Aqueous Solutions Of Methylcellulose Research Articles

In situ observation of gelation of methylcellulose aqueous solution with viscosity measuring instrument in the diamond anvil cell

Gelation of methylcellulose aqueous solution was investigated by a high-pressure viscosity measurement device which consisted of diamond anvil cell, microscope and CCD. And the temperature and pressure dependence of the viscosity of methylcellulose aqueous solution was measured utilizing a rolling-ball technique. The results showed that sol-gel thermal transition of methylcellulose solution occurred at the temperature of 53 °C under atmospheric pressure. Upon compression, it was indicated that the viscosity showed a dramatic change in the vicinity of the pressure of 500 MPa. Parabolic phase diagram of methylcellulose aqueous solution was constructed, and it showed that the melting point was an increasing function of pressure at the first stage and an decreasing function of pressure at the final stage. The mechanism of sol-gel transformation of methylcellulose aqueous solutions was also discussed, it might be assumed that both hydrogen and hydrophobic bonds were involved with the gel formation in the case of methylcellulose aqueous solution.

Impact-induced gelation in aqueous methylcellulose solutions.

Aqueous methylcellulose is an "abnormal" inverse-freezing fluid, which gelates when heated. We ventured to stimulate this phase-transition by mechanical impact, whose resulting shockwaves and local heat could be uptaken by the endothermic gelation. High-speed photography was used to observe this transition in microsecond timescales. This phenomenon enables attenuation of shockwaves.

Bundle formation of supramolecular fibers of amphiphilic diarylethene by depletion force.

Supramolecular nanofibers composed of the closed-ring isomer of a diarylethene formed bundles in a methylcellulose aqueous solution by depletion force while the spheres composed of the open-ring isomer were not coagulated. Upon irradiation with UV light to the suspension of the open-ring isomer, fibers were found to be generated and the formed submillimeter-sized bundles showed a photoinduced shrinking of more than 100 μm under visible light irradiation.

Preparation of Microcrystals of Piroxicam Monohydrate by Antisolvent Precipitation via Microfabricated Metallic Membranes with Ordered Pore Arrays.

Microcrystals of piroxicam (PRX) monohydrate with a narrow size distribution were prepared from acetone/PRX solutions by antisolvent crystallization via metallic membranes with ordered pore arrays. Crystallization was achieved by controlled addition of the feed solution through the membrane pores into a well-stirred antisolvent. A complete transformation of an anhydrous form I into a monohydrate form of PRX was confirmed by Raman spectroscopy and differential scanning calorimetry. The size of the crystals was 7–34 μm and was controlled by the PRX concentration in the feed solution (15–25 g L–1), antisolvent/solvent volume ratio (5–30), and type of antisolvent (Milli-Q water or 0.1–0.5 wt % aqueous solutions of hydroxypropyl methyl cellulose (HPMC), poly(vinyl alcohol) or Pluronic P-123). The smallest crystals were obtained by injecting 25 g L–1 PRX solution through a stainless-steel membrane with a pore size of 10 μm into a 0.06 wt % HPMC solution stirred at 1500 rpm using an antisolvent/solvent ratio of 20. HPMC provided better steric stabilization of microcrystals against agglomeration than poly(vinyl alcohol) and Pluronic P-123, due to hydrogen bonding interactions with PRX and water. A continuous production of large PRX monohydrate microcrystals with a volume-weighted mean diameter above 75 μm was achieved in a continuous stirred membrane crystallizer. Rapid pouring of Milli-Q water into the feed solution resulted in a mixture of highly polydispersed prism-shaped and needle-shaped crystals.

Multiple Thermal Gelation of Hydroxypropyl Methylcellulose and Kappa-Carrageenan Solutions and their Interaction with Salts

The multiple gelation behavior of aqueous solutions of kappa-carrageenan (KCG) and low molecular weight hydroxypropyl methylcellulose (HPMC) was studied with the presence of various salts. Multiple gelation behavior of aqueous solutions of HPMC/KCG/salt mixture were found. The shear viscosity of HPMC/KCG blend increased by one orders of magnitude, while the viscosity of HPMC/KCG/potassium chloride (KCl) mixture increased by three orders of magnitude as compared to HPMC solution at temperatures below apparent gelation. The dynamic elastic modulus of HPMC/KCG blend increased by two orders of magnitude, while the elastic modulus of HPMC/KCG/potassium chloride (KCl) mixture increased by three orders of magnitude as compared to HPMC solution at temperatures below apparent gelation temperature. The gel elastic modulus of the solution blend of HPMC/KCG/salt mixture decreased in the order of KCl > NaCl > CaCl2. Thermal analysis revealed a linear relationship between the depression of melting temperature and the salt concentrations, which is independent of KCG. The free water content computed by enthalpy data showed that free water content decreased with increasing salt concentrations. The secondary peak which typically associated with bound water appeared in the mixture of HPMC and KCG in the presence of KCl. As the concentrations of KCl salt increased, the bound water peak also amplified and lifted to a higher temperature.

Rheological behaviour of aqueous methylcellulose systems: Effect of concentration, temperature and presence of tragacanth

Rheology of aqueous methylcellulose (MC) solutions affected by polymer concentration, temperature, pH, ionic strength (by adding NaCl) and the presence of tragacanth (T) at different polymer ratios (MC:T, 0.25:0.75–0:75:0.25) was studied. Steady-shear and dynamic rheological measurements in a wide range of shear rates and angular frequencies, respectively, were conducted on a controlled stress rheometer. The viscosity exhibited a clear Newtonian plateau for all MC solutions dependent on polymer concentration and temperature. Mechanical spectra indicated the predominance of viscous behaviour for all MC solutions. Experimental data sets were successfully modelled using Cross-Williamson and Maxwell models, being the dependence with temperature established by Arrhenius functions. MC solutions were stable at the tested pH and ionic strengths ranges. MC-T dispersions exhibited a predominant MC effect on viscosity at low shear rates, decreasing the strong shear thinning behaviour of T samples. Cox-Merz rule was evaluated for all samples systems.

STUDY OF VISCOSITY OF AQUEOUS SOLUTIONS OF NATURAL POLYSACCHARIDES

One of the steps of synthesis of biodegradable polymers is preparation of an aqueous solution of raw materials. Formulation of biodegradable films with optimum characteristics requires to undertake a separate rheological study of each aqueous solution. An essential parameter in this step is a uniform thickness, which is achieved by means of specified viscosity parameters. Viscosity of solutions depends on many parameters, among which are composition and concentration of components in a solution, solution preparation temperature, pH of the finished medium, and presence of free ions. This article describes studies and results on study of viscosity parameters of aqueous solutions of natural polysaccharides: agar-agar, hydroxypropyl methyl cellulose and carrageenan. For aqueous solutions of carrageenan and hydroxypropyl methylcellulose, viscosity was measured at 25°C. In addition, viscosity parameters were measured for 1.5% hhydroxypropyl methylcellulose solutions at 40°C and 60°C. Depending on the gel formation temperature, viscosity of agar-agar solutions was measured at 50°C or 70°C. According to the results of experiments, it was found that viscosity of 1.0-1.5% hydroxypropyl methylcellulose aqueous solutions is in the range of 8.0-80.0 cP. Heating to 100°C at pH 6 results in irreversible destruction of hydroxypropylmethylcellulose molecules. Aqueous solutions of agar-agar are similar to hydroxypropyl methylcellulose solutions but agar-agar is able to gelate at sufficiently low concentrations (from 0.5%). Viscosity of 3.0- 5.0% carrageenan aqueous solutions varies within a wide range: 1.5-1400.0 cP. Thus, rheological properties allow to adjust viscosity of the process mixture in the production of biodegradable polymers in the desired range and in different directions.

Salting-out and salting-in effects of amphiphilic salt on cloud point of aqueous methylcellulose

Abstract Methylcellulose (MC) is one of the widely used bio-based polymers derived from cellulose. MC possesses an amphiphilic property, since it contains both the hydrophilic hydroxyl group and the hydrophobic methoxy group in its molecular structure. Due to the amphiphilicity, aqueous MC solution shows temperature-sensitive property i.e. the lower critical solution temperature (LCST) type of phase behavior. On the other hand, a special organic salt, sodium tetraphenylborate (NaBPh 4 ) also possesses an amphiphilic property, since it consists of hydrophilic cation Na + and hydrophobic anion BPh 4 − . Motivated by an interest in the combined effect of the dual amphiphilicity, here we studied the addition effects of NaBPh 4 on the cloud point of aqueous MC. When the additive amount of NaBPh 4 to aqueous MC was small, the cloud point was depressed with the amount of NaBPh 4 , namely the salting-out effect. However, when the additive amount of NaBPh 4 exceeded a certain value, the cloud point was elevated drastically with the amount of NaBPh 4 , namely the salting-in effect. We proposed a hypothesis that the switching from the salting-out to the salting-in is caused by concentration-specific binding of NaBPh 4 to MC; NaBPh 4 mostly dissociates into Na + and BPh 4 − acting as the salting-out salt when the concentration of NaBPh 4 is small, whereas the hydrophobic anions BPh 4 − are bound to the hydrophobic region of MC acting like a surfactant when the concentration of NaBPh 4 exceeds a critical value. The presence of such a concentration-specific binding of anions was confirmed by the electric conductivity measurements.

Microfluidic Fabrication of Hydrocortisone Nanocrystals Coated with Polymeric Stabilisers.

Hydrocortisone (HC) nanocrystals intended for parenteral administration of HC were produced by anti-solvent crystallisation within coaxial assemblies of pulled borosilicate glass capillaries using either co-current flow of aqueous and organic phases or counter-current flow focusing. The organic phase was composed of 7 mg/mL of HC in a 60:40 (v/v) mixture of ethanol and water and the anti-solvent was milli-Q water. The microfluidic mixers were fabricated with an orifice diameter of the inner capillary ranging from 50 µm to 400 µm and operated at the aqueous to organic phase flow rate ratio ranging from 5 to 25. The size of the nanocrystals decreased with increasing aqueous to organic flow rate ratio. The counter-current flow microfluidic mixers provided smaller nanocrystals than the co-current flow devices under the same conditions and for the same geometry, due to smaller diameter of the organic phase stream in the mixing zone. The Z-average particle size of the drug nanocrystals increased from 210–280 nm to 320–400 nm after coating the nanocrystals with 0.2 wt % aqueous solution of hydroxypropyl methylcellulose (HPMC) in a stirred vial. The differential scanning calorimetry (DSC) and X-ray powder diffraction (XRPD) analyses carried out on the dried nanocrystals stabilized with HPMC, polyvinyl pyrrolidone (PVP), and sodium lauryl sulfate (SLS) were investigated and reported. The degree of crystallinity for the processed sample was lowest for the sample stabilised with HPMC and the highest for the raw HC powder.

Thermodynamics of Aqueous Methylcellulose Solutions

The weight-average molecular weight Mw, z-average radius of gyration Rg, and second virial coefficient A2 have been determined between 15 and 52 °C for dilute aqueous solutions of methylcellulose (MC) with three different molecular weights and constant degree of substitution (DS) of 1.8 using static light scattering. These measurements, conducted within 1 h of heating the homogeneous solutions from 5 °C, reveal that the theta temperature for MC in water is Tθ = 48 ± 2 °C, with A2 Tθ, indicative of lower critical solution temperature (LCST) behavior. However, after annealing a solution for 2 days at 40 °C evidence of high molecular weight aggregates appears through massive increases in the apparent Mw and Rg, a process that continues to evolve for at least 12 days. Cryogenic transmission electron microscopy images obtained from a solution aged for 3 weeks at 40 °C reveal the presence of micron size fibrils with a diameter of 16 ± 4 nm, structurally analogous to the fibrils that form upon gelati...

Analysis of Water State and Gelation of Methylcellulose Thermo-reversible Hydrogels by Thermal Analysis and NMR.

The gelation of aqueous methylcellulose (MC) solutions containing polyethylene glycol (PEG) was studied by the combination of differential scanning calorimetry (DSC) and Raman spectrometry. The gelation of MC hydrogels containing PEG occurred in two-steps. First, the gel network was formed by the hydrophobic interaction between MC and PEG at 310 - 313 K, and then, the gel network was formed between MC chains at 323 K. On the other hand, in the MC hydrogels containing PEG and NaCl, sodium ion assumed to be enclosed by PEG, forming a helix with the hydrophobic groups outward. The sodium ion in the gel was expected to be surrounded by the ether oxygen of PEG as crown ether.

Experimental study of the effect of drag reducing agent on pressure drop and thermal efficiency of an air cooler

Effect of polymeric drag reduction agents (DRAs) on pressure drop and heat transfer was studied. Aqueous solutions of carboxy methyl cellulose were used inside an air-finned heat exchanger. Despite the previous studies which indicated the importance of drag reduction just in turbulent flow, results of this study in laminar flow indicated that the addition of DRA increases drag reduction, and decreases the overall heat transfer coefficient.

Properties of composite films of methylcellulose with arabinogalactan

The stress-strain properties of composite films obtained from aqueous solutions of methylcellulose with arabinogalactan are studied. The structural organization and thermal stability are investigated via X-ray diffraction, dynamic mechanical analysis, differential scanning calorimetry, and thermogravimetric analysis. The compositions for which the polysaccharides are compatible in the solid state are found.

Cellulose photonic crystal film sensor for alcohols

A novel photonic crystal sensor, a cellulose film with a three dimensional (3D) colloidal array embedded inside, was fabricated by infiltrating the voids of a 3D poly methyl methacrylate (PMMA) colloidal array with methyl cellulose aqueous solution, followed by thermal curing. When the obtained cellulose photonic crystal film sensor (CPCFS) was immersed in alcohols, including ethanol, n-propanol, isopropanol and n-butanol, its lattice constant and mean effective refractive index increased, which led to the redshift of the reflection of incident light. The redshift of this sensor had linear response to the concentration of alcohol vapors, while its structural color changed from blue to green visually. This CPCFS demonstrates promising potential as an on-site monitoring sensor for alcohols and an inexpensive and minimally invasive breathalyzer in the future.

In Situ Observations of Thermoreversible Gelation and Phase Separation of Agarose and Methylcellulose Solutions under High Pressure.

Thermoreversible sol-gel transitions of agarose and methylcellulose (MC) aqueous solutions on isobaric cooling or heating under high pressure up to 400 MPa have been investigated by in situ observations of optical transmittance and falling-ball experiments. For agarose, which undergoes the gelation on cooling, the application of pressure caused a gradual rise in the cloud-point temperature over the whole pressure range examined, which is almost consistent with the pressure dependence of gelling temperature estimated by falling-ball experiments, suggesting that agarose gel is stabilized by compression and that the gelation occurs nearly in parallel with phase separation under ambient and high-pressure conditions. For MC, which undergoes the gelation on heating, the cloud-point temperature showed a slight rise with an initial elevation of pressure up to ∼150 MPa, whereas it showed a marked depression above 200 MPa. In contrast, the gelling temperature of MC, which is nearly identical to the cloud-point temperature at ambient pressure, showed a monotonous rise with increasing pressure up to 350 MPa, which means that MC undergoes phase separation prior to gelation on heating under high pressure above 200 MPa. Similar results were obtained for the melting process of MC gel on cooling. The unique behavior of the sol-gel transition of MC under high pressure has been interpreted in terms of the destruction of hydrophobic hydration by compression.

Flow patterns of liquid–liquid two-phase flow in non-Newtonian fluids in rectangular microchannels

This paper presents an experimental investigation on the flow patterns of Newtonian/non-Newtonian fluids two-phase flow in T-shaped rectangular microchannels by using a high-speed camera. Three different dimensions of microchannels are employed with 400μm×400μm, 400μm×600μm, 400μm×800μm in depth and width, respectively. The cyclohexane is used as the dispersed phase, and various concentrations of carboxyl methyl cellulose (CMC) aqueous solutions as the continuous phase. Results show that slug flow, droplet flow, parallel flow and jet flow are the main flow patterns for cyclohexane-CMC two-phase flow in rectangular microchannels. The larger the concentration of CMC solutions and the smaller the size of the microchannels are, the wider of the regimes are for the droplet flow and parallel flow. A model is proposed to predict the transitions between adjacent flow regimes for liquid–liquid two-phase flow in non-Newtonian fluids in rectangular microchannels.

Chitosan and Cystatin/Lysozyme Preparation as Protective Edible Films Components

This work characterizes biological, physical, and chemical properties of films formed from an aqueous solution of hydroxypropyl methylcellulose (HPMC), with different concentrations of chitosan (CH) and bioactive cystatin/lysozyme preparation (C/L). The properties of biocomposites were examined by Dynamic Mechanical Analysis (DMA), Fourier’s transfer infrared spectroscopy (FTIR), water vapour permeability (WVP), and tensile testing. Antimicrobial activity againstMicrococcus flavus,Bacillus cereus,Escherichia coli,Pseudomonas fluorescens, andCandida famatawas conducted. Films glass transition and storage modulus were dependent on the C/L and CH concentration. Modulus values decreased during the temperature scan and with higher reagents levels. An increase of CH and C/L concentrations in the films resulted in a decrease in tensile strength from 2.62 to 1.08 MPa. It suggests the hydrolyzing influence of C/L, also observed in smaller peak size ofαrelaxation. C/L addition caused shiftingTgto higher temperature. DMA and FTIR analysis proved that HPMC and CH are compatible polymers. Water resistance was improved with rising CH concentration from1.08E-09to7.71E−10 g/m∗s∗Pa. The highest inhibition zone inM. flavusandC. famatawas recorded at the highest concentration of CH and C/L.

Experimental and CFD investigation of convective heat transfer in helically coiled tube heat exchanger

Experimental studies on isothermal steady state and non-isothermal unsteady state conditions were carried out in helical coils for Newtonian as well as for non-Newtonian fluids. Water and glycerol–water mixture (10 and 20% glycerol) were used as Newtonian, and 0.5–1% (w/w) dilute aqueous polymer solutions of Sodium Carboxy Methyl Cellulose (SCMC) and Sodium Alginate (SA) as non-Newtonian fluids are used in this study. These experiments were performed for coil curvature ratios as δ=0.0757, 0.064 and 0.055 in laminar and turbulent flow regimes (total 258 tests). The CFD analyses for laminar and turbulent flow were carried out using FLUENT 12.0.16 solver of CFD package. The CFD calculation results (Nui, U, T2 and Two) for laminar and turbulent flow are compared with the experimental results and the work of earlier investigators which were found to be in good agreement. For the first time, an innovative approach of correlating Nusselt number to dimensionless number, ‘M’, Prandtl number and coil curvature ratio using least-squares power law fit is presented in this paper which is not available in the literature. Several other correlations for calculation of Nusselt number for Newtonian and non-Newtonian fluids, and two correlations for friction factor in non-Newtonian fluids (based on 78 tests and 138 tests) are proposed. These developed correlations were compared with the work of earlier investigators and are found to be in good agreement.

In situ observation of heat- and pressure-induced gelation of methylcellulose by fluorescence measurement

In situ observation of heat- and pressure-induced gelation of methylcellulose (MC) aqueous solution has been studied by using dynamic viscoelastic and fluorescence measurements. The storage modulus G′ decreased gradually first on heating, and then leveled off in the temperature range from 25°C to 75°C. Methylcellulose solutions were subjected to pressures up to 450MPa by using a high pressure cell. It was indicated that the microviscosity showed a dramatic change in the vicinity of the phase transition point. The T vs. P phase diagram of methylcellulose aqueous solution was constructed, and it indicated that the melting point was an increasing function of pressure. In situ microscopic observation of pressure-induced gelation of methylcellulose aqueous solution was also performed with a microscope, and it could be seen that gel phase of the sample disappeared and sol formed gradually. Pressure-released study by fluorescence measurement also showed that the phase transition of MC solution was reversible.

Evidence for the Coexistence of Interpenetrating Permanent and Transient Networks of Hydroxypropyl Methyl Cellulose

Dynamic mechanical properties of aqueous solutions of hydroxypropyl methyl cellulose (HPMC) were investigated using oscillatory shear measurements. The structure was investigated with light scattering. A systematic investigation of the frequency dependence of the shear moduli showed that HPMC forms two distinct interpenetrating networks. A transient network is formed above about 0.3 wt % by reversible cross-linking of the chains. The elastic modulus of this network is independent of the temperature, but increases linearly with the concentration. An independent permanent network is formed involving a small fraction of the polymers and has an elastic modulus that increases with increasing temperature. Its elastic modulus is history dependent and evolves slowly with time. The transient network collapses at a critical temperature where micro phase separation occurs, but the permanent network is not influenced by this phenomenon. Light scattering showed that the pore size of the transient network is less than 40 nm, while probe diffusion measurements showed that the pore size of the permanent network is larger than 1 μm.