HSC Chemistry-Worked Short Answers
Assess current developments in the use of biopolymers.
In recent times, there has been an increased interest in the use of biopolymers in industry
as an alternative to our dependence on the petrochemicals but to also decrease the burdens
that plastics presents to the environment. An example is the development of
polyhydroxylalkanoates or (PHA’s), as a biopolymer, produced by microorganisms with
very similar properties to polypropylene. The main attraction towards PHA’s is that they
are biodegradable. This is the great benefit of biopolymers. That is obtaining the same
benefits of plastics along with the added benefit that it will break down over time. The
simplest and most common PHA is polyhydroxylbutanoate or PHB. To produce PHB
: biopolymers, produced by microorganisms, that
have very similar properties to polypropylene.
Importantly, PHAs are biodegradable.
The simplest and most common PHA is polyhydroxylbutanoate (PHB).
PHB has quite a different chemical structure from polypropylene, although its
physical and mechanical properties are quite similar.
To produce PHB:
A culture of microorganisms, such as Alcalingenes eutrophus, is placed in a
suitable medium and fed appropriate nutrients so that it multiplies rapidly and
grows into a large quantity.
The main nutrient required is glucose, which is a renewable resource.
The ‘diet’ of the organism is changed to restrict the supply of one particular
nutrient, such as nitrogen.
Under these conditions, the organism is no longer able to increase its
population but instead begins to make the desired polymer, which it stores for
later use as an energy source.
The organism can produce a quantity of PHB from 30% to 80% of its own dry
The organism is harvested and the polymer separated out.
PHB is stable to air and moisture, but under anaerobic conditions it is attacked and
decomposed by anaerobic bacteria.
PHB, and PHAs generally, are still in the early stages of large-scale production and
They have great potential where biodegradability is a prime consideration, such as in:
Packaging, in the form of bottles, bags and wrapping film.
Describe the conditions under which a nucleus is unstable.