Polyhydroxyalkanoate-based Multiphase Materials - Polyhydroxyalkanoate (PHA) Based Blends, Composites and Nanocomposites - page 130

crystallinity and degradation of the final blends. 49,50 The possibility of
blending other polymers with PHA offers the possibility of not only over-
coming the drawbacks of a small processing window and low impact re-
sistance of PHAs, but can also modify the crystallization tendency and
biodegradation rates. Blending with hydrophilic polymers is known to in-
crease the uptake of water and aid in faster biodegradation. The mechanical
properties, morphology, biodegradability, and thermal and crystallization
behaviour have been investigated on different PHBs blended with
other polymers such as poly(vinyl alcohol), polysaccharides, 51,52 poly(e-
caprolactone), 53,54 poly(vinyl phenol), poly(vinyl acetate), 55 poly (lactic
acid), 56 xylogen, 57 and even dendritic polyester oligomers. 58 PHA blends with
other biodegradable polymers have been studied for specific applications
also, for example, PHA-PCL blends were studied for cell adhesion and cell
growth, rubber-PHA blends were studied for e.g. varying the thermal stability
of the blends.
The possibility of H-bonding or formation of donor-acceptor interactions
between PHA and the other blend constituents helps improve blend misci-
bility and reduces the tendency of phase separation. 50 To increase the
compatibility and reduce the tendency of phase separation of the blends,
reactive blending between the components has been developed. For in-
stance, the components have been blended with peroxides. The latter de-
compose to form free radicals that cross-link the polymers 54 in the blend.
The miscibility and compatibility of these polyesters with functional
polymers are well documented. 50,59

d n 2 r 4 n g | 9

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6.2.5 PHA-based Multilayers
Multilayer coextrusion has been widely used, studied and understood in the
domain of synthetic polymers for its effect on the viscosity of polymers, die
geometry, layer distribution, encapsulation, and interfacial instabilities, in-
fluencing the quality and functionality of the multilayer products. 60-62
Despite the number and diversity of studies on multilayer flows and stabil-
ity, only some articles report the use of biopolyester in coextrusion processes.
Different stratified structures were processed by coextrusion and studied. But
very few studies have been carried out with PHA. Most of these are based on
the association between PHA e.g. PHBV, and plasticized starch. 60
Applications of such PHA-based multilayers as commodities are primarily
limited by PHA cost and have been until now by PHA availability, and thus
attention is being focused on products with plastics constituting only a
minor part, such as paper coatings like the plastic film moisture barrier in
food and drink cartons and in sanitary napkins.

6.2.6 PHA Biocomposites
Biocomposites are obtained by the incorporation of macro-fillers (mainly
ligno-cellulose fibres) in a biopolymer matrix. One of the main advantages of