behavior of polyester [241,242]. The homopolymer
of PHB is a brittle material, while the increase in HV
content turns the HB-co-HV copolymer more ductile
[243e245]. The mechanical behavior of PHAs
depends on both the length of the pendant groups and
the distance between ester linkages. PHAs with short
pendant groups are prone to crystallization but
exhibit stiff and brittle behavior, while PHAs with
longer pendant groups are ductile [246]. The wide
performance range of PHA copolymers justified
additional scientific and industrial interest, which led
to the discovery of further bacterial PHAs. PHAs can
be synthesized in molecular weights that depend on
the growth conditions and on the microorganism
speciesdbetween, 200,000 and 3,000,000 Da [238]
(Fig. 16.12).