Study On The Dissolution And Modification Of Cellulose In Quaternary Ammonium Ionic Liquid

With the depletion of fossil resources and the growing environmental pollution,seeking for alternative resources become more important for the sustainable development of our society.Cellulose is an abundant,cheap and renewable resource in nature and has the potential to replace fossil oil for the production of chemicals and materials.However,cellulose is insoluble in most organic solvents due to the intramolecular and intermolecular hydrogen bonds in its structure.This has become one of the main obstacles to broaden the utilization of cellulose.Generally,Traditional cellulose solvents are not favoured due to toxicity and environmental pollutions.An effective solvent system for cellulose dissolution is of great importance for further advances in cellulose conversion.In this study,six symmetric quaternary ammonium ionic liquids and two asymmetric quaternary ammonium ionic liquids were synthesized with an average yield around 85%.The effects of cation structure,ionic liquid/DMSO ratio,dissolution temperature and type of cellulose materials on the dissolution of cellulose were investigated.All these factors were demonstrated to have significant effects on the dissolution of cellulose.Generally,asymmetric quaternary ammonium ionic liquids have a better dissolution ability than the symmetric quaternary ammonium ionic liquids.Both low and high ionic liquid/DMSO ratios have a negative effect on cellulose dissolution;Higher temperature,lower degree of polymerization and smaller size of the cellulose led to faster dissolution.When the ratio of TBAA/DMSO was 0.15(WTBAA = 0.15),1 wt% filter paper could be dissolved within 3.5 min at 25 °C.The maximum cellulose solubility(11.37 wt% filter paper)was achieved with N2226CH3COO/DMSO(WN2226CH3COO = 0.35).In addition,when dissolving the same amount of cellulose,the mixed system with N2226CH3COO/DMSO had a lower viscosity than that with TBAA/DMSO.The mechanism of cellulose dissolution in TBAA/DMSO mixed system was also studied.Microcrystalline cellulose was used as cellulose material and cellobiose was used as the cellulose model compound.The dissolution processes were characterized by 1H NMR,13 C NMR,FT-IR.The conductivity and viscosity of the cellulose solution were also measured.An "ion-pair" and "ion-split" two-stages model of TBAA in the mixed system was proposed based on the results of these characterizations.WTBAA=0.15 was the turning point of the two stages and the mixed solvent displayed the best dissolving ability at this ratio.The interaction between carboxylate anions of TBAA and the cellulose model compound cellobiose,which formed strong hydrogen bonds between(anions)O…H-O(cellobiose),were found to be the key factor of the dissolving behaviour of cellulose in the mixed solvent.Meanwhile,DMSO not only reduced the viscosity of the mixed solvent but also interacted with cellobiose to stabilize the dissolved cellobiose molecule from reforming inter-and intra-molecular hydrogen bonds.Homogeneous modification of cellulose with succinic anhydride was performed in TBAA/ DMSO mixed solvent.Different degree of substitution(DS)values of modified cellulose(DS=0.337~1.191)were prepared by changing TBAA dosage,molar ratio of succinic anhydride(SA)to free hydroxyl groups in the anhydroglucose units(AGU),reaction temperature and reaction time.Succinoylated cellulose was characterized by FT-IR,TGA,XRD,solid state CP/MAS 13 C NMR spectroscopy(CP/MAS 13 C NMR),and SEM.Modified cellulose were used for the adsorption of Cu2+ and Cd2+.The DS value of modified cellulose,pH value of the solutions,adsorption time and temperature were investigated to evaluate the adsorption capacity of modified cellulose.The first two factors showed prefound effect on the adsorption capacity of succinylated cellulose.The modified cellulose had a good adsorption of Cu2 + and Cd2 + at room temperature in a short time.And the maximum adsorption capacity for Cu2+ and Cd2+ were 51.92 mg/g and 50.35 mg/g,respectively.