Environmental Engineering Reference
In-Depth Information
Flavonoids
OH
OH
OH
B
B
HO
O
HO
O
OH
A
OH
A
OH
OH
OH
OH
B
B
HO
HO
O
O
OH
A
A
OH
OH
OH
OH
OH
OH
Condensed polyflavonoids
OH
OH
HO
HO
O
O
OH
OH
OH
OH
OH
OH
OH
OH
OH
HO
HO
O
O
OH
OH
OH
OH
Pecan tannin
Pine tannin
OH
OH
OH
OH
Figure 5.5
Examples of flavonoids with different hydroxyl populations on the A and B phenolic
rings, and representative condensed polyflavonoids from pine and pecan sources [163].
suggesting the use of an additional linker to help close the gaps the methylene
bridge cannot close [163]. Despite its industrial availability, the reactivity of its
phenolic ring A, and the success of tannins in wood adhesives, the chemical has
received little attention in current research which is instead focused on the pro-
duction of biobased polymers.
5.6.1
Recent Work with Tannin Polycondensation
The production of cross-linked foams using tannin-based systems was first
reported in the early 1990s, but it has only recently gained attention in a series of
publications by the Pizzi group at the University of Lorraine, Epinal, France
