Nanocellulose is an amazing natural material. It is produced by taking cellulose – found in wood, paper, cotton, and so on – and disintegrating it into nanoparticles. These can be used to make paper, films, and gels. They can be assembled into super-strong fibres, or blended with other biomaterials to increase strength and reduce production costs. And because they are made from natural plant biomass, they can be considered a quite sustainable product, since they are derived from renewable resources.
The use of nanocellulose is particularly advanced in Japan, where you can find it in pen ink, some clothing, and footwear. It is very lightweight and also very strong, so it is ideal for these applications. Exploitation is not so advanced in Europe, but companies like Cellutech are developing cellulose-based packaging materials and even a bicycle helmet.
Although the material is produced from environmentally responsible renewable resources, the typical methods for disintegrating cellulose into nanocellulose involve a lot of quite nasty chemicals. Sulphuric acid and a chemical called TEMPO are used, which generates a lot of chemical waste. Sustainable industrial development requires us to minimise the production of waste at all levels, and to find alternatives to chemicals that can damage health or the environment.
This is why many researchers, like a team at KTH Division of Glycoscience, are keen on developing enzyme-catalysed nanocellulose production. Enzymes work at moderate pH and temperature conditions, and no harsh chemicals are used in the enzyme reaction, so the ecological footprint of nanocellulose production can be greatly improved.
This new paper is the first PhD publication for doctoral student Salla Koskela. I co-supervise Salla at KTH in Stockholm, helping her to optimise protein production and enzyme assay protocols. Her main supervisor is Prof Qi Zhou, an expert in biomaterials based on natural polymers like cellulose and chitin. Another of Qi’s students, Shennan Wang, was also instrumental in this work thanks to his ability to characterise biomaterials.
In this work, Salla and Shennan showed that we can take one enzyme – belonging to the class called Lytic Polysaccharide Monooxygenases, or LPMOs – and convert spruce wood into nanocellulose fibres. The wood is first chemically treated to remove lignin and form large cellulose fibres. Then, Salla’s enzyme chops those down to nanofibres. The nanocellulose fibres can be formed into nanopaper, which Shennan can investigate for strength and toughness.
One of the people who peer-reviewed this article before it was published praised our nanocellulose production process for being quite easy (it has relatively few processing steps), and having a high yield of nanocellulose production. These are crucial factors to consider if enzymatic nanocellulose production is ever to be implemented at large commercial scale.
Ours is not the first report of an enzyme being used to make nanocellulose, but we were pleased to be able to achieve a highly detailed characterisation of our final material, including producing nanopapers with high strength. We also believe that we are among the first to produce such thin nanofibres of cellulose – ultra-fine nanocellulose can confer higher strength than slightly thicker fibres.
You can read the paper now at Green Chemistry.
Lytic polysaccharide monooxygenase (LPMO) mediated production of ultra-fine cellulose nanofibres from delignified softwood fibres. Koskela S, Wang S, Xu D, Yang X, Li K, Berglund L, McKee LS, Bulone V, and Zhou Q. Green Chem., 2019,21, 5924-5933