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The objective of the study is to elucidate the effect of reaction time and temperature during heterogenous alkali reaction on degree of deacetylation (DD) and molecular weight (MW) of the resulting chitosans, and to establish the reaction conditions to obtain desired DD and MW chitosan products. Chitin was extracted from red shrimp process waste. DDs and MWs were determined by infrared spectroscopy (IR) and static light scattering, respectively. The results are as follow: The DD and MW of chitin obtained were 31.9% and 5637 kDa, respectively. The DD of the resulting chitosan increased along with reaction time and/or reaction temperature. The DDs of the resulting chitosan that were obtained from 140°C were higher than those reacted at 99°C. The highest DD of the resulting chitosans after alkali deacetylation at 99 and 140°C were 92.2 and 95.1%, respectively. The DDs of chitosans increased fast at the beginning of reaction process then slowed over time. The reaction rate and rate constant of the deacetylation reaction decreased with increasing DD of the reactant. The MWs of chitosans decreased along with the deacetylation time. MW of those chitosans reacted at 140°C are smaller than those at 99°C. The rate of chitosan degradation was above 43.6%/h in the initial stage, then decreased to about 20%/h. The degradation rate constants raised substantially in the late stage. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2917–2923, 2003 相似文献
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The objective of the study was to explore the effect of the degree of deacetylation (DD) of the chitosan used on the degradation rate and rate constant during ultrasonic degradation. Chitin was extracted from red shrimp process waste. Four different DD chitosans were prepared from chitin by alkali deacetylation. Those chitosans were degraded by ultrasonic radiation to different molecular weights. Changes of the molecular weight were determined by light scattering, and data of molecular weight changes were used to calculate the degradation rate and rate constant. The results were as follows: The molecular weight of chitosans decreased with an increasing ultrasonication time. The curves of the molecular weight versus the ultrasonication time were broken at 1‐h treatment. The degradation rate and rate constant of sonolysis decreased with an increasing ultrasonication time. This may be because the chances of being attacked by the cavitation energy increased with an increasing molecular weight species and may be because smaller molecular weight species have shorter relaxation times and, thus, can alleviate the sonication stress easier. However, the degradation rate and rate constant of sonolysis increased with an increasing DD of the chitosan used. This may be because the flexibilitier molecules of higher DD chitosans are more susceptible to the shear force of elongation flow generated by the cavitation field or due to the bond energy difference of acetamido and β‐1,4‐glucoside linkage or hydrogen bonds. Breakage of the β‐1,4‐glucoside linkage will result in lower molecular weight and an increasing reaction rate and rate constant. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 3526–3531, 2003 相似文献
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红外光谱法测定壳聚糖脱乙酰度 总被引:4,自引:0,他引:4
以碱量法为对比方法,考察了基于A1655/A3450和A1320/A1420的2种红外光谱计算壳聚糖脱乙酰度方法的准确性。结果表明,红外光谱法虽精密度低于碱量法,但基于A1655/A3450的红外测试结果与碱量法基本相吻合;基于A1320/A1420加的红外光谱计算结果略高于碱量法,与商家标注值相吻合,且不受样品含少量水、残酸或残碱的影响。红外光谱法是一种较为理想的壳聚糖脱乙酰度测定方法,同时采用A1655/A3450和A1320/A1420计算更利于得到准确的测定结果。 相似文献
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Xuguang Li 《Electrochimica acta》2006,51(25):5250-5258
Carbon nanotube supported platinum (Pt/CNTs) catalysts prepared by different Pt deposition methods and on different CNT supports were studied. Colloidal based methods were demonstrated to be more effective than other wet chemistry deposition methods (e.g., impregnation and precipitation) for the preparation of highly dispersed Pt/CNTs. Pt catalyst supported on CNTs with a dispersion uniformity comparable to that supported on carbon powder was achieved using a zwitterionic surfactant 3-(N,N-dimethyldodecylammonio) propanesulfonate (SB12) as stabilizer in a monitored pH environment. It was experimentally observed that oxygen-containing surface functionalities on CNTs can greatly affect the catalyst particle dispersion by manipulating Pt anchoring and/or nucleating sites. Furthermore, it was revealed that the performance of Pt/CNTs based fuel cell is strongly dependent on the electrode fabrication method. 相似文献
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Copper chitosan complexes prepared by different specifications of chitosan and copper sulfate were used as urea sorbents. Experimental results showed that the adsorption capacity for urea of copper chitosan increased with an increasing degree of deacetylation and decreasing molecular weight of chitosan. The urea adsorption capacity of copper chitosan was 120.0 mg/g, when 1.0 g of copper chitosan was admitted to 100 mL of a 1300 mg/mL (pH 6.0) urea solution, with chitosan degree of deacetylation of 84.3% and viscosity molecular weight of 6.5 × 105, at 37°C for 8 h. No elution of the copper from the copper chitosan could be detected under the optimal conditions. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 1520–1523, 2003 相似文献
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Decoration of carbon nanotubes with chitosan 总被引:2,自引:0,他引:2
In this letter, a non-destroyable surface decoration of carbon nanotubes with biopolymer chitsoan via a controlled surface-deposition and crosslinking process is described. The method utilizes the emulsifying capacity of chitosan, the completely different water-solubility of chitosan in acidic and basic solutions, and the crosslinking reaction among chitosan polymers. As the pristine structures of the carbon nanotubes are not recomposed under those treatments, the unique properties of the pristine carbon nanotubes have not been compromised. Combining the properties of carbon nanotubes and the versatility and biocompatibility of chitosan, these chitosan surface-decorated carbon nanotubes could find potential applications in biosensing, gene and drug delivering as well as other chemical and biological applications. 相似文献
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Effects of the degree of deacetylation (DDA) and the molecular mass of chitosan oligosaccharides (CTS-OS), obtained from the enzymatic hydrolysis of high molecular weight chitosan (HMWC), on antitumor activity was explored. The DDA and molecular weights of CTS-OS were determined by matrix-assisted laser desorption/ionization-mass spectrometry (MALDI-TOF MS) analysis. The CTS-OS were found to be a mixture of mainly dimers (18.8%), trimers (24.8%), tetramers (24.9%), pentamers (17.7%), hexamers (7.1%), heptamers (3.3%), and octamers (3.4%). The CTS-OS were further fractionated by gel-filtration chromatography into two major fractions: (1) COS, consisting of glucosamine (GlcN)(n), n = 3-5 with DDA 100%; and (2) HOS, consisting of (GlcN)(5) as the minimum residues and varying number of N-acetylglucosamine (GlcNAc)(n), n = 1-2 with DDA about 87.5% in random order. The cytotoxicities, expressed as the concentration needed for 50% cell death (CC(50)), of CTS-OS, COS, and HOS against PC3 (prostate cancer cell), A549 (lung cancer cell), and HepG2 (hepatoma cell), were determined to be 25 μg·mL(-1), 25 μg·mL(-1), and 50 μg·mL(-1), respectively. The HMWC was approximately 50% less effective than both CTS-OS and COS. These results demonstrate that the molecular weight and DDA of chitosan oligosaccharides are important factors for suppressing cancer cell growth. 相似文献
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The efficacy with which a range of nanotubes could reinforce a high density polyethylene (HDPE) matrix was investigated, in relation to nanotube diameter, purity, functionalization, alignment and nanotube bulk density. Composites were prepared by melt blending multiwall carbon nanotubes (MWNTs) with high density polyethylene (HDPE), followed by the injection molding of tensile specimens. At a 5 wt% loading, the most effective nanotubes were those of large diameter, received in an aligned form with low bulk density, producing a 66% increase in elastic modulus and a 69% improvement in yield stress. This was contradictory to theoretical mechanics calculations that predicted an increasing degree of reinforcement for nanotubes of reduced diameter. This difference was explained by the higher degree of dispersion observed in the composites with MWNTs of greater diameter. 相似文献
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Catarina Motta de Moura Jaqueline Motta de Moura Niege Madeira Soares Luiz Antonio de Almeida Pinto 《Chemical Engineering and Processing: Process Intensification》2011,50(4):351-355
Chitosan is a polysaccharide derived from chitin, mainly of crustacean shells and shrimp wastes. The utilization of chitosan is related to the molar weight and deacetylation degree of the biopolymer. The aim of this work is to study the chitin deacetylation reaction, by the viscosity average molar weight and deacetylation degree of chitosan as a function of reaction time. Deacetylation was carried out in concentrated alkaline solution, 421 g L−1, at 130 °C and the reaction occurred during 4 h. Chitosan paste obtained after 20, 90 and 240 min was used to produce biofilms, which were characterized according water vapor permeability and mechanical properties (tensile strength and percentage tensile elongation at break). During the reaction time deacetylation degree reached 93%, and a 50% reduction in the viscosity average molar weight value in relation to the value of the first 20 min of reaction was found Both reactions presented a kinetic behavior of the pseudo-first order. Biofilm produced from the paste of chitosan with high deacetylation degree showed higher water vapor permeability (WVP), tensile strength (TS) and elongation (E) when compared to films with a low deacetylation. 相似文献
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Amal M.K. Esawi Hanadi G. Salem Hanady M. Hussein Adham R. Ramadan 《Polymer Composites》2010,31(5):772-780
Carbon nanotube‐reinforced polymer composites are being investigated as promising new materials having enhanced physical and mechanical properties. With regards to mechanical behavior, the enhancements reported thus far by researchers are lower than the theoretical predictions. One of the key requirements to attaining enhanced behavior is a uniform dispersion of the nanotubes within the polymer matrix. Although solvent mixing has been used extensively, there are concerns that any remaining solvent within the composite may degrade its mechanical properties. In this work, a comparison is carried out between solvent and “solvent‐free” dry mixing for dispersing multiwall carbon nanotubes in polypropylene before further melt mixing by extrusion. Various weight fractions of carbon nanotubes (CNTs) are added to the polymer and their effect on the mechanical properties of the resulting composites is investigated. Enhancements in yield strength, hardness, and Young's modulus when compared with the neat polymer, processed under similar conditions, are observed. Differences in mechanical properties and strain as a function of the processing technique (solvent or dry) are also clearly noted. In addition, different trends of enhancement of mechanical properties for the solvent and dry‐mixed extrudates are observed. Dry mixing produces composites with the highest yield strength, hardness, and modulus at 0.5 wt% CNT, whereas solvent mixing produces the highest mechanical properties at CNT contents of 1 wt%. It is believed that this difference is primarily dependent on the dispersion of CNTs within the polymer matrix which is influenced by the processing technique. Field emission scanning electron microscopy analysis shows the presence of clusters in large wt% CNT samples produced by dry mixing. Samples produced by solvent mixing are found to contain homogeneously distributed CNTs at all CNT wt fractions. CNT pull‐out is observed and may explain the limited enhancement in mechanical properties. POLYM. COMPOS., 2010. © 2009 Society of Plastics Engineers 相似文献
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The dispersion of three kinds of acid‐treated carbon nanotubes (CNTs) in poly(acrylic acid) (PAA) aqueous solution of different pH and ionic strengths (varied by NaCl, KCl and ZnCl2) was investigated by visual observation, zeta potential, particle size analysis, transmission electron microscopy and scanning electron microscopy. Visual observation revealed that the dispersion of CNTs acid treated at 60 °C for 3 h and at 80 °C for 2 h was poor in aqueous solutions with pH < 2 or pH > 12. The poor dispersion of acid‐treated CNTs may be improved by adding PAA. In particular, PAA improved the dispersion of CNTs with greater COOH content. In a low pH solution (pH 1.5), a higher PAA content resulted in poorer CNT dispersion while in a high pH solution (pH 12.5), a higher PAA content led to better CNT dispersion. For superior dispersion in a basic aqueous solution (pH 12.5), experimental data showed that a greater atomic radius or a higher cationic charge of the added salt may result in faster aggregation and thus precipitation of CNTs. Copyright © 2011 Society of Chemical Industry 相似文献
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We have utilized lysozyme to non-covalently functionalize and disperse double-walled carbon nanotubes (DWNTs) in aqueous solution. Lysozyme preferentially binds and disperses DWNTs with larger diameters. This is a facile and effective method to fractionalize and enrich DWNTs with certain diameters. 相似文献
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Gaurav Kapadnis Anomitra Dey Prajakta Dandekar Ratnesh Jain 《Polymer International》2019,68(6):1054-1063
Chitosan has emerged as a unique biomaterial, possessing scope in diverse applications in the biomedical, food and chemical industries. However, its high molecular weight is a concern when handling the polymer. Various techniques have been explored for depolymerization of this polymer, wherein enzymes have emerged as the most economic method having minimum degrading effect on the polymer and resulting in formation of side products. Chitosan can be depolymerized using a broad range of enzymes. In this study, various enzymes like α‐amylase, papain, pepsin and bromelain were employed to depolymerize chitosan and convert it into its lower molecular weight counterpart. Further, attempts were made to elucidate the process of depolymerization of chitosan, primarily by determining the change in its viscosity and hence its molecular weight. The process of depolymerization was optimized using a one‐factor‐at‐a‐time approach. The molecular weight of the resultant chitosan was estimated using gel permeation chromatography and infrared spectroscopy. These studies revealed a considerable decrease in molecular weights of chitosan depolymerized by pepsin, papain, bromelain and α‐amylase, resulting in recovery of the low‐molecular‐weight chitosan of 76.09 ± 5, 74.18 ± 5, 55.75 ± 5 and 49.18 ± 5%, respectively. Maximum yield and depolymerization were obtained using pepsin and papain due to their enzymatic recognition pattern, which was also validated using studies involving molecular dynamics. © 2019 Society of Chemical Industry 相似文献
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P. Vandervorst C.-H. Lei Y. Lin O. Dupont A.B. Dalton Y.-P. Sun J.L. Keddie 《Progress in Organic Coatings》2006
Nanocomposites of a polymer and carbon nanotubes exhibit high electrical and thermal conductivity and enhanced mechanical properties in comparison to the polymer alone. Film formation from latex dispersions is an ideal way to create nanocomposite coatings with the advantages of solvent-free processing and a high uniformity of dispersion. It is shown here that carbon nanotubes functionalised with poly(vinyl alcohol) (PVA) can be blended with two types of acrylic latex to create stable colloidal dispersions without the need for added surfactant or emulsifier. Waterborne nanocomposite films with optical transparency can be formed. Microscopic analysis shows that the PVA-functionalized nanotubes are finely and uniformly dispersed in the polymer matrix. 相似文献