Enzymes work wonders with biomass. They can be used to catalyse specific reactions in different biomass components, opening possibilities for novel materials. Sustainability is a priority in these treatments.
FinnCERES aims to find new and versatile ways to use and refine cellulose, to substitute non-renewable raw materials and make better use of our natural resources. Enzymes come in handy: we can use them to modify biomass in specific manner using lower temperatures, less energy and water, and avoid hard chemical processes. Since enzymes are biodegradable, they do not produce toxic waste, either.
The industrial world discovered these benefits long ago. Enzymes have been used to treat cellulose to manufacture paper and to break biomass into sugars for making bioethanol. Other application areas include food industry, detergents and animal feed. But there is a lot more to be discovered.
From hydrolysis to oxidation
An example of structural fold of an LPMO*
Most enzymes used in cellulose modification are hydrolytic. However, ten years ago, a new group of enzymes able to oxidize cellulose was discovered. Some can directly oxidize cellulose, others hemicellulose, chitin or starch. When these enzymes are combined with hydrolytic enzymes, the hydrolysis is intensified.
At first, these enzymes were used for making bioethanol. VTT was among the first to explore their potential in the modification of cellulosic fibres. Oxidation reactions are not usually very specific, but these new enzyme treatments are. In order to understand their function better, our partner Aalto University develops and applies methods to analyse their effects on the molecular and material properties of cellulose. They use mathematical modelling to explore the defects in the structure of cellulose crystals and rheology measurements to provide information about the changes in the characteristics of the material.
New materials out of wood
If we want to get rid of cotton, we need alternative sources for textile fibres. VTT has been a pioneer in investigating wood fibre as an option. To make textiles, wood fibre must be dissolved, and this can be enhanced with enzymes, both hydrolytic and oxidative, so that the dissolution requires fewer harsh chemicals. Different enzymes have different effects of product properties, which are anticipated to be translated to textile fibre strength properties. A patent for this is pending, and VTT is now optimizing this system.
Another application area is nanocellulose. Enzyme treatment reduces the energy used for grinding and manufacturing nanocellulose, and the end product is finer. If the cellulose concentration is high – more than 20% – the enzyme treatment can be combined with a mechanical treatment, each boosting one another. This all enables completely new applications for nanocellulose, such as adhesives or flame retardants.
Next steps: resistant enzymes and new tools for specific tailoring of material properties
Enzymes can be delicate and require accuracy in the treatment – otherwise, you might end up deactivating them. To overcome this challenge, with our collaborators, we are now trying to find the most resistant oxidizing enzymes and the optimal circumstances to get the best response. The aim is to control the reaction as well as we can, to maintain enzyme activity and to regulate the oxidation.
We are also broadening our perspective. In nature, lignocellulose components are both synthesized and degraded by enzymes. Hence, there is a wide range of different enzymes with the potential to create novel material properties through specific modification of the lignocellulose components. Or, to use enzymes to produce to pure tailor-made polymers from their sugar precursors. We just need to bring them to the application and find out what they are capable of.
Kaisa Marjamaa Senior Scientist, VTT
* Figure drawn according to the structure of LPMO Tr AA9A (502W) in Protein Data Bank (https://www.rcsb.org/), publication reference Hansson et al. J. Biol. Chem. (2017) 292(46) 19099–19109).