Blends of Polyhydroxyalkanoates (PHAs) - Polyhydroxyalkanoate (PHA) Based Blends, Composites and Nanocomposites - page 77

(P(3HB-co-3HV)/PLA: 25/75 wt%, it showed an increase in elongation at
break compared to the neat PLA (Table 4.1). It was reported that the slight
improvement might be because of the P(3HB-co-3HV) particles acting as a
filler to enhance PLA properties.
Thermal gravimetric analysis (TGA) is known as a popular method to
determine the thermal stability of certain polymers. It was reported by Neill
and Leiper 62 that the thermal degradation of P(3HB-co-3HV) copolymer
occurred through a random chain scission at ester groups whereas the
thermal degradation of PLA occurred through the cleavage of a bond on
the backbone to form a cyclic oligomer. Zembouai et al. 24 reported that the
degradation of each polymer occurred separately and it was found that
the PLA was more thermally stable than the P(3HB-co-3HV) copolymer.
They also reported that the decomposition temperature, T d ,forallthe
blends was between the PLA and P(3HB-co-3HV) copolymer. Therefore, the
thermal stability of the P(3HB-co-3HV)/PLA blends could be improved by
increasing the amount of PLA. The same trend was reported by Nanda
et al. 22 It was reported that the TGA curve for pure P(3HB-co-3HV)
copolymer and PLA was 290 1Cand3751C, respectively. For the P(3HB-co-
3HV)/PLA blend, two weight loss peaks were observed, one at 290 1C
and the other at 375 1C representing the P(3HB-co-3HV) and PLA phase,
respectively, indicating that P(3HB-co-3HV) copolymer and PLA tend to
degrade individually.
In a study by Nanda and co-workers, 22 the thermal properties of
the blend were evaluated using differential scanning calorimetry (DSC).
The T m of P(3HB-co-3HV) copolymer was reported as 152 1CandforPLA,it
wasreportedas1701C. The T m for the blend was found to be in between
these two polymers. Miscibility of any polymer can be determined by
evaluating the T g . A single T g indicates the miscibility of the polymer. One
T g that corresponded to PLA was reported and the T g for P(3HB-co-3HV)
copolymer was poorly observed. They also reported that when the content
of P(3HB-co-3HV) copolymer was increased, reduction in T g from 60 1Cto
45 1C was observed. The same observation was reported by Richards et al. 63
and Modi et al. 64
It was reported by Nanda et al. 22 that the degree of crystallinity of any
polymer blends depends on the orientation, the flexibility of the polymer
chain and nucleation. They also reported a decrease in the T c of PLA from
119 1Cto831C with an increase of P(3HB-co-3HV) copolymer content.
However, no increase in the degree of crystallinity of PLA was observed. The
presence of PLA prevented the crystal growth of P(3HB-co-3HV) copolymer in
the blend. In order to determine the transparency of any material, UV
spectroscopy was used. It was reported that the lower the transparency of any
material, the greater the absorbance of radiation and the lower the trans-
mittance. PLA, being transparent, has low absorbance. As the content of
HV increased in the blend, the transparency decreased. This showed that
P(3HB-co-3HV) copolymer has a dense structure that does not allow light to
pass through it.

d n 2 r 4 n g | 6

.