Characterization of autohydrolysis aspen (P. tremuloides) lignins. Part 2. Alkaline nitrobenzene oxidation studies of extracted autohydrolysis lignin

Alkaline nitrobenzene oxidation of the lignins extracted from extractive-free aspen wood meal after autohydrolysis at 195 °C for periods varying from 5 min to 2 h indicated that these lignins were structurally more condensed in terms of an increase in new carbon–carbon bonds than aspen milled wood lignin. The degree of condensation generally increased with longer autohydrolysis times. It is postulated that condensation involved materials from both the carbohydrate and lignin components of the wood which were generated during the autohydrolysis. The molar ratio of syringaldehyde to vanillin of extracted lignin on oxidation was observed to decrease with increasing autohydrolysis time. It is suggested that syringyl units are preferentially extracted as low molecular weight material.

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Characterization of autohydrolysis aspen (P. tremuloides) lignins. Part 4. Residual autohydrolysis lignin

Canadian Journal of Chemistry ◽

10.1139/v79-422 ◽

1979 ◽

Vol 57 (19) ◽

pp. 2612-2616 ◽

Cited By ~ 14

Author(s):

Morris Wayman ◽

Miranda G. S. Chua

Keyword(s):

Enzymatic Hydrolysis ◽

Time Varying ◽

Residual Lignin ◽

Aspen Wood ◽

Milled Wood Lignin ◽

Wood Meal ◽

Nitrobenzene Oxidation ◽

Infrared Studies ◽

Lignocellulosic Residue

Lignocellulosic residue remaining after autohydrolysis of extractive-free aspen wood meal at 195 °C for periods of time varying from 5 to 120 min followed by extraction with 90% dioxane was subjected to enzymatic hydrolysis to obtain residual lignin. Infrared studies indicated that in the early stages of autohydrolysis residual lignin resembles protolignin, but as autohydrolysis proceeds it changes to resemble more and more the extracted lignin. Residual lignin was found to be higher in carbon but lower in hydrogen and oxygen than aspen milled wood lignin. The methoxyl content was also lower than the reference lignin. From alkaline nitrobenzene oxidation, residual lignin is seen to become more condensed with increasing autohydrolysis time. The insolubility of residual lignin is attributed to the existence of strong bonds between this lignin and carbohydrate.

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Characterization of autohydrolysis aspen (P. tremuloides) lignins. Part 1. Composition and molecular weight distribution of extracted autohydrolysis lignin

Canadian Journal of Chemistry ◽

10.1139/v79-187 ◽

1979 ◽

Vol 57 (10) ◽

pp. 1141-1149 ◽

Cited By ~ 112

Author(s):

Miranda G. S. Chua ◽

Morris Wayman

Keyword(s):

Molecular Weight ◽

Molecular Weight Distribution ◽

Weight Distribution ◽

Blocking Agent ◽

Low Molecular Weight ◽

Aspen Wood ◽

Milled Wood Lignin ◽

Carbonium Ions ◽

Distribution Studies

Extractive-free aspen wood meal was subjected to autohydrolysis at 195 °C for 5 min to 2 h, and the lignin extracted with 90% dioxane. Extracted autohydrolysis lignin was found to be higher in carbon but lower in hydrogen and oxygen content than aspen milled wood lignin. The methoxyl content was also lower than the reference lignin. These differences have been attributed to condensation and incorporation into the lignin of non-lignin components. A lignin extractability curve with a maximum delignification at autohydrolysis time of 30–40 min was found. From molecular weight distribution studies the ratio of high molecular weight to low molecular weight materials varied for the different extracted lignins and reached a maximum at autohydrolysis time of 40 min. A mechanism of depolymerization/repolymerization of the lignin via carbonium ions has been proposed. p-Hydroxybenzoic acid is postulated as contributing to the extractability of aspen lignin by acting as a blocking agent.

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