Synergetic effect of ozone and ultrasonic radiation on degradation of chitosan

Under conditions of continuous ozone gas application and constant ultrasonic radiation (UR), chitosan was effectively degraded. The existence of a synergetic effect of ozone and ultrasonic radiation on the degradation of chitosan was demonstrated by means of determination of viscosity-average molecular weight. The efficiency of the ozone and ultrasonic radiation treatment compared with acid hydrolysis on degradation of chitosan was investigated. In addition, the structure of the degraded chitosan was characterized by FT-IR and ¹³C NMR spectral analyses. The whole initial chitosan's monomer structure still existed in the resulting degraded chitosan with different low molecular weight. The pilot study of the chemical stability of the degraded chitosan was carried out. There was no significant change of the total degree of deacetylation (DD) of degraded chitosan compared with the initial chitosan. The combined O₃/UR technique is promisingly suitable for scale-up manufacture of low-molecular-weight chitosan.     

Preparation and Characterization of Quaternized Chitosan Under Microwave Irradiation

For the first time, N-(2-hydroxyl) propyl-3-trimethyl ammonium chitosan chloride (HTCC) was prepared through a fast, easy and efficient method with the assistance of microwave irradiation, and the quaternized chitosan was also degraded via the microwave irradiation. A comparative study was performed by using the conventional heating method to prepare HTCC. The structure and property of the quaternized chitosan obtained by these two methods were characterized by GPC, XRD, FTIR, NMR, TG and elemental analysis. It was shown that quaternized chitosan was successfully prepared within 50 min via microwave irradiation method, while a much longer time of 6–7 h was needed with the conventional heating method. The substitutions both occurred on the C2 position of chitosan with the two different methods, and their HTCC products had weight average similar molecular weight (Mw), structure and thermal stability. The HTCC prepared by the microwave irradiation method had a little lower degree of substitution (DS) than those prepared via conventional heating with the same mole ratio (6:1) of the intermediate to chitosan. The degradation study showed that the Mw of HTCC decreased rapidly from 4.6 × 10⁵ to 1.1 × 10⁵ in 1 h under microwave irradiation, while it only decreased from 4.6 × 10⁵ to 2.1 × 10⁵in 1 h through conventional heating degradation. These results revealed that microwave irradiation is a more efficient and environment-friendly way to obtain the water-soluble chitosan derivatives and their degraded products.     

Ultrasonic Degradation of Hydroxypropyl Cellulose Solutions in Water,Ethanol, and Tetrahydrofuran

Ultrasonic degradations of hydroxypropyl cellulose (HPC) have been carried out in water, ethanol, and tetrahydrofuran (THF) solutions. In the HPC-water system, cavitation intensity did not increase linearly with ultrasound intensity because of a lower threshold of ultrasonic intensity below which cavitation does not occur. At 27°C the rate of degradation in the three solvents followed the order water > ethanol > THF which is not in line with their characteristic impedance values. The rate of degradation for 20 kHz, 70 W ultrasound intensity was found to increase with a decrease in solution volumes, concentration of HPC, and temperature. Increased rate of degradation at lower temperatures supports the concept based on sonoluminescence experiments that it is the cavitation in a polymer solution that is responsible for ultrasonic degradations and the dissolved polymer molecules do not act as cavitation nuclei. Increased surface tension and density of the solvent are thought to be responsible for improved cavitation at low temperatures. Infrared spectroscopy and x-ray analysis of HPC subjected to ultrasonic treatments remained unchanged, suggesting that there were no chemical or structural (e.g., degree of order) changes on irradiation. The decreases in molecular weights on irradiation arise due to random chain scission whereas similar decreases in Huggins coefficients can be attributed to physical changes (decrease in molecular weight or branching) in the degraded HPC samples.     

臭氧降解法制备壳低聚糖及其结构表征

以85％脱乙酰度、相对分子质量为25×10^4的壳聚糖为原料,在20℃、pH为3、氧气流量0．7m^3／h的条件下降解6h,降解液用氨水调至pH为9,无沉淀,分别用截留相对分子质量为2k、3k、5k、10k的中空纤维膜超滤,获得所需聚合度的壳低聚糖。降解产物的结构用红外光谱、核磁共振碳谱表征,结果说明降解前后的结构基本没有变化。降解产物的聚合度用飞行时间质谱表征,其中经过2k中空纤维膜超滤后的壳低聚糖聚合度主要为4～10。     

Lumped kinetic model for degradation of chitosan by hydrodynamic cavitation

The lumped kinetic model for the degradation reactions of chitosan by hydrodynamic cavitation was investigated in this study. The molecular weight distributions and mass concentrations were determined by gel permeation chromatograph (GPC). The degradation products were divided into several lumps according to their molecular weights. The appropriate number of lumps for the kinetic study was determined by comparing the residual sum of squares (RSS) values among different models. The RSS of six-lumped model (5.36 × 10^?3) was relatively small and the estimation of parameters was simpler than other models. In this paper, six-lumped kinetic model was adopted and the corresponding reaction network was established. The kinetic parameters were estimated with the Levenberg-Marquardt, and the results showed that the degradation reaction of chitosan was mainly dominated by the formation of degradation products with similar molecular weights. The maximum value of kinetic parameters on the diagonal of the reaction network (1.63 × 10^?1) was much larger than that of non-diagonal kinetic parameters (3.78 × 10^?2). According to the results calculated and measured under different conditions, this model could accurately predict the concentration distributions of lumps in the reaction network, and most of the average absolute deviation were smaller than 9.3%.     

Ultrasonic degradation of solutions of poly(vinyl acetate) in dioxan: The effects of the temperature and polymer concentration

The ultrasonic degradation of poly(vinyl acetate) (PVAc) solutions was carried out in dioxan at 25, 30, 35, 40, and 45 °C to investigate the effects of the temperature and solution concentration on the rate of degradation. The kinetics of degradation were studied by viscometry. The calculated rate constants indicated that the degradation rate of the PVAc solutions decreased as the temperature and solution concentration increased. The calculated rate constants were correlated in terms of the concentration, temperature, vapor pressure of dioxan, and relative viscosity of the PVAc solutions. This degradation behavior was interpreted in terms of the vapor pressure of dioxan, the viscosity, and the concentration of the polymer solutions. With increasing temperature, the vapor pressure of the solvent increased, and so the vapor entered the cavitation bubbles during their growth. This caused a reduction in collapsing shock because of a cushioning effect; therefore, the rate of degradation decreased. As the solution concentration increased, the viscosity increased and caused a reduction in the cavitation efficiency, and so the rate of degradation decreased. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 445–451, 2004     

Synergetic degradation of chitosan with gamma radiation and hydrogen peroxide

Chitosan samples were irradiated by ⁶⁰Co γ-rays in the presence of hydrogen peroxide with radiation dose from 10 kGy to 100 kGy. The degradation was monitored by gel permeation chromatography (GPC), revealing the existence of a synergetic effect on the degradation. Structures of the degraded products were characterized with Fourier-transform infrared spectra (FT-IR), ultraviolet-visible spectral (UV-vis) analysis, and X-ray diffraction (XRD). Results showed that the crystallinity of chitosan decreases with degradation, and the crystalline state of water-soluble chitosan is entirely different from that of water-insoluble chitosan. An elemental analysis method was employed to investigate changes in the element content of chitosan after degradation. Mechanism of chitosan radiation degradation with and without hydrogen peroxide was also discussed.     

Effect of neutralization and cross-linking on the thermal degradation of chitosan electrospun membranes

Thermal degradation of as-electrospun chitosan membranes and samples subsequently treated with ethanol and cross-linked with glutaraldehyde has been studied by thermogravimetry (TG) coupled with an infrared spectrometer. The influence of the electrospinning process and cross-linking in the electrospun chitosan thermal stability was evaluated. Up to three degradation steps were observed in the TG data, corresponding to water dehydration reaction at temperatures below 100 °C, loss of side groups formed between the amine groups of chitosan and trifluoroacetic acid between 150 and 270 °C and chitosan thermal degradation that starts around 250 °C and goes up to 400 °C. The Kissinger model was employed to evaluate the activation energies of the electrospun membranes during isothermal experiments and revealed that thermal degradation activation energy increases for the samples processed by electrospinning and subsequent neutralization and cross-linking treatments with respect to the neat chitosan powder.     

Thermal degradation of bisphenol a polycarbonate

Bisphenol A polycarbonate (Makrolon 3000) has been purified and fractionated. Thin films of these samples have been degraded by heating at 200° under continuous evacuation (pressure less than 0- 1 Pa) for periods of several hours. The molecular weight is observed (by gel permeation chromatography) to increase with time at 200°. Eventually gel is formed. The variation of the number- and weight-average molecular weights with heating time and the effect of the initial molecular weights of the polycarbonate samples are consistent, in the main, with the Davis-Golden mechanism of thermal degradation of bisphenol A polycarbonate; i.e. the principal reactions are condensation and trifunctional branching. Chain scission due to hydrolysis of the carbonate linkage is absent under our conditions.     

Synergistic degradation to prepare oligochitosan by γ-irradiation of chitosan solution in the presence of hydrogen peroxide

Synergistic degradation of chitosan by γ-irradiation of chitosan solution (3%) in the presence of hydrogen peroxide (0.25%, 0.5% and 1%) was investigated. The efficiency of the degradation process was demonstrated by gel permeation chromatography (GPC) analysis of the average molecular weight of degraded chitosan (oligochitosan). Structures of resultant oligochitosan were characterized by Fourier-transform infrared spectra (FT-IR) and X-ray diffraction (XRD). Results showed that oligochitosan with Mw from 5000 to 10,000 could be efficiently prepared by γ-irradiation of chitosan solution containing a small amount of hydrogen peroxide at low dose less than 10 kGy. There was almost no significant change in the main chain structure of oligochitosan; however, the obtained oligochitosans lost about 10% of amino groups and the formation of carboxyl groups could not be specified by FT-IR spectra. The morphology state of oligochitosan was essentially amorphous, which differs from that of original chitosan. The combined γ ray/H₂O₂ method is significantly efficient for scale-up manufacture of oligochitosan.     

High-yield synthesis of pure ZnO nanoparticles by one-step solid-state reaction approach for enhanced photocatalytic activity

Zinc oxide (ZnO) nanostructures were synthesized via a one-step solid-state reaction approach in ammonia (NH₃) gas environment with different temperature ramp rates. The so-formed nanostructures were characterized using X-ray diffraction (XRD) for phase identification, where the typical wurtzite hexagonal structure was observed. Scanning electron microscopy (SEM) confirmed the particle size to be in the range 45–50 nm, the same as calculated by the XRD pattern for the ramp rate of 10 °C/min. Energy dispersive X-ray (EDX) spectroscopy and X-ray photoelectron spectroscopy (XPS) confirmed the chemical purity of the samples. The photoluminescence (PL) spectrum indicated multiple near-band-edge emissions and energy-band emissions. Then, these ZnO nanomaterials were used for the degradation of crystal violet (CV) dye under UV light irradiation. The CV solution was completely degraded in 2 hr. The initial photocatalyst and dye amounts of 0.2 g/100 ml and 0.5 mg/L, respectively, were found to be the optimum values for maximum degradation efficiency. The ZnO-based photocatalyst was stable up to three cycles of reuse. These results indicate that the high surface area and porosity of the nanomaterials are responsible for the high efficiency, which was confirmed by specific surface area analysis.     

Effects of initial concentration of LASs on the rates of sonochemical degradation and cavitation efficiency

The effect of initial concentration of linear alkylbenzene sulfonate (LAS: p-octylbenzene sulfonate (LAS C₈), p-nonylbenzene sulfonate (LAS C₉), p-dodecylbenzene sulfonate (LAS C₁₂)) on the rate of sonochemical degradation was investigated over a wide concentration range under Ar atmosphere by 200 kHz ultrasonic irradiation. The degradation rate of each LAS increased with increasing initial concentration of LAS and then started to decrease with the different behavior depending on the types of LASs. This result indicated that the cavitation efficiency was gradually changed by their concentrations and the optimum LAS concentrations for their effective degradation existed. The maximum degradation rates were observed at 250 μM of LAS C₁₂, 1250 μM of LAS C₉, and 2500 μM of LAS C₈, respectively. These optimum concentrations were found to be about four to six times smaller than these critical micelle concentrations (CMCs). It was also found that the maximum degradation rates at the optimum concentrations were observed to be almost linearly correlated with their CMCs. Based on the obtained results, it could be suggested that the micelle formation occurs in the interfacial region of cavitation bubbles during rectified diffusion and this phenomenon reduces the cavitation efficiency. In addition, from the results of the rate of the sonochemical degradation of LASs and the yield of hydrogen peroxide, the existence of thermal gradient in the interfacial region of cavitation bubbles was also confirmed.     

Characterization and Stability Study of Immobilized PQQ‐Dependent Aldose Dehydrogenase Bioanodes

In this paper, glucose oxidizing bioanodes employing immobilized PQQ‐dependent aldose dehydrogenase were prepared and characterized. The enzyme was immobilized on carbon paper in two different polymeric systems: tetrabutylammonium bromide (TBAB) modified Nafion and butanal modified chitosan. Characterization of the bioanodes included electron microscopy, electrochemical evaluation, as well as stability and leaching studies. Results indicate that the operational degradation was the same but the long term storage stability is better in the case of modified Nafion. The performance of the modified Nafion immobilized bioanodes stayed at 70 % of the initial value after 60 days of storing at 4 °C and 25 °C. Compared to TBAB modified Nafion immobilized bioanodes, butanal modified chitosan immobilized bioanodes showed 50 % activity after eight weeks storage at 4°C and one week storage at 25 °C. However, the electrochemical properties of modified chitosan were better.     

Synthesis and hydrolytic degradation of aliphatic polycarbonate based on dihydroxyacetone

The six-membered cyclic carbonate monomer, 2,2-dimethoxy-1,3-propanediol carbonate based on dihydroxyacetone with methanol ketal protected carbonyl group, was prepared by a two-step reaction including protection and ring-closing, starting from dihydroxyacetone. The ring-opening polymerization of 2,2-dimethoxy-1,3-propanediol carbonate was carried out in bulk at 110–140°C initiated by stannous octanoate to give polycarbonate, poly(2,2-dimethoxypropane-1,3-diol carbonate). The effects of different reaction conditions including different catalyst, reaction temperature, molar ratio of monomer to initiator and polymerization time on the polymerization were investigated. Polycarbonate was obtained with the yield of 58.9–91.0%. The number average molecular weight of polycarbonate was in the range of 1.43 × 10⁴ to 13.82 × 10⁴ with polydispersity indexes from 1.31 to 1.91. The protecting ketal group was partly removed by hydrolysis using 50% trifluroacetic acid as a catalyst to give a functional polycarbonate containing 70% ketone carbonyl group, which improved the hydrophilicity of initial polycarbonate. The in vitro degradation tests were carried out in a phosphate buffer solution with pH 7.4 at 37°C, which showed that the modified polycarbonate degraded completely after 5 days.     

壳聚糖超声可控降解及降解动力学研究

通过正交实验法考察了壳聚糖溶液浓度、反应温度、超声强度以及醋酸溶液浓度对超声降解反应的影响,确定了最佳反应条件,制备了一系列不同分子量的壳聚糖.研究了壳聚糖溶液浓度、反应温度以及壳聚糖原料分子参数与降解速率常数的关系.通过红外光谱、X-射线衍射和凝胶渗透色谱对降解产物进行了表征.结果表明,超声降解壳聚糖的最佳条件为10℃,壳聚糖溶液浓度2.5g/L.降解速率常数随壳聚糖溶液浓度和反应温度的降低而增大.高分子量和低脱乙酰度的壳聚糖原料有较高的降解速率和降解速率常数,壳聚糖原料的分子量对降解速率和降解速率常数的影响大于脱乙酰度对其的影响.超声波导致了壳聚糖分子量的降低和产物晶体结构的破坏,但没有改变产物的脱乙酰度和糖残基结构.     

Study of the isothermal degradation of poly(vinyl chloride) by direct inlet mass spectrometry

Films of poly(vinyl chloride) (PVC) were degraded isothermally at 160, 180, 200, 220, 240 and 280°C for 30 min in the ion source of a mass spectrometer and the volatile products of degradation were monitored by direct inlet mass spectrometry, which has the advantage of monitoring several degradation products at the same time. Both the evolution rate of the volatile products and their composition were recorded during the isothermal degradation of PVC. A technique was developed for the preparation of samples that improves the repeatability of the method.     

The photocatalytic performance for Mn-doping SrMoO4 reduced in H2/N2 mixture atmospheres

SrMoO₄ and Mn-doped SrMoO₄ nanoparticles have been synthesized by high temperature thermal decomposition of metal–organic salt in organic solvent with a high boiling point. Then they were reduced in H₂/N₂ mixture atmospheres at different reducing temperatures T_R. Samples were characterized by X-ray diffraction (XRD), UV–visible light spectrum (UV), and X-ray photoelectron spectroscopy (XPS). The XRD and XPS results showed that SrMoO₃ phase appears when the annealing temperature was 700 °C (SMO700). The light absorption edge shifted to the visible range and enhanced the visible light photocatalytic activity. The methyl blue (MB) solution was degraded, and the degradation efficiency was 80.30% in 120 min for SMO700 sample. For the 2%Mn doping SrMoO₄ sample, the efficiency of degradation reached 97.53% when the annealing temperature was 700 °C(2Mn-SMO700). The results showed that a certain amount of SrMoO₃ is helpful to improve the photocatalytic performance of SrMoO₄. In addition, the photocatalytic performance of SrMoO₄ was also related to Mn-doped amount, annealing temperature and annealing time in H₂/N₂ mixture atmospheres. The related mechanism was discussed.     

Microstructure and ionic conductivity of lithium-aluminum titanophosphate

Synthesis from aqueous peroxide solutions provides lithium-aluminum titanophosphate Li_1.3Al_0.3Ti_1.7(PO₄)₃ (LATP) with particles of submicron size and conductivity of (4–5) × 10^?4 S/cm at the room temperature. LATP were characterized using the methods of XRD, DTA/TG, measurement of specific surface area, ionic and electronic conductivity. According to XRD, a single-phase crystalline product with the specific surface area of 8.2 m²/g is formed as a result of precursor sintering at 700°C (the average particle size of electrolyte was 250 nm). Sizes of coherent-scattering region were calculated on the basis of the values of intrinsic broadening of diffraction maximums. Analysis of broadening of diffraction maximums indicates that the size of primary LATP crystallites after sintering at 700°C was 90 nm according to peak (113) (2θ = 24.5°) and 110 nm according to peak (104) (2θ = 20.9°). The synthesized submicron LATP powders are suitable for formation of solid electrolyte films using the method of aerosol deposition.     

Radical ring-opening polymerization of lipoates: Kinetic and thermodynamic aspects

The radical ring-opening polymerization of a lipoate-based monomer, ethyl lipoate, in bulk and in solution was studied at various temperatures and it was found that in all cases, only limited (plateau) conversions were reached, which were lower at higher temperatures and/or at higher dilutions. It was established that a monomer-polymer equilibrium exists with a corresponding ceiling temperature of 139°C. Due to the reversibility of the lipoate polymerization, when poly(ethyl lipoate) was heated to 150°C, it degraded and within 3 h, the molecular weight decreased to less than 15% of the initial value. Likewise, when the polymer was dissolved in anisole and a radical initiator was added, degradation was observed even at 60°C and it became increasingly pronounced at higher concentrations of the radical source. Due to the presence of multiple disulfide groups in the backbone, poly(ethyl lipoate) also degraded in the presence of reducing agents, such as tributylphosphine, yielding the reduced (dithiol) form of the monomer, ethyl dihydrolipoate.     

Influence of molecular parameters on the degradation of chitosan by a commercial enzyme

The degradative activities of neutral protease against chitosan samples with different molecular parameters were characterized. The effects of the degree of deacetylation (DD) and molecular weight (MW) of chitosan on its susceptibility to degradation were investigated. The DD and MW of the chitosans were determined using potentiometric titration and viscometry, respectively. The molecular weight distribution of initial and degraded commercial chitosan was investigated by gel permeation chromatography. Initial degradation rates (r) were determined from the plots of viscosity decrease against time of degradation. The time courses of degradation of chitosans with neutral protease were non-linear and the enzymatic hydrolysis was an endo-action. Classical Michaelis-Menten kinetic parameters were measured by analyzing the amount of reducing sugars and Eadie-Hofstee plots established that hydrolysis of chitosan by neutral protease obeyed Michaelis-Menten kinetics. Michaelis-Menten parameters and initial degradation rates were calculated and compared to determine the influences of DD and MW on hydrolysis. The results showed that higher DD and higher MW chitosans possessed a lower affinity for the enzyme and a slower degradation rate. Those samples with a lower DD and lower MW were more susceptible substrates.