Front Matter

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188 Introduction to Renewable Biomaterials

In general, herbaceous plants, such as grasses, have the lowest content of lignin,
whereas softwoods have the highest lignin content (Jorgensenet al., 2007).
Higher plants can be divided into two classes: hardwood and softwood. It has been
recognized that lignin from softwood is made up of more than 90% of coniferyl alcohol
with the remaining being largelyp-coumaryl alcohol units. In contrast to softwoods,
lignin contained in hardwood is composed of varying ratios of coniferyl and sinapyl
alcohol units (Kirk-Otmer, 2001). Figure 6.7 shows a model structure of lignin from
softwoods. The solvents of lignin consist of low-molecular-weight alcohols, dioxane,
acetone, pyridine, and dimethyl sulfoxide. Lignin softens and depolymerizes with
increasing temperature, which allows the acceleration of depolymerization reactions of
acidic or alkaline nature (Kirk-Otmer, 2001; O’Connoret al., 2007).

CH 3 O
O

H O

OH

OH

O
C

O
OH
O

OCH 3
O

HO

CH 3 O
O OH
HO

OH

CH 3 O
O
C

OCH 3

C
O

CH 3 O OCH 3

HO

O

HO CH 3 O
O

OCH 3

O

O

OCH 3

OH

O

CH 3 O

OH
O

HO

O H

HO

CH 3 O OCH 3

HO

HO

O

OH

OH

CH 3 O

O O

OH
CH 3 O

HO

HO

OH

OH

HO

HO

CH 3 O

OCH 3

OH

Figure 6.7Schematic structure of softwood lignin.
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