Everyone at interpack, the trade fair for the international packaging industry that is taking place in Düsseldorf from 12. to 18. May 2011, is talking about bioplastics Even though they account for less than one per cent of total plastics production at present. The future is definitely “green” where packaging in particular is concerned, however. Austrian scientists predict that 70 per cent of plastic packaging could consist of bioplastics in future Bioplastics. The social trend is positive: higher priority is being given to sustainability not only in power generation but also in plastics production, i.e. to renewable raw materials and closed-loop recycling systems – via the composting of waste. A report about trends and visions, with an answer to the key question: how environmentally sound are bioplastics really?
Bioplastics are a large family of different kinds of polymers. What they have in common is, for example, the fact that they are produced from renewable raw materials, e.g. from such field crops as corn, wheat or sugar beet, or their biological degradability – irrespective of the raw material basis. Ideally, bioplastics combine both these properties. Because a number of conventional mineral oil-based plastics and plastic blends are also biologically degradable, but the residue they produce can be problematic.
When bioplastic of agricultural origin is composted, it disintegrates into its original, non-toxic components, i.e. fungi, bacteria and enzymes convert it into water, carbon dioxide and biomass. The concept is based on nature’s recycling system: when the life cycle of the product ends, the raw materials used for bioplastic production are returned to the production process; alternatively, they are used to generate energy or to obtain biogas.
The word “bioplastic” does not, however, always meet consumers’ expectations, because it is not a protected concept. Products given the name do not by any means always consist of 100 per cent bioplastic; they can instead contain substantial proportions of petrochemical plastic. Coca Cola, for example, recently launched a “plant bottle” on the market that only contains just under one third bio-based material. A bio logo for compostable plastic in the form of a seedling helps to make the necessary distinctions.
Although bioplastics represent a new trend, they are not really new. On the contrary: historically speaking, they were the very first mass-produced plastics, which were manufactured via the chemical transformation of natural materials. The brothers John Wesley and Isaiah Hyatt opened their first factory for the production of celluloid, a plastic made from cellulose (a component of wood) and camphor, in Albany/New York in 1896. Billiard balls, table tennis balls, dolls, spectacle frames and combs are some of the products that were made from it. Celluloid is highly flammable and was replaced by modern thermoplastics long ago.
Galalith, a material produced from casein (milk protein), was invented in 1897. It is very similar to animal horn or ivory and was processed into such products as buttons, umbrella handles and radio housings. Mass production of a plastic also made from cellulose that is generally known by its brand name Cellophane began in 1923. It is used to this day, primarily for packaging and as window material in envelopes. Since it is sensitive to water, cellulose film does, however, have to be coated with polyvinyl chloride for such purposes, after which it is no longer biologically degradable.
Between 1930 and 1950, such products as acrylic glass (“Plexiglas”), nylon, Perlon, polystyrene and polytetrafluoroethylene (“Teflon”) were then manufactured from the fossil raw materials mineral oil and natural gas. Mass production of what are now the standard plastics polyethylene (PE) and polypropylene (PP) finally began successfully as of 1956. Bioplastics lost ground and were basically forgotten as a result. This development was only questioned again for the first time after the oil crisis in the 1970s: it seemed to be economically sensible to reduce dependence on mineral oil due to the increase in the price of the latter; what is a no less important motive is the desire to reduce the consumption of finite, non-renewable fossil resources.
Although there are plenty of arguments in favour of bioplastics, they still hold a very small percentage of the market at the moment. About 250 million tonnes of plastic are consumed around the world every year; only 250,000 tonnes of them are biogenic ((see Bioplastics). The nova-Institut in Hürth near Cologne has calculated that the total consumption of biologically degradable plastics amounted to 60,000 to 70,000 tonnes in Western Europe in 2007. Figures that hide the fact that the growth rates have been immense in recent years. A market survey carried out by Ceresana Resarch, Konstanz, reveals that the consumption of bioplastics based on starch, sugar and cellulose has increased by 600 per cent in the last eight years.
Europe is the leading producer of bioplastics; the industrial association European Bioplastics reports that the manufacturers are concentrated mainly in Germany, Italy, Great Britain, the Netherlands and France. Industry experts are expecting production to increase considerably in the USA too soon and are already claiming that bioplastics are about to move from niche applications to the mass market.
Bioplastics are considered to have the greatest potential in the packaging field, where plastics hold a strong position in general: three grams of film to package one kilo of meat – this ratio is unbeatable. Cheese, bread, fruit, vegetables, eggs, dairy products and beverages are being sold in “green” packaging too in the meantime. The advantage of this for the trade itself is that spoiled food no longer has to be disposed of separately from the packaging. Another obvious solution is to manufacture bags for the collection of compostable waste from bioplastic – or carrier bags for supermarkets, which are used first of all to take shopping home and then, later on when they are no longer needed, to dispose of biowaste by composting them together.
Compostable transport packaging, e.g. bubble wrap, is gaining ground as well. Loose fill used to take up space in parcels, e.g. to protect glass or porcelain from breakage during transport, consists of foamed duroplasts made of starch, which represent the most important basic material for bioplastics: with a market share of about 40 per cent. What is involved here is mostly thermoplastic starch (TPS), frequently with additives (starch blends) - because TPS in its pure form absorbs moisture (it is “hydrophilic”), a property that is of course unwelcome in packaging material. Starch blends repel water, on the other hand.
Although bioplastics are considered to be short-lived products, this is not by any means true of all of them. Depending on the use to which they are put, they can be given a longer useful life, e.g. by reinforcement with natural fibres; the conversion of thermoplastics into duroplasts is possible too. Bioplastics are also used in the production of furniture, electrical equipment and cars as a result. Polylactic acid (PLA) is very versatile, for example. It is produced via polymerisation of lactic acid, which is in turn produced via the fermentation of sugar and starch by lactic acid bacteria. PLA is a transparent material, from which not only packaging films, yoghurt tubs or bottles can be manufactured. It is also suitable, for example, for medical / pharmaceutical applications, which were in fact among the earliest uses for the material. Particular mention should be made here of screws, nails and plates for stabilising broken bones that can be reabsorbed by the body. Thread material and active substance depots made from PLA are in use too. The reabsorption times can be varied specifically in the production process, with the result that the material can be adapted as required, so that it is biologically degradable quickly or continues to function for years. Other advantages are high strength and thermoplasticity; the material does, however, start to soften at only about 60°C. Additives or copolymerisation guarantee temperature stability, e.g. when PLA is processed into cups for hot drinks. At interpack in Düsseldorf, Danone is presenting a yoghurt tub made from polyactic acid I and polylactic acid II. 45 per cent by weight of the BASF plastic Ecovio is accounted for by PLA and this plastic is used, for example, in shopping bags.
Cellulose acetate is another major bioplastic. Cellulose is a natural biopolymer consisting of sugar molecules that occurs in plants as one of the main structural materials. Cellulose accounts for almost 95 per cent of cotton. The figure is up to 75 per cent in the case of hardwood and up to 50 per cent in the case of softwood. Purified cellulose is generally esterified to obtain cellulose acetate, the most important cellulose-based plastic. Cellulose acetate modified with plasticisers was patented as the first injection moulding material as long ago as 1919; it was used to make such products as umbrella handles, steering wheels and ball-point pens.
Polyhydroxybutyrate (PHB), a biologically degradable polyester with properties similar to those of the petrochemically manufactured plastic polypropylene, is a bioplastic that is considered to have great untapped potential. PHB can be manufactured via fermentation based on sugar and starch. Problems are, however, encountered in production of the bioplastic, because the bacteria cells need to be broken down by chloroform or enzymes. Another problem is that three kilos of sugar are needed to obtain one kilo of PHB. PHB blends with special material properties are produced by adding, for example, cellulose acetate or starch; the product portfolio then ranges from adhesives to hard rubber.
In the recent past, companies have been adopting the strategy of replacing the fossil raw material basis of established standard thermoplastics by a carefully chosen renewable raw material basis. Biopolyethylene (PE) and biopolypropylene (PP) have, for example, been produced successfully from sugar cane.
Although much of the above may still sound like wishful thinking and the market may still be reluctant to respond – the positive image that bioplastics enjoy with consumers is being reflected in buying patterns to an increasing extent, so that bioplastics promise to become an attractive economic proposition. Plastics made from renewable raw materials still cost two to four times as much as standard plastics at the present time, however, which is suppressing demand for the time being. Raw material suppliers, at least, are aware of the potential: farmland for growing renewable raw materials is expected to be a key feature of the agricultural mix in future.
Bioplastics do not just have supporters, however – although they do not even need to be recycled, reservations are expressed about their environmental performance, not least of all by the German environmental protection agency. The critical points: growing renewable raw materials leads to agricultural monocultures with high water and fertiliser consumption. The carbon footprint data vary: when they disintegrate, bioplastics do not release more carbon dioxide than their original vegetable materials removed from the atmosphere during the growth phase, i.e. they are climate-neutral. The carbon footprint is, however, less impressive when the transport and process energy is taken into consideration that has to be consumed to produce and market bioplastics. In addition to this, methane is to some extent released during the rotting process and methane is a substance that is even worse for the climate than carbon dioxide itself. And last but not least: as has already been mentioned, many bioplastics are blends containing proportions of conventional plastics that do not rot by themselves but need instead to be heated, which impairs the environmental performance even more.
Conclusion: bioplastics can already be used to replace conventional, mineral oil-based plastics in many different applications. Apart from packaging, mention can, for example, be made in this context of catering products like disposable tableware and cutlery, hygiene articles and containers for cosmetic articles as well as housings for electrical equipment and mobile phones. Bioplastics are essential nowadays in medical applications – particularly for such operation materials as thread and implants that break down inside the body – and have practically no competition there. A great deal of optimisation and thus research still need to be completed, however, before bioplastics become the material of choice in future and no longer remain limited to everyday articles with a short life or technical niches.