Developing Fibrillated Cellulose As a Sustainable Technological Material
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Perspective Developing fibrillated cellulose as a sustainable technological material https://doi.org/10.1038/s41586-020-03167-7 Tian Li1,2,11, Chaoji Chen1,2,11, Alexandra H. Brozena1, J. Y. Zhu3, Lixian Xu4, Carlos Driemeier5, Jiaqi Dai6, Orlando J. Rojas7,8, Akira Isogai9, Lars Wågberg10 & Liangbing Hu1,2 ✉ Received: 31 March 2020 Accepted: 6 October 2020 Cellulose is the most abundant biopolymer on Earth, found in trees, waste from Published online: 3 February 2021 agricultural crops and other biomass. The fbres that comprise cellulose can be broken Check for updates down into building blocks, known as fbrillated cellulose, of varying, controllable dimensions that extend to the nanoscale. Fibrillated cellulose is harvested from renewable resources, so its sustainability potential combined with its other functional properties (mechanical, optical, thermal and fuidic, for example) gives this nanomaterial unique technological appeal. Here we explore the use of fbrillated cellulose in the fabrication of materials ranging from composites and macrofbres, to thin flms, porous membranes and gels. We discuss research directions for the practical exploitation of these structures and the remaining challenges to overcome before fbrillated cellulose materials can reach their full potential. Finally, we highlight some key issues towards successful manufacturing scale-up of this family of materials. Exiting the fossil fuel era towards a sustainable future will require Fibrillated cellulose has attractive, tunable properties and is bio- high-performing renewable materials with low or even net-zero car- compatible, suggesting the potential for practical implementation bon emission. Cellulose is a promising candidate as the most abundant and commercialization. Furthermore, fibrillated cellulose is much less renewable biopolymer on Earth, where it exists as a structural com- expensive than metal and petroleum-based nanomaterials (approxi- ponent in the cell walls of plants and some species of algae, as well as mately 2020 US$0.60 per dry kilogram for papermaking-grade biofilms secreted by bacteria (Fig. 1a)1. In addition to its advantage as a fibrillated cellulose and approximately US$20 per dry kilogram for potentially sustainable material, cellulose enables multiple functions nanoscale fibrillated cellulose)5 and can be manufactured at industrial and transformative applications that derive from its unique multidi- scale, providing an additional economic advantage. The accelerated mensional structure. Cellulose fibres can be separated into fibrils of adoption of fibrillated cellulose is expected to facilitate the shift from decreasing diameter (ranging from less than 100 µm to around 2–4 nm) petroleum- to bio-based products in support of a more sustainable that are ultimately composed of ordered linear cellulose molecular circular economy6 (Fig. 1c). chains (Fig. 1b). Owing to this hierarchical structure, fibrillated cellulose With improved fundamental understanding and control of this hier- features substantial tunability in terms of its morphology and fibril archical structure, we anticipate that fibrillated cellulose could form size2, which enables unique mechanical, optical, thermal, fluidic and the foundation of economically viable, sustainable solutions towards a ionic properties that far surpass those of the parent cellulose fibres. range of near-term applications in high-performance structural materi- In this Perspective, we explore the emerging potential of fibrillated als and biodegradable technologies, as well as far-term applications in cellulose, particularly as a sustainable and practical alternative to cur- optoelectronics, bio-engineering and membrane science (Fig. 1d). In rent technological materials. For clarity, we use the term ‘fibrillated this Perspective, we will discuss the potential, progress and challenges cellulose’ to describe cellulose fibres that have been broken down into of fibrillated cellulose for various practical uses with growing market smaller fibrils3 and we note that nanoscale versions are also referred potential, including multiscale fibres, bioplastics, nanopaper, porous to as nanofibrillated cellulose, cellulose nanofibres and nanocellu- membranes and soft gels. We believe these growing applications, lose in the literature. Wood has been modified via various top-down increasing biorefineries and the commercialization of fibrillated cel- approaches to take advantage of these cellulose fibres within the cell lulose indicate its importance as a sustainable technological material. walls to produce structures such as super-strong wood, transparent wood and cooling wood for lightweight and energy-efficient building applications4. However, such engineered wood does not involve break- Multiscale fibres ing down the cell walls or the cellulose fibres into smaller, free-standing Cellulose has appealing intrinsic mechanical properties, with a theo- fibrils, making it a separate material category that is beyond the scope retical modulus of about 100–200 GPa (about 63–125 GPa g−1 cm3) and of this discussion. tensile strength of about 4.9–7.5 GPa (about 3.0–4.7 GPa g−1 cm3) in its 1Department of Materials Science and Engineering, University of Maryland, College Park, MD, USA. 2Center for Materials Innovation, University of Maryland, College Park, MD, USA. 3USDA Forest Products Laboratory, Madison, WI, USA. 4Sappi Biotech, Maastricht, The Netherlands. 5Brazilian Biorenewables National Laboratory (LNBR), Brazilian Center for Research in Energy and Materials (CNPEM), Campinas, Brazil. 6Inventwood LLC, College Park, MD, USA. 7Bioproducts Institute, Departments of Chemical and Biological Engineering, Chemistry and Wood Science, The University of British Columbia, Vancouver, British Columbia, Canada. 8Department of Bioproducts and Biosystems, Aalto University, Espoo, Finland. 9Graduate School of Agricultural and Life Sciences, The University of Tokyo, Tokyo, Japan. 10Department of Fibre and Polymer Technology and Wallenberg Wood Science Centre, KTH Royal Institute of Technology, Stockholm, Sweden. 11These authors contributed equally: Tian Li, Chaoji Chen. ✉e-mail: [email protected] Nature | Vol 590 | 4 February 2021 | 47 Perspective ab Cellulose ÿbre Microÿbril bundle Microÿbril Elementary ÿbril Wood m ˜ Cellulose chain 100 100 ˜m Sugarcane bagasse 300 nm 150 nm 5 nm 1 nm Bacteria Low Processing challenge High c d Paper Packaging Membranes Bio-engineering +33% 30 total 25 +3% export 20 in GDP Current Near-term Far-termFar-term 15 New value-added products 10 5 Current forest products Value of production of production Value 0 2010 2020 2030 2040 2050 Year Buildings Bioplasticsi OptoelectronicsOl i Fig. 1 | An overview of fibrillated cellulose. a, Several common source millions of 2015 euros (2020 US$1,187 million) and the data used to draw the materials of fibrillated cellulose. b, Schematic description of the hierarchical curve are an estimate. Data from ref. 6 with adaptations provided by authors at structure and manufacturing challenge of fibrillated cellulose. The degree of the VTT Technical Research Centre of Finland for use in communications on fibrillation refers to the extent to which the fibres have been longitudinally behalf of the Finnish Bioeconomy Cluster, FinnCERES123. d, A roadmap of split into thinner fibrils119. The microscopy images were taken from refs. 1,120–122 fibrillated cellulose technologies, including current application in paper, c, Forecast of the total production value of forest-based products in the Finnish near-term applications in speciality packaging, bioplastics, lightweight bioeconomy, used here as an example of the possible impact of new advanced structural materials, and energy-efficient buildings and transportation, as well materials, including those from fibrillated cellulose, which can drive the as far-term technologies, including porous membranes for energy and water, exports and gross domestic product (GDP) growth of a nation. The units are in optoelectronics and bio-engineering. crystalline form7–9, both of which are higher than most metals, alloys, of films made of only nanocellulose fibrils (that is, no other polymers) synthetic polymers and many ceramics (Fig. 2a). This mechanical can reach up to about 300–500 MPa, which is much higher than conven- strength partially derives from the densely distributed hydroxyl groups tional paper made from loosely packed microscale fibres16–22. Aligning (three groups per anhydroglucose unit) on the cellulose molecular cellulose fibrils is another effective design and engineering strategy chains, which are critical for forming abundant inter- and intramolecu- to reduce structural defects (such as pores), to enhance the interface lar hydrogen bonds (Fig. 2b), especially within the fibrils. Van der Waals between cellulose fibrils and fibril aggregates and to strengthen the interactions are also important owing to their longer interaction range molecular interactions at multiple length scales23–25. compared with hydrogen bonding. Furthermore, the fibril network The rich hydroxyl groups on fibrillated cellulose also provide oppor- provides physical entanglement, which helps to toughen the material10. tunities for chemical functionalization and hybridization with other As building blocks, these cellulose fibrils can be processed into various building blocks (for example, graphene oxide26, graphite27, clay28, poly- macroscopic structures (for example, composites and macrofibres), mers29, and so on) to further improve the mechanical properties.