Blends of Polyhydroxyalkanoates (PHAs) - Polyhydroxyalkanoate (PHA) Based Blends, Composites and Nanocomposites - page 83

P(3HB-co-3HV) copolymer in P(3HB-co-3HV)/PCL blends. Qiu and co-
workers 31 also reported that the addition of PCL to the blend reduced
the crystallisation of P(3HB-co-3HV) copolymer. Therefore, the crystallisation
of P(3HB-co-3HV) copolymer reduced after blending with PCL. That
was attributed to the presence of PCL that suppressed the nucleation of
P(3HB-co-3HV) in the blends.

d n 2 r 4 n g | 6

4.3.3 PHAs/Cellulose Derivatives
Zhang et al. 35 reported an increase in the T g of the annealed P(3HB)/ethyl
cellulose (EtC) blend (100/0, 80/20, 60/40, 40/60, 20/80, and 0/100, wt%)
from 44.6 1C to 70.4 1C with the increase of EtC content. However, a melt-
quenched sample of EtC did not exhibit T g . It was assumed that liquid
crystals might exist below T g because EtC is a thermotropic liquid crystal
polymer. FT-IR analysis was also conducted to find the possible interaction
between EtC and P(3HB). Hydrogen bonding of hydroxyls on the backbone of
EtC makes it a rigid polymer with some degree of flexibility. P(3HB) pos-
sesses carbonyl groups that are proton acceptors along the main chain.
A decrease in the absorption bands of hydroxyl groups in EtC was observed
with an increase of P(3HB) content in the blends. However, the absorption
bands of carbonyl groups at 1723-1724 cm 1 in P(3HB) were independent of
the blend composition. It was proven that the hydrogen bonding of the
hydroxyl groups of EtC was stronger than that of the hydroxyl group in EtC
with the carbonyl group in P(3HB). Exothermic peaks corresponding to the
crystallisation of P(3HB) were not detected in DSC traces of P(3HB)/EtC
blends, thus it was concluded that a delay in the crystallisation of P(3HB) in
the blends might be due to the EtC component. Polarizing optical micro-
graphs (POM) of P(3HB) showed the growth of well-defined spherulites at
100 1C. However, no spherulite of P(3HB) was observed for the blends at a
similar temperature. Depression of the spherulite growth was attributed to
the dilution effect of the EtC component as well as the influence of melt
miscibility on the primary nucleation processes. The results obtained had
led to the conclusion that P(3HB)/EtC blends were miscible in an amorphous
state. A SEM of the blends also showed the absence of phase separation as
no distinct phase boundaries were observed.
Chan et al. 66 reported that the degradation rate increased with an increase
of EtC content in the P(3HB)/EtC blends. Approximately 3.5% of the P(3HB)
films' initial weight was lost after 105 days' incubation, whereas P(3HB)/EtC:
20/80 wt% lost about 12% of its initial weight. The influence of EtC on the
biocompatibility of the P(3HB) films was compared using adult olfactory
ensheathing cells (OECs). SEM illustrated that OECs readily attached to
P(3HB) and P(3HB)/EtC: 80/20 wt% and exhibited healthy morphology with
many filament extensions comparable to cells in an asynchronous control
with the absence of biomaterials (Figure 4.4). Blending with EtC also ex-
hibited changes in the surface structure of the P(3HB) polymer. The average
surface roughness, R a , of the P(3HB) films was increased with EtC content.

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