BACTERIAL CELLULOSE profile
by Stefanie Putsch, Dean Weigand & Elena Bangel
Description of the material:
Cellulose is a polymer made from the monomer cellobiose. It is the main component of plant cell membranes and is the most abundant biomolecule. The linkage of the monomers takes place through a condensation reaction in which two hydroxyl groups (-OH) form a water molecule (H2O) and the remaining oxygen atom connects the ring-shaped basic structure of the two monomers. In addition to this strong covalent bond, less strong hydrogen bonds are formed intramolecularly.
Motivation for development:
Bacterial cellulose has a high mechanical stability due to its degree of purity and the three-dimensional nanonetwork. A high degree of resources and energy could be saved in textile production, as the bacteria only need sugar and slightly acidic water for cellulose production. In addition, the material is interesting for medical purposes due to its high biocompatibility. Bacteria cellulose is already being used as a dressing material, overlays on burns or skin grafts. The material is also used as a diaphragm in high-quality headphones.
Properties of the material:
Bacterial cellulose consists of very fine fibres that form a nanostructured network. In contrast to plant cellulose, it is characterised by its special degree of purity (free of accompanying plant components such as lignin and hemicellulose). Especially in the moist state, it has a high mechanical stability, flexibility and high water absorption capacity. Its strength in the moist state is even comparable to Kevlar® or steel.
Types of the material:
Bacterial cellulose can be obtained in two processes. Through static growth, a cellulose film is formed that builds up like layers. This process requires a long culture period (according to ScobyTec approx. 3 months for usable material). In a stirred culture, no homogeneous skin is formed. Due to the rapid cellulose growth, cellulose negative mutants are formed, which are not usable.
Procedure of production:
The production of bacterial cellulose by Acetobacter xylinum and Gluconacetobacter xylinus is carried out by the aerobic fermentation of ethyl alcohol to ethanoic acid. The bacterial cellulose is produced by a cell film on the water surface, which the bacterial culture forms to protect itself from UV rays.
Bacterial cellulose forms a three-dimensional fibre network with very fine fibres, which gives it extremely high tensile strength and stability. It also has a high water absorption capacity and temperature resistance up to 300 degrees Celsius. Furthermore, the material can be processed in many ways. It can be sewn, cut, lasered and is self-adhesive.
The main disadvantage of the material is the long growth phase, which makes it difficult and expensive to produce on a large scale. Furthermore, there are many factors, such as pH, temperature, humidity…, that influence the growth and homogeneity of the material. Another disadvantage is that it is not waterproof when untreated.
Interpretation of the material:
Bacterial cellulose is both biobased and biodegradable. This means that it is obtained from renewable raw materials with the help of bacteria. And, it can also be biodegraded e.g. in domestic compost.
So far, there are no possibilities to recycle bacterial cellulose. Although it is possible to soak dried bacterial cellulose in water again and reshape it if necessary, this is only possible to a minimal extent. It is possible to crush still moist bacterial cellulose residues and obtain a kind of bacterial cellulose papier-mâché after drying, but this has poorer properties than the original bacterial cellulose material.
Due to the rapid degradability of bacterial cellulose, it works well in the biological cycle. In a technical recycling cycle, however, it is difficult to imagine so far.
By drying the material on structured surfaces, one can already give the bacterial cellulose a shape during the drying period. This is theoretically also possible in the growth phase, but since the water loss during drying is so high, much of the structure is lost there. Bacteria cellulose can be easily coloured with reactive dyes. Pigments cannot penetrate the cell structure during growth because it is too acidic. The thickness of the cellulose layer depends on the time of growth. The dried layer can be laseröd, cut, sewn and embossed.
Currently considered areas of application:
Bacteria cellulose is often found in fashion and industrial design. The material is preferably processed as fake or vegan leather and transformed into backpacks, jackets, shoes or even car seat coverings.