Welan Research Articles

Effect of welan gum and nanoclay on thixotropy of UHPC

This study evaluates the effect of welan gum (WG) and nanoclay (NC) on thixotropy of ultra-high-performance concrete (UHPC) matrix made with 0.20 water-to-binder ratio. The mortar mixtures were proportioned with a fixed superplasticizer (SP) content and WG and NC contents varying between 0 and 0.09% and 0 and 0.4%, respectively. The dynamic yield stress of these mixtures varied from 40 to 170 Pa. Similarly, UHPC made with different WG and NC contents were prepared with variable SP dosages to maintain initial mini-slump flow of 200 ± 5 mm. Test results indicate that thixotropy can be enhanced by using WG or NC in UHPC with a fixed SP dosage. On the other hand, for UHPC made with variable SP, the incorporation of WG increased thixotropy, whereas the use of NC had limited contribution to thixotropy. Particle flocculation was correlated to the water film thickness (WFT) onto solid particles in UHPC. The rapid increase in static yield stress immediately after mixing (τfloc) showed a linear growth with the decrease of WFT due to enhancement of particle flocculation. A qualitative approach relating particle flocculation and bridging effect of nucleation of early-age hydration products was proposed to describe the rate of linear increase in static yield stress with rest time (Athix). The model yielded good prediction for UHPC prepared with NC, which was not the case for mixtures made with WG where other factors, such as polymer entanglement and association, can play a major role in controlling thixotropy.

Rheology control of ultra-high-performance concrete made with different fiber contents

The study aims to improve flexural properties of ultra-high-performance concrete (UHPC) prepared with different steel fiber volumes by controlling the rheological properties of the suspending mortar. Welan gum and high-range water reducer were incorporated to control rheology. Optimum rheological properties led to enhanced fiber distribution. Fiber distribution coefficient was proposed and considered to characterize fiber dispersion and orientation. For UHPC with 1%, 2%, and 3% fiber volumes, the highest flexural performance was obtained with mortars having plastic viscosities of 36, 52, and 66 Pa·s, respectively. Beyond these values, further increase in viscosity resulted in greater air entrapment and lower mechanical properties. Prediction model for flexural strength that considers a correlation between fiber dispersion and flexural-to-tensile strength ratio of the UHPC was developed. Viscosity of UHPC mortar was shown to be a reliable indicator to determine flexural-to-tensile strength ratio, and hence predict flexural strength of UHPC.

Efficient biosynthesis of polysaccharide welan gum in heat shock protein-overproducing Sphingomonas sp. via temperature-dependent strategy.

Cell growth and product formation are two critical processes in polysaccharide welan biosynthesis, but the conflict between them is often encountered. In this study, a temperature-dependent strategy was designed for two-stage welan production through overexpressing heat shock proteins in Sphingomonas sp. The first stage was cell growth phase with higher TCA cycle activity at 42°C; the second stage was welan formation phase with higher precursor synthesis pathway activity at 37°C. The highest welan concentration 37.5g/L was achieved after two-stage process. Ultimately, this strategy accumulated welan yield of 79.2g/100g glucose and productivity of 0.62g/L/h at 60h, which were the best reported results so far. The duration of fermentation was shortened. Besides, rheological behavior of welan gum solutions remained stable at wide range of temperature, pH, and NaCl. These results indicated that this approach efficiently improved welan synthesis.

Foaming and rheological properties of hydroxypropyl methylcellulose and welan gum composite system: The stabilizing mechanism

This work reported the effect of welan gum (WL) on stabilizing the foam of hydroxypropyl methylcellulose (HPMC), which compared to konjac glucomannan (KGM) and guar gum (GG). The effects of total concentration and ratio on the foaming properties of the HPMC/WL composite system were studied systematically through the analysis of foaming capacity, foam stability, foam morphology at the macro and micro levels, rotational rheology properties, interface rheology properties, and microstructure. Finally, the interaction forces, conformation, distribution, and rearrangement of HPMC/WL molecules on the interface were speculated to elucidate the stability mechanism. The experimental results showed that when the concentration was 1%, and the ratio of HPMC/WL was 8:2, the foaming capacity was the maximum, reaching 586.66%; when the total concentration was fixed at 1%, the ratio of HPMC/WL was 2:8, the foam stability reached 96.507%. The excellent shear-thinning ability of WL was one crucial factor for the excellent foaming properties of HPMC/WL composite. The high apparent viscosity significantly improved the foam stability of HPMC/WL composite, which was mainly caused by the physical interaction between HPMC and WL molecules after whipping. In addition, the composite foam of HPMC/WL after vacuum freeze-drying presented a porous, dense, and uniform cellular structure. This study expanded the application of WL as a stabilizer for a heterogeneous system and raw material for the carrier of bioactive substances in the delivery system.

Rheological behaviors of a novel exopolysaccharide produced by Sphingomonas WG and the potential application in enhanced oil recovery

A novel exopolysaccharide, named WL gum, was obtained from the fermentation broth of Sphingomonas sp. WG. The effects of temperature and salinity on the rheological properties of WL gum solution and fermentation broth (WL-Fer) were systematically investigated and compared with another exopolysaccharide, welan gum (WG). The results showed that the network structures formed in WL solution were more compact than those of WG. WL solution and WL-Fer were not sensitive to high temperatures (80–120 °C) and only weakly affected by the cations (Na+, K+, and Ca2+). Moreover, Fe2+ and high temperature (100 °C) even enhanced the viscosity of WL-Fer. The results of flooding experiments demonstrated that the enhanced displacement efficiency of WL gum (14.55%) was similar to that of partially hydrolyzed polyacrylamide (HPAM, 13.36%) at 65 °C. And the enhanced displacement efficiency of WL-Fer was as high as 23.31%. It can be concluded that WL gum is a kind of potential and environmentally benign polymer that could be used in EOR, and the fermentation broth could be used directly after dilution.

Use of colloidal thickeners to inject and retain bacterial growth media to repair cracked concrete

This study aimed at developing a bacteria-based method to repair cracks in concrete (crack opening < 1 mm) that would be suitable for full-scale operations and economically viable. CaCO3-producing bacteria were injected into calibrated cracks with bioavailable calcium and nutrients in a suspension thickened with a combination of Welan gum and Attagel® 50. These thickeners have synergistic effects, enhancing viscosity and shear-thinning behavior. These rheology characteristics made injection without drainage possible for crack widths ranging from 150 to 800 µm. Bacterial growth and the associated CaCO3 biomineralization were enhanced in the presence of thickeners.

Construction of a Robust Sphingomonas sp. Strain for Welan Gum Production via the Expression of Global Transcriptional Regulator IrrE.

Welan gum is a widely used microbial polysaccharide produced by Sphingomonas sp. However, an important factor hindering the expansion of its production is the maladaptation of strain to fermentation conditions. In this work, the global transcriptional regulator gene irre was selected as a stress-resistant element. And it was integrated into the site of the genomic carotene synthesis key enzyme gene crtB to construct a robust carotenoid-free welan gum producing strain. Fermentation with the recombinant strain effectively reduced the ethanol consumption and pigment content in the product. The tolerance temperature increased by 10°C without the need for controlling the pH. Under this fermentation condition, welan gum concentration could still reach 20.26 ± 0.25 g/L, which was 187.38% higher than that of the wild-type strain (7.05 ± 0.15 g/L). Transcriptome analysis showed that with the control of IrrE, more than 1000 genes that are involved in multiple pathways, including two-component system, bacterial chemotaxis, flagellar assembly, and cell cycle, exhibited changes at the transcriptional level and jointly allowed the strain to protect against environmental stresses.

Production of welan gum from cane molasses by Sphingomonas sp. FM01

As an extracellular exopolysaccharide, welan gum could serve as a suspending agent, stabilizer, emulsifier and thickener with characteristics that include bio-adhesion, non-toxicity, biocompatibility and biodegradability. In this study, Sphingomonas sp. FM01 was applied to effectively produce welan gum using cane molasses as the carbon source. After pretreatment with phosphoric acid and polyacrylamide, 60 g/L cane molasses combined with 6.0 g/L beef extract, 3 g/L KH2PO4, 0.5 g/L MgSO4, 15 mmol/L H2O2 and 4 mg/L niacin significantly improved the fermentation performance of Sphingomonas sp. FM01, increasing the production of welan gum to 37.65 g/L. Investigation of the rheological behavior of the welan gum obtained from the molasses-welan gum mixture showed it had an acceptable molecular weight and similar rheological properties and better viscosity stability compared to that obtained from sucrose, indicating that cane molasses could be explored as a suitable and inexpensive substrate for cost-effective welan gum production.

The Study of Cationic Modification of Welan Gum

In the present study, welan gum (WG) was modified with a quaternary amine group producing cationic welan gum (CWG) to enhance its thermal and viscosity properties. N-(3-chloro-2-hydroxypropyl) trimethyl ammonium chloride (CHPTAC) was used as the source of the quaternary amine group. The effect of CHPTAC amount in the presence of NaOH was investigated and analyzed using Fourier transform infrared (FTIR), Field emission scanning electron microscope (FESEM), thermal and viscosity analysis. The viscosity results were increases as the amount of CHPTAC increased. From the thermal analyses, it is observed that the CWG has better thermal resistance compared to WG. This study showed that modification of WG by attaching quaternary amine group on the hydroxyl group is promising for the exploration of the high-temperature reservoir.

Effect of different nitrogen sources on the viscosity and rheological properties of welan gum produced by Sphingomonas sp. ATCC 31555.

The current study aimed to determine the rheological properties of welan gum produced by Sphingomonas sp. ATCC 31555 using different nitrogen sources. The viscosity and rheological properties of welan gum produced by Sphingomonas sp. ATCC 31555 from different ratios of inorganic, organic, and mixture of organic and inorganic nitrogen sources were measured under different conditions of pH, rotational speeds, and temperatures and also in the presence of various metal ions. Increasing the proportion of sodium nitrate (NaNO3 ) as the nitrogen source enhanced the viscosity and the ability of welan gum solution to resist high temperatures and salinity. The viscosity of welan gum solution derived from all three nitrogen sources gradually declined when the rotational speed was increased and stabilized at rotational speeds >30 rpm. The elastic modulus and viscous modulus were highest for a welan gum solution derived from 4.0 g/L NaNO3 . The viscosity, temperature, and salt tolerance were superior when a welan gum solution was produced from NaNO3 in comparison with that produced from organic nitrogen source.

Synthesis and characterization of a graft-modified copolymer for enhanced oil recovery

A graft-modified copolymer (cWL-g-A) was synthesized using Welan Gum (WLG), acrylamide, acrylic acid, and O-20 via free-radical copolymerization to be well applied for enhanced oil recovery. The chemical structure of the copolymer was characterized by Fourier transform infrared spectroscopy (FT-IR), nuclear magnetic resonance spectroscopy (NMR), thermogravimetry (TG) and scanning electron microscopy (SEM). The long-term stability, rheology, adsorption, temperature and salt resistance of the copolymer were investigated. The cWL-g-A solution showed superior temperature and salt resistance in comparison with partially hydrolyzed polyacrylamide (HPAM), due to the hydrophobic association of main polymer chain. Particularly in high salinity (230,000 mg/L) solutions, cWL-g-A showed a better antiaging performance at three different temperatures (25, 50 and 65 °C). Oil recovery yielded by cWL-g-A was 14.18% higher than that yielded by HPAM, as known from polymer flooding tests. These results elucidated that cWL-g-A synthesized herein was superior to HPAM in high-salinity and medium-high temperature oil reservoirs.

Carboxylic modification of welan gum

ABSTRACTWelan gum has disadvantages such as poor solubility, low viscosity, and poor crosslinking property, when it is applied in petroleum industry, comparing to guar gum. Two methods for the carboxylic modification of welan gum were developed, carboxyethyl modification and citric acid modification, to improve the solubility in water, viscosity, and crosslinking ability of welan gum in the borax crosslinking system. The solubility time of carboxyethyl modified and citric acid modified welan gum were shortened to 30 and 90 min, respectively. The highest viscosity of citric acid modified product was 49.4 mPa s, the viscosity after crosslinking was raised at least 1.2 times to the highest four times than that before crosslinking. The results indicated three factors affecting the properties of modified products: (1) how many function groups in the modifying agent; (2) the way to connect the function group; and (3) the whole structure of the modifying agent. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020, 137, 48301.

Pore structure and adsorption properties of welan gum modified polyurethane

Welan gum modified polyurethane (WMP) with different welan gum concentrations were synthesized at vacuum conditions. The average pore diameter, porosity, pore volume, contact angle, pore morphology, oil adsorption ratio and absorption energy of WMPs were investigated by nitrogen adsorption analysis (NAA), scanning electron microscope (SEM), energy disperse spectroscopy (EDX), and molecular simulation. The results demonstrated that pore structure is highly dependent on the welan gum content. Moreover, the number of dead-end pores in the WMP decreased more compared to inter-connected, passing, and closed pores. Simulation results showed that the adsorption properties of WMP increased with the increasing welan gum content at a certain level. Welan gum could change the pore shape and improve the irregularity degree of WMP. The gel shrinkage also improves in spite of the hydrogen-bonding interactions. The two parameters of Langmuir isotherms are 42.68 mg g−1 and 0.0245 l mg−1, respectively. The gasoline adsorbability of WMP is smaller than that of diesel. Consequently, welan gum could improve the adsorption heat and the adsorbability of polyurethane.

Rheological behaviors of microbial polysaccharides with different substituents in aqueous solutions: Effects of concentration, temperature, inorganic salt and surfactant

Rheological behaviors of microbial polysaccharides with different substituents in aqueous solutions have been systematically investigated. Both the saccharide side chains and acetyl substituents improve the gelation of welan gum (WG), diutan gum (DG) and gellan gum (GG) in pure water at 25 °C. For the polysaccharides with saccharide side chains (WG and DG), the relationship between the apparent viscosity and concentration conforms to the linear equation, while that of the polysaccharide with acetyl (GG) is exponential. More importantly, the roles of substituents on the stability of the molecular conformation of polysaccharides are significantly depended on the surrounding environment. Disaccharide side chains promote the stability of helical conformation and gel aggregates of GG at high temperature (85 °C) or in the presence of inorganic salts with the ionic strength of 2.0 mol L−1. The stability of gel structure containing acetyl (GG) shows higher temperature/salt sensitivity. Additionally, deacylated gellan gum (GG(d)) solutions transform into hydrogels in the presence of dodecyltrimethylammonium bromide (DTAB). This study will help to obtain a better understanding on the rheological properties of polysaccharides with respect to the conformation and applications.

Influence of the welan gum biopolymer concentration on the rheological properties, droplet size distribution and physical stability of thyme oil/W emulsions

The objective of this work is to obtain a stable and natural antimicrobial delivery system. Thus, the effect of the addition of a natural polysaccharide such as welan gum on the linear viscoelastic properties, flow behaviour, droplet size distribution and physical stability of thyme oil/W emulsions formulated with a wheat-derived surfactant was studied. All emulsions obtained show submicron diameters regardless of the concentration of welan. Emulsion without gum shows Newtonian behaviour under steady shear. Meanwhile, emulsions containing welan gum show a weak gel-like behaviour with higher G′ and G″ values on increasing the content of gum in the emulsion. Their flow curves illustrate a shear thinning behaviour with much greater viscosity than that exhibited by emulsions without gum. This behaviour fits well to the Cross model. The main destabilization process of thyme oil/W emulsion without gum is creaming versus flocculation and coalescence in emulsions containing welan. Rheology, diffraction laser and multiple light scattering techniques have proved that welan gum is an important rheological modifier for thyme oil/W ecological emulsions, it being possible to control the rheological properties of these emulsions by adjusting the concentration of gum. However, welan gum does not improve the physical stability of these emulsions.

Prediction of Sphingosine protein-coding regions with a self adaptive spectral rotation method.

Identifying protein coding regions in DNA sequences by computational methods is an active research topic. Welan gum produced by Sphingomonas sp. WG has great application potential in oil recovery and concrete construction industry. Predicting the coding regions in the Sphingomonas sp. WG genome and addressing the mechanism underlying the explanation for the synthesis of Welan gum metabolism is an important issue at present. In this study, we apply a self adaptive spectral rotation (SASR, for short) method, which is based on the investigation of the Triplet Periodicity property, to predict the coding regions of the whole-genome data of Sphingomonas sp. WG without any previous training process, and 1115 suspected gene fragments are obtained. Suspected gene fragments are subjected to a similarity search against the non-redundant protein sequences (nr) database of NCBI with blastx, and 762 suspected gene fragments have been labeled as genes in the nr database.

Rheology and Flow Properties of Fracturing Gels in Straight and Coiled Tubing

This study involves experimental investigation of rheological and hydraulic characteristics of aqueous based polymeric and surfactant fluids in straight and coiled tubing. The fluids matrix includes guar, HPG, PHPA, welan, xanthan, and surfactant. Bohlin rheometer was used to evaluate rheological and viscoelastic characteristics. For hydraulic characteristics, small- and large-scale flow loops were used. It is observed that all fluids exhibit comparable non-Newtonian behavior and improved viscous and elastic properties. Among polymeric fluids, guar and welan provide better viscosity and suspension properties. Surfactant is significantly affected by the formation of rod-like micelles and other microstructures. Master curves for rheological and elastic properties are developed using the molecular theory approach. The foremost benefit of these curves is its dimensionless form that provides a unique technique to predict viscosity for all fluids. For hydraulic properties, friction losses in coiled tubing are significantly higher than in straight tubing due to centrifugal forces and secondary flows. Surfactant is more sensitive to shear field applied where different microstructures are induced and thus they exhibit better drag reduction characteristics than polymeric fluids especially in coiled tubing with larger sizes. However, in straight tubing, guar shows better drag reduction characteristics than surfactant and other polymers, which diminishes as tubing size increases. However, welan gum exhibits a comparable performance. Overall, all fluids are considered good candidates as fracturing fluids with specific features for each. Unique characteristics of each fluid is discussed and explained in more details within the context of the present paper. Keywords: Microstructures, surfactant, hydraulic, friction, viscosity

Impact of Welan Gum on Cement Paste Containing PCE Superplasticizers with Different Charge Densities

AbstractAs a renewable materials, welan gum is microbial biopolymer which is fermented by bacteria. It is widely used in self‐compacting concrete because of its excellent rheological properties. After adding welan gum, the fluidity of cement will decrease rapidly. So it needs to be used together with superplasticizer. Two polycarboxylate superplasticizer with the acid/ether radio of 2 (PC‐2)and with the acid/ether radio of 6 (PC‐6)were synthesized. By FTIR measurements, carboxyl functional groups exists in the dialysed polymer. The specific anionic charge density measurement shows that PC‐6 provide more COO− than PC‐2 in alkaline solution. And TOC test analysis shows that the adsorbed amount of PC‐6 is higher than PC‐2 with low anionic charge density. PC‐6 with the higher COO− seems to be more affected by welan gum than PC‐2. From the rheological properties of cement paste mixed with PCEs and welan gum, it can be concluded that the addition of welan gum aggravates the trend of shear thickening. Hydration heat flow at different temperatures indicates the selected welan gum is capable of retarding early cement hydration even in high temperatures. Finally, the film forming property of the welan gum was initially studied through water loss rate test, and the film formation mechanism needs to be studied in the future.

Significantly improved production of Welan gum by Sphingomonas sp. WG through a novel quorum-sensing-interfering dipeptide cyclo(L-Pro-L-Phe)

A variety of physiological functions such as exopolysaccharide synthesis, antibiotic production, and primary metabolism are tightly controlled by quorum sensing in microorganisms. In this study, a marine-derived bacterium Sphingomonas sp. WG was found to possess a cyclo(L-Pro-L-Phe)-mediated quorum sensing mechanism. The cyclo(L-Pro-L-Phe) produced by Sphingomonas sp. WG functions as a signalling molecule in this quorum sensing system. It is the first attempt to characterize cyclic dipeptides as quorum sensing signalling molecules in Sphingomonas sp. and the results effectively make the classical quorum sensing theory more perfect. Furthermore, the supplementation with isolated cyclo(L-Pro-L-Phe) resulted in a 15% increase in the production of welan gum secreted by Sphingomonas sp. WG in the submerged fermentation. The data presented in this study will provide evidences for exploring the role of cyclic dipeptides in regulating the production of welan gum.

Linear and non-linear flow behavior of welan gum solutions

Rheological and microstructural properties of welan gum aqueous solutions were studied as a function of polymer concentration in the 0.2–0.6% (m/m) range at fixed temperature 20 °C. Welan gum is an exopolysaccharide produced by Sphingomonas sp. All the systems exhibited a shear thinning and weak gel–like behavior whose parameters were well adjusted to a power law with the concentration. Furthermore, time-concentration superposition methods were carried out to obtain two master curves, one from the flow curves and the other from the mechanical spectra, which made it possible to extend the accessible experimental range. The non-linear viscoelastic properties were also studied by means of parallel superposition tests. The superimposed shear stress induced a change from weak gel to entangled solution behavior. This latter flow behavior is characterized by a frequency crossover that has been shown to have a linear dependence on the superimposed steady-state shear rate. Finally, Cryo-SEM images revealed a network with numerous junction zones between polymer chains.