摘要:

The chromophores responsible for kraft colour have been generally assumed to be derived from the aromatic portions of the lignin molecule. Analytical studies of the high molecular weight dissolved materials from kraft lignin, kraft cooked sugars, and extraction stage effluent by pyrolysis GC-MS, permanganate/periodate oxidation, and UV-visible spectroscopy showed that these materials had a wide variation in aromatic content but similar spectral properties. It is now proposed that carbohydrate degradation products produced by the kraft cooking of sugars are primarily responsible for the kraft colour.

ISSN:0277-3813    

DOI:10.1080/02773819008050233

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

Upon chlorination and extraction, high molecular weight (>1000D) kraft lignin (KL) is degraded to a material which is structurally similar to extraction stage effluent. During bleaching there is a significant decrease in the aromaticity of KL without a concomitant decrease in colour, which would be expected if aromatic residues are the kraft chromophores. Treatment of simple sugars under conditions similar to those of kraft pulping yielded polymeric products which, on treatment with chlorine and subsequential extraction (CE), gave products with similar spectral characteristics to extraction stage effluent. It is proposed that the chromophores responsible for kraft colour are keto-enols probably derived from the degradation of carbohydrates during the kraft cook.

ISSN:0277-3813    

DOI:10.1080/02773819008050234

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

Direct studies of photoyellowed unbleached white spruce refiner mechanical pulp have been carried out using laser Raman spectroscopy, gas chromatography/mass spectrometry (GC/MS) and Fourier transform infrared spectroscopy (FTIR) techniques. A new chromophore, namely, cis-ferulic acid has been detected. The experimental results indicate the presence of both cis and trans isomers of ferulic acid. The former, because of its yellow color, is considered to be a contributor in the yellowing process.

ISSN:0277-3813    

DOI:10.1080/02773819008050235

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

This study examines the influence of ozone on a TMP pulp of tamarack in an independent bleaching stage and as a pre-treatment for hydrogen peroxide bleaching. Ozone charges of up to 6% were used on dry pulp. The results were compared to those obtained with 1% H2O2bleaching. Experiments were conducted at 23°C and 55°C, and pH varied from 3.5 to 10.5. The best bleaching results were reached with acidic pH, with interesting behavior observed at an alkaline pH level. Ozone effectively attacks CO groups in lignin, but lacks the chemical selectivity and high reactivity required to become a good bleaching agent.

ISSN:0277-3813    

DOI:10.1080/02773819008050236

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

Reaction rates and product distributions have been determined for the degradation of phenyl β-D-glucopyranoside in aq. alkali under various conditions. The effects of a stronger nucleophile, variations in hydroxide ion concentration at constant ionic strength, changes in temperature, and the level of18O incorporation from the solvent into the product phenol were investigated. The degradation rate decreased greatly for the 2-O-methyl analog. The results indicate that, at both 100 and 170°C, phenyl β-D-glucopyranoside degradation proceeded by an SNicB(2) reaction. At both temperatures the expected SNicB(2) product, levoglucosan, formed in less than quantitative yields because of competing reactions which occurred after the rate-determining step.

ISSN:0277-3813    

DOI:10.1080/02773819008050237

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

Guaiacylpropanol (4), has been attached at the gamma carbon through a benzyl ether linkage to a macroreticular polystyrene resin. The phenolic site of4was protected as an allyl ether when coupled to the resin. The amount of lignin model4which was attached to the polymer was determined by cleaving the benzyl ether linkage with iodotrimethlsilane (ITS) and quantifying the amount of released guaiacylpropanol. The ITS method was reproducible but not quantitative due to a high model loading (1.29 mmol/g). Both FTIR and13C-NMR were used to characterize the insoluble model.

ISSN:0277-3813    

DOI:10.1080/02773819008050238

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

The reactions of syringyl alcohol with itself and with either a soluble phenol, 3-methoxy-4-hydroxyphenylpropane (guaiacylpropane,13) or an insoluble polymer-bound phenol, guaiacylpropanol (14)1, led to dimeric products. The low (11%), but significant yield of C5-Cα dimer16in the reaction of polymer-bound phenol with syringyl alcohol suggests that soluble lignin units are able to condense with insoluble lignin gels during the course of soda pulping. The yield of the C5-Cα dimer15in the soluble system was four times greater than that of the analogous heterogeneous dimer16. Reactions of the polymer model14were not mass transfer limited.

ISSN:0277-3813    

DOI:10.1080/02773819008050239

出版商:Taylor & Francis Group    

年代:1990

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:10.1080/02773819008050232

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor