Rheological properties of liquid crystalline solutions of ethyl celluloses with different molecular weight in m-cresol

Steady-state shear rheological properties of liquid crystalline solutions of four ethyl celluloses (ECs) were determined at a low shear rate (1 s^?1) and at relatively high shear rates by using two rheometers (cone-plate and capillary types), and were compared with those of liquid crystalline hydroxypropyl cellulose (HPC). The effect of molecular weight (MW) on the viscoelastic behavior was also determined. The viscoelastic behavior was also determined. The viscometric behavior of EC solutions was similar to that of HPC solutions: (1) with respect to temperature, the shear viscosity (η) at shear rate of 1 s^?1 exhibited a minimum (η_min) and a maximum (η_max), and the concentration–temperature superposition for η could be applied; (2) the behavior of η at relatively high shear rates as a function of shear rate or polymer concentration was typical of lyotropic liquid crystals. The MW dependence of η_min was greater than that of η_max for EC solutions. The behavior of the elastic parameters such as Bagley correction factor (v), entrance pressure drop (ΔP_ent), and die swell (B) at relatively high shear rates for EC solutions was essentially similar to that for HPC solutions: (1) the shear rate or stress dependence of the elastic parameters was greatly dependent on whether the polymer solution was in a single phase or biphase; (2) with respect to concentration the elastic parameters showed a maximum and a minimum and the maximum or minimum point for each parameter was not always identical to each other. η for the isotropic or fully anisotropic solutions at a given concentration (C) increased, whereas η for the solutions in the vicinity of the biphasic region showed a minimum, with respect to MW. The slope of η at a given shear rate vs. CM _w depended on shear rate, and this slope for the isotropic solutions appeared to be greater than that for fully anisotropic solutions. ΔP_ent and v at a given concentration showed either a monotonical increase or a maximum or minimum with MW, and this behavior was not fully consistent with that of η. B for the isotropic solutions increased and B's for both biphasic and fully anisotropic solutions were almost constant, with MW.     

Altering the viscosity of cationically modified cellulose polymers by the addition of salt

The concentration dependence of viscosity is examined for four cationically modified cellulose polymers (UCARE? JR400, UCARE? JR30M, UCARE? LR400, and UCARE? LR30M) in both salt‐free and 50 mM NaCl solution. Similarities in the four polymer systems include: Newtonian viscosity in the dilute regime, shear thinning at higher concentrations, four concentration regimes in salt‐free solution, and three concentration regimes in salt solution. The zero shear rate viscosity and the degree of shear thinning increase with increasing polymer concentration in both salt and salt‐free solutions. While the addition of salt to the lower molecular weight polymers JR400 and LR400 resulted in small changes in viscosity across all concentrations, JR30M and LR30M exhibited significant decreases (up to 81%) and increases (up to 57%) in viscosity upon the addition of salt in the semidilute and entangled regimes, respectively. This viscosity increase in the entangled regime (when comparing salt‐free and 50 mM NaCl solutions) is reported for the first time in cationically modified cellulose polymers. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41616.     

Determination of the order parameter in cholesteric liquid crystalline phase cellulose derivatives solutions by refractometry

The macroscopic order parameter S in the cholesteric liquid crystalline phase of hydroxypropyl cellulose (HPC) and ethyl cellulose (EC) solutions was calculated using refractive index data. Haller's extrapolation approach was used. The S calculated was compared with the S predicted from Doi's theory. The calculated values of S for HPC and EC solutions were in the range of 0.4–0.8 within our experimental range, and agreed with the predicted values of S obtained with Doi's theory. This result suggests that Haller's approach is valid for determining S for liquid crystalline solutions of HPC and EC, despite the scattering of the data at higher temperatures.     

Miscibility studies of hydroxypropyl cellulose/poly(vinyl pyrrolidone) in dilute solutions and solid state

The miscibility of hydroxypropyl cellulose (HPC) and poly(vinyl pyrrolidone) (PVP) blends in aqueous solutions was studied using viscosity, ultrasonic velocity, and refractive index techniques at 30°C. The interaction parameters ΔB, μ, and α calculated from viscosity using Sun and Chee methods indicated the miscibility of this blend. This was further confirmed by ultrasonic and refractive index results. The HPC/PVP blend films are prepared by solution casting method and are analyzed by differential scanning calorimetry, X-ray diffraction, Fourier transform infrared spectroscopy, and scanning electron microscopic techniques that confirmed the complete miscibility. This miscibility is due to the strong intermolecular H-bonding interactions between  OH groups of HPC and CO groups of PVP. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Rheological properties and microstructures of cellulose acetate phthalate/hydroxypropyl cellulose blends

Cellulose acetate phthalate (CAP)/hydroxypropyl cellulose (HPC) blends were investigated by means of attenuated total reflection‐Fourier transform infrared spectroscopy, thermogravimetry/differential thermal analysis, shear viscosity, oscillatory shear tests, and atomic force microscopy (AFM). Effect of solution concentrations in 2‐methoxyethanol, blend compositions, and shear rate on the rheological functions reflects the mobility of the chain segments or their orientation—with thinning behavior in the shear field. Specific interactions, such as the hydrogen bonds between polymer components and 2‐methoxyethanol used in casting solutions of films, influence the resulting morphology. Supernodular aggregates with different intensities and dimensions, which involve the coexistence of an isotropic and an anisotropic phase, typical for lyotropic cellulosic derivative liquid crystals at low concentrations, are evidenced by AFM images. This study is useful for applications of CAP/HPC blends in pharmaceutical domains.POLYM. COMPOS., 33:2072–2083, 2012. © 2012 Society of Plastics Engineers     

VIscometric behaviour of Kevlar fibre filled liquid crystalline solutions of ethyl cellulose in m-cresol

Liquid crystalline solutions of ethyl cellulose in m-cresol were mixed with Kevlar® fibres, and the viscometric behaviour with respect to temperature of those filled systems was determined with a cone-plate type viscometer. The viscosity of the systems exhibited a maximum and a minimum at temperatures denoted by T_max and T_min' respectively. The effects of fibre on the critical temperatures (T_max and T_min) and critical concentrations (C_a and C_b) and on the viscosity enhancement are discussed. T_max and T_min decreased with fibre concentration for single-phase anisotropic solutions, whereas they increased for the biphasic solution. The critical concentrations increased with fibre concentration and C_b was more sensitive to the fibre than C_a. The viscosity enhancement due to the fibre depended on the phase of solution. In the single-phase (isotropic and anisotropic), the viscosity enhanced with fibre; however, in the biphasic solution, the effect was not simple. The viscosity enhancement for the single-phase anisotropic solutions with fibre was lower than that for the isotropic solutions.     

Viscosities of molten polymer blends

Pairs of four thermoplastic resins, polystyrene, poly(methyl methacrylate), acetal homopolymer, and nylon-12, were intensively melt-blended in nine proportions from 0 to 100 percent. Capillary rheometry at 210°C was done on each blend; melt densities were also measured on most of them. The dependence of shear stress on Rabinowitsch-corrected shear rate was accurately represented, for all the blends, by a simple empirical model. The dependence of viscosity, at particular shear rates between 5 and 1000 s^?1, on blend composition was examined and we fitted two viscosity-composition models to all the systems by least-squares procedures. The character of the dependence of blend viscosity on composition varied widely for the five binary systems studied, two being monotonic over the whole range of shear rate, two exhibiting clear minima and one displaying mixed behavior, with both a minimum and maximum viscosity seen at shear rates near 250 s^?1. The McAl lister three-body model satisfactorily describes the viscositycomposition dependence in all five systems. A simpler blend rule was useful only in the monotonic systems, and even there it was inferior to the McAllister model.     

Rheological properties of cellulose/chitin xanthate blend solutions and properties of the prepared fibers

The focus of this article is the rheological properties of cellulose xanthate, chitin xanthate, and their blend solutions with cellulose/chitin blend weight ratios of 9.5 : 0.5, 9 : 1, 8 : 2, and 5 : 5 (mostly 9 : 1 blend solutions). The preparation and properties of fibers from 9 : 1 blend solutions and cellulose xanthate solutions are also discussed. The non‐Newtonian index of the investigated solutions was found to vary in the following order: chitin < cellulose < 9.5 : 0.5 blend < 9 : 1 blend < 8 : 2 blend < 5 : 5 blend. Showing a tendency contrary to that of the non‐Newtonian index, the structure viscosity index varies in the following order: chitin > cellulose > 9.5 : 0.5 blend > 9 : 1 blend > 8 : 2 blend > 5 : 5 blend. For 5–9 wt % 9 : 1 blend solutions, increasing the solution temperature aids the improvement of the fluidity of 9 : 1 blend solutions in the temperature range of 10–40°C. The zero shear viscosity decreases in an index manner with the solution temperature increasing. The 7–8 wt % 9 : 1 blend solutions have good filtering and rheological properties and are ideal for spinning fibers. The mechanical properties of blend fibers spun from 7% 9 : 1 blend solutions are lower than those of pure cellulose and are much higher than those of Crabyon fiber, and they still reach the national criteria and fit the need for further processing. This proves that the viscose method which we have developed here is an efficient way of preparing cellulose/chitin blend fibers with satisfactory mechanical properties and processing properties. Scanning electron microscopy photographs show that the surface of 9 : 1 blend fibers is coarser than that of pure cellulose fibers. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Structure‐property relationships of blends of polycarbonate

Three grades of bisphenol‐A polycarbonate—high molecular weight linear, high molecular weight branched and low molecular weight linear—and their blends have been studied by GPC, DMTA, DSC, rheometry and impact measurements. The molecular weight distribution of the blends agred with that predicted from the component's distributions, indicating that no transesterification reactions had occurred during melt blending. The T_g of the blends varied with blend composition according to the Fox equation and was related to the reciprocal molecular weight predicted by the Flory‐Fox equation. The low shear rate viscosity of the blends agreed with a logarithmic rule of mixtures and showed power‐law dependence on the weight average molecular weight. At higher shear rates, shear thinning was observed. The steady shear viscosity correlated well with the dynamic viscosity, as suggested by the Cox‐Merz relation. The stress relaxation behavior of the melt was very sensitive to the blend composition and molecular weight and correlated well with the real modulus. Temperature studies of the dart impact energy showed that only the low molecular weight polymer underwent a brittle‐duetile transition at ea ?30°C and that all the blends were tough at room temperature. The enhanced stress triaxiality inherent in the notched lzod test caused the impact strenght at room temperature to decrease almost linealy with blend composition.     

Flow birefringence and viscosity of cellulose solutions in semi-dilute regime

An attempt was made to study the flow birefringence and the viscosity of the systems of cellulose in aqueous sodium hydroxide and cadoxen solutions. For this purpose alkali-soluble cellulose samples with crystal form I (simply denoted as cellulose I sample), prepared from conifer wood pulp by the steam-explosion method, and alkali-soluble cellulose samples with crystal form of cellulose II (cellulose II sample), regenerated from cuprammonium cellulose solution under specific conditions, were used. The extinction angle χ of aqueous alkali solutions of the cellulose I sample is significantly less shear rate (γ) dependent as compared with that of the cellulose II sample. In the latter system the χ versus γ relations for a given cellulose sample shifted to the higher γ side with decrease in the average molecular weight. The viscosity of the cellulose II sample in aqueous sodium hydroxide solutions is approximately twice that of the cellulose I sample in the same solvent if compared at the same molecular weight, same concentration, and same temperature. The latter solution showed a non-Newtonian property at relatively smaller γ than the former solution did. Spin-lattice relaxation time T₁ (by ¹³C-NMR) of cellulose in cadoxen solution was smaller in cellulose I, suggesting the existence of intra- and intermolecular hydrogen bondings at the C₆ position of cellulose molecules in cellulose I solution. A dynamic light scattering study on cellulose in cadoxen showed that in a 5 wt % solution of cellulose I cellulose particles are dispersed with time into smaller particles and the larger particles could be excluded by ultracentrifuge and in cellulose II solutions the cellulose particles had almost the same size during storage. The above findings indicate that in 5 wt% cellulose I solutions in aqueous alkali or in cadoxen, cellulose I is not dissolved molecularly, but a supra-molecular structure of the solid is at least partly reserved in the above solutions.     

Shear rheology of diluted solutions of high molecular weight cellulose

A steady-state and dynamical rheological study was performed with dilute solutions (1–4%) of high molecular weight cellulose (M_w = 350,000). The solutions are strongly viscoelastic. The steady-state viscosity and the first normal stress difference have a power law dependence on the shear rate. The power law indices have the same dependence on temperature and concentration. These results as well as the correlation between the steady-state viscosity and the real part of the complex viscosity are in good agreement with the Spriggs model. The 4% concentrated solution shows the beginning of a rubber-like storage modulus plateau, suggesting the existence of an entanglement network.     

Effects of trans‐polyoctylene rubber on rheological and green tensile properties of natural rubber/acrylonitrile–butadiene rubber blends

The influence of trans‐polyoctylene rubber (TOR) on the flow property, die swell behaviour and green tensile property of NR (natural rubber)/NBR (acrylonitrile–butadiene rubber) blend compound was investigated as a function of TOR loading level. The pure TOR, NR and NBR compounds were also investigated for comparison with the blend compounds. The shear viscosity of TOR strongly depended on the temperature as well as shear rate. The viscosity of the NR/NBR blend compound was even lower than that of the constituent components at relatively lower shear rates, and the viscosity difference became smaller as the shear rate was increased. The viscosity of the NR/NBR blend compounds was strongly affected by the addition of TOR but the effect became negligible with increasing the shear rate. Both the die‐swell ratio and the surface topology of extrudates were also affected by TOR addition; the dependence on shear rate was much stronger for higher TOR level. The NR/NBR blend compound showed much higher green tensile strength and elongation at break than those of the constituent components. Both the green tensile modulus and strength of the NR/NBR blend compound were greatly enhanced, while the elongation at break was reduced with the addition of TOR. © 2002 Society of Chemical Industry     

Rheological characterization of cellulose solutions in N‐methyl morpholine N‐oxide monohydrate

Three different modes of rheological properties were measured on 11 and 13 wt % solutions of cellulose in N‐methyl morpholine N‐oxide (NMMO) monohydrate, in which concentration range lyocell fibers of much reduced fibrillation are preferably produced. The dynamic rheological responses revealed that the Cox–Merz rule did not hold for these cellulose solutions. Both cellulose solutions showed a shear thinning behavior over the shear rate measured at 85, 95, 105, and 115°C. However, 13 wt % solution gave rise to yield behavior at 85ºC. The power law index ranged from 0.36 to 0.58. First normal stress difference (N₁) was increased with lowering temperature and with increasing concentration as expected. Plotting N₁ vs shear stress (τ_ω) gave almost a master curve independent of temperature and concentration, whose slope was about 0.93 for both cellulose solutions over the shear rate range observed (τ_ω > 500 Pa). In addition, the cellulose solutions gave high values of recoverable shear strain (S_R), ranging from 60 to 100. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 216–222, 2002     

Development and relaxation of orientation in sheared concentrated lyotropic solutions of hydroxypropylcellulose in m-cresol

Shear-induced orientation and the relaxation of orientation after the cessation of shear in 45 and 50 wt% solutions of cholesteric hydroxypropylcellulose (HPC) in m-cresol have been studied in situ by infrared spectroscopy and polarised microscopy. The shearing experiments were conducted at 30-80 °C at shear rates of 1-300 s⁻¹, which covered the director tumbling, wagging and a small part of the steady-state shear rate regimes. The steady-state order parameter was proportional to the shear rate and the proportionality constant increased with increasing HPC concentration and decreasing temperature. The concentrated solutions studied showed steady-state alignment even in the tumbling regime. Three different shear-rate regions with different behaviours of the solutions after the cessation of shear were found in these concentrated HPC solutions. At low shear rates (1-5 s⁻¹, referring to the 50% HPC solution) the polymer remained isotropic during shear but became gradually more oriented a few minutes after the cessation of shear, an observation that was substantiated by polarized microscopy. The order parameter reached a final plateau value and stayed constant at this level for long periods of time (∼24 h). At intermediate shear rates (from 5 to 50 s⁻¹ for the 50% HPC solution), a detectable order parameter was recorded at steady shear and, after the cessation of shear, the structure returned to an almost isotropic state within a few minutes, after which the orientation gradually started to increase to approach a plateau value after about 150 min. At even higher shear rates (∼100 s⁻¹ for to the 50% HPC solution), the initial steady shear order parameter relaxed to an almost isotropic state and remained constant at this level for time periods extending up to 24 h.     

Gasoline desulfurization by a TiO2‐filled ethyl cellulose pervaporation membrane

The TiO₂ nanoparticles were incorporated into an ethyl cellulose (EC) matrix to improve the pervaporation (PV) performance of the membrane for gasoline desulfurization. The microstructures of different EC membranes were characterized by scanning electron microscopy, Fourier transform infrared spectroscopy, and X‐ray and transmission electron microscopy. The PV experiments showed that the hybrid membrane of EC/TiO₂ demonstrated an improved permeation flux (J ) of 7.58 kg m^?2 h^?1 and a sulfur enrichment factor (α) of 3.13 in comparison with the pure EC membrane, with a J of 3.73 kg m^?2 h^?1 and an α of 3.69. In addition, the effects of the operating conditions, including the operating temperature, layer thickness, crosslinking time, feed flow rate, and feed sulfur content level, on the PV performance of the EC/TiO₂ membrane were investigated. Under a 100 mL/min feed flow rate and a 85 μg/g sulfur content, J of the 10 μm thick membrane increased to 7.58 kg m^?2 h^?1 with α of 3.13 compared to the pure EC membrane (3.73 kg m^?2 h^?1, 3.69) at 80 °C with 30 min of crosslinking time. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 : 134 , 43409.     

Swelling behavior of crosslinked hydroxypropyl cellulose films retaining cholesteric liquid crystalline order. I. Effect of temperature

Temperature dependence of the swelling behavior in both water and propanol was determined for the crosslinked hydroxypropyl cellulose (HPC) films retaining cholesteric liquid crystalline order (CLCO) and for the crosslinked amorphous HPC films. The dependence of swelling behavior in water for the films retaining CLCO was different from that of the amorphous films. With increasing temperature, the equilibrium swelling ratio (B_e) for the films retaining CLCO decreased, whereas B_e for the amorphous films increased. In propanol, both films exhibited the same temperature dependence. B_e increased with increasing temperature. The increasing rate of the swelling in transient state showed similar temperature dependence on B_e. The increasing rate for the films retaining CLCO decreased with temperature, but that for the amorphous films increased in water; in propanol, the increasing rate for two types of films increased. The difference in the swelling behavior between the two types of films may be due to the difference in the number-average molecular weight between crosslinks. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 1015–1022, 1999     

Studies on cellulose acetate‐carboxylated polysulfone blend ultrafiltration membranes. III

Enhancement of the hydrophilicity in polymeric membrane materials results in membranes with higher flux and better membrane characteristics. Hence, polysulfone was carboxylated and ultrafiltration membranes were prepared from blends of cellulose acetate and carboxylated polysulfones having various degrees of carboxylation with a total polymer concentration of 20 wt % in casting solution and at different blend polymer compositions. The effects of degree of carboxylation on membrane characteristics such as compaction, pure water flux, and membrane hydraulic resistance (R_m) have been investigated. The influence of the polymer concentration in the blend solution on the performance of blend membranes at various blend polymer compositions has also been investigated and compared with that of blend membranes prepared from blends of cellulose acetate and polysulfone or carboxylated polysulfone with a total polymer concentration of 17.5 wt %. Further, the solute rejection performance of the membranes has also been investigated by subjecting the membranes to metal ion permeation studies using polyelectrolyte‐enhanced ultrafiltration. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 976–988, 2005     

Dielectric investigation of isotropic and anisotropic solutions of cellulose acetate in dioxane

The dielectric and optical characteristics of a sample of cellulose acetate (DS = 2.45) in dioxane solutions were studied at 10–50°C of concentration 10–50 wt% to include both isotropic and anisotropic phases. The study showed that the loss maximum, ε_max″, magnitude of polarization, (ε₀ ? ε_∞), static dielectric constant, ε₀, time of relation, (2πf_m)^?1, and refractive index, n_D, steadily increase with concentration up to the critical concentration (41 wt%) and then decrease. The mean-square dipole moment, 〈gμ²〉, decreases steadily up to the critical concentration then remains nearly constant, indicating that the isotropic solution changes to anisotropic, with smaller mean-square dipole moment. Comparison between the results of cellulose acetate (CA) and those of hydroxypropyl cellulose (HPC) reveals that, at the critical concentration in dioxane, the cholesteric structure of HPC possesses a greater mean-square dipole moment with higher temperature coefficient than does CA. The activation energy of the relaxation process for hydroxypropyl cellulose is higher, indicating a greater intrachain interaction compared with cellulose acetate.     

Rheological,mechanical, thermal,and morphological properties of blends poly(butylene adipate-co-terephthalate), thermoplastic starch,and cellulose nanoparticles

The objective of the present study was the preparation and characterization of poly(butylene adipate-co-terephthalate) (PBAT) and thermoplastic starch (TPS) blends reinforced with cellulose nanoparticles (CNCs) by extrusion. The work was conducted in four steps. Initially, the CNCs were prepared from eucalyptus cellulose pulp by acid hydrolysis. The second step was the preparation of the nanocomposite (TPS-CNC), composed of cassava starch, CNC, glycerol, and citric and stearic acids, by double screw extrusion. The third step was the preparation of PBAT/TPS-CNC blends in twin-screw extruders. In the fourth step, the films were produced by flat extrusion. Blends exhibited similar rheological behavior, increasing the CNC concentration in blends increased the viscosity as a function of the shear rate, and altered the behavior of the shear storage (G′) and shear loss (G″) curves as a function of the oscillation frequency (ω). The presence of CNC in blend provided improvements significant in mechanical properties, with 120% increase in Young's modulus, and 46% increase in maximum tensile. Thermal behavior (thermogravimetric analysis and differential scanning calorimetry) was altered with the incorporation of the CNC, showing a single melt peak (T_m) and a slight increase in T_g, indicating good dispersion between the phases of the blends, corroborating with the fracture surface microscopy of films.     

A structure rheological study of cellulose trinitrate in ethyl acetate

A structure rheological analysis was undertaken with cellulose trinitrates dissolved in ethyl acetate. Empirical scaling laws with molecular mass and concentration were found for the zero shear viscosity η_o and the critical shear rate $ \dot \gamma _C $ at the onset of shear thinning. Values for the apparent chain element A' were calculated from the concentration dependent network strand M_e and extrapolated to zero concentration. They were compared with dilute solution data. From the concentration dependence of the mass of network strand M_e a network with hindered penetration was inferred.