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排序方式: 共有252条查询结果,搜索用时 109 毫秒
21.
I.S. Gaponova S.M. Lomakin G.B. Pariiskii T.V. Pokholok 《Polymer Degradation and Stability》2010,95(7):1177-1182
The mechanism of stable radical generation in lignin under the action of nitrogen dioxide and NO2 - air mixture is considered. The formation of phenoxyl, iminoxyl and acylaminoxyl radicals has been detected by EPR. The proposed mechanism involves a primary oxidative reaction of phenol groups with dimers of NO2 (nitrosyl nitrate) resulting in the formation of phenoxyl radicals and nitric oxide. In the subsequent recombination of phenoxyl radicals and nitric oxide, nitroso compounds and oximes are formed. By reaction of oximes with radicals NO2, stable iminoxyl radicals are formed. This mechanism is confirmed by kinetic dependencies obtained over a wide range of NO2 concentrations. From IR spectroscopy measurements it follows that hydroxyl groups of non-phenolic structures of lignin are oxidised to aldehydes producing acylaminoxyl radicals by reaction with NO2. The kinetic data show that the adsorption of NO2 on the lignin surface is the rate-determining factor in stable radical formation. 相似文献
22.
Stella Rovio Anna Kalliola Heli Sirén Tarja Tamminen 《Journal of chromatography. A》2010,1217(8):1407-1413
Capillary zone electrophoresis (CZE) with indirect UV detection was used in developing a method for the simultaneous determination of inorganic anions, aliphatic and heterocyclic organic acids in various processed samples. The analytes were determined simultaneously in 10 min using an electrolyte containing 20 mM 2,3-pyrazine dicarboxylic acid, 65 mM tricine, 2 mM BaCl2, 0.5 mM cetyltrimethylammonium bromide, and 2 M urea at pH 8.06. Linear plots for the analytes were obtained in the concentration range of 2–150 mg L−1. Relative standard deviations (RSDs) of peak areas during a 3-day analysis period varied from 5.5% for glycolate to 9.5% for oxalate. RSDs of migration times varied between 0.4% and 1.1%. The detection limit (at S/N 3) was 1 mg L−1 for all the analytes studied. The proposed method was successfully demonstrated for the determination of carboxylic acids in eight oxygen treated samples of commercial softwood and hardwood kraft lignin and two red wine samples of Pinot Noir grapes. In the kraft lignin samples the concentrations of carboxylic acids correspond to the oxidation time. The acid concentrations of wine varied considerable. 相似文献
23.
In order to efficiently explore and use woody biomass,six lignin fractions were isolated from dewaxed Caragana sinica via successive extraction with organic solvents and alkaline solutions.The lignin structures were characterized by Fourier transform infrared spectroscopy(FT-IR) and 1D and 2D Nuclear Magnetic Resonance(NMR).FT-IR spectra revealed that the core of the lignin structure did not significantly change during the treatment under the conditions given.The results of 1H and 13C NMR demonstrated that ... 相似文献
24.
The paper manufacturing process remained unchanged for many centuries, until, in the nineteenth century, the crisis of rags led industrialized countries to patent new production processes with different raw materials. This study deals with this period of transition by analyzing four samples stored at the archives of Superintendency Beni Architettonici per il Paesaggio e per il Patrimonio Storico Artistico ed Etnoantropologico (BAPPDAD) of Venice Lagoon, based in the Palazzo Ducale.The samples were analyzed by FT-IR (ATR), SEM-EDS, HPLC-MS/MS and Py-GC/MS. These techniques allow the characterization of various raw materials and adhesives used in various stages of paper production.These analyses have found a gradual introduction of ground wood in the composition of papers from the mid-nineteenth century, and the use of rosin as glue only in more recent documents. 相似文献
25.
Thorsten vomStein Tim denHartog Julien Buendia Spas Stoychev Jakob Mottweiler Carsten Bolm Jürgen Klankermayer Walter Leitner 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2015,127(20):5957-5961
Ruthenium–triphos complexes exhibited unprecedented catalytic activity and selectivity in the redox‐neutral C C bond cleavage of the β‐O‐4 lignin linkage of 1,3‐dilignol model compounds. A mechanistic pathway involving a dehydrogenation‐initiated retro‐aldol reaction for the C C bond cleavage was proposed in line with experimental data and DFT calculations. 相似文献
26.
27.
The possibility of using lignin from the paper industry’s black liquor to absorb nickel (Ni) and vanadium (V), was studied.
The work comprised two stages: first, the identification of lignin’s main functional groups and the surface characterization
of the solid; second, an experimental study of lignin’s behavior towards the Ni and V cations. Results revealed the presence
of aromatic groups as well as substituted methoxy groups on the lignin’s surface. This explains lignin’s adsorptive capacity
exhibited in the experimental evaluations. The removal of Ni and V ions was higher than expected solely through the physical
adsorption mechanism. This higher capacity is associated with a proposed complex formation on the surface of the lignin. For
Ni(II), lignin showed a higher adsorption compared to commercial adsorbents. In the case of V, the behavior is reversed, in
order to elucidate this result, further research is recommended. 相似文献
28.
Jaime Rodríguez André Ferraz Raquel F. P. Nogueira Irene Ferrer Elisa Esposito Nelson Durán 《Applied biochemistry and biotechnology》1997,62(2-3):233-242
The lignin biodegradation process has an important role in the carbon cycle of the biosphere. The study of this natural process
has developed mainly with the use of basidiomycetes in laboratory investigations. This has been a logical approach since most
of the microorganisms involved in lignocellulosic degradation belong to this class of fungi. However, other microorganisms
such as ascomycetes and also some bacteria, are involved in the lignin decaying process. This work focuses on lignin biodegradation
by a microorganism belonging to the ascomycete class,Chrysonilia sitophila. Lignin peroxidase production and characterization, mechanisms of lignin degradation (lignin model compounds and lignin in
wood matrix) and biosynthesis of veratryl alcohol are outstanding. Applications of C.sitophila for effluent treatment, wood biodegradation and single-cell protein production are also discussed. 相似文献
29.
30.
利用磷酸化改性木质素/二氧化硅复合纳米颗粒(PAL/SiO2)作为壁材包埋活性组分异佛尔酮二异氰酸酯(IPDI)制备微胶囊(PAL/SiO2-IPDI). 通过加入少量反应活性更高的聚合多甲基多二异氰酸酯(PMDI), 与水反应形成聚脲, 以增加微胶囊的壁厚. 采用光学显微镜、 扫描电子显微镜(SEM)和激光粒度分析仪(DLS)研究了PAL/SiO2复合纳米粒子掺杂量, 水油比和剪切速率对微胶囊表面形貌、 粒径和壁厚的影响. 结果表明, 所制备的微胶囊呈现规整球形, 壁厚为2.36~3.50 μm, 平均粒径为40.3~201.5 μm. IPDI作为芯材包埋在微胶囊中, 芯材含量约为82.8%. 将制备的PAL/SiO2-IPDI微胶囊添加到环氧树脂中得到自愈合环氧树脂涂层. 其在高盐浓度溶液中的抗侵蚀测试结果显示, 添加质量分数4%的PAL/SiO2-IPDI微胶囊的环氧树脂涂层在划破后能够快速愈合, 显著降低基底的腐蚀电流和腐蚀速率. 纳米压痕实验表明, 环氧涂层的硬度为249.99 MPa, 而添加PAL/SiO2-IPDI微胶囊后硬度增加到302.98 MPa, 弹性模量也有提高. 相似文献