Environmental Engineering Reference
In-Depth Information
OH
HO
O
OH
O
OH
O
OH
HO
O
OH
OH
O
O
Figure 5.6
Representative cross-linked network of the moldable plastics produced by conden-
sation reaction between tannin and FA [181].
5.6.2
Tannins Conclusion
The use of tannins in wood adhesives is well established, but surprisingly little
attention has been given to the application of tannins in other areas. Recent efforts
by the Pizzi group have shown a number of possible applications for tannins.
These include uses in insulation, as catalyst supports, and for active filtration
[168, 178, 179]. In addition, it was shown that it is possible to produce moldable
thermosetting plastics from tannins, with material strengths competitive with
traditional fossil-based thermoset plastics [181].
5.7 Alpha-Hydroxy Acids
Certain AHAs have gained attention over the past decade as potential competitors
for conventional polyesters, such as PET for high-volume uses in packaging and
textiles. This discussion focuses on two biorenewable AHAs: polylactic acid
(PLA) and polyglycolic acid (PGA). PLA was discovered in the early part of the
twentieth century and has gained industrial relevance over the past decade.
Currently, several companies worldwide are producing PLA [182-186]. PLA is a
polyester with stereoisomers, which can be used to tune the properties of the
bulk polymer from amorphous to semi-crystalline. This section describes the pro-
duction of PLA, its properties and current applications in packing and biomedical
applications. Detailed reviews of PLA have been prolific over the past decade
[187-195].
