Steady Shear Flow Behavior Research Articles

Effect of solution pulsed plasma process on the degradation and physicochemical properties of pectin

Pectin was degraded by solution pulsed plasma (SPP). The impacts of discharge voltage and the distance between the electrodes on pectin degradation and its steady shear flow behavior and characterization were investigated. The results showed that the influence of the discharge voltage was higher than that of the distance between the electrodes. The stronger discharge voltage and the narrower distance between the electrodes presented the lower intrinsic viscosity, the greater shear-thinning capacities, and the stronger viscoelastic behavior. FT-IR and 1H NMR analysis demonstrated that SPP treatment did not damage the main structure of pectin. XRD, SEM and HPSEC-MALL analysis revealed that the crystallinity, Mw and <S2>z1/2 of pectin gradually decreased with the increasing discharge voltage and decreasing the distance between the electrodes. The depolymerized pectin molecules exhibited a hard sphere conformation in the aqueous solution. A higher degradation effect had a greater influence on the conformation of pectin.

Effect of pH value and the distance between the electrodes on physicochemical properties of chitosan under SPP treatment

Solution plasma process (SPP) was employed to degrade chitosan. The effects of the initial pH value and the distance between the electrodes on the steady shear flow behavior, structural characterization, molecular conformation, and antioxidant activity of chitosan were investigated. The results revealed that a lower initial pH value and a narrower distance between the electrodes were beneficial to the decrease in viscosity and increase in shear-thinning capacity. Structural characterization of the chitosan by FT-IR and 1H NMR showed that chemical structure of chitosan was not destroyed at different process parameters. The results of XRD, HPSEC-MALLS, SEM, and AFM indicated that SPP degradation clearly decreased the crystallinity, molecular weight, molecular size, and molecular aggregation of chitosan. At initial pH values of 2.8 and 5.8, the molecular weight was 27.16 and 44.25 kDa, at the distance between the electrodes of 4 and 8 mm, it was 35.88 and 66.17 kDa, respectively. The results of DPPH and hydroxyl radical scavenging assays demonstrated that a lower initial pH value and a narrower distance between the electrodes enhanced the antioxidant activity.

The nonlinear rheology of complex yield stress foods

Many foods have a yield stress that allows them to retain a desired shape at rest, but transition into a viscous fluid when being served or consumed. The determination of the yield stress of the food dictates how the foods are formed and packaged, how they are served, and how they are perceived when being eaten. Oscillatory shearing provides an ideal test protocol to map the rheology across a range of time and flow strength scales. We couple oscillatory shearing and an iterative recovery procedure to show that the yielding process is a continuous transition for two common yield stress foods. We show that unrecoverable processes from oscillatory tests are equivalent to the steady shear flow behavior. We show that this yielding behavior can be well approximated by a recently published model that treats yield stress materials as continuous viscoelastic fluids with a rate-dependent relaxation time and has parameters that can be obtained from the linear viscoelastic oscillatory frequency sweep and the steady shear flow curve.

Steady and Oscillatory Shear Flow Behavior of Different Polysaccharides with Laponite®.

The rheological behavior, in terms of steady and oscillatory shear flow, of Laponite® with different polysaccharides (alginate, chitosan, xanthan gum and levan) in salt-free solutions was studied. Results showed that a higher polymer concentration increased the zero-rate viscosity and decreased the critical strain rate (Cross model fit) as well as increasing the elastic and viscous moduli. Those properties (zero-rate viscosity and critical strain rate) can be a suitable indicator of the effect of the Laponite® on the shear flow behavior for the different solutions. Specifically, the effect of the Laponite® predominates for solutions with large critical strain rate and low zero-rate viscosity, modifying significantly the previous parameters and even the yield stress (if existing). On the other hand, larger higher polymeric concentration hinders the formation of the platelet structure, and polymer entanglement becomes predominant. Furthermore, the addition of high concentrations of Laponite® increases the elastic nature, but without modifying the typical mechanical spectra for polymeric solutions. Finally, Laponite® was added to (previously crosslinked) gels of alginate and chitosan, obtaining different results depending on the material. These results highlight the possibility of predicting qualitatively the impact of the Laponite® on different polymeric solutions depending on the solutions properties.

Factors influencing the adhesive behavior of carboxymethyl cellulose-based hydrogel for food applications

Carboxymethyl cellulose (CMC) hydrogels have been used as adhesive materials for food and other newly emerged innovative applications. To increase the knowledge of CMC hydrogel-based adhesives and optimize the preparation and storage conditions in practical, we prepared CMC hydrogels for cigar wrapper application and investigated their adhesive performance as affected by different CMC type, concentration, pH, temperature, and storage time, etc. Two parameters, initial adhesiveness and peel strength were used to evaluate the adhesive behavior of CMC with paper and tobacco leaf. Sample C2 with relatively medium molecular weight and medium degree of substitution values showed the best adhesive performance. Hydrogels prepared using boiled water at neutral pH presented better adhesive behavior, which was not significantly affected by storage temperature (up to 13 days). The wettability, steady shear flow behavior, dynamic rheological properties, and stress recovery performance of CMC hydrogel were measured, and their correlations to the adhesive behavior were discussed.

Molecular Weight Dependence of Associative Behavior in Polyimide/DMF Solutions

Eight 6FDA-TFDB polyimide (PI) samples with absolute molecular weights ranging from 1.25 × 105 g·mol−1 to 3.11 × 105 g·mol−1 are obtained by precipitation fractionation. Rheological experiments are conducted to determine the influence of molecular weight on the associating behavior of PI in N,N′-dimethylformamide (DMF) solutions in a broad volume fraction, including abnormal steady shear flow, solution heterogeneity, and scaling behavior. Abnormal flow behaviors, i.e., multi-region shear thinning and weak shear thickening, are studied, and these behaviors have not been reported in literature. The heterogeneity of PI/DMF solutions is examined by dynamic rheological test. By plotting ηsp versus ϕ/ϕη, four concentration regions of I–IV can be distinguished for all PI samples with various molecular weights. The scaling results in different concentration regions are in good agreement with the associative polymer theory proposed by Rubinstein and Semenov. The scaling exponents do not show molecular weight dependence in concentration regions I and II. In concentration regions III and IV, the scaling exponents change little when the molecular weight is below 242 k but increase when the molecular weight increases from 242 k to 311 k. This work can help us to understand polyimide solution properties from dilute to semidilute entangled solutions, and will guide the polyimide solution preparation for different processing.

Influence of sage seed gum on some physicochemical and rheological properties of wheat starch

The effect of sage seed gum at different concentrations (0, 0.1, 0.25, and 0.5% w/w) on swelling power, solubility index, paste clarity, and steady shear flow behavior of wheat starch dispersion (2%, w/w) was evaluated. Sage seed gum addition enhanced the swelling power at all temperatures chosen (50–90°C). It also increased leakage of starch polymers at temperatures &lt;80°C. In contrast, this addition decreased the activation energy needed for swelling (up to 34.17%) and solubilization (up to 30.85%). The paste clarity of wheat starch significantly decreased in the presence of SSG (p &lt; 0.05). The apparent viscosity increased with the increasing SSG concentration and all the samples exhibited shear thinning flow behavior. Among the rheological model used, Sisko's model fitted well to the experimental data (R2 = 0.988–0.999, RMSE = 0.001–0.0018). Accordingly, addition of sage seed gum up to 0.5% resulted in an approximately twofold increase in η∞, 251‐fold in ks, but a 19% decrease in ns values of wheat starch dispersion. The concentration dependence of the apparent viscosity at a shear rate range of 10–100 s−1 was also analyzed using well‐defined models.

Steady shear flow behavior of sage seed gum affected by various salts and sugars: Time-independent properties

The rheological properties of food hydrocolloids are remarkably influenced by the quality of solvent/cosolutes in a food system. In this work, the steady shear flow behavior of sage seed gum (SSG, 0.5% w/w) at the presence of different levels of salts (KCl & MgCl2, 0–100mM) and sugars (sucrose, lactose & glucose, 0–6% w/w) was studied. It was found that the rheological properties of SSG were affected by the type of sugars and salts and their concentrations as well. Synergistic interaction was observed between SSG and sugars which enhanced the viscosity of gum solutions, while salts addition diminished the viscosity. SSG solutions exhibited a shear thinning behavior at all conditions tested. Various time-independent rheological models were used to fit the shear stress-shear rate data, although the Herschel-Bulkley (R2=0.994–0.999) and Sisko (R2=0.995–0.999) models showed the best results to describe the flow behavior of SSG. In the presence of salts, the yield stress (τ0), consistency coefficient (k), and flow behavior index (n) values decreased. The k and τ0 values enhanced and the n value lowered in the presence of sugars. Divalent cations of Mg2+ and sucrose roughly showed more effect on rheological parameters than others.

Purification of cress seed (Lepidium sativum) gum: A comprehensive rheological study

In this paper, the effects of different purification methods (ethanol (sample E), isopropanol (sample I) and ethanol-isopropanol (sample EI)) on intrinsic viscosity, steady and dynamic rheological properties of cress seed gum were investigated. The gum dispersions exhibited viscoelastic properties, the storage modulus (G′) was higher than the loss modulus (G″), and mechanical spectra of the crude and purified cress seed gums were classified as weak gels. The purified samples had stronger and more elastic network structure than the crude gum (CSG) and the gel network got stronger along the series of I, EI and E. All the gum dispersions indicated shear-thinning behavior and the viscosity of the samples followed the order of E > EI > I > CSG. Herschel-Bulkley model was the best model to describe steady shear flow behavior and Arrhenius-type model was also applied to describe the effect of temperature. Crude cress seed gum and EI showed the highest and the lowest activation energy, respectively. The crude and purified gums indicated thixotropic behavior and CSG exhibited the lowest hysteresis loop area and the highest structural recovery. All the samples revealed random coil conformation in dilute regimes, and chain flexibility and intrinsic viscosity enhanced after purification. Intrinsic viscosity of the purified samples increased along the series of I, EI and E.

Stepwise extraction of Lepidium sativum seed gum: Physicochemical characterization and functional properties

Cress seed gum (CSG) was fractionated using stepwise extraction with water, yielding three fractions (F1, F2, F3) whose average molecular weights ranged from 863 to 1080kDa. The chemical composition (monosaccharide, ash, moisture, CHN and uronic acid contents) and molecular weight of the fractions varied significantly. Generally, the major identical peaks of FT-IR spectra for three fractions and whole cress seed gum were similar. The results of DSC and TGA indicated that F3 had the highest thermal stability and considering the initial decomposition temperature, the decreasing order of thermal stability was F3>F2>F1. Cress seed gum and its fractions exhibited non-Newtonian shear thinning behavior which the Herschel-Bulkley model was successfully described the steady shear flow behavior of samples, and apparent viscosity followed the order of F3>F2>F1. F3 exhibited the best surface tension reducing ability compared to other fractions and CSG. All the samples had good emulsifying capability (>97%) and stability (>96%). The emulsion capacity increased slightly along the series of F1, F2 and F3, whereas, emulsion stability decreased along the same series. CSG and F3 showed the highest and the lowest foaming capacity and stability, respectively.

Influence of variety, concentration, and temperature on the steady shear flow behavior and thixotropy of canary seed (Phalaris canariensis) starch gels

In this study, the rheological properties of starch gels from two varieties of canary seeds (CDC Maria and CO5041) were investigated. The experimental conditions were different concentrations (4, 6, and 8% w/w at constant temperature of 25°C) and temperatures (25, 40, 55, and 70°C at constant concentration of 6%). All samples showed shear‐thinning and thixotropy behavior at studied conditions. The power‐law model (R2 = 0.940–0.987; RMSE = 1.297–15.325) and Casson models (R2 = 0.861–0.975; RMSE = 0.211–0.917) were selected to describe time‐independent behavior of the samples. In addition, the first‐order stress‐decay model (R2 = 0.89–0.98 and RMSE = 2.84–20.79) described the time‐dependent behavior of canary seed starch samples in the study well. The CO5041 starch gel had higher pseudoplasticity at different concentrations than CDC Maria. Both starches exhibited the same shear‐thinning behavior with increasing temperature. With increasing concentration, the canary seed starch samples showed more shear‐sensitive thixotropic nature and faster rupture rate. The CO5041 starch gel exhibited higher extent of thixotropy than CDC Maria starch gel at different concentrations.

Steady shear flow properties of Cordia myxa leaf gum as a function of concentration and temperature

The steady shear flow properties of dispersions of Cordia myxa leaf gum (CMLG) were determined as a function of concentration (0.5–2.5%, w/w), and temperature (10–50°C). The CMLG dispersions exhibited strong shear-thinning behavior at all concentrations and temperatures. The Power-law (Ostwald–Waele's) and Herschel–Bulkley models were employed to characterize flow behavior of CMLG solutions at 0.1–100s−1 shear rate. Non-Newtonian shear-thinning behavior was observed at all temperatures and concentrations. While increase in temperature decreased the viscosity and increased the flow behavior indices, adverse effect was obtained by increasing the concentration. The Power-law model was found the best model to describe steady shear flow behavior of CMLG. The pseudoplasticity of CMLG increased markedly with concentration. An Arrhenius-type model was also used to describe the effect of temperature. The activation energy (Ea) appeared in the range of 5.972–18.104kJ/mol, as concentration increased from 0.5% to 2.5%, at a shear rate of 10s−1.

Steady Shear Flow Behavior and Thixotropy of Wheat Starch Gel: Impact of Chemical Modification, Concentration and Saliva Addition

AbstractThe rheological properties of native wheat starch (NWS), cross‐linked wheat starch (CLWS) and hydroxypropylated wheat starch (HPWS) gels at two concentrations (8 and 12%) and in the presence and absence of saliva at 37C were investigated. More decrease in viscosity was observed for the HPWS (83.33%) gel samples at simulated mouth conditions (SMCs) compared to the NWS (32.05%) and CLWS (23.88%) gel samples. In the absence of saliva, the Herschel–Bulkley and Sisko models were the best ones to describe viscous flow behavior of all starch gels. The highest thixotropy extent was obtained for the HPWS (1.98–9.26) while no statistically significant difference was observed for that between the NWS and CLWS gel samples (P &gt; 0.05). The first‐order stress decay model predicted the closest data in the SMC. The results suggested that chemical modification such as hydroxypropylation and cross‐linking can be used to manipulate or modify the rheological behavior of starch in the mouth conditions.Practical ApplicationsBecause of many nutritional, technological and textural advantages of starch in food and pharmaceutical systems, it is receiving much more attention. Investigation of the changes in such bioactive carbohydrates in gastrointestinal tract has recently been considered. Study of the rheological parameters is one of the ways to find the influence of each digestion process on the structural properties of starch samples. In this work, steady shear flow behavior and thixotropy of wheat starch gel affected by the type of wheat starch (native, cross‐linked and hydroxypropylated), concentration and saliva addition (SMCs) were studied. Investigation of rheological properties in a SMC allows a better understanding of food structure in the mastication condition, which can be used to develop a food product with special mouthfeel or for special consumers like people with dysphagia.

Studies on the steady shear flow behavior and chemical properties of water-soluble polysaccharide from Ziziphus lotus fruit

The extraction of water-soluble polysaccharide from Ziziphus lotus fruit (WPZL) was performed by ultrasonic-assisted extraction method. A Box–Behnken design (BBD) was applied to evaluate the effects of three independent variables (ultrasonic power (X1: 70–100W), extraction time (X2: 10–30min), extraction temperature (X3: 55–95°C), and water to raw material ratio (X4: 5–25)) on the extraction yield of APH. The effect of temperature and concentration on flow behavior of gum solution was studied. WPZL solutions exhibited shear-thinning non-Newtonian flow behavior for concentrations above 0.5% (w/v). The viscosity of fully hydrated gum solutions decreased as temperature increase. The correlation analysis of the mathematical-regression model indicated that quadratic polynomial model could be employed to optimize the extraction of WPZL. The optimal conditions to obtain the highest extraction of WPZL (13.398±0.019%) were as follows: ultrasonic power, 88.77W; extraction time, 29.96min, extraction temperature, 77.73°C and water to raw material ratio 24.44mL/g.

The Rheological Modeling and Effect of Temperature on Steady Shear Flow Behavior of Cordia abyssinica Gum

Steady shear rheological properties of Cordia abyssinica gum, as a novel hydrocolloid, were investigated at different temperatures (30-50°C). The apparent viscosity was drastically affected by temperature, and decreased from 234.9 to 7.46 Pa.s. Cordia gum was exhibited pseudoplastic behavior, which being almost Newtonian at 50°C. Different models including Powerlaw, Herschel-Bulkley and Casson were applied to model rheological trait. The Results were shown that the Herschel-Bulkley model has the best fitness with experimental data. Ascending and descending viscometry data were shown a weak thixotropic behavior particularly at low shear rates. By increasing the temperature in both curves, n decreased and k increased. The apparent viscosities of Cordia gum followed an Arrhenius model and the ηo increased and activation energy diminished as shear rate decreased from 330 to 15/s. Low values of the activation energy implied that Cordia gum can maintain its viscosity at higher temperatures more than BSG and Xanthan. It has a high potential for application in food and neutaceutical products as possess yield stress and pseudoplastic behavior, which enables it to use as an emulsifier, stabilizer or excipient in tablet formulations.

Physical and flow properties of d-limonene-in-water emulsions stabilized with whey protein concentrate and wild sage (Salvia macrosiphon) seed gum

The effect of varying concentrations of whey protein concentrate (WPC, 5–15% w/v) and wild sage seed gum (SSG, 0–0.3% w/v) on interfacial tension, zeta potential, physical stability, droplet size, flow properties and viscosity of d-limonene-in-water emulsions at pH7 was investigated. The results indicated that the addition of SSG had no significant effect on zeta potential while the interfacial tension decreased with increasing gum concentration. For freshly prepared emulsions, the mean diameter of droplets slightly decreased as gum concentration increased from 0.0% to 0.3%. In contrast, protein concentration in the range of 5–15% showed no particular effect on the size of droplets. Storage of samples for a period of 4weeks resulted in an increase in the size of droplets. This was substantially noticeable for the emulsions containing no SSG and negligible for those prepared with 0.3% SSG and 15% WPC. The presence of SSG in these emulsions increased the emulsion stability indices, evidently because of the higher viscosity it imparted to the aqueous phase. The emulsions containing only WPC showed Newtonian behavior, while those consisting of both protein and gum exhibited shear thinning characteristics. Various time-independent rheological models were examined to fit the experimental data; of which Herschele–Bulkley model was found to be the best model to describe steady shear flow behavior of these emulsions.

Studies on the steady shear flow behavior and functional properties of Lepidium perfoliatum seed gum

Flow properties of Lepidium perfoliatum gum, extracted from Qodume shahri seeds, as influences of concentrations (0.5%, 1%, 1.5% and 2%), temperatures (5, 25, 45, and 65°C), salts and pHs were investigated. Among the selected models, power law model well described the rheological behavior of the L. perfoliatum seed mucilage solutions with high determination coefficients, R2 and low root mean square error (RMSE). Non-Newtonian shear thinning behavior was observed at all temperatures and concentrations. While increase in temperature decreased the viscosity and increased the flow behavior indices, adverse effect was obtained by increasing the concentration. The temperature effect was more pronounced at 0.5% L. perfoliatum seed gum concentration and indicated the higher activation energy (Ea: 31614.56J/mol). The viscosity was dependent on type of salt addition, and decreased with salt concentration. This behavior was more evident when using divalent salt. A marked dependence of viscosity on pH was also observed, as pH increased from acidic to alkaline conditions, the viscosity increased until pH of 9 and afterward decreased. The hydrocolloid showed good water absorption capacity (WAC) and imparted relatively high stability to foam and oil-in-water emulsion. However, the gum solubility was low at all temperatures studied (30, 60 and 90°C).

Steady shear flow properties of wild sage ( Salvia macrosiphon) seed gum as a function of concentration and temperature

The steady shear flow properties of dispersions of a new potential hydrocolloid, sage seed gum (SSG), were determined as a function of concentration (0.5–2% w/w), and temperature (20–50 °C). SSG dispersions exhibited strong shear-thinning behavior at all conditions tested, which was even more pronounced than commercial hydrocolloids like xanthan, guar gum and locust bean gum. Different time-independent rheological models were used to fit the experimental data, although the Herschel–Bulkley model (H–B) was found the best model to describe steady shear flow behavior of SSG. An increase in gum concentration led to a large increase in yield stress and consistency coefficient values, whereas there was no definite trend with an increase in temperature. On the other hand, the above-mentioned increases in concentration and temperature did not yield a clear evolution of the shear-thinning characteristics of SSG dispersions. An Arrhenius-type model was also used to describe the effect of temperature. The activation energy ( E a) appeared in the range of 3949–16384 J/mol, as concentration increased from 0.5 to 2%, at a shear rate of 100 s −1. The yield stress values estimated by viscoplastic rheological models were much higher than the data determined by stress ramp method. Apparent viscosity of SSG surpassed many commercial hydrocolloids such as guar gum, locust bean gum, Tara gum, fenugreek gum and konjac gum at the same conditions, which suggest it as a very good stabilizer in food formulations.

Steady shear flow behavior of gum extracted from Ocimum basilicum L. seed: Effect of concentration and temperature

Steady shear flow behavior of basil seed gum (BSG) was investigated between 0.5% and 2% (wt/wt) concentration and temperatures of 5–85 °C. BSG showed shear thinning behavior at all concentrations and temperatures. The Herschel–Bulkley model was employed to characterize flow behavior of BSG solutions at 0.1–1000 s −1 shear rate. The pseudoplasticity of BSG increased markedly with concentration. Flow behavior of 1% BSG indicated a higher viscosity of this gum at low shear rates compared to xanthan, konjac and guar gum at similar concentration. The activation energy of BSG quantified using an Arrhenius equation increased from 4.9 × 10 3 to 8.0 × 10 3 J mol −1 as concentration changed from 0.5% to 2% wt/wt. This indicated a heat-resistant nature of BSG. Increasing the apparent viscosity of BSG as temperature increase from 60 °C showed a sol–gel behavior of BSG based on dynamic oscillatory measurements. The static yield stress was obvious between shear rates 0.001–0.1 s −1 (9.98 Pa for 1% BSG at 20 °C). The existence of the yield stress, high viscosity at low shear rates and pseudoplastic behavior of BSG make it a good stabilizer in some food formulations such as mayonnaise and salad dressing.

Constitutive Curve and Velocity Profile in Entangled Polymers during Start-Up of Steady Shear Flow

Time-dependent shear stress versus shear rate, constitutive curve, and velocity profile measurements are reported in entangled polymer solutions during start-up of steady shear flow. By combining confocal microscopy and particle image velocimetry (PIV), we determine the time-dependent velocity profile in polybutadiene and polystyrene solutions seeded with fluorescent 150 nm silica and 7.5 μm melamine particles. By comparing these profiles with time-dependent constitutive curves obtained from experiment and theory, we explore the connection between transient nonmonotonic regions in the constitutive curve for an entangled polymer and its susceptibility to unstable flow by shear banding (Adams et al. Phys. Rev. Lett. 2009, 102, 067801-4). Surprisingly, we find that even polymer systems which exhibit transient, nonmonotonic shear stress-shear rate relationships in bulk rheology experiments manifest time-dependent velocity profiles that are decidedly linear and show no evidence of unstable flow. We also report that interfacial slip plays an important role in the steady shear flow behavior of entangled polymers at shear rates above the reciprocal terminal relaxation time but has little, if any, effect on the shape of the velocity profile.