Study On The Surface Decoration Of Cellulose Nanocrystal And Its Modification Of Polylactic Acid

Cellulose nanocrystal(CNC)is a kind of nano material extracted from cellulose,which is an ideal nanofiller for polymer.In this paper,CNC was firstly prepared by sulfuric acid hydrolysis and then modified by two different routes to improve the compatibility with the poly(lactic acid)(PLA).Finally,the properties of obtained PLLA/CNC nanocomposites were systematically studied.By adding the inorganic salt to CNC suspension,we successfully increased its thermal degradation temperature by nearly 80 ?.The morphology and structure of modified CNC were measured by AFM,FTIR and XRD,obtained results showed that our method can retain the unique structure of CNC.In order to improve the interfacial action between CNC and PLLA,Poly(D-lactic acid)(PDLA)chains are grafted onto the surface of the CNC,followed by the preparation of PLLA/CNC-g-PDLA nanocomposite.Research shows that the addition of small amount of CNC-g-PDLA could enhance the crystallization rate of PLLA significantly due to the heterogeneous nucleation effect of CNC and the presence of stereocomplex crystals.In addition,the specific stereocomplex interaction in the interphase of PLLA matrix and modified CNC particles results in great improvement of both storage modulus and the heat distortion resistance of the PLLA/CNC-g-PDLA nanocomposites.In regard to some problems existing in traditional methods for surface modification of CNC,a facile and green method based on the esterification reaction between CNC and lactic acid is developd in this paper.The quantitative measurements suggests that most available OH groups of CNC are substituted by few lactic acid units,resulting in a better thermal stability and dispersibility compared with pristine CNC.Benefit from this character,PLLA/LA-g-CNC nanocomposite could be easily prepared.The crystallization rate of PLLA is distinctly enhanced by the addition of LA-g-CNC in the whole temperature range between Tg and Tm.Moreover,the mechanical properties of nanocomposites is also promoted by g-CNC because of its excellent dispersion and compatibility in PLLA matrix.