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2.4.0 Studied polymers
The studied polymers in this thesis are: lignin, cellulose, EVA, PS, and PVC.
2.4.1 Lignin
Lignin is a macromolecular substance formed in the cellular membranes of vegetal cells
that changes them into wood. The term itself comes from the latin word lignum that
means “wood”, the fact reminding of which is probably as superfluous as to “bring wood
in the forest” (in silvam ligna ferre [Horatius]). The precise structure of this substance
has not yet been completely determined. Thus the term “lignin” has to be understood to
designate a complex of aromatic rings with methoxyl groups. It’s an amorph substance
that, once liberated from its linkage with cellulose in the cellular membrane, has brown
or black-brown colour. This is why wood becomes brown when its cellulose is disturbed
and lignin liberated.
Lignin is the second most wide-spread organic compound of the biosphere. This
abundant natural resource is present in all plants, particularly in trees. In wood, it comes
second after cellulose, representing between 15 and 30 % of its weight. Lignin is an
indispensable substance in vegetal kingdom.
Lignin is embedded in between polysaccharidic constituents of cell walls; its function is
the support and conduction. First, it is deposited in the vicinity of intercellular space,
and then, on the level of primary and secondary plant diaphragms. Thus, lignin is in
a state of quasi-total gel, it is situated in the walls in form of cords.
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