Hydroxypropyl Cellulose Polymer Research Articles

Role of surface-purity in photocatalytic activity of nanocrystalline anatase–titania processed via polymer-modified sol–gel

Nanocrystalline titania powders have been synthesized via conventional and modified sol–gel using an alkoxide precursor for different R, the ratio of molar concentration of water to that of alkoxide precursor, and calcination temperature. The apparent first-order reaction rate-constant obtained for the powder synthesized via conventional sol–gel is comparable with that of commercial Degussa-P25. Conventional sol–gel has been modified using the hydroxypropyl cellulose polymer to increase the specific surface area of the photocatalyst; and hence, to further enhance its photocatalytic activity. Although higher specific surface area and smaller average nanocrystallite size have been obtained for the powders synthesized via modified sol–gel, they exhibit reduced photocatalytic activity relative to that of powders synthesized via conventional sol–gel. The deactivation of the present photocatalyst has been explained on the basis of reduced surface-purity of the powders after processing via modified sol–gel as induced by the presence of surface-residual organic compounds.

How we can interpret the T1 dispersion of MC, HPMC and HPC polymers above glass temperature?

The chain dynamics in methyl cellulose (MC), hydroxypropylmethyl cellulose (HPMC) and hydroxypropyl cellulose (HPC) were studied with the aid of field-cycling NMR relaxometry technique in the temperature range from 300 to 480 K that is above the glass transition, but below thermal degradation. The frequency dependence of proton spin-lattice relaxation time was determined between 24 kHz and 40 MHz for selected temperatures. The experimental spin-lattice relaxation dispersion data were fitted with the power law relations of T 1 ∝ ω γ predicted by the tube/reptation model. The exponent's values found from the fitting procedure for MC, HPMC and HPC almost exactly match the ones predicted in tube/reptation model for limit II ( γ = 0.75 ) and in MC also for limit III ( γ = 0.50 ). Remarkably, this finding concerns the polymers in networks formed of the same polymer species.

Temperature Stability and Bioadhesive Properties of Δ9-Tetrahydrocannabinol Incorporated Hydroxypropylcellulose Polymer Matrix Systems

ABSTRACTThe purpose of this study was to determine and compare the bioadhesive profiles of hydroxypropylcellulose (HPC) polymer matrices as a function of Δ9-tetrahydrocannabinol (THC) content. In addition, the effect of processing temperature on the stability of THC and its extent of degradation to cannabinol (CBN) was investigated. A hot-melt cast molding method was used to prepare HPC polymer matrix systems incorporated with THC at 0, 4, 8, and 16 percent. Bioadhesive measurements including peak adhesive force, area under the curve, and elongation at adhesive failure were recorded utilizing the TA.XT2i Texture Analyzer™. Data obtained from these tests at various contact time intervals suggested that the incorporation of THC led to an increase in the bioadhesive strength of the HPC polymer matrices. To determine the stability of THC and the resulting CBN content in the matrices, three different processing temperatures were utilized (120, 160, and 200°C). Post-production High Performance Liquid Chromotography (HPLC) analysis revealed that the processed systems contained at least 94% of THC and the relative percent formation of CBN was 0.5% at 120°C and 0.4% at 160°C compared to 1.6% at 200°C. These findings indicate that the cannabinoid may be a plausible candidate for incorporation into systems utilizing hot-melt extrusion techniques for the development of an effective mucoadhesive transmucosal matrix system for delivery of THC.

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.

The effect of the solvent on the film-forming parameters of hydroxypropyl-cellulose

In pharmaceutical technology, film-forming agents are often applied in solution during the preparation of solid dosage forms. A wide range of polymers have already been examined, but many of the effects of the applied solvent on the properties of the film are still not fully known. The study of these phenomena might be of great help in the preparation of better films. In the present study, the frequently used polymer hydroxypropyl-cellulose was examined in water and ethanol. The latter solvent exhibits better wetting properties for this polymer. It was found that the use of ethanol enhanced the processibility because of the easier atomization and the shorter drying period. Properties characteristic of the chemical nature (wetting, surface free energy and thermal properties) and the physical behaviour (deformation process) of the poured films were studied. Relevant differences were detected only in the mechanical parameters. The sizes of the free volume holes in the differently prepared polymers were also determined, but this parameter proved irrelevant as concerns alterations of the breaking process. The explanation of the differences processibility of the films might be the different strengths of binding between the macromolecular chains. This phenomenon can also explain the different degrees of hydration of the polymer and the changes in the drying process.

Dielectric Relaxation in Cellulose and its Derivatives

The relaxation processes in cellulose, methyl cellulose, hydroxypropyl cellulose, and hydroxypropylmethyl cellulose were studied by dielectric spectroscopy. The dielectric spectra for these polysaccharides were measured in the frequency range from 100 Hz to 1 MHz and in the temperature range from 100 to 450 K. The dielectric relaxation data for cellulose, methyl cellulose, hydroxypropylmethyl cellulose were described by Arrhenius and Eyring equations and interpreted as due to a local motion of chain segments via the glucosidic linkages, so-called fl-relaxation. The same relaxation process was also determined for the hydroxypropyl cellulose polymer in the temperature range of 240{270 K. At higher temperature in hydroxypropyl cellulose another relaxation mechanism occurs due to the reorientation of the side chain built of a few hydroxypropylene groups. The activation parameters of the observed dielectric relaxation processes were determined.

Hydration Forces Underlie the Exclusion of Salts and of Neutral Polar Solutes from Hydroxypropylcellulose

The distance dependence for the preferential exclusion of several salts and neutral solutes from hydroxypropyl cellulose (HPC) has been measured via the effect of these small molecules on the thermodynamic forces between HPC polymers in ordered arrays. The concentration of salts and neutral solutes decreases exponentially as the spacing between apposing nonpolar HPC surfaces decreases. For all solutes, the spatial decay lengths of this exclusion are remarkably similar to those observed between many macromolecules at close spacings where intermolecular forces have been ascribed to the energetics of water structuring. Exclusion magnitudes depend strongly on the nature and size of the particular salt or solute; for the three potassium salts studied, exclusion follows the anionic Hofmeister series. The change in the number of excess waters associated with HPC polymers is independent of solute concentration suggesting that the dominating interactions are between solutes and the hydrated polymer. These findings further confirm the importance of solvation interactions and reveal an unexpected unity of Hofmeister effects, preferential hydration, and hydration forces.

Characterization of cellulosic hot-melt extruded films containing lidocaine

Hot-melt extrusion technology was used to produce thin films containing a model drug, lidocaine, and the cellulosic polymers hydroxypropyl cellulose (HPC) and hydroxypropyl methyl cellulose (HPMC). Two film formulations were extruded and compared, one containing only HPC and the other containing HPC:HPMC (80:20). Thermal analysis of the films using differential scanning calorimetry (DSC) suggested that the drug existed in the amorphous condition, which was confirmed by wide angle X-ray diffractometry. Sustained release of the drug was observed from both of the polymer matrices. Dissolution profiles suggested that HPMC retarded the drug release from HPC:HPMC (80:20) films. However, the mechanism of drug release from both of the films was predominantly diffusion of the drug through the polymer matrices. Incorporation of HPMC also increased both adhesive strength and work of adhesion as compared to the HPC-only films.

Formation and Volume Phase Transition of Hydroxypropyl Cellulose Microgels in Salt Solution

Surfactant-free hydroxypropyl cellulose (HPC) microgels have been synthesized in salt solution. The average size and size distributions of microgel particles have been correlated with polymer concentration, salt concentration, and reaction temperature using light scattering techniques. It is found that the low critical solution temperature of HPC polymer chains decreases upon the increase of sodium chloride concentration. In a narrow sodium chloride concentration range from 1.3 to 1.4 M, HPC chains can self-associate into colloidal particles at room temperature. These particles remained stable in solution for weeks without changing their sizes. The microgel particles were then obtained in situ by bonding self-associated HPC chains at 23 °C using divinyl sulfone as a cross-linker. The volume phase transition of the resultant HPC microgels has been studied as a function of temperature at various salt concentrations. A theoretical model based on Flory−Huggins free energy consideration has been used to explai...

Sol-Gel Synthesis and Phase Evolution Behavior of Sterically Stabilized Nanocrystalline Zirconia

Nanocrystalline as well as submicron sized, non-agglomerated, spherical ZrO2 particles have been successfully synthesized using the sol-gel technique utilizing hydroxypropyl cellulose (HPC) as a polymeric steric stabilizer. The effect of various parameters such as the ratio of molar concentration of water and alkoxide (R), the molar concentration [HPC] and the molecular weight (MWHPC) of HPC polymer as well as the calcination temperature on ZrO2 nanocrystallites size and their phase evolution behavior is systematically studied. The phase evolution behavior of nanocrystalline ZrO2 is explained and correlated with the adsorption behavior of HPC polymer on ZrO2 nanoparticles surface, which is observed to be a function of R, [HPC], MWHPC and the calcination temperature. Optimum synthesis parameters for obtaining 100% tetragonal phase in nanocrystalline ZrO2 are identified for the present sol-gel method of synthesizing nanoparticles.

Effect of HPC and water concentration on the evolution of size, aggregation and crystallization of sol-gel nano zirconia

Nano-sized zirconia (ZrO2) powder is synthesized using sol-gel technique involving hydrolysis and condensation of zirconium(IV) n-propoxide in an alcohol solution, utilizing hydroxypropyl cellulose (HPC) polymer as a steric stabilizer. It is demonstrated that ZrO2 nanoparticle size can be reduced using high R-value (defined as the ratio of molar concentrations of water and alkoxide). It is also shown that ZrO2 nanoparticle size can be reduced further by synthesizing these particles in the presence of HPC polymer. The agglomeration tendency of ZrO2 nanoparticles is demonstrated to decrease due to the steric hindrance created by the adsorbed polymer. The nanocrystallite size and their 'hard-aggregates' formation tendency are observed to affect the high temperature metastable tetragonal phase stabilization at room temperature within ZrO2 particles.

Induction of Chirality in a Cationic Surfactant Nematic Phase by Hydroxypropylcellulose

Addition of the water-soluble chiral polymer hydroxypropylcellulose (HPC) to a cationic nematic lyotropic phase induces cholesteric behavior. In this work, thirteen different well-characterized samples of HPC of known molecular weight and polydispersity were added to an N D phase consisting of myristyltrimethylammonium bromide, 1-decanol, ammonium bromide, and water, and the fingerprint texture of the cholesteric phase was utilized to determine the helical twisting powers (HTPs) of the solutes. Samples with molecular weights ranging from 12,000 to 140,000 were soluble in the concentrated surfactant system. Above molecular weight 140,000 phase separation was observed. The HTP of HPC was found to be independent of both molecular weight and molecular weight distribution of the chiral polymer with a value of 11±1 (µm wt fraction) −1 . HTP appears to depend only on the number density of chiral units in the phase and not on the polymer chain length.

Measurement of Forces between Hydroxypropylcellulose Polymers: Temperature Favored Assembly and Salt Exclusion

The thermodynamic forces between hydroxypropylcellulose (HPC) molecules at close separation have been measured using the osmotic stress method coupled with X-ray scattering. Two force regimes are apparent: a very short ranged, temperature insensitive force that dominates interactions within the last 2.5 Å separation and a longer-ranged force that varies exponentially vs distance with a decay length of about 3−4 Å. The longer-ranged force characteristics are strikingly similar to those found for many other macromolecules. We have previously argued that these characteristics are due to a hydration or water structuring force. The amplitude of the longer ranged force in these condensed arrays decreases linearly with temperature. The force switches from repulsive to attractive at ∼40 °C, about the same temperature at which HPC precipitates from dilute solution. The entropy of the HPC condensed array, derived from the temperature dependence of the force, also varies exponentially vs spacing with a 3−4 Å decay length. Measured forces are also surprisingly sensitive to added salt. Salt acts by its exclusion from the HPC phase. The salt concentration gradient within the space between polymers, inferred from the salt concentration dependence of the force curves, is itself apparently exponential with the about same 3−4 Å decay length as the force and entropy.

The Effects of Formulation Factors on the Moist Granulation Technique for Controlled-Release Tablets

Controlled-release tablets were prepared by the moist granulation technique (MGT), a granulating method that uses very limited amounts of liquid and requires microcrystalline cellulose (MCC) to absorb moisture. Acetaminophen (APAP) was the model drug, and the polymer hydroxypropylcellulose (HPC) served as the controlled-release agent. The effects of varying drug, binder (polyvinylpyrrolidone, PVP), polymer, and MCC levels on granule properties and tablet dissolution were studied. Dissolution testing was carried out in distilled water using the USP paddle method. In all cases, the granules flowed and compressed well. The granule properties were evaluated by calculating the mean particle size for all batches from sieve analysis data. The results indicate that MGT can be applied to control drug release, and at a polymer content of 44.6% or more, the process is robust enough to allow slight variations in formulation factors without affecting drug release.

Synthesis and Light Scattering Study of Hydroxypropyl Cellulose Microgels

The thermally responsive hydroxypropyl cellulose (HPC) microgels have been synthesized and characterized. The microgel particles were obtained by chemically cross-linking collapsed HPC polymer chains in water−surfactant (dodecyltrimethylammonium bromide) dispersion above the lower critical solution temperature of the HPC. The size distributions of microgel particles, measured by dynamic light scattering, have been correlated with synthesis conditions including surfactant concentration, polymer concentration, and reaction temperature. The final microgel size is determined by the balance between the hydrophobic interaction among HPC polymer chains and intermicelle electrostatic repulsion. The swelling and phase transition properties of resultant HPC microgels have been analyzed using both static and dynamic light scattering techniques as a function of temperature and cross-linker concentration. It is found that the increase in the cross-linker concentration reduces the shrinkage extent. The dilute HPC microgel particles (C < 1.0 × 10-5 g/mL) form a stable colloidal dispersion at room temperature and at 44 °C (above the volume phase transition temperature), probably due to steric effects. Adding salt to water leads to a decrease of the volume phase transition temperature of HPC microgels.

Preparation of spray-dried microspheres of indomethacin and examination of the effects of coating on dissolution rates

In this study, microspheres were prepared by the spray drying technique using suspensions of indomethacin (IM) as active substance and coated by three different polymers in order to increase the dissolution rate of IM. Water solutions (0.1, 0.2 and 0.5%) of hydroxypropylmethyl cellulose (HPMC), polyvinyl alcohol (PVA) and hydroxypropyl cellulose (HPC) were used as coating materials. Polyethylene glycol 400 (PEG 400) was added to all formulations as plasticizer. Changes of particles size and surface characteristics of the coated products were examined using optical microscopy and scanning electron microscopy (SEM), respectively. The effects of coatings on the dissolution rates of IM were examined using USP XXIII Method II in water and phosphate buffer pH 7.4. It was observed that coating the IM particles with HPMC, PVA and HPC polymers using the Spray-Drying Technique increased the dissolution rate of IM significantly.

Gas separation by networks made from supramolecular complexes of metal phthalocyanines and a cellulose derivative

Soluble metal phthalocyanines, e.g. PcFe(OCH 2CF 3) 4 form supramolecular complexes with a cyanoethylated hydroxypropylcellulose polymer (AHC) with nitrile groups on flexible spacers. Composite membranes made from these complexes enrich O 2 or CO 2 from a mixture with N 2 or CH 4, respectively. The complexation is concluded from spectroscopic observations and from differences in membrane properties. The surface structure of the membranes was investigated by AFM. Optimal selectivity and permeability were found with membranes containing phthalocyanines with bulky substituents on the macrocycle and metal ions, which are able to coordinate with the nitrile groups of the polymer. Some fluorinated substituents gave high permeate fluxes. Optimal selectivity values found were 3.5 for α O 2/N 2 and 18 for α CO 2/N 2 . For the feed CH 4/CO 2 swelling effects were observed.

Characterization of nanophase titania particles synthesized using in situ steric stabilization

Ultrafine titania particles were synthesized from titanium tetraethoxide (TEOT) dissolved in ethanol. The concentration of water and of the soluble polymer hydroxypropylcellulose (HPC) were varied to control particle size. The HPC adsorbed onto the titania particles during growth, providing a steric barrier to aggregation. Electron microscopy showed that particles smaller than 70 nm were formed at high water concentrations (R &gt; 120 where R is the molar ratio [H2O]/[TEOT]) and in the presence of HPC. The annealing-induced, phase-transformation behavior of these particles (amorphous → anatase → rutile) from 100 to 1000 °C was characterized by x-ray, Raman, and infrared techniques. The conversion of anatase to rutile occurred more readily for particles made at high water concentrations and with HPC. For particles formed by premixing TEOT with HPC prior to hydrolysis at R = 155, an 800 °C anneal yielded a rutile fraction exceeding 95%; particles made at R = 5.5 with no HPC showed negligible conversion at this temperature.

Development of topical drug delivery systems utilizing polymeric materials

Topical drug delivery is important from the view points of improvement of therapeutic effect and reduction of systemic side effects. Utilization of polymeric materials seemed to be as a key for the development of new topical dosage forms including targeting drug delivery systems. Adriamycin ointment for local chemotherapy to breast cancer prepared using polyethylene glycol, ammonium polyacrylate and hydroxypropyl cellulose (HPC) according to an optimum formulation showed an excellent clinical effect in spite of a decreased drug content. Double-layered mucoadhesive sticks for the treatment of uterine cervix cancer were prepared by direct compression of powder mixture of bleomycin, HPC and carboxyvinyl polymer (CP). Drug release property of the sticks could be controlled by the weight of outer layer, drug combining ratio to each layer and coating of core layer. The results suggested a possibility of a "once-a-week" treatment that is preferable for the patients. Magnetic granules for the treatment of esophageal cancer were prepared using ferrite, HPC and CP. Magnetic guidance and retainment of the granules on esophageal mucosa were confirmed using rabbits in vivo. Buoyant sustained release preparations were prepared using chitosan, soybean protein, HPC and other polymers. Usefulness of the buoyant preparations was suggested from the results in vitro and in vivo. Insulin microspheres (IMS) for targeting delivery to the small intestine were prepared by the newly developed method. Employment of enteric coating material (Eudragit) and combination of protease inhibitor protected insulin from enzymatic attack and gave decreased levels of blood glucose by oral administration.

Coagulation kinetics of amorphous colloidal silica suspensions with and without hydroxypropyl cellulose polymer

The coagulation rate constant of submicron silica has been measured as a function of solution pH, salt concentration and hydroxypropyl cellulose (HPC) polymer concentration. Results show that the colloidal stability of silica is dominated by the cation concentration in the presence of salt in the pH range 3–9.5. The stability increases as cation concentration decreases. At low salt concentration and a minimum colloid stability was found in the intermediate pH range 4–8. These results show that differences in the literature values of the critical coagulation constant by relative light-scattering experiments can be explained by the use of the coagulation rate constant analysis. When HPC polymer was present in the solution, the colloid stability of the silica increased. The adsorption of polymer stabilizes the silica suspensions, both at low pH near the isoelectric point and at high ionic strength where it coagulates without the polymer. A monolayer coverage was necessary to provide steric stabilization. At 10−3 M KCl a smaller equilibrium concentration of HPC in solution is needed to give monolayer coverage and steric stabilization than at 1 M KCl and pH 4.2.