Nanoclay intercalation during foaming of polymeric nanocomposites studied in-situ by synchrotron X-ray diffraction

Abstract

The intercalation degree of nanoclays in polymeric foamed nanocomposites containing clays is a key parameter determining the final properties of the material, but how intercalation occurs is not fully understood. In this work, energy dispersive X-ray diffraction (ED-XRD) of synchrotron radiation was used as an in-situ technique to deepen into the intercalation process of polymer/nanoclay nanocomposites during foaming. Foamable nanocomposites were prepared by the melt blending route using low-density polyethylene (LDPE), polypropylene (PP), and polystyrene (PS) with surface treated nanoclays and azodicarbonamide (ADC) as the blowing agent. Foaming was induced by heating at atmospheric pressure. The time and temperature evolution of the interlamellar distance of the clay platelets in the expanding nanocomposites was followed. Upon foaming, interlamellar distances of the nanocomposites based on LDPE and PP increase by 18% and 16% compared to the bulk foamable nanocomposite. Therefore, the foaming process enhances the nanoclay intercalation degree in these systems. This effect is not strongly affected by the type of nanoclay used in LDPE, but by the type of polymer used. Besides, the addition of nanoclays to PP and PS has a catalytic effect on the decomposition of ADC, i.e., the decomposition temperature is reduced, and the amount of gas released increases. This effect was previously proved for LDPE.