At present, people's lives cannot be separated from plastic products, but the massive use of plastic products also brings plastic waste. Nowadays, plastic pollution is one of the most severe environmental problems faced by people. Whether it is plastic production based on petrochemical industry or the post-processing of plastics, it poses a huge threat to ecology and human health. Therefore, there is an urgent need to develop a 100% environmentally friendly plastic substitute, while also having excellent mechanical and thermal properties to meet people's needs. However, designing and manufacturing a sustainable high-performance structural material that meets the requirements has always been a huge challenge.
Academician Yu Shuhong of the University of Science and Technology of China and others reported a high strength (281 MPa), high toughness (11.5 MPa/m2), high stiffness (20 GPa), low thermal expansion coefficient (7×10-6/K) and good thermal Stable all-natural structural material with a density of only ~1.7 g cm-3, which is expected to be a substitute for plastics. Inspired by the multi-scale architecture of the nacre shell, the author proposes a simple and effective strategy to use pure natural raw material cellulose nanofibers (CNF) and TiO2 coated mica flakes (TiO2-mica) to prepare mechanical properties and thermal properties. Sustainable structural materials with better performance than plastics, and with the characteristics of mass production, processability and colorability, can be used to manufacture a series of high-grade, beautiful and durable structural materials to replace plastics. The research was published in "Nature Communications" as a paper entitled "An all-natural bioinspired structural material for plastic replacement".
The microstructure of the biomimetic pearl shell
Inspired by the microstructure of the nacre shell, the author adopts a layered and orderly structural design based on all natural materials (cellulose nanofibers and mica flakes) under a multi-scale system. Figure 1a shows a schematic diagram of the author's effective directional assembly method for preparing all-natural bionic structural materials. Two-dimensional TiO2-mica is pretreated by (3-aminopropyl)triethoxysilane (APTES) to promote the interface interaction between TiO2-mica and nanofibers. The two are fully mixed and cross-linked by Ca2+ to form a hydrogel, which can then be directly pressed into the structural material by the directional assembly method. In the directional assembly process, the directional orientation of the two-dimensional TiO2-mica and the uniform distribution of the one-dimensional cellulose nanofibers can be realized, thereby forming a highly ordered solid structure. This simple, low-cost, large-scale directional assembly method can be used to directly construct high-performance sustainable structural materials with highly ordered solid structures.
Excellent mechanical and thermal properties
The directional arrangement of mica forms a highly ordered solid structure, which makes the material exhibit high strength of 281 MPa and high stiffness of 20 GPa. The cellulose nanofibers and TiO2-mica are closely combined, which can effectively relieve local high stress and give the material stronger toughness. In addition, the structural material has almost no deformation in the temperature range of -130 to 150°C, and its thermal expansion coefficient is more than 10 times lower than plastic at room temperature. Due to good thermal stability and low thermal expansion coefficient, the storage modulus of the structural material is 20 GPa, which remains almost unchanged under a wide temperature change of 25-200°C. Intuitively, all typical plastics are completely softened at 250°C. In contrast, all natural structural materials have not undergone any changes. Such excellent mechanical and thermal properties show that, as an emerging structural material, this all-natural bio-inspired structural material is safer and more reliable than plastics, making it a sustainable, sustainable, biologically-inspired Lightweight, high-performance structural materials.
The strength and modulus of the structural material are two and five times higher than that of most plastics, and can be used as a substitute for plastics to provide sufficient mechanical performance guarantee. Its thermal expansion coefficient and thermal diffusion are much better than plastics, and will not soften at high temperatures, which makes this all-natural bio-inspired structural material very safe and reliable at high temperatures or variable temperatures. In addition, the process method for preparing the structural material has low cost and large scale, and can realize the mass production of all-natural biologically inspired structural materials. And according to different commercially available raw materials (for example, different mica), the author can prepare all natural structural materials with adjustable colors. The structural material also has good processability and can be processed into the required shape and size, showing great potential to replace plastic in practical applications.
Original paper link:
https://www.nature.com/articles/s41467-020-19174-1