Effects of cellulose derivatives and carrageenans on the pasting, paste, and gel properties of rice starches

Effects of different cellulose derivatives and carrageenans on the pasting, rheological, and textural properties of normal (NRS) and waxy (WRS) rice starches were investigated. When suspensions of both NRS and WRS were heated in a Rapid Visco Analyser (RVA) in the presence of the hydrocolloids, increases in apparent pasting temperatures and peak and final viscosities in the following decreasing order were observed: methylcellulose (MC) > carboxymethylcellulose (CMC) for cellulose derivatives and λ- > í- > κ-carregeenan for carrageenans. Slight decreases in peak and final viscosities were observed when hydroxypropylmethylcellulose (HPMC) was the hydrocolloid. Dynamic viscoelasticity measurements indicated that NRS–hydrocolloid pastes were less solid-like than the control, as evidenced by their higher tan δ values, whereas tan δ values of WRS–hydrocolloid pastes were the same as that of the control. Steady shear rheological measurements showed that addition of the different hydrocolloids used increased the apparent viscosity (η_a,100) and consistency coefficient (K) values of both starches with the same trend as that observed during pasting, whereas the opposite trend was observed for the flow behavior index (n) values. The hardness and adhesiveness of NRS pastes were significantly increased by addition of κ- and í-carrageenans, but were unaffected by the other hydrocolloids. A similar effect was observed for WRS, with the exception of κ-carregeenan, in which the hardness of the mixed paste was decreased. The starch–hydrocolloid pastes exhibited a phase-separated microstructure in which amylose- and amylopectin-rich domains were dispersed in a hydrocolloid-rich continuous phase.     

The properties of enzyme-hydrolyzed cellulose in aqueous sodium hydroxide

Pure natural cellulose (softwood pulp) modified with cellulase is allowed to react with sodium hydroxide in a muller, and changes in structure and properties are investigated by FTIR and DSC. The reactivity of cellulose for some dissolving and derivatization processes is shown to be improved by an enzymatic hydrolysis and admixture with sodium hydroxide. The modified cellulose dissolved at 9% (wt) sodium hydroxide at -10 degrees C at 6% pulp consistency, while the DP of cellulose is >350.     

Sorption properties of TEMPO-oxidized natural and man-made cellulose fibers

Cotton and lyocell fibers were oxidized with sodium hypochlorite and catalytic amount of sodium bromide and 2,2,6,6-tetramethylpiperidine-1-oxy radical (TEMPO), under various conditions. Water-insoluble fractions, collected after TEMPO-mediated oxidation, were analyzed and characterized in terms of weight loss, aldehyde and carboxyl contents, and sorption properties. Aldehyde and carboxyl groups were introduced into the oxidized cotton up to 0.321 and 0.795 mmol/g, and into the oxidized lyocell up to 0.634 and 0.7 mmol/g, respectively, where weight loss was generally lower than 12% for cotton and 27% for lyocell. Oxidized cotton and lyocell were shown to exhibit 1.55 and 2.28 times higher moisture sorption than the original fibers, respectively, and water retention values up to about 85% for cotton and 335% for lyocell, while iodine sorption values of oxidized fibers were lower up to 35% for cotton and up to 18% for lyocell than the original fibers.     

Rheological properties of sulfoacetate derivatives of cellulose

Water-soluble cellulose acetate sulfate derivatives (CAS) have been prepared through chemical reaction involving sulfuric acid as a catalyst. These CAS have been obtained from cellulosic materials of different origins (pure cellulose, wheat bran, maize bran) and their rheological behavior in salt-free aqueous solution has been estimated in dilute and semi-dilute regime using dynamic viscoelastic and viscosity measurements. Influence of concentration, temperature of solubilization and temperature of measurement has been investigated. Weak gel-like properties were exhibited at elevated concentration (typically above 7-8 g/L). These systems also exhibited thixotropic properties: the structure was partly broken down upon shearing and recovered at rest. They also displayed thermoreversibility with large hysteresis, the melting temperature being approximately 15 degrees C higher than the temperature at which gelation took place. These overall observations clearly indicate that these distinctive properties arise from intermolecular association of the macromolecular chains of the cellulose derivative.     

Aggregation of some water-soluble derivatives of chitin in aqueous solutions: Role of the degree of acetylation and effect of hydrogen bond breaker

By dynamic light scattering in combination with fluorescence spectroscopy and TEM it was shown that aggregation in aqueous solutions is inherent not only to chitosan, but also to two other water-soluble derivatives of chitin: O-carboxymethylchitin and di-N,N-carboxymethylchitosan. Aggregation is observed even for the samples without N-acetyl-d-glucosamine units, which remain upon incomplete chemical modification of chitin, indicating that specific interactions between residual chitin repeat units cannot be the main reason for the aggregation. At the same time, 7 M urea weakens the aggregation, thus testifying that hydrogen bonding and/or hydrophobic interactions are partially responsible for this phenomenon. The incomplete disruption of aggregates in 7 M urea may arise from crystallization of junction zones between different macromolecules, which makes some hydrogen bonds inaccessible for urea or too stable for breaking by this agent.     

Dyeing and diffusion properties of modified novel cellulose with triazine derivatives containing cationic and anionic groups

Cellulose is chemically modified with the compounds containing cationic and anionic groups. Dyeing and diffusion properties of modified cellulose are discussed. The exhaustion and fixation of reactive dyes on modified cellulose are higher than those on unmodified cellulose. Compared with unmodified cellulose, the dyed modified cellulose also gets good washing fastness. The diffusion coefficients of dyes at different temperature are calculated. Compared with unmodified cellulose, the diffusion of dyes in the modified cellulose shows significant change.     

Stability of Keplerate polyoxometalate macroanionic assemblies in salt-containing aqueous solutions

The solution stability of hydrophilic Keplerate polyoxometalate {Mo₇₂Fe₃₀} macroions was investigated at various ionic strengths. The solution stability varies with the type of monovalent cations with the lowest stability with large, weakly hydrated monovalent cations. Even lower stability was observed when the counter-cations were multivalent cations. Interestingly, the stability of {Mo₇₂Fe₃₀} solutions was found to increase with increasing POM concentration. The close association of monovalent counter-ions around macroions exists in aqueous solution and is likely enhanced at higher macroion concentrations. This behavior can further decrease the net charge on the macroions leading to a decreased electrostatic repulsion, which decreases the screening length of the macroions and causes them to irreversibly precipitate.     

Investigation of the spinnability of cellulose/alkaline ferric tartrate solutions

Dynamic rheology, UV/VIS spectrometry with temperature programming cuvette and reaction calorimetry were conducted on cellulose pulp/FeTNa (NaOH solution containing ferric tartaric acid complex) solutions to investigate their thermostability and spinnability. Color of cellulose/FeTNa solutions changed above 90 °C due to the decomposition of the complex. Thermal activity of cellulose/FeTNa solution started above 130 °C induced by water vapor evolution and complex decomposition. Regeneration of cellulose/FeTNa solutions in a non-solvent (acetic acid and Na-gluconate mixture) resulted in transition from cellulose I into cellulose II structure as revealed by WAXS measurements. Wet-spinning attempts of cellulose/FeTNa solutions yielded fiber-like shaped bodies with a brittle structure.     

Direct dissolution of cellulose in NaOH/thiourea/urea aqueous solution

Untreated cellulose was directly and quickly dissolved in NaOH/thiourea/urea aqueous solution. The mechanism of dissolution was investigated by SEM, WXRD and (13)C NMR. The components of this solvent cannot dissolve cellulose on their own, and the interactions between NaOH and urea, as well as between NaOH and thiourea, play an important role in improving the dissolution of cellulose. Moreover, (13)C NMR spectra proved that NaOH, thiourea, and urea were bound to cellulose molecules, which brings cellulose molecules into aqueous solution to a certain extent and prevents cellulose macromolecules from associating. (13)C NMR spectra of the cellulose solution show that this novel mixture is a direct solvent. Optical microscopy and CP MAS (13)C NMR were used to study the process of dissolution. The results reveal that cellulose is dissolved completely and that cellulose I (cotton linter) first changes to amorphous cellulose chains in solution, and then to cellulose II during regeneration. Moreover, a new, more effective dissolution method is proposed, as confirmed by dynamic rheology measurements.     

Biocomposite films prepared from ionic liquid solutions of chitosan and cellulose

Blends of chitosan and cellulose were successfully produced using 1-butyl-3-methylimidazolium acetate (BMIMAc) as solvent media. Films were prepared from the blends by manually spreading the solution on a flat surface and precipitating the polymers in a mixture of methanol and water. To prevent the shrinkage of films, most of the absorbed water was removed by freeze drying under vacuum. Films prepared from the polymeric solutions were investigated by means of FT-IR, TGA, X-ray diffraction and SEM measurements. The shifting of the bands corresponding to -NH and CO groups of chitosan (FT-IR), the absence of the diffraction peaks at 2θ = 10.7 and 14.9° (XRD), the increased E_a for thermal decomposition for all the polymeric blends (MTGA), and the presence of an apparent homogeneous structure with no phase separation of the two polymers (SEM) provide evidence for the miscibility between chitosan and cellulose in the solid state.     

Supermolecular structure of cellulose/amylose blends prepared from aqueous NaOH solutions and effects of amylose on structural formation of cellulose from its solution

We previously proposed a mechanism for the structural formation of cellulose from its solution using a molecular dynamics (MD) simulation and suggested that the initial structure from its solution plays a critical role in determining its final structure. Structural changes in the van der Waals-associated cellulose molecular sheet as the initial structure were examined by MD simulation; the molecular sheet was found to be disordered due to maltohexaoses as an amylose model in terms of the hydrogen bonding system of cellulose. The structure and properties of cellulose/amylose blends prepared from an aqueous NaOH solution were examined experimentally by wide-angle X-ray diffraction and dynamic viscoelasticity measurements. The crystallinity of cellulose in the cellulose/amylose blend films was lower than that of cellulose film. The diffraction peaks of the cellulose/amylose blends were slightly shifted; specifically, () was shifted to a higher angle, and (1 1 0) and (0 2 0) were shifted to lower angles. These experimental results probably resulted from the disordered molecular sheet, as revealed by MD simulations.     

Ultrasonic study of the kinetics of counterion site binding in aqueous solutions of polyelectrolytes

The excess ultrasonic absorption due to counterion binding has been studied as a function of frequency for a series of polysalts in the range 1–150 MHz. All the relaxation spectra can be represented by a relaxation equation with two relaxation terms. The relaxation frequencies appear concentration independent and the relaxation amplitudes seem proportional to concentration. The low frequency relaxation process appears to depend mainly on the nature of the counterion while the high frequency relaxation process seems to be mostly dependent on the nature of the polyion. These results are quite similar to those obtained in ultrasonic studies of ion-pairing in solutions of divalent sulfates. The kinetic model used for the quantitative analysis of these results has been modified for polysalts through introducing the concept of“counterion condensation”. In this modified model the excess absorption is assigned to the perturbation by the ultrasonic waves of the equilibria between the three states of hydration of ths complex formed by a counterion and that part of the polyion where it is bound. Analytical expressions of the relaxation amplitudes have been derived using classical procedures for this modified kinetic model. In the case of cobalt-polyphosphate (Co-PP), the ultrasonic data together with the results of NMR measurements on either Co²⁺ or Co-PP have been used for the evaluation of the volume changes, the rate constants and the fractions of counterions in the three states of hydration involved in the binding equilibria. The volume changes obtained in this manner depend only slightly on the method of calculation and appear to be consistent with volume changes for outer-sphere and inner-sphere complex formation. These results are discussed.     

Structure and properties of hydroxyapatite/cellulose nanocomposite films

The aim of this study was to develop a new inorganic-organic hybrid film. Nanohydroxyapaptite (nHAP) particles as the inorganic phase was mixed with cellulose in 7 wt.% NaOH/12 wt.% urea aqueous solution with cooling to prepare a blend solution, and then inorganic-organic hybrid films were fabricated by coagulating with Na₂SO₄ aqueous solution. The structure and properties of the hybrid films were characterized by high resolution transmitting electron microscopy (HRTEM), field emission scanning electron microscopy (FESEM), thermo-gravimetric analysis (TGA), Fourier transform infra-red (FT-IR) spectra, wide angle X-ray diffraction (WAXD) and tensile testing. The results revealed that the HAP nanoparticles with mean diameter of about 30 nm were uniformly dispersed and well immobilized in the hybrid film as a result of the role of the nano-and micropores in the cellulose substrate. A strong interaction existed between HAP and cellulose matrix, and their thermal stability and mechanical strength were improved as a result of good miscibility. Furthermore, the results of 293T cell viability assay indicated that the HAP/cellulose films had excellent biocompatibility and safety, showing potential applications in biomaterials.     

Evaluation of viscosities of polymer-water solutions used in aqueous two-phase systems

The dynamic viscosities of dilute aqueous poly(ethylene glycol) and dextran, and poly(ethylene glycol)-dextran-water solutions have been measured. The poly(ethylene glycol) and dextran samples had average molecular masses of 8000 Da and 580 000 Da, respectively. To estimate the values of viscosity of poly(ethylene glycol)-dextran-water solutions, a Grunberg like equation has been proposed which takes into account the influence of poly(ethylene glycol) and dextran concentrations. The relative errors vary between 0.76 and 11.64 in absolute value.