A study on the crystallization and melting of PLA nanocomposites with cellulose nanocrystals by DSC

Poly(lactic acid) (PLA)/cellulose nanocrystal (CNC) nanocomposites with 1 or 3 phr of CNC were prepared by melt mixing and compression molding then their % crystallinities as well as crystallization and melting behavior during the first heating/cooling/second heating process were investigated by differential scanning calorimetry (DSC). Isothermal crystallization at 80-130 degrees C for 5 min was performed during the cooling process to see how the isothermal crystallization affects % crystallinity at 25 degrees C. The % crystallinity at 25 degrees C as well as the crystallization rate of the nanocomposite increased with CNC content and showed a maximum at the isothermal crystallization temperature of 105 degrees C regardless of CNC content. The bimodal DSC melting peaks observed during the second heating process were considered due to the crystals with many defects (a') and the crystals with more perfect structure (a), respectively. Isothermal crystallization kinetic analysis by Avrami equation showed that the Avrami exponents of the nanocomposites were about 1, meaning a rod-or disc shaped crystal growth mechanism. Improving the mechanical properties of the PLA/CNC nanocomposite would be possible because the % crystallinity at 25 degrees C could be effectively increased by changing CNC content and cooling history.