Polyhydroxyalkanoates (PHAs), their Blends, Composites and Nanocomposites: State of the Art, New Challenges and Opportunities - Polyhydroxyalkanoate (PHA) Based Blends, Composites and Nanocomposites - page 5

market demand and intended applications. The selection of suitable PHA
extraction methods depends on several process parameters such as con-
centration of chemicals, reaction time, recovery temperature and pH.
Basically, the impact of process parameters on the effectiveness of PHA
extraction procedures have been studied and proven, but there is a limi-
tation of concrete data on the effect of external factors on PHA recovery.

d n 2 r 4 n g | 1

1.3 Blends of Polyhydroxyalkanoates
Various PHA blends have been developed to improve the performance and to
offset the high price of PHAs. The blending of PHAs will offer more scope to
expand their range of applications. The P(3HB)/PLA blend is one of the most
studied blends, which exhibits mechanical properties that are intermediate
between the individual components. Although PLA and P(3HB) are bio-
degradable polymers synthesized from renewable resources, their potential
applications are hampered due to brittleness and formation of very large
spherulites. 25 Zhao and co-workers (2013) reported the preparation of a
P(3HB-co-3HV)/PLA blend using a co-rotating twin-screw extruder. The melt
mixing was carried out above the glass transition temperature (T g )of
amorphous polymer. The reason for using a twin-screw extruder was to en-
sure that all the specimens undergo the same thermal-mechanical history.
Blending of PCL and P(3HB) offers a good option to improve the perform-
ance of both homopolymers. 26 They had prepared a blend of P(3HB)/PCL by
melting the mixture in an internal mixer with compositions of PCL varying
from 0 to 30 wt% to study the miscibility, morphology and physical-
chemical properties of these systems.
Cellulose derivatives also have attracted much interest for their compati-
bility with P(3HB). 27,28 Ethyl-cellulose (EtC) is also a biomaterial like P(3HB)
that is approved by the FDA (Food and Drug Administration) and is widely
used as a blood coagulant, in coatings for pharmaceutical tablets and
matrices for poorly soluble drugs. Zhang and co-workers (1997) 29 had in-
vestigated the miscibility, thermal behaviour and morphological structure of
P(3HB) with ethyl cellulose (EtC) blends. A P(3HB)/starch blend was pre-
pared either by a conventional solvent casting method or by melt processing
methods, such as injection molding and compression molding after com-
pounding. Two types of maize starch, Starch 1 (containing 70% amylose) and
Starch 2 (containing 72% amylopectin), were blended with P(3HB) using a
melt compounding method at a ratio of 70 : 30 wt% and characterised in
terms of their morphology, structure, thermal, rheological and mechanical
properties. 30 Ikejima and co-workers (1999) 31 had prepared P(3HB)/chitosan
blend films in order to investigate the effect of deacetylation on the crys-
tallisation behaviour of P(3HB). Chitosan is a copolysaccharide with a high
degree of deacetylation. A solvent-casting method was employed to prepare
the P(3HB)/chitosan blend films. P(3HB) and chitosan were dissolved
separately in HFIP (1,1,1,3,3,3-hexafluoro-2-propanol) before blending.

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