Characterization of Compatibilizing Effect of Organoclay in Poly(lactic acid) and Natural Rubber Blends by FT-Rheology

The compatibilizing effect of organoclay in immiscible poly(lactic acid) (PLA) and natural rubber (NR) blends was investigated through small-amplitude oscillatory shear (SAOS) and large-amplitude oscillatory shear (LAOS) tests by varying clay concentrations, mixing conditions, and types of clay. A quantified nonlinear parameter (I-3/1) from FT-rheology and complex moduli (vertical bar G*vertical bar) were used to analyze the structural development of the PLA/NR blends in response to added clays. The nonlinear linear viscoelastic ratio (NLR normalized nonlinear viscoelastic property/normalized linear viscoelastic property) was also introduced to describe morphological changes in the blends. Observation of the TEM images revealed that the drop size of natural rubber decreased as the clay content increased from 0.5 to 3 wt %. However, the NR size did not change above 3 wt % of the clay. The NLR value increased up to 3 wt % and then reached a plateau. The drop size reduction due to increased mixing rates was reflected in the NLR value. In addition, the compatibilization efficiency of various types of clay was in accordance with the NLR value. A reciprocal relationship was observed between the NLR and inverse of the drop size, with respect to the clay concentration, mixing condition, or types of clay. The NLR value could be used to estimate the compatibilizing effect of organoclay in immiscible polymer blends (PLA/NR), even without direct morphological observation.