New Material: Research And Application Of Biosynthetic Cellulose Based Insulating Nanopaper

With the deepening of human exploration of extreme environments such as Antarctica, the moon and Mars, the emerging extreme environmental conditions, including strong ultraviolet (UV) environment, atomic oxygen (AO) and alternate high and low temperature environment, have become the main obstacles for future exploration. In these extreme environments, the physical and chemical properties of materials will change, even leading to damage of important equipment and devices in serious cases. Among the traditional materials, metals and ceramics themselves have excellent mechanical properties and resistance to extreme environments. However, metal materials face the problems of high density and heavy weight, while ceramic materials face the problems of brittleness and difficulty in machining. On the other hand, although polymers have the characteristics of light weight and plasticity, most polymer matrix composites will have problems such as high-temperature softening and low-temperature brittleness after long-term service in extreme environments. Therefore, the design and preparation of a high-performance protective material that can serve in extreme environments for a long time is one of the problems faced by the material field.

Recently, Yu Shuhong, an academician of the Chinese Academy of Sciences and a professor of the University of Science and Technology of China, reported a high-performance cellulose based nano paper material, which can still maintain excellent mechanical and electrical insulation properties under extreme conditions. The nanopaper was obtained by using the aerosol assisted biosynthesis (AABS) method developed by the research team at the early stage to uniformly and tightly entangle the synthetic mica (S-Mica) dispersed in the material using cellulose nanofibers (BC) produced by bacteria. Relevant achievements were published on Advanced Materials under the title of Nacre inspired bacterial cells/mica nanopaper with excellent mechanical and electrical insulating properties by biosynthesis.

Fig. 1 Preparation and structure of composite nano paper. (a) Schematic diagram of the construction process of biosynthetic composite nano paper; (b) Digital photos of nano paper; (c) The "brick mud" structure of nano paper imitating mother of pearl.

The researchers used the AABS strategy to uniformly load the synthetic mica nano sheet into the composite hydrogel with bacterial cellulose, and then obtained the final nano paper material with mother of pearl structure by hot pressing (Figure 1). Thanks to the fine "brick mud" structure of the nano paper, the nano paper obtained has excellent mechanical properties such as high strength (~375 MPa), high modulus (~14.9 GPa), high toughness (~16.44 MJ m-3), foldability and bending fatigue resistance. At the same time, the "brick mud" structure inside the material gives full play to the high dielectric strength of mica, thus giving the nano paper a high electrical breakdown strength (145.7 kV mm-1). Compared with pure cellulose nanopaper, the corona resistance life of the composite nanopaper is significantly improved, and even exceeds that of commercial polyimide (PI) film.

Fig. 2 Comprehensive properties of nano paper. (a) Characterization of mechanical properties of nano paper; (b-c) Comparison between the comprehensive performance of nano paper and the insulating materials in the literature; (d) Comparison of mechanical properties of nano paper before and after thermal vibration; (e) Nano paper bending photos in liquid nitrogen; (f) Thermal expansion coefficient of nano paper; (g) Characterization of the tolerance of nano paper to atomic oxygen; (h-i) Characterization of the resistance of nano paper to ultraviolet light.

In addition, the BC/S-Mica nano paper reported in this study still shows excellent comprehensive performance under extreme conditions such as high and low temperature alternation, ultraviolet ray and atomic oxygen AO, which provides a good choice of protective materials for future exploration of extreme environments.

The relevant research work has been supported by the National Natural Science Foundation of China, the National Key Research and Development Program, the Collaborative Innovation Program of Chinese Universities, and the Key Research and Development Program of Anhui Province.