Biomedical Engineering Reference
In-Depth Information
Table 2.2
Comparison of PHA polymers ' and common plastics ' properties.
Sample
Melting
temperature ( ° C)
Glass - transition
temperature ( ° C)
Young ' s
modulus (GPa)
Tensile
strength (MPa)
Elongation
to break (%)
P(3HB)
180
4
3.5
40
5
P(3HB -
co
- 20 mol%
3HV)
145
0.8
20
50
−
1
P(3HB -
co
- 6 mol%
3HV)
133
−
8
0.2
17
680
Polypropylene
176
− 10
1.7
38
400
Low - density
polyethylene
130
0.2
10
620
−
30
Source: [81] .
in stiffness (Young's modulus) and an increase in elongation to break, producing
more desirable properties for commercial application [5].
It has been widely accepted that PHA
MCL
shows amorphous and elastic proper-
ties with a lower melting point (
T
m
) and a lower degree of crystallinity compared
with short - chain - length PHA (PHA
SCL
) [110, 111]. Interestingly, studies demon-
strated that the presence of over 30% long chain comonomer units such as HDD
(hydroxydodecanoate - C
12
) and HTD (hydroxytetradecanoate - C
14
) in the PHA
MCL
increased the
T
m
and the degree of crystallinity of PHA
MCL
, leading to dramatic
changes in PHA
MCL
mechanical properties [111, 112] making them signifi cantly
different from those of the typical PHA
MCL
[113] .
2.7
Future Directions
PHA has quickly gained interest in both research and industry. Their structural
versatility and characteristics have been investigated and new areas of exploitation
are being discovered. The major drawback for extensive use of these polymers is
their high production cost [114]. In this regard, research is continuing on their
production from cheap raw materials [71, 72].
Decades of study have been dedicated to the composition and material proper-
ties of PHA in this crystallized form. A new perspective for industrial applications
of PHA could be the use of native, isolated PHA granules as nano/microbeads
in biotechnology and medicine. The PHA granules exhibit all important features
of core-shell nanoparticles; their surface has been demonstrated to be easily
modifi ed and activity of surface-exposed proteins of interest could be shown
[24, 83] .
