Packaging Applications of Polyhydroxyalkanoates (PHAs) - Polyhydroxyalkanoate (PHA) Based Blends, Composites and Nanocomposites - page 211

and new technology is available, (vii) specific applications in biomaterials
and nanotechnology areas have been causing a rise in the commercial value
of biopolymers.
With the biopolymers that have been studied since 1991, there has been an
incentive for studying the production of biodegradable plastics with diverse
approaches. Great efforts have resulted in the development of the production
processes of poly(hydroxybutyrate) (PHB) and poly(3-hydroxybutyrate-co-3-
hydroxyvalerate) (PHB-co-HV), two polymers from the polyhydroxyalkanoates
family, from sucrose as a primary carbon source. The technology was trans-
ferred to PHB Industrial S/A company, following different studies for the
characterization and application of PHAs.
PHA polymers are synthesized by a wide variety of bacterial strains with
intracellular carbon and energy accumulation under adverse growth con-
ditions and in the presence of abundant carbon sources. Ralstonia eutropha
(or Alcaligenes eutrophus) is one of the most studied microorganisms for PHA
production due to its ease of growth using renewable carbon sources and the
fact that this bacteria may reach up to 80% of its dry weight as a polymer. 8

d n 2 r 4 n g | 8

9.2.1 Polyhydroxyalkanoates (PHAs)
The term PHA (Figure 9.1) is applied to a family of polyesters accumulated by
various bacteria, deposited in the cells in the form of highly refractive
granules of carbon reserve, energy and reducing equivalents. 7-9 In general,
PHA synthesis by bacteria in a nutrient medium occurs when there is an
excess of carbon source and a lack of one necessary nutrient at least (N, P,
Mg, Fe etc.) for cell multiplication. 6
The polyhydroxyalkanoate is a fully biodegradable polyester in micro-
biologically active environments. It can be synthesized by modified plants or
bacteria from intracellular reserve materials via direct biosynthesis of
carbohydrates from sugarcane, corn, or vegetable oils mainly extracted from
soybeans and palm. PHA production has several advantages: biodegrad-
ability, a decrease of environmental impact, replacement of conventional
plastics and the use of new materials in fields such as medicine. On the
other hand, there is a disadvantage in that PHA production still involves
high costs.

.

O

C

OCH CH 2

R

(PHA)
Where R = methyl or ethyl (short chain length); R = propyl, butyl, pentyl, hexyl or heptyl
(medium chain length); R = more than 14 carbons per repeating unit (long chain length).

Figure 9.1 PHA generic monomer.