In this work, non-derivatized cellulose pulp was dissolved in a cold alkali solution (LiOH/urea) ... more In this work, non-derivatized cellulose pulp was dissolved in a cold alkali solution (LiOH/urea) and chemically cross-linked with methylenebisacrylamide (MBA) to form a robust hydrogel with superior water absorption properties. Different cellulose concentrations (i.e., 2, 3 and 4 wt%) and MBA/glucose molar ratios (i.e., 0.26, 0.53 and 1.05) were tested. The cellulose hydrogel cured at 60 • C for 30 min, with a MBA/glucose molar ratio of 1.05, exhibited the highest water swelling capacity absorbing ca. 220 g H 2 O/g dry hydrogel. Moreover, the data suggest that the cross-linking occurs via a basic Michael addition mechanism. This innovative procedure based on the direct dissolution of unmodified cellulose in LiOH/urea followed by MBA cross-linking provides a simple and fast approach to prepare chemically cross-linked non-derivatized high-molecular-weight cellulose hydrogels with superior water uptake capacity.
Cellulose dissolution and regeneration are old topics that have recently gained renewed attention... more Cellulose dissolution and regeneration are old topics that have recently gained renewed attention. This is reflected in both applications-earlier and novel-and in scientific controversies. There is a current discussion in the literature on the balance between hydrogen bonding and hydrophobic interactions in controlling the solution behavior of cellulose. Some of the key ideas are recalled.
Journal of Colloid and Interface Science, Dec 1, 2018
Diffusing wave spectroscopy (DWS) is a powerful optical technique suitable to investigate turbid ... more Diffusing wave spectroscopy (DWS) is a powerful optical technique suitable to investigate turbid samples in a nondestructive and reproducible way, providing information on the static and dynamic properties of the system. This includes the relative displacement of emulsion droplets over time and changes in the viscoelastic properties. Here, novel and promising cellulose-based oil-in-water (O/W) emulsions were prepared and studied, for the first time, by DWS. Cellulose plays the role of a novel eco-friendly emulsifying agent. The hydrolysis time of cellulose was observed to affect the average size of the emulsion droplets and their stability; the longer the hydrolysis time, the more dispersed and stable the emulsions were found to be. Additionally, a good complementarity between the microrheology (DWS) and macrorheology (mechanical rheometer) data was found. Our work suggests that DWS is a highly attractive method to investigate the stability, aging and microrheology properties of cellulose-based emulsions, providing valuable insights on their microstructure. This technique is thus highly appealing for the characterization and design of novel emulsion formulations.
Colloids and Surfaces A: Physicochemical and Engineering Aspects, Nov 1, 2000
The surface tension of a protein sample isolated from the blue-green algae (cyanobacteria) Spirul... more The surface tension of a protein sample isolated from the blue-green algae (cyanobacteria) Spirulina platensis strain Pacifica was studied using the Wilhelmy plate method. The isolated material was characterised by determining the protein and lipid content, SDS-PAGE electrophoresis, isoelectric focusing, and visible spectroscopy. The protein is capable of reducing the interfacial tension at the aqueous/air interface already at relatively lower bulk concentrations compared to common food proteins. The surface tension of the protein preparation seems to be quite independent of pH, which indicates that electrostatic interactions are of minor importance for the interfacial behaviour. We have also separated out fractions with different interfacial properties by centrifugation. When the protein was spread at the air/aqueous interface, the pressure area isotherm somewhat resembles those recorded for lipids, with a higher collapse pressure than usually observed for proteins. The interfacial behaviour of extracted lipids confirms that remaining traces of lipids in protein powder have only a minor influence on the surface activity of Spirulina protein. The surface-active components are likely to be protein and/or protein-pigment complexes rather than individual protein molecules.
This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY
Anales de la Real Sociedad Española de Química, 2004
olloid science is a mature field. It received a lot of attention in the beginning of the 20 th ce... more olloid science is a mature field. It received a lot of attention in the beginning of the 20 th century with seminal contributions due to Einstein, Perrin, Svedberg and others. After a strong period of fundamental work, the applications received more attention and much of research was performed in industrial research laboratories or by academics with an interest in applications. The progress in the field meant a revolution for formulations with particularly strong applications for pharmaceutical formulations, paper industry, cosmetics, paints, coatings, foods and detergents. However, there is no exaggeration to state that there are very few branches of industry, which do not use colloids in a significant way.
With amphiphilic properties, cellulose molecules are expected to adsorb at the O/W interface and ... more With amphiphilic properties, cellulose molecules are expected to adsorb at the O/W interface and be capable of stabilizing emulsions. The effect of solvent quality on the formation and stability of cellulose-based O/W emulsions was evaluated in different alkaline systems: NaOH, NaOH-urea and tetrabutylammonium hydroxide (TBAH). The optimal solvency conditions for cellulose adsorption at the O/W interface were found for the alkaline solvent with an intermediate polarity (NaOH-urea), which is in line with the favorable conditions for adsorption of an amphiphilic polymer. A very good solvency (in TBAH) and the interfacial activity of the cation lead to lack of stability because of low cellulose adsorption. However, to achieve long-term stability and prevent oil separation in NaOH-urea systems, further reduction in cellulose's solvency was needed, which was achieved by a change in the pH of the emulsions, inducing the regeneration of cellulose at the surface of the oil droplets (in-situ regeneration).
DNA chemical and physical networks have been investigated with respect to their stability and swe... more DNA chemical and physical networks have been investigated with respect to their stability and swelling, and rheological properties. Chemical networks were prepared by cross-linking DNA with ethylene glycol diglycidyl ether (EGDE), and physical networks by association with cationic polymers. Both types of gels display strong elastic properties and have a shear thinning behaviour. Addition of cationic surfactants effectively collapses the chemical gels, de-swelling starting from a critical aggregation concentration (cac) much lower than the critical micelle concentration (cmc) but similar to that for binding of surfactant to DNA in solution. The swelling-deswelling process appears to be reversible; thus the addition of an anionic surfactant to a gel collapsed by cationic surfactant gives a gel volume close to that of the original gel. Physical networks prepared by mixing DNA (either single-or double-stranded) with cationic polyelectrolytes, both derivatives of hydroxyethyl cellulose, one of them carrying hydrophobic groups, show an intriguing asymmetric phase separation and a very different rheological response from that of the polymers alone. Phase maps of the mixtures show three distinctive regions, a two-phase region, a bluish one-phase region and a transparent one-phase region. Effects due to hydrophobic groups on the polymers are relatively minor.
Steady-state and time-resolved fluorescence studies were performed on aqueous solutions of poly(a... more Steady-state and time-resolved fluorescence studies were performed on aqueous solutions of poly(acrylic acid) hydrophobically modified with two very different levels of naphthalene (Np). It is demonstrated that unique information on association phenomena involving hydrophobe-modifed polymers can be obtained from an extended fluorescence study by using data for a less-modified polymer as a reference. For the more highly modified polymer, the presence of excited-state (as well as ground-state) dimers in addition to monomer emission due to locally excited naphthalene gives evidence for hydrophobic association between naphthalene groups. This association becomes, as expected, much less important at higher pH due to the electrostatic repulsion between different chain segments. However, it is noted that even at high pH there is a significant self-association. The coexistence of static and dynamic quenching phenomena of the Np monomer label was also revealed in the time-resolved fluorescence data. The data are compatible with the existence of two types of monomers and one excimer and suggest that the essential contribution to the monomer emission comes from isolated chromophores, whereas excimer formation arises from both a dynamic route (excited Np chromophores able to produce a dynamic excimer) and a static route (excitation of ground-state Np dimers). At room temperature, the dissociative reaction, excimer-to-monomer, can be neglected, and thus the rate constant for excimer formation and decay could be obtained with and without considering the influence of preformed dimers. Temperature has shown to induce different behavior in the polymer photophysics. In the case of the less-labeled polymer, the decays were found to be single-exponential with the fluorescence lifetime decreasing with increasing temperature. From the temperature dependence of the steady-state fluorescence data, the activation energy for excimer formation and the binding energy of the excimer were evaluated at different pH values, through the Stevens-Ban-type plots of the excimer-to-monomer intensity ratio. With the time-resolved data, measured in the temperature range of 5-60 degrees C, it was possible to extract the intrinsic activation energies for excimer formation. The thermodynamic driving force for the intrapolymeric association was found to be dependent on a balance between hydrophobic and electrostatic interactions, which are dependent on the pH, temperature, and hydrophobic content of the polymer.
Colloids and Surfaces B: Biointerfaces, Aug 1, 2018
Exploring the prebiotic effect of cyclodextrins on probiotic bacteria entrapped in carboxymetyl c... more Exploring the prebiotic effect of cyclodextrins on probiotic bacteria entrapped in carboxymetyl cellulose-chitosan particles, Colloids and Surfaces B: Biointerfaces
DNA interacts with insoluble monolayers made of cationic amphiphiles as well as with monolayers o... more DNA interacts with insoluble monolayers made of cationic amphiphiles as well as with monolayers of zwitterionic lipids in the presence of divalent ions. Binding to dioctadecyldimethylammonium bromide (DODAB) or distearoyl-sn-glycero-3-phosphocholine (DSPC) monolayers in the presence of calcium is accompanied by monolayer expansion. For the positively charged DODAB monolayer, this causes a decrease of surface potential, while an increase is observed for the DSPC monolayers. Binding to dipalmitoyl-snglycero-3-phosphocholine preserves most of the liquid expanded-liquid condensed coexistence region. The liquid condensed domains adopt an elongated morphology in the presence of DNA, especially in the presence of calcium. The interaction of DNA with phospholipid monolayers is ion specific: the presence of calcium leads to a stronger interaction than magnesium and barium. These results were confirmed by bulk complexation studies.
The rheological behavior of mixtures containing hydrophobically modified poly(sodium acrylate) (H... more The rheological behavior of mixtures containing hydrophobically modified poly(sodium acrylate) (HMPAA) and surfactants is studied. The hydrophobic groups of the polymer (octadecyl or dodecyl chains) interact with the surfactant molecules to form mixed micellar-type aggregates. In semidilute solution these mixed aggregates act as cross-linkers between the polymer chains, inducing a viscosification or gelation of the system. The strongest effect was
Cyclodextrins (CDs) can form inclusion complexes with a wide variety of molecules making them ver... more Cyclodextrins (CDs) can form inclusion complexes with a wide variety of molecules making them very attractive in different areas, such as pharmaceutics, biochemistry, food chemistry and textile. In this communication we will report on the physico-chemical characterization of cellulose modified with CDs by means of infra-red spectroscopy (FTIR), cross polarization magic angle spinning solid state nuclear magnetic resonance (CP-MAS NMR), polarized optical microscopy (POM) and thermal gravimetric analysis (TGA). Both CP-MAS NMR and FTIR indicate that CDs are chemically attached to cellulose backbone through the formation of ester bonds. Furthermore, the CD-grafted cellulose was dissolved in a "superphosphoric" acid solution but, despite the increase of hydrophilicity due to the modification, POM revealed that grafted cellulose was less soluble when compared to the unmodified polymer. The formation of a complex CD-cellulose network is suggested.
Journal of the Brazilian Chemical Society, Feb 1, 2013
A distinção entre termodinâmica e cinética de dissolução da celulose raramente tem sido considera... more A distinção entre termodinâmica e cinética de dissolução da celulose raramente tem sido considerada na literatura. Neste trabalho, discutimos este tema e fundamentamos as nossas hipóteses recorrendo a experiências simples. É do conhecimento geral que a celulose pode ser dissolvida no solvente aquoso de hidróxido de sódio (NaOH/H 2 O) a baixa temperatura. Neste trabalho, demonstramos que este solvente alcalino pode ser consideravelmente melhorado em relação à sua estabilidade, solubilidade e propriedades reológicas se forem usados diferentes aditivos (sais e moléculas anfifílicas) na fase de dissolução. Este trabalho indica novos caminhos relativamente à dissolução da celulose em solventes aquosos, de uma forma mais econômica e ambientalmente amigável, aumentando o seu potencial comercial. The distinction between thermodynamic and kinetics in cellulose dissolution is seldom considered in the literature. Therefore, herein an attempt to discuss this topic and illustrate our hypotheses on the basis of simple experiments was made. It is well-known that cellulose can be dissolved in a aqueous sodium hydroxide (NaOH/H 2 O) solvent at low temperature but it is here shown that such an alkaline solvent can be considerably improved regarding solubility, stability and rheological properties as a whole if different additives (salts and amphiphilic molecules) are used in the dissolution stage. This work probes new aqueous routes to dissolve cellulose, thereby improving the potential to commercially dissolve cellulose in an inexpensive and environmentally friendly manner.
Nuclear magnetic relaxation rates of H217O, 23Na+, and 25Mg2+ have been measured in aqueous hyalu... more Nuclear magnetic relaxation rates of H217O, 23Na+, and 25Mg2+ have been measured in aqueous hyaluronate solutions. The dependence on solution pH of the relaxation rates has been investigated, as well as the competition behavior of Na+ with Ca2+ and Mg2+. H217O and 23Na+ relaxation rates in chondroitin and hyaluronate solutions have been compared in the interval, 2 ≲ pH ≲ 12.5. The ion binding of hyaluronate can be fully accounted for by Coulomb interactions, with no need to involve chemical specificity. The hydration is only slighly pH dependent, and is comparable in magnitude to hydration of synthetic polyelectrolytes and monosaccharides. Ion‐binding and hydration properties of hyaluronate and chondroitin are quite similar, except at elevated pH. At alkaline pH, an increase in charge density with pH is seen in hyaluronate and, to a much lesser degree, in chondroitin, possibly due to the titration of hydroxy groups. H217O data indicate an alkali‐induced transition in both glycosaminoglycans.
On the viability, cytotoxicity and stability of probiotic bacteria entrapped in cellulose-based p... more On the viability, cytotoxicity and stability of probiotic bacteria entrapped in cellulose-based particles
Current Opinion in Colloid and Interface Science, Apr 1, 2016
Nonionic surfactants have broad applications such as cleaning and dispersion stabilization, which... more Nonionic surfactants have broad applications such as cleaning and dispersion stabilization, which frequently are hampered by strong temperature sensitivities. As manifested by clouding and decreased solubility with increasing temperature, the interaction between water and the oligo(oxyethylene) head-groups is becoming less favorable. Different aspects of surfactant self-assembly, like the critical micelle concentration, micelle size and shape, intermicellar interactions and phase separation phenomena are reviewed as well as suggested underlying causes of the temperature dependence. Furthermore, the effect of cosolutes on clouding and the behavior of related systems, non-aqueous solutions and nonionic polymers, are examined.
In this work, non-derivatized cellulose pulp was dissolved in a cold alkali solution (LiOH/urea) ... more In this work, non-derivatized cellulose pulp was dissolved in a cold alkali solution (LiOH/urea) and chemically cross-linked with methylenebisacrylamide (MBA) to form a robust hydrogel with superior water absorption properties. Different cellulose concentrations (i.e., 2, 3 and 4 wt%) and MBA/glucose molar ratios (i.e., 0.26, 0.53 and 1.05) were tested. The cellulose hydrogel cured at 60 • C for 30 min, with a MBA/glucose molar ratio of 1.05, exhibited the highest water swelling capacity absorbing ca. 220 g H 2 O/g dry hydrogel. Moreover, the data suggest that the cross-linking occurs via a basic Michael addition mechanism. This innovative procedure based on the direct dissolution of unmodified cellulose in LiOH/urea followed by MBA cross-linking provides a simple and fast approach to prepare chemically cross-linked non-derivatized high-molecular-weight cellulose hydrogels with superior water uptake capacity.
Cellulose dissolution and regeneration are old topics that have recently gained renewed attention... more Cellulose dissolution and regeneration are old topics that have recently gained renewed attention. This is reflected in both applications-earlier and novel-and in scientific controversies. There is a current discussion in the literature on the balance between hydrogen bonding and hydrophobic interactions in controlling the solution behavior of cellulose. Some of the key ideas are recalled.
Journal of Colloid and Interface Science, Dec 1, 2018
Diffusing wave spectroscopy (DWS) is a powerful optical technique suitable to investigate turbid ... more Diffusing wave spectroscopy (DWS) is a powerful optical technique suitable to investigate turbid samples in a nondestructive and reproducible way, providing information on the static and dynamic properties of the system. This includes the relative displacement of emulsion droplets over time and changes in the viscoelastic properties. Here, novel and promising cellulose-based oil-in-water (O/W) emulsions were prepared and studied, for the first time, by DWS. Cellulose plays the role of a novel eco-friendly emulsifying agent. The hydrolysis time of cellulose was observed to affect the average size of the emulsion droplets and their stability; the longer the hydrolysis time, the more dispersed and stable the emulsions were found to be. Additionally, a good complementarity between the microrheology (DWS) and macrorheology (mechanical rheometer) data was found. Our work suggests that DWS is a highly attractive method to investigate the stability, aging and microrheology properties of cellulose-based emulsions, providing valuable insights on their microstructure. This technique is thus highly appealing for the characterization and design of novel emulsion formulations.
Colloids and Surfaces A: Physicochemical and Engineering Aspects, Nov 1, 2000
The surface tension of a protein sample isolated from the blue-green algae (cyanobacteria) Spirul... more The surface tension of a protein sample isolated from the blue-green algae (cyanobacteria) Spirulina platensis strain Pacifica was studied using the Wilhelmy plate method. The isolated material was characterised by determining the protein and lipid content, SDS-PAGE electrophoresis, isoelectric focusing, and visible spectroscopy. The protein is capable of reducing the interfacial tension at the aqueous/air interface already at relatively lower bulk concentrations compared to common food proteins. The surface tension of the protein preparation seems to be quite independent of pH, which indicates that electrostatic interactions are of minor importance for the interfacial behaviour. We have also separated out fractions with different interfacial properties by centrifugation. When the protein was spread at the air/aqueous interface, the pressure area isotherm somewhat resembles those recorded for lipids, with a higher collapse pressure than usually observed for proteins. The interfacial behaviour of extracted lipids confirms that remaining traces of lipids in protein powder have only a minor influence on the surface activity of Spirulina protein. The surface-active components are likely to be protein and/or protein-pigment complexes rather than individual protein molecules.
This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY
Anales de la Real Sociedad Española de Química, 2004
olloid science is a mature field. It received a lot of attention in the beginning of the 20 th ce... more olloid science is a mature field. It received a lot of attention in the beginning of the 20 th century with seminal contributions due to Einstein, Perrin, Svedberg and others. After a strong period of fundamental work, the applications received more attention and much of research was performed in industrial research laboratories or by academics with an interest in applications. The progress in the field meant a revolution for formulations with particularly strong applications for pharmaceutical formulations, paper industry, cosmetics, paints, coatings, foods and detergents. However, there is no exaggeration to state that there are very few branches of industry, which do not use colloids in a significant way.
With amphiphilic properties, cellulose molecules are expected to adsorb at the O/W interface and ... more With amphiphilic properties, cellulose molecules are expected to adsorb at the O/W interface and be capable of stabilizing emulsions. The effect of solvent quality on the formation and stability of cellulose-based O/W emulsions was evaluated in different alkaline systems: NaOH, NaOH-urea and tetrabutylammonium hydroxide (TBAH). The optimal solvency conditions for cellulose adsorption at the O/W interface were found for the alkaline solvent with an intermediate polarity (NaOH-urea), which is in line with the favorable conditions for adsorption of an amphiphilic polymer. A very good solvency (in TBAH) and the interfacial activity of the cation lead to lack of stability because of low cellulose adsorption. However, to achieve long-term stability and prevent oil separation in NaOH-urea systems, further reduction in cellulose's solvency was needed, which was achieved by a change in the pH of the emulsions, inducing the regeneration of cellulose at the surface of the oil droplets (in-situ regeneration).
DNA chemical and physical networks have been investigated with respect to their stability and swe... more DNA chemical and physical networks have been investigated with respect to their stability and swelling, and rheological properties. Chemical networks were prepared by cross-linking DNA with ethylene glycol diglycidyl ether (EGDE), and physical networks by association with cationic polymers. Both types of gels display strong elastic properties and have a shear thinning behaviour. Addition of cationic surfactants effectively collapses the chemical gels, de-swelling starting from a critical aggregation concentration (cac) much lower than the critical micelle concentration (cmc) but similar to that for binding of surfactant to DNA in solution. The swelling-deswelling process appears to be reversible; thus the addition of an anionic surfactant to a gel collapsed by cationic surfactant gives a gel volume close to that of the original gel. Physical networks prepared by mixing DNA (either single-or double-stranded) with cationic polyelectrolytes, both derivatives of hydroxyethyl cellulose, one of them carrying hydrophobic groups, show an intriguing asymmetric phase separation and a very different rheological response from that of the polymers alone. Phase maps of the mixtures show three distinctive regions, a two-phase region, a bluish one-phase region and a transparent one-phase region. Effects due to hydrophobic groups on the polymers are relatively minor.
Steady-state and time-resolved fluorescence studies were performed on aqueous solutions of poly(a... more Steady-state and time-resolved fluorescence studies were performed on aqueous solutions of poly(acrylic acid) hydrophobically modified with two very different levels of naphthalene (Np). It is demonstrated that unique information on association phenomena involving hydrophobe-modifed polymers can be obtained from an extended fluorescence study by using data for a less-modified polymer as a reference. For the more highly modified polymer, the presence of excited-state (as well as ground-state) dimers in addition to monomer emission due to locally excited naphthalene gives evidence for hydrophobic association between naphthalene groups. This association becomes, as expected, much less important at higher pH due to the electrostatic repulsion between different chain segments. However, it is noted that even at high pH there is a significant self-association. The coexistence of static and dynamic quenching phenomena of the Np monomer label was also revealed in the time-resolved fluorescence data. The data are compatible with the existence of two types of monomers and one excimer and suggest that the essential contribution to the monomer emission comes from isolated chromophores, whereas excimer formation arises from both a dynamic route (excited Np chromophores able to produce a dynamic excimer) and a static route (excitation of ground-state Np dimers). At room temperature, the dissociative reaction, excimer-to-monomer, can be neglected, and thus the rate constant for excimer formation and decay could be obtained with and without considering the influence of preformed dimers. Temperature has shown to induce different behavior in the polymer photophysics. In the case of the less-labeled polymer, the decays were found to be single-exponential with the fluorescence lifetime decreasing with increasing temperature. From the temperature dependence of the steady-state fluorescence data, the activation energy for excimer formation and the binding energy of the excimer were evaluated at different pH values, through the Stevens-Ban-type plots of the excimer-to-monomer intensity ratio. With the time-resolved data, measured in the temperature range of 5-60 degrees C, it was possible to extract the intrinsic activation energies for excimer formation. The thermodynamic driving force for the intrapolymeric association was found to be dependent on a balance between hydrophobic and electrostatic interactions, which are dependent on the pH, temperature, and hydrophobic content of the polymer.
Colloids and Surfaces B: Biointerfaces, Aug 1, 2018
Exploring the prebiotic effect of cyclodextrins on probiotic bacteria entrapped in carboxymetyl c... more Exploring the prebiotic effect of cyclodextrins on probiotic bacteria entrapped in carboxymetyl cellulose-chitosan particles, Colloids and Surfaces B: Biointerfaces
DNA interacts with insoluble monolayers made of cationic amphiphiles as well as with monolayers o... more DNA interacts with insoluble monolayers made of cationic amphiphiles as well as with monolayers of zwitterionic lipids in the presence of divalent ions. Binding to dioctadecyldimethylammonium bromide (DODAB) or distearoyl-sn-glycero-3-phosphocholine (DSPC) monolayers in the presence of calcium is accompanied by monolayer expansion. For the positively charged DODAB monolayer, this causes a decrease of surface potential, while an increase is observed for the DSPC monolayers. Binding to dipalmitoyl-snglycero-3-phosphocholine preserves most of the liquid expanded-liquid condensed coexistence region. The liquid condensed domains adopt an elongated morphology in the presence of DNA, especially in the presence of calcium. The interaction of DNA with phospholipid monolayers is ion specific: the presence of calcium leads to a stronger interaction than magnesium and barium. These results were confirmed by bulk complexation studies.
The rheological behavior of mixtures containing hydrophobically modified poly(sodium acrylate) (H... more The rheological behavior of mixtures containing hydrophobically modified poly(sodium acrylate) (HMPAA) and surfactants is studied. The hydrophobic groups of the polymer (octadecyl or dodecyl chains) interact with the surfactant molecules to form mixed micellar-type aggregates. In semidilute solution these mixed aggregates act as cross-linkers between the polymer chains, inducing a viscosification or gelation of the system. The strongest effect was
Cyclodextrins (CDs) can form inclusion complexes with a wide variety of molecules making them ver... more Cyclodextrins (CDs) can form inclusion complexes with a wide variety of molecules making them very attractive in different areas, such as pharmaceutics, biochemistry, food chemistry and textile. In this communication we will report on the physico-chemical characterization of cellulose modified with CDs by means of infra-red spectroscopy (FTIR), cross polarization magic angle spinning solid state nuclear magnetic resonance (CP-MAS NMR), polarized optical microscopy (POM) and thermal gravimetric analysis (TGA). Both CP-MAS NMR and FTIR indicate that CDs are chemically attached to cellulose backbone through the formation of ester bonds. Furthermore, the CD-grafted cellulose was dissolved in a "superphosphoric" acid solution but, despite the increase of hydrophilicity due to the modification, POM revealed that grafted cellulose was less soluble when compared to the unmodified polymer. The formation of a complex CD-cellulose network is suggested.
Journal of the Brazilian Chemical Society, Feb 1, 2013
A distinção entre termodinâmica e cinética de dissolução da celulose raramente tem sido considera... more A distinção entre termodinâmica e cinética de dissolução da celulose raramente tem sido considerada na literatura. Neste trabalho, discutimos este tema e fundamentamos as nossas hipóteses recorrendo a experiências simples. É do conhecimento geral que a celulose pode ser dissolvida no solvente aquoso de hidróxido de sódio (NaOH/H 2 O) a baixa temperatura. Neste trabalho, demonstramos que este solvente alcalino pode ser consideravelmente melhorado em relação à sua estabilidade, solubilidade e propriedades reológicas se forem usados diferentes aditivos (sais e moléculas anfifílicas) na fase de dissolução. Este trabalho indica novos caminhos relativamente à dissolução da celulose em solventes aquosos, de uma forma mais econômica e ambientalmente amigável, aumentando o seu potencial comercial. The distinction between thermodynamic and kinetics in cellulose dissolution is seldom considered in the literature. Therefore, herein an attempt to discuss this topic and illustrate our hypotheses on the basis of simple experiments was made. It is well-known that cellulose can be dissolved in a aqueous sodium hydroxide (NaOH/H 2 O) solvent at low temperature but it is here shown that such an alkaline solvent can be considerably improved regarding solubility, stability and rheological properties as a whole if different additives (salts and amphiphilic molecules) are used in the dissolution stage. This work probes new aqueous routes to dissolve cellulose, thereby improving the potential to commercially dissolve cellulose in an inexpensive and environmentally friendly manner.
Nuclear magnetic relaxation rates of H217O, 23Na+, and 25Mg2+ have been measured in aqueous hyalu... more Nuclear magnetic relaxation rates of H217O, 23Na+, and 25Mg2+ have been measured in aqueous hyaluronate solutions. The dependence on solution pH of the relaxation rates has been investigated, as well as the competition behavior of Na+ with Ca2+ and Mg2+. H217O and 23Na+ relaxation rates in chondroitin and hyaluronate solutions have been compared in the interval, 2 ≲ pH ≲ 12.5. The ion binding of hyaluronate can be fully accounted for by Coulomb interactions, with no need to involve chemical specificity. The hydration is only slighly pH dependent, and is comparable in magnitude to hydration of synthetic polyelectrolytes and monosaccharides. Ion‐binding and hydration properties of hyaluronate and chondroitin are quite similar, except at elevated pH. At alkaline pH, an increase in charge density with pH is seen in hyaluronate and, to a much lesser degree, in chondroitin, possibly due to the titration of hydroxy groups. H217O data indicate an alkali‐induced transition in both glycosaminoglycans.
On the viability, cytotoxicity and stability of probiotic bacteria entrapped in cellulose-based p... more On the viability, cytotoxicity and stability of probiotic bacteria entrapped in cellulose-based particles
Current Opinion in Colloid and Interface Science, Apr 1, 2016
Nonionic surfactants have broad applications such as cleaning and dispersion stabilization, which... more Nonionic surfactants have broad applications such as cleaning and dispersion stabilization, which frequently are hampered by strong temperature sensitivities. As manifested by clouding and decreased solubility with increasing temperature, the interaction between water and the oligo(oxyethylene) head-groups is becoming less favorable. Different aspects of surfactant self-assembly, like the critical micelle concentration, micelle size and shape, intermicellar interactions and phase separation phenomena are reviewed as well as suggested underlying causes of the temperature dependence. Furthermore, the effect of cosolutes on clouding and the behavior of related systems, non-aqueous solutions and nonionic polymers, are examined.
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