Recovery and Extraction of Polyhydroxyalkanoates (PHAs) - Polyhydroxyalkanoate (PHA) Based Blends, Composites and Nanocomposites - page 58

The success of PHA as a viable option for petrochemical-based plastics will
depend upon the design and performance of ecient and selective means of
PHA production and recovery. 47 Thus, further investigation on mixed cul-
tures, recombinant microbial strains, cheap carbon substrates and ecient
fermentations has allowed the production of significant quantities of PHA
which can significantly decrease the production cost. 1,20,48 However, there
are diculties in obtaining ecient and cost-effective PHA recovery from
bacteria cells at a valuable level of quality and purity. A commercial recovery
system with a simple, ecient and economical procedure will probably focus
on a non-solvent extraction-based recovery amongst a variety of PHA recovery
methods. In addition, the tolerance of the final product to the conditions
employed is an important criterion for the selection of a PHA recovery
process and the PHA properties have to be considered for the development
of downstream processes. It has been reported that polymer molecular
weight is an important property as it determines many physical and mech-
anical characteristics such as glass transition temperatures, stiffness,
strength, elasticity, toughness, and viscosity. If the PHA molecular weight is
too low, the transition temperatures and the mechanical properties will
usually decrease, which is not suitable for any useful commercial appli-
cations. 49 Depending on the chemical composition and the molecular
weight, PHAs can be converted to a range of finished products including
films and sheets; moulded articles; fibres; elastics; laminates and coated
articles; non-woven fabrics; synthetic paper products and foams. PHAs are
valuable for injection moulding and melt blowing at low comonomer con-
tent and molecular weight. At medium molecular weight, the material is
suitable for melt spun fibres. With higher comonomer content and medium
molecular weight (600 000 Da), applications consist of melt resins and cast
films. Blown films and blow moulding require at least 10% of comonomer
content and high molecular weight (700 000 Da). Above 15% comonomer,
the PHAs are softer and more elastic, finding applications in adhesives and
elastomeric films. 50 Hence, the challenge in the recovery process should be
the maintenance of the original molecular weights while not compromising
the degree of purity for various applications. 51 However, severe degradation
of polymer molecular weight was reported during PHA extraction of
C. necator using sodium hypochlorite treatment. 16 Ramsay et al 13 also indi-
cated that the molecular weight of PHA recovered from C. necator by
surfactant-hypochlorite was about 60% of the original molecular weight.
Besides, surfactant-chelate treatment for 10 min at 50 1C caused a decreasing
in the molecular weight from 402 000 to 316 000 Da. 6 If the process par-
ameters are not controlled properly, a significant reduction of molecular
weight can be observed during PHA extraction using selective dissolution of
NPCM by proton. 19 Therefore, as the extraction process may considerably
affect the polymer features, it is necessary to characterize and compare the
extracted and non-extracted polymer properties to assess the feasibility of the
developed recovery methods on PHA extraction and address the possible
market demand and intended applications. Accordingly, the native PHA

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