Scientists have devised a way to mass-produce environmentally friendly cellulose nanofiber plates at low cost with superior strength, toughness and thermal dimensional stability compared to metals.
In recent years, designing structural materials with high performance of mutually exclusive properties (e.g. strength and toughness) at the same time, especially based on renewable and sustainable nanoscale building blocks, have been steadily garnering interest. When these nanoscale building blocks are assembled into macroscale materials, many extraordinary nanoscale properties can be scaled to macroscopic level and new macroscopic properties that are ascribable to the assembly of individual units emerge.
Cellulose nanofiber (CNF), which can be derived from plant or produced by bacteria, is one of the most abundant green resources on Earth. Many attractive properties including low density, low thermal expansion coefficient, high strength, high stiffness, and easily modifiable surface make CNF an ideal nanoscale building block for constructing macroscopic high-performance materials. However, challenges remain in scaling those extraordinary nanoscale properties, and only macro fibres and films have been prepared by a few strategies thus far.
A team lead by Professor Shu-Hong Yu from the University of Science and Technology of China has devised a robust and feasible strategy to process CNFs into a high-performance bulk structural material with low density, outstanding strength and toughness, and great thermal dimensional stability. The obtained CNF plate (CNFP) has high specific strength [~198 MPa/ (Mg m-3)], which is higher than that of steel, traditional plastic and aluminium alloy. In addition, CNFP has higher specific impact toughness [~67 kJ m-2/ (Mg m-3)] than aluminium alloy and only half its density.
Unlike plastic or other polymer-based material, CNFP exhibits excellent serviceability under extreme temperature or rapid thermal shock and high energy absorption properties. The thermal expansion coefficient of CNFP is lower than 5×10-6 K-1 from 120oC to 150oC, which is close to ceramic materials, much lower than typical polymers and metals. Moreover, after 10 times of rapid thermal shock between 120°C bake oven and −196°C liquid nitrogen, CNFP retains its strength.
Those results show its outstanding thermal dimensional stability, which allows CNFP to potentially be used as structural material under extreme temperature and alternate cooling and heating. Its mass production is also feasible at large scale as CNFP is estimated to cost only $0.50/kg, making it a low-cost, high-performance, and environmental-friendly alternative for engineering requirements, especially as spacecraft materials. The findings were reported in Science Advances. [APBN]