Biopolymers – Material Building Blocks of the Future

Whenever we touch something around us in our everyday and working lives, it is likely to be a synthetically produced material that contains polymers. In order to maintain and improve our standard of living and at the same time make the production and availability of high-performance materials more resource-efficient and climate-friendly, there is no alternative to the constant development of new materials based on the principles of sustainable chemistry.

For the wider use of bio-based polymers in various applications, innovations along the entire value creation cycle are essential, from raw material extraction to processing and recycling. This is the only way to catch up with the economic and technical lead of conventional fossil-based plastics and to accumulate and establish bioplastics on the market and create acceptance for their unique advantages.

At Fraunhofer IGB we are researching developments with different biopolymers. These include polysaccharides such as cellulose and chitin/chitosan, polyesters such as polyhydroxyalkanoates (PHA), polyamides such as proteins and complex polymer networks such as lignin. For the technical production of biopolymers, we finally use the synthesis capabilities of nature. The resulting biopolymers are then isolated from biomass, purified and, if necessary, modified for applications (e.g. PHA, chitin/chitosan, lignin, proteins).

We also obtain monomers biotechnologically, which can be converted into the target biopolymer (e.g. polymalate) by means of further steps.

Furthermore, we are researching bio-based polymers such as caramides (terpene-based polyamides) or polyethylene furanoate (PEF) as a potential PET substitute, which contains the promising polyester building block furandicarboxylic acid (FDCA). Such polymers all contain bio-based monomer building blocks.

Our range of services for the development and production of biopolymers and bio-based polymers thereby spans the entire innovation chain. 

We would be happy to also support you and advise you in an initial consultation!

The raw material base for biopolymers and bio-based polymers

Nature offers a broad repertoire for the biosynthesis of polymers. Depending on the organism, different raw material sources can be used. Plants and microalgae use carbon dioxide to build cellulose or starch by means of photosynthesis. Bacteria that store PHA prefer to use organic substances.

At Fraunhofer IGB, we utilize the entire spectrum of nature's synthesis potential for the production of biopolymers and biobased polymers. This enables us to use a wide variety of raw materials such as CO₂, biogenic raw and residual materials and, as recently demonstrated, even biogenic waste materials.

One main focus is on the renewable raw material wood, including all its components, as well as lignin-containing biomass from agricultural side streams, such as wheat straw. To pulp lignocellulose, the component of the cell wall of woody plants, we use new processes such as organosolv fractionation, in which the lignin is solubilized using organic solvents, e.g. on our pilot plant at Fraunhofer CBP in Leuna. Expanding the raw material base for plastics to CO₂ is another goal that we are actively pursuing.

By using renewable, sustainably produced raw materials as well as biogenic residual and waste materials to produce polymers, we are contributing to the transition to a sustainable economy without fossil raw materials.

Our technologies for the production and modification of biopolymers

In order to be able to replace fossil-based polymers with biopolymers in the future, existing processes must be optimized, new efficient processes must be established and these must be combined into holistic value creation cycles.

By researching different raw material utilization paths and various synthesis strategies, we at Fraunhofer IGB are able to produce various chemical intermediates for polymer synthesis based on biomass. This takes place, for example, via innovative biotechnological or chemical conversions of biomass components such as carbohydrates or lignin. The spectrum ranges from so-called drop-in compounds, i.e. molecularly identical products, to bioplastics with partially new property profiles, e.g. polylactic acid and other bio-based polyesters. We are also contributing to the development of novel bio-based plastics at Fraunhofer IGB by designing and optimizing processes for the purification of the various bio-based monomers and biopolymers.

In the course of the further value creation cycle, the chemically or biotechnologically produced polymer can then also be combined with other polymers or additives in order to tailor the material properties for the subsequent plastic components. Examples include plasticizers, flame retardants, stabilizers, but also (natural) fibers or bio-based carbon fibers. After compounding – i.e. mixing – the bio-based plastics can then be processed into films, molded parts or components. In principle, all conventional processing technologies for traditional fossil-based plastics can be used, although the material properties of bio-based plastics usually require specific adaptation of the process parameters.

Biopolymers such as gelatine or chitosan can also be easily functionalized in order to adapt their properties to the respective applications. We use chemical cross-linking technologies to create tissue-like hydrogels. Through controlled cross-linking, we obtain hydrogels with adjustable mechanical and biological properties. Hydrogels play a role in a considerable number of biotechnological developments or applications in medicine, e.g. for membranes, implants, biosensors or tissue engineering.

At IGB we are working on improving technologies for the production and modification of biopolymers and testing, evaluating and optimizing new polymer building blocks with regard to their material properties and economic production.

Processing

Alongside the development of new bio-based materials, the question of compatibility with traditional material processing techniques arises for industrial and technical applications. Initial fundamental investigations into the processing of new bio-based plastics and materials, for example by means of extrusion and injection molding, are an integral part of our development work. Processing on a very small and small scale is primarily used to advance the development of new bio-based materials not only in terms of application and properties, but also in terms of processability.

Material characterization and testing

In addition to evaluating the processing parameters, a broad downstream method platform is available for standardized testing and analysis of the newly developed materials. This includes rheological, dynamic-mechanical and various thermal analyses.

Besides material characterization, it is important to analyze the materials with regard to desired or known effects, e.g. antimicrobial properties, but also to unexpected adverse effects on humans, which concern both toxicological and immunological aspects. Various cell-based test systems are available at IGB for this purpose, which are suitable for a variety of test procedures such as bioactivity, cytotoxicity and immunogenicity tests or the testing of antimicrobial properties.

Compared to ethically questionable and only partially transferable animal experiments and limited biochemical test methods, such cell-based test systems known as New Approach Methods (NAM) realistically simulate the in-vivo situation and enable the direct analysis of a cell reaction. The Department of Cell and Tissue Technologies at IGB offers a broad portfolio of specific in-vitro model systems, ranging from simple high-throughput cell assays to complex organoid systems and macroscopic, complex 3D tissue models. The core technology is the targeted development of cell-based reporter test systems for the simple and rapid determination of specific endpoints, such as toxicity or sensitization. 

Scaling and production of sample quantities

An essential step on the way from the laboratory to industrial-scale implementation is the production of sample quantities on a pilot scale. With our know-how, experience and technical equipment, we at Fraunhofer IGB are able to optimize developed processes on our pilot plants in terms of economy and efficiency and to provide product samples on a gram to kilogram scale for polymerization and application tests. The pilot plants at the Fraunhofer Center for Chemical-Biotechnological Processes CBP, our institute branch in Leuna, are also used for this purpose.

One example is polyhydroxyalkanoates (PHA), which are produced by some bacteria as natural storage substances and can be produced from a variety of waste materials. Large-scale purification is currently still very cost-intensive. By selecting suitable production strains and establishing a new process management strategy, we have currently succeeded in obtaining a high-quality PHA copolymer with a 3-hydroxyvalerate content of approx. 10 percent from waste streams.

End-of-life scenarios: recycling and biodegradability

In order to achieve maximum carbon recycling and minimize the need for fossil carbon, our aim is to integrate new value creation processes into existing and future material cycles. This also includes life cycle analysis (LCA).

After a component has been used, at the end of its product life cycle, the material should be returned to the value creation cycle through a recycling step. Depending on the bioplastic, there are different ways of doing this: in the case of mechanical recycling, the polymer is recovered directly; in chemical recycling, it is first broken down into small building blocks, which can then be used again for polymerization, thus closing the cycle.

Many bio-based plastics such as starch, PHA and PLA are also biodegradable. Through biodegradation, they return to the carbon cycle in the form of CO₂ without contributing to littering the biosphere. However, the directly and consciously controlled biodegradation pathway as an end-of-life scenario should only be envisaged for those product categories where emissions into the environment cannot be avoided (e.g. various products such as mulch films in agriculture or “liquid“ plastic, e.g. in cosmetics) or where reuse and recycling are not practicable.

Plastics are often still produced synthetically on the basis of crude oil. If they are disposed of by incineration at the end of their use, this is associated with high CO₂ emissions. Due to the climate crisis, there is an urgent need to use climate-friendly resources. Bio-based plastics represent a sustainable alternative in this context: They help to achieve climate and resource protection goals, but also to reduce dependence on foreign production sources and increase the resilience of value chains.

In addition, environmental aspects such as the pollution of the world's oceans by plastic are an urgent problem of our time. The biodegradability of plastics is an important factor, especially when plastics are required for direct use in the environment (e.g. agricultural foils). The biocompatibility of plastics plays an important role in medical and cosmetic applications.

Fraunhofer IGB is making a decisive contribution to the development of new plastics derived from biological sources. Our range can be categorized into three types of polymer: polymers from bio-based monomers, microbially produced biopolymers and other native biopolymers. In the following sections, some examples from our institute will be shown and the specific end products and possible applications will be presented.

The production of bio-based polymers first requires the next smallest components, the monomers. Fraunhofer IGB can produce these biotechnologically by means of fermentation – also from residual and waste streams, in line with the sustainable circular economy that IGB is striving for. In the next step, the monomers are polymerized chemically or biologically, depending on the process used. 

Bio-based hydroxy and dicarboxylic acids as monomeric building blocks for bioplastics

At Fraunhofer IGB, we use various fermentative processes to produce hydroxycarboxylic acids and dicarboxylic acids from biogenic waste streams. Our portfolio includes malic acid, itaconic acid, xylonic acid, long-chain dicarboxylic acids (lcDCA) and lactic acid, which can be polymerized in downstream processes.

When using bio-based carboxylic acids, the desired polymer properties can be achieved not only via the monomer itself, but also via the polymerization conditions. Although the process development, taking into account the substrate, its feed or the microorganism, has no influence on the properties of the target molecule, it is decisive for product concentration and conversion efficiency. In the case of xylonic acid, we were able to achieve titers of over 300 g/L.

Together with project partners, we are also working on the fermentative production of enantiomerically pure malic acid, its further purification and the subsequent production of polymers. Homopolymers of racemic malic acid are water-soluble, biocompatible and biodegradable, but at the same time hard and brittle. In the Malum project, novel biopolymers with higher elasticity and toughness were produced by functionalizing or copolymerizing malic acid with other monomers. Initial application tests have shown that these polymers can be used as laminating adhesives.

Polymers made from bio-based furanoates as a substitute for PET

One very widely used plastic is PET: polyethylene terephthalate. This fossil-based or partially bio-based plastic is used in large quantities for the production of packaging materials, among other things. The term “PET bottle“, for example, is familiar to the public at large. This is why PET is also the focus of the IGB's scientists. At the institute, they are researching the development of a bio-based PET substitute: polyethylene furanoate (PEF), made from bio-based ethylene glycol and furan dicarboxylic acid (FDCA). PEF can be used as packaging material, but also as bio-based fibers. FDCA production is particularly sustainable, as it is carried out using agricultural and forestry waste. In the projects “PFIFF / PFIFFIG – polymer fibers from bio-based furanoates for industrial applications“, IGB was able to further develop this production process for use on a large scale in industry.

Monomer building block long-chain dicarboxylic acids (lcDCA) and plant oil-based epoxides

Another natural starting material for plastics production that is being investigated at IGB is plant oils. These contain bi- and polyfunctional synthesis building blocks. The oils and plant oil derivatives can be converted into interesting monomer building blocks such as long-chain dicarboxylic acids (lcDCA) or plant oil-based epoxides through appropriate functionalization.

The long-chain dicarboxylic acids serve as a bio-based alternative for the production of plastics, which are usually produced on the basis of starch, cellulose and polylactic acid (PLA). They are used, for example, in the production of polyamides and polyesters. Plant oil-based epoxides, on the other hand, can be used as PVC stabilizers, plasticizers, for the synthesis of bio-based resins and coatings or, after further conversion, as components of lubricant formulations.

Researchers at IGB utilize microorganisms for biotechnological polymer production, primarily focusing on polyhydroxyalkanoates (PHA). Microorganisms produce this polymer as a carbon storage under certain stress conditions – specifically: nutrient deficiency and excess carbon.

Polyhydroxyalkanoates – various PHA variations available

The microbial synthesis of PHA offers significant advantages due to the numerous adjustable parameters in the production process, allowing for the production of biopolymers with specific thermal and mechanical properties. There is a vast array of microorganisms and substrates that can be combined, along with various optimization options available within the bioprocess itself. This flexibility enables the precise variation of PHA composition.

Despite these variations, all PHAs share a common trait: they exhibit high biocompatibility and biodegradability, making them ideal candidates for applications such as packaging (e.g. disposable plastic bottles for non-food items), medical implants, and agricultural films.

Fraunhofer IGB possesses extensive expertise and years of experience in PHA production, enabling the institute to produce different PHA variants, especially PHBVV copolymer (poly-3-hydroxybutyrate-co-3-hydroxyvalerate-co-4-hydroxyvalerate) with varying valerate contents, tailored to specific application requirements. The IGB researchers also focus on sustainable substrates sourced from residual and waste streams, including waste cooking oil, volatile fatty acids from wastewater treatment, and crude glycerin. Additionally, larger sample quantities are produced at the institute's scale-up facility in Leuna, Fraunhofer CBP.

European Regional Development Fund (ERDF) program: Baden-Württemberg and the EU support the development of biorefineries

IGB's biorefinery projects are also of central importance here. Biomass is converted in biorefineries and thus developed as a raw material. The Baden-Württemberg Ministry for the Environment, Climate Protection and the Energy Sector has funded five such projects with EU funding from the European Regional Development Fund (ERDF) program “Bioeconomy – Biorefineries for the Recovery of Raw Materials from Waste and Wastewater – Bio-Ab-Cycling“. PHA was also one of the valorization products in two of these projects. In the “KoalAplan“ project, municipal wastewater in sewage treatment plants was converted into PHA, while in the “BW2Pro – Biowaste to Products“ project, IGB valorized the biowaste into biodegradable bioplastics. 

Polymers also occur naturally in the environment. Examples here are plant components such as lignocellulose, from which lignin and cellulose can be obtained, but also substances of animal or fungal origin, such as chitin or its derivative chitosan, which we obtain from crab shells, insect exuviae or residual material streams from industrial fermentation.

Also, we at Fraunhofer IGB are working on the development of proteins as a raw material for technical products, for example by utilizing animal protein residues (feathers, wool) or insect protein, which is obtained from biowaste using our insect biorefinery.

Lignocellulose – residue from woody plants

Lignocellulose is the structural material in the cell wall of all woody plants and the main component of residual materials such as straw or wood – and is therefore available on a large scale, for example from agriculture and forestry. At IGB, it is broken down via fractionation into its components cellulose (C6 sugar), hemicellulose (C5 sugar) and lignin (aromatic compounds) – an essential prerequisite for complete and high-quality material utilization as a renewable chemical raw material. At Fraunhofer CBP in Leuna, a pilot plant is available for this purpose, which can process up to 70 kilograms of wood per day.

Cellulose is used for example to produce glucose through enzymatic hydrolysis. This can be utilized as a substrate for a variety of fermentations and thus replace the higher-value raw material sources currently being used, such as sugar cane or starch. During fermentation, microorganisms such as bacteria or fungi metabolize these carbon compounds and convert them into biomass, but also into a variety of chemicals such as ethanol, succinic acid, butanediol or lactic acid, which can then be further processed into polymers such as bio-polyethylene (bio-PE), polybutylene succinate (PBS) or polylactic acid (PLA). Polymers such as polyhydroxybutyric acid (PHB) can also be obtained directly from sugar by fermentation (see above: Microbial biopolymers).

The basic building blocks of lignin are substituted phenols, especially guaiacol, syringol and p-hydroxyphenol, the proportion of which varies depending on the type of wood. At Fraunhofer CBP, we investigate and scale up various processes for the modification and depolymerization of lignin, which maintain or increase the structure and functionality of lignin. In this way, new, previously inaccessible aromatic structures with new functionalities and thus a new performance spectrum are identified, which can be used in a variety of industrial applications: from the production of fibers and fiber-reinforced plastics, to the use as epoxy/phenolic resins or wood preservative glaze to polyurethane rigid foams.

Chitin: raw material for the production of chitosan

Chitin is the second most abundant biopolymer in the world after lignocellulose and is formed as a structural component by fungi, insects and crabs, for example. In order to convert chitin into chitosan, it must first be isolated and purified using various processes. Here too, the high bioavailability of the resource gives it enormous potential as a renewable raw material. One promising vegan source is fungal biomass from large-scale fermentation processes. The utilization of insect chitin was investigated in more detail at IGB as part of the European Regional Development Fund (ERDF) project “InBiRa – the insect biorefinery“. Chitosan is not only used in the textile industry, for example as sizing agent to protect yarns during weaving, but can also be used as a bio-based flocculant for the treatment of complex wastewater..

Additional properties can be created by chemically modifying chitosan, e.g. water-repellent properties for textile coatings. The applications are very diverse and range from the encapsulation of active ingredients, coatings for medical products, biosensors and diagnostics to cosmetics. 

Valuable protein: keratin from poultry feathers

Another natural resource is feathers, which are a by-product of poultry meat production. The majority of these feathers have so far been processed into meat and bone meal or disposed of as waste. However, this material can also be used sustainably: The keratin contained in the feathers, a water-insoluble structural protein, was researched at IGB in the project “KERAbond – specialty chemicals from tailor-made functional keratin proteins“ as a starting material for the isolation of polythiol-containing peptides. Possible applications are seen in the production of adhesives and specialty chemicals for surface treatment.

By using proteins such as feathers, enzyme-responsive fragments can be introduced into materials, which in principle also allow new recycling strategies. This allows the intrinsic properties of natural polyamides to be utilized, which would not be easily possible using fossil-based approaches.

Modified biopolymers and hydrogels for the life sciences

All in all, the focus of polymer research at IGB is on the production of bio-based plastics, but there are also potential applications for native polymers in the health sector, for example in the form of hydrogels that can be used as tissue matrices or for drug delivery systems. Hydrogels are water-retaining and at the same time water-insoluble polymers. Suitable natural starting materials for such gels include gelatine, alginates or chitosan.

Through chemical modification, we adapt biopolymers such as gelatine, chitosan, inulin or hyaluronic acid specifically to the different requirements depending on the area of application. By adding various chemical functions (e.g. methacrylic groups, thiol groups and benzophenones), we can change properties such as the viscosity, solubility or even the charge of the biopolymer in a targeted manner. With cross-linkable or hydrophobic groups, for example, we can create more stable and insoluble systems such as for the encapsulation of active ingredients or for functional water-repellent coatings. The modification of biopolymers is also interesting for 3D printing processes, as the viscosity can be adjusted independently of temperature.