A tool
for lignin classification was developed based on radar plots
using six descriptors identified as key characteristics for vanillin
(V) and syringaldehyde (Sy) production by oxidation in alkaline medium:
content on β-<i>O</i>-4 structures, noncondensed structures,
syringyl and guaiacyl units, and yield of Sy and V by nitrobenzene
oxidation (NO). A set of lignins was classified according to the radar
information, simplifying the evaluation and discussion of the impact
of the delignification process, wood species, and morphologic part
on lignin. Lignin from tobacco stalks was one of the targets, reporting <sup>13</sup>C NMR and NO characterization data to ascertain the influence
of delignification process. Structural data on lignins
from different hardwoods (eucalyptus, mimosa, and willow), several
parts of the same species (bole, bark, branches, sawdust), and different
delignification processes were also used as a basis for the developed
methodology. The radar plots of tobacco lignins allow classifying
the lignin produced by organosolv process with ethanol as that with
the higher aptitude for V and Sy production with O<sub>2</sub>. This
classification was confirmed by batch oxidation of this lignin as
compared with that produced by organosolv process with butanol. In
the same way, among the processed hardwood lignins, the one produced
by organosolv of eucalyptus bole wood showed the highest intensity
in all descriptors, being classified as a privileged source of Sy
in comparison to Kraft lignins. The reasons behind the differences
on descriptors that gave rise to lignins classification are discussed.
The radar classification can be used as a predictive tool for product
and process design, for both lignin production and application. The
requisite for this is the previous knowledge of the relevant structural
parameters. This is a key step to demystify the lignin complexity
in key descriptors and consolidation of valorization routes in flexible
processing units
