The main structural components of the cell walls in wood are lignin and cellulose. These are long, branched biopolymers which, if extracted in the correct form, could be used in place of man-made plastics, flavourings and glues. This could greatly reduce our reliance on crude oil if this extraction is done on an industrial scale.
Wood is also a particularly attractive source of biopolymers as it is not a food source. This is unlike other common biopolymers such as polylactic acid, which is derived from crops such as corn, sugarcane and cassava. Using wood to produce biopolymers will not create a direct competition with the worlds food supply, something to be avoided if we are to feed the worlds growing population whilst also producing biopolymers on an industrial scale 1.
Unfortunately, the processes required to extract lignin and cellulose for the purpose of forming biopolymers from wood, must be much gentler than those currently available at an industrial scale. For example, the industrial process to extract cellulose from wood for paper production is much too harsh, producing cellulose chains that are too short and in mixtures that are contaminated with other chemicals from the process 2.
Previous research has shown that ionic liquids (a salt in a liquid state) can be used to gently dissolve wood, making lignin and cellulose accessible to enzymes and solvents. However, this pretreatment has only been done in the laboratory, with the process deemed industrially unfeasible due to the high cost of ionic liquids3. Because the process was not fully understood it could not be fully optimised, for example by altering the temperature, and hence could not be made industrially interesting.
But now, scientists from Forschungszentrum Jülich and RWTH Aachen University have elucidated this process4, examining it ‘in operando’ to find out what is really happening at a nanometer level. Firstly, ionic liquid enters the wood through pores, causing the lignin and cellulose matrix to swell. This puts pressure on the surrounding material, causing it to break open, allowing the ionic liquid further into the wood and the lignin and cellulose out. Enzymes can now hydrolyse (cut up) the polymers into shorter chains, which can be easily dissolved and processed.
This research will take some of the guesswork out of the optimisation of the pretreatment process. Thus, allowing a faster development of an industrial production process for a wood based biopolymer, ultimately helping facilitate a faster move away from fossil fuels.
- M., Niaounakis, 2013, ‘Biopolymers Reuse, Recycling, and Disposal’, William Andrew Publishing, pp. 275-290, [Online] https://doi.org/10.1016/B978-1-4557-3145-9.00010-5
- (Forschungszentrum Jülich, 2020, ‘Ionic liquid detonates wood fibers in a few minutes’, Forschungszentrum Jülich, [Online] https://www.fz-juelich.de/SharedDocs/Pressemitteilungen/UK/DE/2020/2020-07-10-zellulose.html Press Release.
- Viell, J., Szekely, N.K., Mangiapia, G. et al., 2020, ‘In operando monitoring of wood transformation during pretreatment with ionic liquids’, Cellulose 27, 4889–4907, https://doi.org/10.1007/s10570-020-03119-4.