Controllable Preparation Of Biomass Derived Nanocelluloses Based On Organic Base-Water Solvent System And Its Mechanism Analysis

As an important type of nanocellulose,cellulose nanocrystals have unique nanocrystal structure and excellent physical and mechanical properties,and they have broad application prospects in the fields of fine chemicals,biomedicine,and advanced materials.However,many problems,such as low yield,uneven particle size distribution,uncontrollable environment,high environmental pollution and high energy consumption,have hindered the development of industrial scale.In view of the problems in the preparation of cellulose nanocrystals,aqueous tetrabutylphosphonium hydroxide(TBPH)solution was used in this study to partially swell and dissolve different biomass materials under mild conditions(40-60 ?,1 h).The preparation of cellulose nanocrystals was then conducted using short-time ultrasonic dispersion after the regeration of cellulose from TBPH solution.The preparation conditions,such as TBPH concentration and temperature,were adjusted to realize the high yield of cellulose nanocrystals and the effective regulation of their crystal structure and size distribution.Finally,the preparation mechanism was also analyzed.The main contents and results are as follows:1.With microcrystalline cellulose and pulp as raw materials,the effects of temperature and TBPH concentration on the yield and morphology of cellulose nanocrystals were investigated to explore the controllable preparation of cellulose nanocrystals.The differences in enzymatic hydrolysis between cellulose residues and microcrystalline cellulose were also investigated.The mechanism of preparation of cellulose nanocrystals by TBPH system was inferred.The results showed that the yield of cellulose nanocrystals under optimal conditions can reach 72.2%.The prepared cellulose nanocrystals were all short rod-shaped,but the size decreased with the increase of TBPH concentration.The crystal structure of cellulose nanocrystals gradually changed from cellulose ? to cellulose ? and ? mixed crystal form,and then changed to cellulose ? with the further increase of TBPH concentration.The enzymatic hydrolysis rate of the cellulose residue was twice that of the microcrystalline cellulose.It was shown that when treating microcrystalline cellulose in TBPH system,hydrogen atoms in cellulose hydroxyl formed hydrogen bonds with hydroxide ions,which promoted the destruction of cellulose hydrogen bond structure and the dissolution of cellulose.After the regeneration of cellulose,the hydrogen bond network was reconstructed to form particles with nanocrystalline structure.After sonication treatement,the nanoparticles crystals were uniformly dispersed in water to form cellulose nanocrystal solution.2.Acidic ionic liquid catalyzed organic solvent-water system was used to fractionate poplar wood,and cellulose-rich materials with different lignin content were obtained by regulating reaction temperature.And the influence of lignin content on the yield and microstructure of cellulose nanocrystals was explored.Based on the above studies,the preparation mechanism of cellulose nanocrystals was analyzed.The results showed that the yield of cellulose nanocrystals decreased with the increase of lignin content.The as-prepared cellulose nanocrystals were all short rods with average length and particle size of 122.3nm and 7.17nm,respectively;Meanwhile,the lignin content showed a significant effect on the crystal structure of cellulose nanocrystals,which gradually changed from the mixed crystal form of cellulose ? and ? to the cellulose ? with the increase of lignin content.It was shown that the cellulose-lignin network was destroyed during the process in the TBPH system.The lignin in the cellulose-rich materials was further removed,and the protons in cellulose hydroxyls formed hydrogen bonds with the hydroxide ions,resulting in the destruction of some of the cellulose hydrogen bond network structures.During the regeneration process,the destroyed hydrogen bond network of cellulose is reconstituted to form particles with nanocrystalline structure.After sonication treatment,the nanocrystals were uniformly dispersed in water to form a cellulose nanocrystal solution.