An investigation into the role of nanoclay and its localization on the micro-structural development and properties of polypropylene-based immiscible blends

Ph.D. (Chemistry)Abstract: This study deals with the influence of nanoclay localization on the morphological development and properties of melt-mixed PP/LDPE/clay and PP/EVA/clay nanocomposites. The main objective of this work was to develop PP/LDPE and PP/EVA-based hybrid materials with better compatibility, thermal stability, and impact strength, and at the same time with relatively good strength, flexibility, and elastic modulus. Blends with various compositions were prepared through melt extrusion. The morphological and dynamic characterizations show that the PP/EVA blends were immiscible for the investigated blend compositions. The presence of EVA in PP induced a beta (β)-phase formation of PP, thereby increasing the elongation-at-break and impact strength. The PP/LDPE blend morphology comprised a major matrix phase and a minor phase, with sub-inclusions of the major matrix within the minor phase. The PP/LDPE blends exhibited partial miscibility at low contents (< 20 wt%) of either phase; however, the phases were immiscible at higher contents. The PP/LDPE blend composition and morphology influenced the impact strength and elongation-at-break. The 80/20 PP/LDPE and 80/20 PP/EVA blends offered a balance between the mechanical and material properties essential for flexible packaging applications. Thereafter, 4 wt% nanoclay was added to modify the morphologies of the blends. The PP/LDPE/clay nanocomposites investigated in this study contained two different types of compatibilizers [maleic anhydride-graft polyethylene (PE-g-MA) and maleic anhydride-graft-polypropylene (PP-g-MA)], which manipulated the localization of clay in different phases. The morphological characterization results show that the nano/micro-structure of the PP/LDPE (80/20) blend could be controlled by incorporating the nanoclay alone or by adding a mixture of organoclay and maleated compatibilizers, a feature which significantly improved the thermal stability and tensile and rheological properties of the blend composites. The..