Bioplastics- the next generation plastics

The accumulation of plastic waste in our environment has become a huge problem. We get some news every other day related to the harm which is caused by its accumulation to not only human population but also to the aquatic life in the oceans. It is a very common assumption made by us that everything when disposed in the sea gets degraded quickly because of the salinity of the water, but plastics, even when disposed in the sea remain there for a considerable period of time, causing harm to aquatic flora and fauna. Recently, it has been reported that plastic traces are found in the salt precipitated from sea water.

Plastics are basically a group of compounds, but what we call plastics in a layman’s language is polyethylene, which is mostly used for manufacturing of carry bags, plastic films, containers etc. It was in 1862 when Alexender Parkes synthesized parkesine (a celluloid made from nitrocellulose and camphor), that the first time plastics were synthesized. Later in 1898, Hans von Pechmann synthesized polyethylene, which was an accidental discovery as he was investigating diazomethane, which he synthesized for first time in 1894. This polyethylene compound has a melting point of 115-135⁰C and density ranging from 0.88-0.96g/cm³. Because of its thermoplastic behavior, soon it became very famous. In 2013, its global production was around 299 million tonnes, which was expected to rise by 450 million tonnes in 2020. But since they are non-biodegradable, they get accumulated over the period of time (get degraded over a period of 200years).

Since the accumulation of plastics was a big problem, scientists began looking for its alternative which is biodegradable as well as possesses same properties as the polyethylene. It was only then that biopolymers or bioplastics came into the limelight. Biopolymers are basically biodegradable polymers which are produced by using micro-organisms. Polysaccharides were probably among the first microbially produced polymers to be considered for the industrial use. Now a days, there are various biopolymers which are used for industrial purpose – Xanthan gum- used as thickner in food industry, Hyaluronic acid- used in ophthalmic surgery, Ribonucleic acid- used as flavouring agent, Polyhydroxybutarate- used as biodegradable plastic.

Polyhydroxyalkanoates are used as bioplastics as they possess a good thermoplastic properties. These are the class of polymers which belong to polyesters. One of the well-known polyhydroxyalkanoates used in the industries is Polyhydroxybutyrate (PHB). PHB is an intracellular storage polymer whose function is to provide a reserve of carbon and energy. The polymer accumulates as distinct granules in the cell and can be usually seen by light microscopy. It is very interesting to note that this PHB is even synthesized in humans also as storage granules in small amounts. For the industrial purpose, various micro-organisms are used, namely:  Actinomycetes sp., Alxaligenes sp., Azospirillum sp., Bacillus sp., Methylobacterium sp., Micrococcus sp.,etc.. The key regulator enzyme in PHB metabolism is acetyl-CoA-acyltransferase, which makes PHB in the cell by a condensation reaction. The synthesis and breakdown of PHB is linked to the metabolic state of the cell and to the carbon flux through inter-mediatory metabolism. These storage granules are then obtained by rupturing the cell.

Fig: Polyhydroxybutyrate

These can be used for variety of purposes, like using them for shampoo bottles, plastic cups and packaging materials. The United States Navy, having despaired of trying to prevent staff throwing the plastic cups used of tea, coffee, water, beer and all overboard, has opted to use PHB cups. Now sailors are free to throw their empty cups into the waves without having any future environmental issues as they will degrade over time.

Imagine using razors and flushing them away? Might block your drainage! No, PHB has found its way into people’s bathrooms. In Japan, the razors made of PHB when thrown into the sewage goes to instant degradation as there are large amount of bacteria present over there.

Now the question arises- if bioplastics are so good, then why are they not produced on an industrial scale? The answer is its cost and brittleness. Cost is a major factor which dominates when we talk about the industrial production of bioplastics. Currently, various agro-industrial wastes are being studied for their potential ability to produce bioplastics and let’s hope the scientific community will come with a solution to reducing its production cost.

Written By-

Nitin Kumar Singh