Effect of polymorphs of cellulose nanocrystal on the thermal properties of poly(lactic acid)/cellulose nanocrystal composites.

Cellulose nanocrystals (CNCs) with different polymorphs CNC I and II were fabricated from native and mercerized microcrystalline cellulose (MCC) by sulfuric acid hydrolysis. CNC I and II were successfully acetylated by a "green" method, which was performed in an ionic liquid of 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM]BF). X-ray diffraction (XRD) proved that the crystal structure of CNC I and II was maintained after acetylation. Transmission electron microscopy (TEM) showed the rod-like structure for acetylated CNC I and spherical crystal morphologies for acetylated CNC II. Thermogravimetric analysis (TGA) revealed that the thermal stability of CNC I and II was enhanced after acetylation. The effect of CNC polymorphs on the crystallization behavior and thermal stability of poly(lactic acid)/acetylated CNC (PLA/ACN) composites was investigated by differential scanning calorimetry (DSC) and TGA, respectively. It was found that compared to ACN I, ACN II was better able to promote the cold crystallization of PLA-based composites, and PLA/ ACN II possessed higher thermal stability.