Bioplastics: an alternative with a future?

As a complement and in some areas as an alternative to conventional plastics, bioplastics appear to be a logical and necessary step for a modern and forward-looking plastics industry. Any discussion of the pros and cons, the future role and the market potential of bioplastics makes little sense without prior clarification of the meaning of the prefix “bio-”, says Prof. Dr.-Ing. Christian Bonten of the Institute of Plastics Engineering at the University of Stuttgart, expressing his reservations.

One prefix, two meanings

Apart from small quantities of substances, biodegradable plastics consist of biodegradable polymers and additives. Special bacteria and their enzymes demonstrably convert biodegradable plastics into biomass, CO2 or methane, water and minerals as soon as the macromolecules have been sufficiently fragmented by other degradation mechanisms. For a plastic to be termed “compostable” in Europe, 90 per cent of it must degrade in clearly defined conditions into fragments smaller than 2 mm within 12 weeks. Only then can composting facilities operate cost-effectively and without disruption.

Biodegradable plastics are not necessarily made from renewable resources and can also be derived from mineral oil. Biodegradability therefore depends not on the raw material, but on the plastic’s chemical structure. Examples of biodegradable polymers are polylactides (PLA), polyhydroxyalkanoates (PHA), cellulose derivatives and starch as well as mineral-oil-based polybutylene terephthalate (PBAT) and polybutylene succinate (PBS). Non-biodegradable, on the other hand, are polyethylene (PE), polypropylene (PP), polyethylene terephthalate (PET) and polyamides (PA), for example.

Bio-based plastics, on the other hand, are renewable resources derived from nature. However, these are not necessarily biodegradable as well. The adjective “bio-based” merely tells us that the carbon atoms in the molecule chains come from today’s nature and are thus “bio”. At present, bio-based plastics are derived from different hydrocarbons such as those found in sugar, starch, proteins, cellulose, lignin, bio-fats and oils. Bio-based polymers include polylactides (PLA), polyhydryoxybutyrate (PHB), cellulose derivatives (CA, CAB) and starch derivatives as well as, for example, bio-polyethylene (PE). The latter is derived entirely from Brazilian sugar cane, has the same properties as conventional polyethylene, but is not biodegradable. The at least to some extent bio-based but not biodegradable polymers also include natural-fibre-reinforced conventional plastics along with polyamides and polyurethanes.

Bioplastics – global output

In global polymer output, bioplastics have not so far figured highly in the roughly 235 million tonnes of plastics materials. Because of the high market growth, European Bioplastics is forecasting world production capacity for bioplastics to reach roughly 5.8 million tonnes by 2016. The study of the nova institute of March 2013 is forecasting output of over 8 million tonnes by 2016 and roughly 12 million tonnes by 2020 for bio-based pAir Jordan X 10 Shoes