331
19
They are polyesters consisting of hydroxycarboxylic acids as monomeric building blocks,
for example, 3-hydroxybutyric acid. The formal
polycondensation of 3-hydroxybutyric acid provides the polyhydroxybutanoate (PHB), the most
important representative of PHA. The methyl
substituent in the chain produces a chiral carbon atom; the methyl group can show either
forward or backward. In the simplest and most
frequent case there is only one conformation, as
in the case of the poly-3-(R)-hydroxybutanoate
(. Fig. 19.8).
There are many other hydroxycarboxylic
acids, e.g. 3-hydroxyvaleric acid, which when
integrated into the polymer structure leads to
an ethyl side chain. Longer 3-hydroxyalkanoates
also occur, with side chains of up to twelve carbon atoms. The hydroxyl group can also have a
position further away from the carboxylic acid
group, as in 4-hydroxybutyric acid, so that no
branching occurs in the polymer (. Fig. 19.8).
All these variants (orientation to the chiral carbon atom, length and frequency of the side chain
(bombyx mori), a butterfly species originally from
China. The cocoon is spun from silk threads by
the caterpillars of the mulberry moth (. Fig. 19.7).
The silk can then be spun off again by killing the
caterpillar in the cocoon, and treatment in aqueous baths and thus be recovered. The production
is relatively complex, and silk is an expensive
product. However, textiles made of silk are highly
desired, especially for clothing due to their fine
structure and excellent wearing properties. The
largest producer of silk is China, followed by
India. Approximately 500,000 tons of silk are produced annually, which requires about 5–10 times
the amount of cocoons to be processed.
Polyhydroxyalkanoates
Polyhydroxyalkanoates (PHA) are naturally
occurring polyesters that are synthesized by
bacteria and serving them as energy and carbon
stores (reserve substance, 7 Chap. 8: Starch as
reserve carbohydrate). They form inside the cell,
especially when there is a lack of nutrients and
oxygen (anaerobic conditions).
. Fig. 19.7 Silk from the cocoons of the mulberry moth (© Stillfx/Fotolia, © KentaStudio/Fotolia)
. Fig. 19.8 Formal illustration of the different monomers in polyhydroxyalkanoates
O
O
O
O
O
∗
∗
R
O
O
O p
o
n
m
(R)-3-Hydroxybutyric acid
3-Hydroxypentanoic
acid
3-Hydroxyalkanoate
with R = C 1 -C 12
4-Hydroxybutyric acid
Polyhydroxyalkanoate:
19.2 · Biopolymer Representatives
19
They are polyesters consisting of hydroxycarboxylic acids as monomeric building blocks,
for example, 3-hydroxybutyric acid. The formal
polycondensation of 3-hydroxybutyric acid provides the polyhydroxybutanoate (PHB), the most
important representative of PHA. The methyl
substituent in the chain produces a chiral carbon atom; the methyl group can show either
forward or backward. In the simplest and most
frequent case there is only one conformation, as
in the case of the poly-3-(R)-hydroxybutanoate
(. Fig. 19.8).
There are many other hydroxycarboxylic
acids, e.g. 3-hydroxyvaleric acid, which when
integrated into the polymer structure leads to
an ethyl side chain. Longer 3-hydroxyalkanoates
also occur, with side chains of up to twelve carbon atoms. The hydroxyl group can also have a
position further away from the carboxylic acid
group, as in 4-hydroxybutyric acid, so that no
branching occurs in the polymer (. Fig. 19.8).
All these variants (orientation to the chiral carbon atom, length and frequency of the side chain
(bombyx mori), a butterfly species originally from
China. The cocoon is spun from silk threads by
the caterpillars of the mulberry moth (. Fig. 19.7).
The silk can then be spun off again by killing the
caterpillar in the cocoon, and treatment in aqueous baths and thus be recovered. The production
is relatively complex, and silk is an expensive
product. However, textiles made of silk are highly
desired, especially for clothing due to their fine
structure and excellent wearing properties. The
largest producer of silk is China, followed by
India. Approximately 500,000 tons of silk are produced annually, which requires about 5–10 times
the amount of cocoons to be processed.
Polyhydroxyalkanoates
Polyhydroxyalkanoates (PHA) are naturally
occurring polyesters that are synthesized by
bacteria and serving them as energy and carbon
stores (reserve substance, 7 Chap. 8: Starch as
reserve carbohydrate). They form inside the cell,
especially when there is a lack of nutrients and
oxygen (anaerobic conditions).
. Fig. 19.7 Silk from the cocoons of the mulberry moth (© Stillfx/Fotolia, © KentaStudio/Fotolia)
. Fig. 19.8 Formal illustration of the different monomers in polyhydroxyalkanoates
O
O
O
O
O
∗
∗
R
O
O
O p
o
n
m
(R)-3-Hydroxybutyric acid
3-Hydroxypentanoic
acid
3-Hydroxyalkanoate
with R = C 1 -C 12
4-Hydroxybutyric acid
Polyhydroxyalkanoate:
19.2 · Biopolymer Representatives