1.1. Introduction
The utilization of bio-based polymers as packaging materials has attracted great
attention in both scientific and industrial areas due to the non-degradable and nonrenewable
nature of synthetic plastic packaging. Polyhydroxyalkanoates (PHA) represent
an interesting alternative to synthetic polymers due to many advantages. Not only are
they biodegradable and biocompatible, but they can also be produced by bacterial
fermentation of renewable resources like cane sugar (Bordes and others 2010). Controlled
fermentation of carbon feed-stock and nitrogen limitation in the presence of suitable
bacteria yields up to 70% of dry cell weight (Ward and others 1977). Poly (3-
hydroxybutyrate) (PHB), the most common PHA, was first discovered in 1926 by
Lemoigne and is now produced on an industrial scale. Depending on the carbon
substrates and the metabolism of the microorganism, different monomers, and thus
(co)polymers, can be obtained. Besides the main polymer PHB, different copolyesters
exist such as poly(hydroxybutyrate-co-hydroxyvalerate) (PHBV), and
poly(hydroxybutyrate-co-hydroxyoctanoate) (PHBO). PHB is a highly crystalline
biopolyester (above 55%) with a glass transition temperature (Tg) just above 0 ºC. PHB is
relatively stiff and brittle. Young‟s modulus reaches 3.5GPa, and the elongation break is
less than 5% (Bordes and others 2010). The PHB melting point (Tm = 170 to 180 ºC) is
rather high compared to other biodegradable polyesters. Its degradation temperature is
close to the Tm and thermal degradation occurs according to a one-step process – namely,
a random chain scission reaction. Packaging materials made from PHA possess excellent
film forming and coating properties. PHAs have properties close to those of
polypropylene (PP) (Brandl and Puchner 1991). The properties of the film can be
adjusted by changing the ratio of hydroxybutyrate (HB) and hydroxyvalerate (HV). A
high content of polyhydroxybutyrate (PHB) gives a strong and stiff material whereas
polyhydroxyvalerate (PHV) has improved flexibility and toughness (Bordes and others
2010). Properties of PHBV can be improved further by using plasticizers (Kotnis and