Polyhydroxyalkanoates (PHAs), their Blends, Composites and Nanocomposites: State of the Art, New Challenges and Opportunities - Polyhydroxyalkanoate (PHA) Based Blends, Composites and Nanocomposites - page 12

in controlling the growth of creeping bentgrass, Agrostis stolonifera. 111
Notably, adjustment of the content of the PHA casing enabled a level of
control over degradation rate and product release.

d n 2 r 4 n g | 1

1.8 Packaging Applications of Polyhydroxyalkanoates
According to Robertson (2010), 112 the main functions of packaging are to
contain, to protect, to be convenient, to communicate and to sell the prod-
uct. The basic functions of a package are to contain a certain amount of
food, unitizing the product and facilitating its transportation, storage, sale
and use. Bucci et al. (2005) 113 reported that PHB can be used in injection
molding processes for the manufacture of food packaging, with the same
equipment used for PP packaging injection. However, the process conditions
should be adjusted according to polymer characteristics. The authors found
a notable difference between PHB and PP bottles in relation to their per-
formance in dynamic compression resistance and a drop test, in that PHB is
as hard a material as PP, but is less flexible. PHB performance was better at
higher temperatures. The physical, dimensional, mechanical and sensory
tests showed that PHB can replace PP containers for food products with high
fat content (mayonnaise, margarine and cream cheese), including storage in
freezers and heating in microwave ovens. Likewise, Muizniece-Brasava and
Dukalska (2006) 114 reported that PHB materials are suitable for sour cream
storage. To improve flexibility for potential packaging applications, PHB is
synthesized with various co-polymers, such as poly (3-hydroxyvalerate) (HV),
leading to a decrease of the glass transitions and melting temperatures. In
addition, the HV broadens the processing window since there is improved
melt stability at lower processing temperatures (Modi et al., 2010). 115 Fabra
et al. (2013) 116 created an innovative way to develop renewable biopolyester
microbial-based multilayer structures with enhanced barrier performance,
which is of significant interest for food packaging applications. The
researchers developed multilayer structures based on polyhydroxybutyrate-
co-valerate with a valerate content of 12% (PHBV12) containing a high
barrier interlayer of zein electrospun nanofibers. The incorporation of
3-hydroxyvalerate (HV) in PHB, resulting in PHBV, has increased impact
strength, elongation modulus, tensile strength and decreased Young's
modulus, making the film more flexible and more resistant (Shen et al.,
2009). 117 The price is very high but PHBV degrades between five and six
weeks in a microbiologically active environment, resulting in water and
carbon dioxide in aerobic conditions. In an anaerobic environment,
degradation is faster, producing methane (Siracusa et al., 2008). 118
A mixture of PHBV with PLA had a positive effect on the elasticity
modulus, elongation at break and flexural strength for different blends.
However, tensile strength did not improve in any of them. In the same way,
Zhang et al. (1996) 119 reported improved mechanical properties for blends of
PHB/PLA compared with the common PHB. In addition, PVA (poly-
vinylacetate) grafted on PIP (poly-cis-1,4-isoprene) and mixed with PHB had

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