A Study On Process And Characteristics Of Amine-Based Nanocrystalline Cellulose Aerogel

Nanocellulose aerogel is a biodegradable porous material with a number of excellent properties such as low density,high porosity,and easy-transform.Amine-based nanocellulose aerogel has the ability to adsorb CO₂ and can apply to CO₂ capture to reduce CO₂ as a kind of greenhouse gas in the environment.Nanocrystalline cellulose was prepared by sulfuric acid hydrolysis from microcrystalline cellulose and eucalyptus pulp individually.The amine-based nanocellulose aerogel was successfully fabricated either by liquid phase method and gas phase method through freeze-drying of nanocellulose hydrogels.The prepared amine-based nanocellulose aerogel has excellent CO₂ adsorption capacity,and the preparation process is determined.The main conclusions of this study are as follows.?1?Nanocrystalline celluloses?including M-NCC and E-NCC?prepared from microcrystalline cellulose and eucalyptus pulp,are fusiform rod-like,whose diameter are mainly distributed in the range of 5-10nm.The length of M-NCC is concentrated in the range of 120-220nm while the length of E-NCC mainly is distributed in the range of 150-300 nm.Compared with the raw materials,the chemical structures of M-NCC and E-NCC prepared by sulfuric acid hydrolysis remain unchanged,and still keep cellulose I-type structure.The crystallinity increases in different degrees.The prepared 2.5-M-aerogel and 2.5-E-aerogel also retain cellulose I-type structure of nanocrystalline celluloses from two raw materials.?2?The sorption isothermal curves of 2.5-M-aerogel and 2.5-E-aerogel prepared from two kinds of raw materials belong to the type IV standard curve,and the types of hysteresis loops are close to the De boer A-type loop.The main pore sizes of 2.5-M-aerogel and 2.5-E-aerogel are mainly concentrated in the range of mesopores,and the nanocellulose aerogels include a few micropores and macropores.The observation and analysis by SEM show that the internal structure of 2.5-M-aerogel and 2.5-E-aerogel are mainly single-layered and multi-layered structures.Under the observation of high multiples,"sheet-like structure"is actually composed of mesh structures.?3?Nanocellulose wet gel was modified by amination and the modification process was optimized and the amine-based nanocellulose aerogel was prepared by freeze-drying in this dissertation.In the liquid phase modification process,the modification process was well detected resulting an optimum reaction condition under 105?of 16h with the modifier concentration12%in the solution of tert-butanol.?4?In the gas-phase modification,the modification process was well detected resulting an optimum reaction condition under 145?of 10h with the modifier dosage 2.40g.?5?Fourier transform infrared spectroscopy analysis shows that the amine-based nanocellulose aerogels prepared by liquid phase method and gas phase method,not only have the characteristic peaks of cellulose I-type,but also have some characteristic peaks related to the modifier AEAPMDS.Hence,the modifier can be load into the nanocellulose aerogel through ethier liquid phase method or gas phase method.?6?Accoding to the XPS analysis,N and Si atoms appear on the scanning spectrum of modified aerogel prepared from tert-butanol as the reaction solution.N and Si show three chemical states,which are NH₂,NH₃⁺,or hydrogen bonded NH₂?H--NH₂?,CN,Si-OC,Si-O-Si,and Si-OH,respectively.N and Si elements are also observed for amine-based nanocellulose aerogel sample prepared by gas phase method,and there are three and one chemical state respectively,which are NH₂,NH₃⁺or hydrogen bonded to NH₂?H--NH₂?,CN and Si-OC,respectively.?7?The prepared amine-based nanocellulose aerogels under the optimal condition are pare yellow.Their internal microscopic morphology does not show any major changes after modification,and remains as a single-layer and multi-layered structures at the low multiples?x500?with SEM and the“sheet structure”is actually showing as grid structure at high multiples?x20000?with SEM.?8?The adsorbed amounts of 2.5-M-aerogel and 2.5-E-aerogel for carbon dioxide are 0.1929mmol/g and 0.1575 mmol/g with the conditions of 25°C and 1 standard atmospheric pressure,respectively.The carbon dioxide adsorption capacity of amine-based nanocellulose aerogels improved greatly with the same adsorption conditions,and the adsorption capacity increased in the range of 1.3820-1.5034 mmol/g.However,the carbon dioxide adsorption capacity of modified aerogels decrease slightly after 5 times adsorption-desorption cycling.?9?The adsorption isotherms of the amine-based nanocellulose aerogels are still type IV.The amine-based nanocellulose aerogels are mainly composed of mesopores as well,and their specific surface areas and pore volume decrease while their average pore sizes increase.