USTC Yushu Hong Academy team: and lightweight, and strong, and tough, dimensionally stable and cellulose-based structural material
Structural material in people\’s daily lives actor indispensable role, however, common metals, ceramics, and polymer-based structural materials have obvious advantages and disadvantages. To prepare all aspects of performance are excellent construction materials, methods, researchers usually taken to these three basic material composite material, a composite structure prepared. However, many studies show each performance of the composite material (such as strength, density, toughness, and thermal dimensional stability) consisting of hard material beyond its highest index, the multi-component composite can be regarded as a compromise Methods. Therefore, the development of a variety of excellent performance are very cheap material body structure is still a major problem faced by the industry. Recently, China University of Science and Technology Yushu Hong academician team developed a kind of bacterialas a precursor to bonding by hot pressing the method of the cellulose-based structural material ( ) preparation mass having a layered structure. The results show that the green density is only CNFP 1.35 g cm -3 , than the bending strength and impact toughness were achieved than 198 MPa / (Mg m – 3 )] and 67 kJ m -2 / (Mg m -3 ), while at the test temperature range of -120 ~ 150 ℃, coefficient of thermal expansion (CTE) only 5 × 10 -6 K -1 . As the Each CNFP performance structural materials used were close to or even higher than that of metal, ceramics, and maximum value of the polymer material, thus Ashby Phase FIG class structure exhibits characteristics of a fourth material. The results show excellent performance from CNFP strong hydrogen bonding between the multistage micro- and nanostructures and its internal cellulose fibers . After this basis, the authors found that pretreatment of the cellulose gel, the interfacial interaction between the reinforcing fibers, CNFP strength and toughness can be further enhanced. The study, entitled \”Lightweight, tough, and sustainable cellulose nanofiber-derived bulk structural materialswith low thermal expansion coefficient \”is published in\” ScienceAdvances \”journal. (attached description link)
CNFP [123 ] preparation divided into two steps: first, Gluconacetobacter produce bacterial cellulose dispersed in water to obtain a preparation of the hydrogel sheet CNF; then stacked togethermultilayer film, at 80 after 1MPa and 100 MPa under conditions of a compression program ℃, after bonding and removal of water, to obtain CNFP of various sizes can be seen from the schematic structural diagram of FIG. 1, is a combination of layers of cellulose CNFP film together, these cellulose films have inside strong interaction constructed by the physical action of fiber bundle and entanglement hydrogen bond, separate film thus high mechanical strength, but are assembled together, the effect of the interface between the film is relatively weak. in order to further improve the mechanical properties of CNFP, when CNF gel state, respectively, of the PVA, PAA, and silicic acid were processed for CNF, CNFP prepared were designated as CNFP-1, CNFP-2 and CNFP-3. [ 123]
. After the acid treatment or PAA, CNF hydrogen bonding between the film greatly enhanced, CNFP flexural strength and modulus, may also be further, can be up to 17 GPa, respectively, 269 MPa engagement [FIG. 2 (B)] . Meanwhile, with respect to a conventional polymeric material, CNFP also has excellent resistance to high and low temperature resistance – its shape remains substantially unchanged at 200 ℃ environment; after temperature difference is 316 ℃ (-196 ℃ ~ 120 after ℃) thermal shock process, and its mechanical strength can be maintained well . In addition to excellent mechanical properties, CNFP thermal dimensional stability much higher than the metallic and polymeric materials, ceramic materials rather , in a temperature range of -120 ~ 150 ℃, only the value of the CTE of 5 × 10 -6 K -1 . Compared with a ceramic material, CNFP having high impact strength can be achieved 87.6 ± 4.3 kJ m -2 .
. After subjected to external stresses on the micron scale, between the first sliding CNFP inner cellulose film, such sliding can be greatly disperse the stress, the stress concentration is avoided; at the nanoscale, hydrogen bonding between the cellulose film is destruction, further dispersed stress, preventing the crack generation and propagation;On the molecular scale, CNF molecular chain is rich in hydroxyl groups, CNFPs deformed when the slide involves a large number of hydrogen bonding, breakage and recombination between the CNF. Finally CNFP OF SHPB impact test carried out, The results are shown at 14,000 s -1 strain rate of high compression, CNFP compressive strength and energy absorption can be achieved and 1600 MPa, respectively 387.5MJ m 3 . [summary]