Recovery and Extraction of Polyhydroxyalkanoates (PHAs) - Polyhydroxyalkanoate (PHA) Based Blends, Composites and Nanocomposites - page 62

impact of process parameters on the effectiveness of PHA extraction
procedures have been well proven and studied in the literature, but there is
a limitation on concrete data for stated observations about the effect of
external factors on PHA recovery.
The extraction method influences the amount of PHA recovered, the sim-
plicity of the subsequent purification steps and eventually the quality of the
final product. However, the processing required for effective PHA extraction
varies significantly in regards to the PHA-producing organisms as different
procedures have various effects on a specific strain and vice versa. 3 On the
other hand, the PHA content of the produced biomass also plays a dominant
role in PHA recovery eciency because a lower PHA content clearly results in a
high recovery cost. This is mainly due to the use of large amounts of digesting
agents for PHA extraction which increase the cost of waste disposal. 66
The final intended application for the PHA will determine the degree of
purity of the PHA granules. For example, in medical applications, it is ab-
solutely necessary that the PHA should be free from bacterial endotoxins and
other contaminating chemicals and solvents. On the other hand, if the PHA
is intended for applications such as mulching film or garbage bags, a lower
degree of purity may be acceptable. Regardless of its final applications, the
molecular weights of the recovered PHA should be suciently high. This is
because the thermal processing of the PHA would result in the reduction of
its molecular weights to some extent. Therefore, it is important to have PHA
resins with as high a molecular weight as possible. In order to obtain PHAs
with a high degree of purity, a more stringent recovery process is needed.
This often results in PHAs with lower molecular weights. In addition, the
recovery yield will be lower. Therefore, the challenge in the recovery process
is to maintain the original molecular weights while not compromising the
degree of purity for various applications. These criteria have to be achieved
in an environmentally friendly manner. Finally, and most importantly, the
cost of the recovery process should be economically feasible. 51
Currently, most PHA extraction processes are based on halogenated
solvent extraction which is costly and may cause environmental problems
and toxicity to humans. Thus, it seems that a practical commercial ex-
traction system with a clean, simple and ecient process for PHA recovery at
a reasonable cost focusing on a non-halogenated solvent extraction-based
recovery needs to be developed. However, halogen-free methods require
further adjustment, depending on both significant process parameters and
external factors influencing their performance, to make the process suitable
for polymer recovery on an industrial scale.

d n 2 r 4 n g | 7

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References
1. S. Khanna and A. K. Srivastava, Process Biochem., 2005, 40, 607.
2. R. S. M. S. Karumanchi, S. N. Doddamane, C. Sampangi and P. W. Todd,
Trends Biotechnol., 2002, 20, 72.
3. Y. Chisti and M. Moo-Young, Enzyme Microb. Technol., 1986, 8, 194.