The Study On Mechanism And Applications Of Cellulose Dissolution In A Quaternary Ammonium Ionic Liquid

This paper mainly focuses on a two-component quaternary ammonium ionic liquid,[B4N]+Ac-/DMSO,in which the solubility and dissolution mechanism of cellulose were studied.According to the mass ratio of[B4N]+Ac-/DMSO,different applications of cellulose dissolution were achieved,including the preparations of regenerated cellulose fibers and surface hydrophobic cellulose nanocrystals(CNCs),and partial delignification and dissolution/regeneration of wood.Cellulose was dissolved in[B4N]+Ac-/DMSO.The effects of degree of polymerization(DP)of cellulose and dissolution temperature on the solubility were researched.It was found that[B4N]+Ac-/DMSO was a good,direct and powerful cellulose solvent system,which can dissolve cellulose with high DP at 55? rapidly.[B4N]+Ac-/DMSO was also a non-derivatizing cellulose solvent system,characterized by FT-IR?13C-NMR and TGA.The cellulose in the solution showed armophous,and slightly decreased thermal stability.The influences of concentration and molecular weight on the rheology of the cellulose solution were characterized by rheometry.Compared with that of other cellulose solvents,cellulose solution prepared with[B4N]+Ac-/DMSO showed lower viscosity.The mechanisms on the interactions not only[B4N]+Ac-/DMSO but also the[B4N]+Ac-/DMSO/cellulose were studied by controlling the mass ratio of[B4N]+Ac-to DMSO(R).The results showed that the solvent system at R=5/5?4/6,3/7?2/8,1/9 was a non-solvent,good solvent,and bad solvent for cellulose,respectively.And the two-component solvent system at R=2.5/7.5?2/8 showed the best dissolving capacity.It was mainly due to DMSO helped to dissociate[B4N]+Ac-into free ions,while too much DMSO will reduce the concentration of free ions.The anion Ac-of[B4N]+Ac-formed H-bond with hydroxyl groups of cellulose molecular chain,which dominated the dissolution of cellulose.Cations mainly control the release of free anions through electrovalent bond.Hence,the dissolving capacity of the solvent system was affected by all the cosolvent,cation and anion.Regenerated cellulose fibers was prepared by complete dissolving cellulose in[B4N]+Ac-/DMSO(R=2/8)with dry jet-wet spinning.Compared with that of the original cellulose,the molecular structure of the regenerated cellulose fibers had no change,but the crystalline form was transformed from cellulose ? to cellulose ? with the decreased degree of crystallinity,and the thermal stability decreased slightly,characterized by FT-IR,SEM,XRD,TGA and DSC.This indicated that during the regeneration process,only physical changes occured.SEM images showed that the resulting fibers were homogeneous with smooth surfaces and circular cross-sections.A nonlinear relationship between DP and fiber properties was observed,while fibers composed of polymers with the higher DP stood out as stronger and stiffer.The successful preparation of regenerated fiber in this solvent system was expected to replace the traditional spinning process.[B4N]+Ac-/DMSO(R=1/9)was used with acetic anhydride for the dissolution of amorphous cellulose and simultaneous acetylation of hydroxyl groups on the surface of crystalline domains of cellulose to prepare cellulose nanocrystals via surface acetylation(ACNCs).The one-pot preparation of surface hydrophobic CNCs(ACNCs)from wood pulpboard is facile and easy.The rod-like morphology and nanometer-scale dimensions of ACNCs were ascertained by AFM and TEM.Successful surface acetylation while maintaining an intact crystalline core was confirmed by FT-IR,CP/MAS 13C-NMR and XPS.Finally,compared with that of CNCs,the thermal stability and hydrophobic behavior of ACNCs were better,characterized using TGA and water contact-angle measurements,respectively.Furthermore,we also demonstrated an easy method of preparing a bionanocomposite from PLA and ACNCs.Lignocellulose(southern yellow pine wood)could almost be completely dissolved in[B4N]+Ac-/DMSO(R=2/8).Approximately 34.6%of the native lignin could be extracted and was assessed.After dissolution and reconstitution,cellulose I in the native wood transformed into cellulose ?;and a gradual decrease in lignin with increased extraction cycles resulted in increased crystallinity index,thermal stability and homogeneous macrostructure in the regenerated lignocellulose,as confirmed by XRD,TGA and SEM images.Membranes cast directly from lignocellulose solutions in the same[B4N]+Ac-/DMSO,were prepared using a papermaking-like process.Morphological and mechanical studies indicated that lignin extraction made the membranes more uniform and flexible.Systematic increases in the fibril lengths and orientations of the membranes were also found with decreasing lignin contents on the basis of AFM.This work demonstrates that relatively efficient partial separation of pine wood and subsequent membrane preparation are possible using[B4N]+Ac-/DMSO.[B4N]+Ac-/DMSO,as a "near room-temperature,efficient,low-viscosity,direct,controllable"cellulose solvent,has laid a good economic and environmental basis for "green,simple,multi-level"processing and applications of cellulose.