Rheological properties and thickening mechanism of aqueous diutan gum solution: Effects of temperature and salts

Host-guest strategy improves rheological properties, conformational stability and oil displacement efficiency of xanthan gum

The low cost and environmental advantages of Xanthan gum make its production and application scale exceed that of other polysaccharides. However, the temperature resistance of Xanthan gum limits its application. In this study, polysaccharide supramolecular Xanthan gum network (XG-β-CD/AD) based on β-cyclodextrin and adamantane was prepared for enhanced oil recovery. The structure of Xanthan gum was characterized by Fourier infrared spectroscopy, nuclear magnetic resonance spectroscopy and thermogravimetric analysis. The rheological properties of the modified polysaccharide network in aqueous solution were systematically studied. The results showed that physical cross-linking of host-guest interacion enhanced the thickening ability of the polymer. Shear rheology, extensional rheology and dynamic modulus test proved that XG-β-CD/AD had excellent rheological properties. The micromorphology, dynamic light scattering and circular dichroism clarified the molecular conformation, the host-guest interaction can improve conformational transition temperature (Tm) and inorganic salt tolerance of Xanthan gum. Under harsh environment (90 °C, 30000 mg/L brine), the oil recovery of XG-β-CD/AD is 6 %-11 % higher than that of XG at the same conditions, showing a better ability to improve the recovery rate. This study provides a research idea for the selection, development and application of biomacromolecular materials.

Effect of hydrothermal treatment on the rheological properties of xanthan gum

In this study, the effect of hydrothermal treatment with different temperatures (120-180 °C) on the rheological properties of xanthan gum was evaluated. When the temperature of hydrothermal treatment was relatively low (120 °C), the rheological properties of the hydrothermally treated xanthan gum was similar to the untreated xanthan gum (pseudoplastic and solid-like/gel-like behavior). However, as the temperature of hydrothermal treatment was higher, the rheological properties of the hydrothermally treated xanthan gum changed greatly (e.g., a wider range of Newtonian plateaus in flow curves, existence of a critical frequency between the storage modulus (G') and the loss modulus (G") in the dynamic viscoelasticity measurement, variation of complex viscosity). Although the hydrothermal treatment showed little influence on the functional groups of xanthan gum, it altered the micromorphology of xanthan gum from uneven and rough lump-like to thinner and smoother flake-like. In addition, higher concentration (2 %) of hydrothermally treated xanthan gum made its viscosity close to that of the untreated xanthan gum (1 %). Besides, hydrothermal treatment also affected the effect of temperature and salt (CaCl2) adding on the rheological properties of xanthan gum. Overall, this study can provide some useful information on the rheological properties of xanthan gum after hydrothermal treatment.

Characterization of emulgels formulated with phycocyanin and diutan gum as a novel approach for biocompatible delivery systems

Phycocyanin (PC), a protein derived from algae, is non-toxic and biocompatible. Due to its environmental and sustainable properties, it has been studied as an alternative stabilizer for food emulsions. In this sense, the main objective of this work is to evaluate the effectiveness of PC and its use in combination with diutan gum (DG), a biological macromolecule, to prepare emulgels formulated with avocado oil. Z-potential measurements show that the optimum pH for working with PC is 2.5. Furthermore, the system exhibited a structured interface at this pH. The surface tension did not decrease further above 1.5 wt% PC. Interestingly, emulsions formulated with >1.5 wt% PC showed recoalescence immediately after preparation. Although 1.5 wt% had the smallest droplet size, this emulsion underwent creaming due to the low viscosity of the system. DG was used in combination with PC to increase viscosity and reduce creaming. As little as 0.1 wt% DG was sufficient to form an emulgel when incorporated into the previous emulsion, which exhibited pseudoplastic behaviour and viscoelastic properties with very low creaming rates. However, the use of PC in combination with DG resulted in a non-aggregated and stable emulgel with 1.5 wt% PC and 0.1 wt% DG.

NMR analysis of the side-group substituents in welan gum in comparison to gellan gum

The physicochemical properties and applications of polysaccharides are highly dependent on their chemical structures, including the monosaccharide composition, degree of substitution, and position of substituent groups in the backbone. The occurrence of side groups or side chains in the chain backbone of polysaccharides is often an essential factor influencing their conformational and physicochemical properties. Welan gum produced by the fermentation of Sphingomonas sp. ATCC 31555 microorganisms has been widely used in food, construction, and oil drilling fields. While understanding the physicochemical properties of welan gum solution has been highly developed, there is still little information about the determination strategy of the glycosyl side groups in welan gum. In this study, the NMR method was established to quantitatively determine the substituent groups in the chain backbone of welan gum. The delicate chemical structures of welan gum obtained at different fermentation conditions were clarified. The composition and content of side substituents were also identified by high-performance liquid chromatography to confirm the accuracy of NMR analysis. The quantitative determination of substituent groups in gellan gum based on NMR analysis was also elaborated for comparison. This work provides insights for profoundly understanding the structure-function relationship of welan gum.

Rheological characterization of artificial paenan compositions produced by Paenibacillus polymyxa DSM 365

Microbial exopolysaccharides offer a sustainable alternative to petroleum-based rheological modifiers. Recent studies revealed that the heteroexopolysaccharide produced by Paenibacillus polymyxa is composed of three distinct biopolymers, referred to as paenan I, II and III. Using CRISPR-Cas9 mediated knock-out variants of glycosyltransferases, defined polysaccharide compositions were produced and rheologically characterized in detail. The high viscosity and gel-like character of the wildtype polymer is proposed to originate from the non-covalent interaction between a pyruvate residue of paenan I and the glucuronic acid found in the backbone of paenan III. Paenan II conveys thermostable properties to the exopolysaccharide mixture. In contrast to the wildtype polymer mixture, knock-out variants demonstrated significantly altered rheological behavior. Using the rheological characterization performed in this study, tailor-made paenan variants and mixtures can be generated to be utilized in a wide range of applications including thickening agents, coatings, or high-value biomedical materials.

Evaluation of Viscosity Changes and Rheological Properties of Diutan Gum, Xanthan Gum, and Scleroglucan in Extreme Reservoirs

The chemically synthesized polymer polyacrylamide (HPAM) has achieved excellent oil displacement in conventional reservoirs, but its oil displacement is poor in extreme reservoir environments. To develop a biopolymer oil flooding agent suitable for extreme reservoir conditions, the viscosity changes and rheological properties of three biopolymers, diutan gum, xanthan gum, and scleroglucan, were studied under extreme reservoir conditions (high salt, high temperature, strong acid, and alkali), and the effects of temperature, mineralization, pH, and other factors on their viscosities and long-term stability were analyzed and compared. The results show that the three biopolymers had the best viscosity-increasing ability at temperatures of 90 °C and below. The viscosity of the three biopolymers was 80.94 mPa·s, 11.57 mPa·s, and 59.83 mPa·s, respectively, when the concentration was 1500 mg/L and the salinity 220 g/L. At the shear rate of 250 s-1, 100 °C~140 °C, scleroglucan had the best viscosification. At 140 °C, the solution viscosity was 19.74 mPa·s, and the retention rate could reach 118.27%. The results of the long-term stability study showed that the solution viscosity of scleroglucan with a mineralization level of 220 mg/L was 89.54% viscosity retention in 40 days, and the diutan gum could be stabilized for 10 days, with the viscosity maintained at 90 mPa·s. All three biopolymers were highly acid- and alkali-resistant, with viscosity variations of less than 15% in the pH3~10 range. Rheological tests showed that the unique double-helix structure of diutan gum and the rigid triple-helix structure of scleroglucan caused them to have better viscoelastic properties than xanthan gum. Therefore, these two biopolymers, diutan gum, and scleroglucan, have the potential for extreme reservoir oil displacement applications. It is recommended to use diutan gum for oil displacement in reservoirs up to 90 °C and scleroglucan for oil displacement in reservoirs between 100 °C and 140 °C.

Formulation and Physical Characterization of a Polysaccharidic Gel for the Vehiculation of an Insoluble Phytoextract for Mucosal Application

Maintaining insoluble plant-based ingredients in suspension and ensuring long-term physical stability is particularly challenging for formulators of green cosmetics. This study aimed to evaluate the structure and applicative properties of gel and gel-cream topical formulations suitable for delivering an insoluble phytocomplex on the vaginal mucosa and maintaining its integrity. For this purpose, we studied the compatibility of Perilla frutescens (L.) Britton phytocomplex (PFP), derived from in vitro plant cell cultures and presented as a powder finely dispersed in glycerin, with different classes of natural rheological modifiers (such as xanthan gum, sclerotium gum, succinoglycan, xyloglucan, diutan gum, hydroxypropyl guar gum derivative) in gel and gel-cream formulations, to meet the needs of the cosmetic market for naturalness and biodegradability. Through rheological and texture analyses, we studied the physico–mechanical properties of the samples, comparing the performances of the chosen polysaccharides to those of acrylic polymeric rheological modifiers, evaluating their contribution in terms of stability and applicative properties. Since a weak-gel rheological pattern proved to be the optimal one to keep the actives in suspension, the associations of tamarind seed polysaccharides with succinoglycan or scleroglucan were the most suitable for the formulation of mucoadhesive gels.

Effect of an inorganic nitrogen source (NH4)2SO4 on the production of welan gum from Sphingomonas sp. mutant obtained through UV-ARTP compound mutagenesis

As one of the most expensive extracellular polysaccharides, welan gum is widely used in biomedicine, food products, and petroleum because of its unique structure and excellent rheological properties. To reduce the cost of welan gum fermentation, together with (NH₄)₂SO₄, which served as the sole nitrogen source, a high-welan-gum-producing mutant, B-8, screened through UV-ARTP compound mutagenesis was used. Under optimum conditions (C:N ratio 25:1, sucrose 50 g/L, (NH₄)₂SO₄ 4 g/L, and adding 8 mM NaCl at 32 h fermentation), the yield of welan gum and sucrose conversion were 18.86 g/L and 0.38 g/g, respectively, which were 98.95% and 137.50% higher than those achieved with the parent strain FM01, respectively. After the same treatment process, IN-welan (obtained with (NH₄)₂SO₄) consumed less 95% ethanol, had higher molecular weight, and exhibited better rheological properties than ON-welan (obtained with beef extract). Transcriptome analysis revealed that (NH₄)₂SO₄ could affect the synthetic pathway and monosaccharide content of welan gum by increasing bacterial chemotaxis and the availability of key intermediates. The fermentation performance of Sphingomonas sp. mutants could further be improved by providing several target genes to the mutants through metabolic engineering.

Biopolymers Produced by Sphingomonas Strains and Their Potential Applications in Petroleum Production

The genus Sphingomonas was established by Yabuuchi et al. in 1990, and has attracted much attention in recent years due to its unique ability to degrade environmental pollutants. Some Sphingomonas species can secrete high-molecular-weight extracellular polymers called sphingans, most of which are acidic heteropolysaccharides. Typical sphingans include welan gum, gellan gum, and diutan gum. Most sphingans have a typical, conserved main chain structure, and differences of side chain groups lead to different rheological characteristics, such as shear thinning, temperature or salt resistance, and viscoelasticity. In petroleum production applications, sphingans, and their structurally modified derivatives can replace partially hydrolyzed polyacrylamide (HPAM) for enhanced oil recovery (EOR) in high-temperature and high-salt reservoirs, while also being able to replace guar gum as a fracturing fluid thickener. This paper focuses on the applications of sphingans and their derivatives in EOR.

Effects of concentrations, temperature, pH and co-solutes on the rheological properties of mucilage from Dioscorea opposita Thunb. and its antioxidant activity

The mucilage from Dioscorea opposita (DOM) dispersions presented shear-thinning behaviour that well fitted to the Power Law model. The effects of different concentrations (2%-10% w/v), temperatures (25-80 °C), pH (3.0-9.0), freeze-thaw conditions (thawed at 25 °C and 4 °C), co-salts (KCl and CaCl₂) and co-sugars (sucrose, fructose and mannose) on the rheological properties were investigated. Generally, higher concentrations, neutral pH, Ca²⁺ and sugars increased the viscosity of DOM, while increasing temperature (25-65 °C) had opposite effects. The results suggested that cross-linked networks exist in DOM, and viscosity changes may be related to the ionisation of carboxyl groups, structural changes and enhancement/reduction of molecular interactions. Particularly, Ca²⁺ could interact with uronic acids of two or more polysaccharide molecules, modify the network-structure through cross-linking with carboxyl groups, and enhance the stronger carboxylate-cation²⁺-carboxylate interactions. Therefore, DOM is suitable for food applications as thickening or gelling agents in aqueous solutions.

Shear sensitive injectable hydrogels of cross-linked tragacanthic acid for ocular drug delivery: Rheological and biological evaluation

Drug delivery to posterior segment of eye has always been challenging. The aim of the present study was to provide a novel injectable, shear sensitive hydrogel based on tragacanthic acid (TA) with three kinds of acetate salts as cross-linker. Rheological properties by strain and shear stress sweep measurements and also dynamic rheological experiments including frequency and time sweep measurements were studied. Biological studies comprising, cell culture, Draize test on rabbit eyes and histopathological tests were done. The results showed the optimized hydrogel was biocompatible, injectable and owning acceptable firmness in rest state after injection. Healing time of the hydrogel was 46 s and was shear-sensitive. It showed no cytotoxicity on HUVEC cells. No allergic reaction was seen in Draize test and histological examination showed integrity of the retinal layers with no evidence of pathological changes, such as deformations, degeneration, or inflammation. TA hydrogel is promising in ocular drug delivery.

Biodiversity and ecology of microorganisms in high pressure membrane filtration systems

High-pressure membrane filtration (reverse osmosis and nanofiltration) is used to purify different water sources, including wastewater, surface water, groundwater and seawater. A major concern in membrane filtration is the accumulation and growth of micro-organisms and their secreted polymeric substances, leading to reduced membrane performance and membrane biofouling. The fundamental understanding of membrane biofouling is limited despite years of research, as the means of microbial interactions and response to the conditions on the membrane surface are complicated. Here, we discuss studies that investigated the microbial diversity of fouled high-pressure membranes. High-throughput amplicon sequencing of the 16S rRNA gene have shown that Burkholderiales, Pseudomonadales, Rhizobiales, Sphingomonadales and Xanthomonadales frequently obtain a high relative abundance on fouled membranes. The bacterial communities present in the diverse feed water types and in pre-treatment compartments are different from the communities on the membrane, because high-pressure membrane filtration provides a selective environment for certain bacterial groups. The biofilms that form within the pre-treatment compartments do not commonly serve as an inoculum for the subsequent high-pressure membranes. Besides bacteria also fungi are detected in the water treatment compartments. In contrast to bacteria, the fungal community does not change much throughout membrane cleaning. The stable fungal diversity indicates that they are more significant in membrane biofouling than previously thought. By reviewing the biodiversity and ecology of microbes in the whole high pressure membrane filtration water chain, we have been able to identify potentials to improve biofouling control. These include modulation of hydrodynamic conditions, nutrient limitation and the combination of cleaning agents to target the entire membrane microbiome.

Comparative Study on Enhancing Oil Recovery under High Temperature and High Salinity: Polysaccharides Versus Synthetic Polymer

The synthetic water-soluble polymer, partially hydrolyzed polyacrylamide (HPAM), has been most widely used for enhanced oil recovery (EOR); however, its poor thermal stability and weak salt tolerance impede further application in high-temperature and high-salinity oil reservoirs. To address such deficiencies, three polysaccharides, xanthan gum, diutan gum, and scleroglucan, were examined in comparison with HPAM on rheological behaviors, shearing resistance, long-term thermal stability, and core flooding test. It was found that all of these three polysaccharides were less sensitive to salinity and shearing time, while HPAM showed a monotonous decrease in viscosity with increasing monovalent cations and shearing history. After 90 days of aging at 85 °C and 10.1 × 104 mg·L-1 of total dissolved solids with 1.0 × 103 mg·L-1 of Ca2+, the viscosity of diutan gum and scleroglucan solutions nearly remained unchanged; on the contrary, the viscosity of xanthan gum and HPAM solutions drops massively. Core flooding tests at 85 °C with the same initial viscosity demonstrated that all polymers showed good transportation in porous media, and 16, 13, and 11% of oil recovery were obtained by diutan gum, scleroglucan, and xanthan gum, respectively, while only 10% was obtained from HPAM. These comparative results may underpin the potential of diutan gum and scleroglucan to be used in the EOR process in HTHS oil reservoirs.

Viscoelastic and shear-thinning effects of aqueous exopolymer solution on disk and sphere settling

In this study, xanthan gum is used as a model exopolymer to demonstrate potential effects of non-Newtonian properties of natural aquatic systems on settling dynamics of particles. Rheological measurements combined with settling experiments using visualization methods revealed that instantaneous velocity fluctuations and a flow pattern formed around a particle are the effects of solution viscoelasticity and shear-thinning properties and that the average settling velocity depends on the exopolymer concentration and particle size. Our study showed that in the considered conditions a disk-shaped particle settles preferably in vertical position with a negative wake behind. The understanding of these processes is essential in technology and engineering and is necessary to improve prediction accuracy of large-scale sedimentation processes and biogeochemical cycles in the ocean involving settling of minerals, marine snow, microplastics, and locomotion of microorganisms.

Changes of flooding reagents' properties under simulated high temperature/pressure conditions in oil reservoirs and their impact on emulsion stability

It is of great significance to know the fate of the polymers and surfactants used for enhanced oil recovery (EOR) in oil reservoirs at a relatively high temperature/pressure. In this paper, the changes of the properties of a polymer (partially hydrolyzed polyacrylamide, HPAM) and a surfactant (petroleum sulfonate, PS) were investigated under simulated oil reservoir conditions (a temperature of 45, 60 or 75 °C and a pressure of 10, 15 or 20 MPa). The impacts of the property changes to emulsion stability were also highlighted. The results showed that the hydrolysis degree of HPAM increased from 24.3% to 28.9%, 29.7% and 35.4%, whereas the molecular weight (M_w) decreased from 7.60 × 10⁶ g mol⁻¹ to 5.43 × 10⁶ g mol⁻¹, 4.49 × 10⁶ g mol⁻¹ and 2.87 × 10⁶ g mol⁻¹ as a function of raising the temperature to 45, 60 and 75 °C with 20 MPa, respectively, for a duration of one week. However, the increased pressure showed obvious prevention effects on the degradation of HPAM M_w in the investigated pressure range of 10–20 MPa. There were no changes in the oil–water interfacial tension for PS solutions after high temperature/pressure treatment. The stabilization ability of HPAM to the emulsion decreased markedly after treatment because of the decreased viscosity attributed to the reduction of molecular weight, while that of PS did not change. It is reasonable to speculate that the influence of back produced HPAM to the stability of EOR produced water will be quite different in different oil reservoirs because of the differences in reservoir temperature, pressure and retention time, and therefore different strategies should be considered in treating the produced water from EOR.

It is of great significance to know the fate of the polymers and surfactants used for enhanced oil recovery (EOR) in oil reservoirs at a relatively high temperature/pressure.

Role of chemical additives and their rheological properties in enhanced oil recovery

A significant amount of oil (i.e. 60–70%) remains trapped in reservoirs after the conventional primary and secondary methods of oil recovery. Enhanced oil recovery (EOR) methods are therefore necessary to recover the major fraction of unrecovered trapped oil from reservoirs to meet the present-day energy demands. The chemical EOR method is one of the promising methods where various chemical additives, such as alkalis, surfactants, polymer, and the combination of all alkali–surfactant–polymer (ASP) or surfactant–polymer (SP) solutions, are injected into the reservoir to improve the displacement and sweep efficiency. Every oil field has different conditions, which imposes new challenges toward alternative but more effective EOR techniques. Among such attractive alternative additives are polymeric surfactants, natural surfactants, nanoparticles, and self-assembled polymer systems for EOR. In this paper, water-soluble chemical additives such as alkalis, surfactants, polymer, and ASP or SP solution for chemical EOR are highlighted. This review also discusses the concepts and techniques related to the chemical methods of EOR, and highlights the rheological properties of the chemicals involved in the efficiency of EOR methods.

Characterizations and rheological study of the purified polysaccharide extracted from quince seeds

BACKGROUND

The functional characteristics of hydrocolloids are mainly dependent on their physicochemical properties. Thus, it is essential to characterize the new sources of hydrocolloids.

RESULTS

Quince seed gum (QSG) is a high-molecular-weight polysaccharide (9.61 × 10⁶  g mol^-1 ) composed of 85.04 ± 2.87% carbohydrate (6.39% l-arabinose, 40.43% d-xylose, 5.60% d-galactose, 5.75% d-glucose and 31.11% d-mannose), 13.16 ± 1.73% uronic acid, 5.77 ± 0.83% moisture, 2.78 ± 0.21% protein, 5.64 ± 0.21% ash, and 0.75 ± 0.09% fat. Our findings indicated that this gum could be introduced as a value-added by-product in the food and pharmaceutical industries. Carbon-13 nuclear magnetic resonance and Fourier transform infrared spectroscopy suggested a highly substituted xylan structure for QSG. In the dilute regime, an increase in the ion concentration was accompanied by a decrease in intrinsic viscosity of QSG. When the salt concentration increased from 0 to 50 mmol L^-1 , the consistency coefficient (as a measure of apparent viscosity) declined. On the other hand, with further increasing of salt concentration, the consistency coefficient (as a measure of apparent viscosity) values increased. Similarly, the G' and G″ values for 10 and 50 mmol L^-1 calcium chloride concentrations were less than in control samples.

CONCLUSION

The rheological behavior of the QSG studied in this paper can provide insight into its potential application in food and pharmaceutical industries. © 2018 Society of Chemical Industry.

Flow, dynamic viscoelastic and creep properties of a biological polymer produced by Sphingomonas sp. as affected by concentration

In this work, the influence of the concentration on the flow behaviour, dynamic viscoelastic and creep properties of diutan gum in aqueous solution was investigated. Diutan gum is a biopolymer which belongs to the sphingans group. To know its rheological properties and its microstructure as a function of the concentration is directly related to the current and future applications of this biological polymer. Mechanical spectra showed a crossover point between G' and G″ which changed as a function of diutan gum concentration. A master curve for the frequency dependence on the η* was obtained. The creep compliance results made it possible to deduce the yield stress value and they were fitted to Burgers model. A shear-thinning behaviour was exhibited by diutan gum aqueous solutions, which was fitted to the Carreau-Yasuda model. Higher G', G″, τ₀ and η₀ values and lower ω_c, J_e⁰, γ̇_c and n values were obtained by increasing the gum concentration, it is being possible to modulate the viscoelasticity, viscosity and shear resistance as a function of concentration. A more complex structure with stronger entanglements between macromolecules of diutan was obtained when the concentration of diutan increases.