Blends of Polyhydroxyalkanoates (PHAs) - Polyhydroxyalkanoate (PHA) Based Blends, Composites and Nanocomposites - page 87

4.3.4 PHAs/Starch Derivatives
According to Zhang and co-workers, 46 the T g of P(3HB) in the blends was not
affected by the addition of starch acetate (SA) as indicated by the constant
temperature at about 9 1C, which was almost similar to pure P(3HB)
homopolymer. Specific interactions between SA and P(3HB) were studied
using FT-IR analysis. Absorption of hydroxyl groups in both P(3HB) and SA
was indicative of intermolecular hydrogen bonding. In P(3HB)/SA blends,
the O-H stretching band of SA presented almost in the same region at
3470 cm 1 as for pure SA while the absorption of carbonyl groups of P(3HB)
in the blends was found to be independent of SA content at 1724 cm 1 . The
C ¼ O stretching band of the carbonyl groups of SA was also constant at
1748 cm 1 . This finding showed the absence of specific interactions
occurring between P(3HB) and SA. SEM analysis illustrated the dispersion of
the SA component in the P(3HB)/SA blends, which was far from uniform,
indicating phase separation between P(3HB) and SA. Based on DSC, FT-IR
and SEM, it was concluded that P(3HB)/SA blends were immiscible. A larger
size of the SA phase was observed for the P(3HB)/SA: 40/60 wt% blend than
for the P(3HB)/SA: 80/20 wt% blend. The crystallisation of P(3HB) from the
melt was also observed using POM under isothermal conditions. Well-
defined spherulites were observed at 80 1C for pure P(3HB). Crystallisation of
P(3HB) was also observed in P(3HB)/SA: 80/20 wt% and 60/40 wt% blends as
indicated by the spherulitic morphology. Although P(3HB) crystallised in
the P(3HB)/SA: 40/60 wt% blend, spherulites were not found visually.
Crystallisation of P(3HB) was not observed in the P(3HB)/SA: 20/80 wt%
blend. The SA component also affected cold crystallisation. Shifting of the
exothermal peaks to higher temperatures indicated the hindrance of mobile
chains of P(3HB) above the T g by the SA component.
Ismail et al. 47 studied the effect of starch content in the P(3HB) filmmatrix
on its degree of swelling in water. Swelling in water and degradability are the
most important characteristics for biodegradable materials. Polymer films
were degraded by surface absorption of moisture and microorganisms. Both
P(3HB) and P(3HB)/starch exhibited a gradual increase in water uptake
during the first two days until it reached a plateau. The water uptake of the
P(3HB) film was lower than that of the P(3HB)/starch blend, indicating that
addition of starch decreased the hydrophobicity of P(3HB). The anity for
water is usually increased by the presence of hydroxyl groups on the surface
of the starch granules. Therefore, the higher the starch content, the higher
the water uptake in the P(3HB)/starch blends. The transport behaviour of
water through the P(3HB)/starch blend is an important characteristic for
biodegradability and applicability. The water resistance of the P(3HB)/starch
blend was reduced with an increase in starch concentration, particularly
above 10 wt%. This observation could be attributed to the capillary moisture
formed by water on a starch basis.
The use of compatibilizers and plasticizers had resulted in the formation
of a finer morphology of blend films, which might produce better

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