摘要:

Aryl migrations taking place during pulping processes are described. Migrations from Cαto Cβare given by “condensed” β-O-4 units and result in fragmentation and the formation of potential chromophoric systems of the stilbene type. Migrations from Cβto Cα, on the other hand, are observed with stilbenoid units and their precursors (β-1 and β-5 units) and afford 1,1-diaryl-2-oxo structures. Both types of aryl migration proceed via 3-membered spiro-cyclohexadienone intermediates. The direction of the aryl migrations may affect the ease and extent of lignin fragmentation and the formation of potential chromophoric groups during pulping processes

ISSN:0277-3813    

DOI:10.1080/02773819208545787

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

Low molecular weight lignols with intact side chains were produced by mild hydrolysis of spruce wood, of unbleached and hydrogen peroxide bleached spruce groundwood and of chemithermomechanical pulp (CTMP). The major monomeric, dimeric and trimeric lignin products derived were isolated by HPLC and characterized by GC-MS and NMR. The behaviour of these products towards photo-oxidation in the solid state on filter paper was studied. Coniferaldehyde structures, the major leucochromophores originally present in spruce wood lignin, were reduced during the CTMP process and eliminated after bleaching with hydrogen peroxide. Diguaiacyl stilbene originating from diarylpropane structures and produced during hydrogen peroxide bleaching were found to be the predominant leucochromophoric structure present in the hydrogen peroxide bleached pulps and these were found to be responsible for the fast photoyellowing of these pulps.

ISSN:0277-3813    

DOI:10.1080/02773819208545788

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

Derivatization of an oxidized lignin sample by suitable fluoroaromatic compounds is described. Integration of the19F NMR spectra of the derivatives allows the determination of the carboxyl content of the sample. Three reagents were investigated : 4-fluorobenzyl chloride, 4-fluorophenacyl bromide and 4-fluoro-phenyldiazomethyl ketone.

ISSN:0277-3813    

DOI:10.1080/02773819208545789

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

Structures of acetylated residual lignin obtained from unbleached beech kraft pulp were investigated by 2D NMR in combination with selective cleavage of non-phenolic α-alkyl ether bonds with pivaloyl iodide generatedin situfrom pivaloyl chloride / sodium iodide. β-O-4 and resinol structures still remained in this polymer lignin. Furthermore, carbohydrates were proved to be linked glycosidically to benzyl carbons of lignin. Possibly this inhibits complete delignification during kraft pulping.

ISSN:0277-3813    

DOI:10.1080/02773819208545790

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

Five purified paucidisperse gymnosperm lignin sulfonate samples (Mw@2,400 to 140,000), prepared by fractionation using ultrafiltration and dialysis, have been characterized in part. The relationship was established between the molecular weights of the fractions and those of the dissolved lignin sulfonates representing nearly all of the total lignin originally present in the woody tissue. The chemical composition, ultraviolet and infrared absorption spectra, intrinsic viscosity, diffusion coefficient, specific volume, hydraulic radius and streaming current properties of the several samples have been determined or estimated as a function of molecular weight.

ISSN:0277-3813    

DOI:10.1080/02773819208545791

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

Theerythro8-O-4′ neolignan IIIb was synthesized and was found to have identical1H and13C NMR characteristics to a neolignan reported as a component of the roots ofNardostachys jatamansi. The NMR spectral characteristics of compound IIIb were also identical with those of a neolignan previously obtained from the roots ofPiper capense, for which the unlikely 8-O-3′ structure IVa had been proposed. Two furthererythro8-O-4′ compounds IIIc and IIId were prepared, and their assigned13C NMR signals were consistent with those of IIIb. At this time, there appears to be no evidence for the existence of 8-0-3′ neolignans as plant extracts.

ISSN:0277-3813    

DOI:10.1080/02773819208545792

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

It has been previously demonstrated that free radicals are produced in the delignification of wood. These free radicals can be utilized to initiate grafting of vinyl polymers to the wood pulp. This simultaneous delignification and graft copolymerization has been referred to as graft pulping. The grafting of a variety of vinyl monomers to aspen wood pulp in alcohol-based solvent pulping has been evaluated in this study. Variables evaluated included cooking conditions, catalysts and two-stage pulping. The analysis of the reaction is complicated due to effects of the vinyl monomers on the delignification process and losses of wood during the extraction sequences. Although only low levels of polymer loading were obtained when single monomers were added to the pulping solvent, much better results were obtained using a binary monomer system of acrylonitrile(AN) and styrene(ST). At a monomer addition level of 10% (1.75% AN, 8.25% ST) to the aqueous ethanol solvent, a 14.6% polymer loading was achieved with the majority of the graft as polystyrene (88%) . The use of a two-stage pulping sequence improved the polymer loading of polyacrylonitrile but not polystyrene. Lignin was the primary site of grafting.

ISSN:0277-3813    

DOI:10.1080/02773819208545793

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

ISSN:0277-3813    

DOI:10.1080/02773819208545786

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor