摘要:

Plant materials, containing14C-labeled lignins, were harvested at intervals up to 1 year after labeling. They were oxidized with sodium chlorite (NaC102) and nitrobenzene. Age of lignin appears to limit the degree of solubilization of lignin by NaC102. Nitrobenzene oxidation solubilized all lignins in wheat, oak, and kenaf but not all lignin in some pine samples. Klason and UV analysis of lignin content were compared with14C-content to determine percent lignin soluble in 3% sulfuric acid (Klason analysis solvent), corrected lignin contents, and UV absorptivity of lignin. Ten to 20% of most lignins were soluble in 3% sulfuric acid. When corrected Klason lignin contents were used, UV absorptivities at 280 nm were about 38 g−11 cm−1for wheat straw and kenaf lignins and 11 g−11 cm−1for pine lignin.

ISSN:0277-3813    

DOI:10.1080/02773818608085239

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

Kenaf, containing unlabeled or14C-labeled lignin was oxidized by nitrobenzene. Reaction products were separated, the14C-content measured, and the products identified by mass spectroscopy (MS) and high pressure liquid chromatography (HPLC). Principal products and their approximate percentage of “original-lignin-14C-content” were: syringaldehyde 20%, oxalic acid 20%, high-molecular-weight species 16%, vanillin 8.2%, benzoic acid and 4-hydroxy-azobenzene 10.7%, neutral species 3% or less, syringic acid 2.4%, vanillic acid 1.5%, and malic acid (trace). Numerous aromatic products at about the 1% concentration level remain unidentified.

ISSN:0277-3813    

DOI:10.1080/02773818608085240

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

Precursors of lignin biosynthesis, ferulic acid and sinapic acid labeled by3H or14C were administered to the differentiating xylem of poplar shoots. Biochemical interconversions between syringyl and guaiacyl type intermediates involved in the biosynthetic pathway were suppressed by administration of precursors in the dark. The process of heterogeneous deposition of guaiacyl and syringyl lignin on the cell wall was visualized by autoradiography. Guaiacyl lignin was deposited in the early stage of the xylem differentiation on the vessel wall followed by deposition of syringyl lignin on the fiber cell wall.

ISSN:0277-3813    

DOI:10.1080/02773818608085241

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

The initial steps in the formation of phenolic resins have been studied by the performance of molecular orbital calculations. The reactions that have been examined are those occurring between formaldehyde and phenol, under basic and acidic conditions. Energies and electronic distributions were de ter rained theoretically, and it was found the reaction is not strictly controlled by the total charge at the reactive centers, but rather seems to be influenced by the electron density in the highest occupied molecular orbital of the reactant molecules.

ISSN:0277-3813    

DOI:10.1080/02773818608085242

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

Isopropanol bisulfite treatment of sugi (Cryptomeria japonica D. Don) MWL yielded a significant amount of lipophilic low-molecular-weight products as well as water-soluble high-molecular-weight lignin whereas with an aqueous bisulfite treatment a very small amount of lipophilic products was formed and about half of the MWL was changed to insoluble and probably condensed products.

ISSN:0277-3813    

DOI:10.1080/02773818608085243

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

Lignin model compounds containing a phenolic “A” ring, α-OH, and β-aryl (ring “B”) ether, with different substituents located on rings A and B, have been synthesized and degraded under a variety of conditions in sodium hydroxide-water (soda). Substituent changes on ring B had a large effect on fragmentation reactions of the models; changes on ring A showed only small effects. These substituent-reactivity relationships indicate that the slow step in the mechanism for model fragmentation under soda conditions is cleavage of the β-aryl ether bond. Vinyl ether formation, a reaction which competes with model fragmentation, is more prominent at low alkali concentration.

ISSN:0277-3813    

DOI:10.1080/02773818608085244

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

Lignin model compounds, capable of forming quinonemethides and having different substituents on the quinonemethide (A) rings and β-aryl ether (B) rings, have been degraded under a variety of conditions in the presence of NaOH (soda), NaOH/Na2S (kraft), NaOH/glucose, and NaOH/AHQ (soda/AQ). Substituent changes on ring B had no effect on the extent of model fragmentation in the presence of excess AHQ and NaSH. Substituent changes on ring A had large effects on fragmentation under soda/AQ and kraft conditions. These substituent-reactivity relationships indicate that the slow step in the mechanism for model fragmentation under soda/AQ and kraft conditions is quinonemethide formation. Conditions aimed at demonstrating the existence of electron-transfer fragmentation of the model compounds gave results which were inconclusive, but demonstrated that equilibrium reactions between quinonemethide intermediates exist.

ISSN:0277-3813    

DOI:10.1080/02773818608085245

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

For adhesive self-sufficiency, the wood industry needs new adhesive systems in which all or part of the petroleum-derived phenolic component is replaced by a renewable material without sacrificing high durability or ease of bonding. We tested the bonding of wood veneers, using phenolic resins in which part of the phenol-formaldehyde was replaced with carbohydrates. Our experiments show that the addition of non-reducing carbohydrates and various polyols to phenol-formaldehyde resol-resins does not adversely affect the dry- or wet-shear strength of 2-ply Douglas-fir panels bonded with the modified resins. Reducing carbohydrates, however, cannot be used as the modifier. In general, addition of about 0.6–1.0 mole of modifier per mole of phenol is optimal in the formulation of carbohydrate-or polyol-modified resin. Preliminary results show that part but not all of the modifier is chemically bound into the resin, apparently through an ether linkage. The water prehydrolysate of southern red oak wood, when reduced with sodium borohydride to convert the reducing sugars to alditols, can be used to modify phenol-formaldehyde resins. This use of wood prehydrolysates can be economically beneficial to processes producing alcohol and chemicals from wood as well as to the wood industry and consumers of bonded wood products.

ISSN:0277-3813    

DOI:10.1080/02773818608085246

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

This is a scanned image of the original Editorial Board page(s) for this issue.

ISSN:0277-3813    

DOI:10.1080/02773818608085238

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor