Preparation Of High Thermal Stability Cellulose Nanocrystals And Its Application In Bioplastics

Cellulose nanocrystals?CNCs?are predominantly obtained by the traditional sulfuric acid hydrolysis process.However,as-prepared CNCs powder features low thermal stability and poor redispersibility due to the existence of sulfonate groups and the hydrogen bond interaction among particles.In this paper,aiming at solving the above shortcomings,by mixing the ionic liquid[BMIm][BF₄]with freshly prepared CNCs without dialysis through a simple rotary evaporate procedure,the simultaneous improvement of thermal stability and redispersibility of CNCs has been achieved.In terms of thermal stability,the initial degradation temperature of modified cellulose nanocrystalline?IL-CNC?can reach 280°C by mixing ionic liquids.In addition,IL-CNC can be stably dispersed in some polar solvents and maintains the unique chiral nematic structure of cellulose nanocrystals in water.By combining FTIR,TGA and DLS measurements,the principle for improving the thermal stability of CNCs has been fully discussed.The poly?lactic acid??PLLA?/IL-CNC nanocomposites were also prepared by the melt-mixing method.We have found that the prepared nanocomposites have no significant decrease in mechanical property,but have a nearly 5-fold increase in elongation at break.We believe that the main reason for this phenomenon is cellulose nanocrystals modified by ionic liquid,which not only has strong interaction with CNCs but also has good compatibility with PLLA.It can play an important role as interface binder to transfer the stress.Therefore,simultaneously improvement in toughness and strength has been obtained in our case.Moreover,the crystallinity of the nanocomposite was also characterized by DSC.As a result,it was found that the crystallinity of polylactic acid was improved,which increased the HDT?heat deflection temperature?of PLLA.In conclusion,we successfully prepared IL modified CNC powder with enhanced thermal stability and redispersibility.This method is green,low-cost and time-saving,which avoids the tedious dialysis procedure after acid hydrolysis of CNC.Our study revealed that the ionic interaction between CNC and[BMIm][BF₄]and the consumption of residual sulfonate acids by rotary evaporation process should be the primary reason for improve the thermal stability.The fabrication of nanocomposites with PLLA indicates that as-prepared IL-CNC powder can be used as toughening nanofiller in PLLA by melting-blend.This simple and effective method will promote the large-scale application of CNCs to making fully bio-based polymer nanocomposite.