Reduction of aluminum toxicity to radish by alkaline oxygen treated kraft lignin

To obtain a soil-conditioning agent for acid soil containing excess aluminum ions (AL), kraft lignin was modified by alkaline oxygen treatment. The growth of radish root in solution and in soil containing AL with or without addition of these lignins under controlled pH was examined. We concluded the following. Growth inhibition of radish roots by AL can be removed by adding alkaline oxygentreated lignins in the range of pH 4.5–4.8 in soil. A similar result was obtained at pH 4.5 in a culture solution. The reduction of AL toxicity to plant may be due to the aggregation between AL and the modified lignin at low concentrations of modified lignin because soluble AL could not be detected. On other hand, elongation of radish root was not obviously inhibited, although the soluble AL in the solution culture was at an extremely high level when the dosage of a modified lignin was high. This suggests that the reduction in AL toxicity to plants was due to formation of a complex between AL and acidic groups of the modified lignin.Part of this report was presented at the 49th Annual Meeting of the Japan Wood Research Society, Tokyo, April 1999 and the 44th Lignin Symposium, Gifu, October 1999     

Spectral analysis of the successive degradation process of kraft lignin by alkaline oxygen treatment

Softwood kraft lignin was subjected to alkaline oxygen treatment in a fundamental study of lignin degradation. Two different spectral changes were observed in the time course of ultraviolet-visible spectra along with the progress of the treatment. These spectral changes could be recognized as proceeding along certain temporal functions that were based on second-order decays with different halflives. The spectral changes were defined as “fast change” and “slow change.” The fitting studies on the amount of total protons on the unsaturated and aromatic systems, the amount of unconjugated phenolic substructure determined by differential ionization spectra, and the amount of methoxyl group with temporal functions showed that two reaction types (formation of muconate derivatives and ortho-quinone derivatives) can be expected as the major modification types occurring during fast change. The fitting study of the time course of infrared attenuated total reflectance (ATR) spectra gave corresponding infrared ATR spectral features of fast and slow changes. The occurrence of the formation of muconate derivatives by fast change was strongly supported by the spectral feature of fast change. On the other hand, it is suggested that the aromatic structure of lignin was further degraded during slow change. In addition, formation of resistant phenolic substructures is suggested as another possible modification type occurring by fast change. Parts of this article were presented at the 13th International Symposium on Wood, Fiber, and Pulping Chemistry, Auckland, New Zealand, May 2005     

Structural changes of residual lignin in softwood kraft pulp treated with manganese peroxidase

Structural changes of residual lignin in unbleached softwood kraft pulp (SWKP) during manganese peroxidase (MnP) treatment were investigated to obtain some understanding of the biobleaching action of SWKP with MnP treatment. Alkaline-extracted lignin from darkened SWKP by MnP showed more intense color and contained moreo-quinone than that from control SWKP. However, no difference in the conjugated-carbonyl was observed between the lignins from MnP-treated and control SWKP. The nitrobenzene oxidation analysis revealed that oxidative condensation of non-condensed lignin in SWKP occurs during an early stage of MnP treatment. These observations were supported by the model experiment in which the lignin prepared from control SWKP was subjected to MnP treatments three times, and the changes of color and functional groups in the lignin were determined after each treatment. These results suggested that an increase ino-quinone and the condensation reaction of non-condensed lignin in SWKP are responsible for the characteristic darkening of SWKP during MnP treatment. It was also ascertained that darkened lignin was degraded and brightened by repeated MnP treatments.     

Catalytic graphitization of hardwood acetic acid lignin with nickel acetate

 Catalytic graphitization of hardwood acetic acid lignin (HAL) with nickel (II) acetate was investigated regarding the production of highly crystalline carbon. Fusibility, one of the unique characteristics of HAL, was preserved with nickel acetate additions up to 0.3% (as the weight of nickel), although the thermal mobility of HAL was depressed by the addition of nickel acetate. An obvious effect of nickel salt as a catalyst on the development of carbon crystallite from HAL was observed for more than 0.2% addition. The development was found to proceed above 850°C. All the resulting carbons had turbostratic structure, and the apparent crystallite size (L _c) was increased with increasing amounts of catalyst, as determined by X-ray diffraction. Thus, highly crystalline carbon was produced from HAL by catalytic graphitization without compromising the fusibility of HAL by adding a small amount of organic nickel salt. Received: December 17, 2001 / Accepted: March 27, 2002 Present address: Department of Wood and Paper Science, North Carolina State University, NC 27695-8005, USA Part of this paper was presented at the 50th Annual Meeting of the Japan Wood Research Society, Kyoto, April 2000 Correspondence to:Y. Uraki     

Reaction behavior of lignin in supercritical methanol as studied with lignin model compounds

 The reaction behavior and kinetics of lignin model compounds were studied in supercritical methanol with a batch-type supercritical biomass conversion system. Guaiacol, veratrole, 2,6-dimethoxyphenol, and 1,2,3-trimethoxybenzene were used as model compounds for aromatic rings in lignin. In addition, 5-5, β-1, β-O-4, and α-O-4 types of dimeric lignin model compounds were used as representatives of linkages in lignin. As a result, aromatic rings and 5-5 (biphenyl)-type structures were stable in supercritical methanol, and the β-1 linkage was not cleaved in the β-1-type structure but converted rapidly to stilbene. On the other hand, β-ether and α-ether linkages of β-O-4 and α-O-4 lignin model compounds were cleaved rapidly, and these compounds decomposed to some monomeric compounds. Phenolic compounds were found to be more reactive than nonphenolic compounds. These results indicate that cleavages of ether linkages mainly contribute to the depolymerization of lignin, whereas condensed linkages such as the 5-5 and β-1 types are not cleaved in supercritical methanol. Therefore, it is suggested that the supercritical methanol treatment effectively depolymerizes lignin into the lower-molecular-weight products as a methanol-soluble portion mainly by cleavage of the β-ether structure, which is the dominant linkage in lignin. Received: December 19, 2001 / Accepted: April 30, 2002 Acknowledgments This research has been done under the research program for the development of technologies for establishing an ecosystem based on recycling in rural villages for the twenty-first century from the Ministry of Agriculture, Forestry and Fisheries, Japan; by a Grant-in-Aid for Scientific Research (B)(2) (no.12460144, 2001.4–2003.3) from the Ministry of Education, Culture, Sports, Science and Technology, Japan; and under the research program from Kansai Research Foundation for Technology Promotion, Japan. The authors thank them for their financial support. This study was presented in part at the 45th Lignin Symposium, Ehime, Japan, October 2000 and the 52nd Annual Meeting of the Japan Wood Research Society, Gifu, Japan, April 2002 Correspondence to:S. Saka     

Infrared spectroscopic study of alkaline oxygen treatment of lignin with ATR technique in aqueous state 1: method for determining quantitative spectra of oxygen-degraded lignin

For the fundamental study of oxygen delignification of kraft pulp, structural changes of kraft lignin during alkaline oxygen treatment were investigated with the use of infrared measurement with attenuated total reflectance (ATR) technique. In the neutralized reaction mixture of alkaline oxygen-treated kraft lignin, there is a significant amount of NaCl, so that the spectral changes of water due to the coexistence of NaCl was investigated, and how to remove the huge absorption of NaCl solution is discussed. Sodium vanillate–NaCl solutions were employed as model solutions for the reaction mixture. Partial least square (PLS) regression was applied for the prediction of NaCl concentration, and the spectrum of NaCl solution was subtracted from the spectrum of sodium vanillate–NaCl solution as background measurement. This allowed us to obtain the vanillate spectra free from the absorption of NaCl solution. In addition, the mathematical method for reconstructing the spectrum of NaCl solution is discussed. The spectrum of NaCl solution is reconstructed as the linear combination of basic spectra calculated by singular value decomposition (SVD), and it was subtracted from that of the sodium vanillate–NaCl solution. By this procedure, the vanillate spectra were also obtained quantitatively, as has been demonstrated in PLS regression study. It was also confirmed that the quantitative spectra of high molecular weight fraction of alkaline oxygen-treated kraft lignin were obtained by the use of this reconstruction technique.Parts of this report were presented at the 52nd Annual Meeting of the Japan Wood Research Society, Gifu, Japan, April 2002 and the 12th International Symposium on Wood and Pulping Chemistry, Madison, USA, June 2003