Efficient dissolution of cellulose in slow-cooling alkaline systems and interacting modes between alkali and urea at the molecular level.

The dissolution of microcrystalline cellulose (MCC) in a urea-NaOH system is beneficial for its mechanical processing. The apparent MCC solubility was greatly improved to 14 wt% under a slow-cooling condition with a cooling rate of -0.3 °C/min. The cooling curve or thermal history played a crucial role in the dissolution process. An exotherm (-54.7 ± 3 J/g MCC) was detected by DSC only under the slow-cooling condition, and the cryogenic dissolution of MCC was attributed to the exothermic interaction between MCC and solvent. More importantly, the low cooling rate promoted the dissolution of MCC by providing enough time for the diffusion of OH- and urea into MCC granules at higher temperatures. The Raman spectral data showed that the intramolecularly and intermolecularly hydrogen bonds in cellulose were cleaved by NaOH and urea, respectively. XPS and solid-state 13C NMR results showed that hydrogen bonds were generated after dissolution, and a dual-hydrogen-bond binding mode between urea and cellulose was confirmed by DFT calculations. Both the decrease of enthalpy and increase of entropy dominated the spontaneity of MCC dissolution, and that is the reason for the indispensability of cryogenic environment. The high apparent solubility of MCC in the slow-cooling process and the dissolution mechanism are beneficial for the studies on cellulose modification and mechanical processing.

Multiphase Flow Hemodynamic Evaluation of Vertebral Artery Stenosis Lesions and Plaque Stability.

BACKGROUND: Atherosclerosis is one of the main causes of vertebral artery stenosis, which reduces blood supply to the posterior circulation, resulting in cerebral infarction or death. OBJECTIVE: To investigate stenosis rates and locations on the development of vertebral artery plaques. METHODS: Stenosis models with varying degrees and positions of stenosis were established. The stenosis area was comprehensively analyzed using multiphase flow numerical simulation. Wall shear stress (WSS), blood flow velocity, and red blood cell (RBC) volume fraction were calculated. RESULTS: Blood flow velocity in 30-70% stenosis of each segment tended to increase significantly higher than normal. Downstream of 50% stenosis exhibited turbulent flow; downstream of 70% displayed reflux. Severe stenosis increases the WSS and distribution area. The mixed area of high and low WSS appeared downstream of the stenosis. The RBC volume fraction at the stenosis increased (maximum value: 0.487 at 70% stenosis in the V4), which was 1.08 times the normal volume fraction. Turbulent and backflow regions exhibited complex RBC volume fraction distributions. CONCLUSION: Flow velocity, WSS, and RBC volume fraction at the stenosis increase with stenosis severity, increasing plaque shedding. Narrow downstream spoiler and reflux areas possess low WSS and high erythrocyte volume fractions, accelerating plaque growth.

Effect of ultrasound on the kinetics of anti-solvent crystallization of sucrose.

The effect of ultrasound on the kinetics of anti-solvent crystallization of sucrose was studied. The influence of temperature, stirring rate, supersaturation and ultrasonic power on the anti-solvent crystallization of sucrose was investigated. The relationship between infrared spectral characteristic band of sucrose and supersaturation was determined with an online reaction analyzer. The crystal size distribution of sucrose was detected by a laser particle-size analyzer. Ultrasound accelerated the crystallization process, and had no impact on the crystal shape. Abegg, Stevens and Larson model was fitted to the experimental data, and the results were the following: At 298.15 K, the average size of crystals was 133.8 µm and nucleation rate was 4.87 × 109 m-3·s-1 without ultrasound. In an ultrasonic field, the average size was 80.5 µm, and nucleation rate was 1.18 × 1011 m-3·s-1. Ultrasound significantly reduced the average size of crystals and improved the nucleation rate. It was observed that the crystal size decreased with the increase of stirring rate in silent environment. When the stirring rate increased from 250 to 400 rpm, the average size decreased from 173.0 to 132.9 µm. However, the stirring rate had no significant impact on the crystal size in the ultrasonic field. In addition, the activation energy of anti-solvent crystallization of sucrose was decreased, and the kinetic constant of nucleation rate was increased due to the effect of ultrasound. In the ultrasonic field, the activation energy was reduced from 20422.5 to 790.5 J·mol-1, and the kinetic constant was increased from 9.76 × 102 to 8.38 × 108.

Hydrodynamic cavitation: A feasible approach to intensify the emulsion cross-linking process for chitosan nanoparticle synthesis.

Chitosan nanoparticles (NPs) exhibit great potential in drug-controlled release systems. A controlled hydrodynamic cavitation (HC) technique was developed to intensify the emulsion crosslinking process for the synthesis of chitosan NPs. Experiments were performed using a circular venturi and under varying operating conditions, i.e., types of oil, addition mode of glutaraldehyde (Glu) solution, inlet pressure (Pin), and rheological properties of chitosan solution. Palm oil was more appropriate for use as the oil phase for the HC-intensified process than the other oil types. The addition mode of water-in-oil (W/O) emulsion containing Glu (with Span 80) was more favorable than the other modes for obtaining a narrow distribution of chitosan NPs. The minimum size of NPs with polydispersity index of 0.342 was 286.5 nm, and the maximum production yield (Py) could reach 47.26%. A positive correlation was found between the size of NPs and the droplet size of W/O emulsion containing chitosan at increasing Pin. Particle size, size distribution, and the formation of NPs were greatly dependent on the rheological properties of the chitosan solution. Fourier transform infrared spectroscopy (FTIR) analysis indicated that the molecular structure of palm oil was unaffected by HC-induced effects. Compared with ultrasonic horn, stirring-based, and conventional drop-by-drop processes, the application of HC to intensify the emulsion crosslinking process allowed the preparation of a finer and a narrower distribution of chitosan NPs in a more energy-efficient manner. The novel route developed in this work is a viable option for chitosan NP synthesis.

Lead ion adsorption on functionalized sugarcane bagasse prepared by concerted oxidation and deprotonation.

Targeting the removal of Pb2+ in wastewater, sugarcane bagasse was treated with nitric acid and an alkaline solution to prepare adsorbents. On a typical adsorbent, the adsorption isotherms agreed well with the Langmuir expression, and the maximum adsorption capacity reached 200.3 mg/g. In the presence of 150 ppm Ca2+, a common cation in natural water, the Pb2+ adsorption capacity slightly declined. In contrast, Mg2+ obviously prohibited the adsorption for Pb2+. The spent adsorbent could be regenerated at least five times through elution with an EDTA solution. EDS and XPS results demonstrated that nitric acid functioned as an oxidant instead of nitrification agent in the treatment of bagasse. The adsorption process was consistent with quasi-second-order kinetics. Based on thermodynamic studies, the changes in enthalpy and Gibbs free energy were calculated to be - 33.3 and ca. - 18 kJ/mol, indicating that the adsorption process was exothermic and spontaneous. The equilibrium Pb2+ adsorption amounts were proportional to the numbers of carboxylate groups on different adsorbents. The binding energies of Pd 4f5/2 and Pd 4f7/2 XPS spectra of Pb2+ adsorbed were 0.6-0.7 eV lower than those of free Pb(NO3)2, indicating the transfer of electrons during adsorption. The conversion of hydroxymethyl groups in sugarcane bagasse into carboxylate groups, as well as the chelation between Pb2+ ions and carboxylate groups, was validated in this work, which is beneficial for the treatment of wastewater polluted by lead ions.

Fast and reversible adsorption for dibenzothiophene in fuel oils with metallic nano-copper supported on mesoporous silica.

Dibenzothiophene (DBT) in fuel oils causes the release of toxic sulfur oxide gases, and it is necessary to remove DBT in fuels. Herein, metallic copper was loaded on SBA-15 mesoporous silica through simple reduction reactions for the preparation of DBT adsorbents. On an adsorbent with a copper loading of 0.3 wt%, adsorption equilibrium was achieved within 5 min, and a DBT removal rate of 90.4% was achieved. The adsorption isotherm agreed with a linear Freundlich model and adsorption capacity was 12.1 mg sulfur/g. Nano-sized copper particles were observed by TEM, indicating the size effect of copper particles in DBT adsorption. A broad band, corresponding to copper-sulfur coordination bonds, was observed at 300-600 cm-1 in the Raman spectrum of DBT-doped adsorbent. Meanwhile, the band at 1233 cm-1 corresponding to C = C (-S) bonds in DBT was shifted to 1229 cm-1 in DBT adsorbed. XPS and Cu LMM XPS spectra proved that Cu(0) was oxidized by DBT sulfur during adsorption. Furthermore, Auger spectra verified that the adsorption of DBT on Cu(0) involved the formation of Cu(I) and Cu(II) species through coordination bonds. The adsorption capacity could be completely recovered via elution. This work sheds light on the removal of DBT in fuel oils with cost-effective efficient adsorbents.

Fabrication of composites with ultra-low chitosan loadings and the adsorption mechanism for lead ions.

Through a facile impregnation-precipitation strategy, chitosan was dispersed on bentonite to prepare an organic/inorganic hybrid composite for Pb2+ adsorption. The strong promotion effect of a small amount of highly dispersed chitosan on the Pb2+ adsorption capacity of clay minerals was unveiled. With a chitosan loading of 0.4 wt%, the experimental adsorption capacity reached 261.3 mg/g. The good dispersion of chitosan played a crucial role in the high capacity. The large proportion of mesopores in the adsorbent facilitated mass transfer, and thereby adsorption equilibrium states could be achieved within 15 s. The adsorption isotherms were consistent with the Freundlich expression. The Pb2+ adsorption capacity was suppressed with the addition of 150 ppm Ca2+ and almost eliminated in the presence of 150 ppm Mg2+. The adsorption enthalpy change was measured to be - 28.6 kJ/mol and Gibbs free energy change was in the range of - 18.4 to - 16.7 kJ/mol, indicating that this adsorption process was exothermic and spontaneous. The FTIR and XPS results demonstrated that the amino groups on chitosan could bond with Pb2+, and contributed to the high adsorption capacity. DFT calculation results showed that the amino and hydroxyl groups in adjacent chitosan units could be tri-coordinated with Pb2+, and the energy of system was greatly decreased due to the coordination interaction.

Ultrasonic assisted water-in-oil emulsions encapsulating macro-molecular polysaccharide chitosan: Influence of molecular properties, emulsion viscosity and their stability.

An ultrasonic technique was applied to formulation of two-phase water-in-paraffin oil emulsions loading a high-molecular polysaccharide chitosan (CS) and stabilized by an oil-soluble surfactant (Span80) at different operational conditions. The influence of chitosan molecular properties, phase volume ratio (φw), Span80 volume fraction (φs) and ultrasonic processing parameters were systemically investigated on the basis of mean droplet diameter (MDD) and polydispersity index (PDI) of emulsions. It was observed that the molecular weight (Mw) of CS was an important influential factor to MDD due to the non-Newtonian properties of CS solution varying with Mw. The minimum MDD of 198.5 nm with PDI of 0.326 was obtained with ultrasonic amplitude of 32% for 15 min at an optimum φw of 35%, φs of 8%, probe position of 2.2 cm to the top of emulsion, while CS with Mw of 400 kDa and deacetylation degree of 84.6% was used. The rise of emulsion viscosity and the reduction of negative zeta potential at φw increasing from 5% to 35% were beneficial to obtain finer droplets and more uniform distribution of emulsions, and emulsion viscosity could be represented as a monotonically-decreasing power function of MDD at the same φw. FTIR analysis indicated that the molecular structure of paraffin oil was unaffected during ultrasonication. Moreover, the emulsions exhibited a good stability at 4 °C with a slight phase separation at 25 °C after 24 h of storage. By analyzing the evolution of MDD, PDI and sedimentation index (SI) with time, coalescence model showed better fitting results as comparison to Ostwald ripening model, which demonstrated that the coalescence or flocculation was the dominant destabilizing mechanism for such W/O emulsions encapsulating CS. This study may provide a valuable contribution for the application of a non-Newtonian macromolecule solution as dispersed phase to generate nano-size W/O emulsions via ultrasound, and widen knowledge and interest of such emulsions in the functional biomaterial field.

Swirling cavitation improves the emulsifying properties of commercial soy protein isolate.

Since emulsifying properties are important functional properties of soy protein, many physical, chemical, and enzymatic methods have been applied to treat soy protein to improve emulsifying properties. In this study, we investigated the effects of swirling cavitation at different pressures and for different times on emulsifying and physicochemical properties of soy protein isolate (SPI). The SPI treated with swirling cavitation showed a significant decrease in particle size and increase in solubility. Emulsions formed from treated SPI had higher emulsifying activity and emulsifying stability indexes, smaller oil droplet sizes, lower flocculation indexes, higher adsorbed proteins, lower interfacial protein concentrations, and lower creaming indexes than those formed from untreated SPI, indicating that swirling cavitation improved the emulsifying properties of the SPI. Furthermore, swirling cavitation treatment significantly enhanced the surface hydrophobicity, altered the disulfide bond and exposed sulfhydryl group contents of the SPI. The secondary structure of the SPI was also influenced by swirling cavitation, with an increase in ß-sheet content and a decrease in α-helix, ß-turn, and random coil contents. In addition, several significant correlations between physicochemical and emulsifying properties were revealed by Pearson correlation analysis, suggesting that the physicochemical changes observed in treated SPI, including the decreased particle size, increased solubility and surface hydrophobicity, and enhanced ß-sheet formation, may explain the improved emulsifying properties of the isolate. Thus, our findings implied that swirling cavitation treatment may be an effective technique to improve the emulsifying properties of SPI.