The invention of the artificial material plastic provided a lightweight, strong and inexpensive material to use for an exhaustive range of applications. However, the long-lasting properties that have made it useful have also resulted in a huge environmental problem.
Most unrecycled plastic waste ends up in the ocean. Through being broken down by waves, sunlight and marine animals, a single plastic bag can be broken down into 1.75 million microscopic fragments called microplastics. These microplastics can end up in our body through the fish we eat or the water we drink.
Cellulose has played a big part in the evolution of most plants on the earth, since cellulose-based materials are used in them for structural support. Cellulose in plants mainly exists in the form of cellulose nanofibers (CNF), which have excellent mechanical and thermal properties.
CNF, which can be derived from plants or produced by bacteria, is one of the most abundant all-green resources on Earth. CNF is an ideal nanoscale building block for constructing macroscopic high-performance materials, as it has a strength (at least 2 GPa) and modulus (138 GPa) almost as high as Kevlar and steel, and a lower thermal expansion coefficient (1 x 10-7 K-1) than silica glass.
The construction of sustainable and high-performance structural materials based on this biodegradable building block has the ability to provide a successful replacement for plastic and help us prevent further plastic damage to our environment.
A team lead by Professor Shu-Hong Yu from the University of Science and Technology of China (USTC) has reported a high-performance sustainable structural material called cellulose nanofiber plate (CNFP) which is constructed from bio-based CNF and is ready to replace plastic in many fields and applications.
This CNFP has high specific strength (~198 MPa/(Mg m-3)) which is 4 times higher than that of steel and higher than that of traditional plastic and aluminum alloys. In addition, CNFP has higher specific impact toughness (~67 kJ m-2/(Mg m-3)) than aluminum alloy and only half of its density (1.35 g cm-3).
Unlike plastic or other polymer-based materials, CNFP exhibits excellent resistance to extreme temperature and thermal shock. The thermal expansion coefficient of CNFP is lower than 5 x 10-6 K-1 from -120 °C to 150 °C, which is close to that of ceramic materials and much lower than that of typical polymers and metals.
Moreover, after 10 rounds of rapid thermal shock between an 120 °C bake oven and -196 °C liquid nitrogen, CNFP retained its strength. These results show its outstanding thermal dimensional stability, which allows CNFP to have great potential in being used as a structural material under extreme temperature and in conditions of alternate cooling and heating.
Owing to its wide availability from raw materials and bio-assisted synthesis process, CNFP is also cheap with a cost of only 0.5 $/kg, which is lower than most plastics.
Through its low density, outstanding strength and toughness, and great thermal dimensional stability, CNFP surpasses traditional metals, ceramics and polymers in terms of these properties, making it a high-performance and environmental-friendly alternative for many engineering requirements, especially in aerospace applications.
CNFP has the power to replace plastic and prevent the plastic crisis from further destroying our environment, as well as having great potential as the next generation of sustainable and lightweight structural materials.
Journal Reference: Guan, Q-F. et al. (2020). Lightweight, tough, and sustainable cellulose nanofiber-derived bulk structural materials with low thermal expansion coefficient. Science Advances. DOI: 10.1126/sciadv.aaz1114