Nanoscaled Reinforcement of Polystyrene Foams Using Carbon Nanofibers

ABSTRACT: Carbon nanofibers (CNFs) are used as both the nucleants and the reinforcements for polystyrene (PS) foams in both batch and continuous extrusion processes with CO2 as the blowing agent. The inclusion of CNFs exhibits substantial impact on the morphology and properties of PS foams. The presence of CNFs results in a decrease in the cell size and an increase in the cell density. Macroscopic strength enhancement of PS foams due to the incorpora-tion of CNFs is experimentally observed. These results are qualitatively explained via a series of nanoscaled observations. Through scanning electron microscopy (SEM), the alignment of CNFs and the polymer-sheathing phenomenon are identified. The protective CNF layers around the cell wall and the substantial polymer–fiber interactions resulted in the enhancement of foam strengths. Thermal properties (heat conductivity, infrared transmission, and thermal expansion coefficient) of the PS foams can also be influenced by CNFs. Intensive shear force exerted by the twin-screw extruder broke the fibers in lengths. The impact of the fiber length on the foam structures (cell size and cell density) is also studied. KEY WORDS: foams, nanocomposites, polystyrene, carbon nanofibers (CNFs), reinforcement