摘要:

Wood-alkali interactions in agueous solution were described with Donnan equilibrium and ionic dissociation equilibrium theories. Theoretical models of three systems, NaOH-H2O-wood, NaOH-NaCl-H2O-wood, and NaOH-Na2CO3-H2O-wood, were developed. Theoretical predictions fit experimental data well. The theoretical modeling also shows good agreement with experimental results reported in the literature when applied to NaOH-H2O-cotton system. Theoretical simulations indicate that carbohydrate hydroxyl groups can be considered as mono-basic weak acids at alkali concentrations lower than 3 M. At higher alkalinities (> 3 M), however, further hydroxyl groups are also significantly ionizable.

ISSN:0277-3813    

DOI:10.1080/02773819308020504

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Reactions of three kind of syringylglycerol- β-syringyl ether type model compounds under alkaline medium were investigated. Sinapyl alcohol and β-hydroxypropiosyringone were formed as phenyl propanoid moieties from syringylglycerol- β-(methyl-syringyl) ether 1 by the β-aryl ether cleavage under soda treatment, while only sinapyl alcohol was formed from syringylglycerol- β-syringyl ether 2. The formation of both two degradation products are quite interesting because there is no nucleophilic additives in soda liquor. A possible reaction mechanisms for the β-aryl cleavage of syringylglycerol-β-syringyl ether type is homolytical cleavage via quinone methide.

ISSN:0277-3813    

DOI:10.1080/02773819308020505

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Periodate oxidation, because of its high selectivity in the degradation of free-phenolic units, has been used along with the combined phenyl nucleus exchange and nitrobenzene oxidation techniques to estimate the distribution of phenolic hydroxyl groups in hardwood lignins. Analyses of the aspen and white birch wood lignin in situ indicate that the percentage of uncon-densed structures having a phenolic hydroxyl group was considerably higher for guaiacyl (∼20%) than for syringyl (−5%) units. Thus, the total phenolic hydroxyl groups of hardwood lignins are largely associated with the guaiacyl propane units.

ISSN:0277-3813    

DOI:10.1080/02773819308020506

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Phenolic hydroxyl groups in three lignin model compounds, guaiacol, acetoguaiacone, and dehydrodiisoeugenol, and in organosolv lignin were blocked by etherification with polyethylene glycol (PEG). Polyethylene glycol modification, even at a low degree of substitution, greatly enhanced the hydrophilicity of the substrate, producing water-soluble substances. When etherified by reaction with PEG-mesylate, the lignin dimer model compound, dehydrodiisoeugenol, was stabilized considerably against light-induced yellowing.

ISSN:0277-3813    

DOI:10.1080/02773819308020507

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Epoxy resins were prepared from hydroxyalkyl lignin derivatives with varying degrees of alkoxylation. The epoxy-functional copolymers were fractionated into narrow molecular weight, chemically uniform prepolymers with good solubility. The epoxy resins were cured with diamine, and the network polymers were characterized by mechanical testing. Modulus and ultimate strength increased with lignin content and ultimate strain decreasing. The resins were comparable or superior to diglycidyl ether of bis-phenol A (DGEBA)-based (control) resins in strength.

ISSN:0277-3813    

DOI:10.1080/02773819308020508

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

The reactions of carbohydrates with anthraquinones in alkaline pulping processes are reviewed. AQ reacts mainly with the short-lived intermediates that are formed in the degradation reactions of wood polysaccharides. Oxidation of the reducing end groups of polysaccharides to stable aldonic acid end groups is marginal and corresponds to less than 1 % of all reactions of AQ. The stabilization of the polysaccharides may be enhanced by the use of salts of alkaline earth metals which increase the relative oxidation rate of sugar enediols and promote the hydride shift reaction of the intermediate aldos-2-ulose end groups to stable hexonic acid end groups. Analysis of the monomeric carbohydrate-derived oxidation products indicates that hardwood lignin probably contains more structures that react with anthrahydroquinone than does softwood lignin. This difference may partly explain the more facile delignification of hardwoods.

ISSN:0277-3813    

DOI:10.1080/02773819308020509

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

The adsorption characteristics of alkanes on high surface area cellulose were investigated by inverse gas chromatography.

ISSN:0277-3813    

DOI:10.1080/02773819308020510

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

ISSN:0277-3813    

DOI:10.1080/02773819308020503

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor