Chemistry Reference
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Figure 8.7 Photographs illustrating material loss of a Mirel
t
PHA plastic bottle cap
through biodegradation when exposed to environmental conditions
(images supplied by Mirel
t
).
In a study by Bucci et al., P(3HB) packaging in the form of a jar and cap were
fabricated through injection moulding, and both the packaging and degrad-
ation properties of the P(3HB) were investigated. Degradation of the jar and
cap was examined in several media including sewage residues rich in organic
material. Complete degradation of the P(3HB) packaging in these media was
of the order of 90 days with no degradation observed in the control of potable
water only; illustrating a useful result for short term water storage options.
64
Figure 8.7 shows the ready environmental degradation of a bottle cap
produced using Mirel
s
PHA resin, which contrasts with the persistence
displayed by conventional petroleum-based thermoplastics (Figure 8.7).
A shortcoming highlighted in the studies by Bucci and coworkers was the
diculties associated with successful injection moulding of P(3HB). The
defect rate of the jar and cap packages was approximately 72%; test samples
were deemed defective through cracking or incomplete injection. Further-
more, P(3HB) has been observed to yield an odour intensity significantly
greater than PP. In addition, its tainting of water, as noted by taste testers,
suggests that P(3HB) is unlikely to be an alternative plastic for water
containment.
65
.
8.7 PHAs for Food and Industrial Packaging
While P(3HB) is unsuitable for injection moulding, its copolymers have been
successfully processed into commercial packaging items. For example,
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