Polypropylene/organoclay nanocomposites prepared using a Laboratory Mixing Extruder (LME): crystallization, thermal stability and dynamic mechanical properties

Nanocomposites based on polypropylene and surface modified nanoclay (organoclay) masterbatch were prepared via melt blending using a Laboratory Mixing Extruder (LME). This work focused on the study of crystallization, thermal stability and dynamic mechanical properties of the nanocomposites. The effect of organoclay content (5, 10, and 15 wt.%) on non-isothermal and isothermal crystallization of the nanocomposites was studied by Differential Scanning Calorimetry (DSC). Thermal stability and dynamic mechanical properties of the nanocomposites were investigated by Thermogravimetric Analysis (TGA) and Dynamic Mechanical Analysis (DMA), respectively. The DSC results showed that the organoclay played an important role in the crystallization of nanocomposites by acting as "nucleating agent" (heterogeneous nucleation). It was confirmed by the appearance of second crystallization peak, which was attributed to crystallization process induced by heterogeneous nucleation of organoclay. There were also a crystallization temperature shift, a reduction in half-time crystallization (t (1/2)), and an increase of crystallization kinetic constants of the nanocomposites. The TGA results showed that the addition of organoclay significantly increased the thermal stability of PP matrix, which was likely due to the characteristic and labyrinth effect of layered silicates/clays dispersed in PP matrix, and also the formation of multilayered carbonaceous-silicate char. A well-known Coats-Redfern method was used to evaluate the kinetic of thermal decomposition. Additionally, the stiffness characteristic of organoclay also greatly improved the dynamic mechanical properties (i.e. storage modulus, G') of the nanocomposites. The DMA results demonstrated that the resistance and durability of PP/organoclay nanocomposites against applied stress and thermal were higher than the PP matrix.