On the other hand, these uncommon thermal proper-
ties could be the result of the blend of the different PHBs
fractions, as the two different molar masses resulted from
the GPC analyses show. Therefore, the results obtained
from DSC and GPC for these extracted PHBs could be
connected to each other. The thermal behaviour of some
polymers is influenced by the chain length and molecular
mass of the polymer used (Rojas de G ascue et al. 2002).
As already reported by Lundgren et al. (1965), lower
molar masses tend to melt at lower temperatures, because
the end groups act as impurities. The different melting
point values are related to polymer fractions which have
undergone different degrees of degradation, yielding poly-
ester with a relatively large fraction of chain ends (low
degree of polymerization). The different peaks of the
melting points from DSC results could be a consequence
of these different chain lengths. Thus, there is evidence
that the synthesized PHB features a blend of different
PHB fractions with different molar masses (different
degrees of polymerization). This matches with the DSC
results obtained from previous studies with this strain
(Rodr ıguez-Contreras et al. 2013).