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Biopolymers: A Leap Towards Renewable Plastics
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The idea of Biopolymers as an alternative to the burgeoning load of Petro-Plastics/Petro-Polymers is not an alien concept for either the scientific community or the layman’s world. It’s well understood that Biopolymers/Bioplastics can debottleneck the scope of utility of plastics and their effect on environment. But, despite this realization and despite the commencement of initiatives in this regard since as early as 1925, not much has been achieved or commercialized till date. This article focuses on highlighting the trends in scientific research and industrial adaptability of Bioplastics, the evolution of concept of Biopolymers in last 8 decades and current status of research on Bioplastics.

Nature offers plethora of Biopolymers, not all of them can be used to replace a polymer as light and as sturdy as Polythene/Polystyrene. Starch, one of the most abundant Biopolymers, was first considered a probable solution to making a biodegradable plastic, but it’s structure and chemical nature is so deviant from the thermoplastics that neither the form nor the properties of thermoplastics could be replicated in starch based plastic. Efforts to create a blend of starch and polythene were also made but only to reach at a disappointing conclusion that though starch component tends to degrade and makes the plastic porous, the residual material is rendered non-degradable and unaltered. Evidently, need of the hour was to find a radically new polymer, whose characteristics could be a replica of the over-adapted thermoplastics, except for their degradability. Readers might be intrigued to imagine the world before crude oil based thermoplastics came into being, and to satiate your curiosity it was none other than Bioploymers only that were abundantly used in day to day applications. Plant resins like Amber and Shellac were materials of choice for making seals, crafts, woodwork finishes etc. Later, John Wesley Hyatt(1869) came up with a bio-plastic to give shiny finishing to billiard balls, which with further research became so popular in the market that from Packaging to Photographic films, everything was based on the polymer discovered by Hyatt. Today we know that polymer as Cellulose (the most abundant Biopolymer on Earth). Infact, cellulose remains one of those ancient Biopolymers, that has retained its industrial usability despite the overhaul of petroleum based polymers. The retention of cellulose can be attributed to its biocompatibility, ability to cast into films and self-sealing nature which comes handy in food packaging and medical devices industry. But, when compared to thermoplastics like Polythene, cellulose still falls short in density range, chemical resistance, molecular weight, ease of production and most importantly cost of production, telling us why the world is obsessed with Polythene/Polyurethane/Polystyrene!

A revolutionary discovery was finally made in 1925 by Lemoigne of Pasteur Institute, France, who observed granular storage materials inside Bacillus megaterium, chemically recognized as a polymer of 3-hydroxybutyrate and popularized as PHB (Poly-(3-hyrdroxybutyrate)). The granules exhibited extra-ordinary properties of water insolubility, resistance to hydrolytic degradation, high tensile strength, high melting point (around 180 degree Celsius), non-toxic nature and most importantly biodegradability. The production of these granules was induced in the bacteria only under stressed environments like nutrient limitation or oxygen stress to act as an energy reserve for prospective starving conditions. But by the same time, petroleum based thermoplastics became popularized owing to their ease of production and abundant availability. It was in the latter half of the 20th century that with the rising concerns about the accumulating plastics and depleting oil reserves, focus shifted towards finding alternatives to the polluting, non-biodegrading and non-renewable resources. By 1974, discovery of monomers other than 3-HB in the granules of Bacillus megaterium growing on different substrates was established. PHB became a member of big family of Polymers termed as PHAs (polyhydroxyalkanoates) thereby making PHAs the most potent candidates for replacing the wide variety of Polythenes (LDPE, MDPE, HDPE, ULDPE etc). Discovery of PHAs in many other bacterial species like Cupriavidus spp., Psedomonas spp. further triggered the research in this area. Such was the surge in the research that Imperial Chemical Industries (UK) came out with the first commercial PHB based bioplastic under the trade name of BIOPOL(TM) in 1980. BIOPOL was produced through a Fed Batch culture of Cupriavidus necator and was a copolymer of 3-hydroxybutyrate and 3-hydroxyvalerate. But the production of BIOPOL is very limited and application till date is confined to surgical sutures, surgical meshes and medical implantable devices. The anarchy of Polybags as we all know, still prevails.

The biggest reason behind the limited acceptability of PHA based bioplastics despite their striking similarities to petroleum based thermoplastics is their cost of production. And this in turn is caused by the chain of steps involved in producing and recovering PHAs. A basic flow diagram of steps involved in producing PHAs is depicted below:

   

This multitude of steps for obtaining PHA makes the entire process unavoidably expensive, unless the production levels at the upstream (Fermentation) level are extraordinarily high. Infact, that’s what the focus of current research has been improvement of upstream stages of PHA production. Genetic modification of strains, different design of reactors, different substrates and different operating conditions have been tried by various groups of scientists across the globe to meet the demand for a successful commercial set-up. Recently (March 2013), US National Science Foundation announced funding for Biopolymers and Biocomposites Centre at Iowa State University to catalyze the research in this area. Similarly, Department of Biochemical Engineering, Indian Institute of Technology, Delhi received a generous grant of INR 42,000,000 to develop a Centre for Excellence in Biopolymers’ Research from Govt. of India. The research is on the go in different parts of the world at an equally active rate, and the time should not be long when we may dump the plastic bags and bottles in the same bin as our kitchen waste.
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