Cellulose is the most abundant biopolymer on the earth. It breaks down the cellulose into structural units with variable, controllable dimensions and extends to nanoscale, called fibrillated cellulose. Due to its sustainable development potential and its functional characteristics, this nanomaterial has a unique technological appeal. To this end, Professor Liangbing Hu from the University of Maryland and others have explored the various uses of fibrillated cellulose in material manufacturing (composites, large fibers to membranes, porous membranes and gels) and the challenges and opportunities faced in actual development.
Based on its layered structure, fibrillated cellulose has considerable tunability in morphology and fibril size, has unique mechanical, optical, thermal, fluid and ionic properties, and has good biocompatibility, so It has great potential for practical application and commercialization. In addition, fibrillated cellulose is much cheaper than metal and petroleum-based nanomaterials, so it has obvious economic advantages. This research focuses on its functional applications, as well as the challenges and opportunities faced in industrial development.
Functional application:
Figure 1.d, Fibrillated cellulose technology roadmap 1) Multi-scale fiber: Cellulose has outstanding mechanical properties, and its theoretical modulus and tensile strength are higher than most metals, alloys, synthetic polymers and many ceramics . And cellulosic materials have the potential for mass production and lightweight. This high mechanical strength comes from the densely distributed hydroxyl groups on the cellulose molecular chain. Some recently developed cellulose composite materials have shown tensile strengths of about 400–1,000 MPa and high toughness as high as about 30 MJ m-3, which are comparable to carbon-based and glass fiber-based composite materials used in vehicles.
2) Films and coatings: Like the micro cellulose fibers that make up traditional paper, fibrillated cellulose or nano cellulose can also be assembled on separate films and coatings, and its thickness is usually less than about 100 μm, usually called "Nano paper". The material has a variety of application potentials. For example, the adjustable porosity and pore size of nanopaper enable its optical properties (for example, transmittance and haze) to be adjusted according to the required application.
In addition to optical properties, nano-paper can be used in commercial packaging applications as well as car window coatings and building coatings due to its porous structure and low thermal conductivity.
Flexible and transparent nano-paper also has excellent applications in the field of optoelectronics. Compared with plastics, nano-paper has obvious advantages, including mesoporous structure and optical coupling to enhance optoelectronic performance.
3) Porous membrane: Fibrillated cellulose membrane is widely used in water treatment. For example, heavy metals or viruses (mainly through size exclusion), batteries/supercapacitors/ion devices (ion selective membranes), solar desalination, water/vapor filtration and thermal energy harvesting (thermally driven ion separation).
4) Soft gel: Fibrillated cellulose is considered a biocompatible material, which can be applied to a series of advanced bioengineering fields, such as wound dressing, tissue engineering, drug delivery, medical diagnosis, smart sensors and Electronic skin. Soft gels made of fibrillated cellulose (such as hydrogels and ionic gels) have the potential to fuse with biological tissues and are of great value for such biological-related fields (Figure 3c).
Figure 3.c, Fibrillated cellulose soft gel for biological applications
Challenges in industrial application: Although the proof-of-concept materials and equipment have been proven, there are still obstacles to the transition of fibrillated cellulose from the laboratory to the market. a) Sustainability: Resources such as fibrillated cellulose are truly sustainable only if their processing is also sustainable. The assessment of the sustainability of fibrillated cellulose needs to consider the technical economy and life cycle assessment analysis based on pilot scale data.
b) Balance between biodegradability and product durability or dimensional stability: Generally, cellulose hybrid materials (for example, nano-cellulose polymer composites) show enhanced durability, but this is to some extent At the expense of biodegradability. If cellulose is to be used as a sustainable and practical alternative to traditional petroleum-based plastics, this issue must be weighed.
c) Fire safety In practical applications, the design of composite materials and structures based on fibril cellulose must also consider ways to improve the fire safety of the material. The researchers demonstrated the ability to modify cellulose with phosphoric acid groups to improve flame retardancy. Or a combination of cellulose and inorganic particles, such as asbestos (aluminum silicate fiber), talc, calcium silicate, calcium carbonate and clay. Opportunities in industrial application: a) The type of raw cellulose raw material has an impact on the performance and manufacturing cost of fibrillated cellulose. When selecting raw materials for fibrillated cellulose, the process-structure-property relationship between plant sources and application requirements must also be considered. Moreover, the choice of medium is also very important, as the production of bacterial cellulose depends largely on the fermentation medium.
b) The properties and manufacturing costs of fibrillated cellulose in different forms also vary depending on its form (for example, size distribution and degree of fibrillation). Therefore, the trade-off between performance and cost must be carefully considered when choosing fibrillated cellulose with different morphologies.
c) The water content of fibrillated cellulose in dry and wet products will play a key role in its storage, transportation and product use. Need to choose a reasonable choice to use wet gel or dry powder.
d) Cellulose and cellulose materials are factors that affect the production cost and performance of fibrillated cellulose, and purity must also be considered in its commercialization. It is worth noting that depending on the application, the performance of high-purity fibrillated cellulose is not necessarily better than that of low-purity materials.
e) Synergy with the paper/wood industry Combining the production of fibrillated cellulose products with the existing forestry and paper industries will be a synergistic approach that can reduce production costs on a large scale.
Li, T., Chen, C., Brozena, A.H. et al. Developing fibrillated cellulose as a sustainable technological material. Nature 590, 47–56 (2021). DOI: 10.1038/s41586-020-03167-7
