Blends of Polyhydroxyalkanoates (PHAs) - Polyhydroxyalkanoate (PHA) Based Blends, Composites and Nanocomposites - page 69

and compression-molded on a Mini Test Press by heating at 200 1C for
1 minute under a pressure of 75 kg cm 2 . After melting, samples were kept
at a given crystallisation temperature (T c ) and isothermally crystallised for
3 days. The melt-crystallised films were about 0.2 mm in thickness and
stored at 220 1C.
The effect of adding PLA on the toughness of P(3HB) had also been
studied by preparing the blends using a melt-compounding method. The
P(3HB)/PLA blends at different concentrations (100/0, 75/25, 50/50, 25/75,
and 0/100, wt%) were mixed in a Haake polylab torque rheometer at 175 1C
for 10 minutes at a constant rotor speed of 50 rpm. The materials were hot-
pressed at 180 1C using a 20 ton lab press and then quenched to room
temperature to obtain 1 mm and 3 mm sheets. 20 A plasticized P(3HB)/PLA:
75/25 wt% blend was also prepared through the melt-compounding method
to create a new type of eco-friendly blend material suitable for single-use
applications, such as fast food packaging. Polyester plasticizer (Lapol 108)
was added at two different concentrations (5 and 7 wt%). 21
It had been reported that the commercial viability of pure P(3HB-co-3HV)
copolymer and PLA alone is dicult, therefore blends of these polymers
were prepared to get a material with balanced toughness properties. 22
Another study reported that the blend of P(3HB-co-3HV)/PLA provides a
way of improving and tailoring the foam morphologies without comprom-
ising the biodegradability. 23 P(3HB-co-3HV)/PLA blends were prepared by
melt mixing in a mixer. All materials were dried in a vacuum prior to use.
The resulting materials were then ground into pellets and then were sent for
compression molding. The compression molding was carried out under a
hydraulic pressure. 24 Meanwhile, Zhao and co-workers 23 reported the prep-
aration of a P(3HB-co-3HV)/PLA blend using a co-rotating twin-screw extru-
der. The melt mixing was carried out above the glass transition temperature
(T g ) of amorphous polymer. The twin-screw extruder was used to ensure that
all the specimens undergo the same thermal-mechanical history. Nanda and
co-workers 22 reported the production of a P(3HB-co-3HV)/PLA blend using a
micro compounder. The polymers were dried in a vacuum prior to use. In
order to obtain the desired samples, the molten mass of the P(3HB-co-3HV)/
PLA blends were transferred to a mini injection moulder.
Since PLA exhibited properties such as brittleness, a slow rate of crystal-
lisation and enzymatic hydrolysis, the practical application of PLA was limited.
P(3HB-co-4HB) copolymer seems to be a suitable candidate as this copolymer
has relatively good toughness, flexibility and high biodegradation rate. PLA was
blended with P(3HB-co-4HB) copolymer by melt compounding. This had re-
sulted in a more favorable blending method as the modified properties were
expected to overcome the drawbacks and provide feasible applications. 25

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4.2.2 PHAs/PCL Blends
PCL is semi-crystalline polyester that exhibits good mechanical properties,
biodegradability, biocompatibility and miscibility with various polymers.