Wood
is a naturally occurring composite, comprising cellulose,
hemicellulose, and lignin. The tightly arranged cell wall components
make the fibers resistant against chemical and microbial degradation.
This natural resisting power of fibers is a technical obstacle during
the degradation of cellulose into sugars. Therefore, removal of cell
wall lignin is necessary in order to make the cellulose accessible.
In this study, ultrathin sections of Norway spruce (Picea abies) branch wood were examined using Raman
and transmission electron microscopy (TEM) before and after extracting
the sections with 1,4-dioxane without resin embedding in order to
study the accessibility of native lignin. The progress of extraction
of lignin was followed by measuring its Raman scattering intensity
at the ∼1600 cm–1 band. It was found that
lignin was extracted not only from the compound middle lamellae but
also from other layers of the cell wall. Changes in the contrast of
TEM images confirmed a decrease in lignin concentration after solvent
extraction. Observed ruptures in the S1 layer indicated
that extraction weakened this layer in particular.
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