Effect of Organo-clay Modifier and Compatibilizer on the Morphological Development and Cold Crystallization Kinetics of Polylactide/Polyethylene/Montmorillonite Nanocomposites

Hypothesis: Among available bioplastics, polylactide exhibits superior properties, including high modulus, good processability, and compostability. However, some disadvantages, such as brittleness and low thermal resistance limit its application in some fields. In order to overcome the limitations of polylactide, it is usually modified by addition of nanoparticles or by blending with other thermoplastics. Polylactide/polyethylene (PLA/PE)-based nanocomposites were prepared using 4 phr commercially modified montmorillonite (Cloisite 30B or Cloisite 20A) and polyethylene-g-maleic anhydride compatibilizer (PE-g-MA) by melt blending technique. The structure and morphology development and also the cold crystallization kinetics of the samples were investigated using X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), differential scanning calorimetry (DSC) techniques and melt linear and non-linear viscoelastic measurements. Findings: The XRD results showed that polymer intercalation into the clay galleries in PLA/PE/Cloisite 30B was higher than that in PLA/PE/Cloisite 20A. The rheological results along with the calculated data of wetting parameter showed that Cloisite 20A in blend nanocomposite could reduce the droplet size through three different mechanisms a: localization of the organoclay in the interface b: increasing the viscosity of PLA matrix and c: decreasing the extent of coalescence process. The FE-SEM micrographs showed that the nodular morphology of PLA/PE/Cloisite 30B changed to a non-nodular morphology in PLA/PE/Cloisite20A. The melt linear and non-linear viscoelastic measurements showed that a stronger 3D-network structure was formed in PLA/PE/Cloisite 20A compared to that in PLA/PE/Cloisite 30B. It was implied that the crystallization rate followed the Avrami equation with the exponent n of around 2. The results also showed that the addition of compatibilizer (PE-g-MA) into PLA/PE/Cloisite 20A or PLA/PE/Cloisite30B decreased modified crystallization rate constant (Zc), because the cold crystallization rates of compatibilized blend nanocomposites were lower than those of uncompatibilized blend nanocomposites and the role of compatibilizer in the transfer of partial organoclays from PLA matrix into the droplets.