Abstract
The electron beam irradiation (EBI) of native lignin has received little attention. Thus, its potential use in lignin-based biorefineries is not fully understood. EBI was applied to selected lignin samples and the structural and chemical changes were analyzed, revealing the suitability, limitations, and potential purpose of EBI in wood biorefineries. Isolated milled wood, kraft, and sulfite lignin from beech and eucalyptus were subjected to up to 200 kGy of irradiation. The analysis included gel permeation chromatography for molar masses, heteronuclear single quantum coherence (HSQC)- and 31P NMR and headspace gas chromatography-mass spectrometry for functional groups, and thermogravimetric analysis for thermal stability. Most samples resisted irradiation. Subtle changes occurred in the molecular weight distribution and thermal stability of milled wood lignin. EBI was found to be a suitable pretreatment method for woody biomass if the avoidance of lignin condensation and chemical modification is a high priority.
Highlights
Electron beam irradiation (EBI) facilitates the controlled degradation of lignocellulosic feedstock, and it may be incorporated in lignin-based biorefineries
In a comparative study in which lignin model compounds were irradiated with EBI, the β-aryl ether bond was more susceptible to radiolytic cleavage when the compound was phenolic, i.e., less methoxylated and vice versa.[4]
As seen for cellulose, EBI statistically favors the attack of large molecules because of their increased surface area
Summary
Electron beam irradiation (EBI) facilitates the controlled degradation of lignocellulosic feedstock, and it may be incorporated in lignin-based biorefineries. When irradiated with an electron dose of up to 90 kGy, the number of peroxy radicals in kraft lignin increased.[6] This was indicative of degradation and demethylation reactions. The current study elucidates the chemical and structural changes in milled wood lignin (MWL) from beech (Fagus sylvatica) and eucalyptus (Eucalyptus grandis × urophylla) after EBI at a dose of up to 200 kGy. For a further point of reference, technical lignin from beech (F. sylvatica) and eucalyptus (Eucalyptus globulus) was included. E. globulus kraft and F. sylvatica sulfite lignin were isolated from spent cooking liquors by adsorption to an Amberlite XAD-7 ionexchange resin, followed by desorption with ethanol Both samples were kindly contributed as a dry powder by the chemistry department of the University of Natural Resources and Life Sciences, Vienna. An injection volume of 10 μL and a flow rate of 1 mL min−1 were used
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