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Biodegradable Odyssey

PET, or Polyethylene terephthalate, is the most common type of plastic used today. It has a long shelf life, no leakage, and flexible design and is safe. Well safe to humans at least. Although this type of plastic has the tick of approval as being recyclable this still does not eliminate its side effects in situations where it may miss the recycling process. Petroleum based plastics such as PET simply won’t degrade (or biodegrade) in our environment, sure enough you can drop a bottle made from PET and it will not break or show any signs of damage, however drop that same bottle in a landfill and it will stay there indefinitely. It might even move into a local river or forest where the bacteria that carry out the process of biodegradation simply turn their noses up out of disgust and move along.

The amazing thing about biodegradable plastics is that they work by breaking down after a certain (reasonable) amount of time spent in the outside environment around us.

Some biodegradable plastics that are:

PHA, PHV, PHH, Polyanhydrides, and starch derivatives.

Biodegradable plastic bag. Source: Google creative commons.

Biodegradable Plastic Bag

I will turn your attention to PHA (Polyhydroxyalkanoates). This is naturally produced polyester by bacterial fermentation of sugar or lipids. They are more specifically produced by bacteria to store amounts of carbon and energy and can be completely exploited to produce biodegradable plastics. Many industrial scale facilities are used to churn out these plastics which can be mixed with several other compounds to produce material that have very different properties.

It is essential that plastics have properties that are practical to modern society and have minimal effect on the environment. For this case, biodegradable plastics serve both these purposes and have risen in popularity over the past years to be established as the ‘in thing’ in regards to protecting our flora and fauna.

The process of synthesizing (Biosynthesis) of PHA comes from the work of bacteria and manipulation from the scientist.

  1. A Culture of microorganisms is put into conditions that favour its replication. This includes nutrients to help them grow and multiply.
  2. Then, by closely monitoring the growth of these bacteria the nutrient composition is changed at a crucial point to trick the bacteria into making PHA.
  3. As much as 80 percent of PHA can be captured from the inside (intracellular) region of the organism.
  4. The PHA, which is in the form of granules, can then be extracted by rupturing the bacteria cell.

On an industrial size scale of PHA production, the polyester is extr4acted and purified for optimizing fermentation of sugar or glucose.

These types of plastics have applications within the medical and pharmaceutical industries due to their biodegradability.

Properties of PHA include UV stability, thermostable, ductile, elastic and show a low permeation to water. A true contestant in the category of biodegradable plastics, PHA has its place in our World.

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Figure 1: Summarized table of common bacteria (First column) used to produce some biodegradable plastics (second column). Source: Google creative commons.

Biodegradable Plastics Table

Sure, we can look only at the advantages of biodegradable plastics, but what are some disadvantages of producing such material and flagging it as a standard around the world? These can include shorter shelf life, plastics that degrade to a point and will not further degrade due to their mixed composition, more costly for in terms of processing and transporting and increased energy consumption to produce the plastics.

Technology to produce PHA is still in development today, but with new ways of synthesizing these plastics and more cost/energy efficient methods employed, PHA and similar biodegradable plastics will one day lead the way in a more sustainable future.

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