Effect of cellulose nanocrystals (CNC) on isothermal crystallization kinetics of polypropylene

Porous cellulose nanocrystal (CNC) agglomerates were prepared using spray-freeze drying (SFD) and incorporated into polypropylene (PP) via melt compounding. PP and PP/CNC nanocomposites (PPCNC) containing 1 wt.% CNC were subjected to a series of isothermal crystallization studies. Differential scanning calorimetry (DSC) showed that the crystallization rate of PPCNC is faster than that of neat PP. Different isothermal crystallization kinetics models, including those proposed by Avrami, Malkin and Tobin, were applied in the analysis of the DSC results. All the above models indicated a faster crystallization rate for PPCNC. However, the Avrami model provided a better fit to the experimental results. All these models exhibited higher activation energy for PPCNC than that of neat PP. PPCNC also had higher equilibrium melting point. Lauritzen-Hoffman nucleation kinetics revealed that the presence of CNC contributed to a higher magnitude of the work required for chain folding during isothermal crystallization. It was also found that the initial lamellae thickness during isothermal crystallization of PPCNC was higher than that of neat PP. This could be due to steric hurdles introduced by CNC particles, leading to a reduction in the transport of the PP chains into crystal units. (C) 2015 Elsevier B.V. All rights reserved.