Hydroxypropylcellulose In Water Research Articles

Liquid crystalline phase behavior and hydration of hydroxypropyl cellulose in water: A liquid and solid NMR investigation

AbstractHydroxypropyl cellulose (HPC) is a functional material with numerous applications as a drug solubilizer, thickener, and stabilizer. Herein, the mobile and rigid regions of HPC are investigated using liquid‐ and solid‐state NMR, respectively, in the high‐viscosity regime of concentrated aqueous samples, below and above the formation of an ordered chiral liquid‐crystalline (LC) mesophase. Liquid NMR 13C relaxation and hydration studies reveal that hydroxypropyl pendant chains remain more fluid than the pyranose sugar rings at concentrations below the formation of the LC phase. The inner part of the pendant chains close to the cellulose backbone exhibits a higher water structuration and a lower water renewal than the outer part and the pyranoses, which likely compensates for their higher hydrophobicity. When the LC phase is formed, the sample viscosity increases and the differences in flexibility and hydration of the pendant chains are reduced with respect to the pyranoses, while the whole system is rigidified. The system is not completely rigid even at concentrations above the formation of LC, as the interaction of water with the pyranoses considerably enhances their fluidity. In contrast, the pendant chains are much less affected.

Extensional flow of stiff‐chain polymer solutions in the semidilute regime

AbstractStiff‐chain polymers are preponderant in biology as structural components of tissue and living cells. Hence, understanding their solution behavior under different flow histories is fundamental. Here, the extensional flow under capillary breakup of isotropic semidilute solutions of stiff‐chain poly‐n‐butyl isocyanate (PBIC) and hydroxypropyl cellulose (HPC) has been studied. PBIC‐chloroform and HPC‐water were studied as the polymer‐solvent interaction tunes the molecular conformation (Romo‐Uribe, J. Appl. Polym. Sci. 2021, 138, e49712). PBIC in chloroform exhibits a rod‐like conformation, and capillary breakup at constant concentration and temperature initially showed an exponential decay of filament diameter D(t) followed by a sudden decrease of D, and finally slow filament thinning. Increasing the molecular weight by threefold increased the breakup time τb by twofold. HPC in water adopts a semiflexible conformation and the filament thinning also exhibited three stages, however the breakup time was shorter than PBIC. Hence, the extensional viscosity as a function of strain of PBIC and HPC solutions exhibited three regimes, where initial constant extensional viscosity ηE was followed by strain hardening and finally a sudden decrease of extensional viscosity as strain increased. It was found that the filament breakup time τb is a function of the radius of gyration Rg.

Optical activity of transparent polymer layers characterized by spectral means

The method based on the channeled spectrum, validated for inorganic optical active layers, is used now to determine the optical activity of some transparent polymer solutions in different solvents. The circular birefringence, the dispersion parameter and the specific rotation were estimated in the visible range by using the measurements of wavelengths in the channeled spectra of Hydroxypropyl cellulose in water, methanol and acetic acid. The experiments showed the specific rotation dependence on the polymer concentration and also on the solvent nature.The decrease of the specific rotation in the visible range with the increase in wavelength was evidenced. The method has some advantages as the rapidity of the experiments and the large spectral range in which it can be applied. One disadvantage is the fact that the channeled spectrum does not allow to establish the rotation sense of the electric field intensity.

Methacrylic acid-triggered phase transition behavior of thermosensitive hydroxypropylcellulose

Methacrylic acid (MAA)-triggered phase transition of thermosensitive hydroxypropyl cellulose (HPC) was studied. The phase transition temperature of 0.1wt.% HPC aqueous solutions was dramatically reduced from 41°C to 8°C as the MAA concentration increased from 0wt.% to 4wt.%. The sharp decrease of HPC phase transition temperature triggered by MAA may be attributed to strong hydrogen bonding between MAA and HPC. It may be proposed that the hydrogen bonding of MAA with HPC restricts the interaction of water with HPC and so reduces the solubility of HPC in water and improves the hydrophobic association of HPC. Furthermore, MAA attaching on HPC polymer chains was polymerized to form surfactant-free PMAA nanogels around ambient temperature when HPC collapsed forming PMAA nanogels. Effect of MAA concentration and polymerization temperature on the size and size distribution of PMAA nanogels was investigated.

Thermodynamics of liquid-crystalline solutions of hydroxypropyl cellulose in water and ethanol

Phase diagrams were constructed and comprehensive thermodynamic analysis was performed for hydroxypropyl cellulose-water and hydroxypropyl cellulose-ethanol systems with the use of the static sorption, calorimetry, cloud-point, polarization microscopy, and X-ray diffraction analysis techniques and the measurement of transmitted polarized light intensity. The concentration dependences of the enthalpy, entropy, and Gibbs energy of the formation of liquid-crystalline phases in the systems were determined. It was found that the formation of liquid-crystalline solutions of hydroxypropyl cellulose in water is associated with the energy term of interaction between the components and that in ethanol solutions is due to changes in combinatorial entropy.

Stability of cellulose lyotropic liquid crystal emulsions

We studied a new kind of W/O emulsions based on a lyotropic liquid crystal as the aqueous droplet phase. The cholesteric phase, a solution hydroxypropyl cellulose in water was dispersed in the continuous oil matrix, paraffin oil or heptane. We made a specific choice of surfactant in order to impose director anchoring conditions at the oil-water interface and orient the liquid crystal inside the droplet. The strong anchoring conditions resulted in a topological defect inside the droplets of size above the critical value R(*). The defect elastic energy creates a barrier against droplet coalescence, the effect of topological size selection. We have studied the orientation of the director inside the droplets and their size distribution.

MICRO-DOT ADHERING FOR PAPER CONSERVATION AND OFFSET APPLICATION OF PASTE

The author proposes a new technique for adhering papers for conservation procedures: micro-dot adhesion. Adhering is one of the key techniques in plper conservation. In some cases, waterbased adhesives such as natural starch paste and synthetic methyl cellulose cause trouble with water-sensitive materials. The micro-dot application of paste provides a minimal quantity of the paste. (The percentage amount of paste is roughly estimated from comparison with a graphic designer's screen: it might be 5% or less of the entire surface.) As a result, the paste stays on the surface and hardly penetrates inside. These facts allow water-based paste to be applied to water-sensitive materials for adhering. This is a very useful advantage for practical conservation work. Conventional starch paste, methyl cellulose and hydroxypropyl cellulose in water can be used. Another advantage is that it minimizes drying time, shrinkage and distortion and prevents the adhered papers becoming hard and solid. Furthermore, it offers easier detaching of the adhered papers. Water is not necessary for removing adhered paper, and inserting a thin spatula will be enough to detach the papers. It means that micro-dot adhesion is an easier, reversible method for paper conservation. Application of the paste can be done by various kinds of printing technique such as an offset technique with letterpress and a stencil technique. An ink-blotter has good shape and structure as an applicator for the paste. Instead of blotting paper, a net covers the bottom surface. The net surface of the blotter picks up paste from the table on which the paste has previously been applied flat. For offsetting, the blotter is then rolled on a paper that is to be used for mending. The paste is transferred to the paper from the net in dots and it is ready to use. For rather larger paper, a stencil is useful. A stencil paper having tiny holes, fixed on a frame at its edges, is used for application of the paste just as it is used for silkscreen printing. A larger amount of paste can be applied through the thickness of the stencil paper. The fluffed-up surface of Japanese paper is used for soft and flexible lining. Japanese paper is easily fluffed up by brushing the surface with a hard brush. The paste is applied on top of the fluffed-up fibres by an offset technique. First the paste is applied on a board, and the fluffed-up paper is then gently laid down on the pasted board. One soft brushing is enough to offset the paste to the top of the fibres. The technique is effective in the case of pasting a hinge-paper tip for matting a print. Sometimes an original print can show partial distortion caused by pasting hinge-paper at the corners. The micro-dots do not need much paste, so the pasted part does not contract as much as in the conventional method, because the paste is applied individually in tiny dots and there are many spaces between the dots. The usual, conventional way of pasting a sheet of paper, large or small, has been flat application by brush, even though the consistency of the paste is controlled. To repair a tear in the page of a Japanese book from the eighteenth/nineteenth century, thinly diluted paste is used to prevent the repaired part becoming hard. But thin paste can easily penetrate too much; blotting paper has to be inserted to dry it and to prevent bleeding to the next pages and shrinkage. Drying takes time. The dot-pasted mending paper is first put in a gutter-shaped paper carrier, and the carrier is inserted between the pages. Then the page is lightly pressed and the cmTier is withdrawn, leaving the mending paper. The mending paper does not adhere as strongly as in the conventional method. But such strong adhesion is not needed, because the book is handled carefully in a mu~eum collection and not treated as it was in private, everyday use. Advantages of the micro-dot technique:

Rheology and Structure of Suspensions in Liquid Crystalline Hydroxypropylcellulose Solutions

The rheology and flow-induced microstructure of filled liquid crystalline polymers (LCPs) are studied. The matrix consists of hydroxypropylcellulose in water. The particle diameters are 28 and 3000...

Self-Association of Hydroxypropylcellulose in Water

The association of hydroxypropylcellulose (HPC) chains above their lower critical solution temperature (LCST, ∼41 °C) leads to metastable nanosphere aggregates instead of precipitation. Laser light scattering (LLS) measurements revealed that the size of the aggregates is dependent not only on temperature and HPC concentration but also on heating history. There existed a narrow temperature range from ∼41 to ∼44 °C in which narrowly distributed metastable nanospheres formed in a few minutes and lasted for a few days without changing their sizes and molar masses. Increasing temperature in this range and increasing HPC concentration resulted in larger and denser nanosphere aggregates. In situ cross-linking of self-associated HPC chains was performed in a LLS sample cuvette at 42 °C using divinyl sulfone as a cross-linker. Formation of HPC gel microspheres was monitored by LLS and demonstrated by allowing the gel microspheres to swell and shrink at temperatures below and above the LCST, respectively.

Effects of particles on the steady state and transient rheology of lyotropic hydroxypropylcellulose solutions

The rheological effects of adding particles to main-chain liquid crystalline polymers (LCPs) are studied. Suspensions of polystyrene particles in liquid crystalline solutions of hydroxypropylcellulose in water are used. Even very small amounts of particles seem to eliminate negative normal stress differences. The complex and unsteady flow field in between particles might interfere with the director orientation and in this manner affect the occurrence of negative normal stresses. Flow reversal experiments on filled systems produce damped oscillatory responses for both the shear stress and the first normal stress difference. In these transients the scaling of time with shear rate, a characteristic of LCPs, is preserved. This indicates that the LCP texture still determines the time scale of the rheological response of the filled system. The textural changes are more rapid when particles are present. This has been observed in recoil and relaxation experiments as well as in flow reversals. When adding particle...

A flow-induced phase inversion in immiscible polymer blends containing a liquid-crystalline polymer studied byin situoptical microscopy

The phase inversion from a morphology of hydroxypropylcellulose in water (HPC50%) droplets in polydimethylsiloxane (PDMS) matrix to a morphology of PDMS droplets in HPC50% matrix can be induced by a change of shear rate, due to a viscosity ratio inversion. Such a process passing through four different transient morphological stages was studied by optical microscopy in a transparent shear device. In a certain concentration region, at a fixed shear rate, after sheets of PDMS were formed, the transition “hesitates” between phase inversion and refined starting morphology. The influence of PDMS concentration, shear rate, elasticity, and phase dimension on the final morphology was investigated and compared with different models given in the literature. The influence of concentration and shear rate on the duration of the transient flow was also studied. We propose a simplified model of breakage of filaments to explain a part of our results.

Influence of the elasticity ratio on the point of phase inversion in an immiscible polymer blend

At a shear rate of 10 s−1, a flow-induced phase inversion has been observed in-situ by optical microscopy on a blend of polydimethylsiloxane with solution of 50% of hydroxypropylcellulose in water for a range of concentrations. By increasing the shear rate up to 30 s−1, the elasticity ratio of the components can be changed without changing the viscosity ratio. The resultant steady-state morphology is not influenced by the variation of the elasticity ratio, contrary to a theoretical model.

An evaluation of the Larson-Doi model for liquid crystalline polymers using recoil

The mesoscopic models for the rheological properties of liquid crystalline polymers proposed by Larson and Doi in 1991 and Kawaguchi and Denn in 1999 are based on phenomenological expressions that describe the evolution of the defect density and the contribution of the “texture” to the stress. In the present work, we attempt to assess some of these assumptions by monitoring how the energy stored in the texture of liquid crystalline materials evolves during shear flows. For that purpose, strain recovery is measured as a function of the applied strain for flow reversal and intermittent flow. Solutions of poly-benzylglutamate in m-cresol, hydroxypropylcellulose in water and a nematic surfactant solution are used as model systems. Although the behaviour is described qualitatively by the model, discrepancies between the predictions and the experiments are observed, especially when the shear history includes rest periods.

Transient rheological behavior of lyotropic solutions of ethyl cellulose in m -cresol

Transient rheological features of anisotropic 30 and 40 wt.% ethyl-cellulose/m-cresol solutions were investigated, taking as a reference other lyotropes like poly(γ-benzylglutamate) in m-cresol, poly(p-phenylene-terephthalamide) in sulfuric acid and hydroxypropylcellulose in water. Strain scaling oscillations before reaching steady state, with a half-period of 20 strain units for 30 wt.% and 22.5 strain units for 40 wt.% in both stress growth and transient viscosity in creep, revealed that director tumbling takes place for ethylcellulose solutions. Large strain recoveries (2–3 strain units) obtained in recoil experiments confirmed the hypothesis of a tumbling regime. In contrast to the majority of reported lyotropes, we did not observe a master curve of strain recovery versus the product of preshear rate by time. This result appears to be associated with the existence of another mechanism of relaxation, in addition to unwinding of the defect texture created by tumbling. Dynamic viscoelastic results after cessation of flow suggest that a slower mechanism of relaxation, associated with texture or polydomain coarsening, takes place.

Quick way to prepare anisotropic solutions of hydroxypropylcellulose in water

Quick way to prepare anisotropic solutions of hydroxypropylcellulose in water

Atomic force microscopy of the banded structure of lyotropic polymers

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Rheology of region I flow in a lyotropic liquid‐crystal polymer: The effects of defect texture

A thorough rheological investigation into the region I flow of liquid‐crystalline hydroxypropylcellulose in water is reported. At low shear rates a region of shear thinning with a power‐law exponent 1/2 is observed over two decades in shear rate. Anomalous transient behavior is seen for applied stresses below the critical stress at the region I–II turnover such that the strain required to reach steady state increases as stress decreases. Recoil measurements show large recoverable strain and similar pseudostrain scaling in both regions I and II. The activation energy for the viscosity is also the same in regions I and II. This rheology combined with in situ flow‐small‐angle light scattering measurements of the defect texture size show the qualitative and quantitative accuracy of the defect texture stress balance previously proposed to explain region I flow.

Interactions between Copper Dodecylsulfate Micelles and Hydroxyethyl or Hydroxypropyl Cellulose in Water at 25°C

The interaction of copper dodecylsulfate [(Cu(DS) 2] with hydroxyethylcellulose [HEC] and with hydroxypropylcellulose [HPC] has been investigated using essentially potentiometric measurements. In the case of HEC, no change is observed either of the CMC or of the degree of counterion condensation of the anionic micelles upon addition of up to 1 weight percent of polymer, indicating negligible interaction between that polymer and the anionic surfactant. In the presence of HPC, bound and free Cu(DS) 2 micelles were detected. The variation of CMC and of the counterion degree of condensation of both bound and free micelles resemble closely those displayed by the same surfactant with poly(vinylpyrrolidone). Also, based on the present observations, HEC is more hydrophilic than poly(ethylene oxide). Cloud point and Krafft point measurements confirm the above interpretation concerning the interaction between the surfactant and both polymers.

In situ X-ray scattering study of anisotropic solutions of hydroxypropylcellulose subjected to shear flow

Molecular orientation parameter values measured by laboratory-based X-ray scattering techniques are reported for liquid crystalline solutions of hydroxypropylcellulose in water subjected to a range of steady shear rates. The global orientation exhibits a marked transition from a low orientation at low shear rates to high values ∼0.5 at higher shear rates. This transition occurs at shear rates in the range of 0.3–1 s −1 and correlates quantitatively with similar transitions observed using small-angle light scattering. This behaviour is attributed to an out-of-shearing plane to an in-shearing plane transition which has been predicted theoretically by Larson and Ottinger.

Velocity profiles in simple shear flow of liquid-crystalline polymers

Abstract The velocity profiles of isotropic and anisotropic solutions of hydroxypro-pylcellulose in water have been measured by a tracer method. The velocity profile is the usual linear one for steady state experiments and also for transient experiments if a short waiting time (less than 3 hours) is left between loading and the experiment. For long waiting times (more than 12 hours), the profile is S-shaped. This could be due to the establishment of a cholesteric superstructure.