| After long-term evolution and development,many natural cellular materials with light weight but superior mechanical properties exist in nature,such as honeycomb materials(wood and cork,etc.)and foamlike structures(such as bone trabeculae,plant parenchyma,and sponge,etc.).Inspired by these naturally existing cellular structures,artificial ultralight,and ultrastiff cellular materials have gradually attracted the attention of researchers,and have rich and wide applications in aviation,military,biomedical,and so on.However,at present,it is difficult for artificial materials to maintain a high strength while being lightweight,because the mechanical properties of materials with disordered pores are strongly dependent on density.Thus the mechanical properties of materials decline substantially with the decrease of density.Uniform and ordered micro and nano structure is one of the key factors in the preparation of ultralight and ultrastiff materials.Therefore,in this study,lightweight and high strength aerogel with ordered structure was prepared by two methods.Firstly,we prepared lightweight and high strength nanocellulose aerogel by freezing casting combined with solvent exchange strategy,and optimized the preparation conditions by adjusting solid content,degree of substitution,concentration,time,temperature,etc.By scanning electron microscopy observation,it was found that the uniform growth of ice crystals in the frozen casting in the aerogel created ordered micrometer-scale honeycomb pores,and played a role in squeezing the cellulose chain.Solvent exchange induced hydrogen bond reconfiguration of the adjacent cellulose,resulting in the formation of a dense nanocellulose network on the surface of the micron-scale pore wall.Infrared analysis showed that the two had no effect on the functional groups of cellulose chain.The uniform and ordered micro-and nano-scale network structure enables aerogel to have a low density and play a full dissipative role in the external stress.The density of aerogel is 210.16 mg/cm~3,the highest compressive modulus is 26.09 MPa,and the highest bending modulus is 42.10MPa.Compared with the aerogels prepared by this method alone,the compression modulus has been greatly improved,and is better than that of some silica aerogels,carbon nanotube aerogels and polymer foams.The relative modulus and relative density show a quadratic exponential positive correlation.In order to further reduce the mass density of materials and improve the strength of materials,we prepared regenerated nanocellulose aerogel scaffolds through dissolution regeneration combined with 3D printing.The alkaluria dissolved cellulose solution has suitable rheological properties,which is conducive to extrude and maintain high fidelity by extrusion 3D printing.3D printing deposits cellulose layer by layer and arranges it in a directional manner.The regeneration process promotes the reconstruction of hydrogen bonds between chains.Due to the existence of macroscopic pores,the density decreased to 180.57 mg/cm~3.The ordered structure of the three-dimensional network scaffold and the formation of a large number of hydrogen bonds contribute to the dissipation of stress,so the compression modulus of aerogel is further increased to 55.52 MPa.We also successfully used 3D printed cellulose aerogel scaffolds for blood purification,showing certain application potential in the field of removing low density lipoprotein.In summary,we constructed an ordered porous structure through two synergistic enhancement methods,and successfully prepared lightweight and high strength cellulose aerogel,which greatly improved the mechanical properties of aerogel while maintaining a low density,providing a new idea for the preparation of high strength aerogel. |
