Particulate rheology and acid-induced gelation of oxidised cellulose (original) (raw)

Influence of aqueous medium on viscoelastic properties of carboxymethylcellulose sodium, hydroxypropyimethyl cellulose, and thermally pre-gelatinized starch gels

Colloids and Surfaces A: Physicochemical and Engineering Aspects, 1999

Neutral and semi-synthetic hydrophilic polymers are widely used in pharmaceutical technology to formulate controlled release drug delivery systems. The behaviour of the gel layer, formed around the hydrophilic matrices after water uptake, is of major importance for the drug release profiles. Rheological properties are related to the gel structure, interchain interactions and entanglements, and erosion and drug diffusion processes. Oscillatory test parameters were observed for highly concentrated Na carboxymethyl cellulose (NaCMC ), hydroxypropylmethyl cellulose (HPMC ), and thermally pre-gelatinized starch hydrogels obtained by the swelling of matrix tablets in a 0.1 mol/dm3 HCl solution (pH 1.0) and a pH 6.8 phosphate buffer. The gel concentration range was 18-30% (w/w). The storage (G∞) and the loss (G◊) moduli, as well as the tangent of the phase angle (d), were obtained under dynamic conditions of non-destructive oscillatory tests, in the frequence range 0.01-4.0 Hz. The pH and the ion type of the environment exert an influence on both the elastic and viscous behaviour of the NaCMC gels. The viscous character of the polyelectrolyte gel is pronounced in the phosphate buffer, while the elastic nature is dominating in the acid medium, as a result of the polymer neutralization. The sensitivity of neutral HPMC gels to pH changes is insignificant. No considerable differences of the functional parameters G∞, G◊ and tan d, depending on the ionic strength, have been found. The visco-elastic behaviour of the pre-gelatinized starch gels is very similar to those of the neutralized NaCMC, regardless of the media used. This type of gel structure may determine a general kinetic pattern of drug release.

Design of Rheological Measurements for Rapidly Gelling Polysaccharides on Exposure to External Cross-Linkers

2018

This research project focused on a range of gel forming polysaccharides, including sodium alginate pectin and gellan gum. All of these materials have ability to form a gel responding to different stimuli, such as pH and crosslinking ions. Their capability to undergo sol-gel transition in presence of mono or divalent cations can often occur in seconds making it particularly difficult to measure the gelation in real time. Therefore, the aim of the work presented in this thesis was to design a new technique that allows commercially available rheological equipment to monitor the gelation progress of these materials. The first part of study involved the design a new method to measure the gelation of alginate and pectin in situ on exposure to an external source of calcium ions. Direct mixing of alginate or low methoxy pectin with divalent cations such as Ca2+ generally produces heterogeneous gels that form almost instantaneously. Therefore, it is particularly difficult to measure the rheo...

Behaviour of gels based on (hydroxypropyl) cellulose methacrylate

Polymer, 2000

A new class of gels obtained from aqueous solutions of hydroxypropylcellulose partially esterified with methacryloylchloride was prepared by UV crosslinking. Measurements of swelling degree and the elastic properties of samples having different esterification degree were treated according to the theory developed for semirigid chains: the values of the n (number of elastically active chains) and x (polymer-solvent interaction parameter) were calculated and used to interpret some experimental behaviours. Moreover, thermosensitive response was evidenced and related to the trend of the enthalpic and entropic components of x as functions of temperature. ᭧ (E. Marsano).

Rheological Properties of Aqueous Dispersions of Xanthan Gum Containing Different Chloride Salts Are Impacted by both Sizes and Net Electric Charges of the Cations

Food Biophysics, 2018

Bacterial cellulose as polysaccharide possessing outstanding chemical purity and a unique structure compared with wood cellulose, attracts great attention as a hydrocolloid system. It was shown, that at intense mechanical action on a neat bacterial cellulose film in presence of water, the gel-like dispersions are obtained. They retain stability in time (at least, up to several months) and temperature (at least, up to 60 • C) without macro-phase separation on aqueous and cellulose phases. The main indicator of the stability is constant viscosity values in time, as well as fulfilling the Arrhenius dependence for temperature dependence of viscosity. Flow curves of diluted dispersions (BC content less than 1.23%) show strong non-Newtonian behavior over the entire range of shear rates. It is similar with dispersions of micro-and nanocrystalline cellulose, but the absolute viscosity value is much higher in the case of BC due to more long fibrils forming more dense entanglements network than in other cases. Measuring the viscosity in increase and decrease shear rate modes indicate an existence of hysteresis loop, i.e., thixotropic behavior with time lag for recovering the structural network. MCC and NCC dispersions even at cellulose content more than 5% do not demonstrate such behavior. According to oscillatory measurements, viscoelastic behavior of dispersions corresponds to gel-like systems with almost total independence of moduli on frequency and essentially higher values of the storage modulus compared with the loss modulus.

Impact of xanthan gum, sucrose and fructose on the viscoelastic properties of agarose hydrogels

Food Hydrocolloids, 2012

Mixed carbohydrate systems are of special interest for the food and non-food industry as they offer a versatile range of unique and novel functional properties. However, intense research is required to understand the complex processes occurring in such systems on a molecular level and to be able to modify them aim-oriented. In food, characteristic properties are based on the physicochemical functions of the biopolymers added. Thus, small deformation tests and moisture analysis have been applied to study the impact of xanthan gum and two types of sugar on the viscoelastic properties, the solegel transition and the water holding capacity of 1% agarose hydrogels. Agarose gels are very elastic, turbid and prone to synaeresis, which impinges on their mouth feeling. Additions of xanthan gum revealed less elastic gels with an unaffected water holding capacity. Progressive addition of two different types of up to 40% of sugar yield an increase of the elasticity of agarose gels, whereby sugar concentrations of 60% partially result in a structural breakdown and thus a significant lower network structure but better water holding. In ternary systems, the effect of the sugar concentration and sugar type used is diminished by xanthan gum. The gelation mechanism of agarose gels with a distinct amount of co-solutes is presumably mainly affected by the water shortage evolved from the competition for it of all solutes present.

Rheological Properties of Hydrogels Produced by Cellulose Derivatives Crosslinked with Citric Acid, Succinic Acid and Sebacic Acid

Cellulose Chemistry and Technology, 2022

Cellulose is the most abundant biopolymer in our world, and a natural, biodegradable and inexpensive resource for biomaterials. This work prepared cellulose-based hydrogels by cross-linking cellulose derivatives using citric acid, succinic acid, and sebacic acid, and explored the rheological properties of the three cellulose-based hydrogels. We found that the viscoelastic properties of this kind of cellulose-based biodegradable hydrogels can be manipulated by hydrogel concentration and using the three different cross-linkers. The cellulose-based hydrogels cross-linked with citric acid (CHCCA) and the cellulose-based hydrogels cross-linked with succinic acid (CHCSUA) exhibited nearly identical rheological behaviors (both linear and non-linear), due to the similar structure of the citric acid and succinic acid. Both CHCCA and CHCSUA showed similar viscoelastic solid gel-like behaviors, and the viscoelastic properties were stronger when hydrogel concentrations were increased. The CHCCA and CHCSUA also displayed nearly identical shear thinning behaviors, among all measured shearing rates. The cellulose-based hydrogels cross-linked with sebacic acid (CHCSEA) exhibited viscoelastic liquid or fluid-like behaviors, which are clearly different from those for the CHCCA and CHCSUA. The CHCSEA showed shear thinning characteristics during high shearing rates, but a Newtonian region at low shearing rates. This work paves the way for developing various inexpensive biodegradable cellulose-based hydrogels with desired rheological properties specific to applications such as cosmetic gels and woundhealing materials.

Further evidence for the gelation ability–structure correlation in sugar-based gelators

Carbohydrate Research, 2001

Eight methyl glycosides of 4,6-O-benzylidene derivatives of the monosaccharides D-glucose, D-mannose, D-allose and D-altrose were synthesized to systematically study the effect of small configurational changes on the ability to gelate organic solvents. Among the beta anomers, only the D-mannose glycoside exhibits a strong gelation ability, whereas in the alpha-series the D-glucose and D-mannose derivatives act as versatile gelators. Also, as a general rule we found that the beta anomers possess a higher ability to gelate solvents than the alpha anomers. The gelation properties are discussed on the basis of SAXS, FTIR, differential scanning calorimetric (DSC) measurements and scanning electron microscopy (SEM) observations. The temperature-dependent SAXS measurements were carried out to elucidate the sol-gel transition temperature. The present study emphasizes that the saccharide family provides, not only valuable information of the structural requirements for the design of new gelators, but also for molecular assembly systems in general.

Physical Gels from Biological and Synthetic Polymers

2013

Presenting a unique perspective on the state-of-the-art of physical gels, this interdisciplinary guide provides a complete, critical analysis of the field and highlights recent developments. It shows the interconnections between the key aspects of gels, from molecules and structure through to rheological and functional properties, with each chapter focusing on a different class of gel. There is also a final chapter covering innovative systems and applications, providing the information needed to understand current and future practical applications of gels in the pharmaceutical, agricultural, cosmetic, chemical and food industries. Many research teams are involved in the field of gels, including theoreticians, experimentalists and chemical engineers, but this interdisciplinary book collates and rationalizes the many different points of view to provide a clear understanding of these complex systems for researchers and graduate students.

Gelation studies of a cellulose-based biohydrogel: The influence of pH, temperature and sterilization

Acta Biomaterialia, 2009

The present paper investigates the rheological properties of silated hydroxypropylmethylcellulose (Si-HPMC) biohydrogel used for biomaterials and tissue engineering. The general property of this modified cellulose ether is the occurrence of selfhardening due to silanol condensation subsequently to decreasing pH (from 12.4 to nearly 7.4). The behavior of unsterilized and sterilized Si-HPMC solutions in diluted and concentrated domains is firstly described and compared. In addition, the influence of physiological parameters such as pH and temperature on the rate of the gelation process is studied. In dilute solution, the intrinsic viscosity ([K]) of different pre-steam sterilization Si-HPMC solutions indicates that macromolecular chains occupy a larger hydrodynamic volume than the post-steam sterilization Si-HPMC. Although the unsterilized Si-HPMC solutions demonstrate no detectable influence of pH upon the rheological behavior, a decrease in the limiting viscosities (K 0 ) of solutions with increasing pH is observed following steam sterilization. This effect can be explained by the formation of intra and intermolecular associations during the sterilization stage originating from the temperature-induced phase separation. The formation of Si-HPMC hydrogels from injectable aqueous solution is studied after neutralization by different acid buffers leading to various final pH. Gelation time (t g )

Rheological Study on Crosslinking and Gelation of Amidated Carboxymethylcellulose Solutions

Chemical and Biochemical Engineering Quarterly

Viscosupplementation is an intra-articular symptomatic treatment of mild osteoarthritis in synovial joints. It normally consists of single or repeated injections of hyaluronan-based fluids, aimed to restore desirable viscoelastic behavior of the synovial fluid and thus recreate the intra-articular joint homeostasis. Recently, a novel viscosupplement based on amidated carboxymethylcellulose has been developed by blending the soluble polymer (CMCAp) with its crosslinked derivative (CMCAg) in appropriate proportions and concentrations in order to ensure an optimal combination of flow behavior and viscoelastic properties. The present work is concerned with the rheological monitoring of the crosslinking reaction performed at 25 °C by starting from aqueous CMCAp solutions in order to describe the time evolution of the linear viscoelastic moduli occurring along the whole gelation process and to individuate how the polymer concentration affects the mechanical response at the sol-gel transition and the fractal dimension of the incipient polymeric network.