Recovery and Extraction of Polyhydroxyalkanoates (PHAs) - Polyhydroxyalkanoate (PHA) Based Blends, Composites and Nanocomposites - page 59

granules of bacterial cells before and after the recovery process can be ob-
served under transmission electron microscopy (TEM) and scanning elec-
tron microscopy (SEM). 52 The PHAs are chemically characterized and
quantified by nuclear magnetic resonance (NMR) spectroscopy. 53 Further-
more, the molecular weight of extracted and non-extracted copolymers is
examined using gel permeation chromatography (GPC). 54 The morpho-
logical state of PHA granules synthesized by bacterial cells can be deter-
mined using liquid nitrogen cooled differential scanning calorimetry (DSC).
Data for enthalpy of fusion and enthalpy of crystallinity are collected during
the second heating cycle. 55

d n 2 r 4 n g | 7

3.4 Conclusion
The main obstacle to the commercial production and application of PHAs in
consumer products is their high cost compared to synthetic plastics. 1 The
recovery of PHA as an intracellular product significantly affects the overall
economics, and therefore, developing a clean, simple and ecient process
for PHA extraction from source materials at a useful level of quality and
purity is a remarkable proposal. 56 Generally, it could be concluded that the
extraction and purification of PHA granules from a cell biomass is a chal-
lenging task especially when one considers the use of environmentally
hazardous chemicals as an unacceptable option in the production of eco-
friendly materials. Various methods such as chemical, biological, mechan-
ical and physical treatments have been developed successfully for PHA
recovery from bacteria cells on a small scale. A useful comparison of the
various types of methods that have been tested for the extraction of PHA
granules from microbial cell biomass including their advantages and dis-
advantages is given in Table 3.1. Moreover, Table 3.2 shows the summary of
purity, recovery yield and molecular weight of PHA recovered from various
organisms by non-halogenated solvent processes, as reported in the litera-
ture. It is seen that the developed halogen-free methods could be considered
as green alternative technologies for PHA recovery, which are able to elim-
inate the usage of harsh organic solvents and their negative impact on the
environment.
Some of the ecient laboratory techniques have no opportunity for
commercialization due to several factors such as high energy requirements,
low accessibility and high cost of the equipment. Hence, significant par-
ameters affecting the performance of recovery processes have to be deter-
mined for their success on an industrial scale. The selection of suitable PHA
extraction methods depends on several process parameters such as con-
centration of chemicals, reaction time, recovery temperature, pH, etc.In
addition, the choice of recovery system, PHA-producing bacteria, com-
position of the growth medium, presence of certain chemical compounds in
the environment, the intracellular PHA content, length of PHA granules, cell
wall structure and economics of process are considered as the most im-
portant external factors affecting the extraction process. 25,64 Basically, the

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