摘要:

Molecular orbital calculations were performed on anthraquinone, the anthrahydroquinone radical anion, and dianion. The semi-empirical, self-consistent fields method of modified neglect of diatomic overlap (MNDO) was used to calculate energetic and electronic parameters for the anthraquinone species. The role of anthraquinone in the depolymerization of lignin is discussed in terms of the proposed adduct and single electron transfer (SET) mechanisms.

ISSN:0277-3813    

DOI:10.1080/02773818908050300

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

The functional groups in wood that may become ionized by the action of sodium hydroxide consist of carboxyl, phenolic hydroxyl and carbohydrate hydroxyl groups. The extent of ionization is dependent on the pH of the solution and causes the establishment of a Donnan equilibrium between the outer solution phase and that associated with the solid phase. Analytical techniques were developed to determine the carboxyl and phenolic hydroxyl contents of extractive-free mildly saponified hemlock and cottonwood meals using equilibration in the pH range of 12 to 12.5. The determined carboxyl contents, 0.158 and 0.127 meq/g OD wood, respectively, were confirmed by conductometric titrations of wood meal samples methylated with diazomethane prior to saponification with NaOH. Further confirmation was obtained from conductometric titrations of saponified and HCl-washed samples with NaHCO3. The last-mentioned method was also applied to unsaponified hemlock and cottonwood samples to obtain their free carboxyl contents, 0.031 and 0.066 meq/g, respectively. The phenolic hydroxyl contents determined on borohydride-reduced wood samples were 0.260 and 0.147 meq/g, respectively. They were used to estimate the percentages of phenolic units present inin situlignins. The results obtained suggest that hemlock lignin contains 15.0%, and cottonwood lignin, 14.2% of phenolic C6C3units.

ISSN:0277-3813    

DOI:10.1080/02773818908050301

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

The negative-ion fast-atom-bombardment (FAB) mass spectra of procyanidin oligomers are characterized by abundant [M-H]-ions and fragmentation that results primarily from retro-Diels-Alder fission and cleavage of the interflavanoid bond. B/E-linked scanning mass spectrometry established that sequence ions result from unimolecular gas-phase decompositions. A quinone-methide mechanism of interflavanoid bond cleavage is proposed to account for observed ions of different molecular weight originating from isomeric upper and lower flavan units. These ions can be used to establish the sequence of monomer units and also to distinguish a linear from a branched trimer.

ISSN:0277-3813    

DOI:10.1080/02773818908050302

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

A method has been developed for determination of isorhapontin in softwood barks. The barks are extracted with aqueous acetone, the dried extracts re-extracted with butan-2-one, and the final extract analysed by liquid chromatography. Of seven softwood barks from five genera, only Engelmann spruce, with 13%, contained more than 1% of the stilbene glucoside.

ISSN:0277-3813    

DOI:10.1080/02773818908050303

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

Graft-copolymerization of methyl methacrylate (MMA) and acrylonitrile (AN) onto CTMP fibers using Fe2+-H2O2redox system was investigated. The proof of grafting was performed by means of FT-IR and gravimetric methods. Analyses of IR spectra of samples after mercerization, xanthation, ion exchange and of samples with different polymer loadings, together with chemical reactions were performed. The variation of the characteristic IR band absorption intensity of MMA (the C˭O groups stretching at 1731 cm−1) and of AN (the nitrile stretching at 2244 cm−1) vs the percent of grafting can be used as calibration curves for quantitative determination. It appears also from the IR spectra analyses, that some of the mechanisms suggested for graft-copolymerization are of very small significance.

ISSN:0277-3813    

DOI:10.1080/02773818908050304

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

The effects of five chemical additives on the deresination of aspen wood during kraft pulping and washing were investigated. Without additives, only about half of the potentially saponifiable wood resin was saponified in the digester. For deresination during pulping and washing, the additives could be ranked according to their effectiveness as follows: distilled tall oil > Canadian tall oil (acid No. 131) > gum rosin > abietic acid, at charges of 1 to 3% on OD wood. A commercial surfactant formulation was found not to be cost effective.

ISSN:0277-3813    

DOI:10.1080/02773818908050305

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

This paper deals with the ultrastructure, lignin distribution and topochemistry in alkaline pulping of wheat straw. The ultrastructure of wheat straw fiber is similar to that of a wood tracheid. The lignin concentrations in various morphological regions of wheat straw are similar to the corresponding regions in birch wood fiber. But the lignin contents as a percentage of total lignin in ML and CC regions are much higher for wheat straw than for wood fibers. This study shows that there is hardly any topochemical effect during the delignification of wheat straw fiber in soda pulping process.

ISSN:0277-3813    

DOI:10.1080/02773818908050306

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

Retention of fines and additives by retention aids is important for pulp yield and paper quality in the pulp and paper industry. Measurement of the adsorption of various proteins on different cellulosic substrates was used to evaluate their potential as retention aids. Commercially obtained proteins and bacterial proteins extracted from aBacillus subtilisstrain showed substantial adsorption on three of the five cellulosic substrates tested. Proteins with high pI values were better adsorbed on cellulosic substrates.

ISSN:0277-3813    

DOI:10.1080/02773818908050307

出版商:Taylor & Francis Group    

年代:1989

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:10.1080/02773818908050299

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor