Steady-shear rheology of concentrated chitosan solutions

The rheological properties of 0.5 - 2.0% (wt/wt) chitosan solutions in steady-shear were investigated as a function of temperature (25C - 45C), acid type (acetic, lactic, and hydrochloric), and ionic strength (0 and 0.2 M NaCl) to determine their flow behavior. Viscosity and normal forces have been determined over a wide range of shear rates and the results are presented using appropriate master curves for the temperature and concentration effects. For the experimental conditions studied, chitosan solutions behaved like non-Newtonian viscoelastic shear-thinning fluids. They show a low-shear rate Newtonian plateau and a high-shear rate non-Newtonian region. All material functions (viscosity and primary normal stress) decrease with an increase in temperature and a decrease in chitosan concentration. The most important parameter affecting the rheology of the solutions has been found to be salt addition, particularly for chitosans dissolved in weak acids where electrostatic effects are believed to be important

Immobilization of Enzymes into a Polyionic Hydrogel: ChitoXan

hree enzymes were immobilized onto polyionic hydrogel, ChitoXan, obtained by complexation between chitosan and xanthan. The biocatalysts used were two proteases (protease type XIX from Fungal d’Aspergillus sojae and the trypsin type II.S from Porcine Pancreas) and a lipase (lipase Type VII from Candida rugosa). The immobilization efficiencies and the relative activities were investigated for these enzymes. The immobilization efficiencies changed with each enzyme and varied between 53 and 80%. Good relative activities were found for the lipase Type VII from Candida rugosa and the protease type XIX from Fungal d’Aspergillus sojae. For the latter, the influence of several factors were studied: molarity of the storage buffer, storage temperature and time of hydrogel, and the enzyme concentration. For the immobilized lipase, hydrolysis of olive oil in aqueous and organic media has been compared. This study confirmed that the lipase modified the external and internal structure of the hydrogel from fibrillar to the formation of globular structures in the presence of lipases

Steady-shear rheology of concentrated chitosan solutions

The rheological properties of 0.5 - 2.0% (wt/wt) chitosan solutions in steady-shear were investigated as a function of temperature (25C - 45C), acid type (acetic, lactic, and hydrochloric), and ionic strength (0 and 0.2 M NaCl) to determine their flow behavior. Viscosity and normal forces have been determined over a wide range of shear rates and the results are presented using appropriate master curves for the temperature and concentration effects. For the experimental conditions studied, chitosan solutions behaved like non-Newtonian viscoelastic shear-thinning fluids. They show a low-shear rate Newtonian plateau and a high-shear rate non-Newtonian region. All material functions (viscosity and primary normal stress) decrease with an increase in temperature and a decrease in chitosan concentration. The most important parameter affecting the rheology of the solutions has been found to be salt addition, particularly for chitosans dissolved in weak acids where electrostatic effects are believed to be important

Dynamic rheological properties of concentrated chitosan soltions

A detailed analysis of the dynamic flow properties of chitosan in solution at different temperatures (25 - 45°C), chitosan concentration (0.5% - 2.0%), solvent type (acetic, lactic, and hydrochloric acid), and ionic strength (0 and 0.2M NaCl) has been undertaken. The storage modulus, G', loss modulus, G" and complex viscosity, ?* have been determined over a wide range of frequencies and the results are presented using master curves. For the conditions studied, at low frequencies chitosan solutions show a constant complex viscosity which decreases as frequency increases. Likewise, storage modulus, G' and loss modulus, G" increase as frequency increases with G" being always greater than G'(?' > ?") indicating that viscous effects are more important than elastic effects. For modelling the oscillatory-shear results we used the generalized Maxwell model. Two empirical equations were used to correlate the data: Cox-Merz rule for viscosity and Laun's rule for primary normal stress difference. Both relations were found to represent our data for the experimental conditions studied. Zapotitlán Appl. Rheol. 14 (2004)

Viscoelastic properties of dispersed chitosan/xanthan hydrogels

In this work a gel was formed by complexation of two natural polyelectrolytes, chitosan and xanthan. Changes in the hydrogels rheological properties have been studied in terms of hydrogel concentration (7-10% w/w), chemical media used for the hydrogel dispersion, and 'test lag time'; i.e., the time between hydrogel dispersion in the chemical media and the start of the rheological test (up to 390 min). The viscoelastic properties of this polysaccharide system were characterized by oscillatory shear measurements under small-deformation conditions and the results show that chitosan/xanthan hydrogels behave like weak gels. The shear modulus increased almost linearly with frequency in the range studied (0.1-65 s-1). The effects of hydrogel concentration and dispersion medium have been related to electrostatic equilibrium and by the presence of counter-ions modifying the internal structure of the hydrogel. © 2006 Elsevier Ltd. All rights reserved

Dynamic rheological properties of concentrated chitosan soltions

A detailed analysis of the dynamic flow properties of chitosan in solution at different temperatures (25 - 45°C), chitosan concentration (0.5% - 2.0%), solvent type (acetic, lactic, and hydrochloric acid), and ionic strength (0 and 0.2M NaCl) has been undertaken. The storage modulus, G', loss modulus, G" and complex viscosity, η* have been determined over a wide range of frequencies and the results are presented using master curves. For the conditions studied, at low frequencies chitosan solutions show a constant complex viscosity which decreases as frequency increases. Likewise, storage modulus, G' and loss modulus, G" increase as frequency increases with G" being always greater than G'(η' > η") indicating that viscous effects are more important than elastic effects. For modelling the oscillatory-shear results we used the generalized Maxwell model. Two empirical equations were used to correlate the data: Cox-Merz rule for viscosity and Laun's rule for primary normal stress difference. Both relations were found to represent our data for the experimental conditions studied. © Appl. Rheol. 14 (2004)

Stability Patterns of Methoxy Phenols under Alkaline Hydrolysis Conditions

this paper is to examine the stability of methoxy phenols under standard lignin alkaline hydrolysis conditions. We are attempting to improve our understanding of the chemistry involved in the degradation of methoxy phenols by identifying the products formed and measuring the kinetics of the degradation reactions. By improving our understanding we hope to learn how to increase the yields of desirable phenolic products from lignin. Reactions were performed in a 75 mL stainless steel reaction vessel. A leak test was performed using N 2 at 1800 psi, thus removing air. The reaction vessel was heated in a fluidized sand bath maintained approximately 10 C above the desired reaction temperature. A thermocouple inside the vessel was used to measure the reaction temperature. A pressure transducer was used to monitor the reaction pressure. After the desired reaction time the vessel was removed from the sand bath and quenched in an ice-water bath. The heat up and cool down of the reactor was recorded so that their contribution to the reaction severity could be included. The reaction products were initially analyzed by high-pressure liquid chromatography (HPLC) on a reversed-phase C18 column. Samples were prepared for analysis by acidifying with sulfuric acid and then diluting 1 ml to 25 ml with 50% methanol. Products and starting compounds were identified by comparison with the UV spectra and retention times of pure compounds. The products and starting compounds were quantified using external standard calibration. The formation of polymeric products was determined using gel permeation chromatography (GPC). Three columns (30 x 0.8 cm each, Polymer Laboratories PL-Gel) each containing styrene-divinyl benzene copolymer gel beads (10 m diameter) with nominal pore diameters of 10 4 ..