Preparation and viscosity behavior of hydrophobically modified poly(vinyl alcohol) (PVA)

In this study, a novel series of water-soluble hydrophobically modified poly(vinyl alcohol) (PVA) is prepared by chemical modification of PVA, with the objective of investigating the polymer's rheological behavior for enhanced oil recovery applications. The solution viscosity of the polymer obtained is studied with respect to the polymer concentration, temperature, salinity, polymer modification, aging, shear rate, and polymer molecular weight. The solution viscosity of the PVA is greatly enhanced by the modification. The modified PVA exhibits a relatively high salt tolerance, typical of nonionic polymers, in the range of 0–7.0 wt % NaCl concentrations, and the viscosity of the polymer solution is relatively invariant with NaCl above 3.0 wt % NaCl concentration. Below 3 wt %, the viscosity shows a maximum then a minimum, an unusual behavior. Generally, the polymer exhibits an almost constant viscosity at high shear rates and a typical shear thinning behavior at low shear rates. In addition, increasing polymer concentration and molecular weight leads to an increase in the polymer solution viscosity. Moreover, the polymer exhibits smaller solution viscosity at a high temperatre, and a slight decrease in viscosity is also exhibited by the modified polymer with aging. Comparison of the viscosities of 18 polymer modifications indicates that the larger the numbers of hydrophobic groups (side chains) in the polymer structure, the smaller the viscosity. Moreover, the longer the hydrophobic groups (side chains) in the polymer structure, the greater the viscosity, if their number is small. © 1995 John Wiley & Sons, Inc.     

Viscosity of concentrated styrene solutions of polystyrene

Viscosities of concentrated solutions of polystyrene of different intrinsic viscosities were measured at varying polymer concentration and temperature. By modifying Martin's equation, an empirical equation correlating the viscosity of the solution as a function of the polymer concentration, the intrinsic viscosity of the polymer, and temperature was obtained.     

顺丁橡胶生产中胶液浓度、平均分子量及门尼粘度与胶液物性常数关联的探索研究

本文通过对顺丁胶抽余油溶液的折射率及粘度的测定来预计胶液浓度、平均分子量及门尼粘度,并得出相应的关联式。为在生产上实现这三个参数的自动控制提供了一种可供参考的方法。     

A study of rheological properties of cellulose diacetate in acetone solution at low and high shear rates

The rheological properties of cellulose diacetate (CDA) with different intrinsic viscosity (IV) and different concentration in acetone solutions were studied at low and high shear rates. The zero-shear viscosity increased and the structural index increased, when the IV of CDA was increased or the acetone solution concentration was increased. Evidence suggested that a sulfate structure may be forming. It is shown that the increase of hemicellulose and sulfur content is associated with an increase of chain entanglements between CDA molecules and the abnormal increase of solution zero-shear viscosity. At a high shear rate, the correlation curve between inlet pressure drop and solution concentration obtained by Bagley method analysis shows an inflection point, which appears to be the critical concentration at which the cellulose diacetate molecular chains in the solution form a long range entangled elastic network. After the concentration exceeds a certain range of above critical points, the entanglement of the molecular chains in the solution is significantly enhanced. The zero shear viscosity inflection point concentration calculated by the rheological curve with low shear velocity and the inlet pressure drop inflection point concentration calculated by the capillary rheological calculation have good consistency.     

Degradation kinetics of poly (vinyl-pyrrolidone) under ultrasonic irradiation

Ultrasonicaton has proved to be a highly advantageous method for depolymerizing macromolecules because it reduces their molecular weight simply by splitting the most susceptible chemical bond without causing any changes in the chemical nature of the polymer. Solution of poly (vinyl-pyrrolidone) in chloroform with different concentrations and different molecular weights at a fined temperature were subjected to ultrasonic degradation. This study confirms the general assumption that the shear forces generated by the rapid motion of the solvent following cavitational collapse are responsible for the breakage of the chemical bonds within the polymer. A method of viscometry was used to study the degradation behavior and kinetic model was developed to estimate the degradation rate constant. The results were indicated that the polymers with height molecular mass degraded faster than the polymers laving low molecular mass thus the rate of ultrasonic degradation increased with increasing molecular weight. It was found that rate constant decreases as the concentration increases. The calculated rate constants correlated in terms of inverse concentration and relative viscosity of PVP solutions. This behavior in the rate of degradation was interpreted in terms of viscosity and concentration of polymer solution. The effect of polymer concentration can be interpreted in terms of the increase in viscosity with concentration, causing the molecules to become less mobile in solution and the velocity gradients around the collapsing bubbles to therefore become smaller and it causes a reduction in the cavitation efficiency thus, the rate of degradation will be decreased. The experimental results show that the viscosity of polymers decreased with ultrasonic irradiation time and approached a limiting value, below which no further degradation took place.     

Ultrasonic absorption and visco-relaxation study of poly(vinyl alcohol) aqueous solution. (A method for the determination of molecular weight)

Ultrasonic absorption and velocity measurements are reported on aqueous solutions of poly(vinyl alcohol) (PV-OH) of different molecular weights and concentrations obtained using a pulsed ultrasonic apparatus operating at 2 MHz and 303 K. The variations in these parameters as a function of concentration are interpreted in terms of changes in the magnitude of the contribution due to relaxation of the backbone and of the side chain acetyl groups. The results show an increase in velocity, density and viscosity with increase in molecular weight and concentration of PV-OH. In contrast the attenuation values decrease with increase in molecular weight. This suggests that interaction is occurring between PV-OH and water molecules. Deviation of the variation of the attenuation with concentration from the ‘ideal’ dilute solution behaviour at high concentration is ascribed to the effects of polymer-polymer interaction. The magnitude of the volume change associated with polymer-solvent interactions is estimated and discussed. A mathematical equation correlating the relaxation amplitude and the molecular weight of the polymer is suggested. This approach was applied to the calculation of the molecular weight of four unknown samples of PV-OH from their measured relaxation amplitudes. The results obtained agree well with those obtained from osmometry.     

Comments on the accuracy of zero shear intrinsic viscosity of high molecular weight polyacrylamide

The intrinsic viscosity of a polymer is traditionally measured with a capillary tube viscometer where the shear rate range is moderately high. Such method is valid when the polymers are non-ionic and have low to moderate molecular weight. The viscosity-shear rate curves obtained for dilute aqueous solutions of two high molecular weight polyacrylamides using two rotational viscometers indicate a strong shear-dependent viscosity in the medium to high shear rate regions. The zero shear intrinsic viscosity of the polymers determined by extrapolation from the high shear rate region to the zero shear condition may result in large errors. Its implication in predicting the molecular weight of polymers using the Mark-Houwink-Sakurada equation is discussed. A rheological equation for intrinsic viscosity as a function of shear rate is proposed.     

Ultrasonic Study of Molecular Association of Polyethylenoxide Aqueous Solutions (A Method to Determine Molecular Weight)

Ultrasonic velocity and isoentropic compressibility measurements are reported on aqueous solutions of polyethylenoxide of different molecular weights and different concentrations using pulsed ultrasonic apparatus operating at 2 MHz and 310 K. The data obtained as a function of concentration indicate the magnitude of the contribution due to relaxation of the backbone of the ethylene group. The results show a linear increase of density, velocity and viscosity values with increasing molecular weight and concentration of PEO. In contrast, the isoentropic compressibility decreases with increasing of molecular weight and concentration of PEO. A mathematical equation correlating isoentropic compressibility and molecular weight of the polymer is suggested. This was applied to the calculation of the molecular weight of unknown samples of PEO from their measured isoentropic compressibility; the results obtained agreed well with those obtained from osmometry.     

A rheological study of the low molecular weight butyl polymer

A rheological study has been performed to characterize the low molecular weight butyl polymers using a couette coni-cylindrical viscometer. The bulk viscosity was determined as a function of temperature, weight-average molecular weight, viscosity-average molecular weight, and shear rate. The temperature dependence of the viscosity, while adequately represented by the Williams, Landel, and Ferry equation, is best described by an Arrhenius equation for the temperature range investigated. The viscosity is shown to vary with the 3.5th power of the weight-average molecular weight above a critical molecular weight and to the 1st power below this molecular weight. Although the ratio of the weight-average molecular weight to the number-average molecular weight usually affects the flow properties of polymers, this was not true for the polymers investigated. The bulk viscosity was found to be independent of the molecular weight distribution for the temperature and shear rate range studied. It has been shown that a definite relationship exists between the bulk viscosity and the viscosity-average molecular weight as determined by dilute solution viscosity. A mathematical model has been developed to relate these two parameters as a function of temperature and shear rate.     

Rheological Behaviors of Polyacrylonitrile/1-Butyl-3-Methylimidazolium Chloride Concentrated Solutions

One of the room temperature ionic liquids (RTILs), 1-butyl-3-methylimidazolium chloride ([BMIM]Cl) was chosen to prepare the concentrated solutions of Polyacrylonitrile (PAN). The rheological behaviors of the solutions were measured with rotational rheometry under different conditions, including temperatures, concentration, and molecular weight of PAN. The solutions exhibited shear-thinning behaviors, similar to that of PAN/DMF solutions. The viscosities decreased with the increasing of shear rates. However, the viscosity decreased sharply at high shear rates when the concentration was up to 16wt%. The dependence of the viscosity on temperature was analyzed through the determination of the apparent activation energy. Unusually, the viscosity of solutions of higher concentration is lower than that of lower concentration. Similarly, the viscosity of low molecular weight PAN was higher than high molecular weight PAN at high shear rates. The dynamic rheological measurement indicates the loss modulus is much higher than storage modulus. The trend of complex viscosity is similar with the result of static rheological measurement. The interaction between PAN and ionic liquid [BMIM]Cl was discussed.     

Rheological properties of highly swollen hydrogel suspensions

The shear rheology of diluted to concentrated suspensions of weakly cross-linked sodium polyacrylate hydrogels were investigated by concentric cylinder rheometry. The size of the swollen gel particles is dependent on the initial size of the dry particle and on the nature of the added salt. Polyvalent salts are more efficient for contracting the swollen particles than monovalent ones. When suspended in water or in monovalent salt solutions, the viscosity at low concentrations shows a behaviour very similar to the one of flexible polymer solutions. Below the critical overlap concentration, the viscosity is independent of shear rate. The intrinsic viscosity is very large, on the order of 10–15 dL/g. This is in agreement with the large size of these swollen particles. Suspensions of such swollen gel particles are thus a good model for extremely high molecular weight polymer solutions. In polyvalent salt solutions different behaviour of the viscosity curves versus concentration was observed. This effect is caused by chemical cross-linking of the hydrogel by polyvalent ions. © 1994 John Wiley & Sons, Inc.     

Rheological behavior of anaerobic adhesives: Rheological profile modelling depending on the composition

A study is done on the influence of fumarate-based thickeners on the rheological behavior of low-molecular-weight poly(ethylene glycol) dimethacrylate monomers diluents, often used as major components in the formulation of anaerobic adhesives. These solutions generally showed pseudoplastic behavior. The Cross equation was selected to determine the viscosity vs. shear rate curves, at constant temperature. The final equation relates the viscosity as a function of shear rate and thickener concentration. In addition, the zero shear rate viscosity evolution as a function of the thickener weight fraction was studied, showing that two critical concentrations were present.     

Thermal and rheological properties of polyethylene blends with bimodal molecular weight distribution

Polyethylene blends with bimodal molecular weight distribution were prepared by blending a high molecular weight polyethylene and a low molecular weight polyethylene in different ratios in xylene solution. The blends and their components were characterized by the high temperature gel permeation chromatograph (GPC), different scanning calorimetry (DSC), and small amplitude oscillatory shear experiments. The results showed that the dependence of zero‐shear viscosity (η₀) on molecular weight followed a power law equation with an exponent of 3.3. The correlations between characteristic frequency (ω₀) and polydispersity index, and between dynamic cross‐point (G_x) and polydispersity index were established. The complex viscosity (η^*) at different frequencies followed the log‐additivity rule, and the Han‐plots were independent of component and temperature, which indicated that the HMW/LMW blends were miscible in the melt state. Moreover, the thermal properties were very similar to a single component system, suggesting that the blends were miscible in the crystalline state. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Modified bead-spring theory of dilute polymer solutions. II. Effects of polydispersity and comparison with experiment

A constitutive equation, previously derived for dilute, monodisperse solutions of linear macromolecules, is extended to include polydisperse solutions. This result, which represents a coupling of continuum and molecular theory, realistically portrays the effects of molecular weight and molecular weight distribution on mechanical behavior. Intrinsic viscosity–shear rate data are well described, and with certain semiempirical modifications the equation also fits normal stress and dynamic viscosity data for slightly more concentrated solutions. Some unusual effects associated with the characterization of macromolecular degradation, in studies of turbulent drag reduction, are also explained.     

疏水缔合聚丙烯酰胺溶液性质研究

用粘度法和核孔膜过滤法研究了实验室自制相对分子质量约1000万的疏水缔合聚丙烯酰胺(HAP)溶液的缔合效应,用粘度计考察了电解质浓度、温度和剪切速率对HAP溶液表观粘度的影响,并与相同测试条件下相对分子质量为1770万的部分水解聚丙烯酰胺3530进行对比。结果表明:HAP溶液在70℃的高温和矿化度为5727的高盐条件下,在1000mg/kg附近存在一临界缔合浓度,在临界缔合浓度以上,HAP溶液粘度迅速增加;而3530不存在临界缔合浓度,粘度增加缓慢。浓度为1250mg/kg的HAP溶液通过核孔膜20mL的过滤时间是347.3min,而相同浓度下3530的过滤时间仅为2.1min。浓度为1000mg/kg的HAP溶液即使在矿化度为30000、70℃的高温、30r/min转速的条件下,粘度仍达到32.8mPa·s,而聚合物3530的粘度仅有4.11mPa·s;当剪切速率增加到140r/min、温度为70℃,用矿化度为5727的模拟采出水配制的HAP溶液的粘度为9.21mPa·s,而3530溶液的粘度仅5.18mPa·s。HAP具有良好的耐温抗盐抗剪切能力。     

Rod-Climbing characterization of kaolinite suspended polyisobutylene solutions

The rod-climbing constants of kaolinite-suspended polyisobutylene (PIB) solutions are investigated from rod-climbing experiments. For a low deformation rate, this particle suspended polymer solution can be regarded as a second-order fluid, and the rod-climbing constant for such fluids is correlated with the rheological properties of the particle-suspended polymer solutions. The rod-climbing constants for kaolinite suspended PIB solutions were found to decrease with temperature and increase with PIB concentration, molecular weight of PIB, solvent viscosity, and particle concentration. The rheological properties were measured using rotational rheometer, and the shear viscosity and the first normal stress difference of the kaolinite suspended PIB solution show the Boger-fluid characteristics.     

Viscosity and molecular weight distribution of ultrahigh molecular weight polyethylene using a high temperature low shear rate rotational viscometer

To obtain accurate measurements of the limiting viscosity number (LVN) or the intrinsic viscosity [η] of solutions of ultrahigh molecular weight polyethylene (UHMWPE), a low shear floating-rotor viscometer of the Zimm-Crothers type was constructed to measure viscosities at elevated temperatures (135°C) and near zero shear rate. The zero shear rate measurements for UHMWPE whole polymer and UHMWPE fractionated by hydrodynamic crystallization were compared with viscosity measurements at moderate and high shear rates (up to 2000 _s^?1) carried out in a capillary viscometer. The limiting viscosity number of UHMWPE decreases, as expected, with shear rate. The higher shear rate data could not be extrapolated to yield the correct zero-shear rate viscosities. Fractionation of UHMWPE gave 10 fractions ranging in LVN from 9 to 50 dL/g. A tentative integral molecular weight distribution for the whole polymer was calculated on the basis of the Mark-Houwink equation, but because it had been previously established only for lower molecular weight polyethylenes, it may not be accurate. A correlation was found between the LVNs for the fractions in the two types of viscometers.     

Viscometric behavior of ternary concentrated solutions of hydroxypropyl cellulose and ethyl cellulose in m-cresol

The shear viscosity of blend solutions of hydroxypropyl cellulose (HPC) and ethyl cellulose (EC) in m-cresol (both HPC/m-cresol and EC/m-cresol systems form lyotropic liquid crystals) was determined by cone-plate-type and capillary-type viscometers. The textures for the same systems at rest and undergoing shear were also observed with a polarized microscope. At shear rate of 1 s^?1, viscosity exhibited a maximum and a minimum with respect to temperature, and this suggested that the phase of the matrix dominated the viscometric behavior of the ternary systems; the blend composition dependence of the viscosity was not additive, and this suggested that HPC and EC were immiscible. At relatively high shear stress, the blend composition dependence of the viscosity greatly depended on the total polymer concentration of the solutions and was quite different from that at low shear rate; the texture of the anisotropic solutions was also different from that at low shear rate. Our findings suggested that the dependence of viscosity on shear and concentration for pure HPC solution was different from that for pure EC solution.     

Determining molecular weight distributions from viscosity versus shear rate flow curves

Using the theoretical approach of Bersted and Slee, we developed a technique of determining the molecular weight distribution (MWD) from the viscosity vs. shear rate flow curve. Each molecular weight fraction was assumed to have a characteristic deformation rate. Below this rate, the viscosity was equal to the zero shear value. Above this rate, the viscosity was reduced to the zero shear viscosity of the molecular weight characteristic of the higher rate. The relationship between the weight fraction of each component and the viscosity/rate curve was derived from these assumptions. The flow curves of very well-characterized polystyrenes were determined. MWDs were then calculated using the BerstedSlee approach and compared with results from size exclusion chromatography. Comparisons were also made with the results of Malkin and Teishev. They used the same assumptions as Bersted and Slee but chose a different methodology for determining the MWD.     

The rheological and structural behavior of silylcellulosics derivatives

The trimethylsilylcellulose (TMSC) samples were characterized in solution by osmometry, viscometry, and gel permeation chromatography. The Mark-Houwink-Sakurada (M-H-S) equation coefficients were determined in chloroform, 1,1,1-trichloroethane, and o-xylene, in all cases the exponent “a” being higher than unit, this indicating a great stiffness of the macromolecules in solution. Also, the temperature dependence of the limiting viscosity number and M-H-S coefficients respectively for TMSC in o-xylene were studied. The exponent from M-H-S equation is also higher than unit, and increases linearly with the temperature. The GPC studies indicates a relative high polydispersity of the studied samples; the polydispersity index being situated between 2 and 3. The change of the crystalline structure as the result of silylation reaction was evidenced, the crystallinity of silyl derivatives depending on the substitution degree (DS), and the molecular weight. The viscous flow parameters for dilute solutions of trimethylsilylcellulose in o-xylene were determined in the temperature range 30–70°C. The temperature dependence of the dynamic viscosity of the solutions obeys an Arrhenius-type equation in which the apparent activation energy is linearly dependent on both the solution's concentration and molecular weight. For preexponential factor no significant dependence on concentration and molecular weight was found. This behavior was attributed to the very great stiffness of the macromolecular chains. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 2277–2285, 2001