The effect of added salt on the flow of highly dilute solutions of poly(ethylene oxide) polymers

Early transition, early turbulence, and drag reduction were detected in flowing solutions of high molecular weight poly(ethylene oxide) condensates. Progressive addition of salt (magnesium sulfate) increased the onset point characterizing deviations from Newtonian flow for 1 ppm Polyox Coagulant solutions and eliminated early transition in the 10 ppm WSR-35 solutions. No further drag reduction was observed when the salt molarity reached the 0.65 level. In the Coagulant solutions the onset wall shear stress characterizing the flow deviation was an inverse function of the intrinsic viscosity of the polymer in the salt solution.     

高分子稀溶液中溶剂对分子特性与流变性能的影响

本文研究了不同溶剂对离子性和非离子性高分子稀溶液的分子构型和流变性能的影响.在部分水解的聚丙烯酰胺水溶液中加入无机盐,测量并计算了分子扩张因数,特征粘度与盐浓度、盐离子价数、溶液pH值的关系.同时使用不同的有机溶剂测量聚丁烯溶液的Maxwell模型松弛时间和分子扩张因数.研究表明,高分子稀溶液可藉调整溶剂性质的方法以达到期望的流变特性.     

Rheological properties of progesterone microemulsions: Influence of xanthan and chitosan biopolymer concentration

In this preformulations study, rheological properties of microemulsions with progesterone (1%) were studied to analyze the effect of xanthan and chitosan at different concentrations (0.5–3%). Steady shear and oscillatory rheological properties were analyzed using a controlled stress rheometer. Steady shear data were satisfactorily adjusted to the Carreau model. For all preparations, shear‐thinning behavior was observed. Zero shear viscosity (η₀) increased with the biopolymer concentration. The results from dynamic experiments showed the behavior of all preparations with xanthan gum and those of chitosan to be characteristic of weak gels and liquid‐like solutions, respectively. The correlation between dynamic and steady‐shear properties (extended Cox‐Merz rule) was satisfactory for the two polymers. The recovery analysis of microemulsions with xanthan showed a total recovery percentage of 90% for the highest concentrations of this polymer. However, microemulsions with chitosan showed practically no recovery. Progesterone release was greater for the microemulsions with chitosan. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Effect of drag-reducing additives on free oscillatory flow

The damping rates of free oscillations in U-tube manometers were measured in water and aqueous solutions of Polyox WSR 301, Separan AP273 and a wetting agent (Aerosol OT). The manometers were made from flexible plastic (PVC) or glass tube. Small reductions of the linear damping constant by low concentrations of Polyox and Aerosol additives in the PVC tubes were attributed to a reduction in surface tension effects. All the additives increased the linear damping constants in both types of manometer, when used at larger concentrations. This was found to be due solely to increased solution viscosity. Large fractional reductions in damping due to Polyox in the PVC-tube systemwere associated with the nonlinear oscillations in the final period of the decay. This effect has not yet been explained.     

Turbulent drag effectiveness and shear stability of xanthan-gum-based graft copolymers

A number of graft copolymers of xanthan gum and polyacrylamide have been synthesized by grafting acrylamide onto xanthan gum using the ceric-ion-initiated solution polymerization technique. The effects of various synthesis parameters such as amount of catalyst, reaction time, and ratio of xanthan and acrylamide on drag reduction effectiveness of the graft copolymers have been studied. The scaling up of grafting reaction has been accomplished in 40-L reactor. The drag reduction effectiveness of the graft copolymers is investigated over a wide range of concentrations and Reynolds numbers. It is shown that the maximum drag reduction obtainable in xanthan gum solutions above 300 ppm can be obtained in solutions of graft copolymers at concentrations of 100–150 ppm. The grafting also improves the shear stability at higher Reynolds numbers. The shear stability of the graft copolymers at constant wall stress has been found to be superior to polyacrylamide and the mixtures of polyacrylamide and xanthan gum. In general, the shear stability of graft copolymers and polyacrylamide is shown to increase with concentration. The drag reduction characteristics and shear stability have been discussed in terms of structural features of the graft copolymers. The drag reduction characteristics of the graft copolymers are found to be similar to those of flexible polymers.     

韦兰胶与黄原胶流变性比较研究

对韦兰胶和黄原胶的流变性(包括粘弹性、温度稳定性和耐盐性)进行了比较研究.结果表明,与黄原胶相比,韦兰胶在相同浓度下具有更好的粘弹性、在低温下更稳定、具有较好的耐盐性.     

Applications of Xanthan gum

Xanthan gum, the extracellular polysaccharide from Xanthomonas comperstris, provides aqueous solutions with properties that are extremely useful in a large number of industrial applications, both food and non-food. These properties, a consequence of xanthan gum's particular molecular shape, are: high at-rest or low-shear viscosity even at low gum concentrations, yield value, high pseudoplasticity, increased viscosity in the presence of added salt depending on gum concentration, stable viscosity over a wide range of temperature and pH in the presence of added salt, synergistic increase in viscosity in the presence of guar gum and locust bean gum, thermoreversible gelation with locust bean gum at appropriate gum concentratins, and gelation with di-and trivalent metal ions and borates under specific conditions. Xanthan gum is thus an excellent stabiliser for a wide variety of suspensions, emulsions, and foams and is highly effective over a range of temperature, pH and ionic strength. In addition, its pseudoplasticity allows the formulation of products which require not only high at-rest viscosity but also low viscosity under highshear application conditions.     

Flow characteristics of three enhanced oil recovery polymers in porous media

This article presents an experimental study aiming to explore the relationship among rheological properties, flow characteristics in porous media, and enhanced oil recovery (EOR) performance of three typical EOR polymers. The results suggest that xanthan gum exhibits a very pronounced shear‐thinning behavior, which is probably also the reason explaining its moderate adsorption extent within porous media (thickness of adsorbed layer, e = 3.1 μm). The advanced viscoelastic properties coupled with the less adsorption extent compared to the hydrophobically modified copolymer (HMSPAM) allow xanthan gum to establish a “piston‐like” displacement pattern and lead up to 49.4% original oil in place (OOIP) of the cumulative oil recovery during polymer flooding. Regarding HMSPAM, the significant permeability reduction of the porous media induced by multilayer adsorption (e = 5.6 μm) results in much higher drive forces (ΔP) in the extended waterflooding stage, which further raises the cumulative oil recovery by 18.5% OOIP. In general, xanthan gum and HMSPAM totally produced 84% OOIP which is 15% higher than the extensively used EOR polymer, hydrolyzed polyacrylamide (HPAM), under the same experimental conditions. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41598.     

Rheology and viscosity scaling of the polyelectrolyte xanthan gum

The viscosity as a function of concentration for xanthan gum in both salt‐free solution and in 50 mM NaCl is measured and compared with a scaling theory for polyelectrolytes. In general, the zero shear rate viscosity and the degree of shear thinning increase with polymer concentration. In addition, shear thinning was observed in the dilute regime in both solvents. In salt‐free solution, four concentration regimes of viscosity scaling and three associated critical concentrations were observed (c* ≈ 70 ppm, c_e ≈ 400 ppm, and c_D ≈ 2000 ppm). In salt solution, only three concentration regimes and two critical concentrations were observed (c* ≈ 200 ppm and c_e ≈ 800 ppm). In the presence of salt, the polymer chain structure collapses and occupies much less space resulting in higher values of the critical concentrations. The observed viscosity‐concentration scaling is in very good agreement with theory in the semidilute unentangled and semidilute entangled regimes in both salt‐free and 50 mM NaCl solution. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Turbulent flow friction reduction effectiveness and hydrodynamic degradation of polysaccharides and synthetic polymers

Two water-soluble synthetic polymers and several polysaccharides were compared for friction reduction effectiveness during increased exposure to turbulent flow. Solutions were passed through a 0.117 × 41.0 cm fine bore tube at a constant solvent wall shear stress of 4200 dynes/cm² and wall shear rate of 4 × 10⁵ sec^?1. After one pass through the tube, greatest friction reduction at low polymer concentrations was in the order poly(ethylene oxide) > polyacrylamide > bacterial polysaccharide from Xanthomonas campestris > guar gum. As a result of mechanical degradation, after 40 passes of 40 ppm solutions, friction reduction effectiveness was in the order polyacrylamide > polysaccharide from Xanthomonas campestris > poly(ethylene oxide) > guar gum. Degradation curves, the effect of concentration on degradation, and boundary layer and pipe flow applications are discussed.     

Xanthan gum: A versatile biopolymer for biomedical and technological applications

Xanthan gum is an extracellular polymer produced mainly by the bacterium Xanthomonas campestris. Traditionally it plays an important role in industrial applications as thickener, emulsion stabilizer and it has been added to water‐based drilling fluids due to its pseudoplastic behavior and thermal stability. The structural properties of xanthan in solution can be tuned by the temperature and ionic strength; under high ionic strength or low temperature, xanthan chains are arranged in helical conformation, whereas under low ionic strength or high temperature, xanthan chains are coiled. Xanthan high molecular weight favors the building up of physical and chemical networks, which have been used as carriers for drugs and proteins and as scaffolds for cells. In combination with other polymers xanthan has been applied as excipient in tablets or as supporting hydrogels for drug release applications, particularly due to its acid resistance. The large versatility of xanthan gum opens the possibility for the creation of new architectures and additional applications involving this fascinating polymer. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42035.     

A comparative study of the effect of different drag-reducing polymers on electrochemical mass transfer

The effect of Polyox, Separan and CMC drag-reducing polymers on the rate of electrochemical mass transfer was studied using the cathodic reduction of K₃Fe(CN)₆ in neutral media at a rotating cylinder cathode. Reynolds number and polymer concentration were varied over the ranges 764–10470 and 10–200 ppm respectively. Under these conditions it was found that the three polymers reduce the rate of mass transfer by a maximum of 47%, 30%, and 17% for Polyox, Separan and CMC, respectively. Mass transfer data in the three polymer solutions was correlated by the following equations: for Polyox: (St)=0.051(Re)^–0.3 (Sc)^–0.644 (u/u ₀ ^–0.7 for Separan: (St)=0.065(Re)^–0.3 (Sc)^–0.644 (u/u ₀)^–0.7 for CMC: (St)= 0.075(Re)^–0.3 (Sc)^–0.644) (u/u ₀)^–0.5 List of symbols I limiting current density (A cm^–2) - Z number of electrons involved in the reaction - F Faraday's constant - K mass transfer coefficient (cm s^–1) - V linear velocity of the cylinder (cm s^–1) - D diffusion coefficient (cm²s^–1) - v kinematic viscosity (cm²s^–1) - d diameter of the cylinder (cm) - u, u ₀ viscosity of solutions with and without polymer respectively (P) - density (g cm^–3) - c concentration of Fe(CN) ₆ ^3– (mol cm^–3) - (St) Stantonnumber=K/V - (Sc) Schmidt number=v/D - (Re) Reynolds number=Vd/u     

Rheological investigation of xanthan gum–chromium gelation and its relation to enhanced oil recovery

Xanthan gum–water solutions with polymer concentrations 0.05–1% w/w and chromium ion content 30–1200 ppm were being gelled at temperatures from 25 to 90°C. A control deformation test (CD test) at a constant shear rate 0.05 s^?1 was performed for all the specimens. Shear moduli of elasticity and in some cases yield stresses and yield strains were determined from these tests. The energy of activation E_a = 93 ± 6 kJ/mol was obtained. The dependence of the gelation rate on the ionic concentration followed a power law with a coefficient of 1.8. There was relatively small dependence of the gelation rate on the xanthan gum concentration. Surprisingly, the maximum obtainable moduli at complete gelation do not depend on xanthan gum concentration in the range 0.2–1% w/w and are about 2400 Pa. The number of the bound chromium ions per monomer unit of xanthan gum is changed from 0.64 to 0.16 for the above measured concentrations of the polymer. High moduli gels on the base of the lower concentrations of xanthan gum were practically not recoverable after mechanical destruction. The assumption was made that the main reason for the profile modification of the flow for enhanced oil recovery in porous media is the yield stress of the gels. The smaller capillaries can even be closed if the yield stress is higher than the maximum shear stress existing in the capillary. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 160–166, 2007     

Miscibility of blends of Aeromonas gum or Erwinia gum with other polysaccharides

Aeromonas (A) gum and Erwinia (E) gum are acidic heteropolysaccharides, which exist in water as expanded chains caused by the electrostatic repulsion between the charged groups. A modified approach, which was suggested to estimate miscibility of stiff polymer in our previous study, was used to determine miscibility parameter μ for blends between A gum or E gum with other polysaccharides, by using viscometry in aqueous 0.1M NaCl solution. When weight ratios of E gum/pectin were in the range of 3 : 7 ∼ 7 : 3, the blends in aqueous solution are miscible. The blends of A gum/xanthan, A gum/pectin, and E gum/xanthan in aqueous solution are obviously immiscible. When the weight fraction (w₂) of A gum or E gum in the mixture solution is 0.7, the μ predicts that the miscibility of blend films was on the order of E gum/pectin > E gum/xanthan > A gum/pectin > A gum/xanthan. These results are in good agreement with those observed by scanning electron microscopy and Fourier transform IR. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 1387–1395, 1999     

Increasing viscosity in entangled polyelectrolyte solutions by the addition of salt

The viscosity of several polyelectrolytes is measured in both salt free solutions and solutions in the high salt limit. At low polymer concentrations, the zero shear rate viscosity decreases as much as 100-fold upon addition of a monovalent salt, namely NaCl. However, as polymer concentration increases, the viscosity difference between polymer in salt free and in monovalent salt solution diminishes. Further, the zero shear rate viscosity becomes independent of added monovalent salt at the critical polyelectrolyte concentration c_D. Above c_D, the addition of monovalent salt increases the zero shear rate viscosity of the entangled polyelectrolyte solutions. The viscosity increase agrees with viscosity scaling theory for polyelectrolytes in the entangled regime. Polyelectrolytes exhibiting an increase in viscosity above c_D in the presence of monovalent salt include three natural anionic polyelectrolytes (xanthan, carrageenan, welan), one synthetic anionic polyelectrolyte (hydrolyzed polyacrylamide), and one natural cationic polyelectrolyte (chitosan). Generally, these polyelectrolytes are relatively high molecular weight (>1 M Dalton), which makes c_D experimentally accessible (e.g., c_D = 0.2 wt% for xanthan). The magnitude of the viscosity increase is as high as 300% for xanthan and nearly independent of monovalent salt concentration in the high salt limit. The increase in viscosity in monovalent salt solution and magnitude of c_D appear to be heavily influenced by the molecular characteristics of the polymers such as monomer weight, molecular structure, and chain conformation.     

Graft copolymerization of methacrylic acid onto xanthan gum by Fe2+/H2O2 redox initiator

The graft copolymer of xanthan gum with methacrylic acid was synthesized in inert atmosphere by using Fentos reagent as a redox initiator. The effect of reaction conditions on grafting parameters [G(%), E(%), C(%), A(%), H(%), and R_g] was investigated. Similar trend was observed on increasing the concentration of ferrous ion and hydrogen peroxide from 4.0 to 20.0 × 10^?3 mol dm^?3 and 2.5 to 10 × 10^?3 mol dm^?3 respectively, i.e., initially grafting parameters increased and after a certain range of concentration grafting parameters showed decreasing trend. Hydrogen ion shows influenced result i.e., small increment of concentration in hydrogen ion presents much increment in percent of grafting. It was observed that the [G(%), E(%), C(%), A(%), and R_g] increased upto 6.67 × 10^?2 mol dm^?3 concentration of methacylic acid after that it decreased. Maximum G(%) was obtained at minimum concentration of xanthan gum i.e., at 40 × 10^?2 g dm^?3. The optimum temperature and time duration of reaction for maximum percentage of grafting were found to be 45°C and 150 min respectively. Thermogravimetric analysis showed that the xanthan gum‐g‐methacrylic acid is thermally more stable than pure gum. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Mechanistic aspects of polysaccharide complexation by quaternary ammonium salts,based on the reaction of Xanthan gum with [1-14C]cetyltrimethylammonium bromide (Part II)

Complex formation between cetyltrimethylammonium bromide (CTAB) and xanthan gum in Xanthomonas campestris fermentation broth has been further used to exemplify the reaction between carboxy group — containing polysaccharides and quaternary ammonium salts. The variation of the molar ratio of xanthan gum: CTAB in the supernatant with variation of addition of quaternary ammonium salt is one parameter of the reaction which shows a definite relationship. Although this molar ratio in the supernatant is high (> 1) during the initial stages of the reaction, when little precipitation of the polysaccharide is occurring; it appears that the ratio must be below a critical value of about one before the end-point of the complexation reaction can occur. The molar ratio of xanthan gum:CTA in the complex is initially exaggerated due to precipitation of polysaccharide with uncomplexed carboxy groups, but this ratio attains a constant value during the final stages of the reaction. A surprising observation of this study was the evidence obtained that CTAB added to X. campestris fermentation broth in excess of the complexation reaction end-point requirement is associated with the insoluble xanthan gum-CTA complex and is not present in the supernatant. Several possible explanations have been put forward to account for this observation. On the basis of this and another recent study, a detailed model of the mechanism of the complexation reaction between xanthan gum and CTAB in aqueous solution has been proposed. Discussion has been given to the implications and applicability of this particular complexation reaction mechanism.     

On the slip phenomenon of polymeric solutions through capillaries

The slip phenomenon through capillaries has been analyzed experimentally using solutions of polyacrylamide and xanthan gum. These polymeric solutions present macromolecules with different conformations in flow. Attention was given to the influence of molecular conformation of those polymeric solutions upon the slip velocity. Considerable variations on the slip velocity were observed when the ionic strength of the xanthan solution was increased and also when the material of the capillaries was changed. Measured magnitudes were much larger in the xanthan solutions than those observed in the polyacrylamide solution.     

Rheological properties and some applications for rhamsan and xanthan gum solutions

The rheological properties of solutions of xanthan gum (Kelzan® D) and three rhamsan gums, S-60, S-130 and S-194, are examined. Effects studied include those of temperature, concentration and (for the rhamsan gums) extent of side chain branching. Solutions of greater viscosity and elasticity at most shear rates result as the degree of branching increases. When compared with xanthan gum, S-194 is found to be less temperature sensitive and more stable to excess shear. The use of these polymers in two commercial applications, i.e. coal–water mixtures and timber preservative emulsions, is also examined. Several advantages are identified when rhamsan gums are used instead of xanthan gum in both cases.     

三赞胶对钻井液性能影响的研究

三赞胶是我国自主开发的一种新型生物胶环保处理剂。重点研究三赞胶在不同条件下（温度、般土含量和含盐量）对钻井液流变性能和滤失性能的影响规律,并与黄原胶进行对比。试验结果表明：在温度低于90℃的条件下,三赞胶钻井液体系比黄原胶钻井液体系具有更高的表观黏度和动切应力,较低的塑性黏度,剪切稀释性能好,而且具有较高的低剪切黏度;当温度高于90℃,特别是在120℃滚动养护条件下,三赞胶钻井液体系的流型调节能力迅速下降,性能不如黄原胶钻井液体系。对三赞胶在不同温度下性能变化的机理进行了分析。三赞胶在抗温性能方面进一步改进后,有望形成复杂结构钻井液体系的一种新型流型调节剂。