Aqueous Solutions Of Hydroxypropylcellulose Research Articles

Biopolymer foams composed of hydroxypropyl cellulose: Fabrication, aqueous stability, and mechanical integrity

We describe the fabrication of biopolymer foams formed from aqueous solutions of hydroxypropyl cellulose, whereby freezing-induced phase-separation and solvent removal yields robust foam structures that are elastic in air and when wet, and that are stable to repeated compression when fully saturated with water. Through mechanisms of phase-separation, pore formation, and covalent crosslinking, we discovered effective methods to prepare microporous HPC foams that resist gelation even when exposed to water for long time frames (at least months). Employing multifunctional carboxylic acid crosslinkers allowed the foams to maintain their integrity when dry or wet, while the presence of α-cellulose as an additive further augmented their mechanical integrity and provided a means to adjust elasticity. The amount of crosslinker employed in the foaming process significantly impacted foam stability and water uptake, while polymeric crosslinkers enabled insertion of sulfobetaine zwitterionic moieties into the foams. Notably, the thermal transition characteristic of HPC solutions and gels proved operative in foam form, as seen in release of water from a saturated HPC foam using a combination of compressive and thermal mechanisms.

Nanocellulose-containing cellulose ether composite films prepared from aqueous mixtures by casting and drying method

A TEMPO-oxidized cellulose nanofibril (TEMPO-CNF)/water dispersion was mixed with an aqueous solution of hydroxypropyl cellulose (HPC), hydroxyethyl cellulose (HEC), methyl cellulose (MC), or carboxymethyl cellulose sodium salt (CMC). The mixtures were converted into TEMPO-CNF/cellulose ether composite films containing 0–5% TEMPO-CNFs by casting and drying of the aqueous mixtures. All the composite films had high light transparency. However, the tensile properties of the composite films of a given TEMPO-CNF content differed for the HPC and HEC, MC, and CMC matrices. The nano-reinforcing effect owing to TEMPO-CNFs was evident in the TEMPO-CNF/HPC composite films, which became strong but brittle. In contrast, the TEMPO-CNF/HEC composite films did not exhibit this nano-reinforcing effect. Transmission electron microscopy observation of the film cross-sections revealed that the TEMPO-CNF elements were homogeneously distributed in the 5% TEMPO-CNF/HPC composite film. In contrast, the TEMPO-CNF elements were densely present on the top and bottom surfaces of the 5% TEMPO-CNF/HEC composite film; the TEMPO-CNFs were heterogeneously distributed in the HEC matrix. The low gelation or aggregation concentrations of TEMPO-CNFs in water may have resulted in the different distribution states of TEMPO-CNFs, depending on the cellulose ether matrix used, and hence the different tensile behaviors.

Phase separation dynamics in aqueous solutions of thermoresponsive polymers

Phase transition kinetics of aqueous hydroxypropyl cellulose solution was studied by using turbidimetric monitoring and mathematical modelling techniques. Based on the nonlinear Cahn-Hilliard equation with a mobility depending on the component concentration, the phase separation has been modeled on a simple one-dimensional Flory lattice. For value set of the interfacial energy parameter, data were obtained on the changing of the average values of the cluster sizes, their mass and concentration. The simulation results allow us to distinguish three stages of the spinodal decomposition: early, intermediate and final. It was found that for the intermediate stage, the kinetics of the cluster mass growth is described by a dependence that is characteristic of the usual diffusion mass transfer; the change in the average cluster size can be represented by a scaling function with an exponent close to 1/3, typical of the systems with a conserved scalar order parameter. It is shown that the concentration of clusters at the final stage is determined by the temperature dependence of the interfacial energy.

The Formation and Elasticity of a Hydroxypropyl Cellulose Film at a Water–Air Interface

The kinetics of spreading of aqueous hydroxypropyl cellulose (HPC) solutions with different concentrations over a water surface and the rheological properties of films formed at the water–air interface have been studied. The performed experiments are distinguished by the fact that the solvent in the polymer solutions is identical to the liquid subphase, while, beginning from a certain concentration, the aqueous HPC solutions are capable of forming a liquid-crystalline phase. The chosen initial polymer solution concentrations correspond to different regions of the phase diagram for the HPC–water system. The contact of a solution droplet with water yields a time-stable spot of an HPC solution layer. In spite of the fact that some solution concentrations correspond to the existence range of a lyotropic liquid-crystalline phase, an isotropic layer is formed on the water surface irrespective of the concentration and phase state of the solution in the droplet. The dynamic dilatational storage modulus of such an interfacial layer at a frequency of 0.03 Hz is equal to 43 ± 2 mN/m; i.e., it almost coincides with the surface tension of the formed interfacial layer.

The Structure of Polymer Clusters in Aqueous Solutions of Hydroxypropyl Cellulose

The viscosity, turbidity, and heat capacity of dilute aqueous solutions of hydroxypropyl cellulose have been studied in a concentration interval of 0.047–1.5 g/l and a temperature interval of 20–80 ∘C. The data obtained testify that, if the temperature does not exceed 40 ∘C, hydroxypropyl cellulose molecules are prolate spheroidal globules with semiaxis lengths of 7 and 490 ˚ A. At temperatures above 70 ∘C, the hydroxypropyl cellulose solution consists of clusters; every cluster is composed of 11 globules and has a prolate spheroidal form with semiaxes of 41 and 490 ˚ A. In the temperature interval from 40 to 70 ∘C, the solution concerned contains both globules and clusters, with the concentration of the latter increasing, as the temperature grows.

Confinement Effects on Polymer Dynamics: Thermo-Responsive Behaviours of Hydroxypropyl Cellulose Polymers in Phospholipid-Coated Droplets (Water-in-Oil Emulsion).

In order to construct the artificial cells and to understand the physicochemical properties of living cells, it is important to clarify the cell-sized confinement effect on the behaviours of bio-inspired polymers. We report the dynamic behaviours of aqueous hydroxypropyl cellulose (HPC) solution coated with phospholipids in oil (water-in-oil droplets, W/O droplets), accompanied by an increase in the temperature. We directly observed the beginning of phase separation of HPC solution using a fluorescence microscope and confirmed the dependence of such phenomena on droplet size. The results indicate that the start time of phase separation is decreased with an increase in droplet size. The experimental results suggest that the confinement situation accelerates the phase separation of aqueous HPC solutions.

Aqueous solutions of hydroxypropyl cellulose, Tween 80 and their binary mixtures: Colloid-chemical aspects

Tensiometry, dynamic light scattering, and rheology have been used to study the colloid-chemical properties of hydroxypropyl cellulose, Tween 80, and binary mixtures thereof in an aqueous medium and at water/decane and water/air interfaces. The efficiency of a reduction in the interfacial energy under dynamic and static conditions, the surface activity of the components, capability of self-organization in bulk and at interfaces, as well as emulsifying efficiency of the systems, have been analyzed. It has been found that, in a narrow concentration range and at a certain ratio of the components, they exhibit a synergetic effect with respect to a reduction in the interfacial energy, with this effect being due to the formation of a Tween 80–polymer bilayer via hydrogen bonding between hydroxyl groups of hydroxypropyl cellulose and ethoxy units of Tween 80.

Dual-responsive semi-IPN copolymer nanogels based on poly (itaconic acid) and hydroxypropyl cellulose as a carrier for controlled drug release

Dual-responsive nanogels were prepared by polymerization of itaconic acid (IA) and copolymerization with methacrylic acid (MA) in aqueous solution of hydroxypropyl cellulose (HPC) and cross-linking with N, N′-methylenebisacrylamide (MBAm) through an easy and green process. FTIR spectroscopy, TEM, AFM, DLS and zeta potential studies confirmed the semi-interpenetrating (semi-IPN) polymer network structure of nanogels. The LCST of HPC was increased to a higher temperature than HPC’s intrinsic LCST, while the presence of the MA comonomer improved the hydrophobicity of the copolymer and reduced LCST to about body temperature and suppressed the excessive nanogel aggregation. It was found that the concentration of reactants impacted the process of nanogel formation. Additionally, an increasing of cross-linker concentration led to a reduced size of HPC nanogels. Besides, the diameter of nanogels was changed with the temperature and pH. TEM and AFM photographs of copolymer nanogels illustrated that the nanoparticles with small diameters (<100 nm) were prepared. With loading the doxorubicin into the copolymer nanogels, the particle size became larger (about 150 nm) and due to the electrostatic interaction of the cationic drug with anionic particles, the zeta potential was increased. Drug release processes were followed at pH = 5.0 and 7.4 and with 37- and 41-°C temperatures, respectively. The maximum in-vitro release studies of drug-loaded nanogels, which is 91% for the pH 5.0 buffer solution at 41 °C, demonstrated the temperature- and pH-sensitivity of prepared copolymer nanogels.

A rheological investigation of sol–gel transition of hydroxypropyl cellulose with nonionic surfactant sorbitan monopalmitate: Modulation of gel strength by UV irradiation

Abstract The interaction of hydrophobically modified biocompatible polymer hydroxypropyl cellulose (HPC) with nonionic surfactant sorbitan monopalmitate (Span 40) in aqueous solutions have been studied using rheology. The associated physicochemical properties of the HPC+ Span 40 mixed system such as cac, psp and cmc were studied as a function of Span 40 concentration. Steady shear rheological experiments indicate that the HPC as well as HPC+ Span 40 systems possesses two distinct regions in the rheogram Newtonian followed by Pseudoplastic behavior, and behave as plastic systems with the value of m parameter in the empirical Cross model equation η 0 − η α / η − η α = 1 / 1 + C ( γ ) m varying between 0.725–0.675 and 2.24–1.58 in the first and second shear thinning regions. Dynamic rheological results suggest that the microstructural changes that occur during thermo reversible gelation of aqueous solutions of HPC and HPC+ Span 40 systems follow a two step mechanism i.e., gelation followed by precipitation. The thermal stability of the HPC hydrogel decreases as the concentration of Span 40 increases. Moreover, increase in the UV radiation dose on 10% HPC increases its gel strength probably due to the formation of active radicals in the polymer which on further reaction results in formation of highly cross linked gel of high viscoelasticity. However, this phenomena was not observed in 10% HPC solution after addition of Span 40.

Is the combination of cellulosic polymers and anionic surfactants a good strategy for ensuring physical stability of BCS Class II drug nanosuspensions?

Ensuring the physical stability of drug nanosuspensions prepared via wet media milling has been a challenge for pharmaceutical scientists. The aim of this study is to assess the combined use of non-ionic cellulosic polymers and anionic surfactants in stabilizing multiple drug nanosuspensions. Particle size of five drugs, i.e. azodicarbonamide (AZD), fenofibrate (FNB), griseofulvin (GF), ibuprofen (IBU) and phenylbutazone (PB) was reduced separately in an aqueous solution of hydroxypropyl cellulose (HPC) with/without sodium dodecyl sulfate (SDS) via a stirred media mill. Laser diffraction, scanning electron microscopy, thermal analysis, rheometry and electrophoresis were used to evaluate the breakage kinetics, storage stability, electrostatic repulsion and stabilizer adsorption. Without SDS, drug particles exhibited aggregation to different extents; FNB and GF particles aggregated the most due to low zeta potential and insufficient steric stabilization. Although aggregation in all milled suspensions was reduced due to HPC–SDS combination, FNB and IBU showed notable growth during 7-day storage. It is concluded that the combination of non-ionic cellulosic polymers and anionic surfactants is generally viable for ensuring the physical stability of wet-milled drug nanosuspensions, provided that the surfactant concentration is optimized to mitigate the Ostwald ripening, whereas cellulosic polymers alone may provide stability for some drug suspensions.

Hydroxypropylcellulose as a novel green reservoir for the synthesis, stabilization, and storage of silver nanoparticles.

Polysaccharides are attracting the vigil eye of researchers in order to design the green synthesis of silver nanoparticles (Ag NPs) of diverse size, shape, and application. We report an environmentally friendly method to synthesize Ag NPs where no physical reaction conditions were employed. Hydroxypropylcellulose (HPC) was used as a template nanoreactor, stabilizer, and capping agent to obtain Ag NPs. Different concentrations of AgNO3 solutions (50 mmol, 75 mmol, and 100 mmol) were mixed with a concentrated aqueous solution of HPC and the progress of the reaction was monitored by noting color changes of the reaction mixture at different reaction times for up to 24 hours. Characteristic ultraviolet–visible spectroscopy (UV/Vis) absorption bands of Ag NPs were observed in the range of 388–452 nm. The morphology of the Ag NPs was studied by scanning electron microscopy, transmission electron microscopy (TEM), and atomic force microscopy. The TEM images confirmed that the size of the Ag NPs was in the range of 25–55 nm. Powder X-ray diffraction studies showed that the crystal phase of the Ag NPs was face-centered cubic. The as-prepared Ag NPs were found to be stable, and no changes in size and morphology were observed after storage in HPC thin films over 1 year, as indicated by UV/Vis spectra. So, the present work furnishes a green and economical strategy for the synthesis and storage of stable Ag NPs. As-synthesized Ag NPs showed significant antimicrobial activity against different bacterial (Escherichia coli, Staphylococcus epidermidis, S. aureus, Bacillus subtilis, Pseudomonas aeruginosa) and fungal strains (Actinomycetes and Aspergillus niger).

Mesoscale modeling of shear-thinning polymer solutions

We simulate the linear and nonlinear rheology of two different viscoelastic polymer solutions, a polyisobutylene solution in pristane and an aqueous solution of hydroxypropylcellulose, using a highly coarse-grained approach known as Responsive Particle Dynamics (RaPiD) model. In RaPiD, each polymer has originally been depicted as a spherical particle with the effects of the eliminated degrees of freedom accounted for by an appropriate free energy and transient pairwise forces. Motivated by the inability of this spherical particle representation to entirely capture the nonlinear rheology of both fluids, we extended the RaPiD model by introducing a deformable particle capable of elongation. A Finite-Extensible Non-Linear Elastic potential provides a free energy penalty for particle elongation. Upon disentangling, this deformability allows more time for particles to re-entangle with neighbouring particles. We show this process to be integral towards recovering the experimental nonlinear rheology, obtaining excellent agreement. We show that the nonlinear rheology is crucially dependent upon the maximum elongation and less so on the elasticity of the particles. In addition, the description of the linear rheology has been retained in the process.

Study of Casting Self-Colored Liquid Crystalline Solid Films of Hydroxypropyl Cellulose

Solutions of lyotropic cholesteric liquid crystalline hydroxypropyl cellulose (HPC) in water would be self-colored due to the selective reflection of visible light, depending on the solution concentration. Colored coating of the liquid crystalline aqueous HPC solutions was attempted to apply. HPC solid films were found which could cast from the liquid crystalline solutions at different conditions such as solution concentration and different drying temperature. Experiments show that both solution concentration and cooling velocity play an important effect in controlling the color of HPC films.

Influence of the elasticity of cellulose solutions on the dispersion of carbon black agglomerates

A counter-rotating rheo-optical tool was used to study the dispersion process of carbon black agglomerates in different suspending media, including the solutions of different types of cellulose, aqueous hydroxypropylcellulose solutions, and polyisobutylene. For each suspending fluid, the mechanism of dispersion (erosion or rupture) was identified, and the macroscopic critical shear stress necessary for dispersion was measured. Checking that the impacts of fluid infiltration and agglomerate size on the macroscopic critical shear stress for dispersion were negligible in our case, we showed that elasticity is a major factor acting on dispersion physics. At a constant viscosity, the higher the elasticity is, the more difficult dispersion is, giving higher critical shear stresses for initiating dispersion. There is a linear correlation between the suspending fluid elasticity and this critical shear stress, independent of temperature. An explication of the influence of matrix elasticity on agglomerate dispersion based on recent numerical simulation is given.

Migration and alignment of spherical particles in sheared viscoelastic suspensions. A quantitative determination of the flow-induced self-assembly kinetics

Flow-Induced Self-Assembly (FISA) is the flow-driven formation of ordered structures in complex fluids. In this paper the effect of shear flow on the microstructure formation of dilute sphere suspensions in a viscoelastic fluid has been studied experimentally by optical microscopy techniques. The system is formed by Polymethylmethacrylate beads suspended in 20wt.% aqueous solutions of Hydroxypropylcellulose at volume fractions ranging between 0.1% and 1.0%. Experiments show that, under the action of flow, beads migrate from the bulk to the shear walls, there forming strings aligned along the flow direction. Strings grow with time eventually reaching a steady-state final length. The alignment kinetics have been quantified by means of an alignment factor, which is a measure of the average length of the strings. The experimental results indicate that both shear rate and particle concentration are relevant factors in determining the alignment factor kinetics. In particular, it is shown that, upon increasing shear rate, strings grow both faster and longer. As a consequence, the characteristic time of the overall alignment process remains roughly constant. It is also shown that an increase in particle volume fraction determines effects similar to an increase of shear rate.

The effects of carbon nanofibre on the liquid crystalline behaviour and cholesteric pitch of aqueous solutions of hydroxypropyl cellulose

The liquid crystalline behaviour of aqueous solutions of hydroxypropyl cellulose (HPC_aq.) in which a small amount of carbon nanofibres (CNF) are dispersed (HPC_ aq./CNF) was investigated. Small spherical anisotropic droplets showing a biphasic state were found in the sample in which f 2 = 45.8 wt%, where f 2 is the weight fraction of HPC and CNF based on the total solids content. A preferential interaction is suggested between the hydrophobic surfaces of CNF and the spherical anisotropic droplets, or domains, of HPC. The samples of HPC_aq./CNF with f 2 lying between 59.4 wt% and 67.3 wt% showed the iridescence characteristic of the cholesteric phase. It was found that the cholesteric pitch multiplied by the averaged refractive index of HPC_aq./CNF was shorter than that of HPC aq. at a given value of weight fractions f 1 and f 2, where f 1 was the weight fraction of polymer based on the weight of the solution alone.

An investigation on the correlation between drug dissolution properties and the growth behaviour of granules in high shear mixer

The aim of this study was to investigate the correlation between the growth behaviour and in-vitro dissolution rate of water-insoluble drugs prepared with high-shear wet granulation. Granules containing nimodipine, microcrystalline cellulose, low-substituted hydroxypropylcellulose and aqueous solution of hydroxypropylcellulose were prepared and the effects of independent process variables, including impeller speed and liquid-to-solid ratio were taken into consideration. The mean granule size, granule-size distribution (GSD), porosity and surface properties were monitored at different kneading times to identify the granule-growth mechanisms simultaneously. A computer-based method was applied to simulate the dissolution behaviour of polydisperse granules based on the GSD data. The in-vitro dissolution rate of drug was high for the early stages of granulation and sharply decreased when coalescence and consolidation of granules started, approaching a flat and low level when granules were sufficiently consolidated. The simulated dissolution results were in agreement with experimental observations and were significantly affected by the GSD, porosity and surface properties of granules during the granulation process. Moreover the GSD was directly related to the granule-growth behaviour and mechanisms. In general, it was concluded that the dissolution properties of nimodipine basically correlated with the growth behaviour of granules in a high-shear mixer. The simulation method based on GSD can be used as a convenient and rapid way to predict the dissolution properties for formulation development and granulation optimization.

Hydroxypropylcellulose templated synthesis of surfactant-free poly(acrylic acid) nanogels in aqueous media

Abstract We report the synthesis and study of surfactant-free poly(acrylic acid) (PAA) nanogels using hydroxypropylcellulose (HPC) as a template in aqueous HPC solutions at room temperature or above. Through the hydrogen bonding interaction of acrylic acid (AA) with hydroxypropylcellulose (HPC), AA absorbed on the HPC polymer chains and triggered the phase transition of HPC at a lower temperature, with increasing AA concentration, than the HPC intrinsic phase transition temperature 41 °C. As AA polymerized to form PAA, the much stronger interpolymer hydrogen bonding triggered the phase transition of HPC at a temperature around room temperature, causing HPC coil-global phase transition to collapse and form nanospheres at room temperature, PAA hydrogen-bonded HPC chains collapsed and formed nanogels chemically crosslinked by poly(ethylene glycol) diacrylate (PEGDA) or methylenebisacrylamide (BIS). The results showed that all the PAA nanogels demonstrated a narrow size distribution with diameters ranging from 60 nm to 600 nm.

Dissolution and Solid-State Characterization of Poorly Water-Soluble Drugs in the Presence of a Hydrophilic Carrier

The aim of this study was to investigate the effects of a hydrophilic carrier on the solid-state and dissolution characteristics of poorly water-soluble drugs. Three poorly water-soluble drugs, ibuprofen, carbamazepine, and nifedipine, were studied in combination with hydroxypropyl cellulose (HPC), a low molecular weight hydrophilic polymer, without the use of solvent. A 1:1 drug-polymer ratio was used to evaluate the percent drug release, crystallinity, and wettability. A drug-polymer ratio of 1:4 was also used in co-grinding process to evaluate the effect of polymer levels on drug release. Dissolution studies were carried out in deionized water. Mean dissolution time (MDT) was calculated, and statistical analysis of MDTs was done following a single factor one-way analysis of variance. The dissolution rate of the drugs was enhanced by several folds by the simple process of co-grinding with HPC. X-ray diffraction studies were done to investigate the effects of physical and co-ground mix with HPC on the crystallinity of the drugs, which indicated a partial loss in crystallinity upon grinding. Differential scanning calorimetry studies were performed in order to identify possible solid-state interactions between the respective drugs and HPC. Wettability of the drugs by a 0.5% aqueous HPC solution was compared with that of water and n-hexane using the "Washburn method." Increased wetting and hydrophilization of the drugs by HPC, enlarged surface area due to particle size reduction, and a decrease in the degree of crystallinity were identified as the likely contributors to dissolution rate enhancement.

Dielectric Properties of the Free Water in Hydroxypropyl Cellulose

We performed dielectric measurements of aqueous solutions of hydroxypropyl cellulose (HPC) with various concentrations in the temperature range between 25 °C and -20 °C. A primary relaxation process due to the motion of free water restricted by HPC molecules is observed at GHz region. The relaxation time and shape parameter of the primary process strongly depend on the concentration of HPC. The change of the dielectric relaxation parameters is interpreted by the results of the formation of a cholesteric phase structure of the HPC molecules.