Biomedical Engineering Reference
In-Depth Information
OH
HO
Lignin-O
OMe
Lignin
OH
O
OMe
OMe
HO
O
O
HO
OMe
OH
O
OMe
HO
HO
HO
HO
O
OH
OH
OH
OH
O
HO
OH
O
OMe
HO
OMe
O
HO
HO
OMe
OMe
O
OH
HO
HO
OMe
O
O
OMe
O
HO
O
OMe
HO
OH
OMe
O
OH
OH
O
OMe
HO
HO
OH
O
O
OH
OH
OMe
O
OH
OMe
HO
OMe
O
OMe
OH
CHO
HO
OH
HO
HO
O
OMe
HO
OMe
O
O
O
OMe
O
O
HO
O
OMe
OMe
OH
(CHO)
HO
OMe
HO
OH
OMe
Fig. 2.5
Structural model of a section of cork lignin [
34
]
The main bond types of grass lignin are the same as those of lignin in wood. The
main bond type of the structural unit is aromatic glycerol-
“
-aryl-ether bonds; these
are fewer than hardwood and are similar to softwood. The proportion of carbon-
carbon bonds, such as
“
“
“
in structural units, is higher than in hardwood. In
the structure of grass lignin, a considerable part of p-hydroxyphenylpropane units
connects with phenylpropane units in its ester form. Taking straw as an example,
60 % p-hydroxyphenylpropane units are connected in the form of its esters. In
addition, grass lignin still contains a small amount of ferulic acid esters.
Because the types and positions of functional groups in different types of lignin
are different, lignin of gymnosperms has different chemical characteristics. Lignin
in gymnosperm mainly contains guaiacyl lignin (G), the G-structure unit of which
has a methoxy group, and is hard to remove in the papermaking process because a
stable C-C linkage was formed by linkage with other monomers. Monocotyledon
mainly contains GSH lignin [
37
].
-5 and
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