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From plants to plastics

In these times of changing climate, sustainable thinking and the growing desire to become less dependent on crude oil, the interest in biobased plastics is growing. Biobased plastics can be either entirely or partially produced from renewable resources using biotechnological methods.

Whether the product be tear-proof ropes in a mountaineer’s equipment, stretchy but stable cling film in kitchen cupboards or ultra light and comfortable running shoes – plastics allow us to do many everyday or leisure activities we would not otherwise be able to do so easily. Plastics not only have a multitude of uses, they are also an important economic factor. 20 million t of plastics were produced in Germany in 2008, amounting to a business volume of 22.8 billion euros. The worldwide production of plastics was around 260 million t in 2007; the production of plastics has been increasing by an average of 9 per cent since 1950.

Crude oil as the basic material

Plastics are almost exclusively produced from oil. In future, the proportion of plastics produced with renewable resources such as wood will increase. © BIOPRO/Bächtle

Up until now, oil has been an indispensable basic substance in the plastics industry. This is because plastics consist of hydrocarbons - the major constituent of oil. Plastics are polymers, i.e. long chains of molecules consisting of components of a lesser or greater size. The type and number of different components used vary from plastic to plastic.

In the simplest case, such as that of the well-known mass plastics polyethylene (PE), polypropylene (PP) or polyvinyl chloride (PVC), the same components are coupled to each other using chemical processes. It takes approximately two kilograms of oil to produce one kilogram of such plastics. This includes the production of the basic plastic components as well as the energy required for the production process. The demand for oil continues to rise as the plastics market continues to grow. In Germany, approximately five per cent of the total quantity of oil used, is dedicated to the production of plastics. In comparison to the 90 per cent that are used for the production of energy and for car fuel, the requirements of the plastics industry are relatively low.

Plastics can be extremely hard and shatterproof, as is the case with the camera casing shown in the photo, which is made of polycarbonate. © BIOPRO/Bächtle

Components produced using biotechnological methods

Nevertheless, the plastics sector would be well advised to consider alternatives to using oil and to think about tapping new resources. The plastics market is directly dependent on the price fluctuation of oil, and all its associated side effects. Biobased polymers could contribute to reducing our dependence on oil, although even here, some basic substances used in biotechnological production such as starch or sugar, are indirectly coupled to the price of oil.

Direct, indirect, pure, mixed

The most important and commonest polyhydroxyalkanoate (PHA): 3-hydroxybutyrate © Wikipedia

There are different ways to produce biobased plastics. The direct path leads to the production of polyhydroxyalkanoates (PHA), which are produced by bacteria and some plants and are polymers with plastics properties.

The indirect, though feasible, paths lead to the production of the basic components of plastics. Many of these components can be produced biotechnologically, but subsequently need to be linked to polymers using chemical synthesis methods. Examples of such basic components are lactic acid for the production of polylactide (polylactic acid), ethanol for polyethanol, modified starch for starch-containing composites, or succinic acid and diaminopentane for polyamides, i.e. nylon.

Another option for the production of biobased plastics is the use of mixtures. One of the plastics components is synthesised chemically and the other component is synthesised biotechnologically. One example of such production methods is 1,3-propanediol, a bivalent alcohol which can be produced from glycerine with bacteria such as Citrobacter, Clostridium or Lactobaccillus. As has recently been shown, 1,3-propanediol is an economic alternative for a particular type of polyester.

The success story of Sorona™

Carpet made from the biobased plastic Sorona. Timberland, a producer of outdoor textiles, also uses this bioplastic. © DuPont

In 1995, Shell Chemical Company started up production of a new type of polyester - polypropylene-terephtalate (trade name CorterraTM). The polyester consists of terephthalic acid (PTA) and 1,3 propanediol. The company decided to use petrochemical production, i.e. oil-based,  methods to produce the two components, as this seemed to be the cheaper option. However, other alternatives exist.

In the same year, the companies DuPont and Genencor signed an agreement whose goal was to produce the sought-after 1,3 propanediol biotechnologically from glucose, which would also enable them to produce polypropylene-terephtalate. The resultant plastic, partially based on renewable resources, was named SoronaTM. As the process developers intended to use corn starch to feed the microorganisms, they selected a genetically modified strain of the bacterium Escherichia coli which can not only produce glucose, its basic nutrient, but which is also able to convert glucose into glycerine in order to synthesise the sought-after 1,3 propanediol. The developers succeeded in improving the biotechnological process to such an extent that it was able to compete with petrochemical methods in terms of costs.

In 2006, eleven years after DuPont and Genencor started working together, the large-scale biotechnological production of 1,3 propanediol from starch began, and this resulted in the production of SoronaTM. As 1,3-propanediol is biotechnologically produced, SoronaTM is about 1/3 biobased. Experience shows that the biotechnological process is far more efficient than traditional methods using oil. In addition, it releases much lower quantities of the greenhouse gas carbon dioxide. Estimates have shown that per 50,000 t of biotechnologically produced 1,3-propanediol it is possible to save a quantity of petrol equivalent to that needed to produce around 38 million litres of benzine.

Zero-sum

The story of Sorona™ leads to two further important aspects that justify the use of biotechnological processes in the production of plastics: the protection of the environment and the climate. If a plastic is produced partly or entirely from renewable resources, it will store atmospheric carbon dioxide during its entire lifespan. If, for example, saccharose is used as the basis for a polymerisable intermediary product, each kilogram of the purely biobased plastic will have bound between 2.1 and 2.5 kilograms of CO2, which the plants have previously withdrawn from the atmosphere. The carbon dioxide will only be released again upon combustion. Therefore, the CO2 balance of purely biobased plastics is, at least as far as the basic substances are concerned, zero. If a smaller proportion of biobased raw materials is used for a certain product, then the CO2 balance is not even, but is still better than purely oil-based plastics.

The biobased plastics also achieve better results in the total balance, i.e. basic substances plus production: around 300 gr carbon dioxide are released per kilogram of a starch-based plastic, about the same amount in the case of polylactide and about 500 gr in the case of polyhydroxyalkanoates. In contrast, approximately two kilograms of carbon dioxide are released per kilogram of polyethylene or polypropylene produced.

Sample calculations

Despite some advantages, biobased plastics are not usually the best choice. Environment- and climate-related aspects are not the only parameters plastics producers and processes take into account. Major issues are price and material properties. Biotechnological processes are not generally cheaper. If an organism requires expensive media or complex cultivation conditions, then a biotechnological process will not generally be the process of choice. Production costs would no longer be competitive. In addition, biotechnological processes often require multistep, time-consuming and technologically sophisticated processing steps to be put in place in order to separate the desired product from cells, cell debris, media components and many other metabolic compounds. At present, this is a clear disadvantage compared to oil-based, chemical-synthetic production methods.

Worldwide key projects

Sugar cane is one of many renewable resources at the beginning of the bioplastics production chain. © Wikipedia/Mette Nielsen

The decision to use biotechnology in the production of plastics has to be taken on a case-by-base basis. At present, it seems that biotechnological processes are gaining in importance in the plastics sector – even in the area of mass plastics. The Brazilian company BRASKEM was the first to lay the foundation stone for a production plant that enables the production of fully biobased polyethylene from bioethanol. The company plans to produce 200,000 t of “green polyethylene” per year from 2011 onwards. BRASKEM estimates the world market for bio-polyethylene at 600,000 t per year. The bioplastic produced by BRASKEM will be slightly more expensive than petrochemically produced polyethylene. It therefore remains to be seen whether the market is ready to pay more for the “bio” label.

In the USA, efforts are also being made to enter the bioplastics business in order to compete with established oil-based products. Metabolix, a biotechnology company based in Cambridge, MA, focuses on the large-scale biotechnological production of polyhydroxyalkanoates from corn starch. It is envisaged that “Mirel™“, short for “miracle of nature”, will become a versatile plastic consisting of 100% renewable resources that are biologically degradable. Working together with Archer Daniels Midland Company, Metabolix plans to start operating a new production plant in 2009 that will produce nearly 50,000 t Mirel™ per year.

Manioc is mainly cultivated in Thailand, and it is envisaged that it will become the basis for the production of bioplastics. © Wikipedia

Frost&Sullivan estimate that the bioplastics market in South-East Asia is set to grow by more than 100 per cent per year until 2015. The Thai government passed a three-tier plan in 2006 with the goal of becoming the biggest bioplastics producer in South-East Asia before 2021. Thailand focuses in particular on polylactide, a polymer based on lactic acid. The country hopes to produce lactic acid from manioc and corn starch using biotechnological means. There is sufficient raw material available - Thailand produces 20 million t of manioc per year and is the world's largest exporter of manioc.

Germany is also increasing its production capacity for biobased plastics. The company Pyramid Bioplastics Guben GmbH is currently constructing a facility in the city of Guben (Brandenburg) to produce polylactide from sugar and starch. The first expansion stage will be terminated and the new plant will be operational in 2009. The plant will then be gradually expanded to a capacity of 60,000 t per year up to 2012. 

The launch phase has begun, but the goal is yet to be achieved

The production capacities and the market for bioplastics are growing. Nevertheless, it is worth noting that the proportion of biobased polymers on the entire market is still very small. The sector is in the launch phase; many things still have to be tested and it can be assumed that price will be an important parameter for the success of bioplastics. Therefore, the indirect relationships between biological raw materials and the petrol market will remain an issue for the producers of biobased plastics. Top on the list of priorities for producers will be the decoupling of the price of biological raw materials such as corn, sugar and wheat from the oil price and the search for additional biological sources of raw materials.

As the example of polyethylene shows, there is a clear competition from the oil producers. The worldwide production volume of polyethylene amounts to around 50 million t per year. A number of oil-producing Arab countries have since discovered the business value of plastics production. They are set to construct many more production plants, which will increase production capacity over the next few years. Experts therefore expect that the polyethylene supply will soon exceed the demand. This strategic reorientation of some oil producers might lead to the ruin of companies such as BRASKEM that were counting on the production of bio-polyethylene for their future business.

Glossary

  • Escherichia coli (abbr.: E. coli) is a coli bacterium that is common in the human intestines. Variants of this bacterium (E. coli K12), which lack certain characteristics of the wild-type bacterium that are vital to survival in the field, are often used in molecular genetics as the host organism for the cloning of recombinant DNA fragments.
  • A gene is a hereditary unit which has effects on the traits and thus on the phenotype of an organism. Part on the DNA which contains genetic information for the synthesis of a protein or functional RNA (e.g. tRNA).
  • There are two definitions for the term organism: a) Any biological unit which is capable of reproduction and which is autonomous, i.e. that is able to exist without foreign help (microorganisms, fungi, plants, animals including humans). b) Definition from the Gentechnikgesetz (German Genetic Engineering Law): “Any biological unit which is capable of reproducing or transferring genetic material.“ This definition also includes viruses and viroids. In consequence, any genetic engineering work involving these kinds of particles is regulated by the Genetic Engineering Law.
  • Selection in a biological context means the assortment of organisms due to their characteristics. On the one hand, this could be natural selection ("survival of the fittest") like in evolutionary processes. On the other hand, selection by man, e.g. breeding, is called artificial selection. Artificial selection is also used in genetic engineering to identify a genetically modified organism due to its new characteristics (e.g. resistance to antibiotics).
  • Plasticity is the attribute of organisms to change their characteristic values under the influence of environmental factors. Therefore, neuroplasticity is the characteristic of neurons to change their response behaviour dependent from their activity. In most cases, the strength of the synaptic transmission is influenced (synaptic plasticity). The neuroplasticity or synaptic plasticity, respectively, is considered to be the basic mechanism in learning processes and in the formation of memories.
  • Polypropylene (abbr. PP) is a thermoplastic polymer of propylene (also: propene).
  • Polyehylene (abbrevation: PE) is the polymer of ethylene. It belongs to the thermoplastic synthetics.
  • Polyhydroxyalkanoates (PHA) are polyesters made by bacteria, which need them as energy reserve. They can be used industrially as packaging or implant material.
  • The term metabolism includes the uptake, transport, biochemical conversion and excretion of substances within an organism. These processes are necessary to build up the body mass and to meet the energy demand of the body. The opposed processes of metabolism are called anabolism and catabolism. Effectiveness of several enzymes could be catabol and anabol. Within one biochemical pathway they cannot work in both directions at the same time.
  • Ethylene is a gaseous plant hormone. It is important for germination and senescence processes in plants such as ripeness of fruits, development of flowers, abscission of leaves in autumn and necrosis of plant parts. Ethylene is used in greenhouses to aerate fruits resulting in increasing maturation.
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