Zero-shear viscosity of dilute to moderately concentrated solutions of poly[2-methoxy-4, 6-di-(p,p′-isopropylidene diphenyloxy)-s-triazine]

Zero-shear viscosities of solutions of poly [2-methoxy-4,6-di(p, p′-isopropylidene diphenyloxy)-s-triazine] in chloroform were measured at various temperatures. The viscosity data were analyzed in terms of Martin's and Fedor's relationships. The temperature dependence of viscosities indicates that the apparent activation energy for viscous flow increases and the preexponential factor, related to activation entropy, decreases with concentration of polymer solution. The parameter Cm, related to volume fraction of polymer φ^m, was found to be linearly dependent on temperature. The viscosity-concentration data were generalized in terms of reduced variables.     

Solution Behavior of Hydrophobic Cationic Hydroxyethyl Cellulose

The hydrophobic cationic hydroxyethyl cellulose (HEC-g-DA) was prepared by grafting HEC with various alkyl ammonium chlorides (DA) in order to improve the thickening properties of cationic hydroxyethyl cellulose. The solution behavior of HEC-g-DA was studied, and showed that the apparent viscosity of HEC-g-DA increased with polymer concentration, and there existed a critical association concentration (Cp*). The alkyl chain length of DA had a great influence on Cp*, which decreased with increasing alkyl chain length; however, too long an alkyl chain of DA reduced the water solubility of the polymer, resulting in a slight increase of Cp*. The effect of temperature and electrolyte concentration on the thickening properties of HEC-g-DA was investigated; the value of viscous flow activation energy (E_a) was minimum for the sample of HEC-g-DA16 (glycidyl-N-hexadecyl–N,N-dimethyl-ammonium chloride), indicating the weakest sensitivity of the viscosity to temperature. In the whole range of shear rate investigated, the solutions of HEC-g-DA displayed the shear thinning behavior of a pseudoplastic fluid. The values of viscous index (n) from the Ostwald model simulation decreased with polymer concentration, indicating an improvement of the shear thinning property of the solution, whereas the increase of the consistency coefficient (k) indicated the enhancement of the thickening behavior of the polymer. With increasing polymer concentration, the molecular association of HEC-g-DA16 became strong, and high-shear stress was required to remove the association, while the difference between G′ and G″ became small, indicating that the elasticity of the system was enhanced at high polymer concentration. The amphiphilic structure of the HEC-g-DA16 molecules contributed to the low surface tension of the polymer.     

Effect of molecular weight on the ultrasonic degradation of poly(vinyl-pyrrolidone)

The ultrasonic degradation of poly(vinyl-pyrrolidone) (PVP) of different initial molecular weights was studied at a fixed temperature. The effect of solution concentration on the rate of degradation was investigated. 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 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. With increasing solution concentration, viscosity increases 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. 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. 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.     

Calculation of the rate constant for the ultrasonic degradation of aqueous solutions of polyvinyl alcohol by viscometry

Ultrasonic degradation of polyvinyl alcohol (PVA) was carried out in aqueous solution at 25 degrees C. In this experiment, the effect of solution concentration on the rate of degradation was investigated. Kinetics of degradation was studied by viscometry method. The calculated rate constants indicate that degradation rate of PVA solutions decreases with increasing of solution concentration (C= g lit(-1)). The calculated rate constants correlated in terms of reverse concentration and relative viscosity of PVA solutions. This behavior in the rate of degradation was interpreted in terms of viscosity and concentration of polymer solution. With increasing solution concentration, viscosity increases and it causes a reduction in the cavitation efficiency thus, the rate of degradation will be decreased.     

High Pressure High Temperature Dynamic Rheometry of Sulfonated Polyacrylamide Solutions in Electrolyte Media as Used for Oil Recovery Applications

Sulfonated polyacrylamide (SPAA) solutions were prepared and the effects of pressure, polymer concentration, and water temperature, pH and salinity on their rheological behavior were investigated using a concentric cylinder dynamic rheometer equipped with a high pressure cell. According to the rheological flow curves the shear stress of SPAA solutions increased less than in proportion to their shear rates; that is, a shear thinning effect occurred. For polymer solutions containing 15,000 ppm of SPAA, shear viscosity, and stress were nearly insensitive to pressure. However, the shear viscosity and stress of SPAA solutions were affected by temperature and this effect was more evident at lower pressure. The flow curves indicated the shear viscosity and stress of the samples increased with increasing SPAA concentration and pH of the water, but were decreased with increasing water salinity and temperature.     

Ultrasound-based treatment approaches for intrinsic viscosity reduction of polyvinyl pyrrolidone (PVP)

The present work deals with achieving viscosity reduction in polymer solutions using ultrasound-based treatment approaches. Use of simple additives such as salts, or surfactants and introduction of air at varying flow rates as process intensifying parameters have been investigated for enhancing the degradation of polyvinyl pyrrolidone (PVP) using ultrasonic irradiation. Sonication is carried out using an ultrasonic horn at 36 kHz frequency at an optimized concentration (1%) of the polymer. The degradation behavior has been characterized in terms of the change in the viscosity of the aqueous solution of PVP. The intrinsic viscosity of the polymer has been shown to decrease to a limiting value, which is dependent on the operating conditions and use of different additives. Similar extent of viscosity reduction has been observed with 1% NaCl or 0.1% TiO₂ at optimized depth of horn and 27 °C, indicating the superiority of titanium dioxide as an additive. The combination of ultrasound and ultraviolet (UV) irradiation results in a significantly faster viscosity reduction as compared to the individual operations. A kinetic analysis for the degradation of PVP has also been carried out. The work provides a detailed understanding of the role of the operating parameters and additives in deciding the extent of reduction in the intrinsic viscosity of PVP solutions.     

Short electrospun composite nanofibers: Effects of nanoparticle concentration and surface charge on fiber length

Short composite nanofibers were fabricated by electrospinning polymer/TiO₂ nanoparticle solutions of 13 wt. % cellulose acetate as a polymer under a voltage of 5.5 kV and at a flow rate of 0.1 μL/min, and the nanoparticles could be added in concentrations as high as 50 wt. %. The length of the short composite nanofibers was significantly decreased from 112 to 70 μm by the addition of at least a 5 wt. % concentration of nanoparticles, and it gradually continued to decrease as the nanoparticle concentration was increased. The length of the short composite nanofibers with a low concentration of nanoparticles was affected by the surface charge of the nanoparticles, and negatively charged nanoparticles readily dispersed to the negatively charged polymers in solution, which resulted in an elongation of the fabricated short composite nanofibers.     

A Rheological Study of Xanthan Polymer for Enhanced Oil Recovery

This study explored the potential application of xanthan gum as a polymer-flooding agent for oil recovery applications in a specific Devonian oil field. Rheological measurements using oscillatory and steady shear were carried out to examine the change in shear viscosity when the polymer was applied under reservoir conditions. The xanthan rheological properties were described by the Herschel–Bulkley and Ostwald models to characterize its non-Newtonian behavior. As expected, the results showed that higher xanthan concentrations raised the polymer viscosity and increased the degree of shear thinning. Addition of alkalis caused the viscosity of the xanthan solutions to decrease, but they maintained their shear-thinning properties. Polymer solutions in typical oil field brine increased in viscosity by ca. 400% for 720 hours storage time. On the other hand, as expected, the solutions lost their viscosity gradually with increasing temperature. However, at reservoir temperature (68°C), the polymer solutions kept more than 60% of their initial viscosity. In oscillatory deformation tests it was observed that all the measured viscoelastic properties were influenced by temperature and confirmed that xanthan solution behaved as a weak-gel. An order-disorder transition exists within the xanthan-brine solutions which responds to changes in solution concentration, temperature and alkalis.     

Structural relaxation and viscous flow in amorphous ZrAlCu

The ternary metallic glass Zr₆₅Al_7.5Cu_27.5 offers a wide temperature range between glass transition temperature and crystallization temperature and is therefore well suited for investigation of the glass transition and the state of the super cooled liquid. The non-linear viscosity change caused by structural relaxation has been measured caused by structural relaxation has been measured using tensile creep experiments on as quenched samples. The increase of viscosity can be described by bimolecular annihilation kinetics of flow defects. The Arrhenius plot of equilibrium viscosity shows a kink at a temperature which seems to be the glass transition temperature. The activation energies of viscous flow below and above that glass transition temperature differ by nearly a factor two. Different microscopic processes responsible for viscous flow in the two regimes of temperature are therefore conceivable. This view is also encouraged by Dynamic-Mechanical-Analysis on relaxed samples, a method to examine the viscoelastic behaviour of glassy materials on different time scales and by recent diffusion measurements on a different system.     

Hansen Solubility Parameters for the Solid Surface of Cellulose Acetate Propionate by Inverse Gas Chromatography

The specific retention volumes, V ⁰ _g , for adsorption of 21 solute probes on the solid surface of cellulose acetate propionate (CAP) were determined in the temperature range 343.15–403.15 K by inverse gas chromatography. In the temperature range studied the retention diagrams drawn between vs. 1/T were found to be linear for all the solutes. Hansen solubility parameters (HSPs) were calculated by relating with the cohesive energy of adsorption of the solutes on the surface of CAP following the Snyder and Karger adsorption model. The three components of HSP decreased linearly with increase of temperature. The HSP of CAP were compared with the corresponding values determined on cellulose acetate butyrate (CAB) and discussed in the light of the chemical nature of the two solid surfaces. Enthalpies of adsorption were found to be more negative for CAP than for CAB.     

Gelation Rheology and Water Absorption Behavior of Semi-Interpenetrating Polymer Networks of Polyacrylamide and Carboxymethyl Cellulose

Gelation rheology and swelling behavior of novel semi-interpenetrating polymer network (semi-IPN) hydrogels based on polyacrylamide are described. These hydrogels were prepared by solution cross-linking of partially hydrolyzed polyacrylamide and carboxymethyl cellulose (CMC), using chromium triacetate. Effects of CMC content on the gelation process and swelling behavior in tap water and different electrolyte solutions were investigated. Study of the gelation behavior using dynamic rheometery showed that the limiting storage modulus of the semi-IPN gels increased with increasing CMC content. Enhancement of storage modulus was more than two times for the semi-IPN gels containing 50 wt% CMC. It was also found that increasing the CMC content decreased the loss factor, indicating that the elastic properties of this gelling system increase more strongly than the viscous properties. The swelling ratio of the semi-IPN gels in tap water, NaCl and CaCl₂ solutions, and synthetic oil reservoir water slightly decreased as the concentration of the CMC increased. The improved storage modulus and slightly decreased swelling capacity in oil reservoir water make these semi-IPN hydrogels potentially good candidates for excess water treatment in oil recovery applications.     

Rheological Characterization of Poly(3,3′-Diaminodiphenylsulfone Terephthaloylchloride) Solutions in Dimethylsulfoxide

Steadyshear and oscillatory shear rheological measurements were performed to characterize the solution rheological behavior of poly(3,3′-diaminodiphenylsulfone terephthaloylchloride) (P(3,3′-DDS-TPC)) in dimethyl sulfoxide (DMSO). The effects of temperature, concentration, and weight-average molar mass () on the rheological properties were investigated. From the temperature dependence of zero-shear viscosity, the flow activation energies, E_η, of P(3,3′-DDS-TPC)/DMSO solutions were calculated. Both the overlap concentration, C*, and the entanglement concentration, C_e, were determined from the concentration dependence of the specific viscosity η_sp. All the P(3,3′-DDS-TPC) solutions, we studied, can be separated into three regimes: the dilute, semidilute-unentangled, and entangled regime with slopes of 1, 1.3, and 3.9, of concentration versus η_sp plots, respectively, which are consistent with scaling predictions for flexible polymers in a good solvent.     

Structural relaxation and viscous flow in amorphous ZrAlCu

The ternary metallic glass Zr₆₅Al_7.5Cu_27.5 offers a wide temperature range between glass transition temperature and crystallization temperature and is therefore well suited for investigation of the glass transition and the state of the super cooled liquid. The non-linear viscosity change caused by structural relaxation has been measured caused by structural relaxation has been measured using tensile creep experiments on as quenched samples. The increase of viscosity can be described by bimolecular annihilation kinetics of flow defects. The Arrhenius plot of equilibrium viscosity shows a kink at a temperature which seems to be the glass transition temperature. The activation energies of viscous flow below and above that glass transition temperature differ by nearly a factor two. Different microscopic processes responsible for viscous flow in the two regimes of temperature are therefore conceivable. This view is also encouraged by Dynamic-Mechanical-Analysis on relaxed samples, a method to examine the viscoelastic behaviour of glassy materials on different time scales and by recent diffusion measurements on a different system.     

Corresponding states principle for newtonian viscosities-temperature effects

In the first part of the paper a superposition method for the polymer solution zero shear rate viscosity η_o as a function of concentration c is reviewed. The method was successful in numerous systems, but it partially failed in four, the worst case being polyisobutene in isooctane, where data were available over the full concentration range and molecular weights (MW) ranged from 900 to 2.5 × 10⁶. It was postulated that the possible cause for this is either MW dependence of T_g which would result in a faster than expected increase in η_o for higher MW samples, or a difference in flow mechanism between the solutions at low and high concentration. In the second part, a new theory for the temperature effect on η_o is proposed. The theory permits linearization of η_o (T) results both for small molecules and for polymeric liquids. In systems where a transition occurs, the linearized plot shows a sharp break. The theory was extended to the concentration dependence of the polymer solution viscosity.

It permits linearization of η_o (c) data, compensates for the MW dependence of T_g, and allows detection of transition points. The theory was tested on solutions of polyisobutene and polydimethyl-siloxane. In both cases, the data were superimposed on a single master curve.     

Track etching parameters for plastics

Abstract

A series of experiments was performed to study the effect of types of etchant, concentration of etchant, etchant temperature and other parameters on track development in cellulose nitrate, polycarbonate resin, cellulose triacetate, and cellulose acetate butyrate plastic. This work has led to a set of preferred etching conditions for each of these plastics. For example, although there were only slight differences in general etching rate when LiOH, KOH, and NaOH were used as track etchants for cellulose nitrate, the alpha particle registration sensitivity was greatest when NaOH was used. Also in cellulose nitrate the general etching rate and the particle registration sensitivity did not change significantly with increasing concentration for hydroxide solutions > 6 N. This was in marked contrast to other plastics which showed a strong concentration dependence.     

Environmental neutron measurements with solid state track recorders

Abstract

The suitability of using ¹⁰B and ⁵LiF in contact with cellulose acetate butyrate (CAB) for the measurement of slow neutron densities has been investigated. The upper energy threshold of clear Diacel cellulose nitrate (CN) and of the CAB have also been measured. The CAB in good contact with thick ¹⁰B or ⁵LiF sources offers good promise for the detection of slow neutrons. For the actual CAB samples used, the CAB-¹⁰B combination had an efficiency of ～1.3 × 10^?2 tracks per thermal neutron incident in a 2π solid angle. The corresponding number for the CAB⁶-Li combination is ～5.6 × 10^?3 tracks per thermal neutron.     

Nanocellulose enhanced interfaces in truly green unidirectional fibre reinforced composites

One of the main problems in fabricating natural fibre reinforced polymers is the poor adhesion between intrinsically polar plant fibres and non-polar polymer matrices. We have developed a truly green technique of modifying natural fibre (hemp and sisal) surfaces to improve the interaction between the fibres and polymers by attaching nano-scale bacterial cellulose to the fibre surfaces. These modified natural fibres were then incorporated into the renewable polymers cellulose acetate butyrate (CAB) and poly-L-lactic acid (PLLA). Unidirectional natural fibre reinforced composites were manufactured to investigate the impact of the surface modification on the fibre and interface dominated composite properties. Both the tensile strength parallel as well as perpendicular to the fibres of the composites reinforced by bacterial cellulose modified natural fibres were found to increase significantly, especially in the case of a PLLA matrix. In case of modified sisal reinforced PLLA the parallel strength increases by 44% and the off-axis composite strength by 68%. Scanning electron microscopy observations of the composite fracture surfaces confirm the improved interaction between the fibre and the polymer matrix.     

Influence of the Substitution Degree on the Dilute Solution Properties of Cellulose Acetate

Modification of intrinsic viscosity, coil size, and preferential adsorption coefficients of cellulose acetate with various substitution degrees in single and mixed solvents was investigated at different temperatures. Miscibility is attained by specific competitive interactions between the solvent-solvent and solvent-polymer systems, which induce modification in the composition of solvent mixtures both inside and outside the polymer coil. The conformational properties in solutions were correlated with the preferential adsorption coefficients, known as depending on the interaction parameters of the polymer/solvent/solvent systems. The intermolecular interactions observed in the cellulose acetate solutions assure the main properties necessary for obtaining membranes with different applications.     

Viscosity and activation parameters of viscous flow of sodium cholate aqueous solution

Viscosity, density and electrical conductance of sodium cholate aqueous solution in dilute concentrations are reported. Concentration and temperature effects on the viscosity are discussed. Molar conductance of the salt at infinite dilution is obtained by fitting experimental conductivity in Quint–Viallard equation. Viscosity data is analyzed by Jones–Dole equation, and viscous B-coefficient and activation parameters are evaluated, which shows a strong effect of sodium cholate aggregation on viscosity flow. Our result shows that salt diffusion is characterized by molecular aggregation, and is enhanced progressively as the concentration of bile salt monomer increases.