Increasing Polymer Concentration Research Articles

Lignosulfonates as charge carriers and precursors forthe synthesis of nanoparticles

The conductometry method was used to study the polyelectrolyte behavior of lignosulfonates in an aqueous solution. Electrical conductivity was found to be a complex function of concentration (8.5 ∙ 10–5– 9.0 ∙ 10 –2 mol/dm3), molecular weight of lignosulfonates (Mw 9250, 46,300), cation nature (Na+, Cа2+), as well as association of free counterions with polyion and temperature (288–353 K). It was shown that the molar electrical conductivity in the Kohlrausch coordinates decreases with increasing polymer concentration due to a decrease in the mobility of dissociated counterions under the action of the electrostatic potential of the macroion. In lignosulfonates solutions, an increase in temperature causes an increase in the number of particles capable of charge transfer. An inflection point was found on the temperature dependences of the electrical conductivity of high molecular weight samples, indicating structural changes in macromolecules. The reasons for this behavior of high molecular weight lignosulfonates in an aqueous solution were discussed. The activation energy of electrical conductivity was calculated, the average value of which is 14.24 kJ/mol for low molecular weight samples, and 12.17 kJ/mol for high molecular weight samples up to the inflection point and 16.49 kJ/mol after. It was found that a bimodal distribution of particles, as well as the formation of a double electric layer on their surface, is characteristic of lignosulfonates obtained. Solvent replacement (nanoprecipitation) yielded lignosulfonate nanoparticles ranging in size from 40 to 90 nm. The shape of the obtained particles is determined by the nature of organic solvent and is independent of lignosulfonates molecular weight. When using ethyl alcohol as a co-solvent, spherical nanoparticles were obtained, and pyramidal lignosulfonate nanoparticles were prepared when using acetone.

Electrospinning of polymer solutions: An analysis of instability in a thinning jet with solvent evaporation

The present study examines the stability of a thinning straight jet in electrospinning process. The linear stability analysis is carried out to obtain the growth/decay rate of axisymmetric disturbance imposed on the thinning jet. The analysis captures the role of solvent evaporation in the stability behavior of the linear path of the electrospinning jet. In contrast to many prior stability analyses which consider the jet as a cylindrical filament with uniform radius, the present study analyzes the stability of a jet which exhibits thinning under realistic electrospinning conditions. Two different polymeric solutions are considered: the poly-isobutene (PIB) Boger fluid with low electrical conductivity and the highly conductive poly-ethylene oxide (PEO) solution in ethanol/water. At low extensional deformation, the rheology of the unentangled PIB-based Boger fluid is described by the Oldroyd-B model. The PEO solution, on the other hand, experiences a very high elongation rate due to the development of strong axial electric stress. The nonlinear rheology of the entangled PEO solution is appropriately described by the eXtended Pom–Pom (XPP) model, a variant of the classical tube model. The analysis reveals that the instability in low conductivity fluid is driven by the capillary forces, whereas the high conductivity fluid exhibits oscillatory conducting mode of instability driven by the coupled effect of axial electric field and surface charges. For both the reference fluids, the increase in solvent evaporation tends to decrease the disturbance growth rate to the extent that the axisymmetric instability is completely suppressed for a strong enough evaporation. The stabilizing role of solvent evaporation is attributed to the enhancement in fluid viscosity and elasticity due to increased polymer concentration upon evaporation. Thus, by suppressing the onset of axisymmetric instability during the straight jet path, solvent evaporation potentially helps produce smooth fibers without bead formation.

Study on the Morphology and Fiber Properties of Nanoclay Added Polyvinyl Alcohol (PVA) Nanofibrous Mats: Effect of Mechanical Dispersion

In this study, polyvinyl alcohol (PVA) polymer and Cloisite 15A, a modified form of organo Montmorillonite nanoclay, are used to produce nanofibrous mats via electrospinning technique. Pure PVA nanofibrous mats from mechanically stirred polymeric solutions at 8, 10 and 12 wt % PVA percents; and nanoclay added PVA nanofibrous mat samples are produced at increased nanoclay weight/ polymer weight ratios (1/13, 1/11, 1/9 and 1/6) using several mechanically stirred nanoclay-PVA solutions at various proportions of nanoclay and PVA polymer wt % in solutions. The viscosities, surface tensions and electrical conductivities of solutions were measured. FESEM (Field Emission Scanning Electron Microscopy) analysis, fiber diameter distribution with Image J software analysis and tensile testing was applied to nanofibrous samples. Increased polymer concentration led to bead-free nanofibrous PVA mats. EDX analysis approved nanoclay is present in samples produced from nanoclay added PVA solutions. Mechanical stirring for nanoclay dispersion enabled smooth nanofibrous structures only in low (1/13) nanoclay weight/ polymer weight ratios and showed very little tensile increase from 1 wt % clay loading to 2 wt % addition. A direct increase in tensile strength wasn’t achieved with nanoclay content increase in PVA nanofibrous mats; this might be due to the effect of poor nanoclay distribution adversely affecting tensile results. Morphological analysis proved that nanofibrous structures were far away from smooth fiber structures as they transformed from smooth nanofibers into non-uniform fibrous structures at increased nanoclay weight/ polymer weight ratios in nanoclay added PVA samples. Keywords: nanofibrous mat, electrospinning, polyvinyl alcohol (PVA), nanoclay, mechanical dispersion DOI : 10.7176/CPER/62-08 Publication date: May 30 th 2020

Spectrophotometric investigation of gel formation in water solution of agar

The temperature and concentration dependences of the transmission spectrum of an aqueous solution of agar are investigated. Measurements taken in the heating and cooling modes show strong thermal hysteresis in the spectral properties. Analysis of the results suggests that the formation of a gel network occurs in a much narrower temperature range than its collapse. The study of the temperature dependence of transmittance indicates that the association bispirals by cooling the solution and responsible for the formation of network occurs at temperature about [Formula: see text]C. A breakdown of these associates by heating of the gel begins at [Formula: see text]C and covers a wide temperature range. The gel point [Formula: see text] and the gel melting point [Formula: see text] increase with increasing polymer concentration, but for [Formula: see text] this dependence is stronger. Growth of turbidity (light scattering) of gel by increasing of agar concentration is due to the increasing of number and size of gel associates.

Modeling and Simulation of Polymer Flooding with Time-Varying Injection Pressure.

Polymer flooding is one of the most incipient chemical-based enhanced oil recovery process that utilizes the injection of polymer solutions into oil reservoirs. The presence of a polymer in water increases the viscosity of the injected fluid, which upon injection reduces the water-to-oil mobility ratio and the permeability of the porous media, thereby improving oil recovery. The objective of this work is to investigate strategies that would help increase oil recovery. For that purpose, we have studied the effect of injection pressure and increasing polymer concentration on flooding performance. This work emphasizes on the development of a detailed mathematical model describing fluid saturations, pressure, and polymer concentration during the injection experiments and predicts oil recovery. The mathematical model developed for simulations is a black oil model consisting of a two-phase flow (aqueous and oleic) of polymeric solutions in one-dimensional porous media as a function of time and z-coordinate. The mathematical model consisting of heterogeneous, nonlinear, and simultaneous partial differential equations efficiently describes the physical process and consists of various parameters and variables that are involved in our lab-scale process to quantify and analyze them. A dimensionless numerical solution is achieved using the finite difference method. We implement the second-order high-accuracy central and backward finite-divided-difference formula along the z-direction that results in the discretization of the partial differential equations into ordinary differential equations with time as an independent variable. The input parameters such as porosity, permeability, saturation, and pore volume obtained from experimental data by polymer flooding are used in the simulation of the developed mathematical model. The model-predicted and commercial reservoir (CMG)-simulated oil production is in good agreement with experimental oil recoveries with a root-mean-square error (RMSE) in the range of 1.5–2.5 at a maximum constant pressure of 3.44 MPa as well as with temporal variation of the injection pressure between 2.41 and 3.44 MPa.

Complex permittivity and permeability properties analysis of NiCuZn Ferrite-Polymer nanocomposites for EMI suppressor applications

The complex permittivity and permeability studies of NiCuZn ferrite-paraformaldehyde (NCZ-PFD) nanocomposites for electromagnetic interference (EMI) suppressor applications are presented. The NCZ Ferrite and nanocomposites were prepared via microwave hydrothermal and ball-milling, respectively. The nanocomposites were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM) the results indicate that the NCZ-PFD nanocomposites were successfully prepared without impurities. The complex permittivity and permeability were measured over frequency range of 8.2-12.4 GHz and 12.4–18 GHz. The results show that for nanocomposites, the values of the real (ε′) and imaginary permittivity (ε″) and imaginary permeability (μ″) increase, while the value of real permeability (μ′) decreases as the polymer content increases. Dielectric relaxations were studied using cole-cole plots of complex permittivity. Magnetic relaxation dispersions were analyzed using cole-cole plots of complex permeability. The possibility to modulate the electromagnetic properties of the composite materials is of a great interest to fabricate microwave absorbing and electromagnetic shielding materials with high performances.

Effects of rheological properties on heat transfer enhancements by elastic instability in von-Karman swirling flow

Elastic instability is proposed as a promising method to intensify heat transfer under very low Reynolds number conditions. However, the onset of elastic instability and its influence on heat transfer is highly dependent on the rheological properties of polymer solution, which has not been revealed. By varying polymer concentration, sucrose proportion and the degree of salinity, the heat transfer performance due to the variations of rheology is investigated in a swirling flow configuration between parallel plates. The results indicate that both the increase of polymer concentration and the reduction of the salinity can induce elastic instability easily, leading to a better heat transfer performance when the swirling velocity is fixed. However, the salinity effects become weakened as the swirling velocity continually increases and the maximum enhancement becomes independent on salinity. In particular, the heat transfer performance based on pure elastic instability shows larger enhancement than that of inertial-elastic instability at low Reynolds number.

Characterizing the impact of thermal gels on isotachophoresis in microfluidic devices.

Thermally reversible Pluronic gels have been employed as separation matrices in microfluidic devices in the analysis of biological macromolecules. The phase of these gels can be tuned between liquid and solid states using temperature to vary fluidic resistance and alter peak resolution. Although separations in thermal gels have been characterized, their effect on isotachophoresis has not. This study used fluorescein as a model analyte to evaluate isotachophoretic preconcentration as a function of thermal polymer concentration and temperature. Results demonstrated that increasing polymer concentration in microfluidic channels increased the apparent analyte concentration. A critical minimum of 10% (w/v) Pluronic was required to achieve efficient preconcentration with maximum focusing occurring in 20 and 25% polymer gels. Temperature of the thermal gel also impacted analyte focusing. Most efficient focusing was achieved at 25°C with diminishing analyte accumulation at higher and lower temperatures. Under optimal conditions, isotachophoretic preconcentration increased an additional threefold simply by including thermal gels in the system. This approach can be readily implemented in other applications to increase detection sensitivity and measure low-concentration analytes within simple microfluidic devices.

Effects of naphthoxy side groups on functionalities of linear polyphosphazenes: Fluorescence, ion response and degradability

Polyphosphazenes with different substitution rates of β-naphthoxy side groups are synthesized through ring opening polymerization of hexachlorocyclotriphosphazene (HCCP), subsequent nucleophilic substitution by β-naphthol in organic solutions. The concentration and solvent effects, ions response, solid-state fluorescence and degradability of these polymers are investigated. It is found that the peaks in excitation spectra redshift with the increase of polymer concentration, and gradually stronger interaction of polymer molecules results in different concentration effects at λex = 300 nm and λex = 355 nm, respectively. It demonstrates that the fluorescence intensity of polymer solution enhance by increasing the polarity of solvents, and iron ions could quench fluorescence of polymer solutions. Moreover, the fluorescence intensities of polyphosphazenes containing β-naphthoxy side groups in solid-state is stronger than those in solution. The highest fluorescence intensities of those in both solid and solution is those polymers with 90% substitution rate of naphthoxy side groups. However, the polymers with lower substitution rate of naphthoxy side groups are degradable easily in acid medium.

Characterization of conformational transition of polymers with low molecular weights in solutions by fluorescence resonance energy transfer

The conformations of polymers in solutions are of great importance, and scattering techniques prevail in detecting these conformations. However, most studies only focus on polymer species with high molecular weights or those well above their entanglement molecular weights, and studies on polymer solutions with low molecular weights, e.g., lower than 10,000 Da, are lacking. Here, the conformation of low molecular weight polymers in solutions with different concentrations was investigated via fluorescence resonance energy transfer (FRET). Based on a site-specific chromophore-labeling protocol, the conformational information of the polymer was inferred from the end-to-end FRET response. In principle, the FRET efficiency increases with increasing polymer concentration since the size of the polymer coil decreases. For low molecular weight polymers, the trend of the FRET efficiency shows the opposite effect as the polymer concentration increases, which is rationalized by the counterbalance of the intrinsic size contraction (static item) of and terminal diffusion (dynamic item) from the polymer coil. The universality of this law is verified by similar results from the polymethyl methacrylate (PMMA) system. This work provides new efforts for the conformational study of polymer solutions and demonstrates that the diffusion effect should be taken into account for low molecular weight polymers but is negligible for polymers with high molecular weights.

BSE‐IA reveals retardation mechanisms of polymer powders on cement hydration

AbstractThe retardation effects of two polymer powders, styrene butadiene rubber and ethylene‐vinyl acetate, on cement hydration and the mechanisms in terms of hydration degree and microstructure characteristics were investigated by the combination of backscattered electron image analysis, scanning electron microscopy, energy dispersive spectrometer, and X‐ray diffraction. Results show that the cement hydration can be significantly retarded by both polymers with the reductions in cement hydration degrees and hydration products thickness. Polymers retard cement hydration by agglomerating the polymer particles on the surfaces of cement grains, forming films in different thickness and bonding the calcium ions in the pore solutions. Consequentially, the formation of C‐S‐H and CH is depressed and the Ca/Si ratios in the hydration product layer are raised. The retardation is enhanced with the increase in polymer content. This work helps understand the retardation effect of polymers on cement hydration in depth, which enables rational development of polymer‐modified cement‐based materials for further applications.

Early transition, relaminarization and drag reduction in the flow of polymer solutions through microtubes

Experiments are performed to investigate the onset of early transition and drag reduction in the flow of polymer (polyacrylamide and polyethylene oxide) solutions through rigid microtubes of diameters in the range 0.49–2.84 mm. We measure friction factor variation with Reynolds number for varying polymer concentrations and tube diameters, and the Reynolds number, , at which the experimental data deviate from the laminar value represents the onset of transition. Crucially, owing to the high shear rates encountered in our experiments, we show that it is important to account for shear thinning of the fluid in the theoretical estimation of the friction factor in the laminar regime. We accomplish this using a Carreau model, and show that the use of laminar friction factor calculated without shear thinning leads to an erroneous overestimation of . The obtained from friction factor data in the present study is in good agreement with that inferred using micro particle image velocimetry analysis in Chandra et al. (J. Fluid Mech., vol. 844, 2018, pp. 1052–1083). For smaller concentrations of the added polymer, there is a marginal delay in the onset of turbulence, but as the concentration is increased further, the transition Reynolds number decreases much below , the usual value at which transition occurs in Newtonian pipe flows. Thus, the present study further corroborates the phenomenon of early transition leading to an ‘elasto-inertial’ turbulent state in the flow of polymer solutions. For concentrations such that there is a delay in transition, if is maintained above the for Newtonian fluids, the flow is transitional or turbulent in the absence of polymers. At such a fixed , if the concentration of the polymer is increased gradually, the friction factor decreases and the flow relaminarizes. With further increase in polymer concentration, the flow undergoes a transition due to elasto-inertial instability. The effect of addition of small amounts of polymer on turbulent drag reduction in the flow of water through microtubes is also investigated. Increase in polymer concentration, molecular weight and decrease in tube diameter causes an increase in drag reduction. The friction factor data for different polymer concentrations, molecular weights, tube diameters and , when plotted with , show a reasonable collapse, where is the Weissenberg number defined as the product of the longest relaxation time of the polymer solution and the average shear rate in the tube and is the ratio of solvent to total solution viscosity. Interestingly, the onset of the maximum drag reduction asymptote, for experiments using varying tube diameters and polymer concentrations, appears to occur at .

Formulation and evaluation of interpenetrating network of xanthan gum and polyvinylpyrrolidone as a hydrophilic matrix for controlled drug delivery system

The prime objective of the present study was to develop novel colon targeting xanthan gum/polyvinylpyrrolidone-co-poly acrylic acid hydrogels for controlled delivery of 5-fluorouracil at colon-specific site by combining the properties of natural and synthetic polymers. Xanthan gum (XG) and polyvinylpyrrolidone (PVP) polymer have been chemically cross-linked with acrylic acid (AA) monomer using ethylene glycol dimethacrylate and ammonium per sulfate/sodium hydrogen sulfite as a cross-linker and initiator, respectively. Different proportions of XG, PVP, acrylic acid and ethylene glycol dimethacrylate were blended with each other to fabricate pH-sensitive hydrogels by free radical polymerization. SEM, FTIR, TGA, DSC, XRD and sol−gel fraction analysis were carried out for characterization and structural analysis of polymeric system. pH-responsive behavior of fabricated hydrogels was investigated by performing swelling studies and in vitro drug release studies at both pH 1.2 and pH 7.4. Toxicity studies were performed on rabbits to evaluate cytotoxicity and biocompatibility. TGA and DSC confirmed that formulations were thermodynamically stable, while FTIR, SEM and XRD revealed the successful grafting of components. By increasing the content of polymer, monomer and cross-linker, gel fraction was found to be increased. Swelling capacity of hydrogels increases with the increase in concentration of monomer, while swelling capacity tends to decreases with the increase in concentration of cross-linker and polymer in hydrogel composition. pH sensitivity of hydrogels was confirmed by swelling dynamic and drug release behavior in simulated gastrointestinal fluids. Toxicity studies confirmed that hydrogels were non-toxic. Drug release kinetics revealed the controlled release pattern of 5-fluorouracil in developed polymeric network. Cross-linked XG/PVP-co-poly (AA) hydrogels can be used as promising candidate for controlled delivery of 5-FU for prolonged treatment period at colon-specific site.

Orange-red and white-emitting nonconventional luminescent polymers containing cyclic acid anhydride and lactam groups

Nonconventional luminescent copolymers poly(itaconic anhydride-co-vinyl caprolactam) (PIVC) and poly(itaconic anhydride-co-vinyl pyrrolidone) (PIVP) emit strong orange-red and bright white emissions, respectively.

Synthesis of Biopolymeric Drug Binder from Plant-based waste

Binders are agents employed to impart cohesiveness to the powdered material during the formulation of tablets which remains intact after compression. As part of continuing efforts to design a cost-effective pharmaceutical grade binder, two different types of plant-based polysaccharides such as hemicelluloses from corn cobs and mucilage from sapota seeds were extracted from domestic waste and used as a binder in amoxicillin tablet formulations using wet granulation technique. Finally the efficiency of the tablet was evaluated by different pre-compression and post-compression analysis. The in-vitro drug release profile of formulated tablets were assayed at different gastrointestinal tract pH. The extracted hemicellulose and mucilage were characterized by Fourier transform infrared spectroscopy (FTIR). All the formulations with natural polymers produced tablets easily and showed satisfactory results. The sapota seed mucilage exhibited better in vitro drug release profile than the corn cob hemicellulose. The dissolution time of the tablets was found to be increased with increase in polymer concentration. Tablets with highest binder concentration showed controlled released dissolution pattern which is more essential and requirement for a good binder. Formulated tablets with sapota seed polymer showed maximum drug release of 83.56% at pH 7.4, and 96.36% at pH 1.2, where the corn cob polysaccharide showed 68.9% at pH 7.4, and 90.9% at pH 1.2. On the basis of drug release behavior it can be summarized that corn cob hemicellulose and sapota seed mucilage can act as excellent binder in dosage forms. Since it is of natural origin and these biopolymers available at low cost it may prove to be better binder over commercially used costly synthetic binders.

Development and Evaluation of In-situ gel containing Linezolid and Diclofenac Sodium in the treatment of Periodontitis

Periodontal treatment aims at reduction of infection and inflammation. Linezolid is a synthetic antibacterial agent of a new class of antibiotics, the oxazolidinones, which has clinical utility in the treatment of infections caused by aerobic and anaerobic bacteria susceptible organisms methicillin and vancomycin-resistant in the treatment of periodontitis. Diclofenac sodium is anti-inflammatory agent and in-situ gel containing Linezolid and Diclofenac sodium in this study may have a potential additive effect. Hence, there is broad scope for research in local application of antimicrobial and anti-inflammatory combination drug (s) in periodontitis. Linezolid and Diclofenac sodium. In-situ gel containing Linezolid in combination with Diclofenac sodium was prepared using combination of carbopol-HPMC and carbopol-NaCMC. The prepared in-situ gel formulation showed satisfactory results for in-vitro gelling capacity, rheology, and other physical properties. In-vitro drug release profile was dependent up on the concentration of polymer, i.e. drug release was decreased with increase in polymer concentration and vice versa. The formulations of batches LDCF1, LDCF2, LDCF3, LDSF1, LD SF2 and LDSF3 failed to extend the drug release up to 12 hours. Thus, the formulation of batches LDCF4 and LDSF4 containing carbopol: HPMC and carbopol: NaCMC in 1: 2 ratios were considered as optimum formulation on the basis of optimum viscosity, gelation time, gelation temperature, gelling capacity, and their capacity to extend the in-vitro drug release up to 12 hours. Hence, prepared formulations showed sustain drug release behaviour.

Stratification of polymer-colloid mixtures via fast nonequilibrium evaporation.

In drying liquid films of polymer-colloid mixtures, stratification in which polymers are placed on top of larger colloids is studied. It is often presumed that the formation of segregated polymer-colloid layers is solely due to the proportion in size at fast evaporation as in binary colloid mixtures. By comparing experiments with a theoretical model, we found that the transition in viscosity near the drying interface was another important parameter for controlling the formation of stratified layers in polymer-colloid mixtures. At high evaporation rates, increased polymer concentrations near the surface lead to a phase transition from a semidilute to concentrated regime, in which colloidal particles are kinetically arrested. Stratification only occurs if the formation of a stratified layer precedes the evolution to the concentrated regime near the drying interfaces. Otherwise, the colloids will be trapped by the polymers in the concentrated regime before forming a segregated layer. Also, no stratification is observed if the initial polymer concentration is too low to form a sufficiently high polymer concentration gradient within a short period of time. Our findings are relevant for developing solution-cast polymer composites for painting, antifouling and antireflective coatings.

Screening Study on Rheological Behavior and Phase Transition Point of Polymer-containing Fluids produced under the Oil Freezing Point Temperature

AbstractFor an increasing implementation of the low-temperature transportation in oilfield, it is urgent priority initially to study the physical and chemical properties to provide the vital technical support for the low-temperature transport of the polymer flooding. In this paper, the rheological behavior of polymer-containing fluid produced from the Daqing polymer flood were first studied for an adaptation of transportation under the oil’s freezing point temperature. The experiments progressed with different temperature, shear rate, water content and polymer concentration which have great impacts on the viscosity of the fluids produced aiming to find the phase transportation point for the application of the low-temperature transportation. It was displayed that a significant discontinuity in the viscosity occurs at some range of water content. Before the phase transition point, presented in W/O (water-in-oil) emulsion, the viscosity was lifted with the increase of the water content while after the phase transition point, forming the O/W (oil-in-water) type emulsion, the viscosity was dropped with an increase of water content. The phase transition points strongly depend on the polymer concentration in the fluids Produced. It was demonstrated that the phase transition points of polymer-containing fluids were 65%, 70%, 50%, 50% and 50%, corresponding to the polymer concentrations of 315mg/L, 503mg/L, 708mg/L, 920mg/L and 1053mg/L, respectively. The characteristics are attributed to the viscous polymer. The fluidity of the fluid produced was decreased with the increase of polymer concentration.

Experimental investigation on convective heat transfer of Shear-thinning fluids by elastic turbulence in a serpentine channel

Elastic turbulence has shown great potential to enhance heat transfer performance at the microscale. Most of the studies, however, have only considered global convective heat transfer performance along curvilinear channels, despite that the intensity of the chaotic flow varies along the streamline, leading to different local heat transfer characteristics. This work systematically investigated the local convective heat transfer performance by elastic turbulence of a shear-thinning fluid in a serpentine channel. The flow visualization along the serpentine channel was obtained and analyzed to show the existence of elastic instability and elastic turbulence. Significantenhancement of mixing was observed with the increase of polymer concentration and bulk flowrate. The variations of pressure drop, heat transfer coefficients and Nusselt numbers along the serpentine channel were analyzed to reveal local characteristics of elastic turbulence. A three-stage pressure drop profile was identified due to the variations of viscosity and elastic turbulence intensity at different flowrates and Reynolds numbers. A non-linear heat transfer performance, which increased with the increase of polymer concentrations, was observed. These are mainly attributed to the increasing intensity of elastic instability, resulting from the balance between normal stresses and streamline curvatures. A large increase of Nusselt number versus Weissenberg number was also revealed due to the coupling of shear-thinning behavior and elastic instability effects.

The differential depression of an oxidized starch on the flotation of chalcopyrite and graphite

It is difficult to achieve a clean separation during flotation when unwanted graphitic material exists in association with valuable copper sulphides such as chalcopyrite. Attempts to improve the separation has been driven by green and innocuous reagents such as starch or its derivatives to ensure environmental sustainability. In this study, the depressive action of an oxidized wheat starch in comparison to the normally used native counterpart during flotation of chalcopyrite and graphite was investigated. Starch oxidation, depending on the degree, yields an uncommon phenomenon of concurrent depolymerisation of the large supramolecular assembly of starch chains as well as generation of CO (carbonyl) and (COO) carboxyl moieties on the starch matrix. Adsorption and AFM imaging measurements were performed and correlated with flotation recovery to probe into the influence of the structural and functional changes due to starch oxidation. The base material (native wheat starch – NWS) exhibited a similar adsorption response on chalcopyrite and graphite with increasing polymer concentration, which corresponded to their similar depression during flotation. However, the oxidized starch (Ox 5/120) produced in the laboratory resulted in significant depression of graphite with a modest effect on chalcopyrite flotation. Ox 5/120 also showed marked differences in adsorption behaviour between graphite and chalcopyrite in consonance with the flotation results. It is clear that starch oxidation has an intriguing effect on the underlying binding mechanisms and conformations at mineral surface governing the separation efficiency.