Comparative Study Of The Structures And Properties Of Different Biomass-derived Nanocellulose Aerogels

With the increasing attention on environmentally friendly materials,the rational development and utilization of biomass materials bacame more and moere important.Cellulose is the most abundant polymer in nature.After purification and fibrillation treatment,nanofibrillated cellulose(CNF)can be stripped from the cell wall,and can be prepared into CNF-based aerogels by freeze drying.Generally,aerogels are made from inorganic materials such as silica,but silica aerogels are weak,brittle and easily broken even under a low tensile or compressive stress.Traditional CNF aerogels also suffer from low thermal stability and low elasticity.These all greatly limits their practical applications.The structure and properties of CNF and its aerogels prepared by different raw materials(cotton,wood,banboo and rice straw)were systematically studied.The CNF were utilized as nanoscale building blocks to construct aerogels.We researched the mechanism of the process of constructing aerogels,in order to establish a scientific basis for the development of the excellent structure and properties of CNF aerogels.The main research results obtained were summarized as follows:(1)The difference of CNF between different raw materials was studied:the content of a-cellulose in Co-CNF was close to 100%,while that in Wo-CNF,Ba-CNF and Rs-CNF were 83.6%,84.3%and 82.1%,respectively.The average polymerization degree of Co-CNF was 2270,which was significantly higher than Wo-CNF(1910),Ba-CNF(1690),and Rs-CNF(1880).During the frequency sweep,CNF suspensions exhibit elastic behavior and their rheological properties are almost unaffected by temperature.(2)The mechanical behaviors of four types aerogels were investigated:0.5 wt%CNF aerogels had a relatively higher specific compressive strengths and modulus.The specific compressive strengths of CoNA-05,WoNA-05,BaNA-05,and RsNA-05 were 10.3,16.3,14.1 and 12.6 MPa·g-1·cm3,respectively.The flexibility and elasticity of CoNA-05 were highest among the four types of aerogels.The height of CONA-05 was compressed to 20%of the original height for 20 times and it recovered to 70%of the original height,while the other 0.5 wt%aerogels were much lower than CoNA-05.(3)The thermal properties of aerogels were researched:the thermal degradation temperatures of all aerogels were above 30?.The high thermal stability of the CoNAs was mainly owing to the high purity(?100%cellulose)and high crystallinity of Co-CNF.The thermal degradation temperatures of CoNA-05 were 318.8? in air and 333.2? in nitrogen.The thermal conductivity of CNF aerogels decreased with the increasing of porosity.The thermal conductivity of the CoNA-05 is 0.0442 W·m-1·K-1 at 25?.(4)Pyrrole is polymerized in situ on CNF to prepare composite aerogels,which still maintained the crystal structure of CNF.The mechanical strength of the composite aerogels were not affected,and electrical conductivity of Co-CNF/PPY were significantly higher than those of Wo-CNF/PPY.Then they were carbonized to obtain active electrode materials as the electrode of sodium ion battery.The electrochemical performance of composite carbon aerogel derived from Co-CNF/PPY was superior to that of Wo-CNF/PPY.