Topic of the Month: May 2015

Polymer chemistry meets biotechnology: plastics from seafood

Polymerchemie trifft Biotechnologie

Not that long ago, it was possible to make clear distinctions between chemistry, process engineering, biotechnology and mechanical engineering. However, the requirements that are being made today and – even more importantly – that will be made in future encourage and demand elimination of the distinctions between the natural science and technical faculties. The development and production of bioplastics based on renewable resources are an outstanding example of this. Current developments present a more varied and also more sustainable picture, as this Topic of the Month report impressively demonstrates.

The world is full of polymers. Life would be inconceivable without them. The word polymer is of Greek origin: the first syllable “poly” means “many”, while the second syllable “mer” comes from “meros” and means “parts”. Polymers consist of numerous chain-like macromolecules that are cross-linked with each other to some extent.

The most important natural polymers

Cellulose is such a macromolecule, that forms the structure of plant cell walls together with lignin and pectins. Cellulose consists of thousands of glucose units, i.e. simply structured sugar molecules. Cellulose is a polymer, the most commonly occurring natural polymer, and is the main component of wood, paper, pulp, cotton, flax, line and hemp. Cellulose forms the basis for the production of viscose fibres, from which yarns for the textile and furniture industry can be manufactured. Viscose is used to produce thermoplastics.

Tool handles, keyboards, steering wheels, ball-point pens and many other products are manufactured from cellulose-based plastic. Plastic films too, as is easy to deduce from the name cellophane. Movie and photographic films used to be recorded on celluloid – the very first thermoplastic to be produced industrially. Cellulose-based plastics were used to make billiard balls and piano keys, where they were practically indistinguishable from ivory. The plastic was, in addition, more resistant and rolled predictably thanks to its consistent material density – in contrast to ivory. Merely for the sake of completeness, it should be added that billiard balls are made from phenolic resin, a thermosetting plastic, nowadays.
Corn

Up to now, renewable raw materials – starch should be mentioned primarily here – have been used in most cases to produce biobased polymers, with the aim of replacing oil-based plastics. © istockphoto

Important natural polymers can be found in both the human and animal world. Proteins are the animal counterpart to cellulose. Proteins consist of amino acids. Hair is formed from fibre proteins, out of which wool or non-woven fabrics can be made. Silk, which is obtained from silkworm cocoons and is a key raw material for sophisticated textiles, is the only endless textile fibre that occurs in nature; its main component: proteins. Leather, which is of course still in widespread use, is produced from the skin of mammals, that incorporates connective tissue and muscles – and is thoroughly polymer cross-linked.

Bioplastics based on natural polymers

According to Fachagentur Nachwachsende Rohstoffe e.V., proteins have only played a minor role in the production of biobased plastics in the past: “The bioplastics made from animal proteins include casein, which already had some significance at the beginning of the plastics age. In the production process, the casein that is obtained from skimmed milk and plastified is cross-linked to form a plastic under the influence of formaldehyde and with the discharge of water. The term casein formaldehyde is commonly used in this context. Casein plastics are only used in smaller niche markets nowadays because of their comparatively inferior properties. Gelatin is a protein-based bioplastic in the broader sense of the word. In addition to its familiar application areas as a food additive, it is used – for example – as a bonding agent or as capsules for tablets. Gelatin is produced mainly from collagen.” [1]

Up to now, renewable raw materials – starch should be mentioned primarily here – have been used in most cases to produce biobased polymers, with the aim of replacing oil-based plastics. It will definitely be quite a long time until this aim can be reached on a large scale and petrochemical products disappear from the market – there are plenty of critics who doubt whether it is even possible. One reason is that there has been a lack of technically suitable raw materials so far. In most cases, vegetable biomass is used, such as cellulose and lignin from wood, starch from corn, wheat and potatoes, sugar from sugar beet or sugar cane, oil from rapeseed, sunflowers and soybeans or from such exotic oil plants as oil and coconut palms. The earliest bioplastics included celluloid (cellulose nitrate, developed in 1856) – as has already been mentioned – from which films used to be made and table tennis balls are still made, as well as cellophane (regenerated cellulose), which has developed from being a simple sweet wrapper to being a modern, multifunctional packaging film – which is biologically degradable too – in the past hundred years. [2]

Crab shells

When shrimp and crabs are processed, large quantities of shells are left over that contain chitin and are both laborious and expensive to dispose of as waste. Source: Fraunhofer IGB

Scientists are still working intensively on finding further attractive raw material sources. Some of them are scientists from the Fraunhofer Institute for Interfacial Engineering and Biotechnology (IGB), to some extent in liaison with Evonik. In connection with the research project ChiBio that is funded by the EU, the Fraunhofer IGB has come up with a remarkable approach: instead of concentrating on renewable raw materials which can also be used in food production, so that any other use is criticised, the Fraunhofer IGB focusses on waste – specifically waste that occurs in large amounts in the fishing industry.

Plastics from seafood

When shrimp and crabs are processed, large quantities of shells are left over that contain chitin and are both laborious and expensive to dispose of as waste. More than six to ten million tonnes of these crustacean shells are thrown away around the world every year, approximately several hundred thousand tonnes of them within the European Union (EU) alone [3]. A small proportion of this biogenic marine resource is, however, already being used – in Asia, for example – to produce chitosan, which is used for biomedical purposes or acts as a food supplement [4]. Due to their higher calcium content, it has up to now been less economic and therefore uncommon to use the shells produced in Europe. It is, however, an important point to note that the proper disposal of waste shells is laborious and expensive because of EU and national regulations. This is exactly where the “ChiBio” project funded by the EU intends to make changes.

At the end of 2011, an international team of partners from the scientific, research and industrial communities headed by the Fraunhofer IGB bio-, electro- and chemocatalysis project group (BioKat) started its work in this context in Straubing. Lars O. Wiemann and Volker Sieber outline the aim of this project as follows in the 2015 Annual Report of the Fraunhofer IGB: “The objective was to establish a multi-stage process based on the biorefinery principle, with which valuable biobased monomers can be obtained for the plastics industry from the chitin of crab shells” [5].

Source: Fraunhofer IGB

Overview above the "ChiBio" project:
Develop improved pretreatment-methods for European (and Asian/African) shell wastes with respect to eco-efficiency and sustainability.
Identify and evolve new enzymes for the depolymerisation of chitin/chitosan to monomeric units.
Develop cheap separation processes for proteinogenic and lipoid by-products.
Evaluate the potential of energy-rich by-products as feed for anaerobic biogas-production.
Establish a novel chemo-enzymatic/microbial route to synthesize N-containing bifunctional monomers starting from glucosamine.
Develop a fermentative production route for bifunctional olefins starting from glucosamine and/or N-Acetylglucosamine.
Upscaling of the full process chain to make needed enzymes/microbial strains available in kg-scale.
Separation of new monomers to polymer grade (minimum of 10 g for initial testing).
Synthesis of novel “sustainable” polymers and characterization of their physical properties.
Study the technical feasibility of new biotechnological methods and synthesise prototypes of the novel polymers for demonstration activities.
Perform process analysis, feasibility study and cradle-to-product life cycle analysis (LCA) of the entire process chain.
Establish a scientific advisory board including members from European fishery companies, peeling factories and enzyme producers.
In addition, ChiBio is aiming towards: broadcasting and dissemination of gained knowledge beyond the consortium to the public and other industrial communities.

Preliminary treatment of crab waste and biogas generation

Appropriate preliminary treatment of the waste was necessary in order to stop the natural process of decay and to prevent contamination of the shells by micro-organisms that are harmful to health. Meat residue had to be removed from the shells and the chitin contained in the shells had to be released. Enzymatic transformation (fermentation) using two strains of bacteria that were discovered by Irish ChiBio partners proved to be an efficient way to do this. Lars O. Wiemann and Volker Sieber report in the 2014/15 Annual Report of the Fraunhofer IGB [5] that the optimised process included a combination of chemical and biotechnological operations; they are said to lead to chitin yields that vary from 13 to 14 per cent in the case of European shell waste to 6 to 18 per cent with Asian shells that contain less calcium. The exact composition of the shell components is apparently largely dependent on the species and is subject to seasonal fluctuations. The chitin content determined in the project is said to have averaged between 14 and 30 per cent.

Optimum exploitation of available resources

The protein and lipid fraction that was separated in the first operation of the process was not discarded; instead of this it was tested in the environmental biotechnology and bioprocess technology department at the headquarters of the Fraunhofer IGB in Stuttgart to determine its potential for the generation of biogas. Lars O. Wiemann and Volker Sieber: “Fermentation of the organic waste fraction (...) produced good biogas yields of 460 to 900 millilitres per gram of organic dry mass within one to two weeks.”

Biotechnologie

Polymer chemistry meets biotechnology: plastics from seafood – will that be made in future encourage and demand elimination of the distinctions between the natural science and technical faculties? Source: istockphoto

Suitable micro-organisms and enzymes were needed to separate the macromolecular chitin and to release saccharide monomers (sugar components); there was a shortage of them. As is the case in the production of biopolymers from cellulose too, fine-tuned enzymatic separation is essential, however. Scientists from a Norwegian research group headed by Professor Vincent Eijsink from the molecular biotechnology department at the Fraunhofer IGB – who participated in this project – succeeded in obtaining and providing suitable (chitinolytic) enzymes (chitinases, chitobioases, hexosaminidases, deacetylases), using new bacterial strains too (e.g. Amantichitinum ursilicas and Andreprevotiaripae) [6].

A certain amount and certain blends of these enzymes were, however, needed, which it was only possible to produce biotechnologically. This was done in co-operation with the Czech company Apronex, which has developed suitable processes for this purpose. Lars O. Wiemann and Volker Sieber: “With the help of co-ordinated enzyme cocktails, chitin from European shell waste was degraded purely enzymatically to form N-acetylglucosamine and/or glucosamine.” The scientists are working on the assumption that “an environmentally sound and economically viable version for chemical chitin separation is therefore likely to become available via further process optimization.”

Biobased monomers for the polymer industry

This does not mean that the development work has already been completed, however. In order to be able to manufacture technically relevant polymers, the sugar components obtained from chitin need to be converted first of all into molecules that have two reaction-specific functional groups per molecule. The scientists are pursing different strategies here. Time will have to tell which of them will in the final analysis prove to be most effective. It is a fact, however, that chitin-based plastics can be manufactured on an industrial scale, e.g. by the project partner Evonik. A film report provides an impressive insight into this.

Source and further information

[1] biopolymernetzwerk.fnr.de/biobasierte-werkstoffe/werkstoffe/protein-basierte-kunststoffe/
[2] biopolymernetzwerk.fnr.de/netzwerk/hintergrundinformation-zu-biokunststoffen/1-was-sind-biokunststoffe/<1A>
[3] FAOSTAT, FAO statistical databases, fisheries data (2001) Food and Agriculture organization of the United Nations, Rome, Italy (www.fao.org)
[4] Kandra, P.; Challa, M. M.; Jyothi, H. K. P. (2012) Efficient use of shrimp waste: present and future trends, Appl Microbiol Biotechnol 93: 17-29
[5] Jahresbericht 2014/2015 des Fraunhofer IGB, S. 90/91
[6] Moss, K. S.; Hartmann, S. C.; Müller, I.; Fritz, C.; Krügener, S.; Zibek, S.; Hirth, T.; Rupp, S. (2012) Amantichitinum ursilacus gen. nov., sp nov., a chitin-degrading bacterium isolated from soil. IJSEM 63: 98–103

Guido Deußing