Barrier Properties of Biodegradable Bacterial Polyester Films - Natural Polymers, Biopolymers, Biomaterials, and Their Composites, Blends, and IPNs - page 59

Polyhydroxyalkanoates--PHA
As pointed out by Lenz and Marchessault in an excellent review (Lenz and Marches-
sault, 2005), Lemoigne and co-workers published their observations and interpreta-
tions on PHA family at the time when Herman Staudinger was proposing the existence
of high molecular weight molecules or polymers, which he termed “macromolecules”.
From the simple PHB homopolymers discovered by Maurice Lemoigne in the
mid-twenties, a family of over 100 different aliphatic polyesters of the some general
structure has been identified (Lenz and Marchessault, 2005; Steinbüchel, 2003). The
main features are reported in Figure 3.
Figure 3. General structure of polyhydroxyalkanoates.
Depending on bacterial species and substrates used for feeding the bacteria and the
conditions of growth, high molecular weight stereoregular polyesters have emerged as
a new family of natural polymers, named polyhydroxyalkanoates. The way of sepa-
ration and purification may also have a certain influence. In addition, the attainable
molecular properties, the molecular weight, and molecular weight distribution are de-
pendent on the bacterial fermentation conditions.
This possibility of preparing various PHA as a function of the substrate was first
revealed by De Smet and co-workers (De Smet, 1983). For example, the polymer con-
sisting principally of 3-hydroxyoctanoate units (PHO) can be formed from Pseudomo-
nas oleovorans in n-octane. And, the polymer with 3-hydroxybutyrate units (PHB) can
be obtained from Alcaligenes eutrophus or from Azotobacter beijerinckii as reported
by Schlegel and co-workers, and Dawes and co-workers, respectively (Oeding, 1973,
Senior, 1973). This family can thus be produced in many grades, differing in composi-
tion, molecular weight, and other parameters.