摘要:

Absorption difference spectra of bleached TMP irradiated with near-uv light exhibited two apparent absorption maxima at π 410 nm and 330 nm. Experiments with borohydride-reduced pulp suggest that photochemical formation of aromatic carbonyls contributes to the λ = 330 nm peak. Chromophore formation followed an apparently first-order rate law, and the rate was unaffected by methylation of phenolic hydroxyl groups, or by exhaustive reduction of carbonyl groups with NaBH4. Methylation of phenolic hydroxyl, while having no effect on the kinetics of chromophore formation, did decrease the maximum change in absorption coefficient, ΔK∞. Treatment of bleached TMP with ascorbic acid slowed light-induced yellowing substantially; significant yellowing occurred only after 2 hours. Light-induced bleaching of a chromophore with λmaxπ 350 nm, possibly a stilbene, occurred during the first 90 minutes of irradiation.

ISSN:0277-3813    

DOI:10.1080/02773819108051083

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

The photoyellowing of papers produced from bleached CTMP is retarded when these papers are irradiated in aqueous solutions containing reducing agents such as Rongalit C and Blankit D. Papers impregnated with the reducing agents showed some photostability when irradiated in the dry state but not when irradiated in aqueous solution. The reducing agents present in these papers also failed to significantly retard the photoyellowing under natural lighting conditions and under simulated solar irradiation. It is concluded that the migratability of the reducing agents is important if photoprotection is to be achieved and that the latter is caused by the reagents bleaching the yellow photodegradation products as well as destroying prodegradent species such as hydroperoxides.

ISSN:0277-3813    

DOI:10.1080/02773819108051084

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

Heating the individual common abietadienoic acid methyl esters withp-toluene sulfonic acid in chloroform led to the formation of methyl abietadienoates other than the equilibrium mixture of methyl abietate, palustrate, and neoabietate that is usually formed by acid-catalyzed isomerization. Of these other methyl abietadienoates, the three principal constituents comprised 10%, 4% and 2% of the monomers; these compounds were isolated and identified as methyl 13β-abieta-7,9(11)-dien-18-oate, methyl 7,9(11)-abietadien-18-oate, and methyl 8,12-abietadien-18-oate, respectively.

ISSN:0277-3813    

DOI:10.1080/02773819108051085

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

The paper describes an analytical method whereby the chemical composition of the polysaccharide fraction of woody materials, including the uronic acids and carbohydrate acid degradation products, can be completely determined. Sealed vessels, termed bombs, are used during the high temperature acid hydrolysis of the materials to retain volatile constituents that would otherwise be lost. High-Performance Liquid Chromatography (HPLC) is used for all of the analyses. The sample preparation procedures are simple and easily adopted into a routine. To demonstrate the reproducibility of the method, triplicate samples of Quaking aspen (Populus tremuloides) and White fir (Abies concolor) were analyzed. No significant peaks in the chromatograms were left unidentified.

ISSN:0277-3813    

DOI:10.1080/02773819108051086

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

The paper describes a novel method for the determination of ultraviolet (UV) light absorptivities for acid soluble lignin (ASL). It was found that the rehydrolysis, or reKlasonation, of Klason lignin continues to release a quantifiable amount of ASL. Thus, previously prepared Klason lignin was repeatedly subjected to reKlasonation and the mass loss after each stage of hydrolysis was quantified. The resulting hydrolysates were satisfactory for determining the absorptivity of ASL at 205 nm. The reKlasonation hydrolysates were found to be spectroscopically identical to hydrolysates prepared from the parent wood species.

ISSN:0277-3813    

DOI:10.1080/02773819108051087

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

The summative analysis of lignocellulosic materials has heretofore been a complicated process or the analysis has been incomplete. The Bomb/HPLC summative analysis method presented in this report results in a complete analysis of woody materials using a sample preparation scheme that is easily adopted into a normal laboratory routine. The method relies on HPLC for the majority of the component analyses. To demonstrate the applicability and reproducibility of the Bomb/HPLC method, ten wood samples, from nine different wood species, were analyzed in triplicate and the summative analysis of each sample was effected. The ten woods analyzed were: American beech (Fagus grandifolia), Quaking aspen (Populus tremuloides), Black cherry (Prunus serotina), Sugar (Hard) maple (Acer saccharum), Red (Soft) maple (Acer rubrum). White ash (Fraxinus americana), Yellow birch (Betula verrucosa), Douglas fir heartwood and Douglas fir sapwood (Pseudotsuga menziesii), and White fir sapwood (Abies concolor). The average summative analysis for the group of thirty samples was 99.13 ± 0.51% on an unextracted basis, 99.07 ± 0.45% on an extractive-free basis. There were no significant unidentified peaks in any of the HPLC chromatograms. The range of mass balance determinations for the group of ten wood specimens on unextracted and extractive-free bases was 98.43 to 99.63% and 98.31 to 99.60%, respectively.

ISSN:0277-3813    

DOI:10.1080/02773819108051088

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

Two wood and two wood-pulp samples were hydrolyzed in triplicate in sulfuric acid. The sugar monomers were separated by anion-exchange chromatography and quantitatively measured with a pulsed amperometric detector. A portion of each sugar solution was neutralized with sodium hydroxide and analyzed for the sugar content in the same manner as the unneutralized hydrolysates. The results from analyses of acid and neutral solutions were consistent. Detection limits for the individual sugars ranged from 25 ng for arabinose to 13 ng for glucose using a signal to noise ratio of three for the detection limit.

ISSN:0277-3813    

DOI:10.1080/02773819108051089

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

Twelve pentacyclic triterpenes were isolated from the outer bark of river birch,Betula nigra.3β-Acetoxyolean-11-oxo-12-ene-28-oic acid was isolated for the first time from aBetulaspecies. 3β-Caffeatoxyolean-12-ene-28-oic acid has been spectrally characterized for the first time. 3β-Acetoxyolean-12-ene-28-oic acid and 3β-acetoxyolean-11-oxo-12-ene-28-oic acid have been demonstrated to be active as antifeedants for the Colorado potato beetle,Leptinotarsa decemlineata.

ISSN:0277-3813    

DOI:10.1080/02773819108051090

出版商:Taylor & Francis Group    

年代:1991

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:10.1080/02773819108051082

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor