under anhydrous conditions required by the particular synthesis of POE. Stable poly(ortho ester) microcapsules containing DHEA were obtained with particle sizes ∼ 1 μm.

Microencapsulation of dehydroepiandrosterone (DHEA) with poly(ortho ester) polymers by interfacial polycondensation.

An original encapsulation process of DHEA was developed, based on the formation of poly(ortho ester) membrane from interfacial polycondensation in an oil-in-oil emulsion. First, the formation of poly(ortho ester) (POE) in solution under anhydrous conditions between a polyol, a lactide diol and a diketene acetal (3,9-diethylidene-2,4,8,10-tetraoxaspiro-[5.5]-undecane) was studied in order to determine the structural and thermal characteristics of the POE polymer. The optimization of the formation of a fine and stable emulsion with the required size distribution was performed in relation with the type of the internal and external phases, the type and the concentration of the surfactant and the stirring rate and duration. The diffusion of monomers and DHEA was evaluated by GC-MS analysis in order to determine the mechanisms of the membrane formation. Finally the synthesis of poly(ortho ester) DHEA-loaded microcapsules was performed under anhydrous conditions required by the particular synthesis of POE. Stable poly(ortho ester) microcapsules containing DHEA were obtained with particle sizes; 1 micro m.

Liquid extraction and HPLC-DAD assay of hydrochlorothiazide from plasma for a bioequivalence study at the lowest therapeutic dose.

The main parameters considered in optimizing the liquid extraction and quantitative assay were the yield, precision, limit of quantification, time required for extraction and concentration, and quantity of solvent. The influence on these parameters of the following factors was examined: nature of the extracting solvent, quantity of solvent, co-extraction solvent, and duration of stirring. Instead of equilibrium parameters of the involved thermodynamic system, a kinetic approach was preferred in terms of the effective partition 'constant', which is not really constant but a function of time and extraction conditions. The final selected method, considered to be rapid and simple, was applied to determine the pharmacokinetics of hydrochlorotiazide (HCT) after administration of Capozide (Bristol-Myers Squibb) tablets containing 50 mg Captopril and 25 mg HCT, to 4 healthy volunteers. The results obtained were in accordance with the pharmacokinetic parameters of HCT reported in the literature.

Microencapsulation of Chlorpheniramine Maleate–Resin Particles with Crosslinked Chitosan for Sustained Release

ABSTRACTFormulation and preparation parameters of drug/ion-exchange particles microencapsulated in cross-linked chitosan were evaluated for controlled release of the water-soluble drug chlorpheniramine maleate (CPM) in a suspension. An emulsion solvent evaporation method was used to produce CPM-resinates embedded in glutaraldehyde (GTA) crosslinked chitosan microspheres (MCSs). Crosslinking extent in the chitosan was monitored by swelling measurements. Controlled release was evaluated by dissolution tests in simulated gastric fluid without enzyme (SGF) and in simulated intestinal fluid without enzyme (SIF). CPM-resinates contained 62% (w/w) of drug. MCSs were spherical, ranging from 82 to 420 μm in diameter, and contained multiple resinates. The sizes of MCSs prepared with safflower oil and Span 80 were controlled by surfactant concentration, stirring speed, and duration of stirring. Maximum crosslinking was produced with 240 mg GTA per 250 mg of chitosan. Maximum drug release from free CPM-resinates was about 60% by 1 hr in SGF, and was about 100% by 3 hr in SIF. CPM release was slower from MCSs crosslinked with 120 mg of GTA compared to 5 mg GTA in both media. By 8.3 hr, the more crosslinked MCSs released about 30% CPM in SGF, and about 60% in SIF. Because of the apparent ceiling on release in SGF, the final experiments were conducted in SIF. Increasing the weight ratio of the chitosan coating to CPM-resinate ratio from 1:1 to 4:1 moderately decreased release profiles carried out to 33 hr. Increasing MCS diameters from 82 to 163 μm moderately decreased release profiles. Microencapsulation of CPM-resinates with crosslinked chitosan demonstrated controlled release of CPM in SGF and SIF without enzymes. The retardation effect increased when the crosslinking extent and chitosan to resin ratio increased.

Role of sequential adsorption of polymer/surfactant mixtures and their conformation in dispersion/flocculation of alumina

The role of sequential adsorption of a non-interacting pair of polymer (polyacrylic acidPAA) and surfactant (sodium dodecyl sulfate-SDS) on alumina particles and in determining the stability of their suspensions was studied with particular attention to the conformation of the polymer. It was found that the sequence of addition is of critical importance in determining the dispersion/flocculation of this system. When SDS was added first, both PAA conformation and suspension stability varied with SDS concentration. Whereas when PAA was added first, the subsequent adsorption of SDS molecules had no effect on either the polymer conformation or the suspension stability. This is attributed to masking of SDS species by the larger polymer chains. SDS can not however be completely masked by PAA chains once the PAA concentration is decreased below the optimal concentration for flocculation. When the stirring duration was increased, the mode of addition showed no effect suggesting that the system then reaches equilibrium. Interestingly, a small amount of pre-adsorbed PAA was found to facilitate the adsorption of SDS.

Structure and stability of human hemoglobin microparticles prepared with a double emulsion technique.

Hemoglobin solutions can be used as blood substitutes but they present some disadvantages often due to their rapid removal from the bloodstream after injection. A possible way of overcoming this problem is to trap hemoglobin inside particles. This study deals with the preparation, structure and stability of poly(lactic acid) and ethylcellulose microparticles containing human hemoglobin obtained with a double emulsion technique. We investigated the manufacturing process of these particles in order to increase the encapsulation ratio of hemoglobin. For this purpose, some parameters involved in the procedure were optimized, such as hemoglobin concentration and duration of stirring: hemoglobin loading increases with its concentration in the preparation and well-defined stirring time avoids a leakage of hemoglobin. Hemoglobin concentration, surfactant concentration i.e. poly(vinylic alcohol), amounts of polymer and solvent (methylene chloride), duration and speed of stirring. The microparticles were prepared with satisfactory yields (60 to 73%). They were spherical and their mean size was lower than 200 microns. The functional properties of entrapped hemoglobin were studied. The encapsulation did not alter hemoglobin and the oxygen affinity of the hemoglobin remained unmodified (P50 about 13.9 mm Hg in a Bis-Tris buffer pH 7.4 at 37 degrees C). Moreover, only low levels of methemoglobin could be detected (less than 3%). Besides, about 90% of encapsulated hemoglobin could be released from microparticles, with a speed related to the internal structure of the particles. The prepared microparticles were stored during one month at +4 degrees C. No degradation of the particle structure occurred and the functional properties of hemoglobin were preserved. These particles could provide a potential source of oxygen in the field of biotechnologies but any application for a transfusional purpose would first require a drastic reduction in particle size.