Rheological behavior of collagen/chitosan blended solutions

Understanding the rheological behavior of collagen/chitosan blends is fundamental to design the optimized collagen/chitosan composite materials. Steady shear, dynamic frequency sweep, thixotropy and creep-recovery tests were investigated to characterize the rheological behavior of collagen/chitosan blends as a function of chitosan content (0%–90% [wt/wt]). All the samples showed pseudoplasticity with shear-thinning behavior. With the increase of chitosan, the viscosity significantly decreased from 862.54 to 0.60 Pa s at 0.05 s⁻¹. The storage modulus and loss modulus also decreased while the dynamic denaturation temperature increased from 39.79 to 45.18°C. Besides, the thixotropy weakened and when the chitosan content reached 70%, the final recovery percentage was only 4.6%. The entanglements between collagen fibers observed by atomic force microscopy became weaker. Finally, the corresponding mathematical models were used to simulate the experimental data, and the obtained parameters might provide some useful theoretical guidance for the processing of the collagen/chitosan blended solutions.     

Rheological properties of aqueous polyacrylamide/NaCl solutions

Rheological properties of aqueous polyacrylamide‐sodium chloride solutions are studied using RheoStress RS100. Polyacrylamide concentration was varied from 0.25 to 1.0% by weight, whereas sodium chloride ranged from 0.0 to 10 g L⁻¹. This range of concentrations is suitable to study many of the polyacrylamide‐sodium chloride rheological properties. Steady flow parameters, yield stress, thixotropic behavior, creep recovery, and dynamic tests are covered in this study. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 1905–1912, 1999     

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.     

Melt rheology of polypropylene reinforced with polyaniline‐coated short glass fibers

This research deals with the melt rheology of isotactic polypropylene (iPP) reinforced with short glass fibers (SGF) coated with electrically conductive polyaniline (PAn). Composites containing 10, 20, and 30 wt % PAn‐SGF were studied. Moreover, a composite of 30 wt % PAn‐SGF was also prepared with a blend of iPP and PP‐grafted‐maleic anhydride (iPP/PP‐gMA). The composites showed linear viscoelastic regime at small strain amplitudes. The onset of nonlinearity decreased as the concentration of filler increased. The time‐temperature superposition principle applied to all composites. The filler increased the shear moduli (G′, G″) and the complex viscosity η*. Steady‐state shear experiments showed yield stress for the composites with 20 and 30 wt % PAn‐SGF. Strikingly, the 10 wt % composite showed higher steady state viscosity than the 20 wt %. Rheo‐optics showed that shear induced disorder of microfibers at a concentration of 10 wt %. However, at 20 wt % concentration shear aligned the microfibers along the flow axis, this would explain the anomalous steady state viscosity values. The viscosity exhibited a shear thinning behavior at high shear rates for all composites. Creep experiments showed that the filler induced greater strain recovery in the composites and that the amount of strain recovery increased as the PAn‐SGF concentration increased. However, the enhancement of strain recovery (as well as shear viscosity) was more significant when using the iPP/PP‐gMA blend, suggesting greater adhesion between this matrix and the filler PAn‐SGF. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

An investigation of melt rheology and thermal stability of poly(lactic acid)/ poly(butylene succinate) nanocomposites

A systematic investigation of the rheological and thermal properties of nanocomposites prepared with poly(lactic acid) (PLA), poly(butylene succinate) (PBS), and organically modified layered silicate was carried out. PLA/PBS/Cloisite 30BX (organically modified MMT) clay nanocomposites were prepared by using simple melt extrusion process. Composition of PLA and PBS polymers were fixed at a ratio of 80 to 20 by wt % for all the nanocomposites. Rheological investigations showed that high clay (> 3 wt %) contents strongly improved the viscoelastic behavior of the nanocomposites. Percolation threshold region was attained between 3 and 5 wt % of clay loadings. With the addition of clay content for these nanocomposites, liquid‐like behavior of PLA/PBS blend gradually changed to solid‐like behavior as shown by dynamic rheology. Steady shear showed that shear viscosity for the nanocomposites decreased with increasing shear rates, exhibiting shear‐thinning non‐Newtonian behavior. At higher clay concentrations, pseudo‐plastic behavior was dominant, whereas pure blend showed almost Newtonian behavior. Thermogravimetric analysis revealed that both initial degradation temperature (at a 2% weight loss) and activation energy of thermal decomposition nanocomposite containing 3 wt % of C30BX were superior to those of other nanocomposites as well as to those of PLA/PBS blend. Nanocomposite having 1 wt % of C30BX did not achieve expected level of thermal stability due to the thermal instability of the surfactant present in the organoclay. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Rheological characterization of room temperature vulcanized silicone sealant: Effect of filler particle size

The rheological properties of silicone sealant filled with different calcium carbonate (CaCO₃) particles varying in size were investigated. It is found that as particle size decreases, the dynamic storage modulus (G′) and shear viscosity (η) increase; whereas, the width of linear viscoelastic region decreases. At low shear rate, a modulus plateau appears and the shear thinning behavior becomes apparent. The reasons for these can be ascribed to the enhanced particle–particle interaction and formation of filler network structure. Moreover, results dealing with the buildup of network structure monitored by kinetic recovery experiments reveal that both the rate of recovery and magnitude of rheological parameters increase with decreasing particle size. This phenomenon is consistent with the data collected from creep and recovery measurements, indicating an enhanced elasticity and network structure. Furthermore, transmission electron microscopy (TEM) observation and mechanical properties tests for cured sealant samples were also carried out to provide an evidence for the discussion further. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers     

Rheological behavior of low molecular weight polystyrene composites containing monodisperse crosslinked polystyrene beads

Steady shear viscosities and dynamic moduli of polymer composites, consisting of crosslinked polystyrene beads and low molecular weight polystyrene matrix, were measured in a cone-and-plate rheometer at different temperatures. Viscosities and dynamic moduli were found to be very sensitive to filler loading and measurement temperature. Steady shear viscosities of 30% and 40% loaded low molecular polystyrene composites showed a power-law behavior over the entire range of shear rates. Storage and loss moduli were initially linear with frequency on double logarithmic plots, with limiting slopes of 0.3 and 0.1. At high concentration of filler particles, they showed a flat plateau at low frequencies, indicating that these systems exhibit a yield behavior. A 20% PS composite loaded with beads of high crosslink densities resulted in poor dispersion of beads as a result of poor dispersion of particles. PS beads 1.16 μm in diameter showed a higher viscosity. It is due to the apparent increase in loading resulting from broken particles. At low measurement temperature, filler effects were suppressed by high viscosity matrix and showed a similar rheological behavior to high molecular weight by PS matrix. We suggest that rheological behavior reflects the state of dispersion of beads in the matrix.     

Rheological investigation of a random copolymer of polyacrylamide and polyacryloyl hydrazide (PAM‐ran‐PAH) for oil recovery applications

In this article, we synthesize and investigate the rheological properties of a random copolymer PAM‐ran‐PAH of polyacrylamide (PAM) and polyacryloyl hydrazide (PAH) and compare with the results of PAM at different temperature (30 and 80 °C) and salinity (0 and 1.0 wt %). At 30 °C, both PAM and PAM‐ran‐PAH exhibited non‐Newtonian rheology with both shear thinning and shear thickening responses. The rheological properties such as viscosity and moduli (G′ and G″) of PAM significantly deformed at elevated temperature (80 °C) and salinity (1.0 wt %), resulting no recovery in viscosity and moduli. On the other hand, the effect of temperature and salinity was found to be least on PAM‐ran‐PAH and showed better stability with the possibility of recovering its original rheological properties. The performance of PAM and PAM‐ran‐PAH was also characterized by enhanced oil recovery tests. The use of PAM‐ran‐PAH for polymer flooding, due to its stable rheology, resulted in an increase in the oil recovery than PAM. In general, the rheological behavior of PAM‐ran‐PAH as a chemical agent proved to be thermally stable than PAM, which clearly supports its use for saline environment and high temperature applications. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44648.     

Thermal and rheological properties of poly(vinyl alcohol) and water‐soluble chitosan hydrogels prepared by a combination of γ‐ray irradiation and freeze thawing

Poly(vinyl alcohol) (PVA)/water‐soluble chitosan (ws‐chitosan) hydrogels were prepared by a combination of γ‐irradiation and freeze thawing. The thermal and rheological properties of these hydrogels were compared with those of hydrogels prepared by pure irradiation and pure freeze thawing. Irradiation reduced the crystallinity of PVA, whereas freeze thawing increased it. Hydrogels made by freeze thawing followed by irradiation had higher degrees of crystallinity and higher melting temperatures than those made by irradiation followed by freeze thawing. ws‐Chitosan disrupted the ordered association of PVA molecules and decreased the thermal stability of both physical blends and hydrogels. All the hydrogels showed shear‐thinning behavior in the frequency range of 0.2–100 rad/s. Hydrogels made by freeze thawing dissolved into sol solutions at about 80°C, whereas those made by irradiation showed no temperature dependence up to 100°C. The chemical crosslinking density of the hydrogels made by irradiation followed by freeze thawing was much greater than that of hydrogels made by freeze thawing followed by irradiation. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Viscoelastic sol–gel state of the chitosan and alginate solution mixture

The rheological behavior of chitosan/alginate solutions was investigated in relation to gelation and polyelectrolyte complex (PEC) formation. Before mixing, the chitosan and the alginate solutions were both homogeneous fluids. However, heterogeneity developed after mixing, accompanied by a serious increase of viscosity. To determine the sol–gel state of the solutions, the viscoelastic variables, such as the dynamic storage modulus (G′) and loss modulus (G″), the loss tangent, and the viscoelastic exponents for G′ and G″, were obtained. Depending on the concentration, the chitosan/alginate solutions revealed unexpected rheological behavior. At a polymer concentration of 1.0 wt %, the chitosan/alginate solution was in a viscoelastic gel state, whereas, at higher concentrations, viscoelastic sol properties were dominant. A viscoelastic gel state for the chitosan/alginate solution was induced based on the weak formation of fiber‐shaped precipitates of a PEC at a low polymer concentration. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 1408–1414, 2007     

Rheological Characterization of Metalized and Non‐Metalized Ethanol Gel Propellants

The gellation of metalized and non‐metalized ethanol with a methylcellulose gelling agent and its effect on the rheological properties (flow and dynamic study) of these gels is reported herein. The rheological study shows that increasing the shear rate reduces the apparent viscosity for a given yield stress (for a shear rate range of 1 to 12 s⁻¹) for both shear rate ranges (1 to 12 and 1 to 1000 s⁻¹) covered in present experiment. The gellant and metal particle concentrations significantly influence the gel apparent viscosity. Distinct changes in thixotropic behavior were observed, while decreasing the concentration of MC gellant and Al metal particles in the ethanol gels. The dynamic study showed that all of the linear viscoelastic regions (LVE) of the gel samples were independent of strain percentage (1 to 10). The G′ values depended on the frequency and exceeded the G′′ values, which indicated a gel‐like highly structured material. The tanδ values showed that all of the ethanol gels were elastic and weak physical gels with a high degree of cross‐linking.     

Viscoelastic behavior of thermosetting epoxy mixtures modified with syndiotactic polystyrene during network formation

The rheological behavior of thermosetting epoxy mixtures modified with thermoplastic syndiotactic polystyrene (sPS) was monitored during the curing of the epoxy resin. The selected thermosetting system was diglycidyl ether of bisphenol A cured with 4,4′‐methylene bis(3‐chloro‐2,6‐diethylaniline) in the presence of various compositions of sPS (from 2.5 to 12.5 wt %). The storage and loss shear moduli of the systems were monitored during network formation. The validity of the Winter–Chambon criterion for the accurate determination at the gelation point from rheological data was demonstrated. The influence of the sPS concentration on the dynamic rheological properties of the samples was investigated. The experimental data showed that at sPS concentrations lower than 7.5 wt %, phase separation induced a quick increase in the viscosity, which was related to a crystallization‐induced phase separation of sPS. For sPS concentrations higher than 7.5 wt %, near the phase‐inversion composition, the rheological behavior of the mixtures was characteristic of a cocontinuous structure. After the viscosity jumped at the onset of phase separation, a decrease in the viscosity was found, and later on, the viscosity increased again because of gelation. Additionally, the influence of the cure temperature on the rheological properties was studied. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 2348–2355, 2006     

Linear and nonlinear melt‐state viscoelastic properties of polypropylene/organoclay nanocomposites

Rheological behavior of polypropylene (PP)/organoclay nanocomposites varying in compatibilizer (PP‐g‐MA) and organoclay concentration was investigated. The samples were prepared by melt intercalation method in an internal mixer. The wide angle X‐ray diffraction patterns and results of rheological measurements showed that the compatibilizer had strong influence in increasing the interlayer spacing. The observed low frequency liquid‐like to solid‐like transition and apparent yield stress in simple shear flows, along with convergence of transient shear stress to nonzero values in stress relaxation after the cessation of flow experiments, were found to be consistent with formation of a physical network in quiescent conditions which could be easily ruptured with applying low shear rates. The values of stress overshoot strain in flow reversal experiments were independent of shear rate, organoclay, and compatibilizer content. From the results of frequency sweep experiments in different nonlinear strain amplitudes it was shown that extended Cox‐Merz analogy was valid in nonlinear dynamic deformations while the shear viscosity showed positive deviation from this analogy with higher deviations at lower shear rates. Results of storage modulus recovery and flow reversal experiments at different shear rates suggested that network structure is reformed with a much slower rate compared to the rotational relaxation of organoclay platelets. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers     

Rheological characterization of carbon black/polystyrene solution systems

Steady‐shear measurements of suspensions of carbon blacks (CB) in polystyrene (PS)/di‐(butyl phthalate) (DBP) solution were investigated as a function of volume fraction (?) of CB to clarify the effect of the primary particle size and the structure of CB aggregates on the rheological properties. The suspensions show a typical shear‐thinning behavior in the range of a shear rate studied. The Casson model was applied to evaluate the viscosity at infinite of shear rate η_∞ and the yield stress σ_y for the suspensions. Relative viscosity η_∞/η_m, (η_m: medium viscosity) thus obtained was compared to the high‐frequency viscosity for the ideal hard‐sphere silica suspensions to evaluate the effective volume fraction ?_eff of CB aggregates. The ?_eff value was larger for the higher‐structure CB with higher DBP absorption value, irrespective of the primary particle size. The yield stress σ_y had almost the same ?_eff dependence for neutral furnace CB/(PS/DBP) suspensions, although it was larger for acetylene black (AcB)/(PS/DBP) suspensions. These results demonstrated that the effective volume fraction is the most important quantity to characterize the CB aggregates on the rheological properties. It was also found that the correction of the medium viscosity changes due to polymer adsorption on the CB surface is important since neutral furnace CB adsorbs PS polymers but AcB hardly adsorbs PS polymers in the solution. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Gas Holdup in Circulating Bubble Columns with Pseudoplastic Liquids

The contributions of pressure drop due to wall frictional losses to the total gas holdup of two‐phase viscous non‐Newtonian systems were experimentally investigated using a 150 dm³ circulating bubble column. The column had a downcomer‐to‐riser cross‐sectional area ratio of 0.54 and a dispersion height of 2.5 m. Aqueous solutions of xanthan gum and carboxymethyl cellulose were used to simulate a wide range of rheological properties. The average wall shear stress was estimated from Al‐Masry's (1999) correlation for the average wall shear rate in external loop airlift reactors. Pressure drop due to wall shear stress was found significantly contributed by 10–70 % to the total gas holdup. This contribution has always been ignored in the data presented in the literature due to the absence of reliable and simple correlations for the average shear rate and shear stress. Corrections to gas holdup were found necessary for non‐Newtonian solutions with concentrations of ≥ 0.5 wt/wt.‐%.     

Effect of volume loading and surface treatment on the thixotropic behavior of polypropylene filled with calcium carbonate

The rheological properties of calcium carbonate‐filled polypropylene were examined using a Rheometrics dynamic analyzer. The study included steady shear test, transient stress growth test with sequential deformation history, and two‐step dynamic oscillatory shear flow. Thixotropic behavior was observed in transient tests for highly filled compounds when volume loading exceeding a critical value at about 20%. The material responses of these viscoelastic thixotropic materials depend on the duration of shear as well as on the rate of shear. The effects of filler on the rheological behavior of highly filled compounds are dominant at low strain rates; however, the effects of activity of the filler are almost negligible at high strain rates because of complete breakdown of the filler network. The timescales for structural changes in filled systems often become long compared with the viscoealstic time constants of the unfilled melt. The magnitudes of rheological properties and the degree of hysteresis appear to increase with increasing volume loading of filler particles. Conversely, surface treatment of fillers, which presumably reduces interaction between filler particles and the extent of agglomeration, results in major reductions of both rheological properties and the degree of hysteresis. The diverse experimental observations are interpreted in terms of a system forming a filler network due to weak interparticle forces. The thixotropy resulting from breakdown and recovery of the filler network is dependent on the characteristic time of the individual test.     

Rheological studies of mixed printing pastes from sodium alginate and modified xanthan and their application in the reactive printing of cotton

The rheology of printing pastes using sodium alginate and modified xanthan as mixed thickeners has been measured by steady shear tests and dynamic strain sweep tests. The rheological results showed that, with a small addition of modified xanthan to sodium alginate, the flowability of the mixed printing pastes was better than that with sodium alginate alone. Subsequently, as the addition of modified xanthan increased, the apparent viscosity at low shear rates increased gradually, and the mixed printing pastes gained increasingly pronounced shear‐thinning features. In addition, the mixed printing pastes with more sodium alginate exhibited mainly viscous behaviour under strain, and the liquid‐like features became increasingly weak with the addition of modified xanthan. On the other hand, the mixed printing pastes with more modified xanthan exhibited mainly elastic behaviour within the linear viscoelastic region, and the solid‐like features became increasingly marked with the addition of modified xanthan. Mixtures of sodium alginate and modified xanthan can be used as thickeners in the reactive printing of cotton, producing a good colour yield, levelness, and outline sharpness. In particular, for large patterns, the mixed printing paste performed best when the ratio of sodium alginate to modified xanthan was 80:20; for fine patterns, it performed best when the ratio of sodium alginate to modified xanthan was 20:80.     

Electrical,thermal, and viscoelastic properties of graphene nanoplatelet/poly(butylene adipate‐co‐terephthalate) biodegradable nanocomposites

Graphene nanoplatelets (GNPs) were dispersed in poly(butylene adipate‐co‐terephthalate) (PBAT) by melt‐blending. Scanning electron micrographs showed good dispersion of GNPs in PBAT at low concentrations while at higher loadings, the platelets became physically in contact forming conductive pathways. Electrical conductivity of PBAT was enhanced markedly with GNP addition with a distinctly faster rate for GNP loadings higher than 6 wt % because of formation of conductive networks. Interestingly, thermal stability of PBAT was also found to increase for GNP loadings above 6 wt %. Dynamic viscoelastic properties of the nanocomposites exhibited significant enhancement with increasing GNPs. In particular, storage modulus showed less frequency dependency in the low frequency region leading to a percolation threshold of between 6 and 9 wt %, above which time–temperature superposition principle failed. Steady shear measurements revealed that GNP incorporation increased the zero‐shear viscosity markedly and intensified the shear thinning behavior. Carreau model well described the shear viscosity of all the compositions. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43620.     

Rheological behaviors of PVA/H2O solutions of high‐polymer concentration

The dynamic viscoelastic properties of poly(vinyl alcohol) (PVA)/H₂O solutions with concentrations of 10 to 25 wt % have been characterized by controlled‐stress rheometry at 30°C. Parameters relating to the linear and nonlinear viscoelasticities include complex viscosity (η*), storage modulus (G′), loss tangent (tan δ), relaxation time (λ), thixotropy, and creep. Change curves of η*, G′, tanδ, and λ with frequency (ω) have been obtained for the PVA/H₂O solutions. Creep and recovery testing yielded compliance (J′) curves with loading and unloading. Shear stress versus rate profiles of the PVA solutions have been obtained through thixotropic measurements. The PVA concentration has been found to have a profound influence on the rheological properties of the aqueous solutions. Four aqueous solutions of 10, 15, 20, and 25 wt % PVA at 30°C exhibited shear‐thinning and showed different transition behaviors of η* and G′ with frequency, and different degrees of creep under constant stress to recovery with time. The 10 wt % PVA solution was viscous and displayed the lowest η* and G′; the 25 wt % PVA solution was viscoelastic and displayed the highest η* and G′; the 15 and 20 wt % PVA solutions showed η* and G′ values and creep to recovery behaviors intermediate between those of the 10 wt % and 25 wt % PVA solutions. The different rheological properties of these PVA/H₂O solutions are considered to correlate with interchain hydrogen bonds and shear‐induced orientation in the solutions. Shearing is able to break the intrachain and interchain hydrogen bonds, and, at the same time, the orientation creates new interchain hydrogen bonding. The reorganization of hydrogen‐bonding mode contributes to the transitions of the macroscopic viscoelasticity with frequency. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Analysis of the performance of polysaccharide membranes in aqueous media as a tool to assist wound‐dressing selection

The behavior of hydrophilic matrixes in the presence of aqueous media plays a pivotal role in the selection of materials that come into contact with body fluids. Because polysaccharides have proven benefits in the treatment of skin lesions, the performance of membranes produced with chitosan combined with alginate [chitosan–alginate (Ch–A)], xanthan [chitosan–xanthan (Ch–X)], or guar gum [chitosan–guar gum (Ch–G)] after exposure to different aqueous solutions and humidity levels was analyzed with the aim of directing their applications as dressings in wounds with different exudate productions. The Ch–X membranes presented a high fluid‐uptake capacity and water‐vapor transmission rate (WVTR); this was attributed to ramifications in the xanthan structure, and the membranes were then recommended for moderately to highly exuding wounds. The Ch–G membranes showed a dense structure and presented low fluid‐uptake capacity; they were more appropriate for low‐exuding wounds or wounds in the advanced stage of cicatrization. Both the Ch–A and Ch–G membranes presented adequate mechanical properties in a wide range of relative humidity conditions and could be considered suitable for use in all body parts. However, as the Ch–A formulation showed limited WVTR, its use should be restrictedly to, at most, moderately exuding wounds. In all cases, the assessment of the wound type by a professional would be required to define the final dressing formulation. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45386.