Friday, June 01, 2012: 02:39:13 PM

Changing Trends towards Biobased and Biodegradable Plastics

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Prof. Ramani Narayan
MSU University Distinguished Professor
Department of Chemical Engineering & Materials Science Michigan
State University Michigan, USA

Plastic materials are pervasive, universally used, and find applications in all parts of our lives, from agriculture to electronics to medical devices to packaging. From 1.65 million tonnes in 1950 to 255.5 million tonnes in 2010 worldwide, plastics usage is expanding and expected to grow at a steady pace of 3–4% per year. In particular, rapid industrialisation in populous countries such as India and China has resulted in an accelerated pace of plastic materials growth. This is because plastics are lightweight (energy saving), low-cost, readily processable, and command unique and versatile properties that can be tailored for specific applications. However, the sustainability of plastics has become a major issue – specifically the carbon footprint and end-of-life issues.

Bioplastics provides a value proposition for reducing the material carbon footprint as well as provide for an environmentally responsible end-of-life – recycling or biodegradability-compostability. The term ‘bioplastics’ embraces two fundamental concepts:

• Biobased Plastics: Plastics in which the carbon in whole or part comes from biological feedstocks as opposed to petro/fossil feedstocks – the beginning of product life.

• Biodegradable-Compostable Plastics for End of Product Life: Designing plastics that can be utilised (as food) by microorganisms present in the disposal system to completely remove the plastic substrate from the environmental compartment. However, using the term biodegradable without defining the disposal system and time to complete biodegradation is misleading. More importantly, if a biodegradable plastic is not completely and rapidly removed (within one year or less) from the target disposal environment (such as composting or soil), the degraded fragments become toxin carriers up the food chain, resulting in serious environmental and health risks. ASTM, European and ISO Standards define and specify the requirements for complete biodegradability and must be strictly adhered to so that serious environmental and health consequences can be averted.

Switching the manufacturing base (the origins of the carbon) from petro-fossil carbon to bio-renewable carbon feedstock offers an intrinsic zero material carbon footprint value proposition. This can be seen by reviewing Nature’s biological carbon cycle. Nature cycles carbon through various environmental compartments with specific rates and time scales. Specifically, the rate of CO2 release to the environment at end-of-life equals the rate of photosynthetic CO2 fixation by the next generation of crops or trees planted resulting in a zero material carbon footprint. In case of fossil feedstock, the rate of carbon fixation is measured in millions of years, while the end-of-life release rate into the environment is in 1–10 years. Obviously this is not sustainable and contributes to additional carbon emissions to the atmosphere with its associated global warming climate change problems. The biobased carbon content can be experimentally determined using C-14 radiocarbon analysis developed and codified in ASTM D6866 standard. This standard allows one to unequivocally calculate the percent material carbon footprint reductions achieved by incorporating biobased carbon content into the product.

The U.S. Government has mandated the procurement of biobased products through its biopreferred programme. EU has its lead market initiatives in the biobased products space. Braskem, a world leading producer of polyolefin resins has commercialised production of 200 ktonne/year bio-PE (polyethylene) resin with 100% biobased carbon content. It is not biodegradable-compostable, but the end-of-life strategy is recycling. Coca Cola, a world recognised brand owner has introduced bio-PET bottles, in which the glycol component is biobased which translates to 20% biobased carbon content and 31% by mass of total plant material content. Even with 20% biobased carbon content, the CO2 savings amount to 17 million tonnes based on 37.5 million tonnes of PET resin used in bottles. The end-of-life is bottle-to-bottle recycling. Nature Works manufactures 140 ktonne/year poly(lactic acid) resin (PLA) at their Nebraska, USA facility and Purac has a 100 ktonne/year lactic acid plant in Thailand. The PLA polymers are 100% biobased carbon, completely biodegradable-compostable and can be recycled back to monomer thermally. There are other biopolyester manufacturing announced like poly(butylene succinate), but not yet in full commercial production.

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