Increasing Polymer Concentration Research Articles

Effect of cooling rate on microstructure, mechanical properties and residual stress of 7075 aluminum alloy

Abstract In this study, the effect of cooling rate on microstructure, mechanical properties and residual stress of 7075 aluminum alloy was investigated. The influence of cooling rate on microstructure, hardness, electrical conductivity of 7075 aluminum alloy was investigated using a Jominy end quench test. Water at three different temperatures (20 °C, 50 °C, 75 °C) and polymer solutions of varied concentrations (5vol.-% and 25vol.-%) were used as a quenching medium. The changes of hardness, electrical conductivity and microstructure properties of the specimens with an increase in distance from the quenched surface were investigated comparatively for different quenching mediums. Tensile tests were applied to determine the effect of the quenching rate on mechanical properties of the specimens. Residual stress was measured using the ESPI hole drilling technique to understand the influence of cooling rate. The results show that the cooling rate decreases as the distance from the quenched surface, water temperature and polymer concentration increases. The changes in material properties such as hardness, electrical conductivity along the material profile decrease as water temperature and polymer concentration increase. Although the hardness and mechanical properties of the material decrease as the cooling rate decreases, the values obtained are convenient for conditions of industrial usage. Residual stress was significantly eliminated by quenching in hot water or polymer solution at a high concentration.

FORMULATION AND CHARACTERIZATION OF MICROSPHERES OF NITAZOXANIDE BY CHEMICAL CROSSLINKING METHOD

The work investigated the design and evaluation of microspheres of Nitazoxanide by Ionotropic gelation technique met. 32 Factorial designs were used and concentration of polymer carbopol-934 (X1) and Ethyl cellulose (X2) were selected as the independent variables. The surface morphology study by SEM indicated that microspheres were spherical with smooth surface. There was no interaction between the drug and polymers, as studied by FTIR study. The prepared microspheres were characterized by entrapment efficiency, particle size micromeritic properties. It was observed that on increasing polymer concentration of formulations, % yield, the entrapment efficiency and particle size were increased whereas % drug release decreased. The In Vitro release study was done using U.S.P. dissolution rate basket type apparatus in phosphate buffer pH 7.4 for 10 hr. It shows that on increasing polymer concentration the drug release of all formulations was gradually decreased. In Vitro mucoadhesion study depicts that as the polymer concentration increased, mucoadhesive nature of the formulation was also increased. The microspheres of NTZ (formulation F9) showed best results due to highest drug entrapment efficiency (85.50%), and percentage drug release after 10.0 hr. was 50.25%. The rate of release followed First order kinetics. The microspheres exhibits good mucoadhesive properties in in- vitro wash-off test at pH 7.4 (Intestinal pH) than pH 1.2 (gastric pH),because the drug was completely absorbed in Gastrointestinal tract, Therefore, it can be concluded that Nitazoxanide Loaded algino-carbopol-934 microspheres can be formulated for sustained drug delivery of Nitazoxanide used in Chronic Hipatitis-C.
 Keywords: Mucoadhesive microspheres, Nitazoxanide, Carbopol-934, Ethyl cellulose, Sodium Alginate, Factorial design.

Concentration effect on the nonlinear measures of dense polyethylene oxide solutions under large amplitude oscillatory shear

In this paper, we study the nonlinear viscoelastic response of concentrated polyethylene oxide solutions under large amplitude oscillatory shear (LAOS). We investigate the concentration effect as a function of strain and shear rate by using nondimensional elastic and viscous Lissajous–Bowditch plots. We also employ the mitlaos software to calculate the intracycle nonlinear viscoelasticity parameters. We find that the transition to nonlinear behavior occurs at lower strain values as the polymer concentration increases. For the higher concentration and at large strain amplitudes, the intracycle elastic stress component is almost zero to a large extent of the oscillation cycle and thus strain-independent. The corresponding stress decomposition in the shear rate domain shows a significant shear rate dependence, with a self-intersection of the total stress curve. By increasing the oscillation frequency and, correspondingly, the shear rate, by one order of magnitude, the intercycle nonlinear behavior does not qualitatively change. The spatiotemporal velocity profiles are obtained using a custom-made particle image velocimetry system. Interestingly, we record nonlinear velocity profiles at approximately 300% strain along with significant wall slip for both oscillation frequencies. The intracycle velocity data close to the stationary plate reveal strong nonlinear velocity waveforms. The results of this study suggest that the number of entanglements per chain is responsible for the strain thinning or thickening behavior in LAOS.

Properties of hooked end steel fiber reinforced acrylic modified concrete

In this study, the effects of fiber on the properties of polymer modified concrete (PMC) were investigated. Hooked end steel fibers with two different lengths but similar aspect ratios were used at 0.5% and 1.0% by volume fraction. Acrylic polymer was added into concrete at 2 different weight ratios, 7.5% and 15% by weight of cement. Four experiments were carried out: slump, compression, flexural and water penetration tests. Results indicated that both fiber content and length, and polymer content played an important role on the properties of fiber reinforced polymer modified concrete (FRPMC) in different ways. In term of workability, the slump increased with the increasing polymer content and decreased when the fiber was added into PMC. For mechanical properties, fiber addition enhanced the load response of PMC and increased the strength and fracture toughness. In term of compressive strength, regardless of PCM type, the strength of FRPMC was found to increase up to about 15% as compared to plain PCM. The effect of fibers was more pronounced under bending load than under compression. The increase in flexural load up to 34% was observed in FRPMC as compared to plain PMC. For water penetration test, fiber at low volume fraction had a negligible effect on the water tightness. However, when the fiber volume fraction was increased to 1.0%, the water tightness was reduced significantly.

Chain-Length Shortening of Methyl Ethyl Hydroxyethyl Cellulose: An Evaluation of the Material Properties and Effect on Foaming Ability

During the past century, plastics have become a natural element in our every-day life. Lately however, an awareness about the fossil origin and often non-degradable nature of many plastics is rising. This has resulted in the emergence of some bio-based and/or biodegradable plastics, often produced from renewable resources. One possible candidate for bioplastics production could be found in cellulose. This paper aims at contributing information regarding a cellulose derivative, which could possibly be used in foamed plastics applications. Therefore, the reduction of the chain-length of a methyl ethyl hydroxyethyl cellulose (MEHEC), assessed by size exclusion chromatography, and the effect of chain-length on the foaming behaviour were studied. The foaming was accomplished with a hot-mould technique using aqueous polymer solutions. The generated steam was here used as the blowing agent and important parameters were polymer concentration and solution viscosity. The density of the produced foams was assessed and was in some cases comparable to that of commodity foams. It was found that reducing the chain-length enabled an increase of the initial polymer concentration for the foaming process. This is believed to be beneficial for creating more structurally stable foams of this type.

Interaction between human serum albumin and cholesterol-grafted polyglutamate as the potential carriers of protein drugs

Currently there is no successful platform technology for the sustained release of protein drugs. It seems inevitable to specifically develop new materials for such purpose, and hence the understanding of protein–material interactions is highly desirable. In this study, we synthesized cholesterol-grafted polyglutamate (PGA-g-Chol) as a hydrophobically-modified polypeptide, and thoroughly characterized its interaction with a model protein (human serum albumin) in the aqueous solution by using circular dichroism, fluorescence methods, and light scattering. With the protein concentration fixed at 5 μmol/L, adding PGA-g-Chol polymers into the solution resulted in continuous blue shift of the protein fluorescence (from 339 to 332 nm), until the polymer molar concentration reached the same value as the protein. In contrast, the un-modified polyglutamate polymers apparently neither affected the protein microenvironment nor formed aggregates. Based on the experimental data, we proposed a physical picture for such protein–polymer systems, where the polymer first bind with the protein in a 1:1 molar ratio via a fraction of their hydrophobic pendant cholesterol resides along the polymer chain. In this protein/polymer complex, there are excess unbound cholesterol residues. As the polymer concentration increases, the polymers form multi-polymer aggregates around 200 nm in diameter via the same hydrophobic cholesterol residues. The protein/polymer complex also participate in the aggregation via their excess cholesterol residues, and consequently the proteins are encapsulated into the nanoparticles. The encapsulation was also found to increase the thermal stability of the model protein.

Fabrication and properties of PVDF and PVDF‐HFP microfiltration membranes

ABSTRACTPoly(vinylidene fluoride) (PVDF) and poly(vinylidene fluoride)‐co‐hexafluoropropylene (PVDF‐HFP) were used to fabricate porous microfiltration membranes via a thermally induced phase separation (TIPS) method, and dibutyl phthalate (DBP) was used as diluent. The effects of polymer concentration on structure and performance were studied in detail. In addition, the effect of incorporation of hexafluoropropylene (HFP) groups on the membrane was also investigated. The formation mechanism was proposed with the assistance of a phase diagram. The results showed that the incorporation of HFP groups resulted in a lower crystallization temperature (Tc) of the polymer/DBP system. In addition, the porosity, pure water flux, and ink solution flux decreased with increasing polymer concentration. In contrast, the water contact angle, ink rejection ratio, and mechanical properties had an increasing tendency. When the polymer concentration was 30 wt %, the obtained membrane was most suitable for microfiltration. Furthermore, the incorporation of HFP groups improved the properties of the obtained membrane, including better hydrophobicity, mechanical properties, antifouling property, and chemical resistance. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46711.

Effect of Polymer Degradation on Polymer Flooding in Heterogeneous Reservoirs.

Polymer degradation is critical for polymer flooding because it can significantly influence the viscosity of a polymer solution, which is a dominant property for polymer enhanced oil recovery (EOR). In this work, physical experiments and numerical simulations were both used to study partially hydrolyzed polyacrylamide (HPAM) degradation and its effect on polymer flooding in heterogeneous reservoirs. First, physical experiments were conducted to determine basic physicochemical properties of the polymer, including viscosity and degradation. Notably, a novel polymer dynamic degradation experiment was recommended in the evaluation process. Then, a new mathematical model was proposed and an in-house three-dimensional (3D) two-phase polymer flooding simulator was designed to examine both polymer static and dynamic degradation. The designed simulator was validated by comparison with the simulation results obtained from commercial software and the results from the polymer flooding experiments. This simulator further investigated and validated polymer degradation and its effect. The results of the physical experiments showed that the viscosity of a polymer solution increases with an increase in polymer concentration, demonstrating their underlying power law relationship. Moreover, the viscosity of a polymer solution with the same polymer concentration decreases with an increase in the shear rate, demonstrating shear thinning. Furthermore, the viscosity of a polymer solution decreased with an increase in time due to polymer degradation, exhibiting an exponential relationship. The first-order dynamic degradation rate constant of 0.0022 day−1 was greater than the first-order static degradation rate constant of 0.0017 day−1. According to the simulation results for the designed simulator, a 7.7% decrease in oil recovery, after a cumulative injection volume of 1.67 pore volume (PV) was observed between the first-order dynamic degradation rate constants of 0 and 0.1 day−1, which indicates that polymer degradation has a detrimental effect on polymer flooding efficiency.

Ring polymers are much stronger depleting agents than linear ones

ABSTRACTWe investigate the conformations and shapes of circular polymers close to planar, hard walls as well as the ensuing ring–wall and polymer-induced wall–wall interactions in ring polymer solutions. We derive, by means of Monte Carlo simulations, the effective interaction potential between the centres of mass of flexible, unknotted ring polymers and a hard wall for different polymerisation degrees N. Adopting the coarse-grained description of ring polymers as ultrasoft, penetrable spheres, mean-field density functional theory is then employed in order to examine ring polymer solutions under confinement. We demonstrate that, below the semi-dilute regime, ring polymers structure close to walls much more strongly than their linear counterparts, their density profiles featuring pronounced oscillations. Moreover, the polymer-induced depletion potential between the two walls exhibits an oscillatory profile reminiscent of hard-sphere systems, with oscillations that intensify upon increasing polymer concentration. The obtained form of the depletion interaction is shown to be qualitatively different in comparison to the case of linear polymer solutions at the corresponding densities.

Improvement Effect of Water-Based Organic Polymer on the Strength Properties of Fiber Glass Reinforced Sand.

The mechanical properties of sandy soil can be effectively improved by the incorporation of water-based polymer and glass fibers. In order to study the reinforcement effects of a type of water-based organic polymer and fiber glass on sand, three strength tests (unconfined compression test, direct shear test and tensile test) and scanning electron microscopy were carried out. A series of polymer content, fiber content and dry density were selected for the tests. The results revealed that the composite reinforcement of water-based organic polymer and fiber glass can improve the strength. With an increase in polymer content and fiber content, the unconfined compression strength, the cohesion, and the tensile strength increase. The internal friction angles maintain a relatively stable state. All three strength properties increase with an increase in dry density. The results can be considered as the reference for sand reinforced engineering.

Transition of phase-separated PBTPA/PMMA solution droplets from core–shell to Janus morphology under UV light irradiation

Here, we report the morphological transition of a phase-separated structure from core–shell to Janus morphology in droplets consisting of a poly(4-butyltriphenylamine) (PBTPA)/poly(methyl methacrylate) (PMMA) blend solution, induced by UV light irradiation. We obtained a phase-separated structure formed by the evaporation of the solvent from polymer solution droplets dispersed in an aqueous solution containing a surfactant. The rate of transition decreased with increasing polymer concentration and diameter of the droplet. It was also found that the transition was caused by UV light with a wavelength of 365 nm, which is mainly absorbed by PBTPA, indicating that this phenomenon is triggered by PBTPA. When the droplet was heated to 75 °C, no transition was observed.

Direct Liquid to Crystal Transition in a Quasi-Two-Dimensional Colloidal Membrane

Using synchrotron-based small-angle X-ray scattering, we study rigid fd viruses assembled into isolated monolayers from mixtures with a nonabsorbing polymer, which acts as an osmotic agent. As the polymer concentration increases, we observe a direct liquid to crystal transition, without an intermediate hexatic phase, in contrast with many other similar systems, such as concentrated DNA phases or packings of surfactant micelles. We tentatively attribute this effect to the difference in stiffness. The liquid phase can be well described by a hard-disk fluid, while we model the crystalline one as a hexagonal harmonic lattice and we evaluate its elastic constants.

Development of a High-Temperature-Resistant Polymer-Gel System for Conformance Control in Jidong Oil Field

Summary The PG Reservoir in Jidong Oil Field is at a depth of approximately 4500 m with an extremely high temperature of approximately 150°C. The average water cut has reached nearly 80%, but the oil recovery is less than 10% after only 2 years of waterflooding process. It is of great importance to develop a high-temperature-resistant plugging system to improve the reservoir conformance and control water production. An in-situ polymer-gel system formed by the terpolymer and a new crosslinker system was developed, and its properties were systematically studied under the condition of extremely high temperature (150°C). Suitable gelation time and favorable gel strength were obtained by adjusting the concentration of the terpolymer (0.4 to 1.0%) and the crosslinker system (0.4 to 0.7%). An increase of polymer and crosslinker concentration would decrease the gelation time and increase the gel strength. The gelant could form continuous 3D network structures and thus have an excellent long-term thermal stability. The syneresis of this gel system was minor, even after being heated for 5 months at the temperature of 150°C. The gel system could maintain most of the initial viscosity and viscoelasticity, even after experiencing the mechanical shear or the porous-media shear. Core-flow experiments showed that the gel system could have great potential to improve the conformance in Jidong Oil Field.

Study on Variation of Physicochemical Parameters of the Polymer/Surfactant Binary Multisystem in Porous Media

The sulfonate Gemini surfactant and hydrophobic associating polymers were prepared with different ratio in multisystem, and we measured viscosity and interfacial tension of the solution before pour it into the core. The multisystem with different ratio was poured into the core, we measured the produced liquid viscosity, interfacial tension, the concentration of polymer and surfactant at core outlet with different injection stage and at different locations after stable, calculated the dynamic adsorption capacity of the binary multisystem, and measured the static adsorption capacity of binary multisystem with different ratio on natural oil sand in Suizhong 36-1 Oilfield. Experimental results show that the stable viscosity of the produced liquid of multisystem increased with increase of polymer concentration, and decreased with the increase of the distance flowed through the core, and these changes concentrated on the first 1/3 of core; the interfacial tension decreased with the increase of mass fraction of surfactant, the stable interfacial tension value after passed through the core was about 7-10 times before solution injected; Multisystem has the chromatographic fractionation in rock.

Mechanical Properties of Polymeric Emboli for Occlusion of Blood Vessels

Investigations of the formation of solid emboli in an aqueous medium of biocompatible solutions of polymers were carried out. Approaches to the production of solid samples for tensile and compression tests were developed and their mechanical properties were studied. It is shown that the ultimate compressive and tensile strength of emboli formed in an aqueous medium slightly decreases with increasing time of aging in water and increases markedly with increasing polymer concentration in the embolizing solution. All the tested compounds exhibit strength sufficient to not be destroyed by the action of blood flow.

Examination of 2-methacryloyloxyethyl phosphorylcholine polymer coated acrylic resin denture base material: surface characteristics and Candida albicans adhesion

The aim of this study is to evaluate the effects of 2-methacryloyloxyethyl phosphorylcholine (MPC) polymer coating with various concentrations onto acrylic resin denture base material on surface characteristics such as contact angle and surface roughness and on Candida albicans adhesion which is the major factor of denture stomatitis. Specimens, prepared from heat-polymerized acrylic denture base material, were divided into control and three test groups, randomly. Surfaces of the specimens in test groups were coated with poly(MPC) (PMPC) by graft polymerization of MPC in different concentrations (0.25 mol/L; 0.50 mol/L and 0.75 mol/L), while no surface treatment was applied to the control group. Contact angles and surface roughness were examined, and chemical composition of the surfaces was analyzed by Attenuated Total Reflectance-Fourier Transform Infrared Spectroscopy (FTIR) to verify the presence of PMPC coatings. Then, specimens were incubated with C. albicans for 18 h and the number of adhered cells was determined. Upon PMPC coating, the contact angle values statistically decreased, but no difference was found in surface roughness values. A statistically significant decrease was observed in C. albicans adhesion in parallel with the increase in the MPC polymer concentration. There was no significant difference between 0.50 mol/L and 0.75 mol/L groups in terms of adhesion. These findings indicated that graft polymerization of MPC on acrylic denture base material reduces the adhesion of C. albicans, and may be evaluated as a coating for prevention of denture stomatitis.

Investigation of Mechanical Properties of Self Compacting Polymeric Concrete with Backpropagation Network

Acrylic polymer that is highly stable against chemicals and is a good choice when concrete is subject to chemical attack. In this study, self-compacting concrete (SCC) made using acrylic polymer, nanosilica and microsilica has been investigated. The results of experimental testing showed that the addition of microsilica and acrylic polymer decreased the tensile, compressive and bending strength of the concrete. The addition of nanosilica and an increase in polymer content increased the bending strength of concrete and decreased the tensile and compressive strengths. Because, in the laboratory, the number of samples were limited and the amount of variation was small, comprehensive results cannot be achieved. With the help of neural networks, estimating any amount within the range of the input data is possible. In this paper, in addition to the experimental results, a backpropagation neural network (BNN) was used to simulate the testing on the strength of self-compacting polymeric concrete. The results showed that the use of the normalized mean squared error, resilient backpropagation training, tangent-sigmoid and log sigmoid transfer functions and five neurons in each hidden layers in a two-layer BNN produced good results with a regression value of 0.95 and error of 0.17.

Gas-liquid membrane contactors: Effects of polymer concentration and solvent type on pore size distribution

This study investigates the effects of polymer concentration and solvent type on the pore size distribution (PSD) of the fabricated gas-liquid membrane contactors (MCs). Eighteen flat-sheet MCs are fabricated using polysulfone (PSf) and polyethersulfone (PES) polymers, with polymer concentration of 10%, 15%, and 20%. Dimethylformamide (DMF) and n-methyl-2-pyrrolidone (NMP) solvents are used to prepare the polymeric solutions. The role of polyvinylpyrrolidone (PVP) on the mean pore size of MCs is also studied. Scanning electron microscope (SEM) analysis is applied to visualize the pore system of the fabricated MCs. Image processing technique is used to obtain the PSD of the fabricated MCs using their SEM images. Experimental results indicate that increasing polymer concentration shifts the PSD of MCs toward smaller pores. Polymer concentration has negligible impact on the mean pore size of the NMP-based MCs. For the DMF-based MCs however, mean pore size significantly decreases by increasing polymer concentration. Also, NMP-based MCs have smaller pore size compared with the DMF-based MCs. Addition of PVP to the polymeric solutions lead to larger mean pores. This observation is very pronounced at low polymer concentration values.

Honeycomb-like PLGA- b-PEG Structure Creation with T-Junction Microdroplets.

Amphiphilic block copolymers are widely used in science owing to their versatile properties. In this study, amphiphilic block copolymer poly(lactic- co-glycolic acid)- block-poly(ethylene glycol) (PLGA- b-PEG) was used to create microdroplets in a T-junction microfluidic device with a well-defined geometry. To compare interfacial characteristics of microdroplets, dichloromethane (DCM) and chloroform were used to prepare PLGA- b-PEG solution as an oil phase. In the T-junction device, water and oil phases were manipulated at variable flow rates from 50 to 300 μL/min by increments of 50 μL/min. Fabricated microdroplets were directly collected on a glass slide. After a drying period, porous two-dimensional and three-dimensional structures were obtained as honeycomb-like structure. Pore sizes were increased according to increased water/oil flow rate for both DCM and chloroform solutions. Also, it was shown that increasing polymer concentration decreased the pore size of honeycomb-like structures at a constant water/oil flow rate (50:50 μL/min). Additionally, PLGA- b-PEG nanoparticles were also obtained on the struts of honeycomb-like structures according to the water solubility, volatility, and viscosity properties of oil phases, by the aid of Marangoni flow. The resulting structures have a great potential to be used in biomedical applications, especially in drug delivery-related studies, with nanoparticle forming ability and cellular responses in different surface morphologies.

Study on Influence Factors and Governance Countermeasures of Movable Gel Prepared with Backfilling Waste Water

Movable gel as profile control and flooding is one of the main measures in tertiary oil recovery in Huabei Oilfield. Many blocks have tight fresh water supplies, but produced waste water can not be discharged. Therefore, preparing movable gel with backfilling waste water has become an inevitable development trend of profile control and flooding. Three different quality of sewage water named SW, YW and ZW were used to prepare gel and then compared with gel prepared clean water. The results showed that the gel viscosity prepared with clean water was 1.5-5.6 times of sewage water at the same formula concentration. For this reason, the effect of Na+, Ca2+, Fe2+ on the gel performance were analyzed. The above ions lead to a decrease in the gel viscosity and poor stability, which can not even be crosslinked. According to the sewage water characteristics, corresponding treatment measures were developed respectively. The best treatment of SW and ZW was increasing polymer concentration followed by the addition of thiourea. The best treatment of YW was also increasing polymer concentration followed by stirring and aeration. The gel viscosity reached to 1800-2500mPa⋅s and maintained at 800-1200mPa⋅s after 90 days at formation temperature. It showed that the treatment can effectively improve the gel viscosity and stability prepared with sewage water. The results provide valuable experiences for the preparation of movable gel with different quality waste water.