Chemistry Reference
In-Depth Information
The second fraction has the some galactose units linked 1 and 4 and others have ether group
linking carbons 3 and 6:
CH
2
OH
O
O
O
and
HO
n
n
OH
OH
A similar polysaccharide is also obtained from seaweeds that is called
agar
. It is similar in
structure, but has less sulfate groups per chain.
Crab and shrimp shell wastes are an abundant source of
chitin
, a nitrogen atom-containing
polysaccharide:
CH
2
OH
O
n
NH
O
The polymer can be deacetylated to yield an amine group bearing polysaccharide.
8.3 Lignin
These polymers are also constituents of wood (about 25-30%) [
18
,
19
]. It is uncertain what the
molecular weights of the polymers are as the materials are quite complex in structure. The extraction
processes of lignin result in considerable loss of molecular weights. The structures of lignin vary,
depending upon the source. Generally, they are considered to be polymers of coniferyl alcohol:
HO
OH
O
An idealized picture of lignin that formed from coniferyl alcohol was published by Freudenberg
[
20
]. It appears reasonable, however, that some lignins might, perhaps, also form in different trees,
from other compounds not coniferyl alcohol, but related to it and also found in woods. Also it appears
plausible that several of such compounds, including coniferyl alcohol, actually participate together in
lignin formation, depending upon the species of wood. Figure
8.1
shows the chemical structures of
some of these compounds.
Many attempts were made to convert lignin to a useful material for coatings and adhesives.
Only very limited success, however, has been achieved. A reaction product with formaldehyde can
be used as a wood adhesive. In addition, lignin obtained from wood pulping by the sulfate process
(as a sulfonate) has been utilized to a limited extent as an asphalt extender and as an oil-well drilling
mud additive.
