Hydroxypropylcellulose Concentration Research Articles

Slow Relaxation Dynamics of Water in Hydroxypropyl Cellulose-Water Mixture Traces Its Phase Transition Pathway: A Spectroscopic Investigation

In this study, we have explored the slow (of the order of several hundreds of picoseconds) relaxation dynamics of water associated with the hydration shell of a biocompatible polymer, hydroxypropyl cellulose (HPC)-water mixture as a function of HPC concentration using time-resolved fluorescence spectroscopy. The relaxation dynamics slows down with a progressive increase in HPC content indicating restriction of the relaxation pathway of water molecules specially beyond a cellulose concentration of 20% wherein an isotropic to liquid crystalline cholesteric microscopic phase separation sets in. The activation energy calculated from the temperature dependent solvation dynamics studies also shows a similar trend. The nucleophilic activity of water molecules in these mixtures is determined by measuring the reaction kinetics of solvolysis of benzoyl chloride, and the reaction rate exhibits a marked decrease as the phase separation sets in. The observed results are correlated with a transition between the 'bulk' and 'bound' type of water molecules present in the system.

Thermal and structural studies of poly (vinyl alcohol) and hydroxypropyl cellulose blends

Polymers and polymeric composites have steadily reflected their importance in our daily life. Blending poly(vinyl alcohol) (PVA) with a potentially useful natural biopolymers such as hydroxypropyl cellulose (HPC) seems to be an interesting way of preparing a polymeric blends. In the present work, blends of PVA/HPC of compositions (100/0, 90/10, 75/25, 50/50, 25/75, and 0/100 wt/wt%) were prepared to be used as bioequivalent materials. Thermal analyses [differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA)], and X-ray diffraction (XRD) were employed to characterize and reveal the miscibility map and the structural properties of such blend system. The obtained results of the thermal analyses showed variations in the glass transition temperature (Tg) indicating the miscibility of the blend systems. Moreover, the changes in the melting temperature (Tm), shape and area were attributed to the different degrees of crystallinity and the existence of polymer-polymer interactions between PVA and HPC molecules. The X-ray diffraction (XRD) analysis showed broadening and sharpening of peaks at different HPC concentrations with PVA. This indicated changes in the crystallinity/amorphosity ratio, and also suggested that the miscibility between the amorphous components of homo-polymers PVA and HPC is possible. The results showed that HPC doped in PVA film can improve the thermal stability of the film under investigation, leading to interesting technological applications.

Temperature dependence of the disintegration times of compressed tablets containing hydroxypropylcellulose as binder.

The dependence of the disintegration times of placebo and active tablets containing hydroxypropylcellulose (HPC), as binder on the temperature of the test medium in the region of 37 degrees is reported. The degree of temperature dependence varied with the HPC lot and concentration in the formulation of certain drugs, such as caffeine. The extent of the temperature dependence could be diminished by reducing the HPC concentration in the formulations. Corresponding trends were observed in drug release behaviour from some of these formulations. The effects observed were interpreted in terms of the thermodynamic behaviour of HPC systems and a specific drug-HPC interaction.

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.

Preparation and evaluation of bioadhesive dibucaine gels for enhanced local anesthetic action

In relieving local pains, dibucaine, one of ester type local anesthetics, has been used. In case of their application such as ointments and creams, it is difficult to expect their effects for a required period of time, because they are easily removed by wetting, movement and contacting. To develop suitable bioadhesive gels, the bioadhesive force of hydroxypropyl cellulose (HPC) was tested using auto-peeling tester. The effect of drug concentration on drug release was studied from the prepared 2% HPC-HF gels using synthetic cellulose membrane at 37 +/- 0.5 degrees C. We investigated the enhancing effects on drug permeation into skins, using some kind of enhancers such as the glycols, the non-ionic surfactants, the fatty acids, and the propylene glycol derivatives. Anesthetic effects of dibucaine gels containing polyoxyethylene 2-oleyl ether were measured by tail flick analgesic meter. The bioadhesive force of various types of HPC such as GF, MF, and HF, was 0.0131, 0.0501, and 0.1346 N, at 2% HPC concentration, respectively. The HPC-HF gels showed the highest bioadhesive force. As the concentration of HPC-HF increased, the drug release increased. As the temperature increased, the drug release increased. Among the enhancers used, polyoxyethylene 2-oleyl ether showed the highest enhancing effects. According to the rat tail flick test, 1% drug gels containing polyoxyethylene 2-oleyl ether showed the prolonged local anesthetic effects. In conclusion, the dibucaine gel containing penetration enhancer and vasoconstrictor showing enhanced local anesthetic action could be developed by using the bioadhesive polymer, HPC.

Extension rheology of liquid-crystalline solution/layered silicate hybrids

The extension rheology of polymer/layered silicate composites based on liquid-crystalline (LC) solution of hydroxypropylcellulose (HPC) in oligomeric polyethyleneglycole (PEG) was studied. The HPC concentration was 60 wt%. Extension experiments have been carried out for materials in the different phase states. Compositions containing Na-montmorillonite (MMT) were prepared by a two-stage method. Final systems may be attributed to solutions of HPC in PEG, which intercalates into MMT galleries. The ordered domain structure of the LC matrix as well as hydrogen-bonded network between HPC and PEG molecules significantly reduce deformation at break and provide a strong nonlinear viscoelastic behavior at extension. Appearance of isotropic phase in solutions leads to a sharp drop of the elongation viscosity. The introduction of clay into LC solution only slightly affects the viscosity value but significantly suppresses the strain-hardening scale. In contrast, loading in biphasic state of HPC-PEG solution with even small amount (1 wt%) of MMT leads to the drastic viscosity increase that does not change in further growth of the filler concentration. Elastic properties of the systems under study demonstrate the similar behavior. This effect likely is caused by the interrelationship between deformability of the LC domain structure and the network strength formed by the clay particles. POLYM. ENG. SCI., 2010. © 2009 Society of Plastics Engineers

Sol/gel transition and liquid crystal transition of HPC in ionic liquid

This work uses an ionic liquid (IL), 1-butyl-3-methylimidazolium acetate, as a solvent to study the sol/gel transition (SGT) and liquid crystal transition (LCT) of hydroxypropylcellulose (HPC) solution. The LCT concentration of HPC at room temperature is 7 wt%, which is slightly higher than its SGT concentration of 6 wt%. For HPC concentrations of over 7 wt%, three rheological approaches were utilized, and the parameters relaxation time, hysteresis ratio and loss modulus (G″) are measured to determine the LCT temperature. The relaxation study concludes that the LC-critical concentration of HPC is 7 wt%. When HPC exceeds 7 wt%, the LC transition temperatures, ranging from 45 to 51 °C, can be measured and are proportional to the HPC concentration. The rheological results are then confirmed by making observations under a polarized optical microscope. All results are highly mutually consistent. Most significantly, the rheological parameters adopted herein can be used as good indicators of the LC transition. Of those indicators, G″ changes distinctly at the LCT point, and can thus be suggested to be the most helpful indicator in determining the LCT temperature.

Oil/water surface rheological properties of hydroxypropyl cellulose (HPC) alone and mixed with lecithin: Contribution to emulsion stability

Hydroxypropyl cellulose (HPC) is a neutral branched polysaccharide derivatized from a wood substrate. Widely used in whipping vegetable creams, HPC is a thickening biopolymer having surface active properties both at air/water and oil/water interfaces. Myglyol/water interfacial rheology was used to characterize the behavior of HPC at this interface in the presence or the absence of lecithin, an emulsifier classically used in combination with HPC. Addition of HPC in the aqueous phase leads to an increase of the surface pressure at the oil/water interface depending on the HPC concentration. The higher the HPC concentration, the shorter is the lag time before the surface pressure increase. The equilibrium surface pressure is about 13–16 mN m −1 whatever the HPC concentration in the studied range. In order to understand the way the HPC positions itself at the interface, a viscoelastic characterization of the interface was performed during adsorption, in the presence and in the absence of lecithin. A comparison to the stability of emulsions containing HPC or HPC/lecithin is made and discussed using droplet size evolution and droplet displacement rate to an upper layer.

Stabilization of hot-melt extrusion formulations containing solid solutions using polymer blends.

This study was aimed at enhancing the physical stability of the drug clotrimazole (CT) and the polymer contained within hot-melt extrusion (HME) films using polymer blends of hydroxypropyl cellulose (HPC) and poly(ethylene oxide) (PEO). The HME films were investigated for solid-state characteristics, moisture sorption, bioadhesivity, mechanical properties, glass transition temperature, release characteristics, and physical and chemical stability of the drug and the polymer within the HME films. The solid-state characterization of the drug and the polymer was performed using differential scanning calorimetry, x-ray diffractometry, and dynamic mechanical analysis. A texture analyzer was used to study the bioadhesive and mechanical properties of the HME films. The physical and chemical stability of the films, stored at 25 degrees C/60% relative humidity or in a desiccator, was studied for up to 12 months. CT was found to be in solid solution within all of the formulations extruded. The physical stability of the drug and PEO in the HME films increased with increasing HPC concentration, but the bioadhesivity and flexibility of the PEO films decreased with increasing HPC concentration. Films containing HPC:PEO:CT in the ratio of 55:35:10 demonstrated optimum physical-mechanical, bioadhesive, and release properties. In conclusion, polymer blends of HPC and PEO were used successfully to tailor the drug release, mechanical and bioadhesive properties, and stability of the HME films.

Diffusion and phase behavior of a hydroxypropylcellulose-poly(ethylene glycol) system

The solubility and interdiffusion between hydroxypropylcellulose samples of various molecular masses (M w = 8 × 104, 14 × 104, 37 × 104, 85 × 104, and 115 × 104) and poly(ethylene glycol) (M w = 400 and 1500) in the range 18–210°C have been studied by optical interferometry and polarization microscopy methods. Oligomeric poly(ethylene glycols) have been considered as solvents for hydroxypropylcellulose. Phase diagrams have been constructed, and Flory-Huggins thermodynamic interaction parameters have been calculated. For the hydroxypropylcellulose-poly(ethylene glycol) 400 system, an LC and crystalline equilibria have been realized. An increase in the M w of hydroxypropylcellulose to 1500 leads to the appearance of a wide region of amorphous phase segregation with a UCST, whereas the liquidus line is conserved at high concentrations of hydroxypropylcellulose. Such a superposition of two kinds of phase equilibrium that is achieved only with a change in M w of the oligomeric solvent has been observed for the first time. For all the systems under examination, the kinetics of diffusion mixing has been estimated and the activation energies of the process have been calculated. The concentration dependences of diffusion coefficients demonstrate jumps in the mesomorphic-transition region.

A Novel Cellulose-Based Hydrophilic Wafer Matrix for Rapid Bioactive Delivery

A lyophilized polymeric wafer matrix was developed for rapid drug delivery via the oramucosal route. Lyophilization produced a porous wafer matrix that allowed simulated saliva (SS) to be rapidly absorbed into the hydrophilic structure. This surge of SS led to rapid disintegration of the wafer matrix. Hydroxypropylcellulose (HPC) was selected as the polymeric material based on its low gelatin potential. Other excipients incorporated into the system were lactose and mannitol as diluents, and glycine was utilized as a collapse inhibitor. A face-centered central composite design was employed to establish the significant effects of the independent formulation variables on the physico-chemical and physico-mechanical properties of the wafer matrix. The formulation variables investigated were, HPC concentration, diluent type and concentration, glycine concentration and fill volume. An analysis of these variables elucidated the influential factors that may be used to form an effective wafer matrix. HPC concentration significantly affected the wafer matrix disintegration rate ( P = 0.003), influx rate of SS ( P = 0.011) and wafer matrix friability ( P = 0.023). Diluent concentration had a significant effect on the wafer matrix tolerance ( P = 0.029) and wafer matrix friability ( P = 0.032). Statistical optimization was performed using constrained and artificial neural network techniques to predict ideal wafer formulation. Karl Fischer titrations revealed the reliability of the wafer matrices when small quantities of moisture were absorbed while being stored under ambient conditions.

Improved Compaction and Packing Properties of Naproxen Agglomerated Crystals Obtained by Spherical Crystallization Technique

Naproxen was crystallized from acetone-water in the presence of different concentrations of hydroxypropylcellulose (HPC). Naproxen particles recrystallized in the presence of HPC exhibited an obvious improvement in their packing, flow, and mechanical properties compared to naproxen recrystallized in the absence of the polymer (control particles). The results showed that the particle size distributions of the treated samples were broader than those obtained when HPC was absent. The agglomerates produced in the presence of 0.25% HPC displayed superior flow characteristics (displaying both a low angle of repose and Carr index) in comparison to samples produced in the presence of other concentrations of HPC. This was attributed to the spherical shape and smooth surface, since the area of contact in the powder bed for spherical agglomerates was smaller than that for other crystal shapes. However it was found that the tensile strength of tablets with the particles isolated in the presence of 1% HPC was increased to a greater extent than tablets produced using the spherical particles. Generally, the tensile strengths of the tablets increased with increasing concentrations of HPC present in the crystallization medium. Differential scanning calorimetry (DSC) and X-ray powder diffraction studies showed that naproxen particles, crystallized in the presence of HPC did not undergo structural modifications.

Experimental study of wet granulation in fluidized bed: Impact of the binder properties on the granule morphology

In this work, the effect of the physicochemical properties of aqueous hydroxypropyl-cellulose (HPC) binder solutions and different pharmaceutical excipients (mannitol and anhydrous CaHPO 4) on the agglomeration kinetics and granule properties were investigated. First, a particle size distribution (PSD) analysis together with a detailed analysis of morphological properties of the excipient particles were performed. Second, the viscosity, density, surface tension and size of the spray droplets of binder solutions with different HPC concentrations were determined and wetting characteristics of the binders on the excipients were measured. Third, several fluid bed wet granulation experiments were conducted for pure excipients and their blends with binder solution of different HPC concentrations in a pilot plant Wurster granulator. The observed granule growth for different binder concentrations was a strong function of the binder concentration and the excipient solubility. For mannitol, a significant “coating” period followed by a slow granule growth was observed for the case with the diluted 5% binder. The “coating” period was significantly shorter for the 10% HPC binder and did not exist for the 15% HPC for which immediate and fast granule growth was observed. For anhydrous CaHPO 4 (trademark A-TAB), no growth was observed for the 10% HPC binder and a long coating period followed by fast granule growth was observed for the 15% HPC. Simple physically based criteria were also evaluated, which employ the morphological properties of excipients (size and surface roughness) together with physical properties of the used binder for prediction of the coating versus agglomeration regime at given flow conditions (collision velocity). As expected, a preferential coalescence and growth of the mannitol granules from the blend of mannitol + A-TAB was observed. Finally, the mechanical and morphological properties of the produced granules were measured and correlated to the HPC concentration of the binder used in the experiments. A clear correlation between the granule porosity (evaluated by X-ray tomography) and the binder concentration was found for the mannitol granules.

Preparation of Cholesteric (Hydroxypropyl)cellulose/Polymer Networks and Ion-Mediated Control of Their Optical Properties

(Hydroxypropyl)cellulose (HPC)/vinyl polymer networks were synthesized in film form from liquid-crystalline solutions of HPC in a mixed solvent of methacrylate monomer/methanol/water (2:1:2 in weight) containing cross-linking agents, via photopolymerization of the methacrylate monomer. Di(ethylene glycol) monomethyl ether methacrylate (DEGMEM) or 2-hydroxypropyl methacrylate (HPMA) was used as the polymerizing monomer, and tetra(ethylene glycol) diacrylate and glutaraldehyde were the cross-linkers for the monomers and HPC, respectively. The polymer composite films, HPC/PDEGMEM and HPC/PHPMA, prepared at ca. 60-70 wt % concentrations of HPC in the starting solutions, were iridescently colored due to the selective light reflection, originating from the cholesteric helical arrangement carried over successively into the network system. When the cholesteric films were immersed and swollen in water containing an inorganic neutral salt, their coloration and optical turbidity varied according to a strength of 'chaotropicity' of the impregnant ions. This ionic effect may be interpreted as essentially identical with that found formerly in the coexistent salt-sort dependence of the cholesteric pitch and lower critical solution temperature for HPC aqueous solutions. It is also demonstrated that visual appearance of the swollen networks can be changed by application of an electric potential of practical magnitude between both edges of the samples of rectangular shape.

Preparation of Polypyrrole by Emulsion Polymerization Using Hydroxypropyl Cellulose

Polypyrrole with particles of uniform diameter was easily obtained from an emulsion of hydroxypropyl cellulose (HPC) and pyrrole by chemical oxidative polymerization, using iron chloride as an oxidizing agent. The particle diameter of the polypyrrole could be controlled by changing the HPC concentration, and it was found that the preparation of water-dispersible polypyrrole was possible. The conductivity of the polypyrrole particles was of the order of 10−1 S/cm.

The Gelation Mechanism of Non-Water Gel Comprising PEG

We have developed a non-water gel comprised of polyethylene glycol (PEG) and hydroxypropylcellulose (HPC) as a gelling agent. We investigated the gelation mechanism of the HPC/PEG system on the basis of a stress-controlled rheometer and an X-ray diffractometer. From these results, we found that two gelation mechanisms coexisted in the HPC/PEG system; the entanglement of interacting HPC polymer chains which behave like a flexible polymer and the cross-linking of the microcrystalline domains of the HPC main chains. In the lower HPC concentration range, the gelation is dominated by the cross-linking of the microcrystalline domains of the HPC main chains. In the higher HPC concentration range, on the other hand, the gelation is dominated by the entanglement of interacting HPC polymer chains.

Determination of surface-bound hydroxypropylcellulose (HPC) on drug particles in colloidal dispersions using size exclusion chromatography: A comparison of ELS and RI detection

Evaporative light scattering (ELS) and refractive index (RI) detection methods were evaluated for the determination of surface-bound hydroxypropylcellulose (HPC) on drug particles in colloidal dispersions. Size exclusion chromatography (SEC) was used to separate HPC from other components of the dispersions. The instrumental parameters of the ELS detector were optimized to obtain maximum peak intensity, adequate peak shape and minimal baseline noise by varying the mobile phase flow rate, nebulizer temperature, and evaporation temperature. The chromatographic method was validated using both detectors. The ELS detector response exhibited second order polynomial and linear double logarithmic correlation with concentration over a 10–300% range while the RI response was linear. The double logarithmic correlation simplified the calculation compared to using the polynomial fit, and it provided more accurate results compared to the linear fit approach. Total HPC was obtained by solubilizing all components of the dispersion and analyzing for HPC. Non-bound HPC was obtained by ultracentrifuging the dispersion and analyzing the supernatant for HPC concentration. Analysis for total- and non-bound HPC in a representative colloidal dispersion gave method precisions with R.S.D.s of 2.5 and 2.2% for ELS, and 4.5 and 2.4% for RI ( n = 4). HPC bound to the surface of the drug particles was determined by difference: % bound HPC = 100% − % non-bound HPC. Resultant % bound HPC values ranged from 22.1 to 25.4% of available HPC. Both ELS and RI are satisfactory detection techniques for HPC quantitation and for determination of the proportion of HPC bound to drug colloid particles, and the assay results are comparable.

Preparation of Hydroxypropylcellulose Membranes using Slow Ionotropic Reactions Configured in an Experimental Design

This study applied a Face-Centered Central Composite Design to prepare various hydroxypropylcellulose (HPC) membranes using slow ionotropic reactions. After the assessment of various salting-out agents, sodium carbonate was selected as the ideal electrolyte capable of inducing sufficient membrane growth. The factors studied included the concentration of hydroxypropylcellulose [HPC] (1-2%w/v), concentration of salt [Salt] (10-20%w/v) and the salting-out reaction time (SORT) (96-144 hours). The experimental and predicted responses in the design included the measurement of the Brinell Hardness Number (BHN), gel thickness, moisture absorption and membrane erosion. Surface morphological examination revealed that the membranes varied from highly porous to closely packed networks. Statistically, the experimental and predicated response values showed no significant differences (p 0.05) based on a one way ANOVA. A significant decrease in BHN was observed as the [HPC] was increased. This was attributed to an increase in the elasticity of the membrane. The increase in moisture absorption was accompanied by an increase in gel thickness and subsequently an increase in membrane erosion around the peripheral areas of the gel structure. In the case of the [Salt], all response values were reduced above 15%w/v, except in the case of the BHN. In the case of SORT, there was a substantial increase in the responses above 120 hours, except once again for BHN. Above 120 hours the matrix became loose due to extensive infiltration and crystallization of salt ions. The interactions plots indicated that the changes among the different factor levels were found to be significant (p 0.05). The average p-values for the changes between levels for each response were: BHN - p 0.035, moisture absorption - p 0.029, gel thickness - p 0.011, and erosion - p 0.042. This technology may be applicable in the development of membrane scaffolds for interconnecting tissues via their role in cell seeding, adhesion and regeneration.

Preparation and characterization of SiO 2/TiO 2 composite microspheres with microporous SiO 2 core/mesoporous TiO 2 shell

SiO 2/TiO 2 composite microspheres with microporous SiO 2 core/mesoporous TiO 2 shell structures were prepared by hydrolysis of titanium tetrabutylorthotitanate (TTBT) in the presence of microporous silica microspheres using hydroxypropyl cellulose (HPC) as a surface esterification agent and porous template, and then dried and calcined at different temperatures. The as-prepared products were characterized with differential thermal analysis and thermogravimetric (DTA/TG), scanning electron microscopy (SEM), X-ray diffraction (XRD), nitrogen adsorption. The results showed that composite particles were about 1.8 μm in diameter, and had a spherical morphology and a narrow size distribution. Uniform mesoporous titania coatings on the surfaces of microporous silica microspheres could be obtained by adjusting the HPC concentration to an optimal concentration of about 3.2 mmol L −1. The anatase and rutile phase in the SiO 2/TiO 2 composite microspheres began to form at 700 and 900 °C, respectively. At 700 °C, the specific surface area and pore volume of the SiO 2/TiO 2 composite microspheres were 552 and 0.652 mL g −1, respectively. However, at 900 °C, the specific surface area and pore volume significantly decreased due to the phase transformation from anatase to rutile.

Wavy texture in pressure-driven startup flows of liquid crystalline polymer solutions through a slit cell: effects of polymer concentration and solution temperature

Dependences of wavy texture on polymer concentration and solution temperature were examined using aqueous solutions of hydroxypropylcellulose (HPC). The phase of aqueous solution of HPC varied from an isotropic (I) system to a liquid crystalline (LC) one through a biphasic (I+LC, LC+I) system with increasing the HPC concentration and/or decreasing the solution temperature. The wavy texture emerged not only in the LC system but also in the LC+I system. Furthermore, induction time of wavy texture was evaluated in terms of apparent shear strain. It is suggested that polydomain structures included in liquid crystalline systems and droplets of isotropic phase in biphasic systems affect the initial stage of emergence of wavy texture at low shear rates.