Ionic Liquids Modification Of Cellulose Nanocrystal And Its Application In Polyvinyl Alcohol

Sulfuric acid hydrolysis is the main method for preparing cellulose nanocrystal（CNC）.It is well known that cellulose nanocrystals having sulfonate are poor at thermal resistance and redispersibility,which greatly limits their development in different fields.Functionalized cellulose nanocrystals is an important way to enrich its application fields.However,the effective modification strategy of cation-functionalized cellulose nanocrystals is still limited due to the electrostatic attraction between the sulfonate and the cation modifier.In this study,we selected the ionic liquids[VBIm][BF₄]as a cationic modifier,used the"bridge"action of lactic acid between CNC and[VBIm][BF₄],to covalently graft the ionic liquids to the CNC surface,without destroying the crystallinity of the CNC.Thus,a green and versatile strategy to modify CNC by ionic liquids is reported.The cellulose nanocrystals modified by ionic liquids（CNC-LA-IL）showed a positive charge,and the Zeta potential of this suspension was reversed from the original negative potential（-35 mV）to a positive potential（+40 mV）,showing hydrophilic property;the re-dispersibility of cationized cellulose nanocrystals is improved and can be stably dispersed in water;In addition,because of many sulfonate on the surface of CNC removing in the esterification reaction,the thermal stability of CNC-LA-IL is significantly improved;And the flame-retardant ionic liquids coated on the surface of CNC makes the weight residual of CNC-LA-IL significantly increase,which provides the possibility of CNC application in the field of porous carbon materials.The CNC-LA-IL was used to fabricating the polyvinyl alcohol（PVA）based nanocomposite films by solution evaporation method.The as-prepared CNC-LA-IL/PVA films exhibited extraordinary optical transparency in the visible wavelength range（400-700 nm）.Of particular note,when the content of CNC-LA-ILs is only0.3wt%,the tensile strength of CNC-LA-IL/PVA nanocomposite was significantly improved from 36.07 to 92.56 MPa and elongation at break increased from 47.76%to166.19%.Furthermore,we explored a possible mechanism of achieving high mechanical properties of PVA nanocomposites.This work provides a green and facile method to prepare high performance PVA nanocomposite with excellent tensile strength and elongation at break.