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.     

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.     

Cellulose-based fibers from liquid crystalline solutions. III. Processing and morphology of cellulose and cellulose hexanoate esters

Cellulose and a cellulose hexanoate ester (DS 0.69) exhibited liquid crystalline behavior in dimethylacetamide/lithium chloride and dimethylacetamide, respectively. The experimentally observed critical volume fraction (V^c_p) of cellulose was lower than that predicted by Flory's theory, whereas the experimental and theoretical values of V^c_p were within 70% of prediction for cellulose hexanoate. The V^c_p value obtained for cellulose hexanoate was lower than that previously reported for cellulose acetate butyrate with a maximum degree of butyration (CAB-3). This indicates that bulky substituents may lower V^c_p values. Fibers were spun from isotropic and anisotropic solutions of cellulose and cellulose hexanoate by a dry jet/wet spinning method. There was an increase in mechanical properties through the isotropic to anisotropic transition with moduli reaching 152 g/d (20.8 GPa) for cellulose fibers. The formation of cellulose fibers with high modulus at large extrusion rates and large takeup speeds (draw ratio) is explained with molecular organization prior to coagulation. This unexpected enhancement is attributed to the air gap that exists in the dry jet/wet spinning process. Similar improvements were not observed for cellulose hexanoate fibers. This is explained with incomplete development of liquid crystalline structure at the solution concentrations from which the fibers were spun. © 1993 John Wiley & Sons, Inc.     

New method for determining the optical rotatory dispersion of hydroxypropyl cellulose polymer solutions in water

The proposed method employs the recorded channeled spectrum of an optical active medium (crystal or liquid solution) placed between two crossed polarizers. The method of channeled spectrum, previously validated for quartz samples, is used to determine the optical rotatory dispersion of hydroxypropyl cellulose solutions (HPC) in water. Both the specific rotation and dispersion parameter depend on the wavelengths of the maxima and minima from the channeled spectrum and on the thickness of the optical active sample. The circular birefringence and its dispersion determined for HPC solutions in water of concentrations 30% and 45% were estimated with a precision of about 0.5%. The rotatory birefringence of HPC in water at 45% is (119.75–57.60)10^?6 and the specific rotation determined in the visible range for these solutions has values between 4782 and 1402 degrees/dm, in agreement with the literature. The specific rotation (angle) of HPC solutions is independent of the polymer concentration and represents a dispersive parameter which decreases with the light wavelength. POLYM. ENG. SCI., 55:1077–1081, 2015. © 2014 Society of Plastics Engineers     

Synthesis and characterization of novel liquid crystalline cholesteryl-modified hydroxypropyl cellulose derivatives

Two new series of cholesteryl-modified hydroxypropyl cellulose (HPC) derivatives were synthesized by performing reactions involving HPC, a cholesterol-based mesogenic dimer (HPC-G1-Chol), or cholesteryl chloroformate (HPC-Chol), all with different degrees of substitution (D _Chol). All of the compounds obtained were characterized by conventional spectroscopic methods. The D _Chol values of the modified HPCs was obtained using ¹H NMR spectroscopy. Thermogravimetric analysis and differential scanning calorimetry (DSC) in combination with polarizing optical microscopy (POM) were used to investigate the thermal properties of the compounds obtained. The glass transitions of the modified HPCs occurred at lower temperatures than the glass transition temperature for HPC, but the glass transition temperatures increased with increasing D _Chol. All of the synthesized polymers formed thermotropic liquid crystalline phases. Polymers with a mesogenic side chain (i.e., the HPC-G1-Chol series) had wider mesophases than HPC and polymers that were derived from HPC-Chol. These compounds were found to be soluble in a variety of organic solvents, so they formed lyotropic liquid crystal mesophases in acetone. The critical concentrations above which liquid crystalline order was observed were 20 and 25 wt% for a sample from each series (HPC-G1-Chol and HPC-Chol, respectively) in acetone. It can therefore be hypothesized that HPC-G1-Chol has a greater propensity to exhibit specific chain–chain association phenomena than HPC-Chol in acetone.     

Novel cellulose derivatives. I. Liquid crystal phase formation in tri-O-α-naphthylmethyl cellulose solutions

Tri-O-α-naphthylmethyl cellulose was prepared by homogeneous phase reaction using SO₂–diethylamine (DEA)–dimethyl sulfoxide (DMSO) as the solvent system. Observations made by dynamic mechanical spectrometry and by cross-polarized optical microscopy revealed liquid crystalline behavior for the concentrated solutions of tri-O-α-naphthylmethyl cellulose in dimethylacetamide (DMAc). Experimental and calculated (predicted) critical volume fraction of the derivative, V^c_p, did not show agreement. It is determined that V^c_p is affected by bulky substituents on the cellulose backbone to some extent. © 1993 John Wiley & Sons, Inc.     

Gas transport phenomena in hydroxypropyl cellulose solid film retaining cholesteric liquid crystalline order

Two kinds of hydroxypropyl cellulose (HPC) films were prepared: one retained cholesteric liquid crystalline order (HPC-A), and another was amorphous (HPC-B). Gas transport phenomena in the HPC-A films were determined at 20°C, which is below the T_g of HPC, compared with those in the HPC-B films, by using mainly oxygen and nitrogen gases; herium and carbon dioxide gases were also used. The permeability coefficient P for the HPC-A films was smaller than that for the HPC-B films by approximately 10 times. The gas permselectivity, defined as the ratio of P for each gas, was affected by the liquid crystalline order, as follows: The permselectivity for the HPC-A films was greater than that of the HPC-B films. The trends of gas permeability and permselectivity for the liquid crystal-forming HPC films were the same as those reported for other liquid crystal-forming cellulosic films. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 70: 1465–1470, 1998     

Recoverable shear strain of liquid crystal‐forming concentrated hydroxypropyl cellulose solutions

The recoverable shear strain (S_R) for the liquid crystal‐forming hydroxypropyl cellulose solutions was determined by means of a concentric cylinder rotational apparatus as functions of shear stress prior to recovery and concentration of the solutions at 30°C. S_R greatly depended on shear stress and concentration; the phase of the solution (the single phase or biphase) governed the dependences of S_R on stress and concentration. S_R increased with increasing stress for the single phase and decreased for the biphase. S_R seemed to be related to the die swell (B): S_R ∝ Bⁿ. S_R exhibited a maximum and a minimum with respect to concentration. S_R for the cellulosic cholesteric liquid crystalline solutions was greater than that for the isotropic solutions. A model was proposed for explaining the greater S_R. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 865–872, 2002     

Static tensile and dynamic mechanical properties of hydroxypropylcellulose films prepared under various conditions

The films of hydroxypropyl cellulose (HPC), which is a lyotropic and thermotropic liquid crystal, were cast under various conditions of temperature and concentration. The effects of the casting conditions on the static tensile and dynamic mechanical properties of the cast films were determined, and the results were compared with those of films prepared by means of hot compression. The tensile properties of the films prepared by both processes (cast and hot compression) were unsatisfactory in comparison with other liquid crystalline polymers, and this was partly due to water absorbed during the test. In dynamic properties, two distinct transitions were detected. The higher one, around 110°C, was associated with the rotation of an unhydroglucose ring and the lower one, around 25°C, was associated with the T_g. There were no marked differences in the properties between cast films and hot-compressed films, except the disappearance of the T_g for hot-compressed film prepared at a relatively higher temperature. The basis for defining the liquid crystalline structure in cast and hot-compressed films are not directly given in this preliminary paper. However, judging from the dynamic mechanical properties and refractive index data for films prepared by both processes, it appears that dimethylacetamide-cast films and films compressed at 180 and 200°C may have some structures related to liquid crystalline phase and that inter- and intramolecular hydrogen bonding play an important role in lyotropic and thermotropic liquid crystalline behavior for HPC.     

Characterization and free radical polymerization of liquid crystalline acrylic acid/cellulose diacetate and N-vinyl-2-pyrrolidinone/cellulose diacetate solutions

Polymerizations of liquid crystalline solutions of cellulose diacetate (CDA) in acrylic acid (AA) and N-vinyl-2-pyrrolidinone (NVP) were conducted in an attempt to prepare molecular composites (polymer blends) processing a rigid rod polymer with liquid crystalline orientation. CDA was found to form liquid crystalline solutions in both AA and NVP at concentrations avove 40 wt% CDA. Polymerization of anisotropic 50 wt% CDA-AA and CDA-NVP solutions occurred with considerable retention of the starting solution anisotropy and yielded homogeneous blends (1 T_g) when the rate of polymerization was fast relative to the phase separation of the free radically polymerizing AA or NVP with CDA. Slow polymerizations lead to phase separated blends (2 T_g).     

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     

Blending as a method of tuning reflection wavelength and helical twisting sense in films and composites of liquid crystalline cellulose derivatives

Ethyl cellulose (EC) with a degree of substitution of 2.41 and a fully acetylated sample (AEC) of this material, form lyotropic liquid crystalline solutions in chloroform and acrylic acid. Above 35 wt% polymer, the solutions exhibit chiral nematic phases that reflect light selectively at a specific wavelength λ₀. For EC solutions the helical twist sense of the chiral nematic phase is left handed, whereas the AEC solutions are right handed.The λ₀ and handedness of the system can be tuned to a given set of values by preparing solutions of EC and AEC in different blend ratios. These can be converted to films or composites, that retain the chiral nematic structure and the corresponding chiro-optical properties, by either casting from chloroform or photopolymerising the (EC+AEC)/acrylic acid solutions to form blend composites of EC/AEC in poly(acrylic acid).The most effective way to control the chiro-optical properties of the dry films was to use the photopolymerisation technique to form composite films of the blends. Such films can be used either as coatings to reflect visible light of a particular colour, or act as a protective layer to reduce UV degradation.     

Photoinitiated crosslinking of hydroxypropyl cellulose in the isotropic and liquid crystal states

The influence of temperature, concentration, and shear rate on the formation of liquid crystal solutions of hydroxypropyl cellulose (HPC) in DMAc and the preservation of the structure by photoinitiated crosslinking were investigated. The rate of changes in the relaxation pattern for the characteristic band texture of HPC liquid crystals after cessation of shear is inversely proportional to the extent of the crosslinking. This shows that the liquid crystalline structure is preserved upon crosslinking. The molecular orientation of the crosslinked films as a function of mesophase organization and concentration during crosslinking was studied.     

A simple approach to the dielectric relaxation behaviour of a liquid crystalline polymer and its application to the determination of the director order parameter for partially aligned materials

A theory for the dielectric relaxation behaviour of a partially aligned liquid crystalline (LC) material is described. It is shown, quite generally, that the complex dielectric permittivity may be expressed in terms of the parallel (?_‖) and perpendicular (?_?) components for the permittivity of the mesophase and S_d, the director order parameter, where ?_‖ and ?_? may themselves be expressed in terms of molecular quantities, including S the mesophase order parameter. The theory is applied to experimental data for a nematic siloxane LC side-chain polymer. The consistency of the derived values of S_d provides experimental confirmation of our approach. In addition, dielectric isosbestic points are observed in both loss factor and capacitance data as the sample alignment is varied, providing further confirmation of our approach. The variation of S_d with time for a sample being realigned from planar to homeotropic in an electric field is determined from dielectric measurements and the form of S_d(t) is briefly discussed.     

Thermotropic liquid crystallinity,thermal decomposition behavior,and aggregated structure of poly(propylene carbonate)/ethyl cellulose blends

Maleic anhydride end capped poly(propylene carbonate) (PPC‐MA) was blended with ethyl cellulose (EC) by casting from dichloromethane solutions. The thermotropic liquid crystallinity, thermal decomposition behavior, and aggregated structure were investigated by differential scanning calorimetry (DSC), thermogravimetry (TGA), and wide angle X‐ray diffraction (WAXD). DSC exhibits thermotropic liquid crystallinity in the rich EC composition range. TGA shows that thermal decomposition temperatures were elevated upon interfusing EC into PPC‐MA. WAXD corroborates that EC and PPC‐MA/EC blend films cast from dilute dichloromethane solution possessed cholesteric liquid crystalline structure in the rich EC composition range, and that dilution of PPC‐MA with EC increased the dimension of noncrystalline region, leading to a more ordered packed structure. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 584–592, 2006     

Zero-shear viscosity of dilute to moderately concentrated solutions of cellulose acetate phthalate

The zero-shear viscosities of dilute to moderately concentrated cellulose acetate phthalate solutions in DMF were measured at different temperatures and the viscosity data were analyzed in terms of Martin's and Fedor's relationships. The [η] values obtained due to the relationships of Martin and Fedor were found to be in very good agreement. The viscosity-concentration data were also generalized in terms of reduced variables. The temperature dependence of viscosities was expressed by the Frenkel-Eiring equation and the free energy of activation (ΔG_v), heat of activation (ΔH_v), and entropy of activation (ΔS_v) of the viscous flow of polymer solutions were calculated. It has been observed that the activation energy for viscous flow increases and the activation entropy decreases with concentration of polymer solutions.     

Air Separation Properties and Stabilities of Blend Membranes of Liquid Crystals with Ethyl Cellulose

Abstract

Air separation properties and stabilities of four blend membranes, 1–30-μ.m thick, prepared from ethyl cellulose (EC) with a small amount of nematic and cholesteric liquid crystals, such as p-heptyl-p'-cyanobiphenyl (7CB), p-pentylphenol-p'-methoxybenzoate (5PMB), benzoate-containing liquid crystal mixture (DYC), and cholesteryl oleyl carbonate (COC), were investigated by the variable volume method. To provide more significant information guiding membrane-based air separation, air was directly used as the test gas. The membranes showed both higher oxygen permeability, P _O2 , and oxygen over nitrogen separation factor, P _O2 /P _N2 , in the temperature range of the liquid crystalline phase. Oxygen-enriched air (OEA) flux, Q _OEA, and oxygen concentration. Y _O2 increased simultaneously with increasing transmembrane pressure difference. Stability studies revealed that the efficiencies of concentrating oxygen using 1–7-μm thick DYC/EC (9/91) membranes laminated to porous polyethersulfone membranes were almost constant for a 120–510-hour operating time. The membrane possessed a Q _OEA of 9.0 × 10^?4 cm³(STP)/s.cm² and Y_O2 of 40% at 30°C and 0.41 MPa for a single-stage process. The results suggest that the membranes could be used effectively in enriching oxygen from air.     

纤维素化学的现状与发展趋势

本文综述了纤维素化学的研究现状和发展趋势，包括近10年来纤维素结构、纤维素衍生物如纤维素磷酸酯、纤维素醋酸酯、纤维素硝酸酯、羧甲基纤维素、羟丙基纤维素和乙基纤维素等，以及纤维素的裂解与能源、纤维素液晶及其复合材料、新型纤维素衍生物及其功能材料的合成、生物技术在纤维素化学中的应用等主要研究领域。探讨了未来20年的研究课题：（1）纤维素制品的高质和高值化；（2）食用纤维素及纤维素保健食品；（3）新型纤维素功能材料的制备及应用；（4）生物技术应用的工业化。     

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     

Morphological and structural-rheological relationship in epiclon-based polyimide/hydroxypropylcellulose blend systems

Blends of hydroxypropyl cellulose (HPC) in lyotropic phase have been prepared with a new epiclon- based poly(amic acid) (PAA) or its corresponding polyimide (PI). The flow behaviour of their mixed solutions in N,N-dimethylacetamide (DMAc) was investigated by means of shear viscometry and oscillatory shear tests. The effect of composition, temperature and shear rate on the rheological functions reflects the orientation or mobility of the chain segments in the shear field. Specific interactions, such as the hydrogen bonds between PAA and the liquid crystalline component, stabilized the resulted morphology. The band texture, typical for lyotropic HPC solutions, evidencing different intensities and dimensions is observed from atomic force microscopy images in PAA/HPC and PI/HPC blends. The paper pursues some aspects concerning the obtaining of mixed alignment layers used in display devices.