Packaging Applications of Polyhydroxyalkanoates (PHAs) - Polyhydroxyalkanoate (PHA) Based Blends, Composites and Nanocomposites - page 223

characteristics. 33 The authors found a notable difference between PHB and
PP bottles in relation to their performance in dynamic compression resist-
ance and a drop test, in that PHB was as hard as PP, but less flexible. They
also concluded that PHB performance tended to be worse than PP per-
formance at refrigerator and freezer temperatures. However, PHB perform-
ance 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
Muizniece-brasava et al. 34 reported that PHB materials are suitable for sour
cream storage.
Basic PHB has relatively high glass transition and melting temperatures.
To improve flexibility for potential packaging applications, PHB is syn-
thesized with various co-polymers such as poly (3-hydroxyvalerate) (HV),
leading to a decrease in the glass transition and melting temperatures. In
addition, the HV broadens the processing window since there is improved
melt stability at lower processing temperatures. 35
Fabra et al. 36 have created an innovative way to develop renewable bio-
polyester microbial-based multilayer structures with enhanced barrier per-
formance of significant interest for food packaging applications. These
researchers developed multilayer structures based on polyhydroxybutyrate-
co-valerate with a valerate content of 12% (PHBV12) containing a high bar-
rier interlayer of zein electrospun nanofibers. It was observed that the
method used for the preparation of the outer layers affected PHBV12's
functional properties, since increased mechanical resistance and water
vapor permeability and transparency decreased in the multilayer containing
outer layers prepared by compression molding to a higher extent than for
their counterparts obtained by casting. The addition of a zein minimum
interlayer produced changes in the mechanical and optical film properties
while the incorporation of the zein nanostructured interlayers significantly
improved the oxygen barrier properties of the multilayer films prepared by
both processing technologies. However, the effect of the interlayer on the
water vapor permeability and limonene depended on zein content.
The incorporation of 3-hydroxyvalerate (HV) in PHB, resulting in PHBV,
increased impact strength, elongation modulus, tensile strength and de-
creased the Young's modulus, making the film more flexible and more re-
sistant. 35 The price is very high but PHBV degrades between five and six
weeks in a microbiologically active environment, resulting in water and
carbon dioxide under aerobic conditions. In an anaerobic environment,
degradation is faster, producing methane. 32
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. 37 reported improved mechanical properties for blends of PHB/
PLA compared with the common PHB. In addition, PVA (polyvinylacetate)
grafted on PIP (poly-cis-1,4-isoprene) and mixed with PHB had better tensile

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